Sram XX mtb rear derailleur 10/11s compatibility and 42t cassette comp.

Discuss light weight issues concerning road bikes & parts.
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alcatraz
Posts: 922
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Hey WWs

This topic is a bit controversial since it goes outside the common use of these items. Also the idea of high cadence climbing might be unusual to many people.

In the hunt for local strava climbing KOM's and recent power training it's become apparent to me that I need to manage power efficiently. More than I have previously.

Now I have a ww bike running 10s sram red with a 28t cassette. This has been enough for 90% of climbs around where I live.

I've been tempted to increase my climbing range to really make 110 cadence climbing possible without blowing up. (Grades of 20-30% come to mind. Any higher and it's hard to remain seated without doing a wheelie.)

The sram 10s mtb derailleurs are apparently compatible with road shifters. Also I remember reading that sram 11s road derailleurs are compatible with 10s if using 10s shifters and cassette.

Doesn't this mean that a sram xx rear derailleur essentially is both 10 and 11s road compatible? Lets say I get a 1099 36t 10s cassette now but may in the future upgrade to an 1199 11s 42t cassette, the same derailleur can still be used.

I'm hoping the answer is yes. It would make the derailleur quite future proof (and light at 180gr).

(Not included in this topic is changing spider on the crank to an MTB spider running 22-26t small ring which brings same low gear ratios with a 28t cassette as the example above on a compact crank would.)

Any input on the matter is appreciated. Thanks!

/a

PS. I am aware that the torque these kind of gear ratios produce can screw up wheel hubs/bearings. I'm a small guy at 60kg so I got a little benefit there. At least I'm looking to even out power distribution by high cadence. Not out of saddle torque wave "explosions" that sound more harmful to me.

Marin
Posts: 2754
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Some facts:

* "Exact actuation" (10s-MTB) derailleurs will work with all Sram road shifters, 10 and 11s.
* "X-Actuation" (current MTB) won't.
* I have an X0 rear derailleur and it won't shift cleanly to the 42t cog on a 10-42. 11-36 ist fine of course.

Your best bet is a current road 1x derailleur (Apex1, Rival1, Force1) since the long cage versions can shift anything from 11-28 to 10-42. I run these combos regulary.

alcatraz
Posts: 922
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Do you mean running the 1x road derailleurs with 10s road shifters should work, right?

Whats the problem with shifting to the 42t? Is the derailleur maxed out with barely any gap between upper pulley and cassette cogs?

One thing I noticed is that if the derailleur is being used with a different sized cassette or derailleur hanger than intended the space between upper pulley and cassette can be big. So perhaps you have to set the cable tension tighter than you should just because it won't shift to the larger cogs when its at the smaller end of the cassette. Maybe a 36t is the largest optimal in that case.

Thanks Marin
/a

grover
Posts: 1123
Joined: Mon Jul 26, 2004 1:06 pm

by grover

Second Marin's experience.

10 speed mtb derailleur compatible with 10/11 speed road shifters. (exact actuation)
11 speed mtb derailleur only compatible with mtb shifters. (x actuation)

I use an XX rear derailleur with SRAM Red 11 speed shifters on my cross bike. Perfect with an 11-36 cassette.
I tried to install a 10-42 cassette with a double ring at the front (36/46). When in the 46 ring the inner plate of the jockey wheel cage fouls on the 42 cog when trying to shift into/out of it. When in the 36 chain ring (eg chain longer, jockey wheel cage not as extended) it worked to shift in/out of the 42 cassette cog but b-tension was so large that shift quality through the rest of the cassette was poor.

1x road derailleurs (force1/apex1/rival1) work with 10 speed road shifters but you can still only use one chainring. They do not accomodate a double chainring.

alcatraz
Posts: 922
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

grover wrote:
Wed Feb 07, 2018 11:30 pm
Is your xx derailleur a medium or long cage? Sounds like you have a total capacity problem. A long cage could fix that

Thanks for the input. I really appreciate it.

