This is not a trick question
I’m currently sitting in the waiting room (blogging via iPhone) at the local orthodontist as my boys both get braces.
Lucky them.
This seems as good a moment as any to ask for theories explaining a curious phenomenon I’ve observed.
And no, I don’t know the answer. I have a theory, but it’s just that — a theory.
So here’s the setup.
The road from the Tibble Fork turnoff to the mouth of American Fork Canyon is an ideal working downhill. With its moderate pitch and loose curves, you can really open up and pedal your heart out. It’s fast. It’s fun.
When I ride this section of the road on my geared road bike, I coast at the same speed as everyone else, more or less.
But when I ride my Lemond Fillmore single speed road bike, I coast much, much faster than the group. The Fillmore is an incredibly fast downhiller. Anyone who has ridden with me will agree.
The question I have is, “Why?”
The Fillmore is stock, apart from the bullhorn bars and TT brake levers I’ve fitted to the end of those bars.
So that’s my question. Why would this $700 bike be such a rocket on the descents?
I look forward to your theories. If you have questions or need additional information, ask in the comments and I’ll do my best to answer.
Comment by Andrew | 07.25.2008 | 12:48 pm
It’s got to be weight. I used to ride a 1985 Trek 500-series. The thing must have weighed in at 25 pounds. I’d rocket down the descents. I bought a carbon fiber bike two years ago that checks in around 17 pounds and try as I might, I can’t go nearly as fast downhill.
Comment by Jon | 07.25.2008 | 12:50 pm
It’s newer, perhaps. bearings are in better shape… rolls better.
Comment by peter | 07.25.2008 | 12:53 pm
I also have a Lemond Fillmore set up as a Fixed Gear.
Love it by the way. I always felt coasting had much more to do with the Wheels – Hubs and Tires but I am no engineer. check in with Dennis at the FFG forum and I bet someone will have a great answer.
Comment by MJ | 07.25.2008 | 12:55 pm
I have a short answer, grease or tires?
And a long answer, resistance. Maybe with a single speed there is less surface area causing bearing friction resistance associated with the single gear area versus cassette body. *pushes up nerd glasses*
I will say though that during my own life at the bike shop years ago, we would adjust the cups on the hubs (during overhauls) until is would just spin and spin. I ride a road bike with an old Dura-Ace Freehub style wheel, and that thing coasts and coasts.
Or it is probaly teflon in that last clear paint coating of the frame.
Comment by Anonymous | 07.25.2008 | 12:55 pm
Weight is the most likely culprit.
Secondary explanation: the pawls in the singlespeed cassette provide less resistance than those in a 9 (10? 11?) speed hub.
Tertiary explanation: Magic.
Comment by Jay Parkhill | 07.25.2008 | 12:56 pm
Have you ever been up/down Fillmore St in SF? It is 22% for at least one block. Any bike named after it naturally accelerates as though it is on that grade.
–
P.S. To help your mobile blogging/commenting- get Disqus or Intense Debate comment systems. You can reply to comments straight from email.
Comment by Drew | 07.25.2008 | 12:57 pm
700$ buys alot of bike. As in it is heavy, quite possibly heavier than the other bikes coasting down the same hill. Gravity sucks, so to speak. Some things more than others.
Comment by Jeff | 07.25.2008 | 12:58 pm
I’d suspect you have better aerodynamics (less drag) on the Fillmore.
Could be any (or all of):
-your position on the Fillmore could be more aero. I suspect this is the most likely explanation.
-less exposed cable (no shift cables) to create drag
-fewer exposed sprockets to create drag
-more aerodynamically efficient frame (shorter chainstays? Better bottle placement?)
Comment by UltraRob | 07.25.2008 | 1:03 pm
Do you have the same tires with the same air pressure?
Comment by Nick | 07.25.2008 | 1:03 pm
By going faster, I’m assuming you’re measuring via GPS or something highly accurate or Fatty’s radar sense?
Also, tell your children that braces are no laughing matter and if they don’t take care of their teeth now, they’ll have to have braces as an adult like I had to. The taunts only get meaner the older you get.
Comment by Big Bird | 07.25.2008 | 1:03 pm
The Filmore has an inferiority complex. It feels threatened by all of the other geared bikes and goes faster in an attempt to compensate.
Comment by hmgf | 07.25.2008 | 1:05 pm
I vote weight as well. I am 6′8″ and weigh far far more at the end of the summer than Fatty does right after the Holidays. I climb slowly, but on the descents I turn on the gravity assist rocket boosters and become basically untouchable.
Comment by 331miles | 07.25.2008 | 1:05 pm
Others have said it, but the biggest factor is probably the mass of the bike. The velocity increases nonlinearly with mass increases (due to gravity).
Comment by DOM | 07.25.2008 | 1:08 pm
You mention downhill. That, by definition, necessitates a hill. That, by default, implies the presence of the hill/mountain gods. As much as they embrace your other “climbing” bikes, they loath the single speed. Notice that it’s harder to climb with the single speed? They push it away when you climb and cast it off a fast as possible should you succeed in climbing their hill.
Comment by Jeff | 07.25.2008 | 1:08 pm
My vote is for weight first, then possibly better aerodynamics from the bullhorn bars (no drops).
Comment by Hamish A | 07.25.2008 | 1:09 pm
I’m siding with Jeff on this one: Aerodynamics.
Mass could play a part as well but I’d be happy betting a Taco lunch on the aerodynamics being better on the LeMond.
Either that or you’ve got serious maintenance issues with your other bikes ;-)
Comment by onetwentyeight | 07.25.2008 | 1:14 pm
Im gonna guess the difference is drag in the freehub body of your road bike. If you have a mavic wheelset, there is a seal at the base of the freehub body where it goes into the hub shell that has a significant amount of drag. pull off the freehub, and take the rubber seal at the bottom out. there is a thick section and a thin section. cut off the thin section, and put the seal back in. fill the freehub body with a thin coating of penzoil motor oil or slick honey, and reassemble. your wheel will spin much better now.
