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I have a Giant Defy 9-speed road bike, and a thief stole the front wheel. I found a good deal on a set of used Bontrager (Edit: Mavic Aksium) wheels, so I bought them as a set. I want to swap both wheels so that they match, and also because the new wheel is 72g lighter. Probably a higher quality wheel overall. The trouble is, it's a 7-speed.

I know how to change a cassette, but I've never changed a hub. I can see that the 7-speed hub is smaller, so 9 gears won't fit. Can I move the 9-speed cassette over? I'm guessing there might be some kind of compatibility issues, but I don't know what to look for.

Edit: I just realized the Mavic hub has a spacer behind the cassette, which can be removed, leaving enough room for 9 sprockets. But now the locknut doesn't quite tighten all the way, it looks like I need to add a spacer of less than 1mm.

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    Your easiest path is to fit the front bontrager wheel and leave the rear as-is. You'll be riding again in minutes
    – Criggie ♦
    Commented Apr 7, 2018 at 4:53
  • So you'll also need to modify your locking-up procedure too. Else your nice new wheel/s could also vanish.
    – Criggie ♦
    Commented Apr 7, 2018 at 5:10
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    Haha yes well the main modification will be not parking in Hollywood
    – Elliott B
    Commented Apr 7, 2018 at 5:32
  • Coincidentally, I've just experienced a similar problem. My rear 9 speed wheel needs replacing, and I have a fairly new 7 speed wheel. Hubs are incompatible spoke patterns, freehub body is different mount. So I have to buy another 9 speed wheel. Nothing else will do.
    – Criggie ♦
    Commented Apr 9, 2018 at 4:08
  • 0.8mm will be the correct size for the spacer. Bike-shops tend to have a box or a drawer full of all different sizes of spacers, often for free.
    – Carel
    Commented Apr 9, 2018 at 19:52

4 Answers 4

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This is why you do the research before buying (and why wheels get stolen).

If you really want to use the 7-speed wheel, you can leave out one cog from the cassette and use derailleur limit screws to prevent it from shifting outside the cassette.

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  • That is a good solution that I missed. It does prioritise form (matched brandname wheels) over function.
    – Criggie ♦
    Commented Apr 7, 2018 at 20:04
  • If you look prebuilt wheels, you'll notice that compared to wheels built from standard components they look wildly different from each other and wheels from different sets will likely look mismatched. It's also very unlikely that spoke counts match so that one could actually take a hub from one set and build it with rim from another.
    – ojs
    Commented Apr 7, 2018 at 21:52
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    IMO front wheels mostly get stolen because idiots think they've secured their bike by locking the front wheel to something. So a thief comes along and steals the idiot's complete bike except the locked front wheel, and then steals the nearest front wheel they can find.
    – David Richerby
    Commented Apr 8, 2018 at 9:55
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Re-sell the nice 7-speed wheelset, then buy a wheelset that has a 9 speed freehub.

You did not get a 'good deal' on the nice 7-speed wheelset because it's not compatible with your bike. I assume you did not realize that the freehub body was a 7 speed when you bought the set - sorry that happened, and I realize that there is a myriad of parts compatibility issues with bikes that is difficult to learn.

As Criggie mentioned you could rebuild the rear with your existing hub - but - you may need new spokes and you need to know how to build a wheel and have the appropriate equipment. Getting a bike repair shop to do it for you will likely cost more than the wheelset in the first place.

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I've done something like this. I had a rear wheel with a 6 speed freewheel, and an 8 speed hub and cassette.

I simply undid all the nipples and re-laced the new hub to the old rim. Fortunately for me, the old spokes were the right length already If your rim needs a different spoke length then this will get expensive. You also need the same number of rim holes and flange holes.

You might be able to unbolt your 9 speed freehub from the original wheel and bolt it to the newer wheel, but there's a very good chance the mountings won't be compatible. There are multiple standards for this fitment and different ways to undo them.

So the single easiest thing to do is use the new front and the old rear wheel.

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Actually width of the 7sp freehub smaller than 8,9,10 ones, also 7speed cassette has a wider space between sprokets, so if you set this wheel, and dicide to turn your transmission to 7, besides the cassette you have to change your chain, shifters, and likely change rear derailleur. But if you want to keep 9, you can swap the freehub. that's no easy to find it separately from hub, but this is can be cheapest decision, and you can keep the wheelset.

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  • Do you have any information about compatibility between freehubs?
    – ojs
    Commented Apr 7, 2018 at 21:54

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