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The Hummer Knowledge Base
Tires & Wheels/Size and Pressure Test:
Date sent: Fri, 16 May 1997 16:41:34 MST
Subject: HML: Tire Size/Pressure Test
OK people, I did the test and here are the numbers...
|Measure the Height between the center of the wheel and the
ground. Measure the distance traveled in 10 revolutions of the
tire Perform above measurements at two different inflation
* Tires were bulging noticably (about as expected for 10#).
|10# *||15-3/8"||91' 4"
Test Result Analysis:
|Reducing the vehicle axle height by about 10% did not reduce the
distance traveled by anywhere near 10%. Actual reduction was
less than 1%.
Since the distance traveled was changed by only about 1%, the
effective torque was also increased by only about 1%. It should
be noted that the rolling resistance of a low-pressure tire is
also higher, so the net difference on torque is probably near
zero, if not negative.
Speedo difference should also be about 1%.
Effective Tire Size (Calculated from distance traveled):
|Do not lower your tires for increased torque.
As mentioned in a previous posting, reducing tire pressure does
greatly increase traction and floatation. These, in addition to
smoother ride, are excellent reasons for reducing tire
Notes for Nit-Pickers:
|The test was performed only once at each tire pressure. The
truck speed during the 10-tire-revolution test was very slow -
about 1 mph. The axle-height to ground was measured at the end
of the test. The tire was turned about 1 revolution at low
pressure before the test was started to allow for tire
deformation while deflating. Test was performed on the rear
tires of a '95 Diesel wagon with very little cargo inside.
Front tires were not deflated, transfer case in H (not HL).
Tires are Goodyear MT tires with about 50% of tread remaining.
Altitude: about 5500'. Ambient Temp: 82 deg. F. Surface used
for testing: graveled asphalt. Grade: between 1% and 2% down.
'95 Diesel Wagon
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