S211 19" Tyre Pressure Question

[Fly_Boy_Rez]

Folks,

I've read a bunch of threads on here about the correct tyre pressures to apply but still it's not feeling / looking right so I thought I'd start a thread.

The car was pre-fitted with Moven 19" rims when bought recently. Unfortunately I've since confirmed my suspicion that the wrong tyre sizes are on there. The fronts Pirelli P Zero D) 225/35 ZR19 84Y and the rears are a budget brand (can't recall which ) 235/35 ZR19 91W.

The fronts are quite frankly stretched and apart from looking ridiculous are exposing the recently refurbished rims to damage despite all attempts to avoid kerbs etc.

The rears look OK, don't look streteched but from a personal perspective I think I'd like something a little wider to help protect the rims.

So, onto the tyre pressures. I've followed the advice that I should use the tyre pressures inside the fuel filler cap:-

Photo 12-10-2013 09 36 35 am by FlyBoyRez, on Flickr

However doing so it just doesn't look or feel right for the Fronts... and I accept the stretch on the fronts will make the look of it all wrong! For example at the rear I have this:-


Photo 12-10-2013 09 36 12 am by FlyBoyRez, on Flickr

At the front this is what it looks like:-


Photo 12-10-2013 09 35 36 am by FlyBoyRez, on Flickr

In terms of feel, the power steering feels heavier than it should, and at low speeds turning the sterring through full lock I get what I can only describe as a rubbery 'Twang' through the wheel!

I appreciate the proper course of action is a set of new tryes of the correct width but present finances dictate otherwise so...I'm happy to up the pressures but before I do I'd like to seek your advice on any pitfalls (other than premature wear of the centre of the tyre) and how high to push them?

Thanks in advance!

Rez

 

[jadatis]

The 210km under and over on the plate suggest its for Y speedrated tyres.
the speed up to wich the needed pressure for the maximum load is used for Y speedrated tyres is 220 km/u , for W speedrated tyres its 190km/h.
The car-maker then keeps it 10km/h under it.

But with these low Aspect ratio tyres( the 35 in the sises, is Hight width division , will shorten it further to AR) you have to keep such high pressures for the savety of the tyres sidewalls , that the middle of the treath wears of sooner, and gripp and comfort are totally gone. I discovered that the maximum load of such tyres is given to high by the tire makers, a thing we users are not allowed to know, but now you do. The rear tyres I know by head that the 91 loadindex stand for maximum load of 615 kg/tyre, but to my estimation you have to substract 20% of that , so maximum load to rules of nature is in fact 592 kg.


Risk of the lower pressures is that you have teriffic comfort and gripp, but at a sertain moment you have a blowing tyre, with all the missery that goes with it.

Also search on the sidewall for something like XL/Extraload/Reinforced, then its a tyre that needs 2,9bar/41psi for the maximum load instead of 2.5bar/36psi of a standard load tyre. most low AR tyres are XL//.
Then try to determine the normal load on the axles to calculate a normal pressure advice. If you give me the needed loads and tyre-data, I can calculate a save lowest pressure for your situation.

 

[Rupert44]

The 210km under and over on the plate suggest its for Y speedrated tyres.
the speed up to wich the needed pressure for the maximum load is used for Y speedrated tyres is 220 km/u , for W speedrated tyres its 190km/h.
The car-maker then keeps it 10km/h under it.

But with these low Aspect ratio tyres( the 35 in the sises, is Hight width division , will shorten it further to AR) you have to keep such high pressures for the savety of the tyres sidewalls , that the middle of the treath wears of sooner, and gripp and comfort are totally gone. I discovered that the maximum load of such tyres is given to high by the tire makers, a thing we users are not allowed to know, but now you do. The rear tyres I know by head that the 91 loadindex stand for maximum load of 615 kg/tyre, but to my estimation you have to substract 20% of that , so maximum load to rules of nature is in fact 592 kg.


Risk of the lower pressures is that you have teriffic comfort and gripp, but at a sertain moment you have a blowing tyre, with all the missery that goes with it.

Also search on the sidewall for something like XL/Extraload/Reinforced, then its a tyre that needs 2,9bar/41psi for the maximum load instead of 2.5bar/36psi of a standard load tyre. most low AR tyres are XL//.
Then try to determine the normal load on the axles to calculate a normal pressure advice. If you give me the needed loads and tyre-data, I can calculate a save lowest pressure for your situation.

A few years back when I ran land rovers with huge wheel tyre combs we used to inflate the tyre to the "book" presure when new and then draw a line across the tyre with chal.

we would drive slowly in a straight line and observe the chalk line "wearing" off the tyre.

if it was light in the centre we would lower the pressure by 2 PSI and light at the edges up the pressure by 2 psi.

We would repeat this until we got an even wear line.

The last set of tyres we got 26K miles out of them and they hit the wear bars at the same time right across the tyres.

it is worth a try, only takes about half an hour on a flat straight road and an obliging friend to walk along site to tell if the chalk line is wearing out.

Hope this helps.

Rup