Pyrometer Tips |
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Table of
Contents |
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- Proper Depth and Location
- Adjustable Tip Probes
- Getting to the Tires Quickly
- Camber Adjustments
- Taking Advantage of New
Tires
- Averaging
- IR Versus Probe
- Summary
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A.
Proper Depth and Location |
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In order to get
consistent and relative tire temperature readings you must be sure to
insert the probe as near to the cord as possible. You must also insert
the probe to the same depth at all locations at each and every tire.
Temperatures should be taken at 3 locations on each tire. Take one
reading at the outside approximately 1.5" from the edge, one
reading in the middle, and one reading approximately 1.5" from the
inside edge. Do every tire the same way at the same depth and location. |
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As you insert
the probe deeper into the tire you will find more heat. If you insert
the probe half way in at one location and then all the way in at another
location you will get temperature differences due to the different
depths. You are trying to see relative numbers based on how the tire is
heating due to camber or loading changes. Improper depth can confuse the
true issue. |
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By inserting the
probe to a depth down near the cord you will also use the surface rubber
to momentarily insulate outside elements such as brake and engine heat
away from your true temperatures. Further, by getting down near the cord
you will also measure heating that is caused by an elastic stretching of
the rubber. If your probe is too shallow you will not see the heat
generated by the pulling of rubber from the tire carcass. |
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Another thing to
consider when using a probe type pyrometer is that rubber is a poor
conductor of heat. The metal probe will suck the heat out of an
insertion hole very quickly as the metal probe transfers heat quicker
than the rubber. At the first tire in a temperature session you should
pre-heat the probe by inserting it in the rubber a few times before
taking your readings. Once the probe is pre-heated you will get faster,
more accurate and relative results. |
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Be careful not
to leave the probe inserted too long in any one location. You need to
measure the temperature rise at its maximum point and no more. If you
wait too long the insertion point will start to cool, giving you
inaccurate readings. |
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Pyrometers with
an anticipation feature speed up the temperature taking process and
automate the procedure so that your readings are taken as quickly as
possible. You simply insert the probe and immediately hit the read
button. The pyrometer will calculate the rate of temperature rise and
automatically lock in the highest reading. The pyrometer will then
prompt you to move to the next location. Pyrometers with anticipation
complete all 12 temperatures in nearly half the time of conventional
pyrometers. |
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B.
Adjustable Tip Probes |
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If you use a
pyrometer with an adjustable tip probe you can set the probe to match
the rubber gauge (thickness) for the different tracks that you run. The
adjustable tip allows you to bury the needle of the probe all the way to
the housing to insure that you are at the same depth each time.
Repeatability increases dramatically and the relativity is better
because you are always down near the cord with your probe tip. |
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C.
Getting to the Tires Quickly |
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You should
always get to your car as quickly as possible to take tire temperatures.
Each time the tires roll across the pavement the cooler pavement is
sucking heat from the tires, which can skew your readings. You should
even have your car stop at the nearest safe place to the track and have
a crewmember waiting to take the readings. |
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D.
Camber Adjustments |
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Your pyrometer
is a tool to see if you need to make a camber adjustment. I like to see
the infield edge of the front tires run 10-15 degrees hot. 10-15 degrees
gives you an indication that you are running the maximum amount of
camber that will not give you excessive tire wear. You should always
monitor the wear in conjunction with your pyrometer readings to insure
that you do not wear out the edge of your tires prematurely. |
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I. Too Much RF Camber |
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Sometimes teams are running
more RF camber than necessary as they are fooled by their pyrometer
readings. If you are running an excessive amount of RF camber the
pyrometer might only show the inside edge at 20 degrees hot. What you
may not see is that if you reduce camber stand the tire up the inside
edge may stay 20 degrees hot. Too much of a good thing so to
speak. |
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Start with a proven camber
or your car builder's recommendation. Slowly add camber so that you can
see the gradual heating of the inside edge. When you run excessive
amounts of RF camber the tire is no longer able to stretch the contact
surface between the sidewalls. The rubber cups and bunches at the
inboard edge due to the excessive camber causing artificial heating, a
loss of grip, and premature wear. |
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II. Too Much LF Camber |
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Because the LF has less load
than the RF, you can sometimes see a visual clue that you have gone too
far with the camber. The outside edge starts to show a strange beveled
angle that is about 3/4" wide right at the outside edge. Instead of
cleanly rolling the rubber off the outside edge the tire gets tipped so
much when turned that it chews off the very outer edge. |
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I would rather have slightly
less than optimum LF camber than too much. The tire performance will
stay all day as compared to excessive amounts. Excessive amounts of LF
camber chews off the outside edge resulting in poor performance after
just a few laps. The car will not reach optimum speed and the
performance of the LF will fall off very quickly. |
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You should strive to adjust
the camber to the maximum limit without overshooting. Correct
adjustments will help the car turn better on both long and short runs. |
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III. Too Much Stagger |
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On occasion you can see too
much rear stagger in your tire temperatures. Sometimes the infield edges
of the rear tires are noticeably hot. Depending on the tire wear
characteristics of a given track, I might tone down the rear stagger to
even out the edge temperatures to insure that the car is good on a long
run. Judgment must prevail, as this is not a hard fast rule. Simply
another variable to consider. |
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E.
