Newbie 996 tyre pressure question
Discussion
I have owned my 996 C4S for around a month or so now, and have been experimenting with tyre pressures. I started with the factory recommended ones and the handling just doesn't feel "right"
After owning a Boxster S for a couple of years and running P Zeros on there the Continentals on the 996 don't seem to give anything like the same feedback and don't give the same confidence levels.
Can anyone out there advise me as to tyre choice or pressures. I am sure the continentals can't be all bad...or are they?
After owning a Boxster S for a couple of years and running P Zeros on there the Continentals on the 996 don't seem to give anything like the same feedback and don't give the same confidence levels.
Can anyone out there advise me as to tyre choice or pressures. I am sure the continentals can't be all bad...or are they?
I'd wager that the front end just doesn't feel right? 
thornettj said:
Handbook for my 2000C2 states 36 front, 44 back, I must admit I thought 44 a touch high!!!, I may try 36-38 back, but I suppose Porsche knows best......
I had new tyres fitted last week and put 36 at front and 44 at rears as my OPC put 40 at rears. It says 36 front and 44 rears in handbook but I must admit this always seems a bit too high to me. Car feels a lot faster though with harder tyres
There are a great many enthusiats who will both follow the recommended pressures exactly and also criticise anyone who dares suggest that there could be a better setting. For those of you not quite so anal - who can think for themselves - I am happy to offer an insight into the factors I think are influencing choice but it is my personal one and I am not going to be drawn into arguments about it.
I think you should remember that when a manufacturer gives a tyre pressure they must provide a safe pressure for a worst case scenario - i.e. perhaps 4 occupants (say two big chaps and two small passengers - possibly all heavy), luggage, 150mph on an autobahn or perhaps two occupants and a fast trip round the Nurbergring etc. They must also cover all different tarmac and air temperatures - slight variations in pressure guages etc and are less interested in the resulting wear rates or comfort than ht ereliability and safety of the car. In these conditions the tyre temperature must still make the tyre safe and stable.
Compare this scenario to one light occupant driving through a busy city each day and never being able to exceed 50mph and the difference in the temperatures in the tyres and the requirements of it - should be obvious.
Now there has always been a compromise between side wall stiffness and the footprint that the tyre presents to the road (the contact shape of the bit that touches the road). If the pressure is too low then the sidewalls are flimsy and the tyre presses hardest on the road on the outer edges of the tread (less contact patch, more twitchy steering, less stable under braking) - whereas if the pressure is too high, the sidewalls become stiffer but the footprint gradually changes until there is so much pressure in the centre that the sides of the tread press down on the road less hard and reduce contact area (but can give lighter steering and good braking stability). With very wide tyres the centrifugal force of the tyre rotating at high speed throws the unsupported centre further out increasing pressure in the centre contact patch so speed is also a factor while changes in camber move the load patch accross the tyre face to the edges more duing track type driving.
A car with altered ride height, different spring rates, different wheel and tyre profiles etc will also require different pressures and even different tyre makes and specifications can need different ideal pressures.
When wheel sizes were around 15" or 16" the sidewalls were high and the suspension not very sophisticated - and so it was better if you were going round a track to keep the sidewalls stiff through high pressures, even though the contact area may have been reduced. But as wheel sizes have increased the sidewalls became lower profile and so it was easier to run lower pressures and still keep relatively stiff and stable tyres.
Now with huge wheels and relatively sophisticated suspension geometry, it is possible to run lower tyre pressures and get good handling and a good footprint on the road.
From all this you should be able to understand that the right pressures for anyone depends upon the tyre, wheel weight, load, speed, conditions and application and that no one setting will be best for very different scenarios.
Even different cornering and braking styles can influence the ideal tyre pressure. Those that brake late and hard and turn in quickly will ideally need different pressures to those that are more smooth and gentle because the former load the sidewalls more and increase tyre temperatures in use.
Usually if you stick to the recommended pressure for normal domestic use - you will wear out the centres of the tyres before the edges because for most domestic use they are too high (to make sure they will be OK if the car was ever used at its maximum designed potential).
So for most domestic use it can save on tyre wear, present a bigger footprint to the road and also be more comfortable to try slightly lower pressures (but never go flat out for long - or round a track - before pumping them up again).
So the best advice is to try different settings - I would say by around 2psi changes at a time and see how it feels until you discover the ideal setting for your usual use and then monitor the tyre wear to see if a little more or less pressure will give you more wear (and hence a better footprint). Once you have got the right settings for yourself don't allow others to talk you out of it just because they find different pressures ideal for them.
Baz Hartech
I think you should remember that when a manufacturer gives a tyre pressure they must provide a safe pressure for a worst case scenario - i.e. perhaps 4 occupants (say two big chaps and two small passengers - possibly all heavy), luggage, 150mph on an autobahn or perhaps two occupants and a fast trip round the Nurbergring etc. They must also cover all different tarmac and air temperatures - slight variations in pressure guages etc and are less interested in the resulting wear rates or comfort than ht ereliability and safety of the car. In these conditions the tyre temperature must still make the tyre safe and stable.
Compare this scenario to one light occupant driving through a busy city each day and never being able to exceed 50mph and the difference in the temperatures in the tyres and the requirements of it - should be obvious.
