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Discussion Starter #1
OK...I'll set myself up for this. I rode a Cyclo-cross bike for the first time last fall and it was faster than stink climbing a hill. At first I thought it was the fact that it weighed 18lbs, but I got to thinkin'. Could the 700c wheels have anything to do with it? Everyone says I'm wrong but let me present this.

If you are in the same gears on a 26" and a 29" wheeled bike. Everytime you turn the crank the distance the wheel travels is different. Let's say you are in a gear where 1 crank turn results in 1 turn of the cassette. For every crank turn, a 26" bike will travel (pi x d = 3.14x26") 81.64". However, the 29er will go 91.06" or 10" further with the larger wheels.

Now the argument I get is that the 29er is not necessarily faster because of the additional effort required due to the larger torque arm of the wheel. In other words, rocks and general frictional resistance create a larger force because they act further out on a 29" wheel (Torque=ForcexDistance). But is it a direct relationship???

My argument is that although the Torque created by "friction" is greater, the rolling resistance is less because the larger diameter rolls over impediments easier. So there is an advantage when it comes to speed.

Also a 29'er will weigh a bit more because it has larger wheels and tires. But my sense is you may pick up at most an additional pound.

So let the discussion begin. Do 29ers have an inherent advantage over a 26" bike based on the Wheel size? Are cyclo-cross bikes fast because of the 700c wheels and the inherent geometry or is it just weight that is involved. If they do have an advantage then why does NORBA and others allow Cyclocross and 29er's to compete head up against 26" bikes??? Shouldn't they have a weight penalty???

Have at it!!! ;)
 

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holy crap you must have taken some pretty heavy engineering courses
you just went way over my head
 

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Do you do when from one moment to another your wheels increase in size? You just shift back. The longer distance per crank rotation is near irrelevant, unless you come "short" with s 20-34t granny gear on a 26" bike already.
 

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Discussion Starter #5
Cloxxki said:
Do you do when from one moment to another your wheels increase in size? You just shift back. The longer distance per crank rotation is near irrelevant, unless you come "short" with s 20-34t granny gear on a 26" bike already.
Cloxxki, why do you say the crank rotation is irrelevant??? If you're gaining 10" everytime you throw the cranks in the same gear, then you are picking up something. I think the issue is can you pedal a 29er in the same gear as a 26er on a given slope? Some argue that you can't because the increase in torque due to the wheel size will catch up to you in the end, but I don't buy it.

It's interesting that everyone points out that 29er's are "smoother" but no one picks up on the circumference issues. Again, I'm surprised NORBA let's them and 700c bikes compete without a handicap. But then again, maybe there isn't that big of an advantage. :confused: Still 10" every stroke would certainly make my girlfriend happy :p
 

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say what???

dugodugo said:
It's interesting that everyone points out that 29er's are "smoother" but no one picks up on the circumference issues. Again, I'm surprised NORBA let's them and 700c bikes compete without a handicap. But then again, maybe there isn't that big of an advantage. :confused: Still 10" every stroke would certainly make my girlfriend happy :p
the difference in circumference and the perceived benefits, from longer, more tractable contact patch to gentler angle of approach with obstacles, is one of the thing that the rabid church of 29 choir here is constantly banging home...

also, stating that there isn't necessarily a gear handicap going to a bigger wheel, that you gain a miraculous 10" of forward motion for every wheel rotation without any extra effort, is kind of presumptuous. my 26" ss has a 35x18 gear on it. the redline moncog 29 i just got in to test has a 32x18. they feel pretty close in pedal speed for a given ground speed. however, the monocog sticks better, longer, before breaking traction. whereas the 26" coconino can be lumped up from a stall a tiny bit easier. if i ran a 35x18 on the moncog, it would kill me (in fact, i ran a 34x18 on a kelly 29 at the 2000 cream puff and the resultant psychological damage from that was brutal enough to scare me away from both ss and 29 for a few years)...

for reference: 34x18x29"=54.77" gear. 32x18x29=51.55". 35x18x26=50.55"
 

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People, people, when calculating gear inches to the 1/100", do at least use 26.5". The rim size difference is 2.5", not 3"!!

