Blue Order

OK, a physics question for all you science types.

I would argue that a 700c wheel is more efficient than a 26" wheel, because given two cyclists turning their cranks and traveling at the same speed, the 700c wheel travels a farther distance with each revolution of the crank. The extra distance traveled may be small with only one revolution, but eventually, over miles, it would add up. The only way for the cyclist on the 26" wheel to travel the same distance at the same speed would be to pedal at a faster cadence.

So at first glance, it appears that the 700c wheel is the more efficient wheel.

However, I'm wondering about 2 things:

1) Have I neglected to account for wheel and tire diamater? I.e., a 26" tire generally has a higher profile than a 700c tire, so when you factor in the diameter of a 26" tire and wheel compared to a 700c tire and wheel, does that higher profile on the 26" tire compensate for the smaller diameter of the 26" wheel?

2) Is there some extra amount of energy that the cyclist on the 700c wheel is using to turn the crank one revolution due to the greater circumference of the 700c wheel?

One last question... Please try to convert your conclusions into lay English.

Jerseysbest

I'm only a lay person who struggled to get a B in college physics. For the other person to travel at the same speed with a smaller wheel, yes, he would have to pedal faster, but he would have a mechanical advantage with the smaller wheel, just as you would being in a lower gear... So yeah, the person with the 700c wheel has to exert an extra amount of energy to travel at that speed, as if you were traveling in a higher gear.

asgelle

Very good, you figured out gearing from the age of the high wheeler where the pedals turn the drive wheel directly. For those of us riding chain drive bikes with one or more gears, the gearing in the drive train removes the diameter from the wheel as a factor in how far the bike moves with one pedal revolution.

Nachoman

Here are a couple of articles addressing the issue.

https://www.precisiontandems.com/artdwanwheelsize.htm

https://www.precisiontandems.com/artbillwheelsize.htm

Falkon 

fastest bicycle ever?

Cyclaholic

You are ignoring gearing. You can gear your 700c and 26" bikes so that at the same speed you're pedalling at the exact same cadence. Even if you're talking about the same gearing, the slightly higher cadence in turning the 26" wheel may actually be more energy efficient. Either way if all other parameters are equal, i.e. weight, frontal area, rolling resistance, etc. then your efficiency won't change.

DieselDan

If both the 700c and the 26" bikes were using the same chainring and rear cog, the 700 would go further. Rides using smaller wheels tend to need a larger big chainring.

Blue Order

Well, I assumed equal gearing in my question. If both bikes are traveling at the same speed, in the same gear, then the 700c bike should travel farther with each revolution. Of course the 26" can gear up or down, but so can the 700c cyclist. Therefore, assuming that they're in the same gear, and traveling at the same speed, the 26" cyclist would have to use a faster cadence to travel the same distance at the same speed.

My question really gets to the two questions I asked-- if the higher tire profile of the 26" is a factor, and if the 700c cyclist is burning more calories to travel the extra distance a 700c wheel travels.

asgelle

Well if they're in the same gear combination (front/rear) then isn't one (if not both) in the wrong gear? Why wouldn't the rider just shift into the proper gear? That is what they're there for. But moving on, if the 26" rider is using a faster cadence to match speed, as you say; then the 700C rider doesn't go any further, does she, and your final question doesn't make sense. But to answer the question as best I understand it, if the 700C rider rides further of faster, she will burn more calories than a slower rider on 26" wheels. Of course that has everything to do with the fact that she's riding faster or father, and nothing to do with the diameter of the wheels. Should you ask the question is a 26" wheel faster or slower than a 700C wheel, the answer of course is it depends.

TrackSmart

Hello there. I'm sure that if you had thought more carefully before posting, you would have put a much more exciting (and sensical) question forward. Here are some questions that you possibly meant to ask:

1) Are narrow tires more efficient than wider tires, given both have a smooth tread and are at full inflation pressure?
A) The wider tire may have similar rolling resistance to the narrow tire assuming both tires are pumped to proper inflation and have smooth tread. Some studies have even shown that 25mm and 28mm tires tend to have lower rolling resistance than 23mm tires However, for a bicyclist traveling at high speed, the largest force opposing them is AIR RESISTANCE, so the small difference in rolling resistance will be less important. The factors resposible for lower rolling resistance in tires are less understand than they should be (tire deformation, etc), but actual measurements of rolling resistance have shown that 23mm tires do not generally have less rolling resistance than 25 and 28mm tires. The evidence also shows that very little (if any) decrease in rolling resistance is gained on a good quality road tire by pumping it up past its rated inflation pressure. Might as well leave the tire at the intended pressure and have a better quality ride.

2. Followup to question one: Will a tall, skinny tire have less air resistance than a shorter, fatter tire? The skinny tire has less girth, but the shorter tire has less height.
A: ? All other things being equal, I suspect the skinner tire would be better than the shorter one given a 26 x 1.5" slick versus a 27 x 1" road tire. But I have not done the math or calculated the rotational movement or drag etc (My physics is rusty...). This presumes similar spoke types and similar tire construction.

