- My model of MX-5 is: NC MK3.0
- I’m based near: Worcester
- I’m looking for technical help or recommendations on: Trackday tyre pressures
Lets try again. Finger trouble when typing the question! Have changed to Toyo Proxes R888R 215/45R17 on OZ Allegerita rims for trackdays, hillclimbs and sprints. I read that they run best with higher than regular pressures. Car has adjustable coilovers, uprated ARB and links as well as a BBRGTi normally aspirated tweak. However, the settings are basically fast road. Advise on optimum pressures would be appreciated.
I’m interested to know where did you read that ??
Hi,
I may be comparing apples with pears as that claim was on both a Lotus and Piston Head forum. It related to lighter cars and I compared it with my experiences with my Westfield SE on Davanti Protoura and Avon trackday boots. The hot run pressures were two or three psi lower than those quoted for the Toyo. I was surprised and confused as the Toyo’s are VERY stiff. I appreciate that the weight of the car has a significant impact and was simply proposing to interpolate figures for my NC. To contradict the forum claims, an extract from the official Toyo R888 blurb quotes the following;-
*“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 too hot.”*
I’m simply trying to establish a practical starting point with the Toyo’s before attempting to bin it at Castle Combe! We will be using Nitrogen to gas the tryes.
Bona fides pic of my Westfield attached.
It will do that even if the air is dry. Gay-Lussac’s law. In direct relationship to the temperature in Kelvin (and don’t forget to add one bar to the pressure for the calculation because it’s total pressure you want not the pressure above ambient which is what you see on a tyre pressure gauge). I wouldn’t think water in the air would make any difference unless there was liquid in there to start with.
I have no opinion worth listening to on correct pressures for the track, but if for example you wanted the tyres to be at normal road pressures when they got hot on track, you would need to start a bit lower so they arrive at the correct pressure when up to track temperature. I’ve seen people check the pressures when they come in after the first run and adjust the pressures so they can get it right.
I’m a gentle track driver using road tyres so I set the cold pressures on my ND by the book and leave it at that. Obviously they must end up a bit harder than they would on the road. In fact I’ll be on a track this week so I’ll check this time and see what they go up to, for my own interest.
Understood. Those words came from the Toyo tyre specialist, not me! I had Boyles Law in mind…. did Thermodynamics in Marine Engineering a milllion years ago! The trouble with many track day tyres (of those I’’ve used) is that they have very stiff construction and do not respond in the same manner as regular road use products. Under inflated and they are useless. Over inflated and they soon cook. Ergo, the request for wisdom from others.
Got it.
No wisdom here but Google AI digs up some familiar looking stuff and actually mentions the Toyo tyre and also suggests optimum tread temperature on track for that tyre lies between 80-100C. I know my Yokohama V105’s (also a stiff sidewall tyre) don’t get anywhere near that but I am not a driving god, Let’s say you want to run at 85C. What “hot” pressure does that imply?
Just using good old Gay-Lussac, if I set my tyres at 29psi when they are at 20C, if I heat them up to 85C they will be at 38.65psi.
What would you like the “hot” pressure to be? Say 34psi using your Toyo man’s table.
So as a starting point you might guess that the ‘cold’ pressure needs to be 4-5psi lower to get the tyres to 34psi and 85C. That seems fairly consistent with some of the advice I have seen.
I think if I wanted to experiment with this I would get an infra-red thermometer.
I’d guess that I get my tyres up to about 50C. That implies they will be at 33-34psi if they start off at 29psi/20C. That more or less explains why the car feels fine when I’ve done a couple of my usual ‘slow’ laps.
This is not advice. Just a thought experiment!
I am using a spreadsheet for this, but in this range a 10C increase adds about 1.5psi of pressure as a rule of thumb.
Thanks for the info. Suffering a slight delay as according to Demon Tweeks, the new OZ rims have yet to be made!! I do have an IR thermometer (somewhere)… I feel a garage rummage coming on! Thanks again.
I said I would do some investigation…unfortunately a couple of weeks ago on the track outing I left it until the afternoon and it rained stair rods for the rest of the day so I didn’t think it was worth checking the pressures at the end of the sessions.
I used exactly 29psi (set cold) and it was fine, wet and dry, for my 7/10ths track driving.
