A 29" has a few % less rolling resistance vs a 26", and that can mean the difference between winning and losing a race.
The 26" will accelerate a bit quicker ( less mass ), but in a straight line race, this advantage doesn't help.
Everything changes when you introduce a hub motor into the mix and we are going high speeds. The higher efficiency/power output of a smaller wheel will overcome the additional rolling resistance at the wheel.
If you are racing hub motor bikes, the 20" wheel will win, 99 times out of 100. But if we are racing mid drive bikes, we want a taller wheel.
You might only be able to buy the stickiest rubber in certain sizes. So, while one tire\wheel size might have a huge contact patch it might only be available in non-sticky compounds...
Let me share some knowledge.
There was a time when winning races was important to me which led to doing lots of coast down testing, wheels, tires, body positions, fairings etc.
Time verse distance with a magnetic reed on the wheel and then downloaded to a spreadsheet.
By carefully studying the results tiny changes could be accurately seen in the numbers.
Smaller diameter wheels do accelerate quicker where conversely a larger wheel does maintained speed longer.
Flywheel effect ... obvious ... right ?
Same brand of tire with same width and casing type have similar traction results regardless of diameter.
Most of the races I did were crits and velodromes.
Very few cyclists actually have the skill to corner fast enough to find the traction limit. (A significant portion of my training time was in tight parking lots with little to no straight sections i.e. looking to find the traction limits)
Smaller wheels have have less frontal area so at higher speed they have less aero drag. (assuming same tire width to larger wheel)
For criterium events the small wheel was an advantage.
Longer road races with few tight turns the bigger wheel comes into play.
I love that i've been reading this forum since 2010 and am still learning new things, like the above.
Kudos for that post!
A small wheel will also reduce the reduction ratios you need for a given motor, which means you can volt up, gear down, and make higher continuous power/torque. In some cases you can also eliminate a gear reduction altogether. The advantages for an electric motor are huge.
All the criteria n road races I’ve seen sanctioned by the uscf required a 700mm standard road bike wheel and smaller wheels weren’t an option. It makes sense having the same wheel size so they end up with roughly the same handlebar height for safety sake.
As far as finding the limits of traction on a dry road.. in my experience on a bicycle when you hit the limit of traction you know because you’re now on the ground. I see moto gp guys slightly sliding out the rear wheel and recovering. I assume they put a bit less air in the front tire for a bit more traction there. If the front tire slides you’re for sure going down
I don’t know much about gp racing but to me, in this age, it seems a contest of traction and it’s the one facet where it’s not controlled by computers and just in the hands of a daredevil at the handlebars
Most of my pedal powered racing was "Human Powered Vehicles" where the rules are : brakes and helmet required, everything else is unrestricted.
This type racing rewards creativity and doing good homework.
As the wheel gets smaller, the transformation of the force applied to the pedal to the wheel decreases. This is not about faster acceleration, but about a sustainable, low-friction driving experience.
My 1974 Norton Commando had 19" rims F/R. Back then tires weren't as good as now, and the thinking was a bigger diameter wheel had a longer contact patch, and therefore more traction for corning. Also better control over pot holes because the tire didn't fall down in the hole as far as a smaller diameter wheel. They must have been on the something because no bike could corner like my Norton, not even Ducati which had 18" wheels. I loved that bike, but I had to spend more time working on it than riding it.
This has been my experience with my Stealth which came with 24" bicycle rims. Out of the box I removed the knobby tires, and only have run street tires. The best bicycle tires I've tried by far are 24 x 2.5 Maxxis, Hook worms. The stock rims were 24" x 31mm wide bicycle rims. Later I changed the rims to 24" x 65mm wide bicycle rims. Comparing the handling using the exact same tires on both size rims, the wider 65mm rims win hands down. The overall tire width went from 2.6", to 3". The wider rims stand out as the best thing I ever did to improve my corning.
FYI, 24" bicycle rims are about the same diameter as 19" motorcycle rims.
That’s a tiny-wheeled scooter and won’t be in any races on the edge of grip.
why aren’t top level street bike racers using bigger wheels. Maybe they’re really on the course to sell a product and there arent any bigger wheels available but they could be made. The race rules likely require the specific wheel size they’re all using but the rules could be changed. It’s essentially a handicap race if they’re not using the best design possible. Sure there’s downsides to the bigger wheel but I think on the courses they ride especially the pluses would outnumber.
If you mean bicycle road racers, there's a point where the aero drag and extra weight of a bigger wheel (and the frame to accommodate it) have more effect than the very slight reduction in rolling resistance and very slightly increased traction it offers.
Even before there were common standard wheel sizes, after the introduction of chain drive racers focused in on wheels about 27-28" in overall diameter. In the very early days of safety bicycles, they might have been up to about 30" overall, but as roads improved, the typical size decreased by a little. I'm inclined to think they couldn't have been too far off from a hypothetical ideal.
If you mean bicycle road racers, there's a point where the aero drag and extra weight of a bigger wheel (and the frame to accommodate it) have more effect than the very slight reduction in rolling resistance and very slightly increased traction it offers.
Even before there were common standard wheel sizes, after the introduction of chain drive racers focused in on wheels about 27-28" in overall diameter. In the very early days of safety bicycles, they might have been up to about 30" overall, but as roads improved, the typical size decreased by a little. I'm inclined to think they couldn't have been too far off from a hypothetical ideal.
Well, there are rotational inertia and gyroscopic precession forces to be concerned about there.
Honda made 23" front wheels for motocross bikes in the '80s, but they didn't stick. 24" and 30" front wheels have only been used for choady kustom-style Hardly Ablesons as far as I can tell. That means they probably hurt performance and handling both, else those choads wouldn't mess with them.
Well, there are rotational inertia and gyroscopic precession forces to be concerned about there.
Honda made 23" front wheels for motocross bikes in the '80s, but they didn't stick. 24" and 30" front wheels have only been used for choady kustom-style Hardly Ablesons as far as I can tell. That means they probably hurt performance and handling both, else those choads wouldn't mess with them.
When you say they didn’t stick, I think u mean on the dirt. Why not?
A road gp course is different enough I wonder if a bigger tire would stick better. Handling beside the point. What’s the fastest turning road wheel size? I assume the bigger the wheel the longer the context patch, probably not even bigger patch overall but somehow sticks to the road better. Following the logic bigger sticks better. more often said as smaller doesn’t lstick as well.
small + wide probably sticks as well as tall + skinny. It's probably a matter of total contact patch.
Larger wheels have more inertia, and better bump compliance, so this may be more desirable for the application at hand ( mountain bike ) or not ( go-kart )
I'm sorry for my vague expression. I mean they didn't catch a following in the market and therefore didn't stick around. I wasn't aware enough to care about them, or a motorcyclist back then, so I don't know if there were any perceived problems with them at the time.
