Cracked RV rubber is a blowout waiting to happen

JOHN MAHLER

SPECIAL TO THE STAR

Q: I am considering buying a camper/RV, based on a one-ton Chevy frame. This 1986 RV is a relatively small four-sleeper and in pretty good shape. The vendor noted that the truck was originally on 800-16 tires (dualies in the rear) and he replaced them with Goodyear Wranglers, size 215/85R16.

My sense (during the test drive) was that the speedo reads low. I was driving at an indicated 100 km/h, but few vehicles were passing me. I suspect I was actually travelling around 110 to 115 km/h, but have no way of knowing.

Could you confirm the difference in rotating size, and let me know how much variance there would be (as a percentage, if possible)? I did check the DOT dates on the tires, and they were made in early 2001 (week 11). So they are dead, although they are in great shape with lots of tread.

A: The reason no one passed you is everyone was waiting for this behemoth to blow a tire, roll over and play dead. Anyway, step one: new tires all around. End of story. Driving a top heavy leviathan with cracking, aging tires is a blowout waiting to happen.

Now to the technical part. An 800x16 tire is equivalent to a 205/100R16. Yes that is correct, aspect ratio is 100. The actual diameter is 33 inches and has a load rating of 2045 lbs. at 60 p.s.i. That is the summary of what you don’t have.

The replacement tires had better be LT215/85R16, load range E or you are in deep trouble. These tires have a load range of 2430 lbs. at 70 p.s.i. and up to 2660 lbs. at 80 p.s.i. So you are covered for carrying capacity.

The circumference of the old tire is 2564.79 mm. The circumference of the new tires are 2424.99 mm. The result is a difference of 5.45 per cent. So the speedometer should actually be low by 0.45 per cent.

Email tire questions to John Mahler at thetireguy_1@hotmail.com. Please include vehicle’s make, model and year, tire brand and size, as well as your name, address and phone number.

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