Tyre Pressures

kiwi · Post by **kiwi** » Sat Jul 18, 2009 8:46 am

Seems an obvious answer

"look in the manual or on the door pillar"

Well I thought so until yesterday when getting 4 New tyres for the BX19 and the Tyre Guy put 35psi in them

I queried him about this and his reply was that with modern Radial Tyres they need to be higher inflated as they last longer

That goes against everything I have been taught and against safety. So is this correct advice?

DLM · Post by **DLM** » Sat Jul 18, 2009 11:55 am

I'd love to hear what an insurance company had to say about that advice after the accident and claim....

Way2go · Post by **Way2go** » Sat Jul 18, 2009 4:47 pm

What do you see so wrong with it?

The Citroen Handbook recommends 32 front and back for mine on 185 which give a better suspension performance than if they were less inflated.
In fact if I was running 165 on the GTi, the handbook recommends 33 front and 36 rear; on 175, 32 front and 35 rear.

(reference Citroen Handbook BX-GB-3001)

Your guy seems to know what he is talking about.

kiwi · Post by **kiwi** » Sat Jul 18, 2009 8:19 pm

Way2go wrote:What do you see so wrong with it?

Your guy seems to know what he is talking about.

BX19TZS Front 29 psi Rear 30psi

Overinflated Tyres on twisty cold,wet, icey roads (its winter here) goes against the Road Safety Ethic I was taught.

MULLEY · Post by **MULLEY** » Sat Jul 18, 2009 11:45 pm

Tyre technologoy has moved on since the bx was 1st made, so i'd guess that the info about inflation pressures is out of date & if the tyre fitter recommended that pressure, unless the manufacturer of the tyres disagreed, then i'd go with with they recommend.

Way2go · Post by **Way2go** » Sun Jul 19, 2009 12:49 am

kiwi wrote:
BX19TZS Front 29 psi Rear 30psi

Overinflated Tyres on twisty cold,wet, icey roads (its winter here) goes against the Road Safety Ethic I was taught.

I'm not so sure that you can classify it as overinflated if it's within the pressure specification for the tyre. At the right pressure, the full footprint of the tyre is in contact with the road which is the safest condition. Same weight of car as GTi but granted that the inflation recommendation for the TZS is lower, perhaps a compromise here for comfort?

Safety is compromised badly too if the inflation is too low as the whole of the tread width no longer contacts the road but only the outside edges.

mountainmanUK · Post by **mountainmanUK** » Sun Jul 19, 2009 9:28 am

I don't know enough about the actual technology of tyres etc., but I do know that the ambient air temperature DOES affect the tyre pressures.
If a tyre is inflated to, say, a recommended 34psi at an ambient temperature of, say, 16 degrees C......then the weather cools down to, say, 0 degrees......the tyre pressure will no longer read 34psi, and consequently will run underinflated.
Similarly, if the ambient temperature rises to , say, 30 degress (as was in the UK a week or so back).....the tyre pressure will also have risen proportionally due to the air within the tyre expanding. That tyre would now be a bit overinflated.
For us in the UK, the alteration is not particularly large, and can really be disregarded, It helps if you check your tyre pressures regularly, especially during any major changes in the weather!

I tend to run my BX 185s at 32 front, 34 rear. although I do increase them a pound or two when winter approaches.

Also, a high speed run will also increase the temperature of the air within the tyre, and hence also increase it's pressure.

Someone with more techy knowledge than me will probably have some statistics to confirm this?

DLM · Post by **DLM** » Sun Jul 19, 2009 10:32 am

Good point on ambient temperature there - and I too would like to know in just way "tyre technology has moved on", though I'm sure it has changed.

Call me a cynic, but I do think it's better to know the reasons for making a statement or an assertion rather than just take it at face value. I might even talk to a local tyre fitter who's proved both helpful and knowledgeable in the past, and who isn't in thrall to a particular supply chain or company.

kiwi · Post by **kiwi** » Sun Jul 19, 2009 11:04 am

Good point about the ambiant temperature and Air Pressure loss because of it. Thats one thing I considered as a good point about Nitrogen which heres the kicker the same Tyre Firm puts in all New Tyres (Firestone NZ).
It was also something else I challenged this Tyre fitter on as to the benefit of Nitrogen in colder temperatures when Normal Road Tyres need heat to work efficantly. You guys are aware of the differance with Snow/winter tyres?

