Maintenance Q&A
Retreads and ultracapacitors

By Paul Abelson, Senior technical consultant

With things getting financially tight, I decided to give retread tires a try. When the dealer inspected my tires, he told me he would retread three of the drives, but would give me trade-in credit for the fourth. I still had between 3/32 and 4/32 inches remaining, more than the legal 2/32 limit. He gave me a song and dance about safety margin and inflation, but it didn't make sense to me. Can you help me out and explain it to me, and maybe help me get some value for my tires?

Yes, to the first part of your question, but sadly no to the second part. Retreading tires has come a long way since the days when you could bring in a used casing and, as long as no cords were showing, they would slap some rubber cement on the tire, wrap new tread rubber on it, put it in an oven-like device to cure it, and send you out the door. Today, we know there's more to making a safe retreaded tire than just the tread.

First, all reputable retreaders inspect the tires inside and out to make sure there is no damage, internal or external, to the casing. The remaining tread will have to be ground off to make sure the casing is round, the right size to accept its new tread, and in condition to bond properly. They need at least 4/32 of tread remaining, preferably 5/32. That gives them something to work with.

They measure at the lowest portion of the tread, so if alignment issues caused irregular wear, they measure where the wear is greatest. If your casing has enough tread, it then goes through a series of non-destructive tests before they do any work on it. Just as imaging allows doctors to see inside people without resorting to exploratory surgery, computers, lasers and ultrasound images allow retreaders to look inside a tire.

They look for damage to the internal structure such as broken wires, often because of underinflation. That's one reason why maintaining proper air pressure is so important. When tires are significantly underinflated, often by as little as 15 psi (undetectable by "thumping"), treads flex excessively, generating heat that weakens internal bonds between components. Flexing can also break steel cords. Try opening a paper clip and bending it back and forth. At first there's no damage, but over time the flex point heats up and the clip will break.

I hope that helps explain what your retreader was trying to communicate. As for getting value out of your used casings, it's too late for your current tires, but if you maintain your tires properly, you should be able to get full value out of your next set. You'll be able to get a good trade-in price or, better yet, have your own tires retreaded. Check for irregular wear and misalignment. Maintain air pressure by gauging them regularly, even if you have an automatic inflation device and remove them with at least 5/32 of tread left.

Last summer, my batteries kept running down because I was using them to run my electric-powered air conditioner. When I got the A/C, I also got four absorbed glass mat (AGM) batteries that were supposed to run it all night. They did, but sometimes in the morning I couldn't get started. I hear there's a new super-duper battery that is only for starting trucks. It just takes one and it weighs a lot less. My questions are as follows: What kind of battery is it, can I install it myself, and if it's as good as they say, can I replace my AGM batteries with the super batteries?

First, check for parasitic battery drain. That's the current drain with the key off and accessories turned off. A little is necessary to power your truck's computer modules, but too much can be a sign of a hidden short or a faulty switch. Assuming that's not what's draining your batteries, the "battery" you're asking about isn't really one as we know them to be. It's called an ultracapacitor.

Batteries rely on a chemical reaction to release electricity for starting engines and running lights, CBs, your truck's computer systems and hotel loads. When a circuit is opened, lead in a sulfuric acid solution turns to lead sulfate and releases electrons that provide power until the acid is depleted and the battery is discharged. The battery is recharged by reversing the current flow, restoring the sulfur to the acid and redepositing lead onto the plates.

Capacitors accumulate electrons on internal surfaces and then release the electrons to do work. When they recharge, they replenish the electrons. An ultracapacitor is just a capacitor with better materials and an improved design. That enables an ultracapacitor to hold an even greater charge than a regular one. That's why just one ultracapacitor weighing less than 25 pounds can start a truck engine down to zero degrees or colder. But because their properties are for high-energy, rapid-discharge applications, they are not replacements for your AGM batteries.

If you are good at electrical work, you can probably install an ultracapacitor yourself. But before you start, make sure you understand the procedures. Maxwell Technologies has a video on its website, as does Purkey's Fleet Electric.

I would suggest replacing one of your four AGM batteries with an ultracapacitor. That will save about 50 pounds. Then add more AGMs and tie them in with your other AGMs. Your battery-powered air conditioner should give you all the cooling you'll ever need and still weigh far less than a generator or auxiliary power unit. LL

(Editor's note: When sending in questions for Maintenance Q&A, please include the make and model of your truck and your vehicle identification number (VIN) as well as your contact information. Paul Abelson tries to respond to every question, whether it's published or not. Send questions to