Comment by onetwentyeight | 07.25.2008 | 1:16 pm
^my tip only works for ksyerium elites and above, as they all share the same freehub.
Comment by chtrich | 07.25.2008 | 1:17 pm
Hubs
Comment by Keith | 07.25.2008 | 1:22 pm
This is only my second comment (my first was about your bike meme), but assuming the hubs and tires are about the same, my money’s on weight. It’s easy enough to test. Put some weights on the geared bike and see if it coasts as fast as the single-speed.
Comment by scarysushi | 07.25.2008 | 1:32 pm
I think you probably store your bikes in close proximity to each other, and at night when you turn out the lights, they get talking. They are clearly competing with each other. You should hire a bike whisperer to find out what is going. My guess is that there is some sort of sibling rivalry and the fillmore is out to prove something.
Comment by rich | 07.25.2008 | 1:43 pm
I’m going to go with the inferiority complex of the SS bike. My geared bike requires more maintenance, is more finicky, has more creaks and squeaks and is generally more of a pain in the butt because she knows I need her and won’t get rid of her.
The SS (in my case a 9-2-5) knows that she’s a toy, built up for fun and not a necessity, so she goes faster downhill, never ever gives me problems, is quiet when we ride and is generally just a pleasure to be around.
(either that or it’s a weight thing like the others have said)
Comment by James | 07.25.2008 | 1:46 pm
I’m gonna throw rolling resistance on the pile of possible reasons. You got ultralight tires on that single?
JLS
Comment by Lizzylou | 07.25.2008 | 1:47 pm
I disagree with a lot of you that it can’t be weight. I ride a lot with my father who has a lot of weight on me. He also has skinnier tires, (23 to my 25), so he has less rolling resistance. If we both go down the same hill, neither of us peddaling, and neither of us breaking, I fly past him despite his theoretical advantages.
Maybe every time you use the geared bike you have a headwind, and when you use the single-speed you have a tailwind. The wind gods work in mysterious ways.
Comment by graisseux | 07.25.2008 | 1:48 pm
It might be your position on the bike or the hubs. I also agree with the assessment that the pawls in the freewheel may slow you down more than those in the freehub.
It’s not weight since–being The Fat Cyclist–the amount your body weight fluctuates is far greater than the difference in weight between the two bikes and I’m guessing you haven’t always weighed the same when observing this phenomenon.
Comment by graisseux | 07.25.2008 | 1:53 pm
Something else just occurred to me: weight shouldn’t be entirely discredited. The wheels on the Fillmore are surely much heavier and their rotating mass allows them to spin for much longer, pulling you along.
Comment by Emily | 07.25.2008 | 1:54 pm
I think its the hubs too. What hubs are you rolling on each bike?
Comment by Don | 07.25.2008 | 1:58 pm
Because Lemond’s name is on it?
Comment by kc | 07.25.2008 | 1:59 pm
I hate to burst everyone’s weighty bubbles, but I have the same issue as fatty, though in reverse. My Specialized Dolce (aluminum) coasts much much faster than my single speed Bianchi SportSX (steel). The Dolce, though aluminum, weighs more than the Bianchi as well. Different tires, same width, same pressure.
Oddly, I have thought the exact same thing as Fatty here on why one coasts sooo much faster than the other, so I’m interested to hear explanations.
Comment by bikemike | 07.25.2008 | 1:59 pm
oscillating variations. i’m pretty sure of it. i’ll run the test on my new 160gb ipod to double check.
did you purchase the “extra gravity package” with the Lemond?
the only other thing it could be is the fact that Greg Lemond weighs more now.
Comment by hades | 07.25.2008 | 2:35 pm
Either drag in the hub, freewheel, freehub, or weight of the rims or rolling resistance of the tires or aerodynamic positioning on the bull horns.
Basically, what I’m saying is that I’m allowing for any theory that isn’t “the bike weighs 5 lbs more”. Do the pros load up on water bottles when they get to the top of climbs so they can descend noticeably faster?
I’m gonna go with “For the same reason that riding a single speed is nothing like not shifting on a geared bike”.
Comment by Jared | 07.25.2008 | 2:37 pm
I would say the mass of the bike also, but not the weight. Also mass doesn’t actually make gravity pull harder since gravity pulls all objects downwards at 9.8 m per second. The answer is simple inertia. Objects that have more mass take more force to slow, so to put it simply resistence against the Lemond Fillmore is futile :D. I’d also bet that the bearings are better, but my first choice is mass.
Comment by Carolyn | 07.25.2008 | 2:46 pm
Um maybe gravity just pulls one differently because it likes it more.
Comment by Jake | 07.25.2008 | 3:15 pm
I think you should ask for a refund on the ultra- light road bike, backed up by video evidence of the Fillmore descending faster.
I used to ride XTR wheels back in the rim brakes day, and they allowed me to descend notably faster than even my road bike with a super-light set up would allow. They were simply very smooth bearings. I topped out on that mountain bike on a road descent at 49 mph. The best I could ever get on the road bike was 47. Freehub resistance is likely a partial culprit, as well. It’s the bearings and the freehub, I say.
Comment by Mike Roadie | 07.25.2008 | 3:20 pm
I have to vote along with the hub/freewheelers. Weight/gravity seems to have an effect where there are greater differences…..hence men usually fly past the ladies down the hill (not including those who ride the darn brakes!!).
You riding two different bikes…..I definitely go with the wheels!
Are the braces going to be Titanium???? Dura Ace???
Campy???
Comment by Mair | 07.25.2008 | 3:31 pm
I have no idea, but Bromptons are good at freewheeling downhill too. My theory on that is small wheel size=less resistance. I have no idea how this theory would fit with some fullsize bike.
Comment by SYJ | 07.25.2008 | 3:33 pm
Aerodynamics. I would guess that riding on the bullhorns puts you in a more stretched out position than riding the drops of your road bike. Also probably affecting things is the height of your bars – given the sloping top tube on your road bike and the horizontal tt on your Filmore, it is possible (likely?) that the top of the head tube is actually lower on the Filmore (to accommodate your less than stratospheric standover). In my case, this is absolutely the case – the top of the headtube on my 53 cm generic fixie conversion (an old steel Fioreli road bike) sits almost 4 cm lower than the top of the headtube on my 53cm Fondriest (with semi-sloping TT).
