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Q & A: Tire Pressure

Hi John

What is correct tire pressure for a MG TD?

I have just purchased a set of radial wide whitewall 165R-15 tires for my
1951 MG TD. To my surprise (horror) there was a big yellow sticker on each
stating, ³Inflate to 35 psi². This would make my light-weight MG ride like a
buckboard! My MG owner¹s manual states that bias tires should be inflated to
18 psi. Most MG TD owners that use radials with tubes recommend 24 psi
front, 28 psi rear. Thus I question inflating to 35 psi. ( I temporarily
inflated my existing blackwall 165R-15 radials (with tubes) to 35 psi. The
additional pressure made the road contact patch so small that the tires
skirted/skipped on the pavement. Obviously a dangerous situation.)

BF Goodrich makes an almost identical wide whitewall 165R-15 tire known as
Silvertown. I phoned their technical representative. He said tires should be
inflated according to the weight on each. He provided me data points for a
curve which is virtually identical to the²LOAD/INFLATION TABLE for 165R15
Radial Tires² provided by the Department of Transportation. There apparently
are standards for each tire size. Shouldn¹t these new tires conform to the
standard?

The basic weights for the TD are as follows:

Front axle 980 lbs (approx 490 lbs per tire, front)
Rear axle 1054 lbs (approx 527 lbs per tire, rear)

If I account for driver and passenger and luggage, etc., the maximum weight
per tire would be approx 720 lbs. According to the DOT Load/Inflation table
for 165R-15, I only need to inflate the tires to 16 psi - very close to the
18 psi recommended in the manual for bias type. However, such low pressure
would make steering stiff.

Do these new whitewall tires really have to be inflated to 35 psi when safe
pressure is normally determined by weight on each tire? There was another
sticker on each tire that read, ³Highway vehicles have tire loading placards
or certification labels affixed to the door edge, doorpost, or in the
vehicle owner's manual that contain the Gross Axle Weight Ratings (GAWR)
for each axle². This implies weight is an issue to be considered when
inflating.

Which do I believe, 1) inflate to 35 psi or 2) inflate to pressure as
calculated from the actual weight on each tire?

Stu

STU!

I have always used 30 in the front; 32 in the rear. My advice would
be to start at 35 front and rear. Drive the car the way you would,
normally. Then drop the pressures to 30. Drive again. Then drop the
p... read more