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Technical FAQ: Revisiting drivetrain cross-compatibility

We have been inundated lately with drivetrain compatibility questions. We’ll address a number of these today, including a comment by a budget-minded college student who tried to marry some incompatible Shimano parts on the cheap.

Could my cogset be out of tolerance?

Dear Lennard,
I bought a 2013 Giant Defy road bike with Shimano Ultegra 6700 compact 34-50 front, a 10-speed 11-28 cassette with a CH-6701 chain. The wheels are Shimano Dura-Ace WH-9000-C24-CL with a 10/11-speed freehub. I like climbing, but my 73-year-old knees don’t, so I bought a SRAM XG 1099 10-speed 11-32 mountain cassette. There have always been two minimally noisy gears in the center of this cassette while on the small chainring. The cassette got pretty loud after 3,000 miles so my LBS mechanic replaced cable housings and lubed and micro-adjusted the rear derailleur back to “new” condition. He also tried a wheel with a Shimano 10-speed cassette to demonstrate that it can run silently.

My questions are:
Is it unrealistic to expect that the 10-speed spacing of my current SRAM single-billet-machined-steel 11-32 cassette should be perfectly compatible with the indexing of my Ultegra 6700 10-speed shifter?

Could I have gotten an out-of-tolerance cassette?

Finally, is there any built-in incompatibility to discourage mixing of manufacturers?
— Alan

Dear Alan,
I have for years mixed SRAM Red one-piece 10-speed cogsets into Shimano 10-speed drivetrains with all sorts of different 10-speed chains on my own bikes. I have never found them to operate silently in all gears no matter what chain I tried; they never operate as silently in all gears as the Shimano cogsets they replaced. My thinking on that was that the shaping of the cog faces and their interaction with the chain is the issue, not the spacing. My experience is that you cannot realistically expect noiseless running performance, but you can expect flawless shifting.

Given that the cogset is CNC-machined, I would doubt that it is out of tolerance, but anything is possible.

As for built-in incompatibility, there are two ways to look at this. From the manufacturer’s standpoint, designing components to work together as a complete system makes a lot of sense for optimizing performance. And there is no particular reason that a component company should strive to ensure that its parts work with drivetrain parts of other manufacturers. You wouldn’t expect the alternator or exhaust manifold from an Audi to work in a Subaru. Of course, designing drivetrains as systems also does serve the dual purpose of discouraging consumers from using parts from other manufacturers. I guess I’m a glass-half-full guy and think that the impetus for doing it is to optimize performance rather than to prevent consumers from using parts from other companies.
― Lennard

How much did Shimano cogset spacing change with 11-speed?

Dear Lennard,
Since they lengthened the FH body for Shimano 11-speed, I’m wondering if the 10-speed and 11-speed cog spacing is close? A friend mentioned that he put a Shimano 10-speed wheel onto his Shimano 11-speed system, adjusted the limit screws, and it “worked fine.”
— Peter

Dear Peter,
Shimano’s spacing between cogs has narrowed from 2.35mm for 10-speed to 2.18mm for 11-speed.

That’s not much, and I’m not surprised that he could get it to work. I haven’t tried it. I would guess that it would be a bit noisy somewhere across the range.
― Lennard

Flawless 10-/11-speed wheel change

Dear Lennard,
I don’t know if you’ve had the chance to experiment yet, but I recently was handed a 10-speed wheel in a race, and it worked perfectly with my SRAM Red 11. Had one dead click of course, but otherwise was quiet, smooth, and precise.
— David

A cautionary tale about Ultegra compatibility

Dear Lennard,
I know that this issue has all but taken over the column this year, but I thought that I would just throw in one note and correction for the 11-to-10-speed compatibility.

I have been running 10-speed 105/Ultegra 6700 mashup on my Trek Madone for a few years, but after a nasty crash last year that involved a squirrel, a concussion, six weeks off from school, and two new wheels, I ended up needing a new RD since my rear mech got crunched as well.

Being on a college student’s budget, I had to take what I could get, and because I worked at an outdoors store, I was able to get a 60-percent off deal on an Ultegra 6800 11-speed RD, which I thought was a real blessing, especially after reading your Sept. 3 column. However, I was in for a world of frustration.