Check the FAQ thread for the real advantages and disadvantages, theoretic, real, or far-fetched.
 

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Discussion Starter #8
Thanks for the input

MtotheF said:
also, stating that there isn't necessarily a gear handicap going to a bigger wheel, that you gain a miraculous 10" of forward motion for every wheel rotation without any extra effort, is kind of presumptuous. my 26" ss has a 35x18 gear on it. the redline moncog 29 i just got in to test has a 32x18. they feel pretty close in pedal speed for a given ground speed. however, the monocog sticks better, longer, before breaking traction. whereas the 26" coconino can be lumped up from a stall a tiny bit easier.
Way cool...thanks for the input....this is real world stuff. So you are saying that you can really feel the difference of the torque reaction from a 29er??? I've never ridden one so I'm a newbie at this. I understand what you are saying about the contact patch, traction, angle of attack and all of that....it's the torque reaction I always wondered about.

Now about NORBA...I guess I'm thinking that yes there is a "torque penalty" but does it balance out the rotational gain??? I hope you understand what I am getting at. The torque "may" catch up to you in the end, but if the course is relatively flat or it's undulating enough where you can catch your second wind on the downhills, ultimately you will have quite an advantage on a Cross Bike or 29er..
 

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six of one, half dozen of another

dugodugo said:
Way cool...thanks for the input....this is real world stuff. So you are saying that you can really feel the difference of the torque reaction from a 29er??? I've never ridden one so I'm a newbie at this. I understand what you are saying about the contact patch, traction, angle of attack and all of that....it's the torque reaction I always wondered about.

Now about NORBA...I guess I'm thinking that yes there is a "torque penalty" but does it balance out the rotational gain??? I hope you understand what I am getting at. The torque "may" catch up to you in the end, but if the course is relatively flat or it's undulating enough where you can catch your second wind on the downhills, ultimately you will have quite an advantage on a Cross Bike or 29er..
for me, it's both good and bad. i love the way they roll out, and they definitely hold momentum. but i don't like the fragility of the wheels and tires compared to similar weight 26" stuff, and i don't entirely love the way they behave in technical terrain. many on here feel differently.

per racing, talking with travis brown recently, he said that he and JHK were doing side by side comparisons last year with identically set up 26 and 29 bikes, and that whenever they swapped off, regardless of terrain, the 29 rider would pull away. for what that's worth.

cloxxi, don't be so pedantic. 26, 26.5, whatever. there is enough variability in tire size that gear inch measurements are at best rough. how do you know the diameter of the 26" tire i was running? fwiw, i'll remember to bring my tape measure whenever i ride from here on out, if it'll make you happier...
 

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I guess he somehow missed the big stone tablets that commanded everyone to purge their lives of all things 26 and worship at the altar of the 29er or risk being smited by the gods. Jeez, people -- sure 29ers roll a little better, but they aren't magic carpets, fer cryin' out loud. :rolleyes:
 

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Li'l Bastard said:
I guess he somehow missed the big stone tablets that commanded everyone to purge their lives of all things 26 and worship at the altar of the 29er or risk being smited by the gods. Jeez, people -- sure 29ers roll a little better, but they aren't magic carpets, fer cryin' out loud. :rolleyes:
But they do grow hair.... :p

BB
 

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Discussion Starter #15
MtotheF said:
for me, it's both good and bad. i love the way they roll out, and they definitely hold momentum. but i don't like the fragility of the wheels and tires compared to similar weight 26" stuff, and i don't entirely love the way they behave in technical terrain. many on here feel differently.

per racing, talking with travis brown recently, he said that he and JHK were doing side by side comparisons last year with identically set up 26 and 29 bikes, and that whenever they swapped off, regardless of terrain, the 29 rider would pull away. for what that's worth.
...
Thanks dude...that is helpful. I could see what you're saying about technical terrain. In a rock garden the larger wheel is going to have a bigger impact on the steering force felt in the bars as you bang your way through it and take side hits. That makes a lot of sense.

