Are these slip-on hub spacers or bolt-on adapter type?
Spacers come either as slip-on hub-centric types held by the wheel bolts, or as bolt-on adapters with their own studs. Check which style this is, since it changes how it mounts and which bolts you need.
Do they fit the factory M4 wheels or only aftermarket ones?
Spacers generally work with both factory and aftermarket wheels as long as the bolt pattern and hub match. Confirm your wheel's specs against the spacer so it seats correctly on either type.
Can I stack two spacers to get more width?
Stacking two spacers is best avoided, since a single spacer of the correct thickness is safer and more stable. If you need more width, pick one spacer sized for it rather than doubling up.
Will spacers interfere with the TPMS sensors?
Spacers sit between the hub and the wheel, so they do not affect the tire pressure sensors inside your wheels. Your TPMS should keep working normally after they are fitted.
When I remove the wheel, do slip-on spacers stay on the hub?
Slip-on spacers are held by the wheel bolts, so they can come away with the wheel when you take it off. Bolt-on adapter spacers stay fixed to the hub, which some owners find handier at wheel changes.
Do wheel spacers help grip or track performance on an M4?
A wider track from spacers can slightly improve cornering stability and grip feel. The effect is modest, so most owners fit them for stance as much as for any handling gain.