Comment by Mair | 07.25.2008 | 3:35 pm
Bromptons are good at freewheeling downhill too. My theory on that is small wheel size=less resistance. I have no idea how this theory would fit with some fullsize bike.
Comment by Rachel | 07.25.2008 | 3:39 pm
It is not weight. This is a classic example used in introductory physics courses. Drop a feather and a cannonball in a vacuum, they fall at the same speed. I had a teacher whose husband is a physics prof, and she insisted that his bike went faster downhill than hers because he is heavier. They switched bikes. His bike, now carrying her, still went faster. It’s not weight.
Comment by John | 07.25.2008 | 3:44 pm
Weight has nothing to do with it–directly. As a guy named Gallileo demonstrated a few hundred years ago, drop a heavy rock and a light rock from a tower & they both reach the ground at the same time. In a vacuum, a feather will dead heat with an anvil.
The difference between the two bikes is due to aerodynamics, bearing friction, and rolling resistance, only the last of which is slightly affected by weight.
Comment by Stephen Waits | 07.25.2008 | 4:07 pm
Those of you saying weight probably did not do too well in your elementary physics classes. Less overall mass will very slightly reduce friction; however, most of you are incorrectly implying that heavier objects fall faster than lighter objects.
The mass that matters here is that of the wheels and tires. Since the wheels are rotating, they are always accelerating, and so mass matters quite a bit. This is probably the main culprit.
Of course, beyond rotating mass, it can only be lower resistance; mechanical and/or aerodynamic. Hubs, tires, frontal area, etc.
Comment by Nick | 07.25.2008 | 4:17 pm
This explains it all. http://www.sportsci.org/encyc/cyclingupdown/cyclingupdown.html#downhill
The key is mass. As explained in the above URL, and a short snippet below.
From a personal experiance as a bigger guy. I am a decent recreational cyclist (Cat 4) but I am a bigger guy. I can kick almost any Cat 1’s butt down a hill that goes beyond their gearing speed. And they have a nicer bike than I do, so I would assume the quality of components leans to their side. I have mass/weight on my side and on a long decent of a couple miles or more, I will win, and my top speed is always higher.
(Note: A common misconception is to note the equal acceleration of two different sized objects in free fall in a vacuum, and assume that the force of gravity on both is equal. The force on the more massive object is greater, being exactly proportional to mass, which is why the more massive object is accelerated at the same rate as the less massive one.)
Comment by Andy in WV | 07.25.2008 | 4:24 pm
wheel/tire weight…rotational inertia
Comment by A in B | 07.25.2008 | 4:28 pm
My Nashbar SS setup also soars past my friends … down down the hills it goes … wEEeeee allll the way!
Comment by KT | 07.25.2008 | 4:47 pm
I think DOM has it correct-er than everyone else; although, the responders weighing in on the gravity angle (get it? weighing? gravity? Ha! Ha! Ha!) have some good points.
Personally, I think it’s the incredible lightness of being you are experiencing when riding that particular bike; it’s a feeling not found on any of your other bikes.
Comment by stevpete | 07.25.2008 | 5:13 pm
Ummm, everyone who is commenting on different sized or weighted items falling in a vaccuum are missing the point of that particular physics lesson, which does not apply in this instance.
Being a man of superior mass, I can assure you that I descend faster than light guys do. Never get in a race with a big stron guy in rolling hills – the big guy will flatten the uphills with high speed from the previous downhill, and pick up more speed, and faster on the next downhill.
But I think we may be forgetting something here. Fatty, please report the actual fully assembled unloaded bicycle weight of your SL Silk, and the Fillmore, as well as the weight of the wheelset for each bike.
Comment by Miles Archer | 07.25.2008 | 5:50 pm
My understand of the forces involved is that rolling resistance goes up at a slower rate than wind resistance. So, at likely downhill speeds, i’d bet on wind resistance.
As to why one bike or another has more wind resistance, I have no idea.
The people who say weight must have failed freshman physics.
Comment by jon | 07.25.2008 | 6:00 pm
Bloggers should all agree to never pose questions that involve science or math… it’s not good for anyone.
If you’re slightly heavier on one bike, then the speed at which wind resistance counter balances the acceleration of gravity will be slightly higher. I.e., just coasting, you will reach a higher top speed.
Saying “why don’t the pros take on weight to descend faster” is not a good rebuttal. They are already able to hit their terminal velocity because they are pedaling, and hard. And the wind at that speed becomes a limiting factor unless they’re gonna take on like another 50 pounds.
Comment by ann | 07.25.2008 | 7:13 pm
It seems that ‘weight’ is the overwhelming answer, with ‘aerodynamics’ and ‘hubs’ close behind.
Use advil generously for the braces kids.
Comment by Rob | 07.25.2008 | 7:15 pm
To all the people saying it can’t be weight, because a feather and a rock will fall together in a vacuum, should try riding in a vacuum some time. However that might make it a little hard to breath.
The concept that applies here is “terminal velocity.” When falling (or descending) an object will continue to accelerate until the force of gravity is equaled out by the force of friction (drag). To descend faster you would need to either add weight or reduce drag.
Comment by Scott | 07.25.2008 | 7:16 pm
As a physics Ph.D. student, I think I should “weigh in” on the weight argument:
Actually, the Gallileo demonstration is an urban legend (or more succinctly, complete BS). If Gallileo were in fact to drop two cannonballs of identical shape but different mass from a tower, the more massive cannonball would in fact fall faster. You all are correct; in a vacuum (as was demonstrated on the moon with a feather and a rock), all objects fall at the same rate regardless of mass because gravity accelerates them at the same rate. In atmosphere, however, more massive objects have a greater force for the same acceleration (F=m*a, a is the same for all objects, but m changes) and this greater force is better able to overcome air resistance. Thus, a heavier cannonball is able to push through the air with more force and fall faster. You can try this experiment very easily with ping pong balls. Fill one with sand and leave the other alone. Drop them both off something high and see with hits the ground first.
