Depth of spacer to run 7 speed cassette on 8/9 speed hub?

[Blue Hills]

I've had reason* to check this out and on the web/webshops have seen the depth of the spacer to go behind the 7 speed cassette given as 3mm and 4.5mm. Which is it?

* I bought some new wheels for a 7 speed bike last September, fitted the 4.5mm spacer that came with them, have just realised that the odd rattling I was aware of in certain gears (I can be a bit leave-well alone with niggling mechanicals) I was hearing in the odd gear was the chain rubbing against my frame (steel so hopefully no real significant weakening of it) when it's on the smallest rear cog. Maybe a smaller spacer would solve this?

I think my rear wheels is currently fitted with this, though I got it from Spa Cyles with the wheel.

http://www.sjscycles.co.uk/wheels-m...te-on-8-speed-hub-body-spacer-each-prod18561/

No cut outs, though I have seen some with cut-outs.

This is 3mm

http://www.wiggle.co.uk/shimano-cas...ano-Shimano_Cassette_Alloy_Spacer-Silver#more

Yes, I know it seems barmy that I've only just noticed but not ridden it too much.

Or could something have happened to the wheel dishing that has caused this?

I use SRAM cassettes but surely this makes no difference? I thought that the key dimensions were the same as Shimano.

 

[Manonabike]

Going by the size of the spacer that came with a set of wheels a few years ago I'd say it's 3mm.

 

[fossyant]

2 x 3mm spacers will have that sorted. I run that on Mavic wheels that are designed for anything upto 10 speed - two 3mm spacers (for my 7 speed kit)

 

[Blue Hills]

mm

Any advance on 3mm, 4.5mm or 6mm?

I'm still puzzled as to why the chain is catching on the frame (ie: small cog too close to frame) - suppose I'll have to take the thing apart and experiment.

The spacer I presume is just to make the lockring grip on the deeper freewheel thingy?

 

[RecordAceFromNew]

Assuming you are not running some modern e.g. Mavic wheels (which as Fossy said require different consideration because they have standardised the freehub width to cut manufacturing/stocking cost to accommodate Campag's cassettes which are wider than Shimano's), either 3mm or 4.5mm should work usually. The reason why there is variation is because while typical Shimano (or compatible) 7 speed cassettes are 32mm wide, 8 are 35.4mm and 9/10 are 36.5mm.

The spacer is indeed just there to ensure the smallest cog sit proud of the freehub so that the lockring can grip on to the cog, nothing else.

Regarding frame rub/clash, have you measured the distance between the locknuts and be sure it is 130mm? and what is the width of the freehub as well as your 7 speed cassette? and does you frame happen to be one that has been cold set from e.g. 120mm between dropouts?

 

[Blue Hills]

Thanks for that Recordace - I'll do some fettling/fiddling tomorow and report back.

 

[simon.r]

I'm still puzzled as to why the chain is catching on the frame (ie: small cog too close to frame) - suppose I'll have to take the thing apart and experiment.

Is it simply that the small cog is too big? A few years ago I had a Kaffenback that was one of a batch that had been manufactured slightly out of tolerance, meaning that the small cog had to be no bigger than a certain number if teeth (11 IIRC)

 

[Blue Hills]

Thanks for the suggestion SimonR - will check it out.

Bit of an update - replaced the 4.5mm spacer with a 3mm one I found that I had around.

Indeed, the lock ring wouldn't tighten properly so that isn't a solution. 4.5mm now back on.

Dug out the old 7-speed hub with 7 speed cassette and tried that on the bike and that didn't seem to have been causing any chain/frame clash problems.

More investigation/head scratching needed ....

 

[Blue Hills]

Update.

Well Simon - you may be onto something - I checked that old grotty 7-speed cassette (Shimano) and it did indeed have just 11 teeth on the small cog - my current one (SRAM), and one I have been using for a bit has 12.

I then managed to get this Shimano one off the old grotty wheel and fit it to my current one and it seems to have relieved the problem almost totally.

One oddity, which I do not understand, is that I got this onto my wheel using just a 3mm spacer and the lock-nut worked fine. The SRAM 7 speed needs a 5mm spacer.

So, progress, though I can't use this Shimano cassette as its too worn and is 11-28 - I need something with more teeth on the big cog (SRAM has 32) but a quick look at various online emporia seems to show that I have diddly squat chance of finding a 7-speed cassette at a reasonable price with 11T small cog and largish big one, so, when I have a mo, seems I'll have to get some 8-speed shifters and new brakes (I currently have 7-speed dual controls).

!!

Still, progress, thnaks to all and Simon - for the moment I've adjusted the limit screw to block the chain going onto the 12T cog so I now have an 18-speed bike

 

[Blue Hills]

Another question linked to this.

I know I could just try it but I thought I'd ask

Would it be a total no no to use put the 11 teeth Shimano cog (on closer inspection it isn't worn much) onto the Sram 12-32 (the 12 is a separate bit) instead of the Sram 12T so that I get the 11-tooth cog to avoid the frame clash with the benefit of the SRAMs larger 32T for climbing?

I'd have to use the Shimano 11T lockring of course.

This would mean that the 11T Shimano cog would have to shift up to a 14T SRAM cog and thence to the rest of the SRAM cassette.

Anyone ever tried such a thing?