My spouse has a Raleigh M40 dating from the late 1990s with 26 inch wheels. It is a seven speed, I can't recall if it is a cassette or free wheel. He and the bike are at our midwest home and I am up north. He wants an extra set of wheels so that he can have one set with a knobby tire for mountain biking and another set with slicks for riding on pavement. He didn't want to spend anything to speak of for this. Well, a friend has a spare set of wheels with an 8 speed cassette on it. He said the wheels are only a couple of years old and he had them as spares for a bike they don't have anymore. He will sell them to me for a token amount, $10.

How do I tell if this will fit his bike? Is the fork size the same on all these relatively modern standard mountain bikes that take 26 inch wheels? Can I use a wheel made to fit an 8 speed cassette on a seven speed by buying a cassette and putting in a spacer? That is what Sheldon Brown suggests. https://sheldonbrown.com/k7.html. I would have spouse count the teeth on the largest and smallest cogs and then I would buy a cassette with the same number.

Chances are good that the frame's rear dropout length and each hub's outer locknut dimension (OLD) are all 135 mm. but it doesn't hurt to check.

Yes, you can use a 4.5mm spacer and 7-speed cassette on the 8-speed freehub.

If I had two wheels and one had a cassette and the other a freewheel, I'd use the one with the cassette for MTBing since it's a stronger setup. If they both took a cassette, I might use the one without the spacer for MTBing (less dish, stronger wheel), depending on other characteristics of the wheels.

I'd also use a wider-range cassette for MTBing (11-32 or 34), assuming the RD can handle that large of a cog, which it likely can.

There's a chance that the positions of the cogs won't be exactly the same between both wheels, so the rear derailer's barrel adjuster and perhaps limit screws may need slight adjustment after swapping, but 7-speed is fairly forgiving of imprecision with its relatively wide spacing between cogs.

Thank you. I'll have him measure the distance to make sure it is 135 and I'll do the same on the wheels. Good plan on using the cassette equipped wheel for the mountain biking. If what he has is a freewheel.

Some confusion on my part - so removed.

Sorry, but I think post #4 only confuses the issue.

As to the need for a spacer: the OP is talking about using a 7-speed cassette on an 8-speed-plus freehub, so of course a spacer is needed.

Yup. I assume you put the spacer on first, then the cassette?

Hi,

Is it true a MTB with a 7 speed freewheel generally will take a 8+ freehub wheel ?
I am under the impression this is not generally true for road bikes, but MTB's ?

Of course a freehub has fixed spacing and my confused comments made no sense.

rgds, sreten.

Yes, spacer first, then cassette. Among other reasons, this configuration will keep the cogs on this wheel in about the same place as the cogs on the other wheel.

For MTBs, it's been my (limited) experience that 135 mm has been standard for some time, even for bikes that originally came with 7-spd freewheels.

With emphasis on the generally, yes.
Supposedly there are 130 mm spaced MTBs out there, but I've never encountered one.
Even the dirt-cheap 6-speed FW equipped "hybrids" I occasionally encounter around here seems to have 135 mm spacing.