The reason for cyclists that air resistance is nonlinear with respect to weight is actually for completely different reason: geometry. Surface area and weight do not increase at the same weight in humans (or in most geometric objects, for that matter. Think about a sphere: SA=4*pi*r^2, while m=density*4/3*pi*r^3. r^2 increases much more slowly than r^3). So while Fabian Cancellara may weigh 60lbs more than Carlos Sastre, roughly a 50% increase in weight, he obviously doesn’t have 50% more surface area. This works to his advantage in a TT, because he can put a lot of extra muscle in that extra mass without adding much drag at all.
Without actually seeing either bike or Fatty riding them, my best guesses are differences in his position that results in better aerodynamics, differences in his tires, or differences in bearing or freewheel/freehub friction.
Comment by Scott | 07.25.2008 | 7:28 pm
I occurs to me that I didn’t explain why I don’t think weight is a big deal. I can’t remember what Fatty’s geared road bike is offhand, but let’s assume that it’s right about around 15lbs, since Fatty is a good citizen and respects the UCI limit of 14.9lbs. The Lemond Fillmore, on the other hand, probably weighs around 20lbs, give or take a few. At first glance that appears like a huge 33% increase in weight. When you factor in Fatty’s weight (which, being a bad reader, I also can’t remember offhand, so I’m going to say around 180lbs for ease of calculation), however, the difference is between 200 and 205lbs, or 2.5%. If he wears a Camelbak on the road like the dork he is, add a few more lbs and that percentage goes down even further.
While there should be a minor difference in coasting speed due to weight, Fatty describes the actual difference as “much, much faster”. I don’t know about you, but I’m certainly not at the level where I can consider less than 3% to by “much, much faster”. Thus, I believe that weight plays a minor role in this effect, while bearing friction, aerodynamics, and rolling resistance can all be significantly greater causes.
Comment by Big Boned | 07.25.2008 | 8:05 pm
Fatty,
I think the SS makes you look fatter (and are therefore heavier)
Comment by Clydesteve | 07.25.2008 | 8:20 pm
This may be OT. Does Tiger ride a bike? What is he doing in all the ads on FC?
Comment by celeriac | 07.25.2008 | 8:36 pm
“Do the pros load up on water bottles when they get to the top of climbs so they can descend noticeably faster?”
Yes. There’s a story about secretly handing off a lead-filled bottle at the top of the Tourmalet, that you can read if you click on my nick. (You’d get a more entertaining debate of you had posted this to r.b.t.)
I don’t think weight is the answer here though. I don’t think it’s hub friction either, or the hubs on the slower bike would be scalding hot at the bottom of the hill and the rubber seals would be melted. My vote goes for aerodynamics, perhaps the aerodynamics of someone who’s all tucked in because he’s on a SS and doesn’t have a gear to pedal in.
Comment by Rachel | 07.25.2008 | 8:56 pm
Has to be the weight! Heavy bikes (and heavy riders too) descend more rapidly. It’s that whole gravity thing…
Comment by Big Mike In Oz | 07.25.2008 | 9:50 pm
As a nerd (and high school teacher and university tutor) specialising in physics it’s time I piped up and sorted out this whole mess.
It’s all about the weight. It’s also got nothing to do with gravity. If you buy a road bike with even a scrap of carbon fibre that bike will ascend like Piepoli evading a vampire. It’s then a simple step to take the assumption that if a bike tend to favour going up, it would conversely resist going down.
Being that the Lemond Fillmore was concieved and constructed in the land where the pushrod V8 is still king, I’m guessing that the BB shell is made of either pure lead or debris from a black hole.
The easiest way to conclude the weight/descending issue is to recreate the Galileo Leaning Tower of Pisa experiment replacing the original objects with a Fillmore and a Tarmac-SL.
$4000 for a couple of frames is nothing compared to the scientific advances available.
Comment by Bike Girl | 07.25.2008 | 10:04 pm
Bike Girl thinks it has to do with your confidence. If you have just made it up the hill on a single-speed, your ego may swell slightly. A swollen ego adds several ounces to the weight of the bike and can actually lubricate wheel hubs.
Comment by Scrod | 07.25.2008 | 10:04 pm
I think we are missing the larger point here.
TWO KIDS GETTING BRACES AT THE SAME TIME!$!$
Will be some time before you buy any major bike equipment. My wallet feels for you.
Faster downhills? Who cares, just enjoy it.
Comment by Julie | 07.25.2008 | 10:15 pm
Tires. Less rolling resistance.
I flew on even the slightest downhill when I replaced my older 23s with new ones.
There’s my vote.
Comment by Lucky Cyclist | 07.25.2008 | 10:33 pm
I have no background to back it up, but I have ridden AF Canyon. It’s fun, but tough to ride without hitting the brakes. If you are in fact heavier on the fixie(or SS as I assume you can’t pedal 40+ mph) it’s more about velocity. After you let off the brakes, your increased mass and presumably similar aerodynamics(my Corolla Langster is the same on bullhorns as being on the hoods,and is also a couple lbs heavier than my Corolla Allez) makes you build up speed and recover quicker than the lighter, geared setup. On the other side, Your brakes are less effective on a heavier bike. That’s why a big free ride rig needs 8″ rotors and an XC bike can get by with 6″ or even 4″. Velocity when the brakes are off. Inertia when the brakes are applied.
Comment by born4felt | 07.25.2008 | 10:36 pm
Obviously, you work more going uphill on the Fillmore, causing you to sweat more, causing a proportionate increase in stinkiness, causing other riders to brake to avoid you, making you seem faster when going downhill.
Science!
Comment by Al Maviva | 07.26.2008 | 5:40 am
The mass of the Fillmore probably helps.
While rocks & feathers, in a vacuum, fall at the same rate, in the real world their rate of fall is dependent on their ratio of mass to frontal surface area. A feather-sized rock has a lot of mass compared to a feather-sized feather, so the rock will fall faster because the increased mass helps it overcome air resistance. 5 pounds doesn’t sound like a lot but when you take into account the fact that you’re constantly accellerating on a downhill until you reach terminal velocity, then the 5 pound difference will have a cumulative effect.
