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Road Gear

Technical FAQ: Chainring and cog compatibility

Lennard Zinn helps readers sort out a variety of component combinations that mix and match shifters, derailleurs, different brands, and more

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Dear Lennard,
Do you know if there are any 52/36T chainrings with a 130 BCD? Am trying to go mid-compact without having to buy a new powermeter (I have a Quarq crankset).
― Chris

Dear Chris,
A little geometry lesson is clearly in order. No, there is no such thing as a 36-tooth chainring for a 130mm bolt-circle-diameter (BCD) crank. That’s because 130 BCD means that the centers of the chainring bolts are 65mm from the center of the crank spindle. But the smallest chainring, with tooth valleys external to chainring bolt holes drilled on a 130mm bolt circle, has 38 teeth. A 36-tooth would not work, because the bolts would be among the chainring teeth! (The valley-to-valley diameter of a 36T chainring is 137mm, but the heads of the crank bolts are 11mm across, so the outer edges of the crank bolts on a 130mm bolt circle scribe a circle 141mm in diameter, thus overlapping where the chain needs to go by 2mm.)
― Lennard

Dear Lennard,
I want to buy a rear wheel for my trainer so I don’t have to change out my trainer tire with my road tires. I am running a 10-speed system but have old 9-speed cogs. Can I use those with my 10-speed system?
― Robert

Dear Robert,
Not if you want it to shift properly, you can’t. Perhaps on your trainer you only use one or two gears, in which case you could adjust your derailleur to run quietly on those, or instead, only use those gears that it already runs quietly on. This may be good enough for your indoor-training purposes. But since the cog pitch (the center-center distance between cogs) is greater on a 9-speed cassette than on a 10-speed cassette, your 10-speed system will only work on a limited number of the rear cogs on a 9-speed cassette.
― Lennard

Dear Lennard,
I have ridden Campagnolo 11-speed for a number of years and have Athena groupsets on two of my bikes.

I am looking to upgrade another bike to 11-speed — I wanted to know if there is a chance that a ‘mix and match’ approach would work.

My idea would be to use Athena Ergopowers (I prefer the ergonomics) with a set of Shimano derailleurs (cheaper than the Campagnolo version) to create a cost-effective 11-speed bike.

I plan to use wheels with Campagnolo cassettes (that I already have) and a Campagnolo (compatible) chain.

Will the gears shift correctly, and are there any other issues that I would need to be aware of in terms of the brakes?
― Finbar

Dear Finbar,
No, the gears will not shift correctly unless you take some additional measures. That said, this setup will work better without modification than mixing Campy 10-speed or 9-speed levers with Shimano 10-speed or 9-speed derailleurs. As for the brakes, if you’re going to use current Shimano brake calipers with Campy levers, those will not work well, either.

Campagnolo 11-speed (and 10-speed, and late-model 9-speed) rear derailleurs have a shift-activation ratio of 1.5, meaning that for every millimeter of cable pull, the derailleur moves laterally 1.5mm. Shimano 11-speed road rear derailleurs, on the other hand, have a shift-activation ratio of 1.4, meaning that for every millimeter of cable pull, the derailleur moves laterally 1.4mm. The cable-pull per shift of a Shimano 11-speed road STI lever is 2.7mm, while the cable-pull per shift of a Campagnolo 11-speed Ergopower lever is nominally 2.6mm, although many Campgnolo levers in the past have also had a variation in cable pull over the range of the gears as well, and I suspect the actual average cable pull for an 11-speed Campy lever is closer to 2.5mm.

Cog pitch (i.e., the center-to-center spacing between cogs, which is also equal to the thickness of one cog in the center of the cassette and its adjacent spacer) of all 11-speed cassettes, whether Shimano, Campagnolo or SRAM, is between 3.76-3.79mm by my measurement. You’ll notice that this is also equal to Shimano’s 11-speed road cable pull times its shift-activation ratio (1.4 x 2.7mm = 3.78mm). So, substitute in a Campy lever, and you get 1.4 x 2.5mm = 3.5mm, which is a smaller jump than the actual spacing between cogs (and even if you use 2.6mm for the Campy cable pull, which I think is inaccurate, you come out with 3.64, which still is narrower than the actual cog pitch). This is why J-Tek made cam-type, cable-pull-adaptor units that increased or decreased the amount of cable pull per shift so that a user could make a “Shimagnolo” mashup work.

In short, the difference in shift-activation ratios between the Campy and Shimano 11-speed rear derailleurs is small enough that shifting will be okay on some of the cogs but not on all of them.

You didn’t say you were changing brakes, but you asked about them. Shimano road brake calipers built for Shimano levers that send the shift cables underneath the handlebar tape require more cable pull than previous Shimano calipers. And those previous Shimano calipers, which work with STI levers where the shift cable sticks out of the side of the lever body, also use the same cable pull as current and past SRAM and Campagnolo calipers. So if you use current Shimano road brake calipers with Campagnolo levers, you will have more leverage and hence more braking power than designed, and you will have too little cable pull to bring the pads to the rim as quickly as designed.
― Lennard

Dear Lennard,
In a past column of yours, you note that 9- and 10-speed cassettes can be used on 11-speed cassette bodies without any problem.

I’ve been looking at new wheels and sometimes the wheels are advertised as “10/11” speed Campagnolo compatible. I contacted one seller and he insisted that the wheels were only compatible with 10/11-speed Campagnolo cassettes.

So, are there cassette bodies which are only Campy 10/11-speed compatible or should a so-called “10/11” speed cassette body be compatible with 9-, 10-, and 11-speed cassettes?
― Collin

Dear Collin,
There is no such thing as a Campagnolo freehub body that is compatible with Campy 10-speed and 11-speed cassettes and not with a Campy 9-speed cassette. The current Campagnolo freehub spline design came in with the advent of Campagnolo 9-speed drivetrains. A Campy freehub body that is compatible with a Campy 10-speed or 11-speed cassette is also compatible with a Campy 9-speed cassette.
― Lennard

Dear Lennard,
In attempting to convert several bikes from Campy 10 to 11, and hoping to use my existing wheels/hubs (if possible), I’ve run into problems finding replacement freehub bodies (i.e., 10-speed to 11) to make my desired hub conversions. I should add that several of these wheels have Shimano or SRAM hubs/cassettes, but they’ve worked reasonably well with spacer swaps, rear derailleur tweaks, and other “tricks” employed to allow Campy 10 shifters to be used with Shimano/SRAM 10-speed cassettes. Unfortunately, I’m about ready to give up on the freehub-swap idea for these wheels, which would have been the simplest, path-of-least-resistance option to letting me run new Campy 11 shifters with any brand’s 11-speed cassettes.

My next option, while still somewhat simple but a good bit more costly, would be to run the new Shimano XTR 11-speed cassette, which I know fits on Shimano/SRAM 10-speed hubs. I don’t mind having the extended range, since most of these wheels are for ‘cross/gravel/dirt and tandem applications. But, my primary question is: is it safe to assume that the XTR 11-speed cog spacing is the same as that on everyone else’s 11-speed cassettes? In other words, will my Campy 11-speed shifters play nicely with the XTR cassette (given that I make the necessary adjustments to the rear derailleur to accommodate the enlarged cassette)? Here’s hoping that’s the case, and I won’t need to purchase a bunch of new rear wheels. Or — if you know of any other solutions to this dilemma, please let me/us know …
― John

Dear John,
Yes, the cog pitch on XTR 11-speed cassettes is the same as on road 11-speed cassettes, whether Shimano, Campagnolo or SRAM, which is between 3.76mm and 3.79mm by my measurement.
― Lennard

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