Tyre pressure/temperatures??

[dragsta]

I do a lot of trackdays at barbagallo and AHG running Michelin pilot powers, while they are a fantastic road/track tyre, Im finding as my pace has increased over time , Im staring to slide and spin up the tyres..

My question is- What is the optimum tyre pressure for track work,
and what should the tyre temperature be after be after doing hard laps?????
I have spent many hours searching for correct advice and so far all I have is at best, peoples opinons or second hand advice..

Im wanting REAL advice PLEASE...

[g0zer]

i only use pilot powers for the rear tyre not the front, since i dont like it when the front is sliding out from under me. i dont know if its optimum but my cold pressures for the rear are as follows:

31psi for rain or very cold temperatures and street riding.
32-33psi for a cold track
33-35psi for a warm to hot track

i am not sure what the optimum tyre temperature should be, but i have been told to target a 5-6psi difference between cold and hot pressure.

ive run them as low as 28psi and find they shred badly and traction can suddenly vanish after a couple of laps. I find running them above 36psi and they start sliding around all over the place.

[ENVEE 2]

Depends on a lot of factors dragsta...ambient temp, track temp, laptimes, riding style, suspension set up, warmers / no warmers

a good starting point with most brands is R 30psi F 30psi cold

It really is a lot of trial and error, and finding what works and feels right for you.

have you dialled your sags and ball parked your suspension? "cue shameless marty MOOSE plug" PM him for suspension set up and tuning

[Stoneville]

H ha Envee, was going to suggest that Chris go see Marty Moose to set his suspension and try that first

[Ausinanas]

[quote=g0zer;964879]i only use pilot powers for the rear tyre not the front, since i dont like it when the front is sliding out from under me. i dont know if its optimum but my cold pressures for the rear are as follows:

31psi for rain or very cold temperatures and street riding.
32-33psi for a cold track
33-35psi for a warm to hot track


I'm no expert but going off what i've read in FAST BIKES

shouldn't it be the other way round ?

31psi for hot conditions and building up psi for colder wheather???

with maybe 1psi more in the front than the rear??

they recommend 30psi front and 29 psi Rear and that was for a guy in Africa wit temps of about 19'c

[g0zer]

Originally Posted by Ausinanas

I'm no expert but going off what i've read in FAST BIKES

shouldn't it be the other way round ?

31psi for hot conditions and building up psi for colder wheather???

with maybe 1psi more in the front than the rear??

there is an ideal temperature where the tyre compound will be at its stickiest

there is an ideal pressure where tyres shape and level of carcass flex is perfect

when ambient/track surface temperatures are not ideal or water is present (which has an incredible ability to suck heat out of a tyre) then anything you do will be a compromise

if tyre pressure is too low its shape will be sacrificed

if tyre temperature is too low it wont stick, if too high it will melt also not sticking

when its cold or raining i drop the pressure to increase carcass flex which increases the tyres temperature

when its hot, i increase the pressure to reduce carcass flex, to reduce the tyre temperature

thats my thinking anyway, it is my understanding that all of a tyres heat build up comes from carcass flex that occurs as a tyre with weight pressing down on it rolls down the road at speed, at least until its hot and sticky enough to start generating heat from friction that only comes when banked over (without sliding off the road), accelerating hard without spinning or braking hard without sliding.

edit: if you want to maximise milage of your tyres for street riding and not square them off so fast then yes, lower pressure in summer and higher in winter. but we are talking about sliding bikes around tearing tyres up not poontling along the river worrying about how many miles we can get out of them

[Ausinanas]

ya could be right but anytime it gets mentioned they always set low psi for warm or hot conditions and have also said that the only time they would use high psi as in around the 40 mark would be in winter in the uk which is fooking cold

[g0zer]

YouTube - yzf R1 following ducati sports classic

[Ausinanas]

yeah cold n wet so more psi in the tire..

if you were wanting to keep the shape of the tire'? and better Grip
wouldn't it make more sense to help them if it was cold by putting in more psi as the tire won't get as hot due too the cold and the air inside won't expand as much ..?
but when its hot less psi as there is more heat which expands the air inside the tire giving the tire the shape it should be ..

[Ausinanas]

nice vid and roads mate looks like ya nearly lost the camera though when it came loose and pointed in the sky.. ..

[g0zer]

Originally Posted by Ausinanas

nice vid and roads mate looks like ya nearly lost the camera though when it came loose and pointed in the sky.. ..

i wouldnt want to try that or braking down hard in the rain at 40psi

[ENVEE 2]

Originally Posted by g0zer

i wouldnt want to try that or braking down hard in the rain at 40psi

but based on your cold set up psi figures youd run around the track with 40+psi on a hot day?
any wonder youre losing grip after a few laps?
with youre overinflated tyres you are MINIMIZING your contact patch. less contact patch= less grip= more spinning= more surface heat= greasier rubber=less resistance to tearing=more wear..

[smeghead]

On Pirelli Diablo Supercorsas the accepted optimum pressure is 28psi f & r hot (track).

Race 3 as it woz cold & a bit wet I started the day at F33 & R31 & worked my way down as the day/track warmed. I did a PB with this (relatively) poor level of grip (I love these Pirellis).