/a

grover
Posts: 1123
Joined: Mon Jul 26, 2004 1:06 pm

by grover

It's medium. But the capacity isn't the issue as the chain length was set for big big. It's that the jockey wheel cage isn't designed to clear a 42tooth as it rotates around that big of a cog.

Companies like OneUp fixed that issue for Shimano 10 speed derailleurs (also designed for max 36t) by making a different inner jockey wheel cage plate. But nothing exists to my knowledge for XX.

alcatraz
Posts: 922
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Forgive me grover for asking once more. You have a setup that really interests me. I think clearing the 42t will ultimately come down to the derailleur hanger then.

Approximately how big is your largest gap between the 42t cog and your upper pulley? (largest = best B screw position)

Not taking chain into account. Low gear limit screw set just right. Measured between a tip on the cog and a tip on the pulley.

I installed a medium cage red derailleur with 36t cassette on a trek domane. Those hangers are a bit longer so I got it to clear with maybe a 5mm gap. This is too small in my opinion but it works. I was surprised. I had to set the B-screw far in but going too far only made it worse. I found backing it to the point where the upper pulley is the farthest away from the wheel axle produced the largest gap. I suggest you to try that with your xx. I couldn't get it right by just trying a few different positions like one would normally do.

I was hoping the xx derailleur be perfect with a 36t but possible to run a 42t in extreme cases. (I do like the looks of that 1199xx cassette :D)

/a

grover
Posts: 1123
Joined: Mon Jul 26, 2004 1:06 pm

by grover

That setup is off the bike now so can't measure. But I recall that I got a big enough gap that it would have worked had the jockey wheel cage not rotated around to hit the cog. You could modify the jockey wheel cage to clear pretty easily. But I didn't want to do that.

alcatraz
Posts: 922
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

grover wrote:
Mon Feb 12, 2018 12:04 am
That setup is off the bike now so can't measure. But I recall that I got a big enough gap that it would have worked had the jockey wheel cage not rotated around to hit the cog. You could modify the jockey wheel cage to clear pretty easily. But I didn't want to do that.
I just ordered a medium cage xx derailleur and an 11-36t xx cassette for my road bike.

My fear is that the total capacity won't be enough with 16t in front (50-34) and 25t in the rear (36-11). Thus I might also contact the inner cage against the largest cog when in the big ring.

What do you think? I was thinking of dremeling a few mm off the cage if necessary. It has a weird design that looks quite excessively big.

/a

grover
Posts: 1123
Joined: Mon Jul 26, 2004 1:06 pm

by grover

You set the chain length for big chainring/big cog on cassette. Using that gear combo will not be a problem as the XX derailleur is designed to accomodate a 36T cassette cog. Your problem will be the chain going slack when in the little chainring and the smaller cassette cogs. This would be fixed by getting a long cage XX derailleur.

alcatraz
Posts: 922
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

grover wrote:
Thu Mar 22, 2018 2:25 am
You set the chain length for big chainring/big cog on cassette. Using that gear combo will not be a problem as the XX derailleur is designed to accomodate a 36T cassette cog. Your problem will be the chain going slack when in the little chainring and the smaller cassette cogs. This would be fixed by getting a long cage XX derailleur.
My friend is running 50/34 and 11-36t on a sram red mid cage derailleur. The chain is nearly (but not completely) slack in small+small. I measured his cage length and it's ~82mm. The xx mid is 80mm.

I'm thinking to put a 16t lower pulley wheel on the xx to get every last bit of capacity. What do you think?

About your problem with the 42t. Have you thought about increasing the upper pulley size slightly to 12/13 to get the cage out of the way? How about dremeling off a little material off the cage there?

I'd suggest trying the 16t lower pulley to increase tension in small/small which should let the cage have a bit more space in big+big by not being pulled forward as much. You'd need a few extra links on the chain though.

I know you didn't ask about it but I've been thinking about mine and your setup.

/a

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