[preparation_h]

Just thought this was interesting.
http://teamhealthfx.com/blogs/dave_harris/archive/2006/01/02/309.aspx

 

[- Jeremy -]

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 -

 

[29inch]

logic dictates that a larger wheel with more rotational mass would take more energy to overcome inertia.

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.

 

[- Jeremy -]

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.

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.

I think of the drivetrain like a lever. On his 26" setup, the larger end of the lever would be where the force is being acted upon (pedal) and the shorter end of the lever is where the force is acting upon (tire / ground). The hub would be the fulcrum. On the 29" setup, that pedal end of the lever would remain the same length, but the tire end of the lever grows in length. Thus, you lose your mathematical advantage while pedaling. To compensate, you'll have to increase the length of the pedal side lever by lengthening the cranks and lowering gear ratios.

Flats, downhills and coasting definitely give the advantage to the 29'er due to the greater rotational inertia and better angle of attack.

- Jeremy -

 

[DeeZee]

Intense Cycles

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 -

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.

 

[crashing_arizona]

data interpretation

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?

cheers,
Sam

 

[derby]

unequal major factors

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.

- ray

 

[ernesto_from_Wisconsin]

ride them

I just ride.

 

[- Jeremy -]

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?

cheers,
Sam

Yeah, Sam. He spent about 2.8% more energy on the 26'er and therefore was roughly 2.8% faster. I just think he rode harder on the 26.

If you took two identical bikes, one 26er and one 29er. Gave them the same parts spec and tires but magically made the 29er weigh the same as the 26er and also gave the 29er ~6% more drivetrain leverage to match the extra ~1.5" wheel radius. Then you slapped on some motor that spun at a constant rate which varies wattage as required and pointed them up a hill. Both bikes should make it to the top in the same amount of time and expend the same amount of energy.

I think the argument that a larger wheel requires more energy to accelerate is negated by the fact that the rotation also carries more momentum and is just as resistant to slowing down as it is to speeding up.

I could be wrong

- Jeremy -

 

[Cloxxki]

>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.
Get a wheel, give it a spin, and lift it. Stop the wheel, lift again.
29" adds 350g per bike, period.
Or do you mean the varying speed of someone pedaling too slowly on a climb? The heavier wheel will also help keep the speed once put back in. It plays even.

>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.
I've got 100 bucks saying you can't follow me through a sequence of nasty turns when riding the 26" versions of my tires. Even though you're right, 29" tires will bite less deeply.
I'll let you in on a secret, that makes them faster! and the place where they bite, being a longer narrower contact patch, places all the pressure where you want it, down the middle, rather than spread over the sides.

 

[- Jeremy -]

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.

- ray

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 -

 

[ernesto_from_Wisconsin]

spreadsheet

He spent about 2.8% more energy...

What a bunch of malarky. He probably spent more energy writing the spreadsheet.

 

[ernesto_from_Wisconsin]

my...

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 -

My triathlon bike is faster than my 29er...what's wrong with that equation? is it the un-aerodynamic knobs?
Is it the fact that my triathlon bike has aerobars and my 29er has the Midge? or that sometimes gnomes cry when poked with frozen french fries?

 

[Nat]

Some questions enter my mind:

• Did he account for differences in physical ability from one bike to the next, meaning how did he know if he was more tired on one ride versus the next?

• Did he have the same nutrition?

• Was he more dehydrated one ride than the next?

• Did he take a leak or poo and weigh less?

• He admits to developing bias. Was there any bias to begin with?

• Was it hotter out one day than the next?

• Did he wear identical clothing?

• Did he get a good night's sleep?

• Did his tires track on exacctly the same line each ride?

• Did his chain have less lube in one trial than the other?

Despite all our efforts to control the machinery and mechanical factors, I've never seen how we can eliminate the human influence on a small sample size. I think you'd have to have a study with a research group of LOTS of participants to see if there's a pattern.

Or, you'd need a machine to propel two bikes with unwavering output, and the two bikes would have to be identical in every way except for wheel size. It would be a dynamometer for bikes. Even then, what machine could adapt to technical terrain and know when to pop a wheelie to most efficiently get over a log? What machine knows how to unweight the rear tire just enough to keep it from slipping under power when crossing a slippery, wet root? Finesse gets us up and down a trail as much as does efficiency.

 

[richwolf]

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.

- ray

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.

I think the real answer of 26er vs. 29er will come on the racing circuits. If a 29er rolls better and is more efficient then why would a racer not use it?? If I spent hours and hours training and watching my diet and beating myself up to compete at a high level, why would I dismiss equipment which would get me to the finish line faster?? Racers are fanatics and will do anything to be number one.

I think people who get 29ers are a lot like anyone who gets a new bike. "Oh it is so much better, so much faster, so much more efficient" and on and on. Usually a lot of the differences noted are due to superior forks, different wheels and tires, nicer components and the fact that new stuff usually works better than old stuff plus the justification factor.

 

[jugdish]

wow, this thread takes all the fun out of riding. can't you all get back to using your big brains for evil purposes and let us get back to the joys of biking?

 

[Nat]

wow, this thread takes all the fun out of riding. can't you all get back to using your big brains for evil purposes and let us get back to the joys of biking?

This happens every winter.

 

[jugdish]

This happens every winter.

sure `nuff.

 

[RobW]

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...

 

[Cloxxki]

Last SS race I did, I won, on a 29" bike
I made the real difference in the endless left-right twisties, 200 real corners over a good 4-mile lap. Simply a higher pace there than any 26" bike could follow. My tires weren't real rollers, but the 26" bikes had to work hard to keep closing gaps in the short straights.
I like these discussions. People get to tell me how much my bikes suck, and next summer they'll to comment it from behind me