Bicycle Mechanics - 7 speed cassettes on 8/9 speed hubs?

I am putting a disc brakes on my new bike wich in turn has freed up a wheelset for my old bike. The wheel set is a deore hubset laced to mavic x139 rims. I want to put this wheelset on my old bike but it has a 7 speed drivetrain which is a mixture of stx and alivio. obviously I will have to buy a 7 speed cassette becuase the bike currently has a freewheel. I noticed on nashbar that they sold a spacer that was supposed to allow you to run a 7 speed cassette on a 8 speed hub. do they make 8 speed spoecific hubs or do they really mean 8/9 speed hubs. will a 7 speed cassette work on my hubset?

The 8 and 9 speed shimano use the same hub. The 9 speed cassette cogs are narrower so they all will fit in the same space as 8 cogs. And yes, adding a spacer will let you run a 7 speed cassette. But why not just get some 8 speed shifters on ebay?

Yes the 7 speed setup will work. HUBS THAT ARE FOR 8/9 speed have a wider spacing than 7 speed so the spacer is the ticket, this is what I have on my Lemond roadbike. 8/9 speed cassetes are the same width, but the 9 speed has a more narrow spacing therefore the index spacing of the shifters is different on 7/8/9 speeds. I hope this helps.

But why not just get some 8 speed shifters on ebay?
Will the 7 spd rear der be able to reach all the gears on the 8 spd cassette? This has me curious since I could always do something like this as well.

But from a cost standpoint, it would still make more sense to get the spacer instead of the shifter unless you were really set on having that extra cog. Seems like a new cassette is in the budget either way.

- Jeff

The seven speed der will cover the gears and my old seven Lx der worked ok with an eight cassette. Some guys have also run nine cassettes with older eight ders.
As a side note, you can probably friction shift an old six der over wide enough range to work with an eight or nine cog set. Your shifting will need to be more precise.

The seven speed derailure will work fine and if you want to keep your 7 speed you need to put a 4mm spacer on the cassette body before you install the cassette.

Your 7-speed shifter may work correctly with all 8 gears of an 8-speed cassette or even with all 9 gears of a 9-speed cassette if you set it in friction mode.

But another option (if you need to buy a cassette anyways) would be to buy an 8 speed cassette, keep your shifters in indexed mode, and place your chain/limit screws according to which 7 gears you want to use.

this is my old bike, which I only ever tide it around town so I was actually going to buy a 7 speed cassette not an 8 speed cassette. The idea was to switch to the new wheelset as cheaply as possible. new shifters are not what I need. for what I use that bike the shimano tourney rapid fire work fine. you can get 7 speed cassettes really cheap on nashbar. also, what do you mean friction mode. I am familiar with adjusting and setting up deraillers but have never heard of this.

[Regarding friction]

Sorry I goofed. Don't ask me why, but I thought of bar-end shifters, which can either be used in friction mode or in indexed mode. If I remember correctly, old thumbshifters also work the same way, but they have been extinct for some 8 or 10 years.

New to forum, I want to thank you all.I have a new sram 7 speed cass and a just aqiured 8 speed wheel .It didnt fit, loose I just ordered an new shim from Ebay. Just search: bicycle cassette shims.I orderd the one w/3 cogs that go into splines,you will see wich one. I dont much know about bikes but I am learning. This 7 to 8/9 speed forum really helped. Just wanted to pass shim info on, its a start for me

http://harriscyclery.net/itemdetails.cfm?ID=2127

4.5mm spacer, not 4.0mm.

Friction shifting is shifting by moving the lever yourself onto the correct gear -- as such it requires more skill, but allows you to basically use any speeds you want on your cassette.

Rapid-fire is indexed for a specific number of gears, usually 7 or 8.

http://www.sheldonbrown.com/upgrade-gears.html

http://harriscyclery.net/itemdetails.cfm?ID=2127

4.5mm spacer, not 4.0mm.
That is correct. Also the spacer is usually installed on the hub before the cassette but some cassettes are bolted together and the bolt heads interfere with the spacer so the cassette won't seat all the way.

There are two approaches to fix this:
1. Remove the bolts and install the cassette as all loose cogs and spacers.
2. Install the cassette on the hub first and install the spacer after the smallest cog and under the lockring.

Either way works.

Thanks, ordered 4.5mm one just now. Grateful

One thing that nobody's mentioned so far is the over locknut dimension (OLD). There's a good chance they are going to be the same but this is one of those times when 1 measurement is worth 1,000 guesses. If it was my bike I'd measure the rear dropout spacing before spending any money.

Good call Retro - I was just going to add that the cheap SRAM 7-speed (12-32t) cassettes sold on Nashbar don't have rivets holding the sprockets together, making installation with the 4.5mm spacer easy. They had a plastic thing holding them loosely, and that's it!

But another option (if you need to buy a cassette anyways) would be to buy an 8 speed cassette, keep your shifters in indexed mode, and place your chain/limit screws according to which 7 gears you want to use.

That wouldn't work too well at all cause the 8spd cassette is spaced closer than the 7spd one. Don't do this.

I rec. both spacers in mail this AM. , and found the 4.5mm TOO thick. I could not start the lock ring,and found the 4.0mm works on my set up( SRAM 7 sp. 12-32t un-known 8 speed hub) Diff in component manufacters?I prob. could of used 3.5mm. Anyway I am satisfied Thanks!

I just thought of another thing you could've done, maybe... if you were able to find the right-sized spacers, you could've spaced your 8spd cogs to 5mm, and just ditched the largest one.

Food for thought

That is correct. Also the spacer is usually installed on the hub before the cassette but some cassettes are bolted together and the bolt heads interfere with the spacer so the cassette won't seat all the way.

There are two approaches to fix this:
1. Remove the bolts and install the cassette as all loose cogs and spacers.
2. Install the cassette on the hub first and install the spacer after the smallest cog and under the lockring.

Either way works.

I solved this problem a third way when I used to run 7 speed on a White Industries 8 speed hub with a Hyperglide-C cassette:

I marked and drilled 3 half-depth "reliefs" in the aluminum spacer to clear the bolts, or rivets, or whatever they were. Worked great.