So in a racing environment it does sound like the 29er's have an advantage on a course that is not straight up hill (like the Angel Fire World Cup Course...talk about straight up!!!). I had a sense that was the case....I wonder why NORBA hasn't figured that out yet. Last year's NORBA Finale was won by a guy on a Crossbike for cryin' out loud.

Hey edo....loved your comment....

"My 29er is the irresistable force and my 26er is the immovable object." :p

I have a Ti HT Airborne LS that I'm playing around with right now. Weighs about 22lbs. I'm looking for a B-29 and I figure if I can build it up at around 23-24lbs it would be real sweet. Just waiting for the component selection (tires, forks, etc) to get a little more developed.....

Keep the big wheels rollin' ;)

Dugo
 

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Tale of the power meter

Put on a power meter...or do some basic physics equations.

Any bike (regardless of wheel size), as long as it weighs the same and the surface is smooth will require the same power to climb a hill. The gearing/wheel diameter simply requires a different torque but when the rpm is changed (in order to get up the hill at the same rate) the power will still be equal. (you could simply change the gear ratio to account for the difference in wheel size)

But two bikes with the same weight/tires/etc. and no power input that are allowed to coast down a smooth hill from a dead stop DON'T get to the bottom at the same time....the one with the smaller wheels will win every time, due to the lesser enertia moment (resistance to acceleration or deceleration) in the wheels.

Real world....the surface is not smooth...now we must factor in the rolling resistance and moment of enertia (that resistance to changes in speed).

Now as soon as someone chimes in and starts saying that "a greater moment of enertia is why I like 29ers because once I get it going I can keep it going easier"...well, yeah that is true, but why does that same guy seem to ride light weight aluminum rims and tires....You would get an even larger moment if you increased the weight of the rim and tire with say, lead weights on the rims. anyone doing that? I think we have just embarked on why the advantage is also a disadvantage at times. (hint, I am not talking about the weight penalty of a 29er)

This is where things get complicated. Suffice to say that 29ers seem to have advantaged in some areas and disadvantages in others.

A 29er is not an unfair advantage...you may think it is, but I think you will find that the guys who whipped you when you had a 26er will still whip you on your 29er. You may feel better about your own riding though.

What is it really all about? Engineering the best machine science/money can provide (like Lance Armstrong), or enjoying the ride on whatever we ride? Personally, I like the 29er because it makes me feel like a kid...when I was little the wheels seemed so big.

Now, I am a big kid.
 

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Finally, a rationale discussion ...

dugodugo said:
OK...I'll set myself up for this. I rode a Cyclo-cross bike for the first time last fall and it was faster than stink climbing a hill. At first I thought it was the fact that it weighed 18lbs, but I got to thinkin'. Could the 700c wheels have anything to do with it? Everyone says I'm wrong but let me present this.
Without reason, everyone is wrong.

dugodugo said:
If you are in the same gears on a 26" and a 29" wheeled bike. Everytime you turn the crank the distance the wheel travels is different. Let's say you are in a gear where 1 crank turn results in 1 turn of the cassette. For every crank turn, a 26" bike will travel (pi x d = 3.14x26") 81.64". However, the 29er will go 91.06" or 10" further with the larger wheels.

Now the argument I get is that the 29er is not necessarily faster because of the additional effort required due to the larger torque arm of the wheel. In other words, rocks and general frictional resistance create a larger force because they act further out on a 29" wheel (Torque=ForcexDistance). But is it a direct relationship???
I've heard many, many people site this as a reason for why 29ers are slower. But if you look at the cassettes and chainrings of racers, you'll find that they prefer pushing bigger gear ratios due to their better strength to weight ratios.

