Q&A with Kit Foster: September 29, 2011

Q. I’ve noted that since the question of tire pressures was posed many months ago there’s been some discussion about pressures for radials and about the danger of old tires, but nothing definitive on the pressure issue. Part of my reason for concern is that I learned some years ago that until recent years, the factory-recommended pressures were sometimes incorrect, as evidenced by wear patterns. Also, about 40-50 years ago, some manufacturers actually installed tires that were barely adequate, or inadequate for the weight of the car. Remember when tires did not carry load weight information? In my own experience, following the manufacturer’s pressures might lead to wear patterns indicating over-inflation, or under-inflation in some cases. Why might that be? Changes in tire manufacturing, load-bearing weight, whatever. So to solve this problem, I acquired a tire wear gauge (much more accurate and useful than a penny), and I check the tire wear approximately every 5,000 miles. On older cars and trucks, I found that by studying the wear pattern over 15,000-20,000 miles, I’d often have to adjust the pressure by a couple of pounds to obtain even wear. Rear-wheel drive vehicles usually wear the right front tire faster than the others, so there needs to be more evaluation of wear patterns on the other tires to formulate the needed changes. The problem for us putting radial tires on antique cars is that we drive too little to learn anything about wear patterns in a reasonable time. When I bought my 1962 Buick, it had new tires, which were clearly over-inflated, thus affecting handling and braking, but improving gas mileage. I’d much prefer to have optimum pressure, so I’m experimenting now, but using the original suggested pressures. Hearing others’ experiences would be interesting.

Pat Jacobs, Snohomish, Wash.

A. Some of us drive our old cars so seldom that if we adhere to the 10-year advice about replacing tires, wear will never be a problem, whether we study the wear patterns or not. In such cases, handling and ride characteristics would seem to be the primary concerns, and these can only be determined by experimentation, particularly if using a type of tire that wasn’t available when the car was new.

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Q. Both you and a reader said (Jan. 30 “Q&A”) you’re running your radial tires on vintage cars at 30 psi. I have Diamondback 235/75R15s on my 1952 Cadillac Series 62 sedan. The folks at Diamondback told me to run them at 44 psi. Does that strike you as too high?

Jim Salmi, Denver, Colo.

A. Your Cadillac weighs slightly more than 4,000 pounds empty. I have a 1995 Chevrolet Suburban that weighs about 4,650 pounds, and I run Dunlop 245/75R16 Radial Rovers at 40 psi. Although 44 seems a little high for your Cadillac, I don’t think it’s wildly off the mark.

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Q. I’ve recently purchased a restored 1952 Ford Crestline from a dealer. I found that the previous owner had passed away, and was told the car had been restored several years ago. It appears it’s been sitting unused (actually abused) for a long time. From oil change stickers and odometer reading, the car has only traveled 190 miles in nearly 10 years. I’ve had many issues (wheel cylinders, bad electrical contacts, etc.), now all cleared up. I now have questions about the tires and how old they might be. They’re B.F. Goodrich Silvertown 7.10-15 four-ply polyester tubeless tires and seem to be correct for the car. They appear to be in good condition, and have no cracks and little wear, but I want to be safe. There are no paint chips on the rims, so I assume they were mounted at the time of restoration. I’ve put about 300 miles on the car, driving to shows, at about 50 mph, but I’m still concerned. Is there any way to date these tires? When did manufacturers have to start putting date codes on tires? I assume that the restorers got these tires through an antique supplier. Even though tires from these suppliers are recently made, are they required to have date codes on them?

Larry Smith, via e-mail

A. Tire codes have been around for 30 years or more, but until 2000 they weren’t useful in spotting 10-year-old or older tires, because the code only showed the year within the decade in which they were made. An 8-year-old tire was coded the same as an 18- or 28-year-old tire. Since 2000, there’s a two-digit year code, so 2011 tires, for example, will have “11” as the last two digits in their DOT code on the tire’s sidewall. The codes are required for all tires intended to be sold in the United States, so you may find some that have made their way in without them. I’m not sure whether “replica” tires of earlier designs must have the codes. I have late-1970s Lester tires that don’t have date codes. In your case, the tires certainly would be 10 years old, or more. I’d change them, if only for peace of mind. In so doing, you might also save your life.

To submit questions to this column: E-mail ron.kowalke@fwpubs.com or mail to: Q&A, c/o Ron Kowalke, 700 E. State St., Iola, WI 54990-0001.

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