Tyre Pressures
- Thread starter mohitos
- Start date
993paul
New member
The pressure varies a bit with your wheel and tyre size as well as load - low profile tyres with larger wheels seem to need higher pressures so on my 18" wheels on a 993 RS I also use 2.5bar front and 3.0bar rear. I dont think load will change pressures by any perceptible amount - however temperatures will - if its a baking hot day - expect 2- 5 psi increase - and if you are caning around a circuit - it will increase by another 5+ psi so you may want to aim off a bit for these conditions if you know in advance.
BTW as I've mentioned before on other threads the B pillar chart conversions of bar to psi are inconsistent. Assuming that bar was the Porsche unit of choice, and based on a conversion factor of 14.5038psi/bar, the chart psi data should be rounded to the nearest whole number from:
Front partially loaded 2.3 bar - 33.36 psi
Rear partially loaded 2.7 bar - 39.16 psi
Front fully loaded 2.5 bar - 36.26 psi
Rear fully loaded 3.0 bar - 43.51 psi
Front partially loaded 2.3 bar - 33.36 psi
Rear partially loaded 2.7 bar - 39.16 psi
Front fully loaded 2.5 bar - 36.26 psi
Rear fully loaded 3.0 bar - 43.51 psi
I could be wrong but I don't think it does, the only way it could go up is if you fully constrained the baloon. A squeezed balloon will burst but this is because the skin is stretched beyond its elastic limit at some point not because the pressure is increased. - I'm now going to Google this just to make sure
davidcross
New member
i stick 40psi in both front and rears and all seems fine
I run standard 34/40 psi; suffering lack of courage to try anything else.
I can't seem to find it now, but I seem to recall an excellent article posted on the forum with in the last year that went into details on the effects of various tyre pressures on the handling.
Hopefully, someone can repost the link.
I can't seem to find it now, but I seem to recall an excellent article posted on the forum with in the last year that went into details on the effects of various tyre pressures on the handling.
Hopefully, someone can repost the link.
ravi911
New member
Thanks both.
I've just done over 1000 miles on a road trip up through England and Scotland on some of the best driving roads in the country - Peak District, Yorkshire Dales, Trossachs, Cairgorm National Park - and the 997 was supreme on the very slightly lower pressures [
]
Amazing ride comfort on our broken surfaces, loads of grip and wonderful, feelsome handling []
I'll post more details of the trip sometime soon.
Cheers,
Ravi
I've just done over 1000 miles on a road trip up through England and Scotland on some of the best driving roads in the country - Peak District, Yorkshire Dales, Trossachs, Cairgorm National Park - and the 997 was supreme on the very slightly lower pressures [
]Amazing ride comfort on our broken surfaces, loads of grip and wonderful, feelsome handling [
]I'll post more details of the trip sometime soon.
Cheers,
Ravi
If you have TPMS then follow its guidance: it's clever in that when you go to the 'info' mode in the instrument display it will show you the air to add/remove to ensure the right pressures at the 20 deg C 'standard'. In other words it know the wheel temp and adjusts accordingly.
'Best' pressures are what the manual says. (2.3/2.7 bar or 34/40psi - with 2 people). These are at 20 degC, and so if you need to correct manually use about 4% per 10 degC temp diff, BUT if you've been driving it, it will be the wheel temp you need to know, not the ambient temp.
Even for a modest track day you don't really need to adjust as these tyres (with N-rating) are designed with stiffer sidewalls (rear notably) to prevent any creep off of the rim - you often hear of people putting extra air in for track days to prevent tyres rolling off of the rims but not necessary here.
No doubt experience track day-ers will chip in with better knowledge for harder use.
'Best' pressures are what the manual says. (2.3/2.7 bar or 34/40psi - with 2 people). These are at 20 degC, and so if you need to correct manually use about 4% per 10 degC temp diff, BUT if you've been driving it, it will be the wheel temp you need to know, not the ambient temp.
Even for a modest track day you don't really need to adjust as these tyres (with N-rating) are designed with stiffer sidewalls (rear notably) to prevent any creep off of the rim - you often hear of people putting extra air in for track days to prevent tyres rolling off of the rims but not necessary here.
No doubt experience track day-ers will chip in with better knowledge for harder use.
ORIGINAL: Lancerlot
and get your tyres inflated using nitrogen as this doesn't cause as much pressure variation when the tyres get hot. [
Regards,
Clive.
How do you work that out Clive? Any two gases exposed to the same temperature increase pressure by the same amount...
The only extremely minor factor is that if you use atmospheric air, it may contain a certain amount of water vapour which when it cools may conceivably condense a small proportion, which in turn may cause a very very slightly greater pressure drop than if it had been either dry air or nitrogen.
Before someone asks "why do aircraft use nitrogen?", the answer is (an Airworthiness Directive) "To eliminate the possibility of a chemical reaction between atmospheric oxygen and volatile gases from the tire inner liner producing a tire explosion" and also to prevent the air in the tyre from fuelling any sort of combustion, especially given that a wheel bay fire is one of your worst conceivable nightmares.
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