When setting up your suspension, do not overlook caster. Positive caster has
the effect of passing road feel to the driver, and it aids in centering the
steering wheel after a turn (it makes the front tires return to straight ahead
quicker). Most cars respond favorably to caster angles between 4-6 degrees
positive. Caster angles in this range have another benefit, when the tire is
steered into a corner the outside tire gains negative camber. If the negative
camber gain is large enough, you may reduce static negative camber (good for
braking). Large caster angles can cause disadvantages in slick conditions, like
rain, when weight transfer is limited. This is because if the weight transfer is
not occurring, the body is not rolling, and the caster angle is still generating
negative camber whenever the wheel are turned. In effect you're generating too
much negative camber for the conditions.
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Pyrometers are excellent tools, everyone should have access to one. They are
most effective when steady state cornering is available (oval track or skid
pad). This is because the surface temperatures of the tire changes very quickly.
On a typical autocross or road course you should consider the last maneuver
performed when reading tire temperatures. If the last corner was a hard right
hand turn, check the left side tires first because they where doing the work and
will be the most accurate.
Many people believe the proper tire temperatures a achieved
when the temperatures are even across the tire. This is true if you are in a
steady state corner all the time, but usually this is not the case. I normally
want my inner temp to be 7-12 degrees hotter than the middle & outer
temperatures. This is because of static negative camber & toe-out settings. If
you use toe-in you'll see more heat on the outside edge. The thing you
absolutely don't want to see is the center temp colder than the edges.
Another tip for stock vehicles with weak-knee posi-trac units, ignore the
right rear temperature it will almost always indicate an over inflated
condition. This is because the rear sway-bar, soft springs, and `limited'
limited slip differential allow the right rear to spin excessively during right
hand corners.
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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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