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Oil Condition Monitoring

under pressure

Keep tires properly inflated

Keep tires properly inflated

We are being extra cautious and taking everything we read this morning with a grain of salt (see the date — yes, we have been fooled in the past). But this one is legitimate: California passed legislation that will require auto shops to check the tire pressure of every car that comes in. This seems like a simple thing to us. In fact, what kind of a shop wouldn’t do this? Simply making sure you’re at the right pressure can boost fuel economy by as much as 3.3%! See other easy ways to increase your mpg.

But we know that more than half of the cars on the road have incorrect tire pressure, and since April is National Car Care Month it seems like a good time to raise awareness about it.

A recent study of cars by the Car Care Council found…
54% had low tire pressure
38% had low or dirty engine oil
28% had inadequate cooling protection
19% needed new belts
16% had dirty air filters
10% had low or contaminated brake fluid


One Response to “under pressure”

  1. “Make sure your tires have the right pressure”. Sounds good, but how do you determine the right pressure? Is there a formula? If so, I’ve never run across it.

    The tire manufacturer publishes a maximum tire pressure, but passes the buck to the car manufacturer for “optimum” pressure. So what do you do when the manufacturer publishes pressures that are patently absurd, and ignores repeated requests for explanation or correction?

    Take the case of a 2004 Volkswagen Golf TDI, shipped with Goodyear Eagle 195/65R15 all season tires.

    The placards on the doorwell and the inside of the gas filler hatch stipulate 33 psi front axle, 42 psi rear axle and spare. The owner’s manual then instructs the owner to add 3 psi more to all-season or winter tires, for a grand total of 36 psi front, 45 psi rear and spare.

    The stock tire is only rated for a maximum of 44 psi BTW. Nor is there a suitable warning placard on the tire wrench to advise the little lady to let 9 psi out of the spare if mounting it on the front.

    If this is not enough to kill anyone’s confidence in these figures, consider that 2002 version of the same model, with identical body, suspension and wheels, and tires of the same dimension, came with instructions to fill both front and rear tires to 26(+3) psi and to add three (3) more psi to the rear axle when the vehicle is fully loaded.

    The dealership, BTW, delivered the 2004 model with all five tires inflated to about 30 psi. I’ve kept it at that pressure, and find I still have more wear on the crown of the tire than at the edges.

    So – is there a formula, or does one have to determine the best pressure in such a situation by brute trial and error? I’d like very much to know how to calculate the best pressure, primarily for optimal steering and braking, and secondarily for economy (tire life and fuel economy). But all I’ve ever seen about this is the boasts of drivers who always run their tires at the tire manufacturer’s maximum pressure and claim they get fantastic fuel economy.

    I don’t much care about road noise or harsh ride. But how do you calculate the steering and braking trade-offs and premature tire wear incurred by overinflated tires?

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