thehammerdog

For the science people can a 26 inch wheel ever be as fast as a 700c wheel? I just got off my 26 inch gravel grinder "elite" 1994 mongoose drop bar heavy steel beast and as I flew down the trail alone wondered just how faster would I be going on a 700c bike?
so does size matter? What is the science.
curious if anyone knows

cyccommute 

If everything is equal, I wouldn’t say it makes much difference. A smooth downhill on a bike with tires having the same rolling resistance, the limiting factor is going to be wind resistance. On a rugged downhill, the larger wheel has a little bit better attack angle on obstacles but that’s only a slight advantage.

AeroGut

If we assume that both wheels have exactly the same type of tires at exactly the same pressure, then the rolling resistance due to tire deformation is essentially the same.
There are two other sources of differences that I can think of. As cyccomute noted, if the surface is not perfectly flat, the 700c wheel has a better angle of attack because of its larger diameter, so it isn't knocked back as much by bumps.
Secondly, the smaller circumference of the 26 in wheel means that it turns more revolutions for the same distance as the 700c. Even well greased bearings will have a small amount of friction and resistance to spinning, and this will be greater for the 26 in wheels that are spinning faster. The wind resistance will also be slightly greater for the spokes on the 26 in wheel because they're moving faster. This will not be offset by the shorter length.

But none of those should be big effects if you're running high pressure tires on smooth surfaces. On a rougher surface or with bad bearings, the effects will be more.

That said, the difference between two different types of 700c tires can be much more than the difference between 700c and 26 in of the same tire.

mrt2you

in real life to the average rider it won't make a difference. it's not the gearing difference between the 2 wheel sizes that holds us back. it's the legs spinning the wheels that make the top speed difference.
to the ultra Olympic level fitness TDF rider yes the 700 wheel should be faster.
on paper for a math exercise yes the 700 wheel will be faster every time. because it's larger, more circumference, giving you more theoretical top speed.

HTupolev

The spokes are not moving faster. They will be static at ground level and at 2x the bicycle speed at the top, regardless of wheel size.

AeroGut

Right. The tips of the spokes are going the same speed, but the 26 in wheel spokes are shorter, so for any given radial distance from the hub, the 26 in spoke is going faster than the 700 c spoke.

HTupolev

That doesn't mean that the spokes are "moving faster", though. As a function of distance from the hub relative to total wheel radius, the speed is exactly the same. Or to put it another way, the distribution of speeds of all pieces of all the spokes looks basically the same in the 26er case as the 700c case (at least if we ignore flange height as a factor). Since the total amount of spoke is higher in the 700c case, there will likely be more spoke-related drag in the 700c case.

terrymorse 

I disagree. Deformation in the contact patch on a smaller diameter tire is greater, therefore rolling resistance of a smaller diameter tire has to be higher.

rhenning

I have some friends the ride Bike Friday Pocket Rocket Pros with 451 20 inch wheels/tires that 90 percent+ of the people riding bikes would have trouble staying with in a race. It isn't wheel size but the rider that decides the speed. Roger

HillRider

That's always the case but not germane to this discussion. Of course, a strong enough rider can overcome a handicap from his bike. Chris Froome could beat almost everyone even if he were on a Walmart BSO. But we are discussing just the effect of wheel diameter and for equal riders, wheel size can effect the outcome.

Andrew R Stewart 

+1. There's a lot of "sounds true" being said in this thread, too bad much isn't true. Real research has been done by many and likely available, for those who really want to know the science. There's an decreasing aero drag but an increasing rolling friction as the wheels get smaller. So the question is where do these competing factors balance out. IIRC the balance is right around the 559/622 wheel size, funny how that's what most adults ride.

The IHPV speed records almost all are done on larger wheels and that's with most of the wheel inside the body work, out of the aero drag potential. If smaller wheels were measurably faster they would be the size of choice.