In the end, I think it's a push. There is increased moment of inertia on the wheel. But as you point out, a single revolution of a 29er tire is greater than that of that on a 26er tire. The wheel will indeed take more oomph to get it to go once around, there is a reason for this, your talking about a larger distance.

Lets look again at the moment of inertia. Yes, it does take fundamentally more energy to turn a larger wheel. But you have have to compare this against the linear inertia of accelerating the frame and more importantly your body weight. What you will find is that accelerating that wheel is INSIGNIFICANT compared to accelerating your body.

For reference, put your bike (whatever size it is) on a repair stand and shift to the big ring and the smallest cog. Now turn it with your ARM!!!!!! That's right, just your SINGLE relatively weak arm. Than take if off the stand and ride it in the same gearing. This simple example should teach you the profound difference between the inertia in your wheels and the inertia in your body. It's relatively insignificant.

And lets remember that once you get your slightly heavier wheels moving, they have more energy in them than a 26er. Any spinning object is effectively a "battery" that stores kinetic energy. You will get all that energy back (though it's really not a lot) when coasting.

My argument is that although the Torque created by "friction" is greater, the rolling resistance is less because the larger diameter rolls over impediments easier. So there is an advantage when it comes to speed.
I would agree with this statement. Translating forward momentum into bumps tends to dissipate that energy via heat through bouncing the wheels. Many of the same people who diss 29ers will extole the virtues of riding big (and typically thin) rubber that absorbs the shocks and keep you going forward instead of up and down.

Also a 29'er will weigh a bit more because it has larger wheels and tires. But my sense is you may pick up at most an additional pound.
Yes, there is extra weight. And if you are a weight weenie, than that it bad no matter what logic is presented. All weight is bad and must be eliminated even it it impinges on the structural integrity of the bike (which will often cause breakdowns and really crappy times). It is a discussion that has NOTHING to do with bigger wheels and more to do with a religious obsession of status. Having the lightest thing makes you better.

I will point out that even though road racers are amazing weight weenies, there has been no push among them to decrease the size of their wheels. If you use the anti-29er reasoning, road racers would the same motivations to revert to a 26" wheel. Better acceleration and less weight, etc...

What is often pointed out in this regard is that the road racer has less need for a "strong" wheel than an off-roader. A 26" rim with the same profile will indeed be "stronger" than the same 29" rim. But this analysis often forgets what you pointed out in the first place. The 29" rolls over things better so you're less likely to get tacoed by that rut not from "strength" but simply from the fact that the 29er wont get caught in it like a 26er will.

All things are a matter of balance. I'm sure a good wheel builder can make a 32 hole 29er wheel just as "strong" as a 26er when you compare them on the basis of who tacoes when running into a 3 ft diameter tree trunk. When it comes to running over roots and logs, the increased angle of attack will negate any advantage of the smaller wheel and will likely save you on your helmet budget. Let's not forget the amount of time saved when you avoid an endo.

-----------------------------------

I don't own a 29er, but I hope to one day. The people around my area bad mouth them. They have no personal experience on one. I think that's largely because most people tend to relate more to personal experience than reason.

I took a 29er out for a test drive at the Fisher dealer and I was impressed. I was rolling over 3" high concrete slabs and they felt like twigs. That was my 280 pound body on 28 whole 29er wheels. I'm not entirely certain that a 28h 26er wheel would have faired so well. My 26er wheels have 36 holes and I'm certain that I need them.

When I do assemble my 29er, it will have 36 holes on strong rims because I just don't want to fool with it. A slightly heavier wheel with more spokes may not "turn as well". However, a tacoed wheel doesn't turn at all.
 