3) Is wheel weight, or the weight of spinning components (cranks, chains) really dramatically more important than stationary weight on a bicycle?
A: https://www.diablocyclists.com/pauldec00.htm
Their conclusion (link above) is that at relatively constant speeds, wheel weight is not significantly different from other bike weight. The main advantage is during quick acceleration, which mostly happens during the first meters of a race. Over longer distances, it would not be as important. Certainly not 2-3 times more important than stationary weight, as the "myths" told by some on this website would have you believe.

Sorry for the long post, but those are wheel questions that are really interesting and that have always fascinated me. I presume you were going for some similar comparisons.

xlntRider79

lets say you had two bikes, one with 26" wheels and one with 700C wheels with no drivetrain and started riding them down a long, straight hill (emiminates the effect of drivetrain input, and gravity affects both riders the same): If the tires have have identical profiles, the guy on the 26" wheels wins because his tires have smaller frontal areas and shorter spokes, resulting in less air drag. (its also possible that the shorter wheel results in a shorter fork, which lets the rider get into a more aero position. Then he REALLY wins big. that's why Tri and TT guys run 650 instead of 700C in the front). However if the 26'er had fatty mountain bike tires, he would lose because those tires would generate more air drag.

asgelle

Or better https://www.biketechreview.com/archive/wheel_theory.htm

asgelle

What about rolling resistance?

You're also oversimplifying the effect of small front wheels. They make little difference when the there is no wind or the wind is directly head on. They only start to matter in crosswinds. This makes sense since it's easy to get a flat back with dual 700C wheels and dropping the shoulders below this point doesn't reduce frontal area but just exposes more of the back. With a crosswind, however, the lower position makes the body look more like an airfoil and drag is reduced.
https://forum.slowtwitch.com/gforum.c...;so=ASC;mh=25;

TrackSmart

Yes, that's another great reference. Their conclusion:
"In summary, wheels account for almost 10% of the total power required to race your bike and the dominant factor in wheel performance is aerodynamics. Wheel mass is a second order effect (nearly 10 times less significant) and wheel inertia is a third order effect (nearly 100 times less significant)."

At speed it's all about wind resistance. Of course, the steeper the climb, the slower you will be riding and the greater the forces of gravity that need to be overcome, and hence the greater importance of overall weight (doesn't matter if the weight is on the bike or the rider). Mt Washington comes to mind. 7.6 miles up an 11% average grade at about 8 mph for the fastest riders. That's one of the few races where weight is truly king. In normal races, being aero takes priority.

MORAL: If you are going to shave weight, do it as cheaply as possible. It does not matter where the weight comes from. So first take it off the rider! Then off the cheapest bike components. Lastly, worry about those super-expensive and fragile wheels...

Blue Order

Er, no.

...

Er, no again. But it's all good to know...

TrackSmart

Sorry I was trying to be nice. I should just be cruel and wickedly honest. You asked a silly question. You might be ********. Kidding of course. But gearing makes your number-of-pedal-revolutions argument invalid. So...

1) You clearly wanted to know if a 700c wheel was more efficient than a 26" wheel.

2) The questions that I posed are the reasons that the two wheel sizes might be different (tire width, wheel height, wheel weight, rolling resistance, overall aerodynamic differences).

So, if these are the things that make the wheels different, wouldn't that naturally be what you'd want to learn about to decide which wheel size is more efficient and why? Maybe my reasoning in this is wrong and I'M the ******** one!?

Ha ha. I do like a good tech talk though. Of course I don't care a whit about this stuff in real life. Luddite that I am, I ride a 25-year-old steel touring bike with all original drivetrain and wheels.

xlntRider79

The OP asked for a simple answer! Once you take into a account contact patch size and sidewall deflection it gets complicated fast. I supposed (somewhat incorrectly) that the smaller tire (at equal inflation pressure on a smooth road) would deflect more and have higher resistance, but this is a constant factor, but I assumed air drag wins out every time because it varies as the square of velocity.

Interestingly, in Bicycling Science, 2nd ed. by Whitt and Wilson (a cool book, but pretty dated) There is a graph (Figure 5.10) showing that small wheeled bicycles (16 inch) are at a significant disadvantage vs. larger wheeled bikes (27 inch) at low speed (20% slower for the same power input at 10 mph), but that advantage exponentially decays as speed increases (it's about 4% at 25 mph)...so for 26 vs 700c, the difference is probably even smaller. So to follow up on my previous post, you'd have to be going down a really long hill to notice any difference.

