Q: Dear Tom and Ray:

My girlfriend and I are having a disagreement over the need to adjust tire pressures on her Jeep Wagoneer when we drive on the beach. She says that she has been given the advice to deflate the tires before going on the beach. This sounds crazy and illogical to me, and I'm an engineer by training. I asked her if she has some kind of device to pump the tires back up when she leaves the beach and wants to drive on the interstate for hundreds of miles to get home. If you do recommend the deflation procedure, how much air do you take out? We are going to a beach house this summer that you can only get to by driving on the sand, and neither of us wants to listen to "I told you so."

-- Bob

A: TOM: Well, Bob, since you seem so comfortable throwing around that engineering credential, I'm sure you're quite used to learning that you're wrong.

RAY: Your girlfriend is absolutely right. The reason you deflate your tires before driving on the beach is because it gives you a wider, softer "footprint" in the sand. And the more actual rubber you can put on the sand, the better your chances of not getting stuck.

TOM: How much air to let out differs from car to car and from tire to tire. Generally speaking, the bigger the tire, the flatter it can run. If I had to guess, I'd say you could run your Jeep on the beach with 12 to 15 pounds per square inch of air in the tires, as long as you don't go too fast or too far. But I'd check with a dealer to be sure.

RAY: You are right, Bob, to be concerned about reinflating the tires. (We're trying to help you save face here, buddy.) If you get back on paved roads with 15 PSI in each tire, you'll surely damage the tires and the rims. So you have to have some way to reinflate the tires when you get off the beach.

TOM: A portable, car-battery-powered air pump is one possibility. A gas station very near the beach access (that you can limp to) is another.

RAY: You might try to contact the owners of the beach house and find out how they deal with this issue, since they obviously have to get to their house and back.

TOM: That'll be better than stopping the first guy you pass on the beach and asking "How much air should I let out of my tires?"--only to find out that when you get the answer, you're already up to your axles in sand.

Dear Tom and Ray:

I have a question about "dry gas." I know some brands contain methanol and some contain isopropyl alcohol. I know isopropyl is recommended for cars with fuel injection. The question is, can I use the isopropyl (rubbing) alcohol I buy in the drugstore? I noticed the label says "contains 70 percent isopropyl." Does this mean the rest is water?

-- Joe

RAY: Yes. And water is exactly the thing you're trying to get out of your tank by using "dry gas" or "gas-line antifreeze." So don't use that 70 percent stuff.

TOM: But if you can find it, you can use "99.9 percent isopropyl" rubbing alcohol, which costs about a third as much as commercial "dry gas."

I also should mention that, personally, I don't believe you really need this stuff. Most gasolines already contain some kind of gas-line antifreeze. But if you do find it helpful where you live, you can put the rubbing alcohol into your tank in the same ratio that you would use for a commercial dry gas product--about 12 ounces of isopropyl alcohol for every 10 gallons of gas.

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