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Understanding all the writing on the sidewall of a tire can be overwhelming. It helps to know what characters you are searching for in order to obtain the tire information you desire. For example, if the tire code was 225/45R17 75L, then 75 would signify the load index and L would signify the speed rating of the tire. Load Index The load index tells you how many pounds a tire can safely carry. As you can see on the load index chart below, the 75 in the example above has been assigned a load carrying capacity of 853 lbs per tire. Multiply the load carrying capacity by the number of the tires on the trailer. As long as that sum is greater than or equal to the assigned GVWR of the trailer, then the tire’s load index is sufficient for its application.  Speed Rating Speed ratings are based on laboratory tests and were established to match the speed capability of tires. In the same tire code example stated previously, L would signify the tire speed rating. According to the attached chart, the speed rating for L is up to 75 mph. It has been proven under testing conditions, that tire can operate for a certain period of time up to 75 mph. Motor vehicles should always be operated according to the speed limit of the roads they travel on. Never exceed the speed rating of the tow vehicle tires or the trailer tires; drive according to whichever rating is lower. Trailer tires commonly have tire speed ratings in the 65 – 75 mph range. Unless otherwise noted, the speed rating for trailer tires is 65 mph. 
4 Comments
ronnie carl plumlee
9/24/2021 07:43:47 pm
i have a double axel rv
Ron Heinkel
1/12/2022 12:24:25 am
There should be a load index number with usually 2 numbers and a letter. G meaning it is a 14 ply tires and most of the time the speed rating is a L on trailer tires and it is 75 mph. Your tires being a 14 ply will have 3 number and a slash and usually 3 more numbers. One rating as a single tire and other is as a dual tire setup. There's a a date code on tire also and it should be after the DOT number and letters and it is a set of 4 numbers. 3 numbers prior to 2000. But the 1st 2 numbers are the week of build and the other 2 are the year. Some tire only have date code on 1 side and other ones are both sides. I hope that I have explained enough for you to get a little idea.
Ron Heinkel
1/12/2022 12:28:45 am
I forgot to mention that trailer tires should be replaced every 3 to 5 years and automotive tires every 6 to 10 years and not a good idea to use any other tires on a trailer because trailer tires have a better sidewall for handling the weight and having them drug sideways on 2 or more axles
Tim
1/20/2022 10:29:41 am
Is a tire load rating calculated at its maximum speed rating? Meaning, are tires rated to carry their maximum load while travelling at their maximum speed? Leave a Reply. |
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