Tyre Pressures

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Neilparry
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Tyre Pressures

Post by Neilparry » Thu Jun 01, 2017 1:24 pm

Just a thought. All that are new to the track experience may find some valuable information in the art of setting your tyre pressures on the day. I know it shows setting up a fwd car but the principal is the same.

Trackdays.ie
HOMETRACK DAY TYRE PRESSURES AND HOW TO SET THEMTRACK DAY INFORMATIONTRACK DAY TYRE PRES
MONDAY, 29 MAY 2017 / PUBLISHED IN TRACK DAY INFORMATION
Track day tyre pressures and how to set them

Ahh the black art of tyre pressures! In motor racing circles, up at the sharp end where championships are at stake, tyre pressures are a closely guarded secret – just ask our co-founder, Stephen Kershaw. A few years ago when he was winning championships in Formula Vee he kept a little black book, not of phone numbers but of tyre pressures! He has pages and pages of notes relating to how his tyres performed relative to the weather conditions, track conditions, damper settings and all kinds of suspension set up variables.



Luckily with track days we’re all just here for a bit of craic and info on tyre pressures certainly isn’t a secret but it is often misunderstood or completely overlooked. The tyre pressures you run on a race track will have a massive impact of your car’s handling and its tyre wear so it’s worth spending a little time getting them right.

On a race track your tyres get hot, when they get hot the air inside them expands which in-turn increases the tyre pressure, the hotter the tyre, the greater the pressure. Track tyres in particular have a temperature and pressure range in which they work best when they’re hot. If a tyre gets too hot it will loose grip. So the idea is to get all 4 tyres operating within their optimum hot temperature and pressure range.

On a circuit that runs clockwise like Mondello Park there are generally more right handers than left handers, this means that the tyres on the left of the car, particularly the front left will have more work to do and will heat up more, which will increase the tyre pressure more than those on the right.



So “what tire pressures should I run?” we hear you ask!

If you’re using standard road tyres, a good starting point is 2-4 psi below the car manufacturers recommended pressures with a target hot pressure of 2-4 psi above.

If you’re using a track day tyre like the Yokohama A048 or Toyo R888 then you want to run them at the tyre manufacturer’s recommended ‘hot’ pressures.

Here’s a couple of examples of manufacturers recommended ‘hot’ pressures

Yokohama A048 tyre pressures 29 to 31 psi hot.
Yokohama AD08R tyre pressures 32 – 34 psi hot.
Toyo R888 tyre pressures 28 – 40 psi hot.
The above makes the assumption that you’re driving a relatively heavy saloon/hatch as weight does have an impact on the pressures you’ll need to run. The chart below is what Toyo recommend for their R888 track day tyre

VEHICLE WEIGHT COLD PRESSURE HOT PRESSURE
Very Light < 800kg 17 – 22 psi 22 – 29 psi
Light 800kg – 1000kg 20 – 26 psi 24 – 32 psi
Heavy 1000kg – 1400kg 23 – 27 psi 28 – 40 psi
Very Heavy > 1400kg 27 – 35 psi 37 – 40 psi


So using the Trackdays.ie EK Civic which weighs 980kg’s and runs Toyo R888r’s as an example here’s how we set the tyre pressures for maximum grip and minimal wear.

First track session: Starting pressures
Looking at the chart above, the civic falls into the top end of the ‘light’ vehicle weight category with an ideal hot temp of 24-32psi. So we want to aim for 30 – 32psi hot. For the first session track we want the tyres to exceed 32 psi so I can bleed them back to 30-32 psi. We start at 28 psi cold all round.
After 5 or 6 quick laps we pit and check the pressures. They’ve have gone up to 38 psi on the left front, which does most of the work at Mondello and just 33 psi on the right rear. So while the tyres are all still hot we bleed out air until they’re all 30psi.

Second track session: Double checking

Now we have the tyres much closer to their ideal pressures we go out for a slightly longer stint to make sure all the tyres will get to their maximum temps. When we come back in the pits we quickly check the pressures and again bleed out air where necessary. This time only only the front left needs 1.5psi letting out, the others are all spot on 32psi

Recording the cold pressures.
After lunch, once everything has completely cooled off we check the tyres again and record their cold starting pressures. Here’s what we found

Cold Pressures:
Left Front: 23 psi
Right Front: 24 psi
Left Rear: 26 psi
Right Rear: 27 psi

You can see that the tyres that do the most work need to start off at much lower temps as they heat up more. So the next time you set your cold pressure for the first track session of the day you might want to start with pressures a bit closer to this – maybe 24psi front and 27psi rear.



