So I’ve currently got a 32 chain ring on my Shimano M7100 crank set. I’m going to be doing the Goats in Portugal again next year and Ed the race organiser has changed the route slightly and is definitely recommending a gravel bike with 38 tooth chain ring.
I’m not buying a gravel bike and sticking with my hard tail 29er which is 1 x 12 gearing.
I’ve bought a 34 tooth chain ring which seems to give me a bit more top speed across the downs but here’s the question.
Why don’t Shimano do a 36 tooth?
Looks like they do a 36t SM-CRM85 chainring for XT M8100
They do in XT and XTR - both compatible with your cranks.
Does your frame have clearance to take a 36T on the current chainline? Many bikes are 32/34T max, which may be why Shimano have less options in bigger sizes.
if you have clearance, SMCRM85A6 (XT 36T) or SMCRM95A6 (XTR 36T) will work.
if tight for clearance, and you can tolerate a wider chainline, the latest generation rings from the new model cranks may fit as they’ll give you a 3mm wider chainline.
SMCRM86A6 for XT or SMCRM96A6 for XTR.
Those look they would do the trick actually. I was too tight to buy the shimano tool for taking the lock ring off but I have the security hex bit set so bought Shimano SLX SM-CRM75 34t to just swap it out.
Ill give the 34 a good test period and if its still lacking in top speed, I'll blow the dust off the wallet.
34x10 is a tall top gear on a 29er MTB anyway...
Don't forget that the increase in circumference from a typical 700x45c Gravel tyre to a 29x2.3" MTB tyre is around 4.5-5%, which is the equivalent of 2 more teeth on a chainring of that size anyway...
Always better to spin out slightly anyway than to run out of gears at the bottom end IMO!