REVIEWS DEALS BIKESHOPS TRAILS

Everyone's favorite topic, gear ratios! but with a twist I hope

1424 Views 5 Replies 5 Participants Last post by BansheeRune, Nov 4, 2021

Redlands R&C

Discussion Starter · Nov 1, 2021

Gear inches, check. Gain ratio, I never bothered to understand it much. My go to lately for my year of singlespeed has been the handy Sheldon Brown gear inches charts. I mostly target 40.x-41.x gear inches for a 29x3" tire and it has worked out reasonably well for me so far.

I should finally get off my ass and finish a fat bike build, which had me contemplating the gear inches again. This bike will be a 27.5x4" wheel.

Does the tire affect the gear inch ratio enough that I should compensate? Given that it can run lower pressures and get more sidewall wrinkle/contact patch would that matter at all?

Save

1 - 6 of 6 Posts

Shinkers

· #2 · Nov 2, 2021

Overall diameter should be about the same so I wouldn't expect a noticeable gearing change from the tire size.

That said, I bought a 24t cog to try on my fatty because riding in snow is a lot of freaking work... I'm also experimenting with lower gearing and dealing with that on descents.

Save

BansheeRune

· #3 · Nov 2, 2021

Gear inches is a very old way of looking at ratios for bicycles. Use inches or use ratio, it still comes back as the same end result.

Save

jmmUT

· #4 · Nov 2, 2021

I imagine the wider footprint and/or the higher rotating mass would have a perceivable effect. I've added a tooth to compensate for going with wider tires in the past, on the same wheels.

Save

Reactions: 1

CCSS

· #5 · Nov 3, 2021

I’d use gain ratios which take more variables into account…. Chainring, cog, tire size and crank arm length. Super easy on Sheldon’s site and a much better way to compare relative effort between different set ups. Also, a 26” or 27.5” fat tire might have the same diameter as a 29er running a 2.4, but it’s gonna have a lot more rotational mass to spin up…. I gear my B-fat bike down accordingly.

Sent from my iPhone using Tapatalk

Save

Reactions: 2

BansheeRune

· #6 · Nov 4, 2021

CCSS said:
I’d use gain ratios which take more variables into account…. Chainring, cog, tire size and crank arm length. Super easy on Sheldon’s site and a much better way to compare relative effort between different set ups. Also, a 26” or 27.5” fat tire might have the same diameter as a 29er running a 2.4, but it’s gonna have a lot more rotational mass to spin up…. I gear my B-fat bike down accordingly.

Sent from my iPhone using Tapatalk

I find ratio to be easier for the way I look at wheels driven by gears. Been doing gears in Transmission, differentials with different wheel/tire aspects for too many decades with bicycles and in the automotive worlds. The virtual dry erase board in my mind was formed through countless hours of experimentation.
With that said, gear inches are meaningless to my method of thought on the topic. I have no benchmark to consider the options from.

Save

Reactions: 1

1 - 6 of 6 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month