Tire pressure recommendations !

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miro-1980
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Tire pressure recommendations !

Post by miro-1980 » Wed May 20, 2009 12:39 am

Hi, to all those with racing experience !

I will be running a track day racing on Fiat track in Tychy , Poland this weekend. My 131 abarth will be on 13" wheels and Toyo semi slick tyres. (205x 60) .

What would be the recommented tire pressure and temperature ?

Anybody has eperience in this area ?

Miro
www.131abarth.pl
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Guy Croft
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Re: Tire pressure recommendations !

Post by Guy Croft » Wed May 20, 2009 2:29 pm

I do.

The only effective way is to start with some nominal setting eg: 25psi F&R, drive and warm up tyres gently and then survey the contact patch on on F and one R.

EG:

http://www.intercomp-racing.com
Enter 'pyrometer' into search.


Note US price - at $1.50 or so to £1 equates to about £272 plus duty and airmail but typically selling in the UK in some mail order outfits for over £400....*

A tyre working well will have a more or less even distribution across the contact patch. Hotter rubber on the mid section means over inflated, hotter on the outer sections means eith under-inflated (or rather radical camber).

My two-penny-worth anyhow, having wasted more time than most on this.


G

* readers - not an excuse to start fighting over prices!

mtbr
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Re: Tire pressure recommendations !

Post by mtbr » Wed May 20, 2009 7:36 pm

Miro,
There is a good outline of the procedure Guy mentions in this previous thread.
viewtopic.php?f=14&t=991

Obviously you will have to adapt the basic principle to a track day environment. You may find a definite temperature gradient across the tires, high on the inside edge to low on the outside. A spread of around 10 deg. C is acceptable. If the temperature is significantly higher or lower in the middle, compared to both edges, the pressure should be adjusted. I use Toyo 888R on my Porsche, I usually see temperatures in the mid 60s, following a cool down lap, responsible pit lane entry and parking. Temperatures whilst out on track are obviously considerably higher.

I would start with the tires pressures around 28 - 30 psi (hot) and work from there. A word of caution, if you feel the tires go "greasy" and start sliding around, back off and let them cool down. It is very easy to wear all the tread from an overheated 888 in around 20 mins. (I found out the hard way)

I have some notes from the competitions manager of Toyo UK with some additional details about the care and use of the 888R radial, I will try to find them. Do let us know how you get on and what pressures you determine are appropriate for your car.

BTW. Optimum pressures for my Porsche 993RS are 34 / 38 psi hot. So the pressures may be higher than you might expect.

Regards, Mark
AMW

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miro-1980
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Re: Tire pressure recommendations !

Post by miro-1980 » Wed May 20, 2009 10:19 pm

Guy, Mark,

thank you very much.

400 quid is a bit much for the racing I do. I am not sure I am yet good enough foe this ti make too much of a difference, though holding in curves is very important as this is where one may loose a lot of time just because the tires just will not grip well enough.
much

I was typically running circa 2,5 atm (ca 36.7 psi), but never actually measured tyre temperature. Will do it this weekend

I have a pyrometer not specifically designed for tires but should measure the temp of a tire in several spots .

Note that the kind of racing we do , is limited to ca 1,5 - 2,5 minutes runs with many curves and/or shikanes( to limit the speed and thus risk for the participants) . So it seems that selecting the right tyre pressure to start off with and to warm up the tires before the run is what we will try to do.

I expect the air tempt to be as much as 27deg.C and the track temp may be as much 37-40 deg C. This will also influence handling in curves.

Practically we will be able to check tire temperature after the first run and see if the differences are significant - and adjust if necessary. We will see if this makes any difference.

Will report next week.

Miro

Does putting not air but nitrogen gas into tires help. The story being that nitrogen is less susceptible to expansion ( read = increase in pressure) with increased temperature?

Any thoughts ?

M

PS : did look at : viewtopic.php?f=14&t=991. Very in tersting indeed.
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mtbr
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Re: Tire pressure recommendations !

Post by mtbr » Thu May 28, 2009 10:05 pm

Hi Miro,
We call your event "sprinting" I have a friend who is very successful at this type of event. He suggests B list* tires like the Toyo 888R are typically worth 4 sec per minute over good A list tires.
*The UK MSA have two lists of tire brands and types, list A and B, which are broadly "genuine road tires" and "road legal track tires".

