Do bigger wheels climb steeper hills?

[GrahamJohnWallace]

Would also like to see one tackle a steep technical section where direction change or wheel placement is required by hopping and moving the bike around. Im sure that the larger bike must get in the way in those situations.

That is definitely true and I have noticed that steering on steep slopes is more controllable when using stems with little or no forward extension.

But I have just realised that an off the cuff comment in my last post may definitively answer my question.

"Though the physics of a tall heavier rider riding a 29er are identical to that of a smaller lighter rider riding a geometrically identical 26".

Someone riding a 29er is exactly the same as someone riding a 26er but with the rider and bike scaled up by about 10%.

And in that scaling up everything, including the physics remain in exact proportion. For example, the tyre footprint will get bigger but so will the weight of the rider and so the ground contact pressure per square inch will remain the same. And so both bikes will experience exactly the same traction in relation to the weight of their rider. All the other forces, reaction forces and their magnitudes and directions all remain in proportion.

The only relative change is that between the wheel diameter and bumpy terrain. So for the 26er the bumps will be 10% bigger, so increasing the rolling resistance.

But what happens if you put a tall / heavier rider on the 26er?
Well this would raise the center of gravity relative to the rear axle height thus making the bike slightly more liable to tip backwards during a steep climb.

And putting a shorter ,lighter rider on the 29er?
This would lower the center of gravity relative to the rear axle and make the bike slightly less likely to tip backwards.

In physics terms it is the angle of a force vector line drawn between the rear axle and the combined center of gravity that determines the point at which the bike will tip backwards. The steeper the angle the greater the vertical component of any accelerating force and the more likely the bike is to tip backwards.

So the relative radius of a 29er wheel will could result in a small increase in the angle of slope that can be ridden before the bike tries to tip backwards. But so in theory would moving the axle backwards and away from the center of mass. Or moving the center of mass forwards and away from the axle. And this is what we are doing when we come forward out of the saddle to tackle steep hills.

So my conclusion from all this waffle is that a 29er would allow you to remain in the saddle slightly longer than when climbing on a 26er.
It would however be much cheaper to move the saddle forward or to strap some heavy weights onto the handlebars or forks. In practical terms, moving the saddle forward 1" on a 26er should give a similar hill climbing advantage to that given by the 1" higher axle height of an equivalent 29er.

 

[FluffyChicken]

Be much cheaper and no doubt quicker to get off and walk/jog/run if it's steep enough for the bike to tip over backwards.

 

[GrahamJohnWallace]

Be much cheaper and no doubt quicker to get off and walk/jog/run if it's steep enough for the bike to tip over backwards.

Yep, anyone who has ridden off-road in the mountains near fell runners will know that they can climb much faster and steeper than any cyclist. They can often descend quicker as they can simply jump over obstacles that would stop a bike. Even bog standard Sunday walkers can climb much steeper slopes.

However, I have a policy of getting off and walking as little as possible. This is because in my mind getting off and walking is to be defeated by the terrain. Therefore, I will expend a vast amount of energy in the attempt to ride up a steep hill even when would be easier to walk it. And I don't care whether anyone else is there to see me succeed, because the challenge is between me and the hill.

Also for some reason, fast non-technical downhills, that many others love, do not interest me that much.

Each to their own, I guess!

Another problem with bikes is that it often takes more effort to push them up a very steep hill, than to ride them up.

 

[wookiee]

However, I have a policy of getting off and walking as little as possible. This is because in my mind getting off and walking is to be defeated by the terrain. Therefore, I will expend a vast amount of energy in the attempt to ride up a steep hill even when would be easier to walk it. And I don't care whether anyone else is there to see me succeed, because the challenge is between me and the hill.

Also for some reason, fast non-technical downhills, that many others love, do not interest me that much.

Right my 2 penneth...

I use Strava for my rides and on my 26" bikes I am noticabley slower than on my 29er. I am a hefty guy (6ft 4 ad 17 1/2 stone) so the 29er geometry just works better for me. I experience better traction and whilst it takes a bit more oooompf to get it going (marginal) once it is going it is easier to keep it going. I too share the "this climb aint gonna beat me" attitude and on the 29er its an easier decision! I'm not super fit, far from it, but maybe as a bigger guy its the 29er that suits me better. As for the how agile it is? I would trade in "agile" for controllable and grounded any day...I dont struggle with technical down hills either...just a different style of riding. In the same way that you would drive different types of car differently the same is true of 26" v 29". I find that I spend more time in the saddle on the 29er than on the 26er where I would have to get out of the saddle.

So back to the original question is it easier to climb on a 29er? For me yes but I appreciate that as a larger guy this could just be that it suits my build/weight better.

