110 double... what rings to pick?
 

Just bought a 1985 League Fuji. Bike was converted to single-speed, using the original 110 BCD Sugino RT crank's 42t inner ring. I'll be going to geared. Got a bunch of freewheels in the parts box, 6 and 7-speed, mostly 12/13 - 26, couple of 12-28s. I've never built a compact double drivetrain before, not quite sure where to go.

The bike will be my vehicle, as well as for recreational riding. My daughter drives, so big shopping trips aren't really an issue. I live in Humboldt County, just south of Eureka, so most rides won't be super hilly. But, then, next year's North Coast 200k might be a thing I do, so one never knows.

What chainring combos would y'all think about? Are there advantage to using a different big ring than the 50 or 46 that all new cranksets come with? Also, are there any front deraiileur weirdnesses to deal with? Rear will be a 9-speed XTR, so no worries there. Friction shifting.

(Yes, I searched. Most threads seem to be about stock combos on newer bikes, or about front shifting issues which friction bikes don't have. This seemed worthy of it's own thread. If not, mods feel free to clobber it.)

Thanks,
--Shannon

I go low. Minimum on 110bcd if 33t. If you want smaller chainring you'd need another crank with smaller BCD. Or going with triple with a triplizer ring from ta or stronglight for 110bcd which allows you to mount a 74bcd ring to the inside but you'd have to bring the chain line outward by around 1.5mm compared to a double.

Other people may tell you that 33 is enough, but I go down to 14 great inches.

For a double, most cranksets come with 16t jump. I use 20t jump with a chain catcher. The chain will rub on the outer chainring when the chain is on the smallest 2 or 3 small-small combinations. But I don't need those gears anyway.

I have an excel spreadsheet with the gear inches of all my bikes calculated. Since I know what gears I like to ride in on my own bikes it helps me understand what a "14 inch" gear is. Also accounts for tire diameter.

If you are happy with the gear range of an existing bike than just stick to that on this bike.

With that said big rings only started dropping down to the 46-50 range when the larger range rear cassettes became popular. With the cassettes you have they always seemed to be 52-42 or 52-39.

On one bike I swapped the 50 for a 46, so 46/34. Works for me because I mostly coast down the hills. I'm not perceptive enough notice it made much difference overall, I'm fine with either.

Here is a nice calculator which lets you compare two drivetrains: https://www.kstoerz.com/gearcalc/compare/ I run 44/34/24-ish on my bikes with 28T max on the rear and find that this gives me the gears I use without useless (to me) >100 gear-inch ratios, and with plenty of low end. I prefer to spin than struggle.

My "new" compact double has 50/34 with a 11/32 cassette and shifts well and reliably even with Sora components. I'm happy enough with steep loaded climbing and fast road descents. I'd be okay with a 46, too. There's one partner I wouldn't keep up with but that's okay. I'm getting used to the 16-tooth shift.

I know plenty of people shift a 9 speed with friction, buy my one attempt at that didn't work so well.

that 110-33t is premium priced and only made AFAIK by TA of France.. 34t is easier & cheaper to get..

with cassettes going to 12t, a 46 outer should be sufficient.

Here is a better more visual gear calculator.
Bicycle Gear Calculator

So, after looking through the parts box, and playing with gear calculators and seeing what's available for purchase, here's what I've decided on:

Freewheel: NIB Suntour Pro-Compe, 14-16-18-20-23-26. Turns out I have a bunch of (12, 13, 14)-26 freewheels, and one 12-28. So, 26T it is, which allows me to use the:

Rear Derailleur: NIB Suntour Superbe, 1980 date code. I've had this since around 2005, when the shop I worked at bought another shop. The other RD I have is a 9-speed XTR, which, as fantastic a derailleur as it is, seems slightly wrong for this bike.

Chainrings (aka, "the actual question I actually asked"): For now, just the 42 that's on the bike. Because poverty. Soon, a 45t for a nice half-step setup, with a nice range for the flat-to-rolling Eureka / Arcata terrain. The sweet thing about this is that it turns out that swapping the inner 42t for a 33t turns the gearing into a wide-range 1.5-step with no other changes! 45T chainrings are easily available, and cheap, so long as one doesn't need ramps and pins, which friction-shift doubles don't.

Thanks for all the help, y'all!

--Shannon