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Old 07-28-11, 11:03 PM   #1
tetonrider
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36T cog w/ DA 7900 -- or XTR RD w/ DA shifters?

Hey, all:
I'm contemplating doing the Everest Challenge, and I think I might like something lower than 34x28 for my bail-out gear.

On a local 2,500' ascent, I find that when not fresh I'm pedaling at ~75rpm up a sustained (5-mile) 8-10% grade.

Here's my situation: I've got a bike currently set up with DA 7900, 50/34 and 11-28. I also have a mountain bike with 2x10 (XTR RD + XTR shifter + SRAM XX 11-36 cassette).

Ideally, I'd like to put an 11-32T cassette on my road bike and call it good. I know Shimano are conservative in their #s for capacity and chain-wrap, and I can be smart about not cross-chaining or using dumb gears (small-small).

Has anyone tried DA7900 with 11-32 (or 11-34 or 11-36?)? What were the results?

Alternately, can DA7900 shifters work with my XTR 980 10-speed RD? A search indicated the pull ratios might be different, but I saw nothing conclusive.

I could also run a DA7800 derailleur (or DA 7800 shifter + XTR RD), if that might work.

Thanks for any leads!
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Old 07-28-11, 11:45 PM   #2
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I've successfully run 11-32 cassettes on 4 different bikes using Ultegra 6700 rear derailleurs, which have the same geometry as your 7900 rear der. Based on my experience, I would say that you -may- be able to do the same. You won't know for sure until you try it.

As far as using a 10-speed Shimano MTB rear der, it's my understanding that they are not compatible with Shimano road shifters. You can use a Shimano or Shimano compatible 9-speed MTB rear derailleur with your 10-speed shifters, it's fairly common.
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Old 07-28-11, 11:54 PM   #3
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Originally Posted by Davet View Post
I've successfully run 11-32 cassettes on 4 different bikes using Ultegra 6700 rear derailleurs, which have the same geometry as your 7900 rear der. Based on my experience, I would say that you -may- be able to do the same. You won't know for sure until you try it.

As far as using a 10-speed Shimano MTB rear der, it's my understanding that they are not compatible with Shimano road shifters. You can use a Shimano or Shimano compatible 9-speed MTB rear derailleur with your 10-speed shifters, it's fairly common.
Thanks for the reply. I think it may be the SRAM road shifters that work with SRAM MTB RDs...so I was wondering if the same was true for Shimano.

Anyway, that is promising that 11-32 + Ulty 6700 worked for you. What front ring setup were you using? Did you have to avoid cross-chaining, or was that not even an issue?

11-32 only buys me one extra gear below the 28. That's certainly nice (~13% lower). Doubt I'd be able to get away with an 11-34 (2 lower gears to choose from, 7% and 17% lower)...but it might be nice.

Too bad I sold my old XT 9-speed RD!

Thank you! Anyone else?

In order to try it, I'd have to buy an 11-32 cassette, so it would be nice to get other opinions first. I could also put the 11-36 cassette I have on there and see if I can get it to shift to the 30T cog as an indicator.
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Old 07-29-11, 09:54 AM   #4
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With many bikes, getting your existing setup to run in the 34 x 28 without pulley-on-cog "rumble" requires maxing-out the B-tension screw, assuming there's enough chain to safely use all the gear combinations. If you want to go lower, and want it to work on the first try, get your new cassette and a 9sp-compatible Shimano mountain RD (I suggest the classic style rather than Shadow-style), such as the RD-M971.

Note that some of Shimano's mountain RDs don't have cable adjusters anymore, so if your frame doesn't have an adjusting barrel as a cable stop, you'll want to add an inline adjuster.
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Old 07-29-11, 06:12 PM   #5
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Originally Posted by mechBgon View Post
With many bikes, getting your existing setup to run in the 34 x 28 without pulley-on-cog "rumble" requires maxing-out the B-tension screw, assuming there's enough chain to safely use all the gear combinations. If you want to go lower, and want it to work on the first try, get your new cassette and a 9sp-compatible Shimano mountain RD (I suggest the classic style rather than Shadow-style), such as the RD-M971.

Note that some of Shimano's mountain RDs don't have cable adjusters anymore, so if your frame doesn't have an adjusting barrel as a cable stop, you'll want to add an inline adjuster.
thanks! will the Shimano 9-speed MTB RD work with a 10-speed cassette, then? very interesting.

my b-tension screw isn't maxed out.

a friend who is not on this forum let me know that he has gotten 11-34 to work with da7800 rd & brifters without modification. interesting.
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Old 07-29-11, 08:48 PM   #6
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Originally Posted by tetonrider View Post
thanks! will the Shimano 9-speed MTB RD work with a 10-speed cassette, then?
Yes, all indexed Shimano RDs--except pre-9-speed Dura Ace and 10-speed MTB--have the same cable pull ratio. They just go where the shifter tells them to.
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Old 07-29-11, 08:52 PM   #7
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thanks! will the Shimano 9-speed MTB RD work with a 10-speed cassette, then? very interesting.
Yeah, it's a fairly common setup on tandems in fact.

Going back to the original post, 75rpm isn't necessarily that bad on a steep climb. But if you're going to be at high altitude, it's a good idea to have a couple lower gears than you normally use. I see from the course info that it tops 10000ft above sea level more than once.
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Old 07-29-11, 10:36 PM   #8
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Yeah, it's a fairly common setup on tandems in fact.

Going back to the original post, 75rpm isn't necessarily that bad on a steep climb. But if you're going to be at high altitude, it's a good idea to have a couple lower gears than you normally use. I see from the course info that it tops 10000ft above sea level more than once.
interesting stuff re: tandems.

i live at 6,300' and am used to high-altitude riding and doing lots of climbs. that said, this is 29,000' of elevation gain in 2 days.

when i'm doing normal power up 8-10% grades (a local climb is ~2,500' vert in ~5 miles), i'm in the high 80s with 34x28. however, that would be lower if riding an all-day pace -- and i can see if the worst happens i might need to bail out. i'm not sure of the grades of the climbs in the everest challenge, and i'm not sure if any are as sustained as what i ride locally.

still, my self-selected cadence on flat terrain is ~105rpm, so replicating that on long climbs and after 200 miles of riding might be nice.

thanks!
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