Tire Pressure
Tires are the most important component on a race car. You can have the fastest engine
or the best possible setup, but if you don't have a set of tires between you & the track, everything else is meaningless. In fact, every single thing you adjust on a race car is for the benefit of the tires. All these adjustments that I've discussed in this guide are all about trying to achieve the best possible grip from the tires to the track. If you have the best grip at all 4 wheels, then you'll have the fastest car on the track.
Tire pressure is yet another adjustment that will aid you in achieving the best possible grip. Tire pressure is simply how much air you have in a tire. The hotter tires get, the more they expand. Air contains moisture. Moisture becomes steam as the air gets hot & increases pressure. WC teams actually don't use air in their tires they use nitrogen. Nitrogen is preferred over air because it doesn't expand as much with temperature changes because it doesn't contain moisture. Since it's impossible to remove all the moisture from a tire, it will still change pressure as temperatures rises. This can be noted after running a test session & checking your tires both hot & cold. When tires expand it changes the size of the tire which in turn changes the weight on that wheel. This can be either a negative or positive situation depending on your chassis needs.
Tire pressures can be adjusted on all 4 tires from as low as 8 psi. to as high as 60 psi. Improper tire pressure can cause an ill handling car. Correct tire pressure can be determined by reading tire temperatures. A tire with a temperature reading higher in the center of a tire indicates an over inflated tire. A tire with a lower center temperature, when compared to the inside & outside of a tire indicates a under inflated tire. Over inflated tires will have a tendency to make the car tight. Under inflation can slightly loosen a chassis but give better grip. Lower tire pressure will also increase the amount of heat in that tire. Excessively low tire pressure produces more heat which can result in quicker wear. Higher pressure tires run cooler, have less drag & will be quicker at higher speeds.
Stagger isn't a direct adjustment we can make in NASCAR Racing. NASCAR regulates the size of their tires which come with stagger already built into the tire. Altering tire pressures allows us to slightly modify the stagger. Stagger is the circumference of the right side tires compared to the left side tires. The best way I can describe stagger is by using a white Styrofoam coffee cup. You know, the kind that is bigger around on the top than on the bottom. Take that cup & lay it over on it's side on a table. Now push it along the table letting it roll. You see how it turns in one direction. This is stagger. Imagine the top or larger side of the cup as the right side tires on a race car. Imagine the bottom or smaller side of the cup as the left side tires. See how it turns left? Stagger on a race car works the same exact way. By increasing tire pressure on the right side, or decreasing pressure on the left we add stagger to the chassis allowing the car to turn left better through a corner especially under acceleration.
One thing to keep in mind when dealing with tire pressures, is that your also changing the weight of the car on the corner your lowering or raising pressure at. By raising or lowering pressure your changing the ride height of the chassis. Changing the ride height adds or subtracts weight from that corner of the chassis. So tire pressure actually reacts like a spring. Adding more tire pressure makes that corner of the chassis a little stiffer. Lowering tire pressure will tend to make that corner of the car softer.
Tire psi synopsis:
Higher psi in RF will loosen the car.
Lower psi in the RF will tighten the car.
Higher psi in RR will loosen the car.
Lower psi in the RR will tighten the car.
Higher psi in the LR will tighten the car from the middle out.
Lower psi in the LR will loosen the car from the middle out.
Higher psi in the LF will tighten the car.
Lower psi in the LF will loosen the car.
The lower the psi in a tire the hotter it will run.
The higher the psi in a tire the colder it will run.
Excessively low front tire psi will create a push.
Excessively low rear tire psi will create a loose condition.
Increasing the split (more RR psi than LR) increases stagger, helping the car to turn in the middle of a corner.
Increasing the split of the left & right side psi (more psi on the right) increases the pull to the left.
Tire pressure allows us to fine tune the chassis. Drastic pressures changes at various corners of the chassis could produce less than desirable results. Keep an eye on tire temperatures. Although your changing the weight on each tire with tire pressure, your changing it to a much lesser degree than with a spring change. If you know & understand how springs work, you'll be that much further ahead when understanding how tire pressure changes effect the chassis.
Tire Temperatures
When I talk about the inside of each tire, I'm referring to the edge closest to the brake rotors or inside of the car. When I refer to the outside edge of each tire, I'm referring to those edges that are furthest from the brake rotors. Tires are marked within NASCAR Racing as O for outside, M for middle, & I for inside. See the accompanying photo for a better understanding of the outside & inside of each tire.
I previously mentioned that every adjustment we attempt to make on a racecar, is an attempt to try an maximize the grip of each tire. By taking tire temperatures of each tire we can "read" how well our chassis is performing. A good tire man can tell how a racecar is handling without ever watching it perform on the track & without even talking to the driver. Tire temperatures are the only scientific proof we have of how a chassis is working. It's easy for a driver to misinterpret how a car is handling. Tire temperatures eliminate that mystery by telling us which corner of the car is over or under worked.
