Today I changed my tyre pressures ... odly enough I was running on 33/31psi (front/back)!!! I don't know how that happened but that's what I must have been running on for the last month instead of 38/36 as I thought ... I must have measured it on a very hot day and after some driving - my bad. Anyway, what that means is that all my comments are related to 33/31 tyre pressures - that is also the tyre pressure I was running for the 'timed session' I did with 2kturkey ... that would imply that I had 'ideal' tyre pressure for the 0-100km/h launches and my 6.15 time could not really be improved by dropping the tyre pressures (on the same day).

Anyway, so instead of dropping the tyre pressures I raised them to 35/35 psi - I'll see how the car will go with this. My initial impression is that the car now has 'some' understeer (instead of 'none' before) ... this could be a good sign :-) I'll test out the back 1st chance I get and see if the back is a bit more planted (it's the off-camber corners that annoy me - that's where the back seems too loose).

 

Today I went for a very good 'hoon' with the 35/35 psi tyre pressures. Tonight I was very happy with the way the car handled. I was throwing it around all kinds of corners (though nothing clearly off-camber) and the car has been very solid and confidence inspiring. Even in a corner that happened to have a water streak running though it, the car behaved beutifully - it steped out but only slightly. I'm noticing with the 35/35 tyre pressures that the car seems to be a bit more willing to understeer - nothing too agressive but I do notice that when I'm getting close to the limit the front starts pushing out ever so slightly. If I then give it a bit more power then the car does this ever so slight 4-wheel-drift. Very pleased with how it handled tonight (and it was a 'quick' night :-)

On the way back I went over a piece of twisty road that I cover almost dayly and I noticed that I was travelling good 10km/h faster though each corner than what I usually do. I usually try and drive at about 8/10th and tonight the 8/10th seemed to be about 10km/h faster (ps. corners between 80 and 120km/h). As I said the car felt very good with 35/35psi ... will stay with it for a while and try and seek out some off-camber corners to see how it behaves.

ps. Can't believe that 2 extra psi in the front and 4 extra psi in the back makes so much difference to this car.

 

It's been a good couple of weeks since I changed my tyre pressure to 35/35 psi (from 33/31 front/back). I've even checked the pressure a few times since and it did need adjusting once by +2psi to get it to 35s ...seems like the pressures are really sensitive to ambient temperature so check it often.

Anyway, I've been throwing the car around a fair bit trying to see how it behaves (99% of the time in the dry) ... I even when around that 'imfamous' off-camer corner a few times (the one I mentioned at the top of the thread). Good news is that I'm back to being impressed by S2000 as the car seems to be very neutral and it takes a lot of effort (on my part) to get the back out. I've taken corners at some decent speeds and the car just grips. At the limit I seem to get a very slight understeer if I keep the power down and if I keep the line tight and throttle to the floor then I can get the back to drift out ... though, I have to generate some decent cornering g-forces to do that. I'm very pleased with that :-) I even tryed eazing of the throttle mid-corner and holding the line to see what would happen - it just transfers more grip to the front, the back sqeels a little bit but did not step out (even did it around an off-camer corner).

I might fiddle with the pressures a bit more to see what it does to the car, but for anyone looking for something that works - 35/35psi seems to do the trick very nicelly. If you think your back is too 'loose' then check your tyre pressures as that seemed to have fixed the problem for me. I still cannot believe how much different the car feels with just 4psi more at the back and 2psi more in the front - now I'm driving something that grips and handles well while before I felt like I was driving something that has good handling up to 8/10s but after that runs out of grip at the back.

 

David,

Very interesting post. DO you have any mods in your car, like x-brace, strut bars ?

 

S2K_Spain, no mods at all on my car. It's totally stock standard and has only about 3.5k km on it.

 

I got some more interesting findings regarding the pressures. I was running 35/35psi (fron/back) for over a month and was pretty happy. The car was neutral, progressive and the back was not loose like it was with the 33/31psi pressures. Though, about a weeks ago I though that's not good enough and I tried something different - I raised the back pressure to 37psi (so now I was running 35/37). Something very odd happened with these pressure settings - suddenly my car was understeering a fair bit ... oversteer almost not existent but understeer anytime I started to 'push' (ie. go fast). I stayed with the 35/37 for about a week just to make sure but 'understeer' was the predominant characteristic of my car ... in some instances it was understereering in situations where I did not think I was going that fast. So, anyone care to take a guess as why the car would develop undesteer when I raised the back tyre pressure by 2psi?! I have one theory - 37psi at the back removes the 'lean' from the back tyre - that 'lean' in turn might have been respponsible for the grippy turn-in. Afterall, if you stiffen the back suspension, you will introduce undesteer. At least that's what I'm thinking happened ... any other ideas?

So today I decided to try something different yet again with the pressures - 33/35psi. 35psi at the back is what I had on the car before when I was happy with it. Now I'm running 2psi less at the front and will see what happens. A quick impression after my 45min 'hoon' tonight was that the car felt good and had good grip front and back. I'm tempted to say that the 'dominant understeer' is gone, but to be 100% sure, I need to find some 'longer' corners where the front is more likely to 'push'. Will report after a week or two and see if this is an improvement on 35/35.

 

[quote]My experience is that higher pressures increase responsiveness but reduce grip. I

 

very interesting thread... i have just experienced the "loose" feel due to improper tire pressure. at first i thought that i needed new tires, but the tread is fine-