Talking of balancing...

Why do tyre fitters remove the sprocket & cush drive before balancing
rear wheels? They strike me as being fairly hefty lumps that should
probably be included for balancing (& I do include them now that I
balance my own wheels).

 

I've done a fair bit of balancing myself. I can't remember whether
I usually leave the sprocket and cush drive in place or not- but
remember that while they may weigh something they're not very far
away from the axle, so any contribution to imbalance is going to be
pretty small unless there's a big chunk of rubber missing from the
cush drive.

If there's nothing stopping you from leaving them in place, by all
means I would balance with the tire and cush drive installed.

 

Perhaps because they are fairly hefty lumps. Fairly hefty lumps with
pointy bits that are not positively retained. If the cush drive slides
out while being spun up then the fitter might receive your sprocket in
his bollocks, perhaps.

Prolly because they're so close to the centre that they won't affect
the balance much.

 

sprockets, cush drives? What are these contraptions?

 

TFFT, I was sitting here wondering. If I'd had to guess I'd probably
gone with lawnmowers with chainsaws next on the list.

 

It doesn't fit on their machine? Besides a sprocket and hub wouldn't
affect the centre of gyration much due to its close proximity to the axle.

Depending on how your balancer holds the wheel, it may be more likely to
wibble about if you're using the hub due to axial misalignment?