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Bicycle Mechanics - Using an SS Shimano RD with 11/28?

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mindundi

01-24-09, 10:54 AM

Hello, I've ordered by mistake the Shimano 105 rear derailleur SS, thinking that GS was meant only for triple crank, and I've ordered also a 11/28 Dura-Ace casette and a 50/34 105 crank. I guess it will be impossible to use 50-28, but the next casette cog is 24, that would be a wrap of 16 crank + 13 casette = 29, that is precisely the SS maximum wrap. Would be possible to use this gear (50x24) and not to return it to the shop? Many thanks.

HillRider

01-24-09, 11:38 AM

Yes, the gearing will work. Be sure to size your chain long enough to be able to use the 50/28 combination. You shouldn't use it because of cross-chaining considerations but it must be possible to avoid damage in the event you do it inadvertently.

What you will probably not be able to use are the 34x11 and 34/12 gears as the chain will be slack in them. This will not cause damage and these gears are not needed anyway.

mindundi

01-24-09, 01:01 PM

I really thank you very much your kind info.

Bill Kapaun

01-24-09, 04:50 PM

The specified chain wrap is 29T, but Shimano is supposedly somewhat conservative.
You may not have nearly as much of a problem as you anticipate.

Part of "how much" will be how lucky you are in sizing the chain.
You're supposed to have at least 1 full link set + whatever fraction of a link set is left over as "slack".
IF you had say, 3/4 of a link set, you should be good, as long as you still normally avoid the BIG:BIG combo. If you try this, TEST to make sure there is still a bit of "tensioning" movement in the RDER.
You MIGHT also be able to make up another "portion" of the slack by CAREFUL MISADJUSTMENT of the B screw. OTOH, that could make things worse!

Another possibility is 1/2 links.
http://sheldonbrown.com/harris/chains.html
I don't know if these are narrow enough for your chain.

Panthers007

01-24-09, 05:07 PM

Shimano always bases their maximum based on the group the component (RD's etc) has as it's maximum. At least according to Sheldon (Our Lord) For instance, Shimano's Ultegra GS and SS RD is specified as 27T maximum in the cassette/freewheel. And that's just bull. They will handle a 30T cog just fine - possibly more. Here is the Harris list with the largest cogs as stated by Shimano:

http://sheldonbrown.com/harris/derailers-rear.html#shimano

Happy Trails!

Bill Kapaun

01-24-09, 05:18 PM