Tyre pressures

[Tony Atkinson]

Hi. 
I’ve a GT6 that was originally fitted with Dunlop SP 10 tyres. The handbook states pressures should be 24psi for the front and 28psi for the rear. 
I’ve just fitted uniroyal 155/80/13 79T as they are modern tyres the original pressures stated seem to low. Has anyone fitted modern uniroyal tyres and if so what tyre pressures would you recommend 

Regards all 

Tony 

[sparky_spit]

Hi Tony - I have Falken Sincera 165/80 tyres on my Spitfire and run them at 27psi front, 32psi rear. They are very good, dry or wet, at those figures. I know the Spitfire is lighter that the GT6, but those figures cant be that far off.

[RobPearce]

I've always found the factory pressures too low for modern tyres. I generally run 30psi all round.

[Velocita Rosso]

Since the hand book and original manufacture,  tyres /rubber/compounds have changed dramatically, along with different manufacturers

In the day ,there were not many tyre makes around over and above the Michelin/Firestone/Dunlops. Nowadays there are numerous manufacturers offering different treads and compounds.

 The spitfire pressures are originally printed as 21 and 26 and we have the GT 6 which has your specs.

However, we run Yoko A 539 and they have a better `stickiness` road holding/handling and run at 30 psi

Also dependent on what/how you use the car.

We have numerous advertisers in the magazine ,and one such company, Longstone Tyres would be glad of your enquiry 

[JohnD]

Tyre pressure is usually taken cold, and then rises as the car is used, to a level  depending on how it is used.    To tell if you are using the correct cold temp for you, you need to assess how you are using the tread rather than just pressure.   Two ways:

1/ Long term.   Buy a tread depth gauge, and record the tread depth across the face of the tyre at regular time intervals.       An over inflated tyre will wear the centre more than the tread shoulders, and vice versa if under inflated.

2/ Measure the tread temperature, after a typical run.    An Infra-red 'gun' is a cheap and convenient way of doing this, but heat will radiate from the surface of the tread quite quickly, so do so immediately you stop.         A tyre thermometer uses a fine needle to take the temp IN the rubber of the tread.  This drops more slowly, but the kit is quite expensive!      Again, an over-inflated tyre will be hotter in the centre.

Then, adjust your cold tyre pressure accordingly

To show that this works, I run Yoko A048 race tyres, semi-soft, at 24-27psi cold, because they get a lot hotter on track!

JOhn

 

[ferny]

Over the years with different tyres I've run;

 

 

 

26F 24R

 

 

 

28F 28R

 

 

 

32F 32R

 

 

 

Right now I'm running 32 all round and I can feel the sideways move around on bends.

 

 

 

 

 

 

 

Basically, the correct tyre pressure is whichever feels right for you and your driving.

 

 

 

 

 

 

[Howard]

Falken provide a free car specific recommendation for any car running their tyres - my T7V8 was 34F 32R

[Tony Atkinson]

Thank you to everyone that replied to my post. I’m going to try 30psi all round and see how that goes. 
Tony 

[Clive]

I find it interesting about how many have migrated to higher pressures. Both here and elsewhere.

My spitfire (about 185bhp) and CV rotaflex runs on 185/60 14 tyres. I have experimented with pressures extensively, on road and trackdays. And the outcome is 25psi all round. I found anything harder feels a bit scrabbly, softer is wooly.

I am certainly no  great driver, and I know some who are far better than me. Most have different ideas and pressures. But as others have said, much is about experiemnting. With a GT6 I would expect different pressures front and rear. The only thing is that as you home in on the best setup, yoiu will need to drive the car harder to decide if it has worked or not. 

And tyres are only part of the equation. The rest of the suspension needs setting up to get the very best out of the cars. But that is a long and can be expensive road....

[Howard]

Clive.

I only changed to the higher pressures after the handling of my new TR7V8 was totally unacceptable compared with my previous 2L 7. The old car ran and handled very well with 28F 30R with Continental 185 tyres - but the replacement just didn't hold the road nearly as well until I obtained the Falken recommendations & while I am still fine tuning around the figures they quoted which are much higher than I expected, but it is clear to me that their tyres only operate correctly at higher pressures.

H

[Tim Bancroft]

I have always run 30 psi on my GT6, seems fine to me.