I’ve just bought a 29er frame forks and wheels from a mate and I am going to swap my 1×10 chainset over from my current Hardtail 26er. I have a 32T narrow wide up front and an 11-36 extended to 40t at the back. I am happy with the cadence I am achieving generally with this set up as it gives me enough pace on the downs and a slow enough winch for the climbs. My lack of mathematical ability is however letting me down with this query:

How will this set up shift when applied to a set of wheels 3″s bigger? Will I be ‘spinning out’ on the descents, or will I find it tougher grinding away up the steeps? Or are these theories thrown out of the window in reality, and I will probably be unable to pick up on any differences?!

I started with a 34t on the front but have gone down to 32t as I was using the bigger rear cogs to much, but now with the 32t I can climb without using the lowest gear.(most of the time). Using 11-36 on the rear. Really depends how fit you are. I’d stick with what you have and see how you go on

Your gearing will be higher across the board using the same kit on 29 inch wheels. Gearing is worked out wheel times chainring divided by sprocket to give gearing in inches

ie.29×36 div 11= 94.9 top gear

I have a 26 FS that was running 3×10.

On my default local trail, i did all the climbs in the middle ring 32T, and didnt use the bottom 2 sprockets of my 11-36 xt cassette. Its not the only place i ride, so when i went 1×10 i used a 34T Hope retainer ring and a 40t t-rex. It was great to ride, and i seldom bailed out into to 40T.

I then got a 650b frame, and when i built it up, i swapped the 1×10 drivetrain onto it. A trip to 7Stanes showed me that unless i was a bit less fit then i was in need of a slightly lower bottom gear as i was finding i was struggling to climb with my usual riding buddies.

Ive got a 29er thats going 1×10, so i started to do some ‘shed maths’.

I got all 3 wheelsets with their tyres fitted, and i measured the radius of each wheel in cm. I appreciate that rolling radius will alter when the rider is sat on the bike, but i chose to ignore it.

so, i got 34cm for a 26″ wheel, 36cm for a 650b wheel and 36cm for a 29er wheel.

using C=2×Pi x R, this gave the following wheel and tyre circumferences, for a 26″ wheel it was 213.6 cm, for a 650b it was 226.2cm and for a 29er it was 238.8cm.

so using equation for distance moved per crank revolution, = C x Fr ÷ Rr

on 26″ with 34Fr and 40 Rr, a crank revolution moves bike 181.6cm

on 650b, same gearing moves bike 192.3cm, however 32Fr and 40Rr moves the bike 180.9cm

and on the 29er 32Fr and 40Rr moves the bike 191.0cm, but order is restored with 30Fr and 40Rr, as this moves the bike 179.0cm

So im guessing i have just worked out what the rest of the world knew, but it was a joy that the experience of riding them tallied with the maths. However if id done the maths first i may not have bought so much redundant kit!

It’s about 10% higher.

It took me several paragraphs to say what richardthird said in 4 words…..

Or are these theories thrown out of the window in reality, and I will probably be unable to pick up on any differences?

You’ll generally notice you’re one cog bigger for any given situation at the back, but you’ll get used to it and it’ll be fine.

It’s about 10% higher.

So a 3 tooth smaller ring would give you the same gears. That’s not an option obviously, but a 30t chainring will get you pretty close.

Jumping from a 38T up front on my 26er to a 33T up front on my 29er (both with 11-36 cassette) resulted in a slightly lower climbing gear, but not much difference at the top end. I may drop to a 30/32T single ring up front in the future with a 10sp cassette, I can see the benefit of this.

In a nutshell… drop down one size on your chainring. E.g. 34T on 26er -> 32T on 29er.

I have kept gearing the same as the longer stays and longer wheelbase seem to make the bike more stable climbing and thus easier to put the power down (comparing my old XC 26er to my new XC 29er). Probably mostly placebo though 😉

I love the breninbeener ‘shed maths’ and oh so happy that richardthird massively simplified it. I guess if I feel the strain after a few rides I might be investing in a slightly smaller chainring. 30t might be on the cards. Thanks for all your input guys, I’ll let you know how I get on!

Best advice, fit what you have, ride it see how it goes then change if required.