I'm heading off to the Jaguar Summer Festival today, being held at the British Motor Museum at Gaydon.

I'm lucky enough to be able drive 3 laps of the Jaguar Land Rover Test Track tomorrow morning in my 4 litre convertible. It's on 225/55 16" tyres and I'm going to raise the pressures a bit for the laps.

It won't be super high-speed as we're under controlled conditions, but I just wondered if anyone had any views on what pressures I should use?

Tks

Paul

 

The sticker on my car says for high speed use use 38 psi, I'd probably start there.

 

Paul
exact tire pressures isn’t ever one number.
It’s achieved by testing under identical conditions. Tire brand, size, wheel size track surface, most of all drivers goal.
I may trade off cornering for braking or acceleration. Depending on competition and track.
Long corners will heat up the outside tires while tight radius corners prefer more equal pressures. Rarely- in fact I can’t ever remember where increasing pressures helped at all.
That comes from 60 years of racing experience some races with professional racers. Or extremely skilled amateur.

 

Usually, increase pressure when using street tires on a track.

i wouldn't bother, its going to be 3 casual laps, unlikely it will be any different from a Sunday drive.

 

I’ve been racing since the early 1960’s. Increasing tire pressure only stiffens sidewalls and rounds out tread reducing contact patch and compliance with irregularities in the track surface.

Yes it is possible to go too far the other direction to low pressure. But starting from mfg’s recommended point is perfect.
Then when the car comes in. As soon as possible lay your hand across the tread surface.
Tires will be hot but since we are talking about street treads not dangerously hot.
You’ll feel what to do. If the edges are hot increase pressure. If the center is hot lower temperature. Feel all 4 tires. If the outside is hot while the inside is cooler you need more camber if the inside is hot and the outside is cool you need less camber. Caster is determined by stability at speed. More caster makes the car more stable. Less caster helps turn in.

 

Thanks for all your comments, Guys.

Unfortunately, it didn't really matter. As Nick surmised, it was far more of parade lap session. Leaving a bit of a gap, I touched 75mph on the straights but that was it. Having said that, it was still good to drive on the circuit where so many Jaguar, Aston Martin & Land Rover prototypes have been developed, a privilege that has never previously been accorded to any club or private group.

The day itself was great, over 1000 Jaguars spanning everything from Swallows to the last F-Type, and all at the home of Jaguar Heritage at the British Motor Museum. So, of course all of the prototypes, concept cars and last of the line models were on display for us. I've been lucky enough to see them all before, but you never tire of seeing the history. My 4 litre Convertible even managed just over 31 mp (UK) gallon, top down, over 375 miles including track laps.

Some notable Jaguar personalities were in attendance, Ian Callum, Sir John Egan (who signed some of my photos) etc etc. One surprise was Tom Walkinshaw's son, Fergus and the engineering test mule of the new TWR Supercat. See the photo below of the 600+ bhp test power plant in the mule. It sounded great with sidepipes! They even agreed that we could bring some XJSs down to their premises to look around the project.

TWR Performance - The Next Generation is Here

Interestingly, the project might even enable some parts to be reproduced as they are using pre-facelift cars for the conversion to customer cars. So, windscreens and rubbers will need to be produced etc.




Tks again for your input. Just a few pics below

Paul




Reims-winning D-Type





The only road-going example of the CX-75





Le Mans-winning XJR9




An early Manual pre-HE in the car park. All original, no restoration and 10k miles from new. Glorious!