eugenek

Would it be possible to get a SRAM road medium cage rear derailleur (such as this SRAM Apex) to work with a 10-speed 11-32 cassette and a 52-42-30 crank?

Or do I stand a better chance of getting this combination to work with a Shimano road long-cage RD?

Or is it safest to go with a mountain RD such as SRAM X7 long-cage?

Specs say that the medium cage SRAM Apex supports the range of a 11-32 cassette, but it is supposed to work with a double crank. Shimano's road long-cage RDs support triple cranks, but they are only rated up to 28 teeth in the rear.

surreal

According to one dealer offering that same derailer, the chainwrap capacity is 37t. Your set up would have a 43t chainwrap capacity. (Subtract 52-30 up front for 22, and 32-11 for 21, 21+22=43.) Short answer is "no", as there isn't enough cage to take up mthe slack on such a wide range. Some folks will tell you that, if you size your chain correctly and avoid crosschaining on the big/big combos, you can get away with it. While this technically might be true, I cannot recommend it b/c you could tear up the RD and possibly injure yourself if you make a mistake.

My question is: why such a massive gear range? Even if you intend to do loaded touring, you'll never need the 52/11. If you don't intend to do some loaded touring or ride in the alps, you'll never need the 30/32. Is this for a 26"wheel touring bike? 20" wheel recumbent?

-rob

surreal

ps- if you dont already have shifters and RD picked out, any long-cage (sgs) shimano derailer should be able to handle this, as most all of them have a 45t chainwrap capacity.

PS s'more: The SGS derailers are mountain bike long cage derailers. Deore, LX, SLX, XT, etc. The road "long cage" derailers are actually midcage, usually referred to as "GS"; these are typically rated to a 28t large cog.

shelbyfv

What shifters do you want to use? I don't think SRAM will operate your triple fd and Shimano won't work with the SRAM rd.

HillRider

There is more to it than strictly chain wrap capacity. Most road rear derailleurs have a large cog limitation. For Shimano it's typically 27 or 28 teeth. For a 32T big cog you will need an MTB rear derailleur.

Also, "avoiding big-big" isn't how you set the chain length if you are going to exceed the derailleur's wrap capacity. You make the chain long enough to allow big-big for safety reasons and you avoid small-small as the chain will go slack but won't do any damage.

surreal

This is an excellent point; running a triple with drop-bar brifters will eliminate the possibility of SRAM rear derailer. I'd forgotten all about that.

HillRider, you make a good point re: strategies for exceeding chainwrap capacity. A friend of mine had been avoiding big/big on his mountain triple with the midcage rear for a long time, but your advice IS a lot better. Personally, my strategy has always been to avoid exceeding chainwrap capacity. =D As for the chainwrap/max cog issue, I addressed that in my second post in this thread, where I suggested an SGS rd. You're mistaken about needing a mtb rd for a 32t max cog; the Apex is rated for a 32t max cog anyway...but no triples allowed. But, yes, Shimano road rear derailers max out at 28 these days. (I had a 105 from the early 90s that handled a 32t; bought it used on an old Bridgestone. Mind-blowing.)

eugenek

Right now I have 8-speed 11-28 and 9-speed 52-42-30. In the long run, I want to move to 10-speed 11-32/53-39. I don't want to change the crank yet (I'll get a couple thousand miles out of mine first), but I thought I'd update the rear and one of the shifters now and postpone the rest till later.

Are you sure about this? I thought that Shimano shifters were compatible with SRAM RD's, as long as the numbers of gears match.

Suppose I get Shimano Ultegra right shifter and Deore XT (RD-M773 SGS) RD, would those work with each other?

surreal

Shelby is right. While most Shimano and SRAM cassette share the same cog spacing if the number of cogs match, the ratio for the cable-pull is way different. Roughly 2:1 for shimano, and 1:1 for SRAM. You'll need to match the number of cogs on the cassette to the number of clicks on the right shifter, AND you'll need to match the brand of rear derailer to the brand of right shifter.

Pepper Grinder

Absolutely positively not compatible.

Yes, those will work.

eugenek

I got the RD-M773 SGS derailer. Don't have the new 10-speed shifters yet, so I tried to connect it to my old 8-speed Tiagra shifters. As far as I can tell, they are not compatible. The range of cable travel in the shifter is about enough for the RD to traverse about 6 chainrings.

P.S. Measured everything with a measuring tape. Old Tiagra RD travels 13/16" smallest to largest ring. Cable travels 7/8". New Deore XT RD travels 1 1/4".

eugenek

OK, I don't get it. I must be doing something wrong.

https://en.wikibooks.org/wiki/Bicycle...ing_Dimensions

Shimano Deore XT is supposed to have the shift ratio of 1.7 (like every other Shimano RD out there). So, 20 mm cable travel x 1.7 = 34 mm = 4.8 mm * 7 = 3.95 mm x 9. It's supposed to work with 8-speed cassettes and with 10-speed cassettes.

But I clearly need 26-28 mm of cable pull.

RD on the small ring:
https://i48.tinypic.com/2l9ib03.jpg
https://i50.tinypic.com/dg2yp2.jpg

RD on the large ring:
https://i48.tinypic.com/33ncdpk.jpg
https://i48.tinypic.com/28c0emg.jpg

https://i48.tinypic.com/2rze69t.jpg

What's going on? Did I somehow mount it incorrectly?

mechBgon

That's a DynaSys rear derailleur, only compatible with DynaSys shifters. There are no DynaSys road shifters. The best XT rear derailleur for your purpose is the XT RD-M770.

eugenek

Aha! You are absolutely right. Now that you mentioned it, I can see in Google that it is a DynaSys rear derailleur, and those have different shift ratios from the rest of the Shimano family. Thanks!

Now, does anyone want to buy a DynaSys long-cage MTB derailer from me?

Kimmo

*cough*

Also, I believe a little jigger exists that goes on your downtube cable stop to allow a double brifter to work a triple.

Well, kinda - you use the brifter to switch between two rings, and the little lever on the device to go to the other one.

Retro Grouch 

I think that's cheating on the wrong end.

Think about how you really ride your bike. Most riders ride mainly in the big and middle chainrings, only shift into the granny for steep hills, and shift out of the granny as soon as they crest the hill. Consequently, you only use the granny chainring with the largest 2 or 3 rear cogs. If you're going to cheat on chainwrap, make sure that you have a chain long enough to safely cover the big/big combination and don't worry about the chain going slack in the little/little.