Now there has always been a compromise between side wall stiffness and the footprint that the tyre presents to the road (the contact shape of the bit that touches the road). If the pressure is too low then the sidewalls are flimsy and the tyre presses hardest on the road on the outer edges of the tread (less contact patch, more twitchy steering, less stable under braking) - whereas if the pressure is too high, the sidewalls become stiffer but the footprint gradually changes until there is so much pressure in the centre that the sides of the tread press down on the road less hard and reduce contact area (but can give lighter steering and good braking stability). With very wide tyres the centrifugal force of the tyre rotating at high speed throws the unsupported centre further out increasing pressure in the centre contact patch so speed is also a factor while changes in camber move the load patch accross the tyre face to the edges more duing track type driving.
A car with altered ride height, different spring rates, different wheel and tyre profiles etc will also require different pressures and even different tyre makes and specifications can need different ideal pressures.
When wheel sizes were around 15" or 16" the sidewalls were high and the suspension not very sophisticated - and so it was better if you were going round a track to keep the sidewalls stiff through high pressures, even though the contact area may have been reduced. But as wheel sizes have increased the sidewalls became lower profile and so it was easier to run lower pressures and still keep relatively stiff and stable tyres.
Now with huge wheels and relatively sophisticated suspension geometry, it is possible to run lower tyre pressures and get good handling and a good footprint on the road.
From all this you should be able to understand that the right pressures for anyone depends upon the tyre, wheel weight, load, speed, conditions and application and that no one setting will be best for very different scenarios.
Even different cornering and braking styles can influence the ideal tyre pressure. Those that brake late and hard and turn in quickly will ideally need different pressures to those that are more smooth and gentle because the former load the sidewalls more and increase tyre temperatures in use.
Usually if you stick to the recommended pressure for normal domestic use - you will wear out the centres of the tyres before the edges because for most domestic use they are too high (to make sure they will be OK if the car was ever used at its maximum designed potential).
So for most domestic use it can save on tyre wear, present a bigger footprint to the road and also be more comfortable to try slightly lower pressures (but never go flat out for long - or round a track - before pumping them up again).
So the best advice is to try different settings - I would say by around 2psi changes at a time and see how it feels until you discover the ideal setting for your usual use and then monitor the tyre wear to see if a little more or less pressure will give you more wear (and hence a better footprint). Once you have got the right settings for yourself don't allow others to talk you out of it just because they find different pressures ideal for them.
Baz Hartech
On the road I run 34 at the front and 42 at the rear. This is on my "facelift" C2 (with M030 suspension) shod with Michelin Pilot Sports on 18" wheels. Given the shoddy state of our roads I prefer this to the factory settings.
Edited by SteveO... on Tuesday 3rd April 13:46
Edited by SteveO... on Tuesday 3rd April 13:47
Very interesting Baz - I got new tyres yesterday and did notice that the centre of the tyres had worn out before the edges and they had been at the handbook recommended pressures. I now have Continental SportContact2 on and I do tend to only have 1 passenger at most so dropping it a couple of Psi might help......
Also, I could have filled with Nitrogen which 'apparently' gives :
25% longer tyre life
5% better fuel consumption
and improves handling and road holding.
Didn't take them up on the offer - wasn't convinced this could be true !!
Also, I could have filled with Nitrogen which 'apparently' gives :
25% longer tyre life
5% better fuel consumption
and improves handling and road holding.
Didn't take them up on the offer - wasn't convinced this could be true !!
Edited by benaldo on Tuesday 3rd April 13:49
benaldo said:
Very interesting Baz - I got new tyres yesterday and did notice that the centre of the tyres had worn out before the edges and they had been at the handbook recommended pressures. I now have Continental SportContact2 on and I do tend to only have 1 passenger at most so dropping it a couple of Psi might help......
Also, I could have filled with Nitrogen which 'apparently' gives :
25% longer tyre life
5% better fuel consumption
and improves handling and road holding.
Didn't take them up on the offer - wasn't convinced this could be true !!
Also, I could have filled with Nitrogen which 'apparently' gives :
25% longer tyre life
5% better fuel consumption
and improves handling and road holding.
Didn't take them up on the offer - wasn't convinced this could be true !!
Edited by benaldo on Tuesday 3rd April 13:49
Nitrogen is better than air AFAIK, you should have taken them up on the offer.
woogie said:
Nitrogen is better than air AFAIK, you should have taken them up on the offer.
I thought on planet earth, air consists of nearly 80% nitrogen anyway. What difference does the stuff inside make if its pumped up to the same pressure ? Does pure nitrogen have better heat transfer properties than air mixture or somthing.
Sounds like people paying £200 for gold core mains cables for their audio systems to me ... gold speaker cables I can fully understand, but a mains cable for heavens sake...
diesel130 said:
woogie said:
Nitrogen is better than air AFAIK, you should have taken them up on the offer.
I thought on planet earth, air consists of nearly 80% nitrogen anyway. What difference does the stuff inside make if its pumped up to the same pressure ? Does pure nitrogen have better heat transfer properties than air mixture or somthing.
Sounds like people paying £200 for gold core mains cables for their audio systems to me ... gold speaker cables I can fully understand, but a mains cable for heavens sake...
see here: www.merityre.co.uk/why_nitrogen.htm
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