wrk101

I am "borrowing" the rear wheel and cassette from an 8 speed donor bike, to put on my 7 speed Trek. In removing the rear cassette, I couldn't help but notice it had a six speed cluster (my term) along with the smallest two cogs being loose fit.

Would it be possible to just reuse the cluster and one of the two cogs? Would I need a spacer of some kind to make it fit?

I try to reuse everything!!!


thanks!

Bill Kapaun

The center to center spacing between 7 & 8 speed cassettes is different, so even if you did, the shifters wouldn't index correctly.

The length of the Free Hub body is also shorter on the 7 speed by a bit vs the 8/9 speed hub.

The actual cog thickness is slightly different, but not much. You could probably get by swapping a cog or 2 between them without major problems. Spacer thickness is about 0.2 MM thicker on the 7 speed.

You'll probably find the "cluster" is held together by 3 rivets/screws. These can be removed.
I've done this to make a "custom" cassette out of 2 different cassettes.
I've also used 7 speed cogs to make an 8 speed cassette by thinning the spacers. Not really recommended unless you have too much time on your hands.

wrk101

Do you think if I bought a seven speed cassette, and put it on the 8 speed wheel, that the hub body difference is small enough I can use it? I can get a seven speed cassette pretty reasonable on Nashbar. The bike (actually frame I am building up) has a seven speed shifter on it, so I need to stay with seven speeds. I was hoping the wheels off the $5 Kona would fit. The front fits well of course.

smovlov

The first question is it indexed shifting? If not you might be able to eek out eight speeds and not have to use a seven speed. Just back the high stop all the way out. If not then a seven speed cassette with a spacer should work.

zzyzx_xyzzy

In reverse order.

For the second question, If you want to run a 7 speed cassette on an 8 speed hub using 7sp shifters, you will have to install a 4.5mm cassette spacer like this:

https://www.jensonusa.com/store/produ...te+Spacer.aspx

For your first question, based on the crib sheet here:

https://www.sheldonbrown.com/cribsheet-spacing.html

You can install '7 of 8 on 7,' but you will also need about a 1.25mm spacer. The sprocket spacing is actually pretty close (5.0 mm vs. 4.8 mm, or 1.2mm over the whole cassette) for indexed shifting with a 7sp shifter but it won't be perfect.

wrk101

I ended up getting a spacer from my LBS, no charge. Apparently, these spacers often come with new 8 speed wheels, to allow them to be used as either 7 or 8 speed cassettes. Spacer worked like a charm!

I did have to mount the spacer on the spoke side of the cassette, as otherwise, it caught the edge of the chain when on the smallest cog.

somegeek

Only dumb question is the one not asked.