Just looking at switching my arkose over to SS for commuting purposes and bumbling around with sprocket/chainring sizes. Why do people generally go for a larger front chainring? I have a 38 tooth on the front so was looking at 14 rear rather having to get both sprocket and chainring for the time being. This gives me near enough the same gear inches as 47/17 (used as example ratio as it was in my head from Patrick Seabase’s instagram) with pretty much the same speed at 90rpm according to bikecalc.com.

Is it purely aesthetic or is there some other benefit?

less noisy and less wear on the teeth.

14 tooth cogs never used to last me any length of time.

Better chain wrap with bigger sprockets = less wear.

Ok, thanks guys, makes sense.

The above is all true.

But the real reason? Looks like you’re pushing a big, manly gear!

APF

Track bike ancestry? Most track bikes have chainrings between 44 and 53t, so converting one for the road it’s easier to find 17/18/19/20t sprockets for the back than it is to find a smaller chainring.

Then when fixies/fakengers took off a mix of availability and aesthetics kept things like that. Unlike say MTB where ground clearance gives an impetus to run 32-something rather than 38- or 44 something, or at the extreme ‘microdrive’ on BMX and trials bikes using 22t front chainrings and tiny 9t cassette drivers.

I doubt 38-14 would wear out unreasonably quickly if you used 1/8th components, but without other conflicting requirements, whyy make it worse than necessary.

Better chain wrap also means less likely to drop a chain.

Worth remembering that front sprockets are pricey, rear ones are cheap. So go for something around 18 at the back and match the front to start. Then you can easily tune gears going up to a 20 or down to a 16.

47:17 would be a good ratio in that the same chain links wouldn’t repeatedly hit the same teeth as they would with 48:16. Probably marginal benefits if any. Might be more of a fixie thing where you need different “skid” spots on tyres.

47:17 would be a good ratio in that the same chain links wouldn’t repeatedly hit the same teeth as they would with 48:16. Probably marginal benefits if any. Might be more of a fixie thing where you need different “skid” spots on tyres.

Huh, and I thought it was just a ratio he’d settled on for his alps type riding, never thought they’d be any science in it. Interesting.

Bigger chainring/sprockets = lower chain tension for a given power output.

And what’s it with the BMX Kidzz and their 11 t sprockets??
That’s only about 6 or 7 full teeth holding the chain at once…
Anyone sheared a tooth like this?

DrP

And what’s it with the BMX Kidzz and their 11 t sprockets?

BMX uses very small chainrings for bottom bracket clearance. Hence the small sprockets. Chain is usually at high tension. Not seen my son break a tooth.

Shimano freewheels don’t come in a 14T, only 16, 17 and 18. So that limits what I can run on the front.

And with large ring/large sprocket it’s easier to do small ratio changes.

Although need to watch clearance at front, I think a 42t chain ring was the most I could easily fit on my old MTB frame without things getting mangled. 15t I think cog at rear.