Following the tyre pressure information in the current Chassis thread re. Race ARB`s / Springs I thought it worth starting this thread to continue discussions ... http://www.clubgti.com/showthread.php?255778-Race-spring-rates-and-ARB-use Tyres have always been a `close to my heart` and even closer to my wallet subject lol, especially since I started hills / sprints / trackdays some twelve years ago with my `simple` Mk1. This is when I contacted Yokohama Motorsport and took advice relative to the spec of my car, whilst taking the advice I did / still do not really understand all the technicalities involved ... as shown by `some` of my previous posts over the years I`ll start with an `old` post which I had saved and credit the original poster ... identified in the final line. HTH`s The following is a copy of an email sent to me by Alan Meaker, who is the motorsport technical manager at Toyo. I can therefore make no claim to fame regarding it's content. The important point (in my view) is that (within obvious safety parameters) pressure is not what you need to be measuring, but the temperatures are. Adjust the pressures up / down to achieve as close to ideal temps as possible. As the previous post said, test, test, test. Have fun Kim. edit: Just remembered that the 888 is available in hard and soft compounds. The usual choice for a saloon type vehicle would be hard (would burn up too fast on a track) but on the hills, possibly use soft compound, particularly on the back. As you can spin the fronts to warm them up, hard may still be better. The R888 has a semi race construction (very stiff) and a race tread compound. The optimum tread temperature range is between 85C and 95C measured using a probe type pyrometer, and ideally a maximum difference across the tread of 9C. The maximum hot pressure we recommend is 40psi. Camber angles up to 5 degrees are permissible but the final setting will depend on tread temperatures. It is advisable to have as much positive castor as practical as castor induces a beneficial camber change during cornering. I recommend that the tyres be put through 2 heat cycles before hard use. The pressures you use will initially depend on the weight of the car, too little pressure on a heavy car can lead to over deflection of the tyre and subsequent failure. Below are some basic settings: VEHICLE WEIGHT COLD PRESSURE HOT PRESSURE Very Light < 800kg 17 - 22 psi 22 - 29 psi Light 800kg - 1000kg 20 - 26 psi 24 - 32 psi Heavy 1000kg - 1400kg 23 - 27 psi 28 - 40 psi Very Heavy > 1400kg 27 - 35 psi 37 - 40 psi As a tyre gets hotter the pressure increases, this is due to the moisture in the air. The cold pressure you set to achieve a desired hot pressure will depend on the conditions on the day i.e. ambient and track temperature, wet or dry. If the day/track is cold you will need to start with a higher cold pressure as the tyre will not get as hot therefore the pressure increase will not be so great. Hot pressures must be balanced side to side. Once the tyres have cooled you will find that you will have a difference in pressure side to side, if you have been racing on a right hand track you will find the offside pressures will usually be higher than the nearside. Changing hot inflation pressures by small amounts can be used to fine tune handling. Reduce Oversteer Reduce rear pressures or increase front pressures Increase Oversteer Increase rear pressures or reduce front pressures Reduce Understeer Reduce front pressures or increase rear pressures Increase Understeer Increase front pressures or reduce rear pressures Achieving the required tread temperatures will depend again on the conditions on the day i.e. ambient and track temperature, wet or dry. You often here competitors saying “My tyres started to go of towards the end of the race”, this is usually due to the tread getting to hot. The tread temperatures are constantly changing through out a race, hotter when cornering and cooler when on the straights and cooling even more when you are slowing to come into the pits. Therefore the temps you record in the pits will be lower than those during the race. So if you record temperatures within the range given above the probability is the temps will be too high during the race. Increasing your tyre pressures will cause your tread temperatures to increase, more pressure stiffens the tyre’s casing which results in the tread having to do more work resulting in the tread getting hotter. Lowering your pressures will cause them to decrease. Inevitably changing one thing will affect other things, the whole set up of your car is a compromise between anything that is adjustable. Last edited by kimducati : Today at 11:51.
