See an expert about your rims

Dear Mike: My son just bought a used car with aftermarket rims. I’m concerned that the centering ring on the hubs is smaller than the corresponding bore on the wheels.

This means the wheels may not center correctly, right? Is this safe?

— W. S., Summerville, S.C.

A: They should be fine. As to whether the rims fit correctly, that’s another letter entirely.

Centering is only one issue. The overall width and offset are also important because they affect handling and steering. The overall diameter of the tire needs to be at least close to the original to avoid changes in gearing that may affect performance. And gross changes in diameter and overall rotating mass may affect ABS performance.

Just making sure the replacement wheels physically fit inside the wheel wells without clearance issues to the fenders, suspension and brakes is only a start. You’ll need to consult someone who has specific data about your rims and your car.

Most modern cars use a centering ring that sticks out 10 millimeters to 12 millimeters from the hub, specifically to make sure the wheel is centered within a few thousandths of an inch when it’s installed. Not all cars have this ring, however.

When you put the wheels on the car, be sure that there is no foreign matter, such as rust or dirt, on the hub or wheel mating surface. This might mean wire-brushing the surface or at least carefully cleaning it with a rag. I prefer to smear a thin coating of anti-seize over the surface to prevent any corrosion from sneaking in — but then, I was raised in the Midwest where they pour salt over the roads almost every day.

Hang the wheel by the studs and finger-tighten the top lug nut, then a bottom stud, followed by the rest. Spin the wheel a couple of times to let it settle, then finger-tighten all the lugs again. Spin the rim to check that it’s centered — the chamfer on the lug nuts will tend to pull the rim toward its center. Unless, of course, you run the first lug nut home with an air wrench instead of tightening all of them gradually.

I’ll say again what I’ve always maintained — never tighten lug nuts with an air wrench, even if you use torque sticks. Torque sticks are short extensions to go between the wrench and the socket, and they’re supposed to limit the torque applied to the lug nut. I find them inaccurate and inconsistent.

Instead, use this procedure: As above, finger-tighten all the lug nuts, then wiggle the rim around and finger-tighten again. Next, use a torque wrench to tighten in a crisscross pattern to half the final torque, and then again to full torque. This will keep the wheel centered, prevent warping of the brake discs, and allow you to remove the wheel again on some rainy night to change a flat with the lug wrench in the trunk instead of an air wrench or a 4-foot cheater.

Dear Mike: Owners of old tractors and antique cars sometimes put 8-volt batteries in their 6-volt systems to give their starters a little extra juice to spin the old motors faster for easier starting.

Is there any harm in this? What does it do to generator polarization or amp/volt readings?

— R. M., Conklin, N.Y.

A: Racers use 14-volt batteries to provide a hotter spark and improved cranking, too. The downside is slightly reduced life of some voltage-sensitive components, like light bulbs and electric motors. Regardless of whether the system is positive or negative ground, it will have no effect on ammeter readings — although a stock 6-volt or 12-volt generator obviously won’t give an 8-volt or 14-volt battery much of a charge.

Many antique voltage regulators can be adjusted mechanically. Racers can buy 14-volt alternators, but many race cars have no charging system, so they simply rely on 14-volt off-car battery chargers to recharge the battery between races. The ammeter will still read properly, and the voltmeter will simply reflect the actual voltage of the system.

Why go 8 volts when you can go 12 volts? If it were my car or tractor, I’d convert it to 12 volts. A good motor shop can rewind the stock starter and generator or alternator appropriately. You will need to replace the bulbs and things like the wiper motors.