Wheely good question

[Vanny]

How about one new tyre on the front, and the other on the diagonally opposite rear? That ought to keep everyone happy...

Sounds like you should work for Kwikfit, that is exactly what they did on my company hack, which got interesting on the very big very fast, very slippy roundabout outside work

[kiwi]

Are we talking tyre manufacturers recommendations as per what is stamped on the tyre? As that wouldn't accommodate the axle weights of each individual car.
On the BX I've always run the tyres at what is stamped on the drivers door pillar and always had good even wear. The Xantia on the other hand used to eat the tyre edges for breakfast! !

This is what I was getting at! Although if you looked at your tyres they are stamped with a maximum inflation pressure. Are you as I was refering to what a Tyre Fitting firm would suggest? I noted over here that Firestone Tyre fitters have this policy of 35psi no matter what or 45 for SUVs, large 4wd, vans. The fitter (also Manger) said to me that what was on the door piller was irrelvant because of tyre technology. Which was not what our local mech said who happens also to be the fire chief. Which line of safety would you follow?

In the event of skidding, due to lock up, wouldn't a slightly under inflated tyre be preferable to a slightly over inflated tyre? Admittedly though at a cost to cornering/handling?!

From what I remember from an advanced driving course back in the UK atteneded by Nigel Mansell, the advice was given correct inflation no more than 2 psi over checked from cold.
Slightly deflated Tyres have only got a use for extra traction on snow/ice or off road. When speeds are kept low and you have no alternative ie chains. !

Has anyone fitted deeper than recommended profile tyres? I'm considering it. It comes down to Kitch's classic quanta of the comfort:handling ratio! I'm sure with the right instrumentation or even mathematics the subjectivity could be removed and we could get car manufacturers to put actual suspensiony springy stuff back into cars instead of differing grades of concrete block!

Go back couple of pages I mentioned having 175/70 fitted on our BXs rather than 175/65. Seems to be the norm to be fitted to NZ BXs! Why I am trying to understand when the deeper profile gives less cornering grip? From what I am reading here it points to larger profiles means more riding on the side walls in corners?

Needless to say I have to admit not noticing any differance in the stability of the two BXs fitted with 65 compared to the one with 70s. I believe there is more to it than just the tyres as the suspension chracteristics between the two cars is noticeable despite using two differant tyre depths.

I will admit to some unease throwing the BX into a corner with the knowledge of slightly larger than recommend tyre. Hard to explain it really the science of whats that tyre doing plays out in your head as you imagine it distorting under the load. Then again I get that feeling when I know the tyre is under 3mm of tread. [/quote]

[kiwi]

I think, to be fair, the Police would only do you if your tyre pressures were dangerously under/overinflated. like having 12psi in one of the front tyres and 58psi in one of the rears.

Well that makes sense, given what we have established that what we think is correct is challengable from what is on the door piller, tyre manufacturers and fitters. A descrepancy of several psi per tyre would be of little defence. Just because the Police feel free to charge you with something you also have the right to challenge that decision providing you have the evidence to support you. End of the day it is the magistrate who decides not the police.

Personally I think that the debate on what the Police would and would not do in the event of an accident regarding tyres is a little off topic in the discussion of what Tyres would suit our BXs especially given this debate is of a international standard.

Your trying to avoid using tyres/methods that are going to reduce the risk of accident and conflict with the local gestapo.

[DavidRutherford]

I mentioned having 175/70 fitted on our BXs rather than 175/65. Seems to be the norm to be fitted to NZ BXs! Why I am trying to understand when the deeper profile gives less cornering grip?

I think you're confusing grip with handling here. The grip from a tyre is related to it's compound, the handling is related to the stiffness of the sidewall. A higher-profile tyre will have exactly the same amount of grip available, it's just that the handling will be less presice and the ride will be smoother/softer.

Also, the whole point of radial tyres is that you don't end up running on the sidewalls at any time, that was a trait of cross-ply tyres. (and a whole different conversation!)

[kiwi]

Conversley, a lower profile tyre will not deform and flex as much under cornering, and so the car's handling will be more presice.

I was questioning your statement here as to the effect of cornering in relation to grip. You seemed to indicate as I read it that higher profile tyres would have less grip or I should say not hold the road so well.

Misinterpretation somewhere along the lines still makes me curious why Both the NZ 19s I have had those deeper than recommended profile tyres on them.

[Vanny]

makes me curious why Both the NZ 19s I have had those deeper than recommended profile tyres on them.

Local rules, if it's anything like Austrlia then there are hundreds of them and they are all daft. You'll likely find that the NZ 19s are only allowed to stall on a Tuesday.