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What's the "Straight Dope"?

Dear Cecil:

I have a theory that, as a nation, we could save about 10 per cent of our gasoline consumption by the simple expedient of making sure our tires are fully inflated. My questions are: (1) What is the relationship between underinflation and gas mileage deterioration (e.g., 20 percent underinflation reduces mileage 10 percent, etc.)? (2) What is the trade-off between tire inflation and tire life? (3) Do the auto manufacturers in fact specify too low an inflation level for tires in order to soften the ride?

Reply to
A VFW
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In my Beetle I use 20 psi in the front and 28 to 32 psi in the rear.

The reason for only 20 psi in the front is so it will have better traction in wet weather.

I think the owner's manual says 18 psi in front tires and 28 psi in the rear tires.

Reply to
Jim Ed

I don't know about nowadays, but car companies used to specify lower tire air pressure for that soft cushy ride. cuhulin

Reply to
cuhulin

keep the fronts at or around the secified PSI .. the bug needs it for traction and ride. even 'nowadays' :-)

Reply to
tricky

unless you have modern tires that are WAY different than recommended... like real low profile fatties :)

Reply to
Jan Andersson

aH yes ! very true Jan :-)

Reply to
tricky

Sorry for the late response, but I just saw this and wanted to chime in.

I doubt the gas mileage penalty is much above a couple percent. On the subject of tire wear, I have a definite opinion, and substantial evidence.

I have a 3/4 ton work van that has a normal load on board of close to half of a ton. It normally wears tires on the outside of the tread on the front wheels, even when closer to no load and with correct tire inflation.

I talked to a guy with a large pickup that had the same problem. He said he ran his tires at 55 pounds, even though the book says 38 pounds. I decided that if he had no problems with that pressure, I could try it, too.

I did, and found that 55 pounds and correct tire rotation gave me even tread wear, all the way across the width of the tire. So yes, I think the given tire inflations are way conservative, to get smoother rides, and to sell more tires.

Reply to
Morgans

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