71 replies to this topic

[chris_uk]

I still think a slight drop in psi to warm the tyre up is the way to go.. Where is scuffs.

[siztenboots]

go up psi , you want to make sure the sidewall is supported so all the force energy goes into the tread block movement and gives you compound heat.

 

generally the more load, the more internal pressure needed

[chris_uk]

At the end of the day the important bit you aim for is the tyre temperatures. So why does is it in the dry we lower the psi to gain heat but you say in the wet you increase psi?

Edited by chris_uk, 03 November 2014 - 01:48 PM.

[PaulCP]

Don't you lower the pressure in the dry to reduce heat. That's why on 888s & ZZRs you aim at 28-30 (although some like to run lower) hot, anything above results in the tyre over heating

Edited by PaulCP, 03 November 2014 - 01:57 PM.

[siztenboots]

I take psi out, to keep the tyre wear more even , rather than overheat the middle tread.

[chris_uk]

are we talking core temp or surface temp?

[chris_uk]

Don't you lower the pressure in the dry to reduce heat. That's why on 888s & ZZRs you aim at 28-30 (although some like to run lower) hot, anything above results in the tyre over heating

Ah fcuk knows .... *throws everything on desk into air* Serioisly tho.. Ive always understood you lower the psi to generate heat.

[siztenboots]

it will overheat the sidewall yes

[chris_uk]

Taken from a random website with no credability. "If we have two identical tires and all other things are equal, the tire with the biggest contact patch will have the most grip on the pavement. And, we know that contact patch size grows as tire pressures decrease, so all we have to do to get more grip is lower tire pressures, right? Well, right up to a point, because we cannot decrease pressures to the point where the tire builds up so much heat that it fails. Heat builds in a tire because the sidewall flexes with each rotation of the tire. When the tire is under load at the bottom touching the pavement, it compresses, then as it rotates and the weight comes off the sidewall relaxes. This compression-relaxation cycle creates heat. That heat dissipates by air passing over the sidewall." So we reduce tyre pressure to increase the footprint and the compressed sidewalls generate heat so lower psi = hotter temps. But is this just on the sidewalls a d not transfered to the contact patch? Id assume so to a degree.

Edited by chris_uk, 03 November 2014 - 02:05 PM.

[Pidgeon]

You're seeking to analyse a complex subject.  Tyre performance is the product of numerous variables.  We can state a certain pressure is ideal for a certain tyre in certain conditions, but it's subjective as well.  Toyo advise 30psi for 888 hot.  Pressures are stated hot as that is when the tyre is performing at its best.  The starting pressure to achieve the optimum pressure is another question again, which becomes more complex when you race and can only set the pressures cold, but need to determine how long the tyre will take to reach an operating temperature and how long will it remain within its operating window.

 

The example you give above may be accurate for a dry track, but will not apply to a wet track, when a reduced contact patch can give superior grip.  The advice I gave was first passed to me by Pete Smith, ex Legends, ex LoT instructor and ex car sharer with a certain John Thorne.

 

You reduce pressure on snow, but that's to maximise traction by allowing the tread to deform to the uneven surface.

[PaulCP]

edit: CBA. If we are being honest with ourselves 99% of us, including me, aren't good enough to exploit the advantages of subtle changes to tyre pressures in wet track conditions. That's why we all have day jobs which are more boring than being a professional racing driver! Just go put and enjoy yourself, sliding about a bit adds to the fun factor

Edited by PaulCP, 03 November 2014 - 03:06 PM.

[chris_uk]

A reduced contact patch is better for wet conditions.. I think your wrong. Also tyres should only be measured by temps not psi. Psi is what we have to control the temps.. But its not what we use to measure a tyres performance.

[chris_uk]

ive done some reading and i think what i was doing was making the assumption that the pressure differences directly controled the temperature differences when what the pressure really does is controls the shape of the tyre which in turn controls the temps.. the higher the pressure the smaller the contact patch becomes which in turn causes a faster heat buildup, so the temp is influenced by the shape of the tyre and the shape of the tyre results in the temperature differences "build up" between cold and hot pressures. so when we go out on track at say 30PSI the tyres start to get hot and increase in temp and with the increase in temp it increases the pressure making the contact patch smaller so we lower the psi in the tyre so when it eventually warms up the contact patch even across the tyre. too little pressure and the middle of the tyre would hardly touch the floor so temp would be too low so the tread would be cool but the sidewalls hot, too much pressure and the middle of the tyre is lifting the sides of the tyre up so temp would be too hot and the sidewalls cool. so theoretically if a tyre ran best at 150c you need to find a pressure that achieve that temp whilst still retaining as much contact patch as possible and this is where other parts of the setup come into play, caster, camber, toe etc. as for a smaller contact patch in the wet, ultimately we know the larger the contact patch the better grip you would have. in the wet having a smaller contact patch will reduce the amount of water that you have to drive through which in tun reduces the chance of aquaplaning, but the reduced contact patch would reduce the lateral grip available to you when cornering. a larger contact patch will mean more water you have to drive though but will give you greater lateral grip when cornering.. so what you want are tyres which can disperse enough water so not to aquaplane whilst giving you as much contact patch as possible. after we have found such a tyre you need to ideally make the tyre temp whatever it should be. probably wrong but will wait someone to explain more.

Edited by chris_uk, 03 November 2014 - 06:07 PM.

[PaulCP]

That's about right and is similar to what P and myself were trying to say (in a summarised direct way) Just don't forget that you can aquaplane whilst cornering so need to decide between contact patch and lateral grip

Edited by PaulCP, 03 November 2014 - 06:22 PM.

[chris_uk]

aquaplaning happens when the amount of water entering a tyres tread pattern is more than the tread pattern can get rid of, so as long as the trtead pattern can get rid of the water the larger contact patch you have the better, the only time the larger contact patch is bad is when the tread cant cope which will cause you to aquaplane. yea? no? i dunno.

[PaulCP]

Yes, so you have to find the optimum contact patch in the wet which is not necessarily the maximum. What you need is the maximum downward mass per sqmm which is not easy to achieve in a lightweight car Do we now agree that you should increase psi in the wet?

Edited by PaulCP, 03 November 2014 - 06:31 PM.

[chris_uk]

yeah..  ..  i was working on the principle that a lower psi would increase the temps (which it does, just not in the right place) and because temps are what controls the tyres ability on track this is what i needed to do.  however i don't fully agree with he reasons P gave, i don't believe that a smaller contact patch will give "superior grip" over a larger one if the larger patch can displace the water it needs.

[Captain Vimes]

Interesting thread. Presumably the same holds true for cold weather as well ie. aim for a 'hot' pressure that enables the tyre to maintain the correct contact patch, which is likely to have a higher cold pressure than on a hot day? So the key question is, what 'hot' pressure should our tyres run at and should we aim for higher/lower load tyres as presumably they'll have different target hot pressures to maintain the correct contact patch?

[Andy_VX]

Thanks for all the replies. The points being discussed were what I was unsure about. In my mind I've always thought that wide tyres aquaplane more therefore a higher pressure would be the way to go. But I suppose it's a fine balance between lateral grip in the corners and aquaplaning on the straights. Im using Goodyear eagle F1's which seem to be good in the wet. I normally run 24/26 psi so will just aim to achieve that as a hot tyre pressure and go from there.

Edited by Andy_VX, 03 November 2014 - 08:51 PM.

[PaulCP]

Recommended hot pressures for 888s and ZZRs are 28-30 psi and is covered on their web sites. Both advise against going into the low to mid 20s Can't comment on other tyres