Today: A reader throws down the gauntlet. See if Tom and Ray goofed in a recent column.

Dear Car Talk

Dear Car Talk | Sep 01, 2007

Dear Tom and Ray:

Hey guys, I found an error in your otherwise good column. The subject was placement of weight in the trunk to make more-effective traction for a rear-wheel-drive car. You stated that the best place to put the weight is directly on top of the drive axle. Sorry, but that is wrong. The most effective place is as far aft as you can put the weight. Let's say you have a car with a 110-inch wheelbase. If you put a 100-pound weight directly over the axle, the rear wheel load goes up 100 pounds. But if you put the weight 40 inches aft of the axle, the rear wheel load goes up 100 x (110+40)/110 = 136 pounds. Of course, the front axle load goes down by 36 pounds, but that is less than 2 percent of its load -- which is negligible. It will be interesting to see how you weasel out of this one! I always enjoy your radio show and your column. Keep up the good work. -- John

TOM: John, you think this is a tough one to weasel out of? You misunderestimate us, my man!

RAY: Actually, you are technically correct. But the reason we recommend putting the weight over the axle was stated in our original column -- and confirmed by your math.

TOM: When you put weight behind the rear axle, you lift weight off the front axle. And since the front axle is key in both steering and stopping the car, we don't think that's a good idea.

RAY: You consider it negligible, but when does it become not-negligible? If you put 200 pounds of weight in your theoretical car, now you've reduced the weight over your steering and braking wheels by 4 percent. Is that enough to argue against doing it? What about 300 pounds? What about a Jersey barrier hanging off the rear bumper?

TOM: On the other hand, by putting the weight directly over the rear axle, or as close to it as possible, you add weight to the rear of the car without lifting the front wheels off the ground. So why not do it that way?

RAY: Or, better yet, forget about the weight and stay home and watch daytime television when it snows. Surely we can all agree on weaseling out of work, can't we, John?

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