Changing cassette size
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Changing cassette size
Question for any bike mechanics out there, or those with the knowledge: I currently run an 11-40 cassette with a XT Di2 derailleur on my 1X gravel bike. Can I change to 11-42 without making adjustments to chain length, and will the Di2 derailleur adjust itself to shift properly to the new size? 11-40's are impossible to find but some online vendors have 11-42 so I'm thinking of going that route.
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Welcome to Bike Forums.
Pointer, there is a Mechanics Forum here on BF that is better suited to this question.
However it will certainly get enough reads here in General to allow it to find help.
All Rear Derailleurs have a "Capacity" spec expressed as two numbers.
1. The largest size rear cog permitted.
2. The tooth difference between the largest and smallest rear cogs. + tooth difference between the largest and smallest front chainrings.
Obviously with your 1X (single front chainring) you are only counting rear cog teeth difference.
If your chosen cassette falls within these specs, the rear derailleur is good to go.
If it falls outside the spec's..... well there are many experienced opinions here to help with that.
All Shimano Specs available here
I think yours is on the far right of this page
As for the chain length.
We can't tell how long your chain is, how long your bike is, and the size of the single front chainring.
Best practice when changing a Cassette is to also change the chain. They tend to wear as a pair.
So one of the many "How to" videos on determining a replacement chain length will suite you well.
All the best
Barry
Pointer, there is a Mechanics Forum here on BF that is better suited to this question.
However it will certainly get enough reads here in General to allow it to find help.
All Rear Derailleurs have a "Capacity" spec expressed as two numbers.
1. The largest size rear cog permitted.
2. The tooth difference between the largest and smallest rear cogs. + tooth difference between the largest and smallest front chainrings.
Obviously with your 1X (single front chainring) you are only counting rear cog teeth difference.
If your chosen cassette falls within these specs, the rear derailleur is good to go.
If it falls outside the spec's..... well there are many experienced opinions here to help with that.
All Shimano Specs available here
I think yours is on the far right of this page
As for the chain length.
We can't tell how long your chain is, how long your bike is, and the size of the single front chainring.
Best practice when changing a Cassette is to also change the chain. They tend to wear as a pair.
So one of the many "How to" videos on determining a replacement chain length will suite you well.
All the best
Barry
Last edited by Barry2; 04-16-21 at 10:15 AM.
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Thanks Barry. I just put a brand new chain on, so that's not an issue. I was just wondering if I could upsize to a 11-40 from 11-42 without making any other adjustments.
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I think I found your RD spec, see the new edit to the Shimano page in my first post.
Chain is likely too short, but ONLY you can determine if the chain is of a suitable length, You may have already cut it on the short/long side... I can't tell.
Barry
Chain is likely too short, but ONLY you can determine if the chain is of a suitable length, You may have already cut it on the short/long side... I can't tell.
Barry
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Thanks all, appreciate the advice! Happy to be here on BF, should have joined years ago. Cheers
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Sorry, I thought noobs could still read PM's.
The PM simply states... please be careful.
If the chain is too short and you attempt to ride the bike, bad things can happen.
Be sure to test the shifting to the large cog when NOT riding the bike.
Didn't want you to bend or break anything.
Barry
The PM simply states... please be careful.
If the chain is too short and you attempt to ride the bike, bad things can happen.
Be sure to test the shifting to the large cog when NOT riding the bike.
Didn't want you to bend or break anything.
Barry
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If you feel like it, you could also take a picture of your rear setup shifted into the smallest cog, and another in the current cassette's largest (40) cog and post here for a looksee. Make sure you include the full derailleur and a jockey wheel assembly.