The bike may also put you in a more aero position, something as simple as having a higher seat and keeping your knees closer to the frame or arms more nearly centered over your knees makes a difference, I’ve noticed ~25-30 watts of power are saved pedaling in the flats with those two modifications when I ride. Bearing drag in the hubs may be a factor too.
Comment by Joseph Camp | 07.26.2008 | 6:14 am
weight is irrevelant with respect to gravity. In a vacuum, feathers and bowling balls descend at equal rates. Note…I said “in a vacuum”. Resistance plays a role in slower descents. I.e. parachute opens (hopefully) and your descent slows. Therefore, you either have better aerodynamics or less mechanical resistance with this bike. Or, you are braver on this bike on descent and not -unconsciously- touching the brakes…you mentioned “TT” brake levers…perhaps they are out of easy finger range considering your descent position.
Comment by LanterneRouge | 07.26.2008 | 7:29 am
Wash your darn bike and take it to Racer for a tune up every once in a while! My guess is that you use the road bike a lot more than the single speed and the frictiony bits are clogged with debris and road detritus and bits of energy bars and the syrupy goo that that all energy drinks revert to the instant they drip from your crumb encrusted lips and touch any part of the bike. The single speed is cleaner because you don’t use it as much.
Comment by Mocougfan | 07.26.2008 | 7:57 am
Bummer. You started by saying you were at an orthodontist. I was hoping this was a dental question. Oh well, I have no idea why one bike is faster. I’d go with the weight of one bike over another.
Comment by Bluenoser | 07.26.2008 | 9:38 am
Ask ron over at the cozy beehive. He would love to sink his teeth into it. Braces or no braces.
I’m going with the Areo/hubs/friction club. Plus uncluttered bikes just look so much faster.
-B
Comment by Shiny Flu | 07.26.2008 | 9:51 am
1 gear means no pedalling down hill (unless you have legs the size of African elephants, you’re using a middle of the road *pun* gear inches, no?).
20 gears gives you that option. It allows you to brake and accelerate again.
On the SS you trying to keep your momentum. So maybe you’re braking less and/or riding more aggressively to achieve that.
Obviously the difference in friction and rotational weight plays a big factor, but I wouldn’t bother trying to analyse it without a physics degree. Also don’t think that it would make that big of a difference. Even between normal Pro bikes and Pro TT bikes the differences aren’t huge like the one you’re describing.
k, thanks, bye.
Depending on how both bikes are set up, one may have better handling/geometry than the other for descending. By ‘better’ I mean better for you.
Comment by Erik | 07.26.2008 | 9:58 am
It’s totally simple mathematics. Single speeds are cool. Going fast is cool. Therefore single speeds are fast. QED.
Fixies are even cooler, so if you flip-flopped that back wheel you’d go even faster. And your knees would catch on fire, which is super way cool.
As for the boring explanations, it is all about drag, and at high descending speeds on a bike, about 90% of that is aerodynamic, and about 3/4 of that is the rider. Yes, a bigger weight with the same drag will be faster, but since Fatty (notice the name, its important here) is WAY bigger than the difference in weight would be, that is unlikely to make a big noticeable difference. And one would hope that mechanical drag (bearings, tires, et al) would be better on the $4k bike and not worse. And they’d make too small a difference to notice due to the aerodynamics. So the only thing left is body position. The SS with bullhorns is getting him lower and longer, so he’s faster. Bullhorns are actually not all that fast, and he’d actually go even faster if he was on the road bike and did the “imaginary aero bars” thing by resting his forearms on the tops. That is super fast. Dumb, but super fast.
Comment by Apertome | 07.26.2008 | 10:16 am
I’m going with the earth’s magnetic field. Steel bike + magnetism = faster.
Comment by Josh | 07.26.2008 | 10:45 am
I gotta set a lot of ya’ll straight on rolling resistance:
Skinny tires have MORE rolling resistance than fat tires. Fat tires roll FASTER, all other things equal.
This has been proven time and again, even by skinny tire making companies. Hard, skinny tires only have less AIR resistance, which is important at higher speeds.
That is all.
Comment by BunE | 07.26.2008 | 10:54 am
Lasers.
Its all Lasers.
Comment by Scott | 07.26.2008 | 12:53 pm
Josh,
The “all things being equal” is where the argument for skinny tires comes in. Sure, at 90psi they’re the same, but it’s hard to run a 30mm tire at 120psi or higher. Also, skinny tires weigh less. So, they are actually faster in racing conditions.
Comment by celeriac | 07.26.2008 | 2:04 pm
A thin tire has more rolling resistance than a fat tire at equal pressures. However, you’d have to be really friggin dumb to run tires of different widths at the same pressure, so this is a useless comparison. If a fat tire and a thin tire are inflated to the same pressure, the fat tire gives a *harsher* ride. Try it yourself.
Comment by Jared | 07.26.2008 | 2:22 pm
wow Fatty tossed the gauntlet on this one apparently. I want to switch my answer to black magic, but fatty is neither black nor magical :(
Comment by Josh | 07.26.2008 | 3:17 pm
@scott & celeriac
The things you’re saying are all true. For tests on a metal drum. Hard, smooth tires run faster on hard, smooth surfaces.
In real world tests, just letting a bike and rider roll down a hill, fatter tires are faster even at lower pressures. In fact, there seems to be a sweet spot for a given width, a pressure that makes the tires fastest. This is likely because it allows for the correct size and shape of the tire patch, and absorbs the little bumps in the road better at lower pressures. Running a fatter tire at a comfortable pressure will not give you increased rolling resistance.
It will, however, be heavier, and is likely to have more initial rolling inertia, which will resist rapid acceleration. The key is to match your tire to your style of riding, and to hit your ideal weight. If you like to sprint or set up break aways, go smaller and harder. If you’re in it for the long, steady haul, fatter is better.
