Do you know what speed your tires are rated for on your car? You’ll see speed limits posted everywhere you drive, so one might assume that you go the speed limit. However, certain vehicles actually have limited speeds depending on their tires. You may have heard that all trailers have a limit of 55 mph. Is this true? Read on to understand trailer tire speed ratings fully.
What Is a Tire Speed Rating?
A tire speed rating is the highest speed tires can function at properly while carrying their load safely. For a trailer, that load is the trailer’s total weight.
Keep in mind that weather, wear and tear, and tire inflation also impact how fast you should travel, not just the trailer tire speed rating. Speed limits always supersede if your tires’ speed rating exceeds the posted limit. It doesn’t mean you should drive faster than the limit even if your tires can handle it.
Where Can I Find My Tire Speed Rating?
You can easily find the specific rating for your trailer tire speed if you know where to look. You can usually find it in the owner’s manual or on the tire’s sidewall. If you can’t locate it in those two places, then you may find it designated on the driver’s side door.
Keep in mind that tire speed ratings you find posted in the manual or vehicle are recommended but the tires may have been changed. The only place to safely get tire speed ratings is from the tire itself.
Using the tire’s sidewall for the information, you’ll need to decode all of the numbers that come with the tire. Simply, the tire speed rating is the last letter of the description on the sidewall. For example, if a tire reads 2015/60R15 91V, the tire speed has a V rating.
Pro Tip: Knowing tire pressure is crucial for your adventures so we found The Best RV Tire Pressure Monitoring Systems to use on your RV tires.
How Do I Read My Tire Speed Rating?
Now you know that the letter is a rating, what does it stand for? Tire speed ratings originated in the 1960s in Europe. Then, there were only three ratings: S, H, and V. Now there are over 20 ratings, each designated with a specific letter of the alphabet, including A1-A8, then onto B, C, D, etc., all the way up to a category labeled “ZR.”
The A1-A8 range has a tire speed rating range of 3 mph up to 25 mph. The labels of B through V range from 31 to 149 mph, with the ZR ratings starting at 168 mph to 186 mph and beyond.
Common trailer tire speed ratings are generally between 65 and 75 mph and labeled as G, J, K, or L. If you cannot locate a tire speed rating for your trailer tires, it’s best to err on the side of caution and stick with the lower number.
For the complete table of tire speed ratings, click here.
Why Do We Need Tire Speed Ratings?
Trailer tire speed ratings are in place to keep the tire from failing at its highest capacities. You’ll drive safer on the road when going at the recommended speed from the tire manufacturers. These manufacturers tested the tires and set the maximum ratings to keep them from getting damaged.
When a tire is rolling it has massive centripetal acceleration forces that act on the rubber. These forces are held in check by the construction of the tire, many times with nylon or steel bands inset into the rubber.
When speeds exceed the design these bands can break and increase the likelihood of a tire failure. In addition to the strength of a tire, speed increases heat in the rubber due to the tire flexing more quickly. Higher heat can break down rubber and cause damage as well.
It’s not uncommon for a vehicle that has been driven beyond its tire speeds to also exhibit a shake or wobble due to damaged tires. More than one teen who drove their parent’s car a bit too fast has been caught because of speed-damaged tires. (speaking from a bit of personal experience here)
Why Are Trailer Tires Rated lower?
In the past, most trailer tires were only rated at 55 mph. Today most trailer tires are rated as high as 87 mph. In general trailer tires have lower speed ratings than car tires, however.
Trailer tires are typically constructed differently than car tires to keep the cost down. Most trailer tires do not see as many miles as cars so manufacturers don’t build them to last as long or perform as well. Because of these construction differences they typically have lower speed ratings.
The primary construction difference is between bias-ply or radial-ply tires. Many trailer tires are bias-ply because it’s a cheaper construction technique. This type of tire can withstand heavy loads, but it’s not as strong in corners or at speed. We always recommend you choose a radial tire if you plan to do a lot of highway driving at high speeds.
Pro Tip: You’ve cared for your tires well and are about to hit the road, but will your RV tires operate properly? Not necessarily, which is why you need to know How Long Do RV Tires Last?
What Would Happen if You Went Faster Than the Tire’s Speed Rating?
If you travel faster than the recommended trailer tire speed rating, it could result in a catastrophe. When pushing tires to the limit, you put immense stress on the tire and build up heat and air pressure. Doing this also increases your chances of having a blowout, which can be dangerous for you and anyone else on the road.
It’s always safest to drive the recommended tire speed to prevent injuries to self, others, or property. The campsite you’ll stay at will be there even if you arrive two hours later than planned.
Are There Any Trailer Tires Rated Higher than 55 MPH?
Most trailer tire ratings stay between 55 and 75 mph. However, you’ll find trailer tires rated higher than that on the market today.
The rating ST, or special trailer tires, can handle 80 mph and beyond. These can withstand higher speeds while carrying heavy loads and, just like typical trailer tires, come with stiff sidewalls to reduce trailer sway.
Does Tire Speed Rating Really Matter When Towing a Trailer?
Yes, even more so than in a car. Most cars have tires that are rated well within the capabilities of the vehicle but trailer tires are different. You can easily pull a trailer with a vehicle rated for much higher speeds. This is why it’s critical to know your trailer’s speed limit.
By following the recommended tire speed rating, you have a lower risk of a blowout or having to over-correct. So, when towing a trailer, make sure to follow the speed rating for everyone’s safety.
Do you know your tires’ speed rating? Drop a comment below.
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Case W Garrison
Friday 10th of September 2021
Our new fifth wheel actually has "Maximum 75MPH" molded into the tire side wall in big letters. Quite handy, and removes any doubt!