Taking Advantage of New Tires |
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New tires are a
big investment. Whenever a new set goes on the car I put more value in
the tire temperatures from the sticker tire run and make sure that I get
good temperature readings. When the tires are new they will have more
friction and generate more heat than at any other time. The additional
heat and added friction can provide subtle clues that may not be seen
with worn tires. |
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Further, new
tires are not worn down on any part of the contact patch. Therefore,
your readings are not skewed by an area on the tire that has already
been ground off. New tires have more friction so the tires are less
likely to slide or spin. The temperatures more closely reflect the heat
generated by tire loading. Looking at the effect tire loading gives you
an indication of what the car will do in the future. Hopefully the car
is already fast for the main event, but the new tire temperature
opportunity might guide you into adding a touch of bite or putting in
more stagger based on what you learn from your readings. |
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Be prepared and
insure that you get a good temperature reading when new tires go on the
car. |
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F.
Averaging |
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Temperature
averaging is a good tool when your car is fast and only needs fine
tuning. Tire temperatures are of little value when your car is in left
field. If you car is handling poorly than the front tires will slide
early in the turn and the rear tires will slide on exit. The sliding
overheats the tires and can make the temperature sheet look
balanced. |
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Temperature
readings are more valuable as you get faster and faster. You can use the
temperatures to assist you in fine-tuning the chassis. You might see
something in the numbers that lets you look into the future allowing you
to make a fine adjustment that improves the handling of the car on a
long run. |
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Some memory
pyrometers calculate the temperature averages for you. These devices
really save a lot of time and allow you to use averages as another tool
to fine tune your racecar. You can also use a simple calculator to
accomplish the task. |
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Averaging Tips |
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By using historical
information and common sense you can learn to see potential problems in
your tire temperatures. Below are some scenarios based on tire
temperatures and some potential cures. |
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Left Average is
abnormally cooler than Right Average |
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- Lower the panhard bar
- Smaller sway bar or less sway bar
load
- Softer right side springs or stiffer
left side springs
- Less stagger
- More left side air pressure or less
right side air pressure
- Less left side shock rebound
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Rear Average is hotter
than Front Average |
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- More front spring rate if car is
unstable in
- Less rear spring rate unless car
pushes on exit
- More sway bar or more sway bar load
if loose in the middle and on exit
- Lower panhard bar
- More front air pressure if center of
tire is cool
- Less rear weight if loose on entry
and not loose on exit
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Front Average is hotter
than Rear Average |
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- Less front spring rate if car is
stable on entry
- More rear spring rate unless car is
unstable on entry
- Less sway bar or less sway bar load
if car is tight in the middle and on exit
- Raise panhard bar
- Less front air pressure if center of
tire shows hot
- More rear weight unless car is loose
on entry or in the middle
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Cross LR to RF is Hotter
than LF to RR |
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- Less diagonal weight
- More stagger
- Smaller sway bar or less load
- Raise panhard bar
- Less LR spring rate unless car is
loose on exit
- Less RF spring rate unless car is
loose on entry
- More LF spring rate
- More RR spring rate unless car is
loose
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Cross RR to LF is Hotter
than LR to RF |
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- More diagonal weight
- Less stagger
- Bigger sway bar or more load
- Lower panhard bar
- Less RR spring
- More RF spring
- Less LF spring unless car is
unstable on entry
- More LR spring will help hook up on
exit
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The temperature
averaging suggestions are merely a starting point intended to provoke
thought. There are more variables than listed above. Driver feedback,
track conditions, racecar type are all factors that can cause variances
in the suggestions listed. Real racetrack specifics need to out way
generalities. |
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G. IR
Versus Probe |
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Probe type
pyrometers are better for use on tires if used properly. Infrared type
pyrometers measure only the tire surface and do not get inside the
rubber to find the true results. The rubber down at the cord is
insulated away from the outside elements providing for more accurate
readings. Rubber at the cord is also heated due to elastic stretching of
the rubber. Probes can reach in and see this heat. |
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Infrared
pyrometers measure only the surface. The surface will be cooler as heat
is dissipated off the surface very quickly due to the outside air
cooling and simply rolling across the cooler track temperature.
Typically the surface temperature is 20-40 degrees cooler than
temperatures taken with a probe. Infrared temperatures will also be
affected by artificial brake heat and engine heat. |
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You can use the
infrared pyrometer for tire temperatures but it is a compromise. Your
camber temperature curves will not be shown with as much clarity.
Temperature differentials will be more dramatic with a probe allowing
you to be more precise in your camber adjustments. |
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Infrared
pyrometers do work well for surface temperatures such as track
temperature, cockpit temps, header temps, brake temps, and the like.
Probe type pyrometers do not work well for surface temperatures. |
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H.
Summary |
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Used properly
tire temperatures will allow you to see what the racecar is going to do
on a long run as the tires heat and wear. You will be able to see
through what might be covered up by the extra grip from your new tires
as racecars always feel better when the tires are fresh. |
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You can learn to
anticipate what the car is going to do on long runs by using temperature
averaging as a tool. Temperature averaging is of little benefit if the
balance of the car is dramatically off. Remember your readings have more
meaning as the car approaches optimum handling. Temperature averaging is
of most benefit when your car is already very fast and you are looking
for that final edge. |
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Written by: |
Jeff Butcher |
Longacre Racing
Products, Inc. |
11/15/00 |