Do bigger wheels climb steeper hills?

[makster]

I'd markedly quicker up hills on my regular ride on my 29er hardtail than I've been on anything I've ever ridden up previously, and in a year when I've had serious fitness issues due to injury.
I thought biggers wheels were a marketing scam....until I tried them!

 

[GrahamJohnWallace]

Undoubtedly - I have a rigid 29er running 3" tubeless tyres (Surly Knards), I can climb stuff that a fitter and younger me repeatedly failed to ascent in the last 22+ years on various bikes. Even more so with tubeless tyres, which can be run below 10 psi, which puts down twice the footprint of a 26 tyre - I was out today with my mate riding his top-range, full suss Specialized 26er and he was doing lots of walking. Even better, my I left him for dust on long, downhill trails too. We have lots of steep, sandy climbs around here that are the beating of any regular MTB. There's no hype - I designed the frame and had it custom built for me to do a job

But is what you are experiencing down to the larger wheel size? The big volume ultra low pressure 3" tyres? Perhaps something in the geometry of the bike you designed? Or the combining of these and other factors?

Could an old bike running 3" low pressure tyres, hill climbing tuned geometry climb just as well? The only old bike I know of that matches such a description is the 24" wheeled Dingbat. And I don't know of any surviving examples. What I can confirm that what you say of wide tubeless tyres run at very low pressures is correct. The traction is incredible, and this alone may explain what you describe with your bike. But I know that this approach also works with smaller wheel sizes because my 26" Cleland NRS can climb a local 44% incline that many other bikes cannot. Including modern ones.


My question is not whether bikes with 3" low pressure tyres and sorted geometry can climb steeper hills. From my own experience I know that they can.
But can a bog standard 29er? Which is geometrically very similar to a 26er but with higher axles and a longer wheelbase.

I have gone through the physics involved in cycling steep hills but cannot find a clear reason why raising the wheel axles another inch from the ground would make a bike a climb considerably better. And this is before factoring in the downside of the longer rear end. Which in my experience is a common trait in bikes that cannot climb my local 44% test hill.

I am currently building a 29er that will use wide ultra low pressure tyres. So that might help me to test these issues.

 

[GrahamJohnWallace]

I'd markedly quicker up hills on my regular ride on my 29er hardtail than I've been on anything I've ever ridden up previously, and in a year when I've had serious fitness issues due to injury.
I thought biggers wheels were a marketing scam....until I tried them!

I am quite happy with the concept that bigger wheels can roll faster over rough ground and so theoretically climb faster than a 26" bike of the same weight. But my particular interest here is whether 29er wheels allow you to climb significantly steeper hills. As claimed by a local bike shop assistant.

 

[makster]

I'd markedly quicker up hills on my regular ride on my 29er hardtail than I've been on anything I've ever ridden up previously, and in a year when I've had serious fitness issues due to injury.
I thought biggers wheels were a marketing scam....until I tried them!

I am quite happy with the concept that bigger wheels can roll faster over rough ground and so theoretically climb faster than a 26" bike of the same weight. But my particular interest here is whether 29er wheels allow you to climb significantly steeper hills. As claimed by a local bike shop assistant.

There's nothing on my route that's beats me on any of my bikes, so I can only go on how fast I get up them

 

[GrahamJohnWallace]

It is an interesting point you raise makster. Because the properties required for a bike that can ride up hills quickly are not the same as those needed for a bike that can climb very steep slopes.

To climb well you need good rear wheel traction, a stable platform with a high rearward tip over angle and ultra smooth power transmission.

But to ride up hill quickly you need light weight, efficient power delivery and low rolling resistance.

 

[makster]

I'd have thought that smaller wheels would be better, the steeper the hill gets.
Surely a small wheel accelerates quicker so should be easier to keep turning slowly?
Lets face it though, kids in bike shops rarely know more than what they've been told by a sales rep.
One in my lbs refused to believe there are specific pads for ceramic rims :roll:

 

[clubby]

Just going from my experience I find my 29er less prone to wheelying on steep climbs. I put this down to a number of factors, some of which may be specific to my frame (cannondale flash 29er). Bottom bracket is lower in relation to axles compared to a 26er. Longer wheelbase. Better traction. This lets me keep more weight on the back, stopping it spinning out, while not worrying about the front wheel coming up.
That said, other factors can also play into it. My 29er is lighter than my other bikes and also has a longer stem, keeping more weight over the front.
A lot of it a the moment may be due to most 29ers being designed as XC/race bikes while 26ers are full sus or hardtails designed around long forks.

 

[Retroms68]

In my experience it boils down to a combination of many factors. But if you take away rider fitness and gearing by assuming the riders of each bike are as fit as each other and that the gearing is set up the same , it then comes down to traction and geometry. The 29er puts down a slightly bigger footprint , has a longer wheelbase and if the centre of gravity has been messed with to account for being higher then physically the 29er has the advantage.

However I strongly doubt they are the magical climbing machine that suddenly makes you a better rider as described by some young scroat of shop assistant in the bike shop.

Most of us were riding up scary steep stuff on our lightwheel steel 26ers when they were still having nappy changes.

 

[GrahamJohnWallace]

In my experience it boils down to a combination of many factors. But if you take away rider fitness and gearing by assuming the riders of each bike are as fit as each other and that the gearing is set up the same , it then comes down to traction and geometry. The 29er puts down a slightly bigger footprint , has a longer wheelbase and if the centre of gravity has been messed with to account for being higher then physically the 29er has the advantage.

As far as I understand it, for the same tyre pressure, a 29er has the same footprint area as a 26" tyre of the same width but that footprint is longer and narrower. And the key difference is that with the 29er you can enlarge the footprint buy running lower pressures with less risk of the rims grounding.

In other words at 10psi a 26" tyre is flat, whilst a 29" still has flotation.

However I strongly doubt they are the magical climbing machine that suddenly makes you a better rider as described by some young scroat of shop assistant in the bike shop.

Not a young scroat but a guy in his late 30's/early40's. And it's a specialist mountain bike shop staffed by enthusiasts who actually ride off-road. However he didn't want to justify his opinion beyond saying that I couldn't know how good they are until I had ridden one up a steep hill. And the 650b bikes I have been successfully riding up steep hills for the best part of 30years apparently don't count. So apparently only 29ers can excel on hills. 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".

Most of us were riding up scary steep stuff on our lightwheel steel 26ers when they were still having nappy changes.

I have been riding steep scary stuff since the spring of 1984 and so 'am now getting quite good at it. I do know of one local slope that I haven't seen anyone climb. And would be love to be able to fine tune a bike so that I could conquer it.

 

[Retroms68]

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.