When you have your car (if you've got one) cleaned in r.l. then usually the tires get painted with tyre dressing to make them black and look clean.

So when you wash a car or just find a clean car driving round in game it will have painted tyres
(the tyre wall when it is clean is now about 50% darker) - its not so noticable at night but it is in the day

comes in two flavours -
1. just the texture (add yourself to the vehshare.wtd) if you have another mod etc.

2. a full .wtd file with no other mods except the painted tyres texture (you'll still need to replace the .wtd archive in vehicles.img)

which ever you choose use spark or another gtaiv editor