I have a 40/52 currently, with a Shimano Z-something FD (forget off hand) -- nothing fancy. I've been thinking about changing to a 34/46, but out of curiousity, what about keeping the 52 and doing 34/52? I can't imagine the shifting being all the smooth, going from small to large; but what are the recommendations for max split between the two chainrings?

I've been thinking 34, as that would go 15% down--the extra gear that I've wanted--and 46 as it would keep FD change to 12T, or about 2 gears worth. But I'd probably miss that 52 on some of the long downhills; more importantly, 46-ish chainrings are not too cheap (at least to me). I'm not against something like a 36 or perhaps a 38; but I'm not sure that a 38 would give the full amount of drop that I might like. I'd love one of those triple 30/42/52 (well, maybe as a 30/40/52, as I've liked my current 40), but I suspect that is more work than it is worth on my bike.

The freewheel is a 6 speed 13-30, btw. 110 BCD chainrings too. Thanks for the comments.

Depends on the crank. Most modern double can't go smaller than 36 on a 130 bcd.

If a 34 fits, you will probably have some serious chain rub against the big chain ring in the small/small and the two next gears up. A 40/30 gear is pretty small (36 gear inches!), I would stay with what you have.

I wanna keep what I have, but I keep getting tired on the longer rides (25 miles), and wind up alternating between mashing (50rpm) and spinning (90rpm) on the hills. I haven't mapped all my routes, but I'm getting wiped out on 5% grades, especially after I've been riding for more than a hour (not 5% continous!). With fresh legs, I can just barely spin up a local 8% hill w/o having to stand; I'd hate to have to do that when tired. I've thought about taking it easier on my rides, but I'd never make it up any hills then.

Thanks on the advice. Maybe I'll keep an eye out for a 38, but I won't go crazy on changes then.

Since you have a 110 BCD crankset, I would suggest going to 50/36 or 48/34. Be sure that your front derailleur can go low enough, if it is a clamp-on there shouldn't be a problem. A braze-on type FD may not adjust low enough. If needed you should be able to compensate for the smaller chainrings with smaller cogs in the back. Personally I don't like more than a 14 tooth differential in the front, and less would be better. The bigger the shift the bigger the cadence change.

Al

It's a clamp on FD. The current 12T jump isn't too bad, but not exactly what I would want to be constantly shifting (I bet the newer ones with pins might be better). At the moment, I only use the 52 on downhills, when I can actually start pushing that higher gearing--on flat ground, I almost never am in the 52. I'll push 40x15, occasionally 40x13 if it's a slight slope with tailwind.

I find the 40 is just about the right size, but lacks at either extreme. I really really want a triple, every other chainring setup (in a double) is pretty much a compromise for me. Such is life I guess.

How about a different Free Wheel with a 34T cog?
You could possibly even fit a 7 speed if you have friction shifters?
I don't know if your Rder will handle 34 though.

https://sheldonbrown.com/harris/freewheels.html

I've thought about the 34 Megarange, but I don't like the 34->24 jump. I'm finding the 30/25/21/18/15/13 all to be usable gears on my current freewheel. Still, it would be about the extra 1 gear down, I have to admit, and not far removed from the price of a chainring. Plus, it'd have tighter gears for those few roads that are flat... Thanks for point it out, something else to think about.