In the cold & wet the tyre temp gradiant is less so the pit start pressure is higher to get to optimum track pressure, in the heat it's the opposite. Also in the wet higher pressure keep the tread open to clear the water.

In the cold & wet, when grip is a lot less, getting feel from the bike is more important so instead of dropping pressure to get more temp from carcase flex try softening the suspension a bit. If you can read what the bike is telling you about the level of grip then everyone wins & everyone is safer.

[g0zer]

Originally Posted by smeghead

On Pirelli Diablo Supercorsas the accepted optimum pressure is 28psi f & r hot (track).

Race 3 as it woz cold & a bit wet I started the day at F33 & R31 & worked my way down as the day/track warmed. I did a PB with this (relatively) poor level of grip (I love these Pirellis).

In the cold & wet the tyre temp gradiant is less so the pit start pressure is higher to get to optimum track pressure, in the heat it's the opposite. Also in the wet higher pressure keep the tread open to clear the water.

In the cold & wet, when grip is a lot less, getting feel from the bike is more important so instead of dropping pressure to get more temp from carcase flex try softening the suspension a bit. If you can read what the bike is telling you about the level of grip then everyone wins & everyone is safer.

imho there is risk of confusion between pressures for track tyres and street tyres.

a pilot power (or any street tyre) is no where near the stickiness of a diablo supercorsa.

a sticky race tyre is designed to withstand constant abuse. Its never not accelerating flat out, spinning as fast as the bike can go, braking to the point of skidding or cornering to the point of sliding.

the faster you want to go the stickier the tyre needs to be and somewhat counter intuitively a softer compound tyre is harder to put heat into ie: it needs that abuse to achieve operating temperature.

a street tyre like the pilot power is designed to be sticky at much lower temperatures than a DOT race tyre and come up to operating temperature under conditions much less abusive than a race track.

finally i dont disagree with you envee, scroll up you will see i dont run higher than 35psi in a rear pilot power (and thats for a 38C track day). Ive not run 40psi in a tyre since i was riding 250's and a complete n00b although i thoroughly recommend learning on 250's with BT45's or similar at 42psi

edit: i suppose the best advice is if dragsta has found the limit of pilot powers, it may be time to start rolling on something designed for the track. although somewhere in twist of the wrist keith code advocates learning to ride fast and to slide a bike around on less sticky tyres. its a lot easier and safer to practice sliding at 40 degrees of lean angle than at 50.

[Spock]

Originally Posted by g0zer

i 31psi for rain or very cold temperatures and street riding.

You want more pressure, not less, on a wet road.

What works in the dry (ie. lower pressure = more grip) doesn't work in the wet.

The smaller contact patch and greater force exerted on a smaller contact patch will 'squeegee' water away from the contact patch more effectively and reduce the chance of aquaplaning (sliding).

This is why narrower tyred bikes are less likely to slip and slide on wet roads than wide-tyred bikes.

[g0zer]

i cannot disagree with anything anyone has said, it all makes sense. but i also feel that my wet weather traction is better at lower pressures than high.

well, i will repost the vid and let my wet weather lean angle and 3rd gear power wheelies in the wet be seen..

[Spock]

Originally Posted by smeghead

On Pirelli Diablo Supercorsas the accepted optimum pressure is 28psi f & r hot (track).

You cannot use hot tyre pressures unless you also have an electronic pyrometer (surface temperature gauge).

As an example, a 'hot' tyre with 28psi could have started off with 10psi cold but equally so, could have just as easily started off with 14psi. So 'hot' pressures are meaningless.

If you don't have a pyrometer - and know what the ideal opertaing temperature for your brand of tyres is - then you'd be better off (as gozer said) looking at the pressure rise from cold to hot.

(I'm no racer but I am an engineer and I understand Boyles laws! )

[ENVEE 2]

Originally Posted by Spock

looking at the pressure rise from hot to cold.

You mean the pressure rise from COLD TO HOT dont you?


Thats where the trial and error comes into things.. and all the factors come in to play(track temp,ambient temp, riding style etc etc)

Im sure what smeggy was saying is, he knows where his tyres work/feel best at HOT psi, and sets(ballparks) his COLD psi accordingly, from knowing how much pressure differential COLD TO HOT he usually gets..
(for my riding style and current laptimes 3-6psi depending on track temp)

Im sure a Michelin pilot power is not that bad a tyre for the track, and a good rider could lap in low 60's easily on them...Set up suspension(sags, etc), trial and error with your pressures till you find what you feel best on, warm up tyres appropriatly before ripping into hot laps, understand what your bike is saying to you around the track, dont push and crash, enjoy

[Spock]

Originally Posted by ENVEE 2

You mean the pressure rise from COLD TO HOT dont you?

Yes of course
- have corrected my post.

[g0zer]

Originally Posted by ENVEE 2

(for my riding style and current laptimes 3-6psi depending on track temp)

Difference is also more useful for adjusting pressures, if you measure them before you roll out onto a track and measure them when you roll off and record a pressure change of 7PSI and inspect the wear pattern.. then you can increase pressure say +2psi and again measure cold to hot difference. Ultimately using differences is more accurate since a cold pressure value is affected by ambient temperatures and if you are experiementing with pressures at a track day then there will also be residual heat ect.