what tyre pressure

[Anonymous]

I think the car had bridgestones on the front and yokohama's on the rear (or something like that)

[Anonymous]

Yesterday, I eventually checked my tyre pressures for the first time ever (I have RE040s on a post facelift).

They were all @ 32psi! Seems Mr T are to thank for this, since it has been a few months since I got my last set of replacement alloys.
Wouldn't you think that a Toyota garage would at least be able to put in the correct tyre pressures ? makes you wonder how well they do other things such as servicing etc.

I assume they did similar when I got my previous set off replacement alloys a year earlier? I've always thought it was a bit wobbly when taking bends at  anywhere above 70 mph! Seems I have probably never had the correct pressures throughout my ownership!

[mrsmr2]

I've never had Mr T put the correct pressures in.  I had 4 replacement wheels recently and they put different pressures in each tyre - ranging from 1 psi out to 4 psi!

When I was using mine regularly, I would check the tyres every weekend.

[ChrisGB]

Hmmm

Tyre pressures for beginners:

Tyre pressures should be checked at least once a week and before a long journey. Tyres should also be inspected for cuts, bulges, nails other damage at time of pressure check. A brief visual check every time you get into the car can show if a flat is imminent.

Check the tyre pressures when the tyres are cold. Remember every 10 deg C will add around 1 psi to the measured pressure. A tyre sitting in the sun may have 20+ degrees C more temp than one measured in the evening. A tyre that has been run may be 40 deg C hotter than normal temp.

Don't forget to check your spare as well. It is easy to look like a tw@t when getting a flat spare out.

My experience with Toyos on another car tells me they are quite porous and need checking very regularly.

And for those with a little more knowledge:

The manufacturers generally use a tyre pressure that will give a optimally shaped contact patch. This is a product of tyre diameter, width, profile and load applied.

Dropping the pressure from the recommended setting will generally make the contact patch longer, thus the tyre, if on the front, will give a higher initial turn in rate as there is a greater contact patch length. This can also change the centre of the contact patch relative to the steering axis, so may also mimic a change in castor. Finally, the patch will potentially be wider at its ends, so the steering will generally have forces acting upon it averaged out over a more square patch. This in turn leads to less steering feedback but heavier steering. Finally, the tyre can roll more on its rim and will have uneven force across the tread width, resulting in rolling of the tyre carcass under load, uneven wear (tread edges) and of course, reduced overall grip. Transition between grip and slip may well be softened a little, making driving near the limit of adhesion easier. Alternatively, the deformation of the tyre may get to a point where snap loss of grip occurs.

Increasing the pressures will have the opposite effect to reducing them. The contact patch will become shorter, this will make the steering feel more direct as the feedback can be improved. The higher pressure will also lead to lower rolling resistance, potentially an effect similar to reducing castor (as drag is reduced and the patch gets wider relative to its length). The contact patch will be reduced in size, so outright grip may suffer. Transition between grip and slip can become very sharp as the lack of conformity in the tyre will potentially prevent deformation to accommodate roll induced geometry changes from the car. Pressure will be applied unevenly to the tread leading to increased pressure down the middle of the contact patch (increased force per unit area also) leading to worn middle section of tread.

In both cases, the wet running of the tyre may be adversely affected if the contact patch bias is mismatched. So running T1-R under inflated may cause the middle section of the tyre, the bit that does most drainage, to be pushed clear of the road surface by standing water, leaving the edges with their small void area to work toward drainage. A bad thing. Similarly, over inflating a Yokohama A043 with its wide centre rib may be bad as the drainage bits either side of centre and on the shoulders are relatively under loaded.

So adjusting the pressures from stock by small amounts will allow an individual to fine tune handling to taste, but done to excess will cause potentially unacceptable handling and wear trade off. For my money, I would not go past +/- 2 psi as consistently running at 2 psi out is known to cause visibly uneven wear. Others may find the trade off acceptable.

My front 040s are due for replacement. The 81V rated stock 185/55 R15 is currently not available, so may be thinking of something a little different.

A last thought for those new to the MR2 experience. The car responds well to a gentle approach to steering. Feed the front end in by increasing steering angle gently and it turns in fine. Hoik it in and you can get understeer. So before changing pressures, try not over driving the front end.

Chris

[heathstimpson]

I've never had Mr T put the correct pressures in.  I had 4 replacement wheels recently and they put different pressures in each tyre - ranging from 1 psi out to 4 psi!

Don't worry all dealerships seem to be consistant with this  s:? :? s:?