Help with tire pressures

TURBO2GO

TURBO2GO

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Doc to follow up with what you and Billy talked about HERE....

1) How do I find the "optimal" pressure for my tires?

2) Should I go one session and then measure immediately and try to adjust that way? what is the best way to get optimal "hot" pressure?

3) Should I keep the F&R the same if the optimal pressure for the tires is the same?

Next Friday I am running at Lime Rock. It will probably be hot, in the 80's or 90's. I am running stock 2005 wheels. My tires are stock sizes, 215/40/17 and 255/40/17, Dunlop Star Spec Z1. Is there a good starting point?
 
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Invest in a GOOD tire pressure gauge and a PROBE TYPE tire pyrometer (NOT an infrared gun).

Optimal tire pressures depend on many factors (Vehicle weight, tire size/compound, alignment, camber, suspension, etc...). To simplify things, 'generally speaking' R-compound and 'street' tires generate the most grip at 36-40psi hot for a 2,500-3,500lb car. I use 38psi as a HOT starting target.

Depending on track temperature, the colder the track, the closer you should set your COLD/starting pressure to your ending HOT target pressure.

A PROBE TYPE tire pyrometer will help determine how effectively your setup is using the tires and how to adjust alignment, camber, tire pressure, etc... *Make sure to stick the probe all the way into the tire (~8mm) -you will not pop the tire. Also do not measure the tire close to the edge of a tread block.

I personally do not like the factory pressure reccomendations -which were set for street use, because when the rear pressures increase north of 40, 42, 45psi hot, you will reduce your rear contact patch and grip, while the fronts are in their ideal operating pressures - resulting in an oversteering tire pressure bias.

My baseline setting is to target 38psi hot all around and adjust from there. On a cold day, I might start off at 34psi cold then bleed the pressures down to 38psi immediately after I get off the track (with no cooldown lap). In following sessions, I would check the pressure before you go out but probably not change the pressure. In the middle of the day, 32psi might be a good starting point since in hot days, tires can increase 6-8psi.

Depending on the balance of the car, you can dial in more understeer by increasing the front tire pressure above 38psi, or if the car dosn't turn, you can increase the rear pressures above 38psi (to say 40-42psi) to free the car up.


Turbo: The Dunlop Star Spec Z1 is one of the best street tires out there (almost Yokohama AD08 performance for a fraction of the cost). The above should apply for most street/R-