corinthincamo

If 34/15 is similar in ratio to 42/18. What if any draw backs would there be to running a smaller chainring and cog. Are there measurable efficiency gains either way?

Tomo_Ishi

I think you are better off with 42/18. I think 15T might be too small and chain might skip. Sheldon Brown said gears and chains are less strained with big gears (given same gear ratio), too. (Go to https://sheldonbrown.com/singlespeed.html and look for an entry under "Big or Small?"

He also said clearance could become a problem, though. You should check in with Cyclocross forum to find out about the clearance you need.

queerpunk

i too have heard from trackies that larger chainring/cog combinations are more efficient.

i saw the title of the thread and was gonna chime in and say "i rode 42x18 for a few cross races and it was good."

'course if you don't want to spend money on a new cog and cr, you could just do the 34 15 or whatever you've got.

wearyourtruth

the reason a smaller chainring/cog combo is beneficial for cyclocross is the clearance of the chainring. a cyclocross frame is already designed with a higher BB for this. it's simple... the smaller your chainring, the taller the obstacle you can roll over without trouble.

it is true what has been said about chain wear though. a 15t will wear your chain out a little faster than an 18t.

as for efficiency, it's pretty much identical.

Cynikal 

I run a 38x17 with is about the same. It's what I had in the parts bin and works. SS CX kick a$$.

mihlbach

This is nonsense.


A+

corinthincamo

Great info. I am going to run 34/15 see how things go. I'll report back with my opinions once cross season gets under way. Thans

Dion Rides

I think you can post this in every thread, on every board, on BF.