Tyre Pressures

Archives of Posts to the NZ MX5 List back in 2006
EricW
See my 5 and raise you.
See my 5 and raise you.
Posts: 95
Joined: Wed May 24, 2006 7:07 pm
Location: Whangaparaoa

Tyre Pressures

Post by EricW » Wed Feb 01, 2006 7:58 am

That's interesting Terry, because it rather flies in the face of
manufacturers recommendations.

I have a light car, the MX 5 for which the recommendation is 28 PSI, a
medium weight car, a Mazda 626, for which the recommendation is 32 front and
28 rear and a heavy car, the BMW 528, ( and you would think BMW know a bit
about roadholding and comfort) which has different recommendations according
to speed and load. I have never really had too much problem with the makers
recommendations.

The BMW usually runs with only me in it, and the recommendation is only 28
all round, increasing to 30 for "sustained high speed" Even fully loaded,
with a road weight of about 2.2 tonnes, and sustained high speed, the
maximum pressure recommended is 35 PSI

It runs on 235/16 Bridgestones

There is a very noticable difference in ride and grip if you have been using
the car fully loaded and fail to adjust the pressure down after you go back
to normal loads. It's the only time I see the traction control operate, the
tail can get quite loose on a wet road, but not if the tyre pressures are
correct for weight.

Paradoxically, I once had a Toyota Corolla, new in about 1993, as a company
car. It recommended 26 PSI, but I ran it at 40 PSI, which was the only way
to achieve reasonable steering loads round town. The grip improved
noticeably and the tyre life was excellent.

So I guess the real answer is that you get guided by the makers and then
experiment to find what feels right to you

Eric

EricW
See my 5 and raise you.
See my 5 and raise you.
Posts: 95
Joined: Wed May 24, 2006 7:07 pm
Location: Whangaparaoa

Tyre Pressures

Post by EricW » Wed Feb 01, 2006 7:58 am

That's interesting Terry, because it rather flies in the face of
manufacturers recommendations.

I have a light car, the MX 5 for which the recommendation is 28 PSI, a
medium weight car, a Mazda 626, for which the recommendation is 32 front and
28 rear and a heavy car, the BMW 528, ( and you would think BMW know a bit
about roadholding and comfort) which has different recommendations according
to speed and load. I have never really had too much problem with the makers
recommendations.

The BMW usually runs with only me in it, and the recommendation is only 28
all round, increasing to 30 for "sustained high speed" Even fully loaded,
with a road weight of about 2.2 tonnes, and sustained high speed, the
maximum pressure recommended is 35 PSI

It runs on 235/16 Bridgestones

There is a very noticable difference in ride and grip if you have been using
the car fully loaded and fail to adjust the pressure down after you go back
to normal loads. It's the only time I see the traction control operate, the
tail can get quite loose on a wet road, but not if the tyre pressures are
correct for weight.

Paradoxically, I once had a Toyota Corolla, new in about 1993, as a company
car. It recommended 26 PSI, but I ran it at 40 PSI, which was the only way
to achieve reasonable steering loads round town. The grip improved
noticeably and the tyre life was excellent.

So I guess the real answer is that you get guided by the makers and then
experiment to find what feels right to you

Eric

Colin
Need, more, 5-ing, time....
Need, more, 5-ing, time....
Posts: 101
Joined: Fri May 19, 2006 9:42 am
Location: Petone

Tyre Pressures

Post by Colin » Wed Feb 01, 2006 11:02 am

Hi all,

Pressures are a fantastic topic; they have an enormous amount to do with
temperatures, and we should all love those! :)

The new in NZ Mx5 I own states clearly that the pressure should be 28 psi.
Why?
It was set at that for, the original lightweight Bridgestone's that came
with the car.
Also for the smooth roads of the USA and cosseting ride required to sell
cars there. The USA was correctly identified as the market that would make
or break the sales needed. Mazda as a company were under serious financial
pressure at that time.
Our roads are just not made the same, and our driving styles are not the
same. So why would the pressure be the same? It's unlikely that it would.

The choice of pressure is made more difficult by the variety of construction
used by tyre manufacturers. The side wall deflection is perhaps most
crucial, and the factor that most influences people to choose low profile
tyres to control.

Bmw do know a great deal about road holding and comfort. They dont bother
themselves with knowing about our roads. Their largest market is? And they
dont change the tyre specs for us. They may specify a locally available
tyre, and dont want to print new stickers or books so the pressure issue is
left unattended. They are not alone in this. A Jap import 'Euro' car often
has the same sticker and same pressure recommendations as a NZ new car.
Different tyres, different roads, different driving styles and the pressure
is the same? I dont accept that as correct or more importantly, safe.

