Handling with different tyre pressures

[Guest]

Since I bought my Boxster S a couple of months ago I had been driving around without checking the tyre pressure and was loving the fact that nothing I could do would even make a screech from the tyres let alone a skid.
The reason I enjoyed this so much is because although I am not a terrible driver I do enjoy the feel of acceleration and tight corners every now and again just to get the blood pumping.
However, to get to my question, I recently pumped up the rear tyres having noted they were incorrectly set at about 32psi instead of 36psi and I have noticed quite different driving characteristics.
If I accelerate a bit harder than normal (but nothing extreme) around a small bend doing about 15 mph the back end slides out a bit. I initially thought it was just a greasy road but it happened again somewhere different on a shallower bend but with more acceleration. Again I thought it was me just being a bit over zealous until later I was on a road joining the M40-M42 with a very shallow bend on a rise (speed signs say rated at 50mph). I was doing 70mph, the same speed I had done this road previously in a BMW 3series and my Boxster before the tyre pressure change but this time I became wary of doing anything because the back end felt very light.

On an 18" Boxster S the pressures are 36psi rear and 29psi front aren' t they?

 

[Brian Halling]

I have been enjoying a fast blast through the Alps for a number of years, and I sometimes drop the tyre pressures by a few psi to improve grip. For my Boxster 2.7 17ins wheels this means by 3psi front and rear.

The bad news is that it increases the wear significantly; last year' s Alpine trip took 2mm off the rears in 2,000 miles. The good news is that I have been very glad of that extra grip on a number of (hairy) occasions.

I would use the standard pressures for normal use unless you plan something special that needs a bit more grip.

 

[NicD]

Richard,

The Porsche recommended tyre pressures are not to be followed slavishly. There is a technical procedure to evaluate the optimum pressure involving measuring the surface temperature across the tyre. The correct pressure is when the temps are as equal as possible. This works OK on the track, not so easy on the road. I personally run two pounds front to back differential, so around 32-34psi.

Equally important is the correct chassis set up. We have a " track day " settings that give zero toe in and some negative camber. This improves turn in and grip.

email me if you wish these sent to you

Nic

 

[Guest]

Thanks for the replies it has helped me decide to try a lower pressure as apposed to sticking to the porsche guidelines.
I will probably drop a couple of pounds off the back to see if it sorts it out, after all I would rather spend more money on tyres than on a new car due to an unexpected skid.

Thanks again.

 

[Guest]

I have found a cracking website for choosing tyres for porsches. You enter year/make/model, order your priorities in choosing a tyre and then you are presented with a list of tyres with prices, reviews etc.

go to http://www.tirerack.com/tires/index.jsp and click on ' shop by car' .

 

[Mark_Bennett]

TireRack is a good site, but be aware that it is USA based, and does not necessarily show the same tyres (tires!) as are available in Europe.

Another source of tyre information, and which brands are suitable for the intended driving style, is available in Christophorus. I do not have the issue at hand, but I do remember a quite comprehensive article sometime over the last year or so detailing which approved brands and sizes are best for which intended use.

 

[Guest]

I' ve tried both the Porsche OE Michelins and the Bridgestones, and found the wet road grip for both deteriorated markedly after about a third of the their wear life. (I get about 15,000 on the rear on 17" ). Any one got any views on the best wet surface tyres for the Boxster? Or whether 15,000 is good or bad, for that matter!

 

[Mark_Bennett]

John,

I attended a talk by Pirelli at the Sussex region last night.
At this they said that Porsche and Pirelli now recommend that tyres are changed every couple of years as they " go off" (they lose essential oils that stop them drying out aparrently - I should perhaps of asked if moisturiser would help [] )
They also said Porsche recommend changing the tyres at 3mm of tread depth min, rather than the 1.6mm legal requirement, although I think this may be just a " common sense" measure if the car is to be used in the wet.

How old are your tyres? Was the 15,000 miles done over a long time? Was it including track use? Lots of factors can affect tyre life/grip (as I' m sure you are aware!)

Mark

 

[Guest]

Mark, tyres lasting more than 2 years, what a lovely dream! No, I get through 15,000 in one year, but I do change them at 3mm. The wet weather grip at the rear went off after about 3 or 4 months, when I guess there was no more than 2mm of wear.

For road use, I beleive wet weather grip is the main issue - Any Porsche recommended type is going to be 100% fine in the dry at road use speeds.

Any thoughts between Michelin and Bridgestone, or whatever?