ratios, gear inches, wheel diameter- Mtbr.com

# Thread: ratios, gear inches, wheel diameter

1. ## ratios, gear inches, wheel diameter

Back in the old days when if it was a mountain bike, it had 26" wheels, so describing gearing in terms of ratios made sense. Nowadays, with larger wheels, speaking in terms of ratios doesn't make sense, but I still see a lot of people talking about 2:1, 34x17, etc.

Seems like we should be comparing gear inches not ratios. 2:1 on 29" wheels is a lot higher gear (more gear inches) than 2:1 on 26" wheels.

2. Originally Posted by OldSkoolMark
Back in the old days when if it was a mountain bike, it had 26" wheels, so describing gearing in terms of ratios made sense. Nowadays, with larger wheels, speaking in terms of ratios doesn't make sense, but I still see a lot of people talking about 2:1, 34x17, etc.

Seems like we should be comparing gear inches not ratios. 2:1 on 29" wheels is a lot higher gear (more gear inches) than 2:1 on 26" wheels.
Gear inches is what I've used for quite some time now, since 2006 when I bought a 29er. It works great and Sheldon's (RIP) gear inch calculator works every time.

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3. Yup. I hate discussion about gear combos when no one talks about tire size. A 27.5x2.25 and a 29+ tire are the same gear combo are not the same thing.

4. Please, everybody knows the smart kids have long moved past gear inches and gone on to gain ratio.

5. I am running 48.4 gear inches...

6. Using the application Gear Calculator.

48.41 here as well, on 3 of my single speeds.

I can make 11 mph comfortably at 76 rpm.

Gain is 3.62, but I don't understand that.

The ratio is 1.67

Sometimes I want an easier "gear".

7. I'm running 32x18 on 29x2.2 tires. Y'all do whatever math with that makes you happy. :beer:

8. Gain ratio takes into account your crank length, which gear inches does not. #cranklengthmatters

When is someone going to invent a gear calculator that takes into account my oval chainring? I want to know my ratio at each position in my pedal stroke.

9. The weight of the wheelset matters too. When are we going to have that discussion? Carbon valors vs a stick redline wheelset

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10. Weight doesn't matter in this context. This is just looking at the mechanical advantage your drivetrain can give you.

Originally Posted by Rod
The weight of the wheelset matters too. When are we going to have that discussion? Carbon valors vs a stick redline wheelset

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11. Lots of variables indeed. I've always ran 180mm cranks on single speeds on general principle that you need more leverage if you've only got one gear. Will have to look into the gain ratio thing.

12. Originally Posted by Jack Burns
Using the application Gear Calculator.

48.41 here as well, on 3 of my single speeds.

I can make 11 mph comfortably at 76 rpm.

Gain is 3.62, but I don't understand that.

The ratio is 1.67

Sometimes I want an easier "gear".
Gain ratio of 3.62 means if you rotate the pedals 1 inch, your wheel will travel 3.62”; if your pedal travels one foot, your wheel travels 3.62 feet...

Same with miles, millimeters, kilometers, or any other measurement of distance...

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