Yokohama A539, tyre pressure

[simple]

I've done about 30,000km on my Yokohama A539's now - I think they're
quite a decent tyre, although wet performance still doesn't match the
Bridgestone RE711 (Fletcher & I swapped wheels for a few weeks
recently, to see what the other's tyres were like).

I was running Fletcher's tyres at a rather high pressure of 37psi -
not planned that way, but I didn't have a gauge or valve extender
which could reach the valves properly - had to use the gauge on my
tyre pump. Couldn't measure them until I took them back to Fletch.
After this experience, I thought I'd try firming up my tyres, from my
previous norm of 30psi to 35psi. It seems that they're quieter on
hard cornering now, and generally feel good. Needs more testing, but
I think the higher pressure suits me better.

In practice, driving for the conditions, the Yokos have never been
responsible for any scares. I'd buy them again. May well be doing
so about 10,000km from now.

The RE711 is amazingly quiet - only once did I provoke a squeak out
of them when I did a nasty gear change on a bend. No squealing when
sliding around corners. The A539 is much noisier.


Karl.

(Note: I don't have a lot of experience of different tyres - just
Dunlop Monza 200 [scary], Falken Zeix ZE-something [OK], A539 [pretty
good], RE711 [great] - you can evaluate my opinions accordingly)

[Sean Craig]

Try going the other extreme ... carefully ... i run as low as 26psi on
my yokos and also bridgestone comp ta. heaps more grip!!! my boss
(editor of NZ Classic Car) runs 26psi in his P6000s.

On Thursday, September 19, 2002, at 11:15 PM, Karl Mowatt-Wilson wrote:

[...]

[lou Girardin]

Interesting post Sean, I've always believed that the lower the tyre profile,
the less pressure is needed. This does vary from brand to brand though. It's
old school thinking that you need high pressure for high speed, it comes from
the days of 80 to 100% aspect ratios.
Lou

[Sean Craig]

True. As well as better grip i also have a much better ride than before.
also consider the weight of the 5. lighter cars tend to thump crash if
you run a higher tyre pressure. i'm going to try running my 539s at
24psi. i'll let you know the results.


On Tuesday, September 24, 2002, at 10:27 AM, lou Girardin wrote:

[...]

[Lindsay]

If you want to go fast, higher pressure = less rolling resistance.

Kiddies doing burnouts in their skylines will find it's easier to break the back loose with higher pressure as the wheel transfers the energy faster to the tyre surface making it easier for the energy to be turned into smoke instead of momentum. And that's why drag cars run such high profile tyres - to keep the driving wheels from turning all that energy into smoke at launch.

The lower profile the tyre is, the higher the pressure you need to run. This is because the lower volume of air in the tyre needs a higher pressure to carry the weight of the car. For example, mountain bike tyres run at 30 - 50 psi, road bikes run at 90 - 120 psi. This is also the same reason space saver tyres need to run at 60 psi.

Lower tyre pressure will result in faster tyre wear around the edges, and reduced braking performance. Higher than ideal pressure will also cause uneven tyre wear through the centre, and at a certain point also compromise braking safety.

You won't notice the impact of a low profile tyre being under inflated as fast as a high profile tyre - heavy steering etc - because the side wall provides more support for a low profile tyre. In time however, the tyre wall will become damaged, and the tyre will be a safety liability.

You'll get the most grip from the tyres by having them inflated correctly so the tyre surface is sitting as evenly as possible on the road surface. The only way to do that is to have the tyre inflated to the right pressure for the profile of the tyre and the weight of the car.

In general manufacturer recommendations are set at the comfort end of the safe range. Ideally, I'd be thinking about running about 32 psi in most MX5s unless it's less than 50 profile.

Cheers,
Lindsay

[...]

[Sean Craig]

all good ... my main thing is grip while cornering and so far 26psi has
proven to produce the best cornering results. tyre wear is not a factor
that i'm concerned about. when we test drive cars at work we often shoot
on race tracks around the country and use MX5s for photo cars. so it's a
good time to test out things like different tyre pressures in our own
cars and for me 26 is it. i find that hard cornering on our bumpy nz
roads at higher tyre pressures tends to make the rear skip to much. true
that 32psi might be the best for wear etc and for the average driver of
an MX but i personally found that 26psi suits my driving


On Tuesday, September 24, 2002, at 02:58 PM, Lindsay wrote:

[...]

[lou Girardin]

I don't really agree with this Lindsay, the reason for low profile tyres is to
give a stiffer, more responsive sidewall, and to sell tyres to rice boys. Bike
tyres have a very high aspect ratio.This is why it's more difficult to tell
when tyre pressures are low on low profile tyres. The tread belt arrangement
controls the profile of the road contact area. Higher pressure = less rolling
resistance because less tread is contacting the road. Space saver tyres run
high pressure to give adequate load bearing capacity in such a small tyre. One
exception is F1 tyres, they're high profile and low pressure, but this is a
function of suspension design and tyre regs rather than an ideal set-up.
Lou

[zorruno]

I have a nice story re this - but it will have wait until I've run my new
tyres in and have more to tell...

I'm going for a drive down waikato way tomorrow so I'll be able to test them
a bit better.

[Nigel]

So if you did this all in one morning, I'm assuming you used a warm tyre as
the base for the pressure?

I too run my A539s at 26psi and have found it to be a better grip,
particularly on bumpy corners and in the wet... but this is set when they
are cold - ie: first thing on a Sat morning before the car moves out of the
carport. You'd be surprised (well, I was, you guys might not be at the
variation in pressure as the day warms up and after you've been driving for
a while... I've checked a few times and it ends up around the high 20's/low
30s.

