Hi everyone i was just wanting to pump up my tyres as I've not done this for like the whole of this year I was wondering if there's anyway I can find out how much I should do them? I bought them off a friend along time ago and totally forgot what he said,

35psi all round.

Open the drivers door and you will see a sticker on the pillar, that tells you the recommended pressures for different conditions

Thats no good im afraid as Tony at WIM has found a flaw in the set up on the IS from factory.....trust me its 35PSI

I always thought it was 32PSI????

You sure its 35 mate??

Im sure Tony will look at this soon

Yep, Tony recommends 35

Depends on the set up of the car and how YOU drive and the loads you normally carry. I had the IS set-up at 35 on the rears and 33 on the front.

Agreed.....i have had mine set at stock suspension set up and when it was lowered @ -40 and 35psi seems the way forward for me,mostly town and a bit of m/way driving with very minimal tread wear.

Forgot to add that adjusting to the 35psi is useless until you've had a geo done at the Dr's and having a fine tune.

Historically the pressure for the 215-45/17 on the IS200/300/SC needs to be 35psi front and rear. This re-position is born from 200 or so cars observed and monitored by wim over a two year period concluding research regarding the habitual tyre wear issue that plagued the marques mentioned.

To add support to this theory tyre wear, Geometrical or pressure related is now foreign to this club

While we are on the subject.... has any one got their tyres filled with nitrogen?

One well known garage over here do this as an option and say it is more consistent as its not as easily affected by differences in meteorological conditions....

I'm abit skeptical about it.... but open to suggestions

Thanks for the response will post tyre details tomorrow as I have 19's but if I go about 33 it will prob be alright for now... it will be intresting to see what they are at the moment.

Nitrogen will be the assassin to compressed air, a progressive step forward for the Motorist.

It's a scam. Air is 78% nitrogen anyway. The coefficient of expansion of nitrogen is about 80% of that of air so the difference in the change in pressure for a fixed rise in atmospheric temperature will be tiny.

The use (and extra cost) of compressed nitrogen instead of compressed air is justified in high pressure systems where it gives significantly reduced risk of fire, but for the pressure and volume of air in a car tyre I can see no point other than to relieve the credulous of their cash.

Can i remind you we are talking 'dry nitrogen' so not susceptible to the reaction of moisture in compressed air! or maybe i'm wrong? Nitrogen inflation is mandatory in the muti-billion pound aircraft industry and used for absolute inflation in the muti-million pound F1 industry.. all wim centres would use nitrogen at £0 additional cost to the customer, many other companies already follow that example.

But doesn't that mean you'll also need to top up with Nitrogen each time?

The thing that the two examples given have in common is high cost. I worked in the aircraft industry as a designer for a long time and nitrogen is used for the safety reasons that I have already quoted. Typical aircraft pressure systems may operate at around 1500 psi and it makes all kinds of sense to ensure that any gases within them are inert.

I have yet to hear a single good reason for putting nitrogen, as opposed to compressed air, into a normal car tyre. The idea that the use of nitrogen is cost free is at least questionable. All the costs of running a business are passed on to the customer in some way, otherwise the business goes broke. Offering a fancy but uneccesary service may of course attract custom and generate business, but it doesn't make that service essential.

The moisture content of compressed air is important in applications that pass significant volumes of air through the system e.g. in the "windy" tools used in industry. But the air inside a tyre is to all intents and purposes a small fixed volume in which the water vapour remains suspended and is a tiny proportion of the total volume of gas. I can see no reason why it should give me any concern as a motorist.

If needs be then the owner can recover the pressure with compressed air, all this will do is filter the advantage of nitrogen.... We are in a transition period between air and nitrogen, we can all agree on that! but over time it will become the recognized standard.

ok mine are Proxes T1-S
What i could read on the tyre was 215/35 ZR19 85W

So how much would you recommend mr Wim, thanks again..

Ok.. can i ask this then? why is there a differential pressure guide for motorway driving, have a look in the book or on the door you will see specific alterations, i ask you this 'why!'

Because the performance of the tyre structure is affected by the temperature at which it is run. Running at high speed causes an increased rate of instantaneous flexure which raises the temperature of the tyre. Increasing the initial cold inflation pressure stiffens the structure and reduces flexing. Running at constant speed below the maximum operating speed of the tyre results eventually in a tyre temperature equilibrium and that equilibrium is achieved at a lower temperature if the initial cold inflation pressure is higher.

The actual operating pressure inside the tyre results from the initial cold inflation pressure together with the partial pressures that result from heating the constituent elements of the inflating fluid. Elementary thermodynamics will tell you that any ideal gas in a measured volume with the same pressure and temperature will will have exactly the same number of mols of the gas. If you increase the temperature of each of the gases by the same amount the pressure will increase by exactly the same ammount. The equation is pv=nRT.

The guidance on my car calls for no increase in pressure until a speed in excess of 100 m.p.h. so it's pretty academic for most of us.

There is no advice that I can find in my handbook about the benefits of using nitrogen instead of air. I can find nothing on it from Lexus.

The one technical tip that I could find (from GM) concludes (and I quote) "the realized benefits to our customer of inflating their tyres with purified nitrogen are expected to be minimal"

They printed the last four words in red, but I don't know how to do that.

This topic has become boring - I'm done.

Me too... sorry the 200 or so cars, the two years free research and the exterior evolution for nitrogen inflation in reply to this topic is boring! Although i find your explanation and sums regarding the gasses involved fascinating you failed to notice the fundamental reason why nitrogen is more efficient than compressed air?....... (moisture) now i am done!

On another topic the one i started I have done them all to 33psi and it's greatly improved, one tyre was down to 21psi no wonder it's been a bit strange... From now I'll be checkin every month or so thanks for the help guys

you should be checking every week matey, or before a very long journey, whatever comes first.

then thats what I shall do my friend

I recommend 35psi... The way wim operates means we re-check the Geometry to ensure the figures suit the car and customer, of the 200 or so IS200 the only repetitive problem has been under inflation. The 33psi listing for the car is within reason nothing more than a suggestion, a 2psi increase is a safe manoeuvre and will not jeopardize the drive or safety.

Thanks mate I'll do that today then...

I'd give 35 psi a go I've been had mine at that for about 18 months and found it made a big differance..

wondering . on my altezza ive 18" wheels and use good year f1's on the side of the goodyear it says max psi of 50 but dose that mean i should have it at 44 or so ? should i actually be using it lower ? normally theres just myself in teh car

35-37psi max imo.

Tony -

I assume we are talking 35psi (cold) ?

If you remember you set mine to 35psi but I had just driven 10 miles (in the summer). The following morning when they had cooled I checked them again and they were down to 31psi which I immediately raised back to 35psi.

Tony .. 1 more question .... hows the tolerance on the air pumps at the gas stations? Do they tend to be accurate?