hub washer required?
 

I got a new rear cone for a hub. It is ever so slightly wider than what it replaced. It turns out if I remove the washer between the cone and locknut I can just about get the same distance from the cassette to the derailleur hanger. My question is, is this washer required for a mechanical reason or is it merely as a spacer?

Thanks

It actually might prevent the chain from moving back off the smallest cog.
That's dependent on cog size and chain stay "geometry".
I've had to insert an extra 1mm spacer on the DS when changing "something" (it's a long time ago) to a 12T cog from a 14T after that problem developed.
Depending on how your "serrations" etc. are configured, it might cause other minor problems like not staying locked or being difficult to loosen.

"ever so slightly wider than what it replaced."
Actual numbers work better than reading your mind.

I don’t see an issue with removing the washer if you still have chain clearance from the dropout. You are basically just putting 2 jam nuts together. Without the washer, it might make it harder to separate down the road, but since adjustments are NDS, that shouldn’t matter.

You should put the wheel in a truing stand to center (re-dish) after the washer is removed.

John

I have a hub that I did this to. It is difficult to separate the locknut/cone. Found some 0.3mm wavy washer that I may fit in there next time I'm in there.

If the dropout/freehub body gets too close, you may have a problem if you plan to use a domed alloy cassette lock-ring. A flat steel lock-ring, like Shimano uses, may help