I have a very cheap, yet very old, 26" Chinese rear wheel with a freewheel hub mounted on my MTB. The hub, bearings and cones are shot, but the rim is still good.

I have two Shimano cassette hubs FH-RM20 and FH-RM50, that I got very cheaply on eBay. I was hoping to get the freewheel hub swapped for one of the cassette hubs at a local shop for 160 baht (~£3) - labour is cheap in Thailand.

However, after originally having said that the hubs could be swapped, once I had taken the cassette hubs to the shop to show them, the lady in the shop has now told me that the hubs could not be fitted. Due to language issues, I wasn't given any explanation as to why.

The number of spokes is the same (36) and the spoke holes diameter is 45 mm in both the freewheel hub and the cassette hub, and the spoke bases (i.e. the holes for the spokes) are 67 mm wide (or rather, apart) on both types of hub. So, the fit (i.e. dimensions) would appear to be the same.

I am not sure whether the shop was expecting my to want to swap for another freewheel hub, and having the cassette hub instead is the problem. So, my questions(s) are:

  • Is it possible to swap the hub types, or
  • Does it lead to other issues, such as offset issues? Can the same spokes not be used?

I am tempted to just try to swap the hubs myself and then go back to the shop to get the spokes tightened properly, but I don't want to mess up my current wheel if it is not possible - the bearings may be shot but it can still get me around (just about).

Keeping costs to a minimum is a priority, hence why I am not going for a new set of Formula hubs, AlexRims RM19 rims and Pilar spokes for ~3000-4000 baht (~£70-100), However, I don't want another cheap Chinese hub, so that is why I am attempting this hybrid solution of a good cheap second hand Shimano hub and the existing cheap rim.

Please note that this is a different question to Can I convert freewheel hub to use cassette?, as I actually want to swap hubs and not convert them.

FWIW, I currently have a 7 speed freewheel gearset (Shimano MF-TZ07), and I have a Shimano CS-HG41-7ac to use for the cassette.

  • Is it possible your new cassette-based hub was a 8+ speed width? A 7 speed cassette is its own unique width, and would need spacers behind to fit on a 8speed hub. Also, the OLD measurement should be the same to minimise problems.
    – Criggie
    Jun 29 '20 at 12:00
  • 1
    As an update, four months on from having successfully swapped the hubs and relaced the wheel spokes myself, I can say that it was a definite success. Note that I ended up purchasing a new cheap (180 baht) Chinese wheel, in order to use only the new rim and spokes, with the Shimano hub, rather than reuse the old (and rather battered) Chinese rim and spokes. Nov 21 '20 at 5:30
  • Thank you for the followup - that's much appreciated, and well done with your upgrade.
    – Criggie
    Nov 21 '20 at 10:21

You say the bike is old, and a 7 speed freewheel hub can be 126 or 130mm over locknut dimension, and the cassette hubs you have will be 135, so that could be one mismatch they saw. But most freewheel hubs on 7-speed bikes from the past 30 years or so have been 135.

Other than that, what you propose should work. The shop might not have realized a conversion of this sort is usually not a big deal.

Note that the flange to flange spacing alone is not exactly what's important. It's the center to flange dimension on each side. Sometimes this is expressed by giving a flange to flange dimension plus an offset dimension, which accomplishes the same thing. But that said, between the hubs in question here, the center to flange numbers are probably almost identical barring an OLD mismatch as above.

Dropping in a new(er) cassette on an otherwise worn drivetrain can cause issues with skipping under load. There are many questions here about this. The shop could have decided to balk at getting into those potential issues.

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