Andy Holden

Can anyone give me any guidance about the correct tyre pressure for slicks fitted on 16" wheels?

I imagine it is less than road tyres used for the track, but I'm guessing!

Thanks

Andy

Tim W

iTrader: (1)

Right, with Darren Soothill's assistance try the following:-

Start with 30 psi front and rear, assuming 18/62-16 Tyre (18=185mm tread width, 62=620mm diameter, 16 = wheel size) this tyre is designed for an optimum rim width of 7" (ie standard UK MY98 on wheel) when on this rim size and inflated to 30 psi the effective tread width becomes 205mm.

To check the best tyre pressures with slicks on a particular track a tyre pyrometer is needed. In another words you need to check the temperature accross the tread after the tyre is warmed up.

If the centre of the tyre is cooler than the edges the pressure needs to be increased, if the edges are colder than the centre then the pressure needs to be decreased.

There will be a difference between the inside and outside edges, the centre tread temperature should be between them.

Hope this has completely confused you

Andy Holden

Confused? Certainly

The tyres are 18/62-16's fitted to 98MY wheels. So if I follow you correctly, I do 30psi all round, then using my carefully calibrated tyre pyrometer (my finger) if the middle of the tyre is cooler than the outers, I need more pressure?

Easy

P.S. Who is Darren Soothill, I've heard his name mentioned before?

Tim W

iTrader: (1)

Careful Andy your carefully calibrated pyrometer may get singed but in essence you've got it!

The tyres get very hot, plus ideally you need to measure the temperature just below the surface, with a probe. And pyrometers ain't cheap!

On a track day your pit crew will need to have fire proof fingers, or a digital thermometre of some sort. Try not to get runover lying in the pit lane checking the rear tyre temperatures .

The tyre temperatures will equalise very quickly after coming off the circuit, particularly after a cool down lap, work fast!

Darren BTW is the person sitting next to me who has just sold me his old road tyres! He has an Sti V Type R with a full complement of Scoobysport accessories, he seems to spend more time (and money) on the track than on the road!

[This message has been edited by Tim W (edited 20-06-99).]

Tim W

iTrader: (1)

Before you ask Darren does have a set of road legal tyres on another set of wheels...

Darren Soothill

Andy

Which slicks and compound have you got and how much did you pay for them?

I am using Michelin S4's as they are a hard compund as one of my aims was for them to last which they seem to be doing. At Brands Hatch they where excellent and getting up to temperature quite easily and providing alot of grip.

At Wroughton they didnt work anywhere near as well I think this was a combination of the surface and the amount of dust/grit around that meant the car was sliding alot more but this was excellent fun!

My mainreason for buying the slicks is to save the road tyres I can get these particular tyres for £50 a corner +Vat which means they are 1/2-1/3 of the price of a set of road tyres and they seem to be on for lasting about 4 trackdays which means they will be lasting about twice the length of time of the road tyres.

The warning on Tyre temperatures is quite a serious one as they can get towards the 200 DegreesF area.

andymac

How come slicks appear to be cheaper than road tyres ? Other than the obvious-not in wet weather... What's the catch ? Is there more stress on the cars components because of the increased grip ?

cheers

Andy

Andy Holden

Thanks for the tips.

I spent ages trying to find out where to get slicks with not much success. Following a lead from a guy who used to stage an Escort, I contacted Motorsport Tyres and eventually ended up with 4 part used Michelin S7E's, with about 3mm of tread left on them - paid £25 each plus VAT. No idea what compound - is it marked on them? I'm a bit wary of part worn tyres so I will be very careful with them at first until I am confident they are all ok! I am told they were off a Renault Spyder.

Like Darren I'm trying to save my road tyres. The best price I could get for new slicks (again Michelins) was £70 inc VAT. Any other quotes I got were more than road tyres - defeating the object! I'd be interested in the £50 ones for next summer - unless for some reason it doesn't rain at Donnington in November!

Darren Soothill

S7B is the compound this is a soft Medium compund circuit slick Circuit slicks go from S6 soft compund up to S9 hard compound. The S4 is a Hard Compound Rally Tyre. Rally Tyres go from S0 through to S4. I am not quite sure of the differences between the tyres though other than the advice I was given which was that the Hard compound Rally tyre is about equivlent to a Medium compund Circuit Tyre.

The S4's that I have can be got for £50+vat from Fairfield Motorsport 01656 725000 they also do alow of part one tyres and moulded slicks as well. They also only charge £2.5 a tyre for next day delivery!

Generally it is thought that unless a car has had the suspension modified then the standard suspension cannot cope with the grip produced from the slicks and this can lead to the car getting up on two wheels.

Also unless you have a pretty good set of brakes you may find that that the brakes have overheated before the slicks have got upto temperature.

You also have to be careful the first couple of laps out as well as Slicks take time to warm up and again if you havent got a car with a good suspension setup then it will take you longer to get the tyres upto temperature as you cant work them as hard.

For a car on Standard suspension it is not reccommended to got to a full slick but to goto a moulded tyre which wont have the ultimate grip of the slick but will give you suspension a chance!

I know that Pete had some moulded slicks in at one point I dont know if he has sold them. But the other option is to look at what is known as an R Rated tyre examples of these are the Yokohama A032R this tyres is road legal so you could drive on it too the circuit but if you look at the tyre you will get the idea.

Another Tyre I have had suggested is the Pirelli P Zero C but I understand this tyre is quite hard to get hold of but talking to David Yu of Skyline/Evo Fame he was going to get some of these next for his Skyline as if you saw the State of his S02's which had lost the tread from the inside edge you would understand why and I am not talking about wearing out here the tread blocks had just gone as though they had been cut off!

Darren

Andy Holden

Well I've now used the slicks mentioned above and started at 30psi all round (at Oulton Park yesterday).

At this pressure the tyres were not getting up to anything like the right temperature and the back of the car felt quite nervous. Its also the first time I've ever got wheelspin at 40 ish mph in the Scoob, accelerating down the dip before the start/finish straight.

I tried 26psi all round in the afternoon and it was much better. The more I pushed it, the better the grip got - but as Darren said, my brakes weren't really up to the job.

Still, it was a nice feeling outcornering a heavily modified NSX, and at £25 a corner, can't complain!

Darren Soothill

I was up at Cadwell on Thursday and spent alot of time in the car on the track and was running the fronts at 30 PSI and the rears at 28 and the car was running fine and the slicks where getting very sticky although it was a hot day. In fact they got so hot that when you brought the car in off the track and stopped then came to drive off I was taking chunks of Tarmac with me as I was melting the tarmac under the wheels! The only tyre that wasnt getting upto temperature was the drivers side rear but then that is to be expected as that tyre doesnt get much work!

The only real problem I had was at the end of the day when I wore out the Brembo brake pads these pads where only 1/3 worn on Monday and I managed to take out 2/3 in the one track day!

Darren

Chris

I bought a set of the 3-groove slicks off Pete Croney. Does anyone have any details on these? Why the grooves? What wear/grip will they have?

On Bushes: Pete told me that the guy from Leda said that the Impreza suspension bushes are amongst the best he's ever seen on a road car!!

Chris.