Independent of specific trials, what the mass of humans that have done this stuff before have sensed and thus chosen certainly has meaning. Andy (who should pull out his copy of Bicycling Science and check)

WizardOfBoz

Agree with Terry. I think that there's a reason that TdF riders don't use 650c or 26" wheels. And (correct me if I'm wrong) but the MTB racers uses 29ers. Yes? I think contact patch size is one thing. The amount of deformation of the tire for a smaller wheel is greater, and some of that deformation is inelastic. Probably a more pronounced wattage difference at higher speeds.

The other thing is the ability to roll over bumps and pits in the track. For the right size pit, a 26" tire might get more caught up than a 700c.

Is the 10% diametral difference between 700c/29er vs 26" (622mm vs 559 bead seat) diameter significant in terms of speed for most folks? Probably less for short races. Not anything to even notice for leisurely rides. For a longer road trip or race, might make a difference in seconds or minutes, depending upon road surface quality.

And last, for those of us who are taller, a frame built around 700c wheels will fit better than 26" or 650c wheels (that is, 622mm vs 559 or 571mm BSD). So a proper size frame vs too small a frame would add a significant difference in efficiency for larger riders.

But I think that the answer is a question. "What do you plan to do with the bike?" If you are a shorter rider that does mostly short rides over tracks with lots of climbing and short downhills, maybe 26" is fine. But 29er might handle bumps better. A larger rider that rides longer rides at higher speeds might want to consider a 700c bike.

I would add a suggestion, though, that if you are having a blast riding your bike with 26" wheels, continue to do so! Don't let dreams of optimal gear hamper your enjoyment of riding.

rhenning

Hillrider I totally disagree I was off topic. Your topic was wheel sizes and it was to show you your whole concept is wrong and makes size little difference. The Tour de France comments are wrong because the governing body decides what sizes may be used period. Roger

terrymorse 

When it comes to rolling resistance, size does matter. Larger diameter tires have lower rolling resistance.

If strong riders are fast on a tiny wheeled bike, they will be faster on a 700c wheeled bike.

AndreyT

As usual, statements that attempt to objectify "the science" make least sense of all.

"The science" says that wheel size does not matter at all. Everything else (e.g. rolling resistance, air drag, etc.) is not "the science", but rather purely empirical factors. It is true that they can be incorporated into "the science" of it as well, but that would require a considerable amount of additional input (e.g. tire parameters), which happens to be missing from this thread. So, no, there's no "science" here beyond the simple claim that size makes no difference. Everything else is just guesswork of "afternoon yap" quality.

A question stated in the original post can only be answered by a practical experiment. If you want to involve "the science" here, it would require a lot more serious and methodical approach.

terrymorse 

Incorrect.

Tire rolling resistance is a function of the amount of deflection in the contact patch, and larger diameter tires deflect less than smaller diameter tires. Therefore, all other parameters being equal, larger diameter tires have less rolling resistance. This is not "just guesswork".

xroadcharlie

All else being the same, I would think the 700C tire, Which is about 1" taller then the 26" would be faster. but the difference is so small the average cyclist needn't consider it when buying or upgrading a bike. If you like the bike with the 26" wheels, fine. Most new bikes seem to be the 700c. That seems to be a good size for balanced overall performance.

More important then a 3% difference in tire height is tire tread, suppleness (60 tpi is better then 30), Compound, and with all tires pressure. And remember rolling resistance makes up a very small part of the equation on a road bike.

If tire height is so important, How do some skateboarders keep up with bikes with their 70mm wheels. And rollerblades with tiny wheels roll so effortlessly, As do shopping carts when a light wind blows it through the taillight of you car.

Shahmatt

Air resistance aside, wider tires are faster than narrower tires.

https://www.schwalbetires.com/tech_i...ing_resistance
https://www.schwalbetires.com/wider_faster_page

Reynolds 

Not always- fat bikes aren't faster.

HTupolev

I can't imagine where a 7% speed difference would arise between a 25 and a 32, all other things being equal. To arise purely from aerodynamics would require a whopping 20% difference in CdA to the bike+rider system, like dragging along an entire extra bicycle. To arise purely from rolling resistance, if we started from a quality performance road tire, would require something in the neighborhood of a doubling in crr. Even splitting the difference demands confusingly enormous numbers, like many tens of % increase in crr alongside a 10-15% increase in CdA.

