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vav
03-24-2013, 01:09 PM
Hello forum; any idea what is the biggest cog I can run on a 9 speed 6503 RD?
FD is 6503 and crankset is also 6503 30-40-50 FWIW.
Thanks a bunch
V

Ralph
03-24-2013, 01:25 PM
On a friends bike.....I just put a 30-42-53 (Campy Centaur ) triple on an otherwise Shimano bike. It has a 105 9's short cage RD, assume it has same capacity as the Ultegra short cage RD.

Got it to work OK with 8 speed cassette with a 28 tooth large cog. Not sure if anything larger than 28 cog would clear the upper pulley, the way the triple 30 pulls the cage around for the shift. With the chain about as tight as you would want it in big to big......RD only works over about 1/2 of the rear cassette with short cage, chain hangs slack over the small cog half. Imagine with a 30-40-50, with another link or two from chain vs what I did, it would work over another cog or so in rear. You might shift to a 30 rear cog without too much interference.

Tomorrow, I'm putting a medium cage 9's RD on it with a cassete with a 30 tooth large cog. I expect the upper pulley to clear the 30 cog with med cage RD, and with med cage be able to use most of the cassette in 30 ring. May still have a cog or so slack. Doesn't matter anyway. Kinda doubt if a 32 would clear pulley with triple and Med cage. But bet you could use a 32, med cage, with compact double (chain w/b shorter). And I changed FD to Campy Centaur 10's Triple. Worked well with 8's chain and bar ends on his bike. Probably change to 9's chain when current 8's chain wears out.

Chance
03-24-2013, 05:30 PM
Hello forum; any idea what is the biggest cog I can run on a 9 speed 6503 RD?
FD is 6503 and crankset is also 6503 30-40-50 FWIW.
Thanks a bunch
V

Shimano rating for the 6503 FD is 22 teeth max front difference. RD rating is 11T minimum sprocket, 27T maximum sprocket, and 37T of total capacity. How much you can cheat beyond the safe Shimano ratings depends on bike specifics. One of my 9-speed bikes is running an 11-28 cassette which exceeds max sprocket by 1 tooth and max capacity by 2 teeth but works just fine. Could probably go more but haven't tried for lack of need.

Although you didn't ask, if your goal is to get lower gears for climbing, you may want to consider replacing the granny 30T chainring with one a little smaller. Your post mentions 30-40-50 rings which aren't standard Shimano 6503 (standard was 30-42-52), but if correct, it will make using a smaller granny even easier. Many use 28T or 26T granny rings with success. Some guys even use 24T granny rings although shifting performance can become much more difficult to set up just right unless the middle and large rings are down-sized considerably at same time. Anyway, using a smaller granny ring may be easier than using a larger large cog. Just another option to consider.

cmbicycles
03-24-2013, 05:54 PM
You Can also switch to a 9s XT rear dérailleur for addional capacity on the rear cassette. I believe that would take the max cog from a 27 to a 32t. Just be aware that shimano 10s mountain derailleurs will not work with your shifters, so it has to be non-dynasys

vav
03-24-2013, 08:55 PM
@ chance; you are right; crankset its a 30-32-52.

@ Ralph; I believe RD is a mid cage. I'll try a 30 tooth and see what happens.

@ cmb; I am really trying to avoid swapping RD. Its mostly flat where I live. I am thinking D2R2 as my climbing ride this year, but its only one ride. Rest of the year even with a 28 I'll be fine

Thanks guys

Ken Robb
03-24-2013, 09:23 PM
I get perfect performance from 6500 52-42-30 and 12-27 6500 cassette.
I have a 12-28 cassette made by another manufacturer for 6500 gruppo but I have never used it.

I have a pal with 6500 double who swaps his Ultegra RD for a 9 speed XT and a 9 speed 12-34 cassette for his annual trip to BIG mountains around the world. He says his 6500 brifters shift it perfectly too.

Ralph
03-24-2013, 09:26 PM
If it's a med cage RD, will be 74 MM from center to center on pulleys.