Are 29ers worse on slow climbs?

The only difference I can really notice between 26 and 29 inch wheels is the pivot point of the front axle.

This + rear axle pivot + better at rolling over ‘patter’.
I still want a 29er back…

I don’t have a formula for that 🙁

Do you have to factor in the larger radius as well?

Yes. At a factor^2.

I think i did the calc before, think it came out along the lines of a 29er wheel having a 25% (from memory, could be a little out) larger moment of inertia than a 26″ wheel. So in a very naive way, any mass you have in the rim/tyre area, feels like 25% more on a 29er when accelerating per unit mass.

An example, take a 400g 29er rim, it would take as much effort to spin up as a 500g 26er rim, from and to the same angular velocities.

But then you have to factor in the fact the larger diameter of a 29er gives a larger linear velocity (rolling speed) per unit of angular velocity vs a 26″ wheel, ie a 29er wheel will be rotating slower than a 26 at the same rolling speed, therefore you don’t have to angularly accelerate a 29er wheel as much as a 26 to get from/to the same rolling speed. I have a feeling this will cancel out a majority of that 25% figure i stated above.

I think it actually does just come down to the fact a 29er wheel is simply heavier cos it’s bigger, i think someone else did some mass stuff as a proportion of rider weight, it makes naff all difference. The 29″ wheel size isn’t the cause.

completely subjective non-scientific input from someone who rode 29er exclusively for 18 months and recently tried 26 wheels again (after riding them for 20+ years previously).

I stand up more climbing on the 29er as each pedal stroke really seems to drag me up more than the 26er – it is noticeable. On the smaller wheels I will tend to focus more on smoothing out pedal strokes from the saddle. Perversely I use higher gears on the big bike almost never using the small chainring. My local training loop is dispatched in 10 minutes less on the 29er. But I really have to wrestle the 29er about and doing manuals is just took much hard work, the 26 bikes feel zippier and I am building a new one to make the most of this trait.

I only ride hardtails on flats and have to climb pretty steep hills on every ride locally. I also don’t have lungs like Indurain but I do have legs like Hoy – well not quite, but I am sure physiology and technique play a part in the experience too. I.E another random could come along on the same bikes and same trails and find it completely different.

I just realized that’s a long winded way of just repeating what has already been said – sod the physics and the rhetoric.

I have a feeling this will cancel out a majority of that 25% figure i stated above.

Yes, I think it cancels out exactly (if I’m remembering this correctly), so the energy required to accelerate a wheel up to some velocity is just the mass of the wheel multiplied by the square of the velocity and is independent of radius. The energy required to accelerate all the non-rotating bits to the same velocity is 1/2 mass times velocity squared of course, hence the rule of thumb that rotating mass is twice as important as the stuff that doesn’t rotate.

Well, that’s how I remember it anyway. Either way the difference between a 26 and a 29 inch wheel is probably below what any of us could detect.

Perversely I use higher gears on the big bike almost never using the small chainring.

on my old 26er RM I got a 22/36 11-32 drive chain, found I was dropping to the granny a lot when climbing due to the 36t “big” ring (normally run a 22/32 chainset). Swapped all that over to my 29er frame when I got it and… I hardly ever drop into the granny despite the gearing being higher due to the wheels. Dunno why this is.