Dura Ace RD 7900 Chain Wrap
07-28-15, 11:12 AM
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Dura Ace RD 7900 Chain Wrap
The chain wrap capacity of a RD-7900 is 33t, I am looking to go 34t has anyone tried and can verify it will work before I make the RD purchase?
50/34 + 12/30
Thanks!
50/34 + 12/30
Thanks!
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nine mile skid on a ten mile ride
07-28-15, 11:49 AM
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There's always fudge room to the long side. You're one tooth short of the theoretical wrap capacity. Even if there were zero fudge room, the worst case is that you cut the chain for the 50/30, and it's too long for the 34/12 combination, which you wouldn't use anyway. the 34/13 combination (next position) is within the limits.
So you're OK as far as wrap goes, and I'll assume (and/or leave it to you to confirm) that you're also OK on the maximum size capacity.
So you're OK as far as wrap goes, and I'll assume (and/or leave it to you to confirm) that you're also OK on the maximum size capacity.
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
07-28-15, 01:33 PM
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I use that gearing on two bikes. One has the 7800 rd, the other has 7900. Both work fine.
07-28-15, 04:46 PM
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Just be absolutely certain the chain is sized long enough to allow the big-big combination (50x30 in your case) for safety reasons. If the chain is a bit slack in the 34x12 gear, no harm is done and that's a useless combination anyway.
07-28-15, 07:10 PM
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Thanks everyone for your responses!
I currently have a Dura Ace RD7800 I may try with a 12/30 and see what happens before purchasing a RD7900.
I currently have a Dura Ace RD7800 I may try with a 12/30 and see what happens before purchasing a RD7900.
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nine mile skid on a ten mile ride
nine mile skid on a ten mile ride