I want it to be the case that your data is representative of reality in general... If 32 down to 25 is worth 7%, then 53 down to 25 is likely worth at least 20%, maybe more. In that case, if I only swapped my drop-bar mountain bike over to 700x25, its performance would not only leapfrog past my entire road stable, it would become the fastest road bike in existence by a substantial margin. I'd be able to cruise around in the 25mph ballpark solo for hours at a time like it's no big deal.
But I don't believe it strongly enough to drop $300 on a pair of Motolites to find out.

I do agree that this is very significant, and probably the most glaring omission from any calm-condition test protocol. Forcing the yaw to zero allows the pieces of the bicycle to draft each other effectively, minimizing the extent to which fat tires are exposed to the wind, and even helping them fair each other. In a strong crosswind, everything becomes much more exposed to the wind, and the fronts and backs of both wheels have nowhere to hide.

I have noticed that the drop-bar MTB is at its biggest disadvantage compared with my normal road bikes when there's a strong crosswind. The winds barely affect its handling, but there's no lack of resistance.

Unca_Sam

This is an incomplete question. There is no answer because we don't know if the other variables are controlled. If the question assumed that the wheels are spinning at the same RPM, the wheel with the larger circumference should travel farther.

My newtonian physics are too rusty to be useful, but I suspect that, with different size wheels of the same mass mated ti the exact same system with the exact same power input, the difference would favor the larger wheel less. A larger circumference reduces mechanical advantage; you're shortening the lever arm you're working from.

Any actual application of this will be lost to uncontrolled variables like rider output, gearing differences, rolling resistance, etc.

mrt2you

this is a invalid comparison.
on a skate board the wheels do not power you forward your leg does by pushing off the ground, they just roll to carry your weight. wheel size doesn't have much effect with speed on a skateboard.

on a bike the wheels are the driving force that moves you forward. because the wheel powers you forward the larger wheel will make a difference.

as i posted earlier and others have posted along the same lines. to the average rider the wheel size won't make much difference. wheel size effects fit on short riders and that part makes a speed difference. the biggest difference maker is the engine powering the wheel size, not the size of the wheels being powered..
with strong riders a larger wheel will give them a better gearing difference that theoretically will give them more top end speed. this only makes a difference if the engine powering the wheels has enough power to make the wheels faster in the comparison test.

Unca_Sam

I'll say any perceived benefit or detriment from your perspective will be overwhelmingly psychological.

Look at the testing around wheel size at the elite level. Narrower tires should present less area for wind resistance and thus be faster, right?
Testing concluded that wider tires are faster, and that drag is less of a factor when the rider is more comfortable, and thus performing better.

Get a 29'er and report back with results.

Wilfred Laurier

All things being equal aside from wheel size...

Smaller wheels will have a slightly higher 'rolling' resistance from tire deflection and (to a much lesser extent) bearings.

Larger wheels will have a slightly higher aerodynamic resistance from being taller and therefore having a larger frontal area.

Triathletes, time triallers and track racers used to (or still do?) use smaller wheels - 650C iirc - esp. in front, for the aerodynamic advantage. As speeds go up, aerodynamic resistance goes up exponentially but rolling resistance generally increases linearly.

But unless going for top performance, most of this makes little difference. If you have an old road bike with 650C wheels and your twin brother has an old road bike with 27" wheels, it's probably not the bikes' fault that you're slower.

Kapusta

How much faster (or if) a 700c wheel is over 26” depends on the terrain and application.

For holding straight line speed over rougher terrain, 29” mtb wheels do have an advantage over 26”.

However, “fast” can mean more than just holding straight line speed.

I will say that more and more MTB racing disciplines (enduro, XC, DH), have been steadily moving to larger wheel sizes over the years.

OTOH, many gravel bikes have actually downsized to 650b (or offer the option to do so). However, I think that has more to do with the ability to run higher volume tires then with wanting a smaller diameter wheel.

Alone those lines.... I can imagine some circumstances in rough terrain where a 26 inch wheel in a frame that could clear large volume tires (like 2.3s) could be faster than a 700c wheel limited to 42s.

So, to answer your question....... it depends.