When taking durometer reading the tire should be mounted
on the rim with the proper air pressure. This supports the tread to make your
durometer reading more accurate. Remember a durometer is a pressure sensitive
device. If the tire tread face is compliant when you attempt to use the
durometer the readings are not accurate. Speaking of accuracy, two people could
use the same durometer on a tire and get different readings based on how much
pressure they applied to the durometer.
When using a durometer on Autocross compounds you would
normally see a higher initial reading with the durometer reading dropping
"settling". EX: the initial durometer reading is 60 but the needle drops until
it stabilizes at 54. This characteristic is
rebound, This type of reading indicates low rebound characteristics.
Using a durometer on a tire at room temperature is less
than desirable. Ideally you want to test the durometer of your tire at the
temperature the tire is going to see at the track. Manufacturers use compound
heat curves to help them predict how a compound reacts during competition.
Manufactures use really cool scientific instruments but you can check the heat
curve of your tire at home. To chart a heat curve you need the following:
pyrometer, durometer, heat lamp, paper,
pencil. Take a durometer reading at room temp, record the temperature and
durometer reading. Heat a spot on the tire with the heat lamp, while keeping
tract of temperature readings using the pyrometer. Take durometer reading every
20 degrees. If it's an autocross tire chart the durometer reading from 100 to
180 degrees, road race tires 140 to 220 degrees. I would expect the durometer
readings of autocross tires to soften at 100-110 degrees and stay consistent to
160 to 180 degrees. Road race compound tires the durometer reading should be
consistent from 140 to 220 degrees.
An autocrosser wouldn't want a tire which didn't soften
until 140 degrees, this tire would be almost useless the first couple of runs
(unless the air temperature was hot). Charting heat curves are most useful when
comparing different compounds or brands of tires.
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- The Hoosier Radial Seems to work with these initial settings:
- Autocross pressures on concrete:
- End of car with engine
48-58lbs
- Other end of car 34-44 lbs.
- Pressures can
usually be dropped 6-12lbs if run on a low traction surface.
Road race pressures:
- End of car with engine 34-46lbs hot
- Other end of car
32-40lbs hot
Under inflation will kill the radials. A thin ring will form on the outside
shoulder, it will look like you took your fingernail and scooped the shoulder
off the tread. If you see this ring forming on your tires, add 6lbs of air
immediately. Another indicator of under inflation is the Hoosier Radials will
feel `mushy' in transient response. We have noticed a 10lb range where the
pyrometer will report ideal air pressure settings. On the low side of the range,
the tire was `mushy' in response and tire wear was not acceptable. The high side
of the range produced the best times and tire wear. Recommendation, start high
with the air pressures and work Down. This may result in a lack of grip if you
grossly over inflate the tire, but you won't wear off the outer edge like under
inflation will.
When setting the optimum air pressure for any race tire it's best to use a
pyrometer! You CAN NOT use the method of `chalking the sidewall' to set the air
pressure for Hoosier radials. This technique will cause premature wear from
being under inflated. At no time should you ever have roll over onto the
sidewall of a Hoosier radial. The bias ply tires however, chalking the sidewall
will get you close to the proper air pressure. For maximum performance and tire
life you should use a pyrometer.
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When putting Hoosier Radials on the car for the first time, many people
experience understeer (even cars which previously over steered). This is caused
by increased rear traction and the need for more negative camber in the front.
You need to tune this out as soon a possible to keep excessive front tire wear
from occurring.
The Hoosier Radial does require more negative camber than brand X, but not as
much as you think. Keep in mind excessive negative camber affects braking, and
causes under steer during initial corner turn in.. If you require more than 2-2
½ degrees static negative camber, you should look at stiffer springs/roll bar to
limit body roll or change the camber curve to gain more negative camber.
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The Hoosier Radial contains no steel belts like other competition radials.
This results in significant weight savings (2-6lbs. per tire). Since tires are
part of the rotating mass, this should not be overlooked. A 15lb reduction in
mass rotating at axle speed is like adding 6.5 horsepower.
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It is left up to the racers judgment to run tubes in slicks. As a
manufacturer, we suggest to leave it up to the customer unless the tires have an
air retention problem. The added weight of the tube is not necessary. By
running a tube in a slick, it is actually like applying an extra piece of rubber
to the sidewall of the tire, thus making the sidewall stiffer.
Use proper tube according to circumference of tire. Use following chart to
determine proper tube for your application.
74/84-13 fits 74-84" CIRC. with 8-12" tread width
80/88-15 fits 80-88" CIRC. with 6-11" tread width
86/100-15 fits 86-100" CIRC. with 11-13" tread width
94/106-15 fits 94-106" CIRC. with 15-19" tread width
If the tube is not the correct size for tire, the tube will make a bulge or
indentation in the sidewall of the tire. When seeing this problem, check tube
for proper fit. Natural rubber tubes, as compared to synthetic or man-made
rubber tubes, are suggested for racing purposes. Natural rubber has a tendency
to stretch more with heat and force applied, whereas synthetic rubber has a
tendency over time become hard and brittle, thus causing the tube to split and
deflate.
All drag D.O.T. Quick Time tires are tube type tires and as a manufacturer we
recommend using tubes while running on the street. At the track when racing,
Quick Times are safe to run without tubes. Once again, the racer is ultimately
the one to make the decision about running tubes at the track.
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