Bottom Line
Maintenance Q&A
The good and bad of AGM batteries, wide-base tires

Q: I have a 1999 Peterbilt 379 with a 3406E at 600 horsepower with nearly 1.1 million miles. When I purchased the truck, it had four batteries with 750 cold cranking amps that did not last very long.

Three years ago, I installed three “Cat Racing Batteries” with 1,000 CCA each. They were great but now need to be replaced.

I am considering switching to Odyssey’s absorbed glass mat batteries. If you believe the sales pitch, they should be good until I retire. I would like your input on this. What size battery would I need to start on cold winter mornings?

A: Trucks take Group 31 size batteries. Diesels need 1,800 cold cranking amps to start (at zero degrees, the temperature at which CCA is measured.) The Odyssey is rated at 1,090 amps at zero. Two batteries will provide enough starting power. If that were the only consideration, I’d recommend two.

However, batteries power other things when the engine is off – entertainment systems, refrigerators, fans and more.

To measure staying power for comparing batteries, engineers use reserve capacity – the number of minutes a battery at 80 degrees will maintain a steady 25 amp load before voltage drops to 10.5.

Absorbed glass mat batteries, or AGMs, take a great deal of abuse. The Odyssey has a 205-minute reserve capacity. In theory, two batteries will yield almost seven hours and three will give more than nine hours. This compares favorably to other AGM Group 31 batteries. Odyssey is by no means the only AGM battery available. Optima was first, and now virtually all manufacturers make AGMs.

You will probably need three AGM batteries to provide for “hotel loads.” Count the amp draw of everything that will be on with your engine off, and multiply by engine-off hours. Add 30 percent for inverter inefficiency. Two batteries may work if loads are not too great, but that could affect battery life.

 AGM batteries are far more expensive than flooded cell batteries. How long do you expect to keep the truck? Also, AGMs work with your truck’s charging system, but require different external chargers. Testing procedures are also different. AGM batteries can be ruined by the wrong equipment or procedures.

Q: I’ve been reading the pros and cons of wide-base tires versus duals. I’m looking to purchase a new trailer and trying to decide if I should buy them. Any recommendations?

A: Wide-base tires reduce weight and fuel consumption. One wheel and tire weighs about 75 percent of two wheels and two tires. And single wheel and tire costs are higher, but overall they’re less than two wheels and two tires.

Sidewall flex is a major contributor to rolling resistance. By eliminating half the sidewalls, half the energy needed to flex sidewalls is eliminated. The result is between 4 percent and

5 percent better fuel mileage. You also get improved ride, directional stability and lateral stability. That can especially benefit tanks and bulk tankers because they have a lower center of gravity with greater track width, which cradles the tanks at a lower height.

Initial driver concerns included the inability to “limp home” and the lack of replacement tires. Never limp anywhere on one remaining dual. It overloads and overstresses the remaining tire and does severe internal damage. You risk a catastrophic blowout with the remaining tire.

Today, wide-base tires are as durable and reliable as duals. They are available at virtually all truck stops and tire centers. But they are sensitive to tire pressure, and they wear irregularly if they’re underinflated. They can be recapped, but only at qualified facilities. LL


Paul Abelson can be reached at