Tyre pressures

[Shifu]

Yes I was of the same understanding as you until I went through the school of hard knocks & was educated by blokes like Craig White at Bridgestone and basically the larger the contact patch is the harder it is to generate heat the smaller the contact patch the more friction is concentrated in one spot measuring psi is more accurate as opposed to temp mainly because you are only measuring the surface temp and not the carcase you would be looking for an 70-90deg off track but with places like PI being an left hand track you could get 30deg difference from one side of the tyre to the other I have been racing on Bridgestone's slicks now after using Pirellis Dunlops and Michies and my rear tyre pressure's are down to 18psi cold and do 1.40's around EC. I race with Mick from Madaz and reckon he would be of the same opinion Ill ask him next time I see him.

Sorry mate but you are confusing things here. The heat generated at the contact patch is only marginal in comparison to heat generated inside the tire due to internal friction. The cold tears would not occur otherwise. And the size of the patch is only a concern as far as the tire wear goes. That is why in Moto GP it is always a problem. They can not afford large contact patch that makes the tyre last longer because of overheating so it is a fine line between keeping the temperature within the optimum range and having a tyre last long enough. (I ommited here the influence of different compound hardness and how it affect the handling as to not complicate it any further)
You contradicting yourself by saying that your pressure goes down to 18 psi (that makes for a massive contact patch ) and then saying that the larger the patch the harder it is to generate heat.
The bottom line is that the tire can only work properly (as designed) within certaing teperature range and the pressure is the main factor that affects it. So the only way to determine correct pressure for a given tyre on a given day and track is to monitor its temperature. Maybe that is why the pyrometer is the most important instrument when the teams are testing tyres. Ask your mate from Bridgestone or do some research.

Do you really think 38 - 44 psi is a good suggestion? Cheers.

[pan]

I say go 28 Rob

[Ward P]

Make sure you a decent gauge, Every one at the track seems to be different.

[06BUSA]

My heads spinning from all that reading off pressures, patches, layers lol. I had none off that when I flew to Melbourne, hired a car, drove to the island, hired a bike from the Californian Bike School and rode all day:-) even when another guy crashed his hire bike they gave him another one lol. All too easy!

[Driller]

Ok don't want to confuse things What you say about internal heat generated is right about 80% the rest is tyre surface contact bottom line is you want is a 4-6psi increase from cold to hot off track regardless of what pressure you start so if you get a 7-8psi increase let a couple out if your only getting 2-3psi increase put a couple in with this simple rule you will get the most out of your day and gear my example of 18psi (tyre specific design) and lap times was an example of where you need to be to get the most out of slicks. And theres one really important factor your not mentioning ( The Rider input) that's why I started of asking approximate lap times because if speed is down and not generating internal heat all you have is this big cold contact patch and when the rider gets hungry on the throttle coming out of corners making up for low corner speed tearing occurs as for suggesting 38psi this is only a ball park but in no way would I regard this as bad advise this is for a (Road specific tyre) (Not a race tyre) and a average rider and if at that pressure your over heating the road tyre on the track maybe its time to look for a different tyre.( I have been researching at race tracks for the last 3 years. ) Would be interested to know where your getting all your information from.

[aussiemonster]

For a road rider, on road tyres, another way to look at it is this.
Tyre pressure increases with heat (hot air expands), on road tyres you're looking to drop the pressure enough so that when it heats up, the pressure is the roughly same as your normal road riding pressure. Depending on how hard you ride, this could be 3 to 5 psi front and rear or maybe a little more.
You then need to measure the pressure ASAP when you come in at the end of the session to check what the pressure is when hot and adjust the pressure as required to be similar to your road riding pressures.

The advantage of this (for a road rider) is that the bike and tyres will feel much the same as when you're riding on the road. It's what I've worked to when I've gone to the track and always provides consistent feel and no surprises.

It's also a safe way to start, and you can then play around with the pressures more as you become more experienced if you want to.

[captainrob]

For a road rider, on road tyres, another way to look at it is this.
Tyre pressure increases with heat (hot air expands), on road tyres you're looking to drop the pressure enough so that when it heats up, the pressure is the roughly same as your normal road riding pressure. Depending on how hard you ride, this could be 3 to 5 psi front and rear or maybe a little more.
You then need to measure the pressure ASAP when you come in at the end of the session to check what the pressure is when hot and adjust the pressure as required to be similar to your road riding pressures.

The advantage of this (for a road rider) is that the bike and tyres will feel much the same as when you're riding on the road. It's what I've worked to when I've gone to the track and always provides consistent feel and no surprises.

It's also a safe way to start, and you can then play around with the pressures more as you become more experienced if you want to.

I went with 30/30 and they came in after the first session with 32/34. So I brought them back to 30/30 and never touched them again. I think you're right, and I will play around next time when I can get some lap times to compare.