# Same gear ratio with a smaller ring?

Hi Lee,
I just got a Black Market MOB and want to run a gear ratio (single speed) as close to 36-17 as I can, but with a smaller front and rear sprocket. Can you tell me how to compute this or just tell me what the closest is?
Justin

 The more you click, the more I can post. Lee Likes Groceries dot com!

Hey Justin,

Chainring / cog = ratio

36 / 17 = 2.12

— — —

Chainring / ratio = cog

Say you want to run a 32 up front.

32 / 2.12 = 15.1

— — —

You can rock a 32 x 15.

Braaap!

5 replies
1. Justin Brown says:

Thanks…as usual, you are the man.

2. Miles says:

Lee Like Math

3. leelikesbikes says:

I love math — up to trigonometry … that’s when I knew I’d be a writer … 🙂

4. nathan says:

oh noes 17 is prime!

5. Jeff Kendall-Weed says:

A lot of BMX kids love their 25-9 set ups. I’ve never ridden it, but in theory you could go all the way down to 24/11. That would be a 2.18 ratio, quite close to your current setup.

The advantages to doing this would be more clearance and less drivetrain weight. The disadvantages would be that such small gears would wear out a bit faster, as the same amount of force from a 36 tooth sprocket, with roughly 18 teeth distributing the load, would be applied to a 24 teeth, with only 12 teeth on the chain. Anyhow, give it a shot if you want.