Newb SS gearing/teeth questions- Mtbr.com

1. Newb SS gearing/teeth questions

So i plan on picking up my raleigh xxix this coming saturday. I have been riding my trek 4300 in one gear most of the time trying to learn to flow over things and keep my momentum up. Im mostly using 34teeth up front and 18teeth at the rear on 26in tires. The raleigh comes with 33/20 on 29s which seems to be a bit too low. How can i get a similar feel to what i have been riding on my 26er?

2. 34:18 on 26" wheels equates to about 49 inch gearing, whereas 33:20 with 29" wheels is approx. 47.8 inches - not a lot of difference then and any "feel" difference is likely to be down to the different bikes/wheel sizes and not because of any gearing issues.

I'd get used to the bike first and if you think it's still geared too low after that then go to 33:19 (50.3") or 33:18 (53") or whatever you like really....

33:20 seems in the ballpark to me though.

3. Awesome. I have been looking for that info and could not find it anywhere. Thank you very much. I can't wait to beat on my new ride.

4. Originally Posted by The Diesel
Awesome. I have been looking for that info and could not find it anywhere. Thank you very much. I can't wait to beat on my new ride.
It's just a little maths - take the number of teeth on the front chainring and divide that by the number of teeth on the rear sprocket (eg. 32T divided by 16T giving you 2 as a result).
Then multiply that by the nominal wheel diameter in inches (26" or 29" usually) and you get this "gear inches" answer (eg 2 X 29" = 58 gear inches).

It's really just a way of comparing effective gearing across different wheel sizes....

5. Originally Posted by Andy R
It's just a little maths - take the number of teeth on the front chainring and divide that by the number of teeth on the rear sprocket (eg. 32T divided by 16T giving you 2 as a result).
Then multiply that by the nominal wheel diameter in inches (26" or 29" usually) and you get this "gear inches" answer (eg 2 X 29" = 58 gear inches).

It's really just a way of comparing effective gearing across different wheel sizes....
Wow that's so simple. I have asking around on other forums and searching for this info and nobody seemed to want to help a newb. Thank you for taking the time to inform me. I'm a mechanic by trade so naturally I want to know everything about my bike and how it works.

6. I've often thought that it would make more sense if instead of just using the wheel diameter in the formula, the actual circumference was used instead - either by measuring one wheel rev. on the ground (like when calibrating a computer) or multiplying the wheel diameter by 3.142 (Pi). Then, once you factored in the actual gear ratio you'd see how far you travelled per pedal revolution.

So in your case where the gearing on your 26er is 34:18 that would give you 26" x 3.142 = 81.7" x your gear ratio which is 1.88:1 giving you 154" travelled for each complete crank revolution.
Compared to your 29er which would be 29" x 3.142 = 91" x 1.65 = 150" for each crank revolution.
So at least with this method you actually see just how close to each other those ratios actually are - if you want to be really accurate measure the actual diameters though, as tyre size makes quite a difference.( in the calculation, I mean..)

And yes - I have too much time on my hands....... (before someone else says it !)

Andy.

7. I see now. I think I'm gonna want a taller gear like an 18 or even 17 tooth cog.

8. Originally Posted by The Diesel
I see now. I think I'm gonna want a taller gear like an 18 or even 17 tooth cog.
33:17 on a 29er would be too tall a gear for me (well, round here anyway....) but only you know what sort of riding you do, I guess.

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