Cycling UK Forum

Dear All,
I managed to cadge a rear wheel from a mate after mine was stolen. It is the right size in that it is 700 and the thing slots into the rear forks, but it has 8 cogs whereas my shifter (a Dawes Kalahari) is only for 7 speeds. Should it work like this, albeit missing gear cog 1 or 8, or will it make a racket as it scratches the cogs incessantly?
Also, would I be able to remove the '8 cog block' and replace with a '7 cog block' and if so, how difficult is this?
Many thanks,
Dave

This link from Sheldon Brown covers all sorts of interesting stuff including the removal and replacement of cassette sprockets from a freehub.

It begins with a bit about the difference between a freewheel and a freehub. In fact, so few 8 speed freewheels are produced yours is almost certainly a freehub.

There may be an issue over the make of the freehub in that there is not much interchangeability between makes if you want to replace a cassette. I think the queston about changing between 7 and 8 speeds is usually asked the other way - by people wanting to increase their number rather than decrease it. There is a section on the Sheldon Brown link if you scroll down past all the charts of different spacings.

Also have a look at this from the CTC desktop. In particular, you will see that although Campag spacing is the same between 7 and 8 speed, Shimano, which yours probably is, isn't (if that makes sense. Shimano 7 is 5mm, 8 is 4.8mm. It's not something I have ever done so I cannot advise if just ignoring a sprocket would work.

It would appear that the cassette size is different and a 7-speed cassette wouldn't fit onto an 8-speed freehub body. So your options are to buy a new wheel with the correct 7-speed freewheel. Or change your right hand shifter to work with 8 speeds

No, there's a simpler solution. The 7 speed cassette will fit - all you need is a 3mm spacer (cost about 2-3 quid) which you fit at the back before dropping the cassette on.

Dear Hamster,
I am going from a 7 speed cassette to putting a wheel with an 8 speed cassette already on it - where does a spacer come into it?
I had hoped to just stick the wheel on, and then ride it....realising that I would miss either gear 1 or gear 8...!
Dave

there seems to be 2 queries on the go here
1. Will an 8 speed hub fit into the frame between the dropouts? I don't know without looking and measuring. Have you tried putting it in? does it fit? Yes=no problem there then, no - how tight is it?

2. Can you simply slide a 7 spd cassette onto the 8 speed hub? Probably yes. Hamster is saying a big washer on the hub first before you put on the casette to take up the slack. Splines etc should be the same. (Im assuming its all shimano fitting)

Why not get an 8 speed right hand shifter and enjoy the benefits(?) of 8 speed?

davidsmedley999 wrote:Dear Hamster,
I am going from a 7 speed cassette to putting a wheel with an 8 speed cassette already on it - where does a spacer come into it?
I had hoped to just stick the wheel on, and then ride it....realising that I would miss either gear 1 or gear 8...!
Dave

Re-use your old 7s cassette. With Shimano systems you can usually also get a 7s shifter to work OK across 7 cogs of an 8s, athough it can get a bit rattly if the cables are old or dirty.

David
This has all got a bit confusing, hasn't it?
7 & 8 speed systems use the same chain, so unless the new wheel has a much bigger low sprocket than the one it replaces there should be no problem there.
I havent tried it but there does seem to be support for your hope that you can just fit and use. If you have indexed gears then you will undoubtedly need to "discard" a sprocket - set your mech limit screws accordingly.
If the resulting gear change is acceptable, then job done.
If it doesnt work well enough then you have two options.
The first would be to obtain and fit a 7 speed cassette. This would be a tad narrower than an 8 speed and so it would be necessary to use a spacing washer behind it in order for it to be properly secured. A good bike shop might be able to let you have some old ones.
IMO the better choice would be to change your gear shifter for an 8 speed. The main advantages of doing so would be that you wouldnt need the special tools to change cassettes and you would in future have access to a larger choice of spares. If you look on ebay you should find a large choice of shifters from about £15 a pair (new stock, from traders!).

Just reread your original post - its not hard to change a cassette but you would need to get a chain whip (to hold it still) and a cassette remover (looks like but different from a freewheel remover) and something to turn it with, like a large adjustable spanner. The tools alone would probably cost as much as new shifters.