Technical FAQ: Drivetrains and tubular tape
Determining chain, cog wear
I’ve been diagnosing a friend’s bike (Specialized Ruby Elite, 105), after I replaced a badly-worn chain (1%). Her LBS said they swapped the chain 1,800 miles ago. The wear I found at 1% says to me that’s more like 6,000-7,000 miles on that chain (Tiagra HG4601, correctly-oriented with writing on the outside, jointing pin in leading hole of plate, no link binding).
Also they say that they replaced the 105 5700 cogset (11-28T) — but the new chain skips under heavy load on all cogs, not just the smallest few.
Looking at the cogs, the teeth have burrs on them commensurate with 6,000-7,000 miles, comparing with a now-retired Tiagra cogset of mine the same age.
Hanger alignment, rear mech alignment, indexing are all fine.
Am I correct in thinking that a very badly worn 11-28T cogset might skip on the larger cogs as well as the smaller ones? I’m used to seeing skipping on smaller ones due to the reduced diameter/fewer links engaged, this is the first time I’ve seen skipping on all of them.
And is there a tool that can accurately gauge cogset wear?
Yes, a badly worn chain can cause any one of the cogs to become so badly worn that it slips. It doesn’t matter how big the cog is; what matters is how much torque is applied to it for how long.
To understand why that is, consider a worn, elongated chain running over a cog. Since the spacing between pins is greater than it is supposed to be, it is also greater than the spacing between valleys on a new cog. So when the rider is pedaling, the only chain roller that is applying force on the cogs is the one at the top of the cog; the other rollers are not pressed against their teeth because of the chain’s elongation. So, the fact that it has a lot of teeth on it does not protect a large cog from the damage more than a small cog. The chain, if it doesn’t skip off of that top tooth, will mash out the trailing flank of that top tooth to effectively move it further away from the next tooth coming up behind it. And once this reshaping of the cog progresses enough, a new chain will skip on the cog.
1,800 miles is a surprisingly small number of miles to inflict that much damage to the chain and cogs, if it’s a small rider.
The Rohloff HG-Check is the tool you want to check cog wear.
Shimano Ultegra/SRAM compatibility
I’m interested if, since SRAM hasn’t changed its shifters-derailleurs cable pull ratio since going from 10- to 11-speed, is there a slight chance of compatibility between Shimano Ultegra 6600 10-speed RD and any of SRAM’s 11-speed (right) shifter/brake calipers?
I know that it works, vice versa though, with Shimano mountain bike 10-speed SLX shifter and SRAM X9 RD, that I have on my bike.
— Tomislav, Croatia (Europe)
No, that will not work. Not even close.
The rear derailleur’s shift-activation ratio — the amount of lateral movement of the rear derailleur divided by the amount of cable pull to generate that amount of lateral movement (i.e., the number of millimeters of lateral displacement of the rear derailleur per millimeter of cable pull) — is built into the derailleur. And the cable pull — the amount the cable moves with each click — is built into the shifter. The cable-pull per shift multiplied by a derailleur’s shift-activation ratio is equal to the distance the derailleur’s chain cage moves laterally with each shift, and, to shift properly, this must be equal to the distance from the center of one rear cog to the center of the next (the cog pitch).
Cable pull x Derailleur shift-activation ratio = Cog pitch
Cog pitch is equal to the thickness of a cog (other than the largest or smallest cog) plus the thickness of the spacer separating it from the adjacent cog. Cog pitch decreases as the number of cogs increases. Shift-activation ratios, cable pull, and cog pitches vary not only with the number of rear cogs but also from brand to brand, and even sometimes from model to model within a brand.
A Shimano 10-speed road rear derailleur has a shift activation ratio of 1.7, and a SRAM 11-speed road shifter has a cable pull of 3.1mm, so:
3.1mm x 1.7 = 5.27mm cog pitch
That’s close to the 5.5mm cog pitch of a Shimano 7-speed cassette, but I don’t imagine that was the cassette you were hoping to use. That 5.27mm cog pitch is nowhere close to the 3.76-3.77mm cog pitch that the Big Three (Campagnolo, Shimano, and SRAM) all use on their 11-speed cassettes.
Are you using that ShimSram combo you mentioned on an 11-speed cassette? It should work, because the cable pull of that Shimano SLX 10-speed shifter is 3.4mm, and the shift activation ratio of the SRAM X9 rear derailleur is 1.1, so:
3.4mm x 1.1 = 3.74mm cog pitch
This is almost exactly the cog pitch of all three above brands of 11-speed cogsets. If not, the cog pitch of Shimano and SRAM 10-speed cassettes is 3.95mm, so you might be able to get away with that combo in a class-B shifting quality through maybe half of the cassette.
More on Carogna tubular tape
Just watched your video on installing Carogna tubular tape. Amazing! This seems like a game-changer in many ways. One main question:
Assuming I can’t get all the glue off previously used tubular tires or wheels, would it be OK to use the tape anyway? Or do you suggest only using it on “virgin” tires/wheels?
I don’t know the answer to your question, not having tried it, but I can guess and I can encourage you to experiment.
If you can get the rim clean and not the tire, the top surface of the Carogna tape is so sticky and thick that I think it would probably work fine. I’m confident it would stick to the old glue on the tire, and as long as the glue lumps were not super huge, I imagine it would fill in well enough.
As for not being able to get the rim clean, that might be more problematic, since the glue on that side is not thick enough to conform around the lumps.
You could try it and see what happens. If you already have the tire off, you would only lose the cost of the tape to give it a try and see if holds. Let me know if you do try it, please.