It appears to me that the safety margin, as stated in load capacity, for LT tires compared to ST tires is 10%. In other words, the 3640 lb load rating in the ST tire is not reduced at all. But a load capacity in an LT tire is reduced 10% because of passenger use. To get to the 3042 lbs, it is at 3380 before safety reduction.
That still means that a 3640 lb ST tire is higher rated than a 3042 LT tire by 260 lbs (3640-3380).
It appears to me that the safety margin, as stated in load capacity, for LT tires compared to ST tires is 10%. In other words, the 3640 lb load rating in the ST tire is not reduced at all. But a load capacity in an LT tire is reduced 10% because of passenger use. To get to the 3042 lbs, it is at 3380 before safety reduction.
That still means that a 3640 lb ST tire is higher rated than a 3042 LT tire by 260 lbs (3640-3380).
Actually, that 10% derating applies to the situation where passenger car tires are used on an MPV, trailer, truck, or bus. In that case, the maximum legal load is 10% less than the weight rating stamped on the tire. In addition, there is an additional 6% derating when passenger cars tires are used on MPV, trailer, truck, or bus. In addition, LT tires are derated by 6% except when used on trailers with no passenger seating positions.
The approximately 20% difference between the ratings between ST tires and LT tires is something different, and it is due to the fact that ST tires are not legal to use on vehicles other than trailers. Also, all ST tires are speed rated at 65 mph, while LT tires are usually speed rated much higher. That higher load that you can carry on an ST tire of equivalent size is only safe up to 65mph, while the LT tire is rated to carry less weight, but at a higher speed, as well as to handle the stress of acceleration on the drive tires and the stress of steering on the steer tires.
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2001 F350 XLT 4X4, shift on the fly, 38 gal fuel tank, running boards, sliding rear window, black, crew cab, long bed, 4.10, automatic transmission, 11,500 gvwr, 20,000 gcwr, 7500 gvw, dual rear wheels, 7.3l turbo diesel, completely stock, 114,00 miles when purchased, now has 125,000 miles, repairs so far: starter, batteries, cps.
2005 Nomad Rampage toyhauler made by Skyline. 11,500lb gvwr.
Last edited by DonWarkentin : 07-29-2008 at 05:33 PM.
Reason: Correction
I'm not sure I understand that explanation. What I did get from it was that ST tires (or at least some of them) can carry more weight than the same size E-rated LT tire, but they must be run at 65 or less. In other words, even with the safety margin percentage eliminated, putting the two on an equal footing, an ST can carry more weight than an LT of the same size. Maybe the ST design is superior for load because the designers were able to build it for that purpose at the expense of speed, acceleration, and steering. The old story of trade-offs.
The Cheapest Off-Brand LT is still a WAY better tire than the best ST, IMO. I've never had an LT separate on a trailer, and every ST I've ever owned either separated, bubbled the sidewall, or exploded before I noticed a symptom. I'd much rather run a 120% loaded LT than an 80% loaded ST. If you look at them close before or after they blow out, they're just a CHEAP tire. Casting flaws, lumpy sidewalls, irregular beads, just flat poorly made, every one of them.
I wouldn't put G614's in the category of "trailer tires". They're more of a scaled-down truck tire, very well made and TOUGH! I have had excellent service out of a couple sets on a triple-axle gooseneck equipment trailer, doing deliverys. That means many miles of gravel, and they held up well.
I have Korean LT7.50R-16's on my other trailers, and they're far, far better tires (33X0 lbs. rated 12-plys) than any of the junk ST's that came on them. ST tires are a scam - they design them to not last.
I'm not sure I understand that explanation. What I did get from it was that ST tires (or at least some of them) can carry more weight than the same size E-rated LT tire, but they must be run at 65 or less. In other words, even with the safety margin percentage eliminated, putting the two on an equal footing, an ST can carry more weight than an LT of the same size. Maybe the ST design is superior for load because the designers were able to build it for that purpose at the expense of speed, acceleration, and steering. The old story of trade-offs.
It depends upon what question you are asking.
If the question is, "What tire will allow me to carry the heaviest legal load?", then the ST tire of equivalent size will allow you to carry a heavier legal load compared to the LT tire. Legally, the ST tire is allowed to carry heavier load than the LT tire because it is illegal to use the ST tire on drive or steer axles where it would be subjected to greater stresses, and because the maximum speed of ST tires is limited to 65 mph, plus, the ST tire will not be used on a vehicle carrying passengers.
If the question is, "What tire will give me the greatest margin of safety when the load that I am carrying is below the legal maximum that either tire could carry?", then the question is a little bit more difficult to answer. Maybe the LT tire that is rated to carry 3042 lbs up to 100 mph in a vehicle carrying passengers and mounted at any location, including steer, drive, or trailer axle really gives a greater margin of safety when carrying 2500 lbs compared to the ST tire that is rated to carry 3640 lbs up to 65 mph only on a trailer axle but not on a steer or drive axle. Don't automatically assume that the 3640 lb tire must have a greater margin of safety compared to the 3042 lb tire just because the load rating is higher.
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2001 F350 XLT 4X4, shift on the fly, 38 gal fuel tank, running boards, sliding rear window, black, crew cab, long bed, 4.10, automatic transmission, 11,500 gvwr, 20,000 gcwr, 7500 gvw, dual rear wheels, 7.3l turbo diesel, completely stock, 114,00 miles when purchased, now has 125,000 miles, repairs so far: starter, batteries, cps.
2005 Nomad Rampage toyhauler made by Skyline. 11,500lb gvwr.
I decided on the Bridgestone Duravis R250 all-steel LT tire, similar to the Michelin XPS Rib. It was only $20 cheaper than the XPS, but the measurements were better for my rig, which has only one inch between the front and rear wheels. Not too many people seem to know about the R250. Hopefully, it will perform as well as the XPS.
The Duravis R250 is an all position, Q (99mph) speed rated tire, with one steel side belt and 3 steel tread belts, same as the XPS. Made in Japan. It is mostly used on ambulances, rescue vehicles, motorhomes, and large delivery trucks. It weighs 60 lbs (the Michelin XPS Rib weighs 56 lbs, as does the GY G614). The Denman I was considering weighs 44 lbs, so I figured to heck with the bigger Denman load rating and go with my common sense about which tire is tougher.
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