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Gearing changes and chain length

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Gearing changes and chain length

Old 05-15-18, 07:41 AM
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PixelPaul
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Gearing changes and chain length

i have a Sram Rival 1 drivetrain. If I switch between a 42T and 48T chainring and a 12-25 and 12-28 cassette will I have to also modify my chain length?
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Old 05-15-18, 08:00 AM
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of course , to have more teeth, they must be larger circles. so will be a larger circumference.
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Old 05-15-18, 08:46 AM
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Absolutely!

As fietsbob indicated, the chain has to be long enough to safely cover the big/big combination. If you ever accidentally try to shift into the big/big combination it will be on a hill when you are seriously bearing down. You're derailleur arm will bend into the spokes and cause a ton of damage in less time than it took me to type this sentence.
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Old 05-15-18, 09:34 AM
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It's going to depend on how long your chain currently is. It's possible that when it was initially setup, whomever built it cut the chain long enough to be able to accommodate the larger ring/cog combination, but it's impossible for anyone on here to be able to say definitively.

So, short answer is basically what everyone else has said. You'll have to check it when you've made the swap, so you should assume "yes".
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Old 05-15-18, 11:30 AM
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Old 05-15-18, 02:38 PM
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If you go from a big-big of 42/25 to 48/28 you will have added 9 total teeth and will need a chain 4-1/2 half-links longer. So realistically 5 half-links and probably 6 half-links to get the proper end match. That assumes your current chain is just long enough to allow shifting into your current big-big. If it won't allow you to shift into big-big now, be CERTAIN that it will after the gearing change. If it currently allows big-big and has extra slack, you might get away with fewer additional links
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Old 05-15-18, 03:27 PM
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Originally Posted by Retro Grouch View Post
Absolutely!

As fietsbob indicated, the chain has to be long enough to safely cover the big/big combination. If you ever accidentally try to shift into the big/big combination it will be on a hill when you are seriously bearing down. You're derailleur arm will bend into the spokes and cause a ton of damage in less time than it took me to type this sentence.
OP has a single chainring setup, there is no big-big. His current minimum derailleur wrap is on the 42-25, and his future minimum wrap is on the 48-28, so he's adding 9 teeth. If his chain is too short he probably won't be able to get it in the big cog at all, but there's a lot less chance he's going to throw it into the spokes than with a double chainring fatal up shift on the front.

So the answer is - if your chain is already 5 links (or more) too long, then you won't need to change it. No harm in checking; have a new chain ready though, 5 extra links is pretty sloppy mechanics.

Last edited by DiabloScott; 05-15-18 at 03:41 PM.
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