The information I am going to discuss below, is what I've learned over the years working on real race cars. Some of the tire testing information I will mention below has given me various results within the sim. Some of this information transfers over to the sim rather well. Use this information to the best of your advantage to better understand the concept behind reading tire temperatures.
Tire temperatures are taken with a tool called a tire pyrometer. This tool is inserted into the tire on the inside, middle, & outside of each tire to give us readings across the surface of the tire. By comparing tire temperatures across the surface of the front tires we are able to tell if we have proper camber angles, proper toe, proper weight distribution, as well as proper tire inflation. By reading the average temperature of the RF & comparing it to the average temperature of the RR we can tell if the chassis is loose or tight. Comparing diagonal averages indicate the proper amount of wedge in the chassis.
The optimal tire temperatures should be in a range of 190 to 240 degrees. Keep in mind that the hotter the tire the quicker it will wear out. It's important to realize what the outside & inside of each tire is. The inside of each tire is the edge closest to the brake rotors or inside of the car. The outside edge of each tire are those edges that are furthest from the brake rotors. See photo above for outside & inside edges of tire temperatures.
On a short track it is normal for the outside edge of the RF tire & the inside edge of the LF to be 5 to 10 degrees cooler. This is because of the way the tires travel down the straightaway. On a larger track with longer straights, this spread will be even further. On an oval, the RF tire will have more negative camber, thus resulting in the inside edge of the tire contacting the track more than the outside edge giving you the higher temperature. On the LF you will run with more positive camber, so just the opposite holds true. While cornering these temperatures should even out if you have the correct amounts of camber & or weight transfer. The more camber you run, the higher these spreads will be. On a small track were you spend a lot of time cornering, you'll find the spread not as high. This is because your spending more time cornering than on the straights, thus distributing the temperatures across the face of the tire more evenly. If you try to achieve even temps across the tire you may develop a push. This is telling you that you have too much positive camber. Although the tire may be flat on the track, on a straightaway, the tire will not be flat on the track while cornering.
By comparing the average temperature of all four tires you can see which corner of the chassis is working harder than the other. To figure the average temperature of a tire, add the 3 temps across the tire & divide by three. If your RF is a lot hotter than the other three tires your probably pushing because the RF is doing too much work. Work on cooling that tire off by lowering the RF spring and allowing the other tires to share some of the work load. By comparing the RF average to the RR average you can tell if the chassis is loose or tight. The RF should be about 10 degrees hotter than the RR. If it's higher your probably pushing. If it's lower your loose. A tire is being under worked when it's temperature is a lot lower than the other three tires. When a tire is cooler or under worked, try concentrating on that corner of the car. Try adding weight to that corner of the car to increase the temperature of that tire. If a tire is a lot hotter than the other 3 work on making that tire cooler.
It's also informative to compare right & left side, front & rear, as well as diagonal averages. Print & use the tire temperature sheet I've provided to help track all this information. To see if you have the proper wedge, average the RF & LR tires & compare them to the two front averages & two right side averages. Your diagonal average should be 5 to 10 degrees cooler than both the front & right side averages. If it is warmer you have too much cross weight. If it's cooler then you need more cross weight or wedge.
The best way to decipher tire temperatures is to run 10 laps on a particular setup & monitor tire temps. Don't expect to learn everything reading the temps only once. It will take a number of 10 lap sessions to sort everything out that is going on with the tires. When analyzing tire temperatures it should be done in a specific order. This is because a problem in one area may mask a problem in another area. Here is what I do.
Run 10 laps, adjust front cambers. Run another 10 laps.
Adjust tire psi. Run 10 laps.
Adjust toe if needed. Run 10 laps.
Adjust wedge. Run 10 laps..
Adjust for tight or loose condition based on RF & RR average. Run 10 laps.
Look for overheated or overworked tire. Adjust on that corner. Run 10 laps.
Repeat the process all over again. Run 10 more laps.
When checking tire temperatures it is important to make sure your not locking up the brakes or making any sudden changes in your steering outputs. These will all create erroneous tire temperatures readings. Let me try to simplify how to read tire temperatures by giving you this guideline.
A tire with too much NEGATIVE camber will show an excessively higher temperature at the INSIDE edges.
A tire with too much POSITIVE camber will show an excessively higher temperature at the OUTSIDE edges.
A tire that is OVER inflated will have a higher middle temperature than the inside & outside edges.
A tire that is UNDER inflated will have a lower middle temperature than the inside & outside edges.
A car with too much toe OUT will show higher temperatures on both INSIDE edges of the front tires.
A car with too much toe IN will show higher temperatures on both OUTSIDE edges of the front tires.
A RF tire that is HOTTER by more than 10 degrees over the RR indicates a tight condition.
