Tires

I can't speak for the other tire manufacturers but, as far as Goodyear is concerned, we formulate the compounds for the sidewall of the tire with materials that resist ozone and ultraviolet rays. This is because tires on motorhomes are typically on the vehicles much longer than tires on working trucks and need more resistance to ozone and UV rays. Also, the tread of the tire is designed to resist heat. Motorhome owners are more likely to unintentionally overload their tires.

Besides contacting the tire manufacturer and finding out exactly the thickness of the "undertread", the best way to assure yourself of how much you can cut away is to cut a section out of a scrap tire like the tires you will be regrooving. Our tires are all marked "REGROOVABLE" despite the fact that very few are ever regrooved. Regrooving is somewhat of an art and it is an art that few people possess. Unless you know what you are doing or feel confident that you know someone who does, I wouldn't recommend doing it.

If anyone out there wants to comment on my answer here, I will more than welcome it. I assume that all vehicle odometers and speedometers calculate distance and speed by counting tire revolutions. By changing the diameter (and the revolutions per mile) of the tire on the vehicle, you can't help but affect the accuracy of this reading. In this case, since the revs/mile are less for the new tire, the odometer will think the vehicle has gone farther than it really has gone and the speedometer will say it is going faster than it really is. In this case, the difference in the revs / mile between the two tire sizes is less than 1%, so at normal highway speeds, the speedometer will be less than 1 mph off and the odometer will be off less than 1 mile for every 100 miles traveled.