Comment by Hamish A | 07.26.2008 | 5:53 pm
Josh – then can you explain to me why when I swapped from 28s to 23s on my Bianchi (inflated to the same pressure, I’m retentive about that) My overall speed increased? It can’t be all about wind resistance.
Less area in contact with the road = less resistance to rolling (due to the whole ‘less surface to generate resistance’ thing, I’d assume).
Comment by Erik | 07.26.2008 | 6:30 pm
Hamish, that’s a good question. It isn’t less surface area in contact with the ground – that’s purely tire pressure and your (and your bike’s) weight. Most likely the 23’s are much better tires, and have a more flexible casing and a fancier tread, maybe with a harder center section that gives lower rolling resistance. At descending speeds, though, the 5mm of width may make a pretty big difference in speed, I think?
Comment by Heatherann | 07.26.2008 | 8:00 pm
My hubby ( the bike rider in my house) says bushings and tires is his guess. But without seeing the bike he can’t say for sure. Let me know if he could be right.
Comment by boots | 07.26.2008 | 9:56 pm
FATTY, I don’t know didly about one bike being faster, but I have had some experience with kids and braces. Try to negotiate an upfront payment to cover the complete program. You should be able to get a discount, but more importantly you are effectively insuring yourself if one of the boys’ treatment lasts longer than estimated – for any reason. One of ours did, mainly becuse he “forgot” to put retainers in at night, and not having to shell out $$ each office visit was a godsend. The second boy actually finished slightly ahead of schedule, but we were so proud that any financial consideration was dismissed. Think about it.
PS: I chalk my coasting speed up to Tullio Campagnolo’s obsession with quality.
WIN Susan
Comment by Rocky | 07.27.2008 | 8:49 am
You are descending with the same (essentially) group of people on both bikes, right? Your friends ride light road bikes, too. And I assume they ride similarly weighted SS’s, too. That being the case, the only material difference is your bike, vs. theirs. Trade one of your friends bikes on a ride and see if it changes – if that friend descends faster than the rest of the group, and you descend in the pack, it’s your bike (wheels, weight, magic, fairies pushing from behind because they like the name “Fillmore,” or something bike-related.
All of the physics explanations (though theoretically correct) have little bearing on your question, since all of the variables are the same, or close to the same. The difference is the bike, and it is likely then, your wheels.
Comment by Surestick | 07.27.2008 | 8:50 am
I’m going to disagree with those that say weight simply because The Fat Cyclist says that the speed difference he noticed is in comparison to the other riders in the group he is riding with. I’m assuming that in the group there are riders both heavier and lighter than him, additionally a few pounds difference in bike weight isn’t that much percentage wise compared to the combined bike/rider weight.
Also, assuming pure downhill coasting without pedaling everybody should accelerate at the same speed.
My guesses:
- Either there’s less resistance (aero, rolling resistance or bearing/freehub drag) or…
- The position/geometry of the SS lets you descend with more confidence and carry more speed in the corners so it seems like you are coasting faster.
Comment by Redheadstepchild | 07.27.2008 | 11:21 am
Simple. The mountain gods smile at you for climbing with a single speed.
Comment by John Swanson | 07.27.2008 | 2:06 pm
Just some thoughts. The force associated with gravity is linear with weight. Bearing drag is also (mostly) linear with speed, hence weight in this example. Similarly, aerodynamic drag is *quadratic* with speed.
Looking at it in order of magnitude terms, the aerodynamics dominate so unless the total system weight changed by >10% (i.e., bike weighs twice as much) or the bearings in one of your bikes is nearly seized, I’d guess that the difference in speed is due to improved aerodynamics.
Breaking it down further, the object with the largest surface area is likely to have the most drag. In this case, the rider. So I’d hazard a guess that your position has changed in subtle, favourable ways.
Based on my own measurements of wheels, I doubt that’s the cause of the difference but it may be a contributor.
Or I could be “out to lunch”…
Comment by tibiker | 07.27.2008 | 4:35 pm
“Come on guys, perhaps you need a refresher…it’s all ball bearings”
Actually I think the aerodynamics argument makes the most sense.
Try riding down a sustained hill and watch the difference in speed when you lift your head up and down a few inches, move your hands in to the stem (Ulrich like) or out on the hoods or move your knees in to the tt or out a little.
Comment by Anonymous | 07.27.2008 | 9:33 pm
aerodynamics first… bearings/hubs/tires (aka mechanics aka “frictiony bits”) second… weight last
or maybe your road bike is just chicken.
Comment by SurlyCommuter | 07.27.2008 | 10:06 pm
Hmmm – your SS Lemond goes faster without any explanation? I hate to be the one that breaks this too you, but you must have been thinking this all along… your SS is doping! You must hang it on the wall and not ride it for 2 years. Unless… are all your friends relatives of Lauren Fignon?
Comment by buckythedonkey | 07.28.2008 | 4:05 am
@ Scott: you said it all.
@ Nick: ditto plus a great link.
To vacuum-dwellers and purveyors of snake oil physics: read those entries please.
@hmgf: I concur with your observations. I challenge you to a duel! :-)
I do think, however, that there is a better, more interesting way to prove this. To that end I have a couple of experiments that I would be grateful if Fatty would conduct.
EXPERIMENT 1: The Role of Mass
Note 1: “the road from the Tibble Fork turnoff to the mouth of American Fork Canyon” will be referred to as “the Hill”.
Note 2: Fatty will make all descents wearing normal cycling attire ((cycling shoes, cycling socks, cycling bibs, Fat Cyclist jersey, cycling eyewear, cycling gloves and cycling helmet) unless specifically stated.
Note 3: when performing timed descents of the Hill Fatty will risk all to record the lowest possible time.
Note 4: the Core Team will endeavour to video Fatty. Special efforts should be made to position cameras on any corner with a decreasing radius and/or adverse camber.
Note 5: although it might be a fun aside, can somebody make sure that guy with the rock throwing fixation doesn’t come along and muck up all of this science?
OK, here we go.
DESCENT 1: Fatty will wear normal cycling attire and perform a timed descent of the Hill on his Fillmore.