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Discussion Starter #18
The big Unit got it I think....

unit said:
Any bike (regardless of wheel size), as long as it weighs the same and the surface is smooth will require the same power to climb a hill. The gearing/wheel diameter simply requires a different torque but when the rpm is changed (in order to get up the hill at the same rate) the power will still be equal. (you could simply change the gear ratio to account for the difference in wheel size)
Unit....you nailed it I think. Both bikes will require the same power input to get to the top. The factor is who wants it more. Face it, riders do not optimize their power input. The guy cranking up the hill on his 26" HT may only be putting in 90%...while the guy on the 29er feels the resistance of the larger wheels, gets out of the saddle and hammers it at 100%....yea he's gaining 10" on each pedal stroke but he's having to put out the effort. If the course is undulating enough he can recover and keep his gains. However, as you correctly point out, it's all Kinetic Energy....the dude on the Hardtail could get out of the saddle too and selecting the right gear, put out 100% and have a higher RPM, negating the wheel gain of the 29er. Good point....I'm with ya.

unit said:
But two bikes with the same weight/tires/etc. and no power input that are allowed to coast down a smooth hill from a dead stop DON'T get to the bottom at the same time....the one with the smaller wheels will win every time, due to the lesser enertia moment (resistance to acceleration or deceleration) in the wheels.
Not sure about this though....you point out resistance moment, but what about reciprocating mass??? I think perhaps that they will get to the bottom at the same time as well, because the reciprocating mass is balanced out by the resistance moment...I could be wrong though.

unit said:
A 29er is not an unfair advantage...you may think it is, but I think you will find that the guys who whipped you when you had a 26er will still whip you on your 29er. You may feel better about your own riding though.
Hell...I got whipped by a guy on a single speed the other night and he gave me a 4lb weight advantage on my HT....you've convinced me though that the 29er doesn't have an inherent advantage.

unit said:
What is it really all about? Engineering the best machine science/money can provide (like Lance Armstrong), or enjoying the ride on whatever we ride? Personally, I like the 29er because it makes me feel like a kid...when I was little the wheels seemed so big.

Now, I am a big kid.
Right on dude!!!!!! :D
 

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Like a rolling stone

unit said:
But two bikes with the same weight/tires/etc. and no power input that are allowed to coast down a smooth hill from a dead stop DON'T get to the bottom at the same time....the one with the smaller wheels will win every time, due to the lesser enertia moment (resistance to acceleration or deceleration) in the wheels.
By this reasoning, if you put two ball bearings at the top of an incline and release them, the smaller one should reach the bottom first. I don't believe it for a single second.

Yes the larger bearing will require more torque to reach the same ROTATIONAL velocity. But that rotational velocity will equal a LINEAR velocity that is greater than that of the smaller bearing.

What about resistance? Lets assume it's optimum, a perfectly flat metal incline. We will assume the balls are also perfect spheres. We will also assume that the surface and the balls do not deform. If you measure the contact distance on both balls, you will find they travel EXACTLY the same distance.

In the real world, you do have to consider frictional resistance in the surface as well as air resistance in the body. When you figure in an uneven surface (it wouldn't be fun without one) I think you'll find the 29er reaches the bottom first because it travels straighter. Your forward momentum is not redirected into vertical motion and bouncing as much as on a 26er.
 

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I find that once the trail points down, my 29" wheels just WANT TO GO. No way that tiny bit of extra weight is resisting the bike to start to roll. Gravity is pulling harder on the wheels too, which evens it out.
Maybe on a speed record attempt, where you rolls down a snow wall, the greater frontal area of of the 29" tire will keep it from taking advantage of the lower rolling resistant. Maybe.

Reality : I find myself coasting and even braking my 29"er when riding downhills among 26" bikes that are being pedaled.
Reality : on flat smooth ground, my non-race 29" tires (don't own any yet, and only the Kenda Karma's exist) just don't roll as well.
Reality : 26" bikes on the supertires of their choice can't stay with me on winding singletrack. Not even with a fitter, more technical rider aboard.
Realtity: a 26" bike on my rear wheel will have to lift off for most every corner to not overshoot it, and then close a gap by pedaling harder while I never hit my brakes and never had to spin back up to speed.
 
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