While you’re at it

Once you’ve checked your tyre pressures, we’d highly recommend torqueing your wheel nuts after each track session. We find that on our cars at least a couple of nuts will have come loose by a quarter of a turn or so. If left unchecked they could become extremely loose by the end of the day.

Heading home
If you’re driving back home in your track car you should return the tyres to the car manufacturers cold tyre pressure recommendation as the pressures you use on track will more than likely be much too low for the road.



A final word:

This article really only scratches the surface when it comes to tyre pressures and tyre tech but it’s a good starting point for the beginner. To find what works for you and your car/tyre combo you’ll just have to experiment and record what you find. If you really want to get technical we’d recommend talking to the tyre manufacturer with details of your specific set up. You could also get yourself tyre pyrometer and start measuring temp differences across the surface of your tyres. This can give you valuable info on setup. A maximum ten percent variation across the surface of the tyre is ideal

If the tyre is hotter in the centre it may indicate the tyre is over inflated.
If the tyre is hotter on the edges it may indicate the tyre is under inflated.
If the tyre is progressively hotter towards the outside the car may need more negative camber or is being over driven.
If the tyre is progressively hotter towards the inside the car may have too much negative camber.


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Re: JDM Castle Combe 2017 - Track Sessions

Post by 13Black » Thu Jun 01, 2017 2:07 pm

Mr Holmes, would you be able to divulge the cold and hot pressures you see with you fancy tyre dongle?
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Re: JDM Castle Combe 2017 - Track Sessions

Post by ChrisHolmes » Thu Jun 01, 2017 4:13 pm

245/35R18 Pirelli P Zero Direzione all round
All have worn the inner and outer shoulders over the past 6k miles and six track/event days which suggests that the 32psi cold pressure is too low.
I leave the pressure at that for track use and I have seen it rise to 38psi when the tyre temp is up in the 50'C area.
Currently running at 36psi as an experiment.
The tyres are not good at all when its cold and damp but in the dry they are superb on track.
The TPMS system at c£75 is excellent value for money as it has internal sensors for temp and pressure. Others that I have seen retailed here in the UK are c£150
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Re: JDM Castle Combe 2017 - Track Sessions

Post by Dr. FrankenRex » Thu Jun 01, 2017 4:17 pm

32psi cold is too low?

That's weird, although perhaps to do with sidewall stiffness as the AD08Rs are, according to Yokohama, run at 32-34psi hot...
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Re: JDM Castle Combe 2017 - Track Sessions

Post by ChrisHolmes » Thu Jun 01, 2017 4:44 pm

13Black wrote:Mr Holmes, would you be able to divulge the cold and hot pressures you see with you fancy tyre dongle?
This is the system that I purchased back in 2016. Its gone up in price a bit though!

http://www.ebay.co.uk/itm/Solar-TPMS-Ti ... SwgQ9V3Wy5

Just spotted the same unit from another supplier at a lower price

http://www.ebay.co.uk/itm/4-Internal-Se ... 1253433650
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Re: Tyre Pressures

Post by Peter Cox » Fri Jun 02, 2017 2:14 pm

Mini Cooper - in the lead, before nearside front wheel tore off!.tif
we’d highly recommend torqueing your wheel nuts after each track session.

Absolutely right. However, when I raced my Mini Cooper many years ago the problem wasn't the nuts but the strength of the wheel My offside front tore through the nuts on the last corner of the last lap - and I was well in the lead!

So for track days and racing also make sure that your wheels are up to it.

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Re: Tyre Pressures

Post by wgimenes » Fri Jun 02, 2017 4:41 pm

I'll bring my torque wrench.

Someone must bring the socket, though.

:-)

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Re: Tyre Pressures

Post by warpc0il » Fri Jun 02, 2017 7:47 pm

My nuts automatically tighten as I hit the apex :roll:
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Re: Tyre Pressures

Post by ChrisHolmes » Fri Jun 02, 2017 8:25 pm

Mine retract in the pit lane!
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