I'm building a bike in which I want to run a 10 speed drivetrain with compact 50/34T crank with an 11-32 cassette. I know SRAM offers road rear derailleurs that will work with this sized cassette and crank (APEX, RIVAL) but I can't quite understand if I can do the same with shimano...

Shimano does make road rear derailleurs with medium cages but the max cog size is 30T, so I run the risk of the jockey wheel hitting the biggest cog which is no bueno. And then when I look at shimano's 10 speed mountain derailleurs their pull ratio is totally different thank the typical 2:1 so i can't even use those. sooo... what can i do to make this work for shimano? 9 speed mountain derailleur.... will that even work with a 10 speed shifter?

Didn't the 9-speed Tiagra use a 11-32? Otherwise it looks like it wouldn't work.

This is my approach. It may or may not work for you, I think it depends on geometry of the derailleur hanger

The new 5700-A rear derailleur is spec'd at 30T. Currently you have to run a Tiagra 10 speed cassette for 30 but ultegra/105 probably out this year. Close enough?

On my CX bike, I ran an older 105 derailleur (spec'd for a max 27 cog) with an 11-32 cassette. It worked but the clearance was really tight so I went to a mountain bike derailleur. An ultegra derailleur spec'd for 27 works like a dream with a 28 large cog on my road bike.

What I'm saying is that a derailleur that is spec'd for a 30 max cog may work just fine with a 32.

I run a 10 speed compact crank with an 11-34 cassette. I use a Shimano 9 speed mtn RD. Works fine and I know a half dozen other folks doing the same. My preferences for the RD are non-rapid rise and non-shadow. The LX T661 is kind of hard to find but may be a little nicer than a Deore or regular LX. Other option are older XT.

I run an 11-34 on my touring bike (9 speed) but use a Deore derailleur. No issues.
I also run on another bike the new 30T cassette with a short cage ultegra RD. Again no issues.

I have a 50/34 with an 11-34 (9 spd) cassette and Dura Ace bar end shifters. Rear derailleur is a Tiagra long cage. Works great.

Depending on the "B" adjustment on some frames you can push 32 teeth with something like the Ultegra GS RD. I just done that on a 9 spd set up. Some chatter but seems ride-able.
I suspect a 9 speed mtb RD may work on your 10 speed set up. If so then IRD has cassettes all the way up to 11-34 for 10 speed road.

You will need:

* Shimano XTR M971 SGS Rear Derailleur

Search is your friend

There are several threads that mention using the Shimano 9 spd MTB rear derailleurs like XT RD-M771 with 10 sp shifters. I just put this on my bike with 6600 shiftes, ultegra compact crank and this M771 rear der. So far it works fine.

OP - Since it's going to be on a road bike, I'd get the 12-32 cassette instead. It tightens up the gaps between cogs somewhat.

If the road bike can't use 11 ring, who can?

It can certainly be used, it's just that having the closer gearing is more conducive to keeping your cadence where you want it, be it uphill, downhill or on level ground. IMO, that's more useful than using the 11t cog on the occasional downhill that you spin out on in the 12t cog.

if a road bike needs a 32 while running compact, he probably doensn't need an 11.

Quite the opposite. The 32 is for going up 8% grades. The 11 is for going in the other direction.

Odd, I run a standard + 12-27. I'm a weaklin and that's more than enough gear to get up such grades. I don't think a standard + 12 can keep up to a 6% descent without spinning madly, let along a compact... you're better off tucking like hell!

Anyways, not here to steal the thread, just agreeing that a 12 is probably better than 11.

Is sustained 160 W / 157 lb a "weaklin"?

https://www.kreuzotter.de/english/espeed.htm

It gets you up a 8% grade at 5.2 mph.

With standard in front and 27 in the back, 5.2 mph = 46 rpm.

Now plug -8% grade and you get 35mph. drop the calculation to 1 watt and you get 32. In other words, you're better off with a good tuck than less tuck + spinning a compact/11 IMO. especially if it equates to better gear selection to climb, which is where it's really needed. And yeah, I guess I sustain a bit more power than that, but I'm 200lbs

I think the 32 is for going up 20%+ grades.

At least that is what I bought it for.

Its not about the theoretically useless 11-50, its about the very usable 12-34 cutting down on the front shifting.

Interesting. You have a point, all I can say is that I have 250 miles on my 11-32 cassette and I haven't noticed any gearing deficiencies.

Biggest gaps between gears on SRAM PG1070 11-32 is and SRAM PG1070 12-32 are identical, in the same place, and just under 16% (19 to 22). 11-32 has a 15% gap going from 13 to 15, 12-32 has an additional 14 chainring.

hamster - If it works for you, great! That's why the options are out there.

For me, the 14t cog is important. In a 34-14 combination, 90 rpm gives ~17 mph. For me, that's a comfortable cruising speed. Using the small ring in a headwind, the one tooth gap among the four smallest cogs makes it easier to maintain a comfortable cadence. My own preference for a cassette is 12-27, which gives a one tooth gap from 12-17. I don't notice the gaps on the larger cogs as much as on the smaller ones.

The 2009 Specialized Tricross Sport Triple came with an 11-32 9-speed cassette and a Deore RD. It works just fine - mine has Tiagra shifters, I think Tiagra FD and Deore RD. The Rockhoppers have 11-34 9-speed cassettes so I imagine I could put one of those on the Tricross if I felt the urge.

its Why I chose Sram...................







just sayin.............