I am currently trying to convert my wifes old road bike to 650b wheels and had a quick question. I believe it has the clearance to do this. The bike is a Nishiki Modulus with Shimano Exage EX gears, I believe it's a 1991. It has a 7 speed cassette and Index shifters.

Budget is an issue, so rather than get new wheels built on the existing hubs, I though I might pick up some an inexpensive Shimano Deore 8/9 rear wheel on ebay, and was wondering if the current 7 speed cassette I have would fit on this? Do I just need to add a spacers or would there be a compatibility issue?

Spacing should not be an issue as the bike is 126mm and the wheel is 130mm.

Thanks!

4.4-4.5mm spacer on the back of the cassette. You can jimmy something or buy the prefab'ed spacer for that. Works just fine.

Excellent thanks!

Just in case you get a 8-9 speed wheel that comes with a cassette
You can literally use that cassette with your 7 speed shifters.

Yes, it shouldn't work since the cogs are spaced differently, but it works reasonable well until you actually install your 7 speed cassette.

I think it works because of that side to side play that is built into most derailleurs.I forget the term for this intentional slop, but it is important.

Yes, there will be some gears that will be too noisy, and will slip/change/slip change- but it will be much less annoying that you would think.

I currently use a 8 speed XTR cassette-with one cog removed-with my 7 speed indexed twist shifters-shimano- on a Trek 730-roughly 1994. I do it because I wanted to use the 34 t cog of the old XTR, not the 30 t the 7 speed cassette came with.The 700c wheel is for 7 speeds-can't take 8 or 9 cassettes.

I ride intervals up and down the river levee, so I need low gearing.
Shouldn't work, but it does-strictly a cheapout-I would rather have a 13/34 7 speed cassette, but $$-$30- is short.
Charlie

7-speed and 8-speed hyperglide are spaced the same. You can run an 8-speed cassette with 7-speed shifters (or vice versa) no problem. 9-speed and 10-speed are different though.

To answer the OP's question, yes you can easily put a 7-speed cassette on an 8/9-speed wheel. You'll probably have to add a spacer.

I don't think the wheel comes with a spacer, but good to know none the less. Thanks again.

They are close but not exactly the same. Center-to-center spacing for Shimano 7-speed cassettes is 5.0 mm and for 8-speed cassettes it's 4.8 mm. Over 7 cogs the mis-match is 1.4 mm which can cause rough shifting and noisy running at one end or the other.

You can usuallu make it work adequately by getting the rear derailleur centered exactly over the 4th or 5th cog on an 8-speed cassette so the misalignment is minimized at both extremes.

Like Hillrider said- not exactly the same spacing, but if you tinker with it a bit, it will work ok.I removed one cog so it-the 8 speed-became a 7 speed and would fit on the hub.
Strictly a cheapout, but it works ok.

One minor thing. Take a look at the back side of your cassette. Most of them are held together with some skinny little bolts or rivets. Either way the protruding heads have to come off. I throw the bolts away and install the cassette one piece at a time. I grind the rivet heads off with a file or a bench grinder and the cassette stays in one piece.

The other way around the bolt/rivet heads is to install the spacer after the smallest cog but under the lockring. That worked well for me with a 12 or 13T smallest cog. I don't know if the spacer will clear an 11T cog.

Hmm I didn't know that. I have a 7-speed Shimano freewheel on a bike that came with an 8-speed Freehub (different wheelset.) I'm running the original 8-speed shifters and it indexes perfectly. Not a problem in practice, perhaps. Not for me anyway.

Edit: I went the other way too! My road bike was equipped with 7-speed Uniglide, now it's 8-speed Hyperglide. I'm still using the original 7-speed downtube shifters to go through all 8 speeds. The largest sprocket is a friction shift past the last indexing point, but the derailer set screw makes this a non-issue.

FastJake
I have an 8 speed twist shifter and planned to install it with my 8 speed cassette turned into a 7 speed. I didn't bother because the 7 speed shifter works just fine.

My calculations say 4.8X7= 33.6 divide by 8= 4.2 so the same thing won't work with a 9 speed.
Charlie