Heavy hauling requires picking suitable tires
I’m considering new tires for my GMC 2500 and want to plan ahead for possible RV usage. This may be either a trailer, fifth wheel or large camper — jury is still out. What advice do you have for me to consider regarding strength and sizes? — Larry M.
It’s great to plan ahead like this! You’ll be looking at LT (light truck tires) and will want to keep the load range, ply rating and/or load index numbers in mind. Typical 3/4 ton and 1-ton truck tires should be load range E (10 ply) as opposed to D (8 ply) or C (6 ply) found on lighter duty trucks. Often you’ll see load index numbers instead, such as 121/120T, which indicates 3,195 maximum load pounds per tire— 3,085 if used in dual wheel configuration. (T is the speed rating: 118 mph.) The dual rating considers the possibility of one tire carrying the load should the mate fail. Readily available charts indicate load range vs. pounds per tire, and speed ratings, for other values.
Tire size and aspect ratio also contribute to strength. Generally, a larger tire with a taller profile (75 series rather than 70) will carry a higher load rating. For example, my truck came equipped with LT245/75/16E tires (3,042 pounds, 12/116S) with a 30.4-inch diameter. When it was time for replacement, I upgraded to LT265/75/16E tires (3,415 pounds, 123/120R, 31.6-inch diameter), upping the load capacity of the four tires by 1,492 pounds. This was compatible withmy rim width and was the largest size I found that would not rub front tires against the fenders during sharp turns. A larger size 70 series tire would have also fit but had about the same load capacity as the originals.
It’s important to remember that regardless of how sturdy the tires may be, one should not exceed the truck’s gross vehicle and rear axle ratings.
How critical is it to get a “check engine” light fixed? I’ve noticed a lot of people driving around with this light on. — Victor
An illuminated “check engine,” also called “service engine soon,” light indicates a fault is occurring in the engine management system that is inferred to cause excessive exhaust emissions. There are perhaps a hundred or more possible causes for this, some more important than others. If the engine runs abnormally at all, immediate service is important, particularly an engine misfire (chugging/bucking/ shaking— most noticeable on acceleration) which if severe enough will result in a flashing light. There can be other causes, such as a faulty gas cap seal, that have no effect on engine performance, or perhaps an intermittent fault that only causes brief symptoms.
Besides the obvious concern of increased exhaust emissions and possibly reduced fuel economy, one needs to consider the possibility of catalytic converter or engine damage should the engine operate abnormally. With the proliferation of inexpensive code readers and scan tools, it shouldn’t be difficult to have the cause quickly checked. A web lookup of the DTC (diagnostic trouble code) can shed light on the possible cause and likely severity of effects— if any— on engine performance.