Gear

Technical FAQ: Shifting problems and cog spacing

Among this week's questions is one from a reader whose bike continues to mis-shift despite repeated tries to remedy it

Diagnosing a mysterious shifting problem

Dear Lennard,
I have a shifting problem that has baffled everyone. Recently I had a new carbon road frame built up with NOS Shimano 7800 components. The frame has internal cable routing. The wheels are Dura-Ace 9000 11-speed. I only put 350 miles on it when the first chain stretched and was replaced. The shifting has never been perfect and somewhat noisy at best. My shop diagnosed it as a faulty rear derailleur. We installed a new 7900 derailleur with the same results. The shifting on the rear “ghost shifts,” sometimes jumping 2-3 gears at a time. I am running an 11-25 cassette. The problems occur mainly on the big ring. The problem gets more vexing when going from the 53 to a 39 or back, as this completely throws the rear shifting off.

The shifting issues occur typically when going from one gear to the next. It’s slow to change and then it typically slams into gear. Going down the gears is typically worse than going back up. [Rear gears] 21-25 are unusable on the big ring.

In the last week, we have tried three different wheels, various cassette spacers, new cassettes, replaced the shifter cable and housing, and four different rear derailleurs. Nothing works.

Is it possible that the frame could be out of square from the factory? If so, how can this be checked? Could it be that the internal cable routing is hindered some way inside the frame?
— Brian

Dear Brian,
It sounds to me like the front and rear derailleur cables might be twisted around each other inside the frame.

Have you checked for this? You might see some movement of the opposite derailleur when pushing a shifter.
― Lennard

Dear Lennard,
Cable crossover in down tube was very obvious to the new shop I took it to, combined with the fact the original mechanic had also installed too short a chain (they had installed a chain for triple ring which also added to the problem). Thanks for helping out; everything seems good now.
— Brian

Dear Brian,
Great!
― Lennard

Mixing Shimano and SRAM

Dear Lennard,
I just bought a TT handlebar set with brakes and Microshift Index TT shifters (10-speed), and was wondering if I’d be able to use the shifters with my SRAM 10 (-speed) rear derailleur? One of the shifters is non-index and is supposed to be used for the front derailleur. If the index shifter does not work with the rear derailleur, I should be able to use the non-index shifter, right?
— Brendan

Dear Brendan,
That shifter is designed to work with Shimano derailleurs, and the shift actuation ratio of a Shimano road 10-speed rear derailleur is 1.7 — quite a bit different from SRAM road’s “Exact Actuation” ratio of 1.3.

In other words, no, the indexing would not work. The Microshift 10-speed right TT shifter should pull, like a Shimano 10-speed lever, 2.3mm of cable with each shift. The lateral movement of the rear derailleur is equal to the cable pull for each shift times the actuation ratio, which would be 2.3mm X 1.7 = 3.91mm. The cog pitch (distance between the centers of the teeth on adjacent cogs) on Shimano and SRAM 10-speed cassettes is nominally 3.95mm. (Round both off to the one-decimal-point accuracy of the other two measurements, or 3.9mm.)

On the other hand, that shifter would move a SRAM 10-speed rear derailleur laterally 2.3mm X 1.3 = 2.99mm (or 3mm, rounded off). So, the shifting would be abysmal or non-existent on your 10-speed cassette, because the derailleur would only move about three quarters as far as it should with each shift.

Yes, you could in theory use the non-indexed shifter with the SRAM rear derailleur, but I suspect it would be finicky to shift and difficult to fine-tune to run noiselessly.
― Lennard

Dear Lennard,
After using Shimano for the last 10 years, I decided to switch to SRAM Red 10s this season. I know that Shimano and SRAM 10-speed cassettes are compatible, but I am wondering what combination of spacers are needed so that when you swap a wheel there are no adjustments to the derailleur?

I only ask because I put my new SRAM cassette on my Mavic Ksyrium wheel with the 1mm spacer and 2-ish mm spacer that I have always used with my Shimano cassettes and the SRAM cassette stuck out further than the lockring on the axle.

I’d like to be able to rotate between three sets of wheels on my bike without having to adjust the derailleur every time I switch from a wheel with a Shimano cassette or a SRAM cassette.

I am finding mixed information on the Internet. Some say the 1mm spacer is not needed for a SRAM cassette on a 9-speed freehub.

Is it true that SRAM 10-speed cassettes are the same width as Shimano 9-speed cassettes?
— Rick

Dear Rick,
Cassettes from those two brands should be completely compatible. Shimano and SRAM 10-speed cassettes both have a nominal 3.95mm cog pitch, and Shimano and SRAM 9-speed cassettes both have a nominal 4.35mm cog pitch. They should be similar in total width, but whether a 10-speed cassette from either brand is exactly the same width as a 9-speed cassette of either brand is something I’m not entirely sure of and, being on vacation in Mexico, can’t check right now. But I will do my best to calculate it.

The total width of a Shimano or SRAM 10-speed cassette should be 9 X 3.95mm + 2mm (for the thickness of one cog) = 37.6mm, while the total width of a Shimano or SRAM 9-speed cassette should be 8 X 4.35mm + 2mm (for the thickness of one cog) = 36.8mm. So, the total width of a Shimano or SRAM 10-speed cassette may be about 1mm wider than that of a Shimano or SRAM 9-speed cassette. That could be the 1mm you found discussed on the Internet. So I’d try leaving off that 1mm spacer on the Mavic freehub (and still leaving the Mavic 2mm spacer behind the cogs; you only take that out to put on an 11-speed cassette).

I’m not clear from your question if you’re switching to SRAM 10-speed from Shimano 10-speed or Shimano 9-speed. I’m guessing it’s the latter, and that 1mm difference could be part of the issue.

One thing I’d wonder about if I were you is the shape of the cassette lockring. I’ve found many times that SRAM’s domed 10-speed aluminum lockring sticks out further than a flat steel Shimano lockring; I’ve had bikes where the SRAM lockring dragged on the dropout, and if I switched to a Shimano lockring, the wheel spun freely. Perhaps that could account for the cassette sticking out beyond the end of your axle.
― Lennard