Cassette spacer to bring mech swingarm away from spokes?

[Manc33]

After swapping to a different cassette, it seems to sit closer to my spokes when in the lowest gear. It is again perilously close. Whats the problem with just adding a 2mm spacer onto the rear freehub and adjusting the limit screws on the rear mech accordingly?

Honestly of all the dozens of "problems" I have with my bike this is the oddest one, there's like 1mm between the mech swingarm and the spokes in the lowest gear. I can take 2mm but not 1mm come on.

If this won't affect shifting, I have to do it.

I could just add in a small sprocket behind the cassette.

It is a 8 speed cassette on a 9 speed freehub body.

[Edwards]

I remember a spacer being used for 7 speed being used on some 8 speed hubs. So provided it all fits I do not think you would have a real problem.

[Dave W]

Shimano supply a spacer on some of their cassettes. Offhand I can't remember which ones need it. Probably yours. Bike shops should have odd ones lying around I would have thought - they are shaped to fit the freehub body so have the cut aways to match. Probably got a couple in my toolbox.

[robgul]

Several of my bikes have spacers behind the cassettes (7 on an 8 hub etc) - as suggested they are a common part - LBS or SJS will supply, in varying thicknesses. On my No1 touring machine I have a wide spacer and have not fitted the smallest cog on the cassette ... I can't ride that high a gear comfortably so why not - it also improves chainline.

Rob

[MartinC]

Any spacer you put behind the cassette (assuming it's on the correctly size freehub) will rob the lockring of thread engagement. I'd be reluctant to lose any of this because it's minimal anyway and you need to torque the lockring up fairly tightly. Shimano supply a 3mm spacer to put a 7 speed cassette on an 8/9/10 speed freehub - if you really concerned about the spoke clearance you could use one of these and drop one sprocket from your 8 speed cassette.

[Brucey]

is your rear mech correctly aligned/ in good condition? If not it may have to run very close to the spokes in bottom gear.

I don't recall any 9s hubs that need a spacer with an 8s cassette fitted, with the possible exception of an XT style one (with its own spider) and even then not always.

cheers

[Valbrona]

No point in fitting a spacer unless cage is rubbing against spokes.

[Manc33]

is your rear mech correctly aligned/ in good condition? If not it may have to run very close to the spokes in bottom gear.

I don't recall any 9s hubs that need a spacer with an 8s cassette fitted, with the possible exception of an XT style one (with its own spider) and even then not always.

cheers

"XT style" well this is an Alivio 8-speed which I thought might be "based on" the old XT 8-speed, or I might have even read that somewhere.

Either way the Sora HG50 I took off wasn't so close to the spokes and now the HG-51 is.

I already have bent my mech hanger out a bit in the past, from the last time it was close to the spokes (put on a new set of wheels). Half the time I am sure just me tightening the rear mech on cause it to bend, after all its made to give before damaging your frame or derailleur. You can't have it all.

What if I just deliberately bend the hanger out?

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EDIT: Deliberately bent the hanger out about 10mm and tightened the mech back on (which made it bend in slightly) to achieve an overall clearance of about 4mm/5mm in the lowest gear. It is changing gear just as smoothly as before. I can tell now though looking at the swingarm, it is bent out but why care if it changes gear smoothly and is a safe distance from the spokes in the lowest gear.

I need to change the mech because I am using a 37t total capacity mech on a bike with 45t capacity. It works, but its dodgy because the rear mech doesn't like the sudden slack caused by shifting from outer to middle and the chain can get caught up on the ramps/pins and so on, I figured out I need a SGS mech.

People say "Its OK just make sure you don't change into small>small or go near it and its fine", nope... because a mech like that can't cope with the sudden change in chain tension whereas a SGS will.

Swingarms have got longer and longer over the years.

On a road mech with a short cage, it is something like a 63mm cage. On older "medium cage" (like Ultegra 9-speed) it is a 75mm cage. Now later, on a Shimano 105 10-speed (RD-5701) called a "medium cage", it is 87mm. So the "medium cage" road mech of today like a 10 speed 105 has a longer cage than the old "medium cage" used to be! Then there's MTB long cage or "SGS" and those are 95mm or even 100mm and take up to a 45t total capacity.

Running a 6500 rear on a 28t sprocket I had to turn the b-tension around and it is only just about doable.