Numbers and Letters on Tires Tell a Story
Question: Every day I scan the newspaper for sales on tires. I drive a 1967 Ford Falcon with a tire size B-78-13. How can I match up my size with what is listed in the sale ads?--B.G.L.
Answer: The system for rating tire size has completely changed since 1967, but a few companies still sell new tires under the old size designations. But if you’re shopping for the best deal, it’s probably worth understanding the new system as well.
The new system tells you a lot more about a tire than the old alphabetic designations. For example, you can now determine the width, profile and suggested usage just from the designation.
Your Falcon could take one of several sizes, including a P-175-80r13, a P-185-75r13 or a P-195-70r13, based on recommendations from the Rubber Manufacturers Assn. Each portion of this designation tells you something about a tire.
Take, for example, the P-175-80r13. The P indicates that the tire is for a passenger vehicle and that it is sized in the metric system. The first number, 175, is the cross-section of the tire from sidewall to sidewall, measured in millimeters.
The 80 is an aspect ratio, which tells what the tire profile looks like. This tire is 80% high as it is wide.
The “r” indicates it has radial-ply construction. A “b” indicates a belted bias-ply tire and a “d” indicates a non-belted bias-ply tire. The 13 means it fits a 13-inch-diameter rim.
Q: I have a 1968 Chevelle V-8. I use leaded gas. Now, some people tell me that I can use unleaded super. I am mixed up. What should I use?--S.M.
A: You should continue using leaded regular. Under a new federal law, lead content in gasoline was drastically reduced to .1 grams per gallon, down from 1.1 grams per gallon before last July.
Although there is no universal agreement about the effects of the reductions, most experts believe few problems will arise. Lead plays an important role in lubricating the valves and valve seats in your engine.
Any damage to your engine would probably take years to show itself. Your car may very well reach the end of its life well before the lead reductions cause problems in the engine. At any rate, using the reduced-lead gas will be far better than switching to unleaded.
Q: I have a 1975 Chevy Monte Carlo with a new 350-cubic-inch engine. After short trips, the car will not turn over until after it has cooled. I replaced the starter and solenoid twice. In November, the car broke down on a trip, and a service station replaced the coil and electronic ignition. It did the same thing in December, and I again replaced the coil and electronic ignition. Just recently, the car did the same thing again. What would cause this type of problem?--M.C.C.
A: You may have two different problems. Some electronic modules fail when they are overheated. Possibly, the electronic module was placed too close to a heat source when the engine was rebuilt. The coil also has a heat shield on it to protect it from engine heat.
Hot engines typically cause electrical resistance to increase in the wiring that carries large amperage to the starter motor. So, good electrical connections are critical. You should also check the battery.