Now on a rough road, the ratio of "roughness" to wheel diameter makes a huge contribution to the rolling resistance. But for that discussion, I'd check out the 29er vs 26er threads in the MTB forum

Blue Order

Gearing would only make it invalid if the rider on the 26" wheeled bike had gearing and the rider on the 700c geared bike had no gearing. Assume that both bikes have the exact same cranksets (same number of teeth on each chainring, same number of chainrings) and the exact same freewheels/freehubs (same number of cogs, same number of teeth on each cog). Each rider is able to gear up or gear down to the exact same gear combinations the other rider is able to gear up or down to. If that is the case, then the gearing is irrelevant, because as soon as the 26" wheeled rider gears up, or gears down, the 700c rider can and will do the same.

Your responses regarding resistance are good ones, and I didn't consider those factors, although they certainly figure into the equation. However, they do not address the questions I raised. I am not wondering what makes one wheel more efficient than the other; I am wondering if calories burned vary depending on wheel size (assuming that all other factors are equal)-- i.e., does it take more calories to push a 700c wheel than it does to push a 26" wheel, due to the extra distance traveled. If it does take more calories, then it would be a factor to consider in the efficiency question. On the other hand, if it takes exactly the same number of calories to push a 26" wheel as it does to push a 700c wheel, then the 700c wheel would be the more efficient (not accounting for resistance). I am also wondering if the higher profile of the 26" tire creates a tire/wheel diameter that is so close to the 700c tire/wheel diameter as to make the question moot.

Hey, me too!

DieselDan

BTW: it's not about the bike.

DCCommuter

I think this is the answer that you are looking for: If two riders are pedaling at the same cadence, and one is going faster than the other, the one who is going faster has to be pushing harder on his pedals -- and thereby burning more calories.

Having a bigger wheel is no different from shifting into a harder gear. If you shift into a harder gear, and keep up the same cadence, you go faster, but you have to work harder.

Wheel design is much more important than wheel size. The reason that most road bikes have 700c wheels is that most wheels designed for road use come in that size. Ken Kifer has a great riff on the subject:
Since he wrote that, 29-er tires for mountain bikes have come along, and 650c tires for road bikes have been introduced, which are about the size of the other two type of 26" tires, but different.

TrackSmart

The number of watts should be almost the same. So the answer to your question will, again, have only to do with 1) the gearing (i.e. mechanical advantage not the physical gears on the bike) that results from the wheel change and 2) what cadence our engine (aka the rider) is most efficient at pedaling.

Changing wheel size, while keeping all other factors equal, is the same thing as changing gears.

If we take a bike with 700c wheels and ONLY change wheel diameter to 26" - but nothing else - it just means that you have lowered all of your gears on the bike by the difference in wheel circumference. In this case, you have about 4 less gear-inches on the 26"-wheeled bike across your entire gear range.

Will the number of calories the rider burns change, even though the amount of work (watts) remains the same regardless of wheel size or gearing? Well, if a "human motor" is most fuel efficient at a cadence of 90 rpms, then the bike whose gearing allows them to stay within that cadence more often will be the most efficient in terms of calories per distance. Again, actual work (force x distance, measured in Watts) will be exactly the same. However, if the "engine" is more efficient at a particular cadence, it will burn less fuel at gearing allows it to pedal at 90 rpm - or whatever the ideal cadence is.

(PS: The most efficient cadence for a particular rider will vary. For some it will be 80 rpm. For those who have trained to ride at a higher cadence, it might be 120 rpm. Individual body physiology will also play a role in this.)

Blue Order, does that make sense? Do you understand the relationship between wheel size and gearing (aka mechanical advantage - not physical gears)?

I hope that helps answer your question!

Blue Order

That's what I suspected, but wasn't sure about. That answers the question. So when considering efficiency, in addition to distance traveled per revolution, one must also consider things like resistance and calories burned.

So the reason i was wondering all this is because I've decided to convert a mountain bike into a commuter, but I wasn't sure about the efficiency of those 26" wheels; when I started to think about it, I realized it was a more complicated question than just "distance traveled per revolution."

I wonder which wheel size is more efficient...

TrackSmart

I'm glad you used the laughing emoticon. Otherwise I might have taken you seriously and started to cry

So you get it now. Wheel size = gearing. It's the reason why those guys back in the day (before chain drives) kept putting bigger wheels on the front of their bikes - you could get a higher gear with a bigger wheel!

Now you know why I thought this post by Falkon was HILARIOUS!:

Blue Order

And cadence will need to rise or fall, depending on wheel size, to maintain speed when mechanical advantage rises or falls, correct? So if I'm understanding this, a rider maintaining a cadence of 90 rpm on a bike with a higher mechanical advantage (bigger wheel) will ride farther (or faster) than a rider maintaining the same cadence on a bike with a smaller wheel. Therefore, the bike with the larger wheel will travel farther on the same output of energy, and is therefore more efficient. Is that correct?

EDIT: I think my conclusion is wrong. The energy output is not the same...

Yep! thanks!

vulcan

work in = work out

energy cannot be created nor destroyed