And to those who say that they leave friends on 29ers behind on group rides? It could be that you are just fitter! Maybe you should try a 29er and like Makster and I the scepticism may disappear and you could find to your surprise that the "fad" does have some substance....

Doug

 

[GrahamJohnWallace]

I find that I spend more time in the saddle on the 29er than on the 26er where I would have to get out of the saddle.

That confirms my theory that one effect of the higher rear axle height should be that you can ride steeper hills in the saddle. I intend to calculate exactly how much steeper.

So back to the original question is it easier to climb on a 29er? For me yes but I appreciate that as a larger guy this could just be that it suits my build/weight better.

What I do know is that you do not always need large wheels to climb steep hills as is demonstrated in the following video:
http://www.youtube.com/watch?v=mW6-ETJO2N0

Maybe you should try a 29er and like Makster and I the scepticism may disappear and you could find to your surprise that the "fad" does have some substance....

I would not describe myself as a sceptic. More curious / intrigued, and in search of explanations, hopefully answers?

I have briefly ridden 29ers and appreciate that some, but not all, are excellent climbers. I actually own two 700c wheeled mountain bikes. A new one that I haven't built up yet, and the other was made in 1982, but I have never ridden it because the steering tube was cracked when I bought it. I should get the frame back from the repairers at the weekend. Then I can start work on restoring it.

 

[velomaniac]

Ignoring the roughness of the terrain, climbing hills is down to power/traction/gearing plus of course balance. 29er only really wins in dealing with rough terrain. Some riders climb faster than others and thus its really down to the 1 H(human)P(pedaller) engine. Mines rubbish

 

[Woz]

Seriously, would a good test be to put some wide drop-bars on a BMX to shift the body weight lower and forward (assuming you will be riding off the saddle) and still rely on decent traction?

 

[GrahamJohnWallace]

Seriously, would a good test be to put some wide drop-bars on a BMX to shift the body weight lower and forward (assuming you will be riding off the saddle) and still rely on decent traction?

The contradiction is that you want the body weight forward to keep the front down yet at the same time rearwards over the rear wheel to maintain traction. Interestingly, the small wheeled Segway's superb climbing ability does not depend on the riders body weight being very far forward of the axle. But it does depend on the body weight being well away from the axle. In fact high above it. In this respect the Segway is behaving as a form of third class lever with the fulcrum at the axle, the output at the handlebars and the input in between where the motor is attaches to the body. The interesting thing with a third class lever, the human arm for instance, is that the longer they are the more rubbish they are at lifting weights.

This takes me back to 1984 when I owned two mountain bikes, a 26" F.W.Evans ATB fitted with wide deep drop bars and a 650b Cleland Aventura with high BMX style bars and a bolt upright riding position. Climbing on the Evans felt great but the moment you lifted out of the saddle the rear wheel would spin out. The Cleland was the opposite and you had to constantly battle to stop the front wheel lifting. However when standing out of the saddle and moving your body weight up and forwards it became a superb steep hill climber. Nowhere near as good as the Segways though.

I feel sure that in order to be a good steep slope climber a BMX would need high handlebars and very short chain-stays.

We still have not identified a good explanation of how wheel size could play a significant role in climbing ability!
Perhaps analysing the effects of putting big wheels on a Segway, might tell us something?

 

[Woz]

Conversely to your suggestion, if you look at some of the Moto X hillclimb bikes, they are built with a very long rear swing-arm and the rear tyre has paddles for grip (http://www.bignastyhillclimb.com/Data/S ... bbike1.jpg).

All things being equal, I'm of the view wheel size is not a factor at all in climbing steep hills. If anything, assuming perfect traction, a better climber would simply be a lighter bike - thus smaller wheels.

 

[GrahamJohnWallace]

Conversely to your suggestion, if you look at some of the Moto X hillclimb bikes, they are built with a very long rear swing-arm and the rear tyre has paddles for grip (http://www.bignastyhillclimb.com/Data/S ... bbike1.jpg).

There is plenty of room for a much bigger rear wheel on those hill climbing motorbikes. You would think that they would all use larger wheels if that would help them win competitions.

All things being equal, I'm of the view wheel size is not a factor at all in climbing steep hills. If anything, assuming perfect traction, a better climber would simply be a lighter bike - thus smaller wheels.

You may well be right. Of all the factors that influence the maximum incline that a bike can climb, relative wheel diameter may not be important apart from the bigger footprint produces more traction argument.

I've done the analysis of what putting larger wheels on a Segway would change:
1/The Segway would be taller. (Though this does not alter how the physics effect it as it climbs).
2/ The point where the wheel contacts the slope moves up the slope as the wheel gets bigger. Therefore the Segway would need to lean forward more in order to balance/find the point of equilibrium.
(This effect could be significant?) If not, I am running out of ideas!