Can a trailer cause wear to a truck, just by staying attached for long periods?

Dear Car Talk

Dear Car Talk | May 01, 2008

Dear Tom and Ray:

Please settle an argument here at the fire station. We have a Ford 550 pulling a 25-foot box trailer (gross vehicle weight 10,000 pounds). Here's the question: When this truck and trailer are not in use, does the weight of the trailer damage the truck? Are we causing damage to the leaf springs or suspension of the truck by leaving the sitting trailer attached for long periods of time? Is it necessary to unhitch the trailer when it's not used? Thanks for your input, and I hope to keep my money. -- Mike, Virginia Beach (Va.) Fire Department

TOM: Well, you don't tell us which side you came down on, Mike. So, while we appreciate the $20 you slipped into the envelope, we'll just have to pocket it and tell you the truth.

RAY: The answer is, it depends. What it depends on is the "tongue weight." That's the downward weight applied by the trailer's tongue -- which is the part of the trailer that extends forward, and that attaches to the ball on the truck's trailer hitch.

TOM: Imagine, if you will, that the trailer is perfectly balanced, that if you removed it from the truck, it would balance perfectly on its wheels, tilting neither backward nor forward. Then your tongue weight is zero. You're putting no downward weight on the back of the truck.

RAY: In reality, the tongue weight is never zero, but here's a test you can do. Unhitch the trailer, and let the tongue sit on the ground. Then try to lift it. If two of your biggest, bruisingest, damsel-in-distress-savingest firefighters can't lift the tongue, then you're leaving too much weight on the back of the truck, and you will weaken the suspension over time.

TOM: If your guys can't lift it easily, that means you're resting more than a few hundred pounds on the back of the truck. That'd be like having a mother-in-law living in there full time. And that WILL make the springs wear out sooner.

RAY: But if you guys can lift the tongue fairly easily, that means the tongue weight is negligible, and not worth worrying about.

TOM: And, of course, if the tongue weight is too heavy, you also have the option of rebalancing the trailer's load. You can shift a few beer kegs and a Barcalounger or two from the front to the back. Good luck, Mike.

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