In addition to ambiant temperature I have altitude veriance of average 600 to1200 metres as a factor! Despite the arguements and dismissing of Nitrogen in Tyres thats the Only benefit I have found of that gas with Air Pressure stability and higher road temperature running. How much truth to that arguement is again open to debate! Actually there is one other benefit from a fire point of view with Nitrogen being inert and less fuel for a fire possibly able to extinguish a Tyre fire.

I think we all have the right to be cynical to claims and this one of tyre technology and higher pressures does concern me, especially considering (and I have only noticed this on Air Cylinders) that higher altitudes show higher pressures.

You see my point of concern? If these tyres are over inflated above what the Car Manufacturer recommends and then you take them to an altitude that increases that pressure further are they then unsafe?

This is the First time I have ever heard of "Tyre Technology" being used as an excuse for a tyre pressure, which seems to be a standard no matter what the car make. Being the weekend have not had the chance to check over tyre outfits advice so be keen to here what the UK perspective is considering NZ Road Safety conflict so much and is a contradiction to the term safety.

DLM · Post by **DLM** » Sun Jul 19, 2009 11:14 am

Definition from an old Oxford Pocket Dictionary:

"Technology - study and use of the mechanical arts and applied sciences"

Not the way it's used nowadays by somebody with a vested interest in selling you their gizmo, or "solution" looking for a problem/application.

kiwi · Post by **kiwi** » Sun Jul 19, 2009 11:33 am

Very true and thats how I am seeing this and I am going to be waiting and posting the email I shot off to Firestone NZ for clarification of its Tyre Inflation Policy

mountainmanUK · Post by **mountainmanUK** » Sun Jul 19, 2009 12:47 pm

Kiwi,
Considering both the altitude and temperature variations that you "suffer" from (or enjoy!

)......I would suggest that you try to stay in the middle of the recommended range for your particular tyres, but check them frequently.
If they are in the mid-range, going down to lower altitudes would move the internal pressures slightly higher, in relation to your start altitude, but should still keep them within the safe range. Similarly, going up the mountain would slightly reduce the internal pressures, but still allow them to remain in the safe range.

I guess that it may be best to initially setup the tyres somewhere halfway up the mountain!!

Of course, all this may vary dependent on the manufacturers recommendations, rather than the word of your local tyre guy, who may just be quoting recommended pressures for one particular make only?

It may eactually be worthwhile to keep a record of the pressures, at the extremes of altiutude and/or temperature that you encounter....as a point of reference for yourself and others.

Interesting topic this....with lots of variables!

MULLEY · Post by **MULLEY** » Sun Jul 19, 2009 11:07 pm

The compounds they use in the tyres, such as silica & sidewall thickness

and I too would like to know in just way "tyre technology has moved on", though I'm sure it has changed

Unfortunately i'm not that much of a geek, otherwise i might be able to quote all the extra properties that modern tyres have which one's of 10-20 years ago didnt have.

A search on the www might provide more evidence of tyre technology changes.

I certainly think tread patterns of modern tyres seem to have advanced quite a bit & help with wet weather conditions etc....

kiwi · Post by **kiwi** » Mon Jul 20, 2009 2:13 am

Email returned

Thanks for your email concerning suitable tyre pressure for your Citroen BX 19.

Bridgestone NZ Ltd’s policy on tyre inflation is firstly to support the vehicle manufacturers

recommendations.

As you are no doubt aware, tyres have a varying minimum and maximum inflation pressure range

dependent on type and including load and speed category and intended usage.

Ride comfort versus optimum tyre performance provides ongoing debate.

Best regards,

Tony.

Tony Rynbeck

Technical Services Advisor

Bridgestone NZ Ltd

So now I will go back and ask why 35psi seems to be the standard pressure they use to fill anyones tyres after speaking to a couple of other people who had tyres fitted there.

Mountainman UK, a good point I doubt that its really been looked at but now my curiosity has been perked as to the effect of altitude on the pressure in my Tyres. Given that they now have all got Nitrogen in them thats going to be an interesting experiment comparing to the Air Filled Spare as well and comparing to the Other BX that does not have Nitrogen in its tyres.