tow rated 20" tires?

[Craig M]

There are some nice looking 20" tire and wheel set available for the Tahoe and Suburban's now. The 20 tires are the low profile ones (275-50R20 and similar). They are usually high rated for speed, but frequently not so well rated for load and sidewalls. Anyone know if there are any acceptable 20" low profile tires available? Similar to the load range E that we use on the 16" tires

[tanker]

This is out of my league, but if they are 20" rims with tires, and will fit a suburban or Tahoe, I would think that not much tire (rubber)between rim and road, and that may make it ride rough. Might be good looking, but don't know how they would handle weight. smile.gif

[CleviteKid]

Tanker is correct - the general principal of tire design is that the load rating depends on two things, the volume of air in the tire, and the pressure of that volume of air. Stronger sidewalls and treads allow for higher air pressure and more load capacity. Bigger tire sections (tread to wheel, and tire width) provide for more air volume and more load capacity.

If your target 20" tires are strong enough to carry enough air pressure to compensate for the much smaller volume, they would ride about as well as Fred Flintstone's rock-solid rollers ;)

Dr. Lee :cool:

Disclaimer: I worked for Ford on the Explorer-Firestone situation. Inflation pressure is CRITICAL, so please check yours frequently.

[Craig M]

Ok doctor Lee, explain that one to me. I understand how tire pressure and width would affect tire capacity. The tire area in contact with the ground times the pressure should give one the capacity of the tire. I do not understand how tire volume would have any direct affect on capacity. All things being equal, in theory the shorter sidewalls should allow higher tire pressure. Because most low profile tires are built for speed not load capacity, all things are not equal. The 90 psi Michelin 16 inch tires are definitely better than the 35 psi Toyo's for our trucks. But if a 90 psi low profile tire were developed if would produce less sidewall flexing that the 75 or 85's we now have. And you are right, it would probably ride like a rock because of no air cushion .

[CleviteKid]

The volume of the tire acts like (in fact it IS) a big air spring. The bottom of the tire deflects and decreases the volume a little bit, and the pressure goes up a little bit. If the volume is small, the % compression is too big, the pressure goes up too much, and the temperature increase due to the compression (remember how a diesel engine works?) is also too high and degrades the tire.

Another way to look at it is: the tire has to deflect until the area of the contact patch, times the internal pressure, equals the weight that that tire is supporting. Say we have a 7 inch wide tire at 60 psi, trying to hold up 1/4 of a 10,000 pound truck (that is 2500 pounds, for the math-challenged). The contact patch has to be 5.9 inches long for equilibrium. This requires a 0.3 inch deflection of the sidewall on a 30 inch diameter tire. If the sidewall is short, that is a big % deflection, and the deflection will overheat the tire as it runs down the road.

Don't take chances with safety-related components, like tires ! ! !

Dr. Lee :cool:

[Craig M]

Ok, it took me a while to understand what you are saying but I think I got it now. For the tire to have the 9.55 inch contact area we are putting a "flat spot" on the bottom of the tire. Drawing a 9.55 line at the bottom of a 30 inch diameter circle, creates teh .3" deflection you discuss. Had nt thought about that part the the "flexxing" of the tire.

[Perry]

There are some 20" tires w/the reinforced sidewalls which have a capacity of about 3000lbs. This is the same load carrying capacity of the 245/75-16 LR-E tires .

I think all of these tires though are the 305/50-20 size, which over an inch taller than stock.

www.tirerack.com (http://www.tirerack.com) has a pretty good selection of tires and if you click on specs of a particular model, it will give you the circumference and load capability.

Perry - running 265/75-16 BFG A/T KO LR-D w/3042 lbs max load

[Craig M]

Thanks Perry, good site to see tire spec's. Seems that most of the 20's are maximum of 50 psi, The normal for load range E is 80 psi. I did see a couple of tires that were in the 3000# range, but most tires were in the 2000# to 2200# range. Since they were all rated at 50 psi, I am suspicious of the one that said 3000#. If it is not rated close to 80 psi I am suspicious.