And does it really matter that much? I've been riding around on my geared commuter for the day at 48/19 which is about the same as 42/17 and it works pretty decent for me. The SS conversion I'm doing though is on a road bike, 27" that I want to finish this weekend. Any suggestions for that? The area I ride in has plenty of hills, and I don't think I'll have too much of a problem.

Am I nitpicking this to death? I just want my first SS to be successfull, and an enjoyable ride.

Thanks

Go with 42/16 because you can get a cheaper (but very good quality) Dura Ace cog.

They are very similar and not enough to lose sleep over. I've run both of those combos on my bike and I notice the diff. between them mostly on the down hills, I like the harder gear better.

Personally I like the 17t cog simply because every gearing will be relatively prime which is good for tire wear, rim abuse, teeth wear and the like. Others acuse me of being obsessive and that may be true too.

Try a 42x15 gear ratio... a little over 77 gear inches. I find that this ratio allows me to tackle most hills in relative comfort, yet still be able to keep up or beat most of the roadies that I encounter.

I went back to a larger cog the other day and couldn't stand it. Almost too much spinning for my taste. YMMV depending on the terrain, but thats just my input.

-Pete

I like an all around larger tooth count. I ride 77" but on 47/16. It makes it harder to throw a chain. But between the two quoted, it's not such a big deal. It's about a 6% difference between the two.

(BTW, by Sheldon's calcs, 42/15 is 73.6" or 75.6" depending on whether you're on 700c or 27" wheels. https://www.sheldonbrown.com/gears/)

Hmm, I used the SSconvert program to give me number based upon 700c wheels. Interesting discrepencies.

And I thought I was so tough...

Formula:
diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket.

Thanks for all the replies. I think I'll just flip a coin LOL. Really though I'll go 42/16 since that'll get me where I want to go I think. Like was said, its only a 6% difference.

Thanks again!