Chain dropping after wheel change
 

Hi there,

I changed the rear wheel on my road bike. I had been using my good set (fulcrum) on it, while on the turbo trainer.
My mechanic said I should change to another wheel, because there was no point wearing out the expensive wheel on the turbo.

I switched over the tyre, tube, cassette and spacers. Problem is that now in the lowest gear the chain drops / comes off.

What's my best course here, add another spacer to try to fix the wheel offset, or invest time adjusting the derailleur stops and gear indexing.
I am nervous of the latter - because it will mean spending time adjusting and readjusting with the thumb adjuster.

The bike is a 2021 Cube Attain Race - their endurance model. Thanks.

Sounds like the two wheels don't match up WRT indexing adjustments and/or range limits. My first thought is to do a simple der adjustment and check the indexing coordination between the lever, the cassette and the upper der pulley. Could there be other issues? Sure,but start with the obvious and common. Andy.

well, you COULD reset the axle centering, if the axle is a cup/cone type, then recenter the Rim to the hub........ :D

get out your JIS-cross screwdriver and reset the limit screws, then reset the cable tension.
a good sharp #1 phillips screwdriver will work too.... the phillips with a 1/4" shank is too big.

Is this a 10sp cassette on an 10/11sp freehub? Did you put the spacer behind the cassette?

Also - wahoo kickr core 2s are going for a good price at the moment. No need for a wheel then and opens up a world of more engaging virtual training & racing.

Likely inserting the correct spacer is the way to go...it puts the cassette at the same alignment position as the current wheel/rear derailleur position on the bike thus not requiring constantly readjusting the rear derailleur as you go from road to trainer and back again.

What about the highest gear? Can you successfully switch the cassette to the smallest cog?

Doh I thought he meant the smallest cog. I am an idiot.

adding a spacer behind the cassette will cause the lockring to not engage the freehub threads.

the HG freehubs are set to the correct distance from the dropouts when made... only an extremely low budget hub or an axle set that's been changed will cause the cassette to be out of alignment with the frame more than a millimeter or so.
a 7 speed cassette on a 8-9-10-MTB11 freehub will already have a spacer in place, or the lockring won't press on the cassette much if at all.... the looseness is obvious.

i'd first suspect that the wheel in question has had the axle parts shuffled or replaced at some point in it's life.

Update: i just now measured three 8-9-10 rear freehubs... 6mm from outside axle locknut to the freehub body lip.. two shimanos and one formula... and 3mm from outside cassette lockring to outside locknut, with the same 8sp. cassette on them, hand tightened by me to my max hand torque.... Consistent and Standard... across three decades of HG hubs... an old LX paralax. a Deore XT, and a walmart level Formula disc hub.

if it's a thru-axle converted to QR, then all bets are off.
i recently ran into a Thru-axle wheel/hub stuffed forcibly into a 135 frame, after the NDS end cap had been removed... it was a 148 boost, originally... now at 142mm...
the frame has now been lightly modified to allow easier install, and fit that pie plate 11-51 12 sp. setup in the bike.

depends...

Yeah that’s why I asked if it was a 10/11sp freehub. Those are 1.85mm longer than a 8/9/10sp freehub.