A RF tire that is COLDER by more than 10 degrees over the RR indicates a loose condition.
A tire with the HIGHEST average temperature is the corner of the car that is being most worked.
A tire with the LOWEST average temperature is the corner of the car that is being least worked.
A RF & LR diagonal average that is the same or higher than the front & right side average indicates too much wedge.
A RF & LR diagonal average that is more than 10 degrees lower than the front & right side average indicates not enough wedge.
Let me reiterate once again that the results you see may vary. Using these guidelines will give you a better idea of what your trying to achieve & should get you in the ball park of a quicker more stable setup.
Lets look at a few examples.
RF
I----M----O
208--202--194
Indicates too much negative camber.
RF
I----M----O
194--202--208
Indicates too much positive camber.
RF
I----M----O
204--188--197
Indicates an under inflated tire.
RF
I----M----O
204--210--197
Indicates an over inflated tire.
RF
I----M----O
204--198--194
Indicates correct camber. Overall average temp is 198.6.
RR
I----M----O
227--225--223
Overall average temp. is 225.
If the RR & RF temp above came off the same car we would have a very loose racecar. The RR is approximately 26 degrees hotter than the RF. If this RR is also the hottest tire on the car, it indicates the RR is doing the majority of the work in the corners. This is the corner of the chassis I would work on. We need to take some weight of this corner to cool this tire. I'd start by going with a weaker RR spring. This should cool this tire & tighten up the chassis.
RF
I----M----O
215--192--186
Outside edge is too cool indicating we need more positive camber. Average temp. is 197.6. Let's compare this with the RR below taken on the same car.
RR
I----M----O
190--188--186
Average temp. is 188. This tire is 10 degrees cooler than the RF indicating a neutral handling chassis. This should be good, but we could be faster with a camber change on the RF. Let's adjust the camber on the RF, run another 10 laps & take temps again below.
RF
I----M----O
200--195--190
Camber looks much better now. The average temp is 195.
RR
I----M----O
192--190--188
Average temp. is 190, but now when we compare the average of the RF & RR we find our temperatures too close to each other. After the camber adjustment we no longer have a neutral handling car, but one that is now on the verge of becoming loose. Your general feeling may be that the camber change made the handling worse, and it very well may of. But were still heading in the proper direction. You may have to take a step backwards at 1st to take 2 steps forward later. We can now work on increasing the temp of the RF or work on cooling the RR to increase our average split between the RF & RR. To increase the heat in the RF try a stiffer spring. To decrease the heat in the RR try a weaker spring. Either way you will make the car tighter. How much of a change depends on how much it changes your tire temps. Run another 10 laps & review your temperatures again. Eventually you should be faster than your neutral handling setup with improper camber in the RF.
As you can see from the above example there isn't always an immediate cure. Chassis setup is sort of like solving a puzzle. Experiment & learn as you test. Always keep in mind that you may be going the correct way, but there could be an adjustment elsewhere that may be masking your initial change. Because of this chassis setup can become very frustrating for the novice and experienced alike. For every change you believe your making for the better, it will have an adverse effect elsewhere in the chassis. If for example your car feels great going into & through the middle of a corner, but is loose on exit, you have to tighten it up somehow. Curing the loose condition exiting the corner now has probably messed up your chassis going into the turn. Now you must loosen it up again. It's a constant battle of give & take. Hopefully by monitoring tire temperatures you can eliminate some of the mystery of how & why a chassis is reacting like it does.
Tire Temperature synopsis:
Optimal temp range is between 190-240 degrees.
The hotter the tire the quicker it will wear.
The hottest tire on the car is the tire that is being worked the most. The coolest tire is the least worked.
Work on the corner of the chassis that is either the most overworked or least worked 1st.
A tire with too much NEGATIVE camber will show an excessively higher temperature at the INSIDE edges.
A tire with too much POSITIVE camber will show an excessively higher temperature at the OUTSIDE edges.
A tire that is OVER inflated will have a higher middle temperature than the inside & outside edges.
A tire that is UNDER inflated will have a lower middle temperature than the inside & outside edges.
A car with too much toe OUT will show higher temperatures on both INSIDE edges of the front tires.
A car with too much toe IN will show higher temperatures on both OUTSIDE edges of the front tires.
A RF tire that is HOTTER by more than 10 degrees over the RR indicates a tight condition.
A RF tire that is COLDER by more than 10 degrees over the RR indicates a loose condition.
A tire with the HIGHEST average temperature is the corner of the car that is being most worked.
A tire with the LOWEST average temperature is the corner of the car that is being least worked.
A RF & LR diagonal average that is the same or higher than the front & right side average indicates too much wedge.
A RF & LR diagonal average that is more than 10 degrees lower than the front & right side average indicates not enough wedge
source: http://www.racelinecentral.com/RacingSetupGuide.html
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