Shave 1.85mm off to get an 11s road cassette onto a 10s hub

Question

Does anyone have experience removing material to get an 11s road cassette onto a 10s hub?

As per the hub standards, the difference between the width of a 10s and 11s freehub body is 1.85mm. The back of the cassette I'm considering (11-28t shimano CS-R7000) has plenty of material that could be removed from the aluminium block that holds the 4 biggest cogs, including a small (~0.5mm?) lip that could be taken off evenly with relative ease. I'm worried about removing material symmetrically past that, as any divergence from planar would cause the cassette to sit unevenly on the freehub stops and wobble.

There's also a bit of material I could remove from the stops on the freehub body, though I'd be happier to ruin this cassette than have to replace the hub if this goes wrong. I've been (past ~2 years) using an 11s HG800 cassette which fits 10s hubs and dishes slightly, so I'm not worried about spoke clearance as the distance from the dropout to the big cog should be the same (or less if it's a tight fit). It's a Fulcrum 7 wheelset but the hubs are unmarked, rear one is 24h, 8L/16R.

I don't have access to a machine shop, but I've got a die grinder/dremel/angle grinder/files etc.

Has anyone tried this? Did you have trouble removing material in a radially symmetric way? I do see this poorly-received answer to a related question, though he says it must be done by a qualified machine shop (like his company).

Edit 1: I do see that I can get a compatible replacement freehub body for ~$100, which is not cheap but is a reasonable alternative/backup option

Edit 2: Thank you everyone for the informed advice. I'm going to try taking material off of the freehub body but plan on replacing it with a real 11s body if it doesn't work out.

Answer 1

While awaiting a replacement 11s Freehub, and after reading about folks accomplishing this hack, I decided to give it a try. I noticed the 36mm required distance was the outer edge of the ring of material at the base of the freehub. I just needed to remove the raised portion at the base of each of the splines so the cassette would sit further on to the freehub. I fixed the freehub vertically in a bench clamp and used a cylindrical grinding attachment on a Dremel to remove the material at the base of each spline.

The results are mediocre looking, but the 11s Shimano R7000 cassette fit on the hacked Freehub far enough to let the 11t cog get some purchase and the lock ring threaded normally. I rode approximately 80 miles over a couple of days without incident, and shortly after the true 11s freehub arrived, made the switch.

Here's a few photos (I am not proud of it but it did function. Because of the risk of spoke clearance issues, which I was ignorant of at the time, I don't recommend this hack, especially if an 11s replacement hub is available for your wheel).

Answer 2

With your specific wheel, you may need the freehub body replacement.

For Miche MTB hubs used in road-disc applications, I take the freehub body to a friend with a lathe and cut 1.8-1.9mm material off the freehub as there is material left to do this and the splines run deep enough. There is spoke clearance on these probably because of the 135mm axle.

With your racing 7 freehub you will probably find that the difference is split: the higer gear is closer to the frame and the lower gear is closer to the spokes than with the 10sp freehub rather than everything moved in one direction.

I wouldn't make the cassette modification by hand as it needs to be aligned properly if you want reliability.

Answer 3

As you're seeing, in many cases the capability exists to trim the cassette and/or the freehub body to get the 1.85mm needed.

1.85mm may not sound like a lot, but note that interference between the rear derailleur cage and drive-side spokes can occasionally be an issue that comes up even on un-hacked 10 speed road bikes. Typically it will be the outer spokes on a j-bend hub.

You need clearance in this area to both accomodate flex and also prevent destruction of the frame, wheel, or rear derailleur should the bike be ridden with minor hanger misalignment.

34t+ 11-speed cassettes put this area of the RD further down away from the spokes, but with a 28t or less you will have to be very careful here on a j-bend hub. (Usually there's a lot more clearance on straight-pull).

I don't have any great ideas for taking down the cassette with simple tools. One fairly simple approach could be to use a safe-side file on the freehub body as you spin it backwards in a truing stand or bike. Using only moderate hand pressure it should be possible to keep it even.

Answer 4

Given that you can get a replacement freehub, it seems like you have little to lose by trying to machine off the material freehand.

I have no personal experience. However, my understanding is that the poorly-received answer you linked to is correct: you can do machine down the stops on the freehub body. Not all freehub bodies have long enough stops to get you 1.85mm of space. An alternative is to machine down the lip on the rear of the cassette. Lasco Concepts, who wrote the answer you linked to, offers this service as well. (NB: I'm linking to their web store, I have no personal affiliation.) Or this guy on the Weight Weenies forum did a combination of both, plus he needed to machine a bit off the hub shell also. Not all hubs have enough space on the freehub body to machine down; the Weight Weenies poster had Shimano factory wheels, and my understanding is that Chris King classic hubs also don't have enough space. There may be others. If Fulcrum offers a replacement freehub body, I am less worried about this, since it indicates that there's enough clearance in the system.

In principle, the cassette does not have to be done by a qualified machine shop. That said, you do raise the issue of tolerances. Every manufacturing process has variance. If you're operating a CNC machine, the variance is presumably very small. If you're operating by hand with a jig to hold the freehub or cassette steady, I'd assume the variance is larger. Without a jig, I'd assume the variance is a bit larger still. If you don't machine the splines to equal length, the cassette may not sit straight on the freehub, and it might have some lateral play, and that might affect your shifting. One bike store owner I talked to offered cassettes like these at one time, but my recollection is that he discontinued them as his machining partner couldn't achieve adequately precise tolerances.

I lack the skills to measure and mark the appropriate length on the freehub body, and I don't have the equipment to do so anyway. If you do, then it seems more logical to try the freehub body first, since you'd just be replacing it if you fail, and I don't anticipate many people wanting Fulcrum 10s Shimano freehub bodies on the used market. Some possible considerations are:

1. Think about a strategy to make sure you're machining the splines down an equal distance. Do you have an accurate enough caliper or other measuring tool?
2. Can you mark the desired length adequately?
3. How do you plan to hold the freehub body steady when you're machining/filing?