goldfinch

Spouse has a bike set up with a mountain group, Shimano Deore. The rear is a 10 speed, 11-36. The crankset has gears of 22, 34 and 42. The front derailleur is a Shimano M-611. The largest ring in front the specs say it will handle is a 42. The shifters are Shimano Deore indexed trigger shifters. And, to be complete, the rear derailleur is a M615 Shadow +.

My spouse would like higher gearing. Maybe a 46 or 48. The bottom end can be higher than a 22, but that would require a new crankset. What would we need to change? Is the rule for the front derailleur capacity hard and fast? Could we push the big ring up to a 44 or 46? What options does he have?

Bill Kapaun

You can probably make it "usable", but expect a decrease in shifting quality.
As you go to a larger big ring, you have to raise the FDER.
That means it'll be higher than it should be for the 2 smaller rings.
Also, as you get into the 46T range, the curvature of the FDER is "less correct".
"Mountain" FDER's tend to be designed (curvature) for either 42ish or 48ish large rings, with appropriately sized smaller rings to give approx. 10 tooth differences between rings.

As an afterthought, you might check to make sure larger rings are even available for your crank BCD.

Reynolds 

That's true on paper, but I've used a FD intended for a 22-32-42 with a 26-36-48 and it worked OK, then changed the 48 for a 44 and worked OK too. YMMV, however.

goldfinch

How would I find out if there are larger rings available for the Deore M610 crank that is on the bike? Googling isn't helping. I can find Deore M610 cranks that are 48/36/26, but they are pricey. Would any four bolt ring work? I know that there is ramping, how does that effect what I might get?

Bill Kapaun

You have to determine the BCD and number of holes your current crank has.
Then use your favorite search engine-

Sheldon Brown's Bicycle Crank/Chainring Bolt Circle Diameter Crib Sheet
The center to center column is the distance between adjacent holes.

It appears your rings are 104/64mm BCD's
Verify though-

Also, it seems there's a lot of rings dsigned for single speeds out there, so be aware.

Both my bikes have cheaper Shimano 110/64BCD triples, originally 22-32-44.
I needed to go the other way because of my emphysema.
After doing my calculations, a 37T ring was what I came up with, but odd sizes aren't to be had. At least not inexpensively.
So, I ordered a 36 and a 38.
The bike with the 22-32-38 shifts fine.
The one with 22-32-36 needs a bit of "help" to get it to the large ring. I basically have to overshift it a bit to get it to shift.
The FDER looks godawful high on it, but has to be that way to clear the middle ring when down shifting.

Originally, both bikes had FDER's designed for 28-38-48.
I installed FDER's for 22-32-42/4 and it didn't really improve things enough to justify the expense.

Here's a pic of how ugly the 22-32-36 install is-

FBinNY 

The first question is whether an aftermarket supplier offers larger rings to match your crank, or your budget for a replacement (and the related BB if necessary).

As to FD capacity, there are two basic issues, height and curvature. If you raise the FD (assuming there's room) for a larger chainring, the bottom of the cage may now be too high for the 22t granny.

Then there's curvature. FDs made for smaller rings have smaller radius curves in the cage. So they don't follow the curve of the ring properly and the effect is the same as wearing a hat that's too small. They touch first on the heel and have to be kept high at the center.

So, if you can find a ring, then it's a question of trying and seeing what you see. If it work, all is good. If you can't set the height properly, it's an FD too.

I suspect, that you could probably fudge it up to 46t, but probably not 48.

goldfinch

OK folks, I think I get it. And Bill, I did figure out that it is the 104/64 BCD. I'll see if I can find a 46t ring to see if it works and if it helps. Otherwise, it sounds like a major change and probably not worth it.

Thanks everyone.