I'm not sure I agree.- Jeremy - said:logic dictates that a larger wheel with more rotational mass would take more energy to overcome inertia.
My use of "inertia" in this case would be by the book as "resistance to change in motion." Any motion, whether it be moving or not. And I agree, once the wheel is up and moving, that larger rotational inertia becomes your friend, which is why I believe that the 29'er would have the advantage over the 26'er only if the drivetrain and crank ratios are adjusted to match on each bike.29inch said:I'm not sure I agree.
There's a very slight difference in effort to get the wheel turning from a dead stop, but that's not overcoming interia. After that first 10 feet or so from a dead stop, inertia becomes your best friend, and you work to maintain it. This a portion of the reason 29ers are faster, smoother, and less fatiguing over same distance/terrain.
I like what Intense cycles did. They compared a 26” Spider to their 29” prototype. Similar component groups and tested the two head to head. Comparing two totally different bikes is not a valid comparison.- Jeremy - said:Interesting...
His data says that he expended less energy at the hub on the 29". This simply tells me that he didn't pedal as hard on the 29'er. Or couldn't pedal as hard... Perhaps 180mm cranks would give him the edge. Then again, 180mm is only 2.8% longer (per arm) than 175mm.
He even admits that his ride on the 26'er was more "spirited". I interpret that as "pedaling harder". Maybe I'm wrong, but it just seems to me that he rode harder on the 26'er. Then again, he also rode some nasty, beefy tires on the 26'er that require way more energy to roll than the Fast Trak 29's. I'd like to see him ride Fast Trak 26's.
All things being equal in the drivetrain, I admit that logic dictates that a larger wheel with more rotational mass would take more energy to overcome inertia. That's why I advocate the use of longer crank arms and lower gearing on 29'ers. Or growing stronger legs
If it's possible to match drivetrain and cranklength ratios to wheel / tire size, then I think that the 29'er would be at least as fast on uphills and definitely faster on downhills.
- Jeremy -
crashing_arizona said:Is he interpreting the data correctly? He states that the power numbers for the Fuel are higher and equates that as being good. Don't higher power numbers mean you are expending more energy to make the same climb?
derby said:A third performance problem with bigger wheels for more aggressive riding is cornering grip. Due to greater ground contact, he tires just cant don't bite into the ground as deeply using the same tread, and so they slide out sideways noticeably more easily than smaller wheels.
My triathlon bike is faster than my 29er...what's wrong with that equation? is it the un-aerodynamic knobs?- Jeremy - said:I don't agree. The 29's carry a longer, more narrow contact patch. A tire of the same pressure deforms itself to the ground until an equal amount of pressure is reached on the air inside the tire. Therefore, a 29" tire has an equal size contact patch (say in mm^2), just in a different shape due to the larger diameter. So when leaning into a corner, and depending on the tire, a greater number of cornering knobs can contact the ground at the same time vs. a 26" tire. Which is evidenced by the 29" riders who swear up and down that they can rail corners with more speed and stability than they ever could on 26".
- Jeremy -
I think a bigger contact patch is preferable and gives better traction and grip while cornering. Why do downhill racers go to bigger tires?? Following you logic, 1.5 inch tires or even 1 inch tires would grip better but nobody uses them for serious off roading.derby said:Interesting test.
Much repetition and rest between tests would be required for more valid results. But on the surface the test with lots of climbing seems to represent two major performance problems with bigger wheels.
2 big factor differences:
A. The rims and tires are heavier on the 29'er, hurting climbing speed due to the repeated outer wheel acceleration/deceleration cycles normal to pedaled climbing. You'd need to add about a 1/4 pound or so of weight to each tire of the 26'er to match the difference in rim and tire weight of the 29'er tire. The flywheel effect to maintaining momentum of the bigger wheels won't completely offset the inertia differences when climbing. The flywheel effect becomes greater as speed increases, and almost nil at a slower climbing pace.
B. The final drive rate (crank cycle to distance covered) favors easier spinning in the same ring/cog combo with the smaller wheels. The 29'er has a much higher final drive for climbing gear options. Spinning is most efficient for climbing.
A third performance problem with bigger wheels for more aggressive riding is cornering grip. Due to greater ground contact, he tires just cant don't bite into the ground as deeply using the same tread, and so they slide out sideways noticeably more easily than smaller wheels.
Overall, somewhat like bigger cars or motorcycles usually have better comfort, so are bigger wheels bikes. You may not be able to cover distance quite as quickly or energy efficiently, but the pleasure level may be much greater. If you want to race to win, then smaller wheels rule, but not too small or they won't float the bumps very well.
Larger, taller, and heavier riders may benefit more (or have less efficiency loss when climbing) than smaller and lighter riders when using bigger wheels.
I still want a 29'er.
derbyA third performance problem with bigger wheels for more aggressive riding is cornering grip. Due to greater ground contact said:I call BS on this one. You gotta spend more time on one. Mine hooks up in the corners like velcro compared to my (now gone - sold to finance another 29er) C'dale...