With the short runs, you can get quite a lot of variance in your data because individual driving errors have a greater effect on the overall result. Sometimes it is better to work from the tire wear. The tire never reaches a stable hot working temp during the run, so you aim to be slightly under inflated at the start, about perfect in the middle and slightly over inflated at the end of the run. There are all sorts of fancy tread depth gauges, however good results can be obtained using a simple set of vernier calipers (carefully.) Measure tread depths at 3 points across the tread width and at 4 points around the circumference of the tire. Measure to the wear markers, not the bottom of the rain grooves.

Provided the wear is reasonably even across the working area of the tread then you are close to the correct pressures. One important point to note is that there are small triangles on the outer sidewall of 888s and other tires. The tires must be inflated so that the wear does not go beyond the tips of the triangles. i.e. if the tire is under inflated it will deform enough that the car will roll the tire under the wheel and wear the sidewall on the road surface.

By measuring tread depths, before and after an event, you can check how well the tires were inflated and also how much tread was used. Keep a note of the number of heat cycles on each tire as well and then you will be better able to assess when to relegate a set of tires from competition to practice.
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mtbr
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Re: Tire pressure recommendations !

Post by mtbr » Sun May 31, 2009 7:18 pm

Hello Miro,
Here is some imformation originally poste by Alan Meaker on a VX220 forum. Hopefully it will shed further light on your tire pressures question.

My name is Alan Meaker, I am the Motorsport Manager for Toyo Tyres (UK) Ltd.

I was at Rockingham on the Saturday 1ST March at the LOT trackday and worked with a couple of cars using our R888 tyre regarding pressures and tread temperatures.

What I would like to do is to offer some advice on tyre temperatures and pressures and how to achieve the best from our tyres when taking part in either trackdays or racing.

The R888 has a semi race construction (very stiff) and a race tread compound. The optimum tread temperature range is between 85C and 95C measured using a probe type pyrometer, and ideally a maximum difference across the tread of 9C. The maximum hot pressure we recommend is 40psi. Camber angles up to 5 degrees are permissible but the final setting will depend on tread temperatures. It is advisable to have as much positive castor as practical as castor induces a beneficial camber change during cornering. I recommend that the tyres be put through 2 heat cycles before hard use.


The pressures you use will initially depend on the weight of the car, too little pressure on a heavy car can lead to over deflection of the tyre and subsequent failure.

Below are some basic settings:

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


As a tyre gets hotter the pressure increases, this is due to the moisture in the air. The cold pressure you set to achieve a desired hot pressure will depend on the conditions on the day i.e. ambient and track temperature, wet or dry. If the day/track is cold you will need to start with a higher cold pressure as the tyre will not get as hot therefore the pressure increase will not be so great.
Hot pressures must be balanced side to side. Once the tyres have cooled you will find that you will have a difference in pressure side to side, if you have been racing on a right hand track you will find the offside pressures will usually be higher than the nearside.


Changing hot inflation pressures by small amounts can be used to fine tune handling.

Reduce Oversteer Reduce rear pressures or increase front pressures
Increase Oversteer Increase rear pressures or reduce front pressures
Reduce Understeer Reduce front pressures or increase rear pressures
Increase Understeer Increase front pressures or reduce rear pressures


Achieving the required tread temperatures will depend again on the conditions on the day i.e. ambient and track temperature, wet or dry.

You often here competitors saying “My tyres started to go of towards the end of the race”, this is usually due to the tread getting to hot.

The tread temperatures are constantly changing through out a race, hotter when cornering and cooler when on the straights and cooling even more when you are slowing to come into the pits. Therefore the temps you record in the pits will be lower than those during the race. So if you record temperatures within the range given above the probability is the temps will be too high during the race.

Increasing your tyre pressures will cause your tread temperatures to increase, more pressure stiffens the tyre’s casing which results in the tread having to do more work resulting in the tread getting hotter. Lowering your pressures will cause them to decrease.


Inevitably changing one thing will affect other things, the whole set up of your car is a compromise between anything that is adjustable.

Some of you are also asking about different compounds. Originally we only had one compound ‘GG’ (medium hard), but we have now introduced some sizes in a ‘SG’ (soft/wet) compound. This was done primarily for sprint/hillclimb (around 60 second runs) where the distances covered are relatively short and you need the tyres to work/heat up very quickly. This is not a compound I would recommend for race/trackday dry use as the tyres will go off very quickly.

The sizes that will be available are:

185/60R13, 205/60R13, 195/50R15, 205/50R15, 225/45R16, 225/45R17.