DESCENT 2: In addition to normal cycling attire Fatty will secrete upon his person or Fillmore an additional payload not to be less than 30 kg (approx 65 lbs). It matters little how this weight is made up. Tungsten or depleted uranium ingots inserted into the Fillmore’s seat tube would be ideal, but bowling balls or lead sheeting would do the trick. Thus kitted out, Fatty will perform a timed descent of the Hill.
MY EXPECTATION: Fatty will be faster on Descent 2. A lot faster. Indeed, Fatty might crash, which will be a surefire indication that he was going faster. Case closed!
It might be fun to repeat the experiment with Kenny doing the riding. Or the guy with the rock throwing fixation.
EXPERIMENT 2: The Role of Aero
DESCENT 1: Fatty will wear normal cycling attire and perform a timed descent of the Hill on a recumbent, just for the hell of it (for tips, see: http://www.ozhpv.org.au/huff/docs/huff44.pdf).
OBSERVATIONS: The Role of Aero
The aero question needs to be answered! Fatty, please provide head-on and side-on photos of your riding position on each bike so that we can all have a laugh, er, ascertain significant differences in position.
You might want to do the Observations before the Experiments in case, you know, anything happens.
Comment by blinddrew | 07.28.2008 | 5:09 am
Sorry guys but Erik has got the idea. Rolling resistance increases proportionally to speed and on a well set up bicycle this is a tiny amount of the overall effort (hence the difference is likely to be negligible). Gravity applies a constant acceleration, generally heavier riders will descend SLIGHTLY faster because their greater inertia means they will ride out minor decelerations (though bumps, turns etc). Wheel mass makes more difference than non-rotational mass because it is constantly accelerating. However the mass difference for the bikes is all but negligible assuming Fatty’s mass is constant
However all of this becomes insignificant compared to wind resistance. This is because wind resistance increases in proportion to the square of the speed. By the time you get up to decent descending speeds the other decelerators are providing such a tiny percentage of the overall resistance that they cannot be making Fatty “much, much faster”.
Aerodynamics is all when it comes to any kind of speed trial (unless you’re in a vacuum)
Comment by StrongBad | 07.28.2008 | 6:26 am
My theory is that your riding buddies are messing with your mind :)
Comment by Rob | 07.28.2008 | 8:54 am
Is it a climb to the Tibble Fork turnoff?
If so then Fatty is most likely climbing faster on the Fillmore. Then when he crests the hill, and starts the descent, he can accelerate to his top speed a lot faster; or possibly to a higher top speed.
Comment by Robert | 07.28.2008 | 9:52 am
My guess is you begin the downhill using a lower gear and your entry speed is higher with the filmore creating more momentum for the hill.
Comment by arvy | 07.28.2008 | 10:10 am
I’m with “Scott” here. and I know little physics. The standard hubs on the Lemon are truly lovely and very smooth. mine is six month’s old and hopefully will remain this way.
Comment by Caloi Rider | 07.28.2008 | 10:31 am
I don’t know if this one has been tossed out yet, but is there a difference in your position on the bike? I’m willing to be the handlebars are a smidge lower or a few centimeters more narrow than the bars on your conventional road bike.
Despite my feather weight, I can sometimes out-descend the bigger guys just by switching my position around.
Comment by steve sax | 07.28.2008 | 10:36 am
This is certainly generating a lot of “snake oil physics”, isn’t it?
Scott really must be a physics grad student. The bits he presents are technically correct, but of little use in answering the question. Goos work!
John Swanson and Al Maviva get passing marks.
Nicely done, gents.
The rest of you may want to enroll in Physics 221,
Classical Mechanics, which I will be offering this
Fall quarter.
For the snake oil fans, here’s my bit:
What Scott was looking for is that, for identical
shapes but different sizes – like two spheres falling
through air – the ratio of the terminal velocities is
the sixth root of the ratio of the masses.
As has been pointed out, this is rather small just
due to a small difference in bike weight. Too small.
Final analysis: the shapes are just not the same. A
slight change in head, elbow, or knee position -with
the feet at 9:00 and 3:00 and the hands in the drops to act as a control for body position- will have a
noticeable effect on terminal velocity. Try it ou on
your next ride.
It’s all aerodynamics.
You’re welcome.
Comment by Jared | 07.28.2008 | 11:00 am
I don’t like the aero answers simply because I don’t believe in aerodynamics. It’s all dark magic and people who practice being aerodynamic should be burned as witches.
Comment by Clydesteve | 07.28.2008 | 11:52 am
Another thing that occured to me aerodynamics-wise, is that different bikes may make it more or less comfortable to place the pedals in the ‘correct’ aero locations of 3:00 and 9:00, as mentioned by Steve Sax, above. Depending on the top bar location, sometimes it feels better to coast with legs at 12:00 and 6:00, which is probably less aero.
