HELP! with tires, switching to 16" rims.

[Bill M.]

"I don't understand "derating".
Does a 4,000# car weigh more than a 4,000# truck or trailer?

No. They weigh the same. But the trailer puts more force on tires than the car. On a car the wheels are spaced near the corners. So only about 25% of the car weight can be on each wheel. A car has a long, soft spring travel compared to a trailer.

Dual and triple railer axles are close to each other. How the trailer sits determines if there is more force on one axle or the other. When a dual or triple axle trailer turns it puts a large sideways loading on the tires. When the trailer suspension runs out of travel it hits a stop and puts sudden loading on the tire. All in all trailer use is hard on tires.

[willapus]

Originally Posted by m.hony

I don't understand "derating". Does a 4,000# car weigh more than a 4,000# truck or trailer?

Took me awhile to get the difference. They weigh the same, but exert different force loads. Therefore, "P" tire load ratings are not equal to LT load ratings. The increased height of the center of gravity on trucks decrease the load capacities of P tires by about 10% (from tirerack.com). The p tires sidewalks aren't as rigid as the lt's. I have noticed a great change in the way my sequoia handles. Without the tt, my sequoia, with lt tires, rides much more like a truck even with a low 50 psi, but at hwy speeds, unhitched and say 70-75ish mph the crosswinds don't push it around as it did with the P tires. Btw same truck and same make, model, tread, and size of tire just comparing P to LT tires. I'm using general tire grabber hts LT 245/75R16 on the sequoia and kumho lt 225/75R16 on the streamline. I love the general tire and the kumho have about 4000 miles on them and seem just fine.

[Ridgerunner3]

Another interesting twist to add:

A P235 75 15XL tire has a derated rated capacity of about 1985 lbs.

An LT235 75 15 load range C tire has a normal capacity of 1985 lbs.

There is really no load carry capacity difference between these two tires when used on a trailer.

[m.hony]

So- could willapus put LT tires on the Deuce and tow his trailer?

[willapus]

Originally Posted by Ridgerunner3

Another interesting twist to add: A P235 75 15XL tire has a derated rated capacity of about 1985 lbs. An LT235 75 15 load range C tire has a normal capacity of 1985 lbs. There is really no load carry capacity difference between these two tires when used on a trailer.

Looks like the LTs are about 10% heavier

[willapus]

Originally Posted by m.hony

So- could willapus put LT tires on the Deuce and tow his trailer?

Trunk is too long

[m.hony]

Meaning?
There is 8' of Buick beyond the rear axle?

[CapriRacer]

Originally Posted by m.hony

So- could willapus put LT tires on the Deuce and tow his trailer?

First, the limiting factor for towing isn't always the tires. Sometimes it's the transmission or the brakes. I'll bet that GM lists the deuce and a quarter with about a 1,000 # towing capacity - and that would have been with the old bias ply tires that came on it.

Second, I'm not entirely sure the issue of derating P type tires for truck and trailer use is because of the sidewall stiffness. I suspect it has to do with the stiffer suspension and the fact that trucks and trailers are more likely to be operated on unpaved roads.

[Martin R]

I am in the middle of dumping my OE GYM tires and 15inch rims and switching to 16 inch TO3 rims on my 30ft International. I know most reports on the Michelin LTX M/S2 are positive but I am curious to hear of any experience with the Bridgestone Duravis R500HD ?

[switz]

Attention folks contemplating the 16" SenDel and Michelin tire conversion. Here is a useful tidbit of information straight from the horse's mouth. Airstream recommends 125 to 130 foot pounds of torque on the lug nuts on these SenDel rims.

[Steve & Mary]

Thanks for the info. I mounted my new 16inch SenDel wheels and BF Goodrich tires last week and haven't yet applied the correct torque. I'll go with the 125-130.

[Wingeezer]

Originally Posted by switz

Attention folks contemplating the 16" SenDel and Michelin tire conversion. Here is a useful tidbit of information straight from the horse's mouth. Airstream recommends 125 to 130 foot pounds of torque on the lug nuts on these SenDel rims.

Interesting to note that - as far as I now know - quoted torque values are intended to be used on threaded fasteners that are NOT lubricated.

For some time, (Probably many years!) I have been putting anti-sieze compound on lug nuts to avoid rusting. That means that I have surely been over-torquing the connections, but who knows by how much?!

Last time I had the wheels off, I did not apply anti-sieze and in fact tried to wipe off the old traces. To do a proper job, I likely would need to wash the threads well with some sort of degreaser at this point.

Luckily no wheels have fallen off yet!

I wouldn't be at all surprised if an applied torque of say 90 ft-lbs on a lubricated thread could equate to an equivalent torque of perhaps 125 ft-lb on a dry fastener in terms of the effective bolt stretch.

Brian.

[Tireman9]

Originally Posted by CapriRacer

snip

Second, I'm not entirely sure the issue of derating P type tires for truck and trailer use is because of the sidewall stiffness. I suspect it has to do with the stiffer suspension and the fact that trucks and trailers are more likely to be operated on unpaved roads.

The de-rating of Passenger tires goes back to the days of station wagons. The idea was that the "normal" operation of cars was with less than max load most of the time while station wagons were operated closer to max load a greater portion of the time. The result was higher failure rate on station wagons.
Basically the de-rating applies to "multi-purpose passenger vehicles". Today the SUV has replaced the station wagon of the 50's and pick-ups are quite different and civilized for passenger use to the point that they come with passenger type tires.