Best way to use chainring larger than MTB frame limit?

Equipment
1

I’m thinking about jumping on the drop bar MTB fad. I have a Boost-spaced 2017 Santa Cruz Chameleon with a Race Face Cinch crankset. The frame has a listed max chainring of 36t, presumably round, but I’d like to go with a 40 or 42, if possible. I’m thinking that I somehow need to move out the chainring far enough to clear the chain stay. I’m not sure what my options are, but if I have to replace the crankset, I’d like to know that whatever I replace it with will work.

What have others done for their drop bar MTBs? MTB double, fat bike crankset or spindle, crazy BB spacer options??

2

Have you looked into eThirteen cassettes with a 9T cog? It’ll help with top end without sizing up your chainring.

1 Like
3

The chainring is dished? Can you flip it over? That’d give you a test with the ring pushed 5mm out.

4

Other than using a 2x crank and putting the ring in the outboard position I dint think there is a way.

Although on another thread a guy said his shop just threw in a couple of spacers on the drive side and it worked. Not sure how though.

Joe

5

Thimk you can get zero-offset chainrings, which gives you an extra 3mm.

But tbh I don’t think its a good idea. I’d want a bit of clearance between the chainring and the frame, otherwise anything stuck on the chainring can wedge in the gap and damage the frame or even the chainring (and end your ride). Also your chainline will not be ideal and you might get issues shifting.

I’d look into either running a double or a cassette with extra small cogs instead.

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6

Would go 2x even if the frame cleared a bigger ring, and I think the Cinch is easy to convert. Check here:

How To Convert Race Face’s Turbine Cinch Crank for Fat Bike Use - Singletracks Mountain Bike News

7

Zero offset chainring works well. That is what I’m doing on my epic. Just leave some margin and it should buy you 2-4 teeth on the chainring.

8

Sram is really easy in this regard, as they(and other 3rd parties) offer 6mm, 3mm, and 0mm offset rings. Garbaruk makes direct mount Cinch rings, and they vary their offset as the size increases, with close to zero offset for their 40t versions, so that might work for you.

Truly though, I think people are way over geared on their drop bar mtb’s with tires greater than 2.0"… With so many running 10t cassettes, the difference in top speed between a 36t chainring and a 40t chainring is 10 additional RPM’s… 36t x 10t is well over 30mph at 100rpm(vs 90rpm in a 40t), which should be a manageable cadence for any durations that you’re actually traveling that speed, which won’t be much if you’ve decided a mtb is the right bike for the course.