A huge number of accidents both minor and serious could be avoided if the
plagues of NZ tyres were eliminated and they are 'under inflation' and
'uneven inflation' whether deliberate through lack of knowledge or
deliberate though ignoring the need to regularly check them.

There is also a good many cars in NZ with incorrect tyres for the rims, size
wise.
For example: A tyre with a 185mm nominal width is best suited to a 6" rim.
(I know there is a mix of imperial and metric there, dont' question it. It
has just evolved that way)
A Tyre with a nominal 195 width is best suited to a 6.5" rim. Other size
rims can be used with some compromise. A 195 tyre on a 6" rim will always
have the sidewalls pulled in near the bead. This gives them a tendency to
lift the outside of the tyre off the road. Rounding the tread. Reducing
contact patch and, as the car corners possibly squealing easily and losing
some stick ability or traction.

As I said at the top pressure and temperature are totally related. What you
are also doing when you alter the pressure is altering the temperature that
the tyre will achieve. Road tyres have to cope with quite a range of hot or
cold roads and the heat build caused by cornering and the flex in the tyre.
That is why road tyres are a compromise. Some better than others.

A tyre for racing does not have to conform to those compromises and so will
be very good at one end of the spectrum and likely very poor at the other.
I should add here that I am not in the tyre industry and am not an expert (x
being the unknown quantity, and a spurt being a drip under pressure)

All this adds up to is that our roads here have a very different surface and
are likely to be patched and uneven and worn and very definitely under
maintained.

So my thinking is that if you have a correctly sized tyre of reasonable
quality the pressure should be...

For Auckland motorway and suburban streets: no lower than 28psi (will give
that Hollywood cruise)

For the rest of New Zealand: absolutely no lower than 30psi. (I have never
heard an advanced driving instructor suggest anything less.)

Right all of you that got to the bottom, Well done!
That lot should put the cat firmly among the pigeons. lol.

Oh.. I almost forgot to tell this; in the eighties I had a new car that the
owners and manufacturers recommendation was this: 'Do not operate the
vehicle with the head restraints removed.' Mine was a Sigma glx with
removable front headrests. My colleagues was a base model with low back
seats and no headrests. His book had the same instruction though!

You have to smile at that stuff.


Cheers

Colin Partington
Cell: 021 782748

From ben.nakagawa@gmail.com Fri Apr 27 17:43:36 2007
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Date: Wed, 1 Feb 2006 12:04:55 +1300
From: Ben Nakagawa <ben.nakagawa@gmail.com>
To: MX5List <mx5list@mx5club.org.nz>
Subject: Re: Tyre Pressures
In-Reply-To: <462d1ee10601301950u70a27b22l24fdac84f66aaab0@mail.gmail.com>
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<200601310243.k0V2hZ628600@plus43.host4u.net>
<462d1ee10601301950u70a27b22l24fdac84f66aaab0@mail.gmail.com>
Precedence: list
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I rechecked the pressure this morning and It was 30psi.
I remember that When I bought the car it was about 25psi but then I pumped
up a little.

I would try little more higher pressure some time...


Ben


On 1/31/06, Ben Nakagawa <ben.nakagawa@gmail.com> wrote:
[...]
- Dave.


--
Ben Nakagawa
Ben.Nakagawa@gmail.com
--
Ben Nakagawa
Ben.Nakagawa@gmail.com
Colin
021 869 231

Colin
Need, more, 5-ing, time....
Need, more, 5-ing, time....
Posts: 101
Joined: Fri May 19, 2006 9:42 am
Location: Petone

Tyre Pressures

Post by Colin » Wed Feb 01, 2006 11:02 am

Hi all,

Pressures are a fantastic topic; they have an enormous amount to do with
temperatures, and we should all love those! :)

The new in NZ Mx5 I own states clearly that the pressure should be 28 psi.
Why?
It was set at that for, the original lightweight Bridgestone's that came
with the car.
Also for the smooth roads of the USA and cosseting ride required to sell
cars there. The USA was correctly identified as the market that would make
or break the sales needed. Mazda as a company were under serious financial
pressure at that time.
Our roads are just not made the same, and our driving styles are not the
same. So why would the pressure be the same? It's unlikely that it would.

