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BMC blast with Shimano Deore drivetrain of 10 gears (1x10) requires too fast a cadence for 90% of my rides, can the chainring of 32t be replaced with a 44t or 42t chainring?

Explanation: I commute by bike to work every day and have done some touring, so why not a gravel bike? I have a nice Bianchi road bike for the weekends (only) and my daughter and grandson are into mountain biking on easy trails and I would like to join in w/o having to buy a third bike. My 28 year old mountain bike had 3 chainrings but I only use the 42t chainring.

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  • What kind/model of crankset does it have? You can always change the whole crankset, if you maintain the chainline. Nov 21, 2022 at 15:15
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    Can you confirm your BMC blast is a 27.5" wheel size? It was hard to find much information on the bike, and some of that information was referring to bikes intended for children
    – Andy P
    Nov 21, 2022 at 15:48
  • I assume you've done the cadence calculation already? 90rpm on 32x10 means you're traveling at 37km/h. What sort of sustained power numbers do you intend to push to go faster than that on the road? Nov 24, 2022 at 14:19
  • Also, if you're truly after a road and trail worthy bike a double chainring would probably be a fantastic solution to your gearing challenges. Nov 24, 2022 at 14:31

2 Answers 2

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1x mountain bikes frequently come with very flared chainstays to boost tyre clearance. This usually comes at the expense of limited clearance for larger chainrings.

I was unable to find any documentation for this bike, but judging by the images I could find, it looks like you might be able to fit a 36t but not much more. It would be best to contact BMC support directly to find out the maximum size.

I would however suggest that you almost certainly dont need a 44t chainring on a MTB. Professional male MTB riders are using 36-38t chainring on their 1x system. A 44/10 top gear would be comparable to what most amateurs have (but barely use) on a road bike and allow speeds of ~65km/h.

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  • Thanks for the responses. I have not bought the bike yet so I will get the info from the bike shop and take a close look at the chain stays as you suggest. The tires will be changed to 2.1 slicks as commuting is the main use for the bike which will replace a very old specialized with a 42t chainring. I have been hit by cars 3 times on it, so it was a very good bike to last 28 yrs.
    – Tony Reyes
    Nov 21, 2022 at 16:23
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    OK - the chain stays will not be a problem and according to my mechanic the only question is if the biggest cog will work. So I had it ordered to see. Perhaps the chain must be enlarged. Thanks and I will let you know how it works because this set-up is perfect for commuters that want 2" tires and ride a trail or MTB for bad roads, jumping onto the curb or riding on the road side to evade traffic.
    – Tony Reyes
    Nov 21, 2022 at 18:25
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I agree previous answers, 44 or 42 tooth chain ring seems very large, being as you've not brought the bike yet perhaps a better idea might just to be just buy a bike more suited to your use.
There are many capable MTB options which have 2x drivetrains which might offer the gear range you're after.

Even though on your old bike you might have only ever used the largest chain ring, the cassette at the back was probably larger making up the difference, maybe 12-14 tooth smallest gear.

My HT came with a 32 tooth chain ring, and I also thought it seemed quite small, but after trying it, I've got no problem.

And would also add, there isn't much I can't ride on gravel bike that I can't ride on my HT MTB (as long as I take my time)

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