Track day tyre pressure advice

[820]

I am planning to do a track evening at Brands Hatch later this month but not sure what to set the cold tyre pressures to.
General spec is my old Vitesse, total weight 1200-1250kg most of the weight is to the front.
So I have gone for front tyres Dunlop DZ03G hard compound, rears Dunlop DO1J soft compound.
What about 30psi front, 28psi rear.
any experience with these or input welcome, thanks
Jim

[indyz12]

id go much lower for cold temp. id say warm them up and then set them at about 25-28 max.
225/35/18 on a pug 206 pushing 230 brake, 1000kg (stripped then caged) and we had pressures of 22psi all round. we ran toyo 888

[ChasR]

A good starting point is to ensure the tyres are at the book figures when they are hot and move from there.

[820]

Thank you for the replies indyz12 and ChasR.
How much pressure increase can I expect from the cold tyre to a tyre that has done say 4 or 5 laps, looking at your figures indyz12 I should expect 2 to 6 psi increase, this sounds a likely figure depending on ambient temps and how hard they are worked I guess.
These are 215/45R17, the standard pressures are 34psi front and 28 psi rear

[marcmoss]

Two options

Full them with nitrogen and then they will stay at the same pressure with increased usage and heat

Or

Run them at a lower pressure and probs 6-8 pounds lower than normal and then the heat will bring the pressures up to their correct operating temps.

Whatever you do don't run them at normal pressures and then remove pressure when they get hot, it's a fatal mistake that so many people make. The sidewalls will go super soft.

[darrenh]

agree with the others, usually see about 10-12psi increase after coming in.

[ChasR]

May 7, 2015 22:18:16 GMT marcmoss said:

Two options

Full them with nitrogen and then they will stay at the same pressure with increased usage and heat

Or

Run them at a lower pressure and probs 6-8 pounds lower than normal and then the heat will bring the pressures up to their correct operating temps.

Whatever you do don't run them at normal pressures and then remove pressure when they get hot, it's a fatal mistake that so many people make. The sidewalls will go super soft.

I've had two garages do that on two sets of racing tyres I have had. I used to run my 205 GTi with around 22PSi in them from cold and the NS2-Rs on the Escort with 24PSI. I may go lower in the Escort truth be told but we shall see.

[820]

I don't have access to Nitrogen so looking at your experience above, as the first few laps will be fairly tame I will go 26 front and 24 rear, come in and check them immediately then base any adjustments on the increase.
Thanks for the advice that is a big help, I will update this thread with the results.

[vitesseefi]

May 7, 2015 22:18:16 GMT marcmoss said:

Two options

Full them with nitrogen and then they will stay at the same pressure with increased usage and heat

Sorry, no. Ideal gas law applies to nitrogen too, so it will expand when heated just like any other gas and increase the pressure.

This debunks some of the nitrogen hype
powertank.com/truth.or.hype/

Nick

[ChasR]

Even if Nitrogen does work it is useless if you heave leaky rims. Rim sealer can help reduce this but it only works half of the time IME.

[docjock]

May 8, 2015 22:29:40 GMT vitesseefi said:

May 7, 2015 22:18:16 GMT marcmoss said:

Two options

Full them with nitrogen and then they will stay at the same pressure with increased usage and heat

Sorry, no. Ideal gas law applies to nitrogen too, so it will expand when heated just like any other gas and increase the pressure.

This debunks some of the nitrogen hype
powertank.com/truth.or.hype/

Nick

Totally agree. (plus, air is 78% nitrogen anyway )

OP, just keep checking and adjusting temps after each session.

If unsure of what hot temps to use, I'd do a couple of warmup laps, come in and check temps. Use those numbers as your baseline.

[docjock]

Also, if you're running semi-slicks, make sure your not going to have oil pick-up problems if you don't have a baffled sump.

(apologies if I'm teaching granny to suck eggs)

[820]

Not at all docjock, all advice is appreciated and taken on board.
The sump does have a basic baffle set up from the factory but you reminded me that last time I had this car on a track was 7 or 8 years ago at Castle Coombe and there was a problem with oil filling the breather catch tank which was mounted low in the engine bay with no return, it filled quickly and the only place for the oil to go was out the vent and sprayed onto the left front brake. I only managed a few laps and the day was over.
The tank is now mounted high in the engine bay level with the cylinder head but now with a gravity return to the sump, this has not been tested and will need monitoring on the day to.
So definitely 3 or 4 laps and in to check the oil return and tyre pressures as well as being aware of the new custom front brake set up.
Thanks
Jim

[820]

Ordered myself a new analogue tyre pressure gauge with a clear easy to read face, 0-60psi, only a cheapy off ebay so didnt expect it to be spot on when checked against a calibrated workshop gauge but it reads 2psi low at 29psi! so checked other gauges I have and found
both my PCL inflators read 29psi
A very old slider type read spot on at 29psi
Ebay rubbish 27psi
Electric pump, new supplied in a German car 24.5psi, the worst of them all.

After looking into it a bit more I need to get myself a Halfords £10 digital gauge, came out best in a group test of 10 cheap digital gauges, all accurate to within 1psi or stick with my old slider type that has been knocking about in my toolboxes for god knows how many years, still reads spot on.

This week I have learned, it is worth checking any gauges, footpumps or petrol stations gauges you are using to set your pressures, chances are they are wrong and probably by quite a lot.

[edvaldez]

It fully depends on how hard you are going to drive, but that said i think you may need to start quite a bit lower, 18-22 psi is optimal for road tyres on a car with the sort of weight yours is.
                             front
I used to run   16.5        17      on my cinquecento, although this was the setup for Cadwell park and the pressures would change at different tracks.

                      16          16.5
                            rear

[820]

Cheers edvaldez, I did the Track evening although I forgot to check the pressures immediately after each session I got these readings
Tyre pressures went from front 25psi to 34ish, rears 26 to 34ish, so from that what do you reckon next time, start with front 24psi and rears the same or 23psi?

[edvaldez]

Well they have gained 9 psi from and eight rear so I'd drop to 19 or 20 front and 1/2 - 1 psi higher rear.

As you start pushing harder you might start noticing one end being slightly livelier than the other and you have the option of either dropping pressures on that axle or raising them on the other. Bear in mind .5 psi can make a massive difference in grip etc.

[820]

I might not go quite that low yet, maybe somewhere between then, F 22psi R 21psi, as the car felt really good tyre wise, maybe a bit to much understeer into Druids but that could be me, the back of the car felt perfect, and looking at all the track day pictures taken of all cars I wonder how much front tyre sidewall deformation is correct, mine looked good yet some others were pulling the tyre out of shape.
Aiming to go again August/September time so will be a bit better prepared this time, thanks