Tyre pressures for track.

[Nuddy]

NC MX-5 Hankook Ventus TD Z221 215/45R17 on 17 x 8 rims

I checked the tyre pressures cold as they came from the previous owner and found them to be 19 psi
I left them at that and found they went up to 24 psi hot.
The grip was awesome when hot, not so much when cold.
I am told 24 hot is too low.
What pressure do others recommend.

Also I am doing a hillclimb on the weekend.
The Hankooks will not get up to temperature on a hillclimb so I will run the Michelin Pilot Sport tyres on the stock rims.
Any thoughts on cold pressures for those?

[Red_Bullet]

Nope, never used those tyres, but you are way lower than my NT01's. FWIW. I usually start around 25 PSI cold, and end up letting some air out to end up around 28-29 hot for running sprints.

[Magpie]

I would suggest doing tyres temps to get the correct pressures, however it sounds like you will not have time to do this.

Running less pressure will heat the tyres up faster due to the additional flex, so maybe for the hill climb run a little less than normal.

[Nuddy]

I was trying quite hard to warm the tyres on the warm up lap but still had 2 spins at SMSP and 3 at Wakefield, all on the first timed lap due to cold tyres.
There is no way they would be any use at a hillclimb.
I will use the Michelins and thinking of starting at 30 cold.
As for the Hankooks, Guess I'll start at 25 cold and go from there.
If I can get hold of a tyre pyrometer what temp should I be looking for?

[Magpie]

4 types

1. Non contact - infra red type, however this only measures the surface temperature. Cheap options are available however one with a wide range can also be used on brake rotors/calipers.
   Example https://www.jaycar.com.au/non-contact-thermometer-with-dual-laser-targeting/p/QM7221
2. Contact - takes the internal temp of the tread of the tyre
   Example http://www.longacreracing.com/products.aspx?itemid=1721&prodid=11677&pagetitle=Temperature+Compensated+Digital+Tire+Pressure+Gauge
3. Real time - very expensive due to the number of sensor, motorsport items and work best with data logging
   http://www.izzeracing.com/products/infrared-temperature-sensors.html
4. Thermal imaging - again not the cheapest
   http://www.thermalimagingcamerasaustralia.com.au/

Helpful article
http://949racing.com/using-a-tire-pyrometer-949-Racing.aspx

[Nuddy]

Thanks Magpie, great article. I will get a contact pyrometer.
I went to the Hankook website but could not find any info on temp or pressure for their tyres.
I will aim for the 150 to 190 degrees, assuming Degrees F.

[Dan]

32 hot is what I ran the Z221's on. They went up to there from around 24-26 cold depending on what side they were on and the track.

For street tyres I'd probably run 37-38 hot.

I assume the reason the track tyres were 19 PSI was because they hadn't been on the car for over 6 months not because I'd run them at that pressure.

Regarding a tyre pyrometer get one of the ones magpie linked which you stick in the tyre as the surface ones aren't really accurate.

I looked more for tyre temperature distribution on the (with the expectation that the inside would be slightly less) but Hankook publish optimum temps for their tyre on the website which you can use to judge them if you want
http://m.hankooktire.com/content/dam/ht ... ersion.pdf

Look at the wear on the tyres after you are finished with the semis and judge if the camber is too much for you, personally I got a good wear distribution across the tyre but if you aren't as aggressive on the tyres as me it is possible that less camber will work for you.

Sent from my Pixel XL using Tapatalk

[Nuddy]

I got a digital pyrometer and probe from Jaycar, $110. Reads to 1 decimal place.

Didn't get to use it at the hillclimb as the tyres were cold to touch. Less than 30 degrees C.

[Magpie]

When asking other people about what temps/pressures their tyres are always ask what size rims they are using.

For example a 205/50/15 on 6.5" rims will require more pressure hot than the same tyre on a 8" rim.

[Nuddy]

I've learned a lot from this thread. Mainly I asked the wrong question in the first place.
After reading: http://949racing.com/using-a-tire-pyrom ... acing.aspx i realise that pressure is just a means of achieving the required temperature.
And more important than the actual temperature is the temperature gradient across the tyre surface.
Optimal pressure is likely to be different for each wheel on the car and different for different tracks.
Cold pressure gives a starting point, then hot pressure will be adjusted to give the best temperature gradient for each tyre.
This will vary with different tracks and with the same track on different days and even throughout the day.
949 Racing - Supermiata: "What I am trying to indicate here is that no one can tell you what optimum pressure is so don't ask. Get a pyrometer, learn how to use it and become your own expert."

[Dan]

The problem with that approach is that if you don't drive the car aggressively enough you won't get it up to temp, then you'll lower the pressures and end up with a car that doesn't perform as well.

This is basically the same thing that a lot of people do when they soften the rear sway bars or coilovers because the car "oversteers", a lot of the time the issue is the driver not the car and by softening the rear you end up with a car you gimped trying to make it faster not realising you are actually making it slower.

The only thing I'd modify based on pyrometer readings would be camber but even then you can just 'read' the tyre and see where it's being worn to make a decision on settings, the camber settings on the car were basically come to in this way from Daniel Deckers assessing the tyre wear to determine if it had the right settings which were basically validated by me looking at pyrometer readings.

To give you a story about setup I went through a similar exercise with sway bars when I first got the MX5 and I was doing 12's with Coilovers/sway bars/headers. Daniel Deckers set the car up to with settings which almost everyone in the club said was "wrong". I persisted in driving with his settings as I knew that Daniel knew his sh*t being one of if not the fastest NC driver in NSW and eventually ended up in the 9's without changing settings so in the end he was right but it took me learning to drive the car before I realised the potential of the settings.

The car is setup to go pretty fast already, if I was you I'd keep the car like it is, stick with somewhere around 32psi hot like most people are at on most brands of semis and is what your car did its times on and when you are doing quick times then play with pressures to make tenths or hundredths of a second.

[Nuddy]

I certainly won't be moving away from Daniel Deckers' settings.