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. http://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.