30t to 32t or 34t

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Posted: Apr 14, 2021 at 1:26 Quote
I just got a new bike with 1 x 12 Shimano Deore/SLX drivetrain:
- 30T upfront
- Shimano Deore M6100 10-51 cassette

Even on the toughest climbs, I'm not using the two largest cogs on the cassette.

Two questions:
1) Since I'm not utilizing the two largest cogs on the cassette, should I go to a 32T or 34T upfront?
2) If I do go to 32 or 34T, do I need to replace the chain?

TIA!

Posted: Apr 14, 2021 at 3:15 Quote
i suggest looking at your frame manufacturer.
some manufacturers have a max chainring size depending on your size frame.

i run a 32 and i sometimes bail to the 51 on long climbs and i rarely get to the 10t on the trail.

do you think you'll go fast enough to get to 10t with a 34t chainring?
you might have the problem of unused gears on the opposite end.

Posted: Apr 14, 2021 at 4:07 Quote
I would go to a smaller cassette. Taking away weight vs. adding it. I run a 30/45 combo. If you are not using the top two, this will be plenty.

Posted: Apr 14, 2021 at 4:21 Quote
shimshonite wrote:
I just got a new bike with 1 x 12 Shimano Deore/SLX drivetrain:
- 30T upfront
- Shimano Deore M6100 10-51 cassette

Even on the toughest climbs, I'm not using the two largest cogs on the cassette.

Two questions:
1) Since I'm not utilizing the two largest cogs on the cassette, should I go to a 32T or 34T upfront?
2) If I do go to 32 or 34T, do I need to replace the chain?

TIA!
You can go 34 in front and you will still have largest cog as "backup". You should probably change chain because it could be link longer. Maybe current have enough slack - you will not knpw until you measure it. Changing casette would in ideal world mean also change rear deraileur with shorter cage deraileur otherwise you have looong cage without use. And its much cheaper to change front cog than cassete Smile
You can go to http://gears.mtbcrosscountry.com for comparing ratios.

Posted: Apr 14, 2021 at 5:04 Quote
Long cage would work. Shimano has a long cage for their XTR der with a 45, using it for 1 or 2x systems.

Posted: Apr 14, 2021 at 15:23 Quote
Most new bike can fit a 34t chainring, and since you aren’t using your 2 biggest cogs, get as big as your bike can fit. I switched from 32t to 36t and was able to use the original chain. I thought a longer chain would be needed, but everything has been working fine for 4 years. I bought a new chain when I switched chainrings, but it is still in the box.

Switching from 30t to 34t will make your 2nd largest cog ratio similar to what your 3rd feels like now. You still won’t use the 51 cog. I live near sea level with some hills, and 36t x 11-40 works for me but 36t x 10-42 would be perfect.

Posted: Apr 16, 2021 at 0:43 Quote
Thank you all for the valuable feedback!

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