Maintenance Q&A August/September 2020
Q: I’m usually a fan of your articles, but I think you led me in the wrong direction this time. I was due for new tires, but because you like retreads I figured I’d try them. The handling is OK, but I’ve lost almost a mile per gallon. I’ll never use retreads again.
A: When we spoke, you did everything right. You nurtured your tires, you replaced the tires at 5/32 inch tread depth so that the retreader had ample margin to buff the casing, and you even labeled which of your drive tires came from which position.
You drove to a reputable, brand-name tire retreader and left your truck while they worked on your tires. You even got the proper replacement tread for your type of driving. But you neglected to account for the differences in tread depths between new treads and your treads.
As tires wear, tread depth diminishes. Thicker treads require more energy to flex and therefore affect miles per gallon. You compared the mileage you’re getting on new, thick treads with the mileage you were getting with your old thin treads, the ones you replaced. It is common with both new and retreaded tires to lose up to a mile per gallon when replacing tires. What you experienced was a normal condition.
Every time something happens on your truck that consumes energy, that energy is created by burning fuel. This pertains to running the air conditioner, which will drop your miles per gallon, to charging your batteries and flexing your tires.
If you have old records of what your miles per gallon were when you got your truck (after the initial break-in period) with the miles per gallon you were getting before taking your tires for retreading, you will find a gradual improvement due to tread wear. This may not always have been obvious because of wear effects in the engine and with the injectors, but it should still be noticeable. I don’t think your loss of mpg was at all abnormal, just a normal reaction to the physics of the situation. As the tires wear, miles per gallon will rise.
Q: I got my first and probably my last set of retreads at my favorite independent truck stop. I don’t like the big chains because their prices are generally too high. The retreaded drive tires make the truck wander in the lane. Things just don’t feel right. I know you like retreads because they cost less, but now I’ve found the reason they do.
A: The big truck stop chains generally use major retread companies as their suppliers, the ones affiliated with tire manufacturers. Many have retread specialists in their tire shops. Small independent truck stops often source their tires from the least expensive supplier and merely group drive and trailer tires together. You may wind up getting a set of eight drive tires with multiple casing manufacturers and sometimes even different drive tread patterns. The source of the casing is very important in achieving a proper ride.
Tire casings differ by the position they are intended to be used. Steer tires undergo the greatest stress with heavy lateral and braking forces exerted. As they wear down, they become suitable for use in other positions. While legal on all but buses, steer tires are almost never used as retreads. But they are very good drive tires. Problems arise when different brands of steer tires are retreaded for use as drive tires.
Some truck stops just group these together as “drive tires” without regard to tread pattern, casing type, or any other physical characteristic. The truck stop matches the diameter of the tire and the tread pattern as closely as possible in order to give you drive tires. Because of the subtle variations between tires, you may wind up with a perfect set of tires or a set that is significantly mismatched. This can be compounded by the use of casings designed for medium- or regional-duty use mixed in with over-the-road tires.
The best way to order retreads is to use the casings from your truck that you have been satisfied with.
Keep in mind the proper inflation pressure is not always 100 psi per tire. In fact, that is rarely ideal even if you run at 80,000 pounds on every trip. Depending on the tire size, ideal inflation could be 80 or 85 psi.
If you ever curb your tires, make note of it. If it happens too frequently, the casing may be damaged internally and may not be suitable for retreading. If a tire in your set needs replaced, a large-scale dealer can more easily locate a casing from your manufacturer in the right size.
All the large retreaders have nondestructive test procedures that can identify internal damage in a casing. They thoroughly examine every tire before allowing it to be retreaded. Once the casing is found suitable for retreading, it is buffed down to as close to a uniform size as possible, and the new tread is applied to the newly prepared surface.
More checks are made to determine proper adhesion has been achieved. When these steps are followed, retreads are just like new tires and are used on commercial aircraft and emergency vehicles and by most municipalities. They have proven themselves in extreme service.
It is not uncommon for a casing to be retreaded three to four times safely. There are times when it makes sense to be frugal and choose lower-cost suppliers, but when dealing with tires, especially retreads, I would stick with the brand names and the large chains. I think when you get the right retreads you will be happy with your selection. LL
In July 2020, Paul Abelson discussed braking bad and tire life in his Maintenance Q&A column in Land Line Magazine.