Are you guys talking cold tyre pressure, or warm?

Nig.

[Sean Craig]

cold ... the boss told me that he has dropped down to 24psi with his
P6000s


On Wednesday, September 25, 2002, at 06:23 PM, Nigel wrote:

[...]

[Sean Craig]

i have also done 'blind tests' when i had no idea how much air was in my
tires and slowly let pressure down until best grip was found. once again
24-26psi (cold) gave me the best result. must remember that every tire
will vary from company to company but so far with the P6000s Yoko 539s
and Comp TAs between 24 and 26psi has been the best for me.

On Wednesday, September 25, 2002, at 06:23 PM, Nigel wrote:

[...]

[Gary Morrison]

If I understand it correctly, when you set a low tyre pressure, and then drive
enthusiastically, you'll see more pressure increase than if you set a high(er)
pressure when cold. I recall Colin Partington (are you there Colin?)
explaining to me a technique he used on the track involving pressure
measurements, looking at the rise, as a means of picking the pressure that was
best for the conditions. (This when a pyrometer was not available, and
considering that the pressure rise is a result of thermal effects)

Gary

[Don Warrington]

Hi all,

Never let it be said that I neglected an opportunity to wave the flag of
Physics! For the same increase in temperature, the pressure increase is
higher for a higher starting pressure. As a rough guide, it will follow the
ideal gas law,
pressure x volume = constant x temperature
where the constant is larger for more air in the tyre. So a given % increase
in the temperature will give the same % increase in the pressure, which is a
larger pressure change for a higher starting pressure.

To actually use the equation to predict change in pressure see below - avoid
this if you don't care. The rule of thumb on racing circuits is apparently
that 10 degrees F (=5 and 1/2 degrees C) temperature increase produces 1 psi
extra pressure, and that pressures typically rise 4-10 psi during a race.

From the TV report on the last F1 race, their tyres typically run at 110-120

C, and the heaters they warm the tyres with pre-start take them up to about
80-90 C.


However
To get real numbers from this, you need to remember that the 'temperature'
in has to be in degrees K (= Kelvin = absolute) temperature - the
temperature scale which has its zero at absolute zero = -273 degrees C. So
our ordinary 20 degrees C is 293 degrees K, and if the gas in the tyre warms
up to 60 degrees C, which is 333 degrees K, the pressure will rise by the
factor 333/293 = 1.14

Then you also need to know that the pressure to use is

At 09:11 AM 9/26/02 +1200, you wrote:

If I understand it correctly, when you set a low tyre pressure, and then

drive enthusiastically, you'll see more pressure increase than if you set a
high(er) pressure when cold. I recall Colin Partington (are you there
Colin?) explaining to me a technique he used on the track involving pressure
measurements, looking at the rise, as a means of picking the pressure that
was best for the conditions. (This when a pyrometer was not available, and
considering that the pressure rise is a result of thermal effects)
[...]

[Gary Morrison]

Good stuff, but I understood that a tyre that is less inflated will see much
more activity in the rubber (its able to flex more) which will give rise to
additional heating, hence more pressure rise... is this not correct?

[Don Warrington]

Hi Gary,

At 03:30 PM 9/26/02 +1200, you wrote:

Good stuff, but I understood that a tyre that is less inflated will see much
more activity in the rubber (its able to flex more) which will give rise to
additional heating, hence more pressure rise... is this not correct?

Yes - dead right.

As I said, higher initial pressure means a larger increase FOR THE SAME
TEMPERATURE INCREASE, but then as you say, that probably ain't so - the
higher pressure means less flexing which means a smaller temperature change.
Which effect 'wins' in practice I don't know, though it does seem that the
(possibly larger) pressure increase from a lower initial pressure couldn't
be enough to produce a higher final pressure than in the tyre which started
at a higher pressure. No hare and tortoise effect, because by the time the
pressures became equal, the 'low pressure' tyre would now be as stiff as the
other.

[On the other hand, this depends on how much of the stiffness comes from the
air, and how much from the rubber casing - as I thought more about it, it
seemed to be opening a can of worms, and that is why I decided to back off
and not send the email. (Except that I then made a mistake, and sent the
mangled one anyway.) I'm not sure what the answer is.

One quote from "Race Car Vehicle Dynamics" by Milliken (father and son),
which is generally a source to be relied on: "Tire pressure and temperature
are interrelated - lower initial pressure results in more rubber distortion
and higher temperature, which in turn results in higher 'hot' temperature."
[I can agree with that, though as I said, I can't see how it could give you
higher final pressure.]

Don

[...]

[MN]

Yes but all this also presumes the alignment is correct. Just to add another
dimension to the discussion, at the Taupo Clubman's meeting last weekend the
driver of the MX5 that was racing measured the tyre temperatures properly
(i.e. outside edge, middle, inside edge and found about 17 degrees
difference (if I remember correctly) between the inside edge and outside
edge of one tyre indicating a potential alignment issue on that corner. The
muffled thumping from that corner also added to the suspicion something
wasn't as it should be. When we race (a mate's MR2 because the wife won't
let me race our 5 - yet) the first thing we make sure is that the tyre
temperature is consistent across the tyre and then start on raising and
lowering the pressures to improve grip and to try and get equal temperature
between all 4 tyres, without losing grip which leads to raising and lowering
the suspension which leads ... and into the black art of suspension and
tyre tuning you go, especially so at Taupo where basically all the load is
going on the right side and the right rear in particular. Its even worse on
very cold days as it was last Saturday when its hard to get the tyres up to
temperature but the pressures can't be reduced much before side wall flex
comes into play. Its all so much easier when its just for the road.

Mark