Comment by Mirco | 07.28.2008 | 12:21 pm
Alright. Weight matters. Negligibly. Rolling resistance matters. Negligibly. Aerodynamics matters. HUGELY. To the armchair physicists: weight does affect the potential terminal velocity of an object, but only when there is air resistance. It’s a matter of the surface area to weight ratio. A smooth, painted styrofoam ball will not fall as fast as a smooth, painted steel or whatever ball. Initially, it will accelerate at the same rate, because gravity is a constant. But once they’re moving quickly, and yes, air resistance increases exponentially with speed, the light ball will have a more significant acceleration, relative to its weight. Because, after all, air resistance is an acceleration, and velocity change is the product of mass and accelerative force. at the same speed, the two balls will have the same air resistance, but the light one will be more significantly ‘accelerated’ than the heavy one. k. now, that example is for an object in free fall. put it rolling on a hill, and the effect of gravity changes, it still tries to accelerate to terminal vertical velocity, but the hill is in the way, leading the object to squirt out horizontally. In a world without friction, this would result in a ridiculously fast system. This means that the resistive forces have a greater effect on the moving object, because the force responsible for the motion is weaker, while the resistive forces remain the same. Aerodynamic resistance is by far the biggest resistive force here, with tires a distant second, followed by frame compliance and lastly, hub friction. The rider is by far the biggest, widest, and roughest thing on the bike, and his(in this case) position is the most important factor contributing to his drag. Motorcycle racers race in the tuck position to minimize their drag, then pop up to brake into corners. This does two things: Presents an air brake, further slowing them down, and reduces the load on their arms, which is significant. Next time you’re going down a hill, bend forward until your head is on the stem, hold that for a while, then quickly sit up to your highest position, and feel yourself slow. Then stand on the pedals. Gives you an idea about how major air drag is. the weight of the wheels is not a large influence here, because there is little change in velocity. Yes, the wheels are constantly accelerating from a stop at the road, to twice the overall speed at the top, back down to zero, but the overall balances to net zero, and in the case of simply coasting down a hill, has no appreciable effect. in rolling ups and downs, wheel weight has an effect, because a light wheel will allow faster acceleration at the apex, and a heavy wheel will carry speed forward at the up-break. As has been mentioned before, hub and freewheel friction does matter, only so insignificantly that it’s ridiculous to even talk about it, in the face of other factors. It’s a drop in the ocean. Tires, we all know, have resistance, and less so the higher the pressure, to a point, where the tire bounces and jarrs off of irregularities, rather than rolling over them. This is where frame compliance comes in. This is where my detailed explanations break down. just as a tire can become less efficient if it is inflated too hard, a frame can take that resonance and spit it out as speed, or it can feed it back into the road as drag. Exactly how this does it, I don’t know, I’m not a metallurgist frame designer, like the guys at Lemond are when they designed a bike to descend well. Also, since there are corners, the frame design can influence how well the tires roll during cornering. Less tire deflection in corners leads to a faster corner. This is quite possibly the biggest factor in why the Fillmore squirts down this hill like greased owl shit, more than the other bike, if all other things are equal, or inconsequentially different.
Comment by HP | 07.28.2008 | 1:18 pm
I didn’t even take a minute, or 45 to read all the comments….
Reasons its faster:
1. Weight
2. Rolling resistance (slightly)
3. Simple bike magic. It wants to go fast.
Comment by HP | 07.28.2008 | 1:23 pm
Now I’m glad I didn’t read all the comments. wow!!
Comment by Clydesteve | 07.28.2008 | 1:32 pm
OK, so a lot of cylists are nerds. We see your point, Elden.
Comment by KT | 07.28.2008 | 5:27 pm
Yeah, I’m with Clydesteve on this– there are way too many smart people on bikes who comment on this blog. My head feels full of cotton stuffing and I feel extra dumb.
I still think it’s all due to incredible lightness of being. Or it’s all the snake oil you used.
Comment by Stephen Waits | 07.28.2008 | 6:28 pm
@steve sax, professor of physics. I hope you plan on teaching your students a little something about rotating mass, in addition to aerodynamics.
Comment by Paul | 07.28.2008 | 8:54 pm
The science posts were wonderfully educational and fit with my own findings: wind (aerodynamic resistance) plays the biggest role. Thank you physics people =)
Also thanks to those of you with a sense of humor who kept this whole thing readable.
Science!
Comment by PsySal | 07.28.2008 | 10:15 pm
Has to be aerodynamics, unless there is a really very major difference in rolling resistance (unlikely). Aero resistance increases with the square of velocity, so in a fast situation it’s going to mainly be that.
Comment by Red | 07.29.2008 | 6:26 am
Most people seem to think weight. But I don’t but it. I have the same thing. I have a 24 year old Trek 720. That think is a coasting race car. It’s amazing. I have other bikes of similar weight that don’t coast the same.
I have had the same question.
Comment by The D | 07.29.2008 | 12:23 pm
1) Heavy, hard tires
2) Heavy rims
3) Aero position
4) Longer gear cresting the hill
5) Less FW drag
= Fast Fatty Downhill on the Single Speed.
Comment by Unknown | 08.2.2008 | 2:19 am
The reason is that on a single speed, you have a lot more initial speed when you come over a crest. On a geared bike you are riding on a very short gear. It takes a lot of time to get up to speed and back to longer gear. On a single speed you are always in 48/16 or something. So when you start the descent, it takes no more than two powerful pedal strokes to get to coasting speed.
That and weight and tires.
The freewheel teeth have absolutely no effect.
Comment by ross | 08.2.2008 | 8:47 am
Has nobody considered the dynamic balance of the wheels? If you have a valve hole on one side and not on the other that makes for a bit of a difference in mass on either side. Take that wheel out of the frame and spine it quickly and you have a big wobble to deal with. That wobble will slow you down. Its amazing just how many manufacturers don’t balance their wheels. My new mid range mavics descend a lot faster than my old mid range shimano wheels.
Comment by JT | 08.2.2008 | 10:56 pm
This is my first post on this site–which I think is pretty cool.
I’ve had remarkable luck in this respect with my last two bike purchases–which were also my first two new bicycles–a Trek 8000 (2004) and Trek 1500 (2007). They both coast faster than any other bike in any tour I’ve ridden. People have actually commented to me that they didn’t see me do one pedal stroke over several miles at a shot.
Both the mountain bike and the road bike came with Bontrager Select wheels, which are made by DTSwiss. I never cleaned out and regreased the hubs on the these wheels because I was afraid it would effect this outstanding performance. And sure enough the hubs were still excellent long after I had worn out the rims and eventually trashed one wheel on the mountain bike.
When I trashed a wheel on the mountain bike, I switched from the Bontrager Selects to Mavic. The new wheels, with their fancy sealed bearings and all, just can’t compare. They’re very good but unremarkable when it comes to coasting.
So I say it has to be something about the hubs, probably the quality of the bearings and where they seat. Or more likely it’s the quality of the craftspersonship of the people who originally put them together.
Comment by JT | 08.2.2008 | 11:00 pm
Freewheel? Of course it has an effect. The whole shabang is only as fast as it’s slowest part. The freewheel does provide some resistance.
But I don’t think it would be so significant as the quality of the parts and craftspersonship in building the hubs unless it was a reeeeeally crappy freewheel.
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