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We've got a bike where the front hub (Shimano Alfine dynamo) uses a Center Lock rotor and the rear hub (also Shimano, go figure) uses an ISO rotor. The front hub is giving me fits trying to sort out why the rotor rubs intermittently, so I thought I'd try replacing the rotor.

My thought is to get a Center Lock adapter and use an ISO rotor so that both ends of the bike would use the same type of disc. Seems like it would make life and maintenance a bit simpler.

Question 1: Is there any reason why this would not be a good/acceptable idea? Are there substantial advantages to Center Lock?

Question 2: Does the adapter convert a Center Lock hub to an ISO hub or does it convert an ISO rotor to a Center Lock rotor? In other words, do I attach the adapter to the hub (and leave it there) or do I attach it to the rotor and move it from rotor to rotor as they wear out?

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  1. The advantage to centre lock is that it's easier to change rotors. You undo one nut and slide the rotor off. ISO requires 6 bolts to be undone/redone. It's also possible to build a lighter rotor more easily, and you can make smaller centre lock rotors than ISO ones (should you want a 50mm rotor)

  2. The adaptor does both, that's a question about how you choose to look at it.

Both these questions seem to assume you'll be changing rotors around a lot, when most people very rarely do this. Right now you have a problem so you're focused on the issue, but once you have something that works you'll likely not deal with that area of the bike again. So I'd be worried less about how much work it is to do a part of the current task, and more about whether you can stop the rotor rubbing.

In my experience the intermittent rubbing is never related to the mounting setup, once it's installed correctly and assuming there are no mechanical failures. Basically, if you can make it work even for a short time that's not the problem.

The most common cause of "sometimes it rubs, sometimes it doesn't" is bent rotors, so the slight variation in caliper return-to-centre means sometimes there's a rub. But that's an easy fix - put a straight rotor on and see what happens.

The other, more annoying issue, is that not all wheels sit tightly in the dropouts. That means that the wheel can shift slightly, usually under heavy braking. When that happens you'll often get rubbing that won't go away until you release the axle and re-seat the axle in the dropouts. At which point the rubbing goes away until next time you brake heavily. That's a design issue, and unfortunately the standard we have makes it inherent to the way bikes are built. It's more of an issue on front brakes (where the braking force pulls the wheel out of the dropouts) than the rear (force is up or back depending on caliper location).

Fixing the latter problem is tricky, and the solution I've used is a washer on the outside of the dropout sized so it engages with the "lawyer lips" all the way round. It also needs to snugly fit the axle, obviously. Which usually means filing, and is a tremendous pain in the proverbial.

A more permanent but still ugly solution is to use a welder to fill in the dropout a little then file it to exactly match the axle you have. Then repaint the fork (or frame) and re-file the new paint off the contact area (so you can get the wheel in). The real solution is to use through axles that bolt solidly in place, or mount the caliper on the right hand side fork blade instead of the left one. Hardly anyone does either of those.

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I purchased a Shimano SM-RTAD05 Center Lock disc rotor adapter, so now I can – at least partially – answer the question.

Shimano SM-RTAD05 parts

The answer to my second question is that the adapter converts an ISO rotor into a Center Lock rotor (as opposed to converting a Center Lock hub into an ISO hub) – in other words the adapter will need to be moved from rotor to rotor, it can not be left on the hub as you change rotors.

This adapter uses a Hollowtech II bottom bracket tool (e.g., the Park BBT-9) to engage the outside of the lock ring rather than a cassette remover. That was a bit of a surprise, though I could have noticed it if I'd looked carefully at at the photos. On the other hand there is no need that I see to use the supplied lock ring, so I just used the old one which has the internal splines for the cassette remover. Also, the bolts are Torx T-15 rather than the T-20 I was expecting.

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if you realy want to put an ISO rotor: yes, put the adaptor but it won't make anything simpler. You should buy a new centerlock rotor and replace the bended one that sure is causing you the rub problem.

  • I was thinking it would make maintaining our bikes a bit simpler since they would all be able to use one kind of disc (160 mm ISO). – dlu Oct 19 '15 at 17:37

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