Another subject is the introduction of our Proxes R1R. This tyre was due to be launched at the beginning of 2008, unfortunately this has been delayed to at least mid 2008 but there is a good chance it will be latter than this. Regarding sizes, initially we will have a rear fit (225/45ZR17) but not the front (195/50R16).

I hope this is of some use to you.

If I can be of any further assistance please give me a call.

01933 414537


Best Regards
AMW

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miro-1980
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Re: Tire pressure recommendations !

Post by miro-1980 » Sun May 31, 2009 9:59 pm

Hi Mark,

This was very informative and most useful piece. Thank you very much.


As far as our track day last week : it turned out , it was not so easy to get the temperature reading it.

Each run was ca 2.5 min and the cars were started every 30 sec. ( all 100 of them) - so there was a que for each start , and even if we were able to heat up the tires up , they would have gotten cold just waiting in a que.

Recording the temperature was hard because there was only two of us ( me and the co -driver) and we could not stop right after the run to take the reading - we had to pas through time recording by the judges and this allowed the tyres to cool down. When we got back to the park the tyres had the time to cool off completely.

The air temperature was around 18-20 dec C. , but it was a bit windy and with high clouds obscuring the sun often. The track was dry and not to hot ( I estimate around 24-25 deg C. Also the temperature gauge I have turned out to be useless.

Nevertheless , we put 1.5 kg/cm2 in the front and 1.3 kg/cm2 in the rear ( which is 22 psi and 19 psi respectively). Just acting on experience we nicely fell into the recommendations by Alan Meaker.

We have experienced no problems with the tyres grip. ( It was a Fiat test track and the traction was generally excellent due to the quality of the turmac.)

The posts on this thread have made us aware of new elements to consider and keep in mind a well as gave us excellent guidance as to the tyre pressure and temperature.

Our next event is on June 2oth. Hopefully by this time w will be able to get a proper tyre pyrometer. Also the event will take place on an old airfield. The set-up is such that we have a goo chance to actually get the tyres properly warmed up before each start and record the temp after and before each run. This should give us some good future reference.

In out events the difference of 4-5 seconds per run may mean a difference between success or failure so gaining as much just on tyres would be a significant advantage.

Again thanks a lot !

Miro

PS : To give you also a sense of participation - here is one of our photos from Tychy
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tychy abarth.jpg
tychy abarth.jpg (67.2 KiB) Viewed 4379 times
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rmerrell
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Re: Tire pressure recommendations !

Post by rmerrell » Wed Aug 03, 2011 12:36 pm

Can I just expand this thread slightly by adding my experiences for Yokohama 048R. After witnessing a lot of contradictory behaviour in the paddock (where the 048R is the control tyre for our series), I contacted Yoko and spoke to their motorsports specialist.

His guidance to me for the 048R that the hot operating pressure target is 25psi. After discussing the details of my car (Alfa Giulia GT - RWD front engine layout - total weight 820kg excluding driver) he suggested 26/24psi F/R. I'd been running nearer 30psi and immediately beat my PB for the track.

He basically said, whatever the conditions, I should be running to that operating pressure. It means, on a warm day, starting at around 18psi on the rear which is right on the safety limit of the tyre.

The only exception was in "monsoon" conditions where he suggested adding a couple of psi.

Guy Croft
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Re: Tire pressure recommendations !

Post by Guy Croft » Wed Aug 03, 2011 12:42 pm

Do you have a *pyrometer? It would be interesting to compare its readings across your hot tread with the expert's recommendations. Would I be correct in assuming his settings are based on tyres of fairly contemporary diameter & aspect ratio where the pressures are in-part a function of the weight distribution?

That all changes when you radically alter the wheel and tyre combo, by my exp anyhow..


(*see my post above)

G

rmerrell
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Re: Tire pressure recommendations !

Post by rmerrell » Wed Aug 03, 2011 1:45 pm

I have an IR temperature gun - though he was fairly ambivolent about tyre temperatures which took me a bit by surprise. They seem more interested in looking at tyre wear over time and the discolouration caused by overheating (my fronts could run more negative camber, for instance, though would start to reduce braking capability and I already have caster wound well on)

As for tyre sizes, the 048Rs seem to be pretty limited - I'm running 205/50 R15s - and, yes, the weight distribution is factor (hence my F/R offset for front engine layout). Several other racers have contacted Yoko and received similar advice with good results. I think I now have my suspension in a good enough steady set-up to begin experimenting with tyre pressures a pound or two either side of these recommendations.

I was impressed by how willing Yoko were to discuss set-up. I can share contact details on specific request (don't want to abuse their goodwill by posting mobile phone numbers on-line)

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