Over the last 4 months, I've noticed an irritating trait towards vague steering in my scoob (MY 98 5 dr). Low speed cornering particularly lacked the poise which I'm sure was there when I first got the car. I couldn't work out what was wrong until today.

Several possibilities to explain this existed:

1. tyre choice - at the moment I have 2 Toyo T1-S at the front and 2 Firestones at the back (at least until they wear out). Ideally I would have 4 Toyos but I grudge scrapping 2 tyres with 4 mm of tread.

2. steering geometry - possibly out due to kerbing injuries.

3. tyre pressures - set at 33 psi front and 31 rear (seems to be popular settings according to previous posts).

4. suspension/steering fault - subsequently checked and found to be OK.

I have ruled out 1. as the likely cause. The Firestones were never bad tyres and when on the front wheels, were at least as good as the OEM Bridgestones (RE010's).
I did not have confidence in my local dealer's ability to check the tracking so I managed to find a place nearby who have experience in setting geometry for rally cars and were very familiar with scoobs. I had the tracking checked today.
Result - absolutely optimal. Not quite 'Provdrive' settings but not far off and equal front and back.
I was left thinking that the problem must be the mixed tyres. But I thought that it might be worth experimenting with tyre pressures.
The difference this made amazed me.
What seemed to affect the steering the most was the rear pressures. They were originally set at 31 psi so I dropped these to the recommended 28. Immediately this smoothed out cornering and increased turn-in. I experimented with dropping the pressure at front. 30 psi improved turn-in at low speeds but at higher speeds felt unsafe.

In the end I opted for guess what - standard pressures: 33 psi at the front and 28 at the back.

The point of my rambling is to demonstrate that tyre pressures do seem to be very important to steering feel and that simple measures such as a few psi increase or decrease can make a big difference.

D.

Yes, I agree absolutely. It seems that a difference of one or two PSI will change the handling balance and grip quite significantly.

I am experimenting with a real-time remote pressure and temperature sensing device (SmartTire), which I hope will enable me to find the optimum pressures for my car and driving style (and keep an eye out for punctures).

It is interesting to see how much of an increase in pressure and temperature you get once the tyres are warmed up. I find that if I notice a slight difference in feel, I can usually see a corresponding change in the readings.

I'll post some more info when I've collated results, but a high speed cruise will generate over 110 degrees f contained air temperature, and the pressure at the front rises from 33psi to 41!. I wonder what it would climb to on-track?

Cheers,

Alex