Tires have a lot of different responsibilities. In the snow, they need tread for traction. In the rain, the tire pattern can help direct water off of the road surface for better control. And, if you’re using your vehicle to tow a camper, the tire pressure and load capacity affects safe handling, especially at highway speeds.
How do you know that your tires are ready for towing your RV for your next camping trip? Here’s a little tire lesson that will help you rest assured and may even explain some things you didn’t know.
Auto manufacturers are very good at pairing tires and vehicles. So if you keep your tire pressure at the recommended psi and keep all loads within the towing specifications you find in your Owner’s Manual, you’re all set.
But if you have changed your tires to another tire size or you need new tires before you head out, you nay need to go through some calculations.
Let’s say that the original tires on your vehicle were size P275/65R18.
Because of the P you know that it’s a passenger tire. This is also referred to as a P-Metric tire. You will find this number in your Owner’s Manual and on the inside of your door jam.
275 = is the width of the tire in millimeters
65 = is the aspect of tire width to sidewall. In this case the sidewall is 65% of the tire width
R = means it’s a radial tire
18 = the diameter of the wheel, in inches; the part of the car where the tire is installed.
Upon a closer inspection of the tire itself you will also see a number before and after the size P275/65R18.
It may appear like this: M+S P275/65R18 114 T
M+S = means it’s a mud and snow tire
114 T = 114 refers to the max load carrying capacity (2601 lbs.) and T is for the maximum speed (In this case it is 118mpg) In the US, all specifications for tires and rims are set by the Tire and Rim Association, Inc. (TRA). That’s where these numbers are derived from.
There’s also very small type on the tire that tells the maximum load (that same 2601 lbs) and the maximum tire pressure.
But there’s more to be aware of and consider…any time a P-Metric tire is installed on a SUV, Light Truck, or Van the Max Load Capacity is reduced to 91%. So for instance, let’s say that the P-Metric tire has a Max Load of 2601 lbs. – when multiplied by 91% the load maximum is reduced to 2367 lbs.
Your next question is probably, “So what’s the pressure of the tires supposed to be if I’m towing with a SUV and utilizing the 91% rule.”
You might be surprised to learn that you SHOULD NOT inflate tires to their maximum when towing. With P-Metric tires you should always following the manufacturer’s recommended tire pressure. On the specific tire we used in this example, although the maximum psi is listed as 44 on the tire wall, the tire should only be inflated to 35psi – even when towing. More air will not add additional load carrying capacity to the tire.
This will only cause excessive wear in the center of the tires and may also cause handling problems while towing. Again, this is a value set by the TRA.
Remember, this is just referring to your vehicle’s tires, not the unit you are towing. That’s an entirely different “tire talk.”
So what do you do if you need new tires for your tow vehicle before you hit the road? Brandon Pickering, General Manger of Pickering’s Auto Services in Lakewood and Arvada, Colorado tells us, “Although we do offer tires to our customers, we do not carry and stock them at the auto center for a good reason. Being able to order tires for all different tire manufacturers allows us to choose tires specifically that will meet your exact needs.”
“Once we help you select the tire, you need to know that not having stock does mean that we usually need the car left for the day to allow time for tire delivery but is usually easily done in a one day timeframe. So, if you’re planning a road trip vacation, we can also work with you and pre-order tires to allow for a quicker turnaround time when scheduled in advance, just give us a call or schedule online.”
Read more about tires and towing HERE