Two different bike shops and four mechanics couldn’t figure it out, so I took it back into my own hands and gave it a shot. Turns out that 6800 levers pull less cable per shift than 6700, and so the cable actuation ratio on the RD has to be different.

Because of this, I had to find a way to combine a shifter and derailleur with different actuation ratios. I dug around and learned about the Hubbub technique via Sheldon Brown. And so I found a way to reroute my cables to make up for the difference.

Just wanted to let you know that it is possible, just not easy, and definitely not recommended. To all out there: don’t be me, don’t be cheap, and go all the way on 11-speed if you can, or stick just with 6700; it’s pretty nice.

Then again, getting Di2 solves all of these issues as I’ve read, but that’s just a pipe dream for this 21-year-old Cat. 4. Maybe after I’ve been racing for more than a year I’ll start saving up. Until then, I’ll take my Frankenbike.
— Luke

Dear Luke,
Thanks for writing about the challenges you’ve overcome. As I said in that Sept. 3 column you reference, I had not tried this combination and was only aware that the front derailleur was not compatible. Thanks for letting me know that the rear derailleur also is not.

That rerouting of the cable around the cable-fixing-bolt trick is a good one and worth trying when needing to better match derailleur travel with cog spacing; I believe that unlike the illustration caption indicates on the Sheldon Brown site, it actually makes the derailleur move further with each shift, rather than less far. Thanks for explaining how you upgraded the washer on the 6800 rear derailleur that prevents doing this.
― Lennard

Matching road and mountain bike drivetrains

Dear Lennard,
I saw your exchange with Eric on Feb. 4 and had a couple of thoughts:
1) I regularly run an 11-36 10-speed cassette with a Dura-Ace 10-speed 7900 compact drivetrain. As you point out, the 10-speed Shimano MTB RDs will not work with the 7900 shifters. However, older nine-speed Shimano MTB RDs will work with 7900 shifters. My favorite is the Deore XT RD-M761. It is nice because it has an adjuster barrel on the RD.

2) An even slicker solution is E-tube Di2, because it allows you to easily swap between an 11-speed drivetrain for regular use and a 10-speed drivetrain with an 11-36 for mountainous trips [E-tube is Shimano software with a plug-in connection into any junction in the system that allows customization of Di2 electronic shifting functions —Ed.]. All you need is one of the new 11-speed Di2 groups, an older 10-speed RD-6770 [Di2 rear derailleur] with a long cage (e.g. K-Edge), and a 10-speed 11-36 cassette. Swapping the RDs is very easy if you use an 11-speed chain with a quick link. Just take off the chain and 11-speed RD, put on the 10-speed RD and chain, plug in the E-tube connection, and go. In my experience, the new Shimano 11-speed chain will shift perfectly with the 10-speed RD. Once you have each RD adjusted, you do not even need to readjust after a swap.

One final note is that I think it might be possible to make this work without an expensive K-edge cage by swapping a new 6870 Ultegra GS [long-cage Di2 rear derailleur] cage onto a RD-6770, but I am not sure if the b-tension screw could be extended enough for the top pulley to clear.
— Rob

Dear Rob,
Thanks for those ideas. I did mention that Shimano nine-speed MTB rear derailleurs work with Shimano 10-speed road shifters in that same FAQ, in the answer to Tom. For riders with 11-speed Di2, your second solution is a fantastic option!

I should point out that if you want to interchange Shimano derailleur cages, you can use a cage from a cable-actuated rear derailleur on a Di2 rear derailleur. In other words, you don’t have to use the cage from a RD-6870 GS (long-cage 11-speed Ultegra Di2 rear derailleur) on the RD-6770 (short-cage 10-speed Ultegra Di2 rear derailleur); you can use the cage from a RD-6700 (long-cage 10-speed Ultegra cable-actuated rear derailleur) on the RD-6770. That still doesn’t answer whether the b-screw can be adjusted far enough to clear a 36T cog, but I have heard that it can be adjusted far enough to clear a 34T.
― Lennard