The choice of pressure is made more difficult by the variety of construction
used by tyre manufacturers. The side wall deflection is perhaps most
crucial, and the factor that most influences people to choose low profile
tyres to control.

Bmw do know a great deal about road holding and comfort. They dont bother
themselves with knowing about our roads. Their largest market is? And they
dont change the tyre specs for us. They may specify a locally available
tyre, and dont want to print new stickers or books so the pressure issue is
left unattended. They are not alone in this. A Jap import 'Euro' car often
has the same sticker and same pressure recommendations as a NZ new car.
Different tyres, different roads, different driving styles and the pressure
is the same? I dont accept that as correct or more importantly, safe.

A huge number of accidents both minor and serious could be avoided if the
plagues of NZ tyres were eliminated and they are 'under inflation' and
'uneven inflation' whether deliberate through lack of knowledge or
deliberate though ignoring the need to regularly check them.

There is also a good many cars in NZ with incorrect tyres for the rims, size
wise.
For example: A tyre with a 185mm nominal width is best suited to a 6" rim.
(I know there is a mix of imperial and metric there, dont' question it. It
has just evolved that way)
A Tyre with a nominal 195 width is best suited to a 6.5" rim. Other size
rims can be used with some compromise. A 195 tyre on a 6" rim will always
have the sidewalls pulled in near the bead. This gives them a tendency to
lift the outside of the tyre off the road. Rounding the tread. Reducing
contact patch and, as the car corners possibly squealing easily and losing
some stick ability or traction.

As I said at the top pressure and temperature are totally related. What you
are also doing when you alter the pressure is altering the temperature that
the tyre will achieve. Road tyres have to cope with quite a range of hot or
cold roads and the heat build caused by cornering and the flex in the tyre.
That is why road tyres are a compromise. Some better than others.

A tyre for racing does not have to conform to those compromises and so will
be very good at one end of the spectrum and likely very poor at the other.
I should add here that I am not in the tyre industry and am not an expert (x
being the unknown quantity, and a spurt being a drip under pressure)

All this adds up to is that our roads here have a very different surface and
are likely to be patched and uneven and worn and very definitely under
maintained.

So my thinking is that if you have a correctly sized tyre of reasonable
quality the pressure should be...

For Auckland motorway and suburban streets: no lower than 28psi (will give
that Hollywood cruise)

For the rest of New Zealand: absolutely no lower than 30psi. (I have never
heard an advanced driving instructor suggest anything less.)

Right all of you that got to the bottom, Well done!
That lot should put the cat firmly among the pigeons. lol.

Oh.. I almost forgot to tell this; in the eighties I had a new car that the
owners and manufacturers recommendation was this: 'Do not operate the
vehicle with the head restraints removed.' Mine was a Sigma glx with
removable front headrests. My colleagues was a base model with low back
seats and no headrests. His book had the same instruction though!

You have to smile at that stuff.


Cheers

Colin Partington
Cell: 021 782748

From ben.nakagawa@gmail.com Fri Apr 27 17:43:36 2007
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Date: Wed, 1 Feb 2006 12:04:55 +1300
From: Ben Nakagawa <ben.nakagawa@gmail.com>
To: MX5List <mx5list@mx5club.org.nz>
Subject: Re: Tyre Pressures
In-Reply-To: <462d1ee10601301950u70a27b22l24fdac84f66aaab0@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
References: <20060130202653.WGXE18564.mta2-rme.xtra.co.nz@202.27.184.228>
<200601310243.k0V2hZ628600@plus43.host4u.net>
<462d1ee10601301950u70a27b22l24fdac84f66aaab0@mail.gmail.com>
Precedence: list
Message-ID: <AUR20D.A.R8G.XGZMGB@L733>

I rechecked the pressure this morning and It was 30psi.
I remember that When I bought the car it was about 25psi but then I pumped
up a little.

I would try little more higher pressure some time...


Ben


On 1/31/06, Ben Nakagawa <ben.nakagawa@gmail.com> wrote:
[...]
- Dave.


--
Ben Nakagawa
Ben.Nakagawa@gmail.com
--
Ben Nakagawa
Ben.Nakagawa@gmail.com
Colin
021 869 231

EricW
See my 5 and raise you.
See my 5 and raise you.
Posts: 95
Joined: Wed May 24, 2006 7:07 pm
Location: Whangaparaoa

Tyre Pressures

Post by EricW » Wed Feb 01, 2006 12:17 pm

You raise some good points Colin, however, the fact remains that, sticking
to the manufacturers specs, for the type of driving the manufacturer was
anticipating when he built the car, does seem to work. Ok, if you are going
to up the power drastically and race the car, or drive it in a racing
manner, you will need to do something different.

As I said, The BMW definitely handles best when the tyres are correct for
the load, and that set of tyres, (Bridgestone Potenzas), has run nearly
100,000kms on the car. Could you really ask for much more?

Eric

EricW
See my 5 and raise you.
See my 5 and raise you.
Posts: 95
Joined: Wed May 24, 2006 7:07 pm
Location: Whangaparaoa

Tyre Pressures

Post by EricW » Wed Feb 01, 2006 12:17 pm

You raise some good points Colin, however, the fact remains that, sticking
to the manufacturers specs, for the type of driving the manufacturer was
anticipating when he built the car, does seem to work. Ok, if you are going
to up the power drastically and race the car, or drive it in a racing
manner, you will need to do something different.

As I said, The BMW definitely handles best when the tyres are correct for
the load, and that set of tyres, (Bridgestone Potenzas), has run nearly
100,000kms on the car. Could you really ask for much more?

Eric

Simon Lord
See my 5 and raise you.
See my 5 and raise you.
Posts: 98
Joined: Fri Sep 22, 2006 1:09 pm
Location: Albany

Tyre Pressures

Post by Simon Lord » Wed Feb 01, 2006 1:43 pm

If anyone is interested, I run Pirelli P6000s on my NA. These were
originally set to 28psi and I was very disappointed with them on turn-in
compared to the unknown Japanese tyres that were on the car before. I
actually went back to the fitter in Newmarket to discuss, and having tried
them he put the pressures up to 36psi. This improved things but I felt they
were a little too skittery that hard so have run them on 32 for the past 2
years. Basically, I don't think they are a very good tyre for the MX5 and
wouldn't buy them again, but my advice to anyone would be to test different
pressures and see what provides the best ride/handling compromise given your
own style of driving.

Simon
97 SR Ltd (sparkle green)
Email: simon@franchise.co.nz

Simon Lord
See my 5 and raise you.
See my 5 and raise you.
Posts: 98
Joined: Fri Sep 22, 2006 1:09 pm
Location: Albany

Tyre Pressures

Post by Simon Lord » Wed Feb 01, 2006 1:43 pm

If anyone is interested, I run Pirelli P6000s on my NA. These were
originally set to 28psi and I was very disappointed with them on turn-in
compared to the unknown Japanese tyres that were on the car before. I
actually went back to the fitter in Newmarket to discuss, and having tried
them he put the pressures up to 36psi. This improved things but I felt they
were a little too skittery that hard so have run them on 32 for the past 2
years. Basically, I don't think they are a very good tyre for the MX5 and
wouldn't buy them again, but my advice to anyone would be to test different
pressures and see what provides the best ride/handling compromise given your
own style of driving.

Simon
97 SR Ltd (sparkle green)
Email: simon@franchise.co.nz

Simon Lord
See my 5 and raise you.
See my 5 and raise you.
Posts: 98
Joined: Fri Sep 22, 2006 1:09 pm
Location: Albany

Tyre Pressures

Post by Simon Lord » Wed Feb 01, 2006 3:05 pm

You're right about the sparkle green. It might have been on Bridgestones
originally but it wasn't when I got it - have just checked back and my note
from when I replaced them says 'some Japanese brand I've never heard of'.
Good point about using the tyre designed for the car but not only does
technology change but NZ roads are different from US/Japanese roads because
of the coarse chip. When the time comes to replace them I'll weight up
Bridgestone vs Toyo's, I expect - they seem to be the top picks on this
list.

Simon
97 SR Ltd (sparkle green)
Email: simon@franchise.co.nz

Simon Lord
See my 5 and raise you.
See my 5 and raise you.
Posts: 98
Joined: Fri Sep 22, 2006 1:09 pm
Location: Albany

Tyre Pressures

Post by Simon Lord » Wed Feb 01, 2006 3:05 pm

You're right about the sparkle green. It might have been on Bridgestones
originally but it wasn't when I got it - have just checked back and my note
from when I replaced them says 'some Japanese brand I've never heard of'.
Good point about using the tyre designed for the car but not only does
technology change but NZ roads are different from US/Japanese roads because
of the coarse chip. When the time comes to replace them I'll weight up
Bridgestone vs Toyo's, I expect - they seem to be the top picks on this
list.

Simon
97 SR Ltd (sparkle green)
Email: simon@franchise.co.nz

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