Thread: G vs E?
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Old 08-30-2013, 11:37 AM   #8
Irlpguy
Montana Master
 
Join Date: Oct 2012
Location: Chilliwack
Posts: 1,520
M.O.C. #12935
For starters: every tire sold in America and Canada "must" have a DOT (Department of Transport) stamp on it. Likewise every tire must have the tires load capacity @ maximum air pressure stamped on it. There are a number of other things mandatory but the most important are the DOT load rating and air pressure.

A good many years ago tires were rated by the actual number of ply's in the sidewall of the tire. At some point a standard was developed where an alphabetical rating was developed to indicate the tire was "rated" at 10 ply (E) or 14 ply (G) and so on. That means only that the tire might have only 6 "actual" ply's but with new materials and designs it could then be rated at 10 ply or whatever.
The alphabetical reference is with respect to "ply rating" of the tire.

On this forum and others you may see references to "reserve capacity" and in most instances the information is incorrect and riddled with inaccuracies.

The DOT capacity of a tire is what it is rated to carry and stamped on every tire, it does not matter if it is a P passenger, LT or ST tire, that DOT rating is it's capacity at the maximum air pressure also listed on the tire. There is no reserve beyond that number, but what has been circulated suggests there is more "reserve" in an LT tire than in a ST tire which is simply not true.

DOT regulations require that the weight on all drive wheels on a passenger carrying vehicle "must" not exceed 94% of the max capacity of the tire.. This means the vehicle and it's load cannot exceed 94% of the capacity of the tires used. Reserve Capacity is the 6% that is required on those vehicles only. The DOT does not require that a trailer manufacturer reserve any amount of the rated capacity of the tire and may show a capacity up to the full amount stamped on the tire. Therefore no reserve.

The differences stated above do "not" in any way give a LT tire more reserve capacity than an ST tire. Anyone who questions this should look up the DOT regulations.

With respect to lighter RV's with 6000 lb axles or less then they can use a LT tire which will not diminish their axle capacity by using them. The LT tire is rated for higher speed and many have steel sidewalls and have been recommended many times by folks who are using them and fellows in the tire business. I think you are far better off to go to an LT tire on lighter units. They will last longer and will not be damaged by exceeding the 65 max MPH on a ST tire.

I would not put an E rated LT tire on any trailer that has 7k axles, and in fact believe it to be illegal. That is my opinion and I have not been able to get an answer from the proper authority in the US, but I do know it is illegal in several if not all Provinces in Canada.

If your RV has a GVWR approaching 15,000 lbs and has 7k axles I would recommend changing the tires to a G (14 ply) rated tire.

Before anyone starts a war with me, I apologize to DQDick because he has mentioned this previously circulated article, but it has been debunked by others who have stated the DOT requirements and numbers that are the same as I have stated above. I would post one or more of those challenges here but they are too lengthy.

Get the best tire you can afford, do not use a tire which is not rated for the load you are likely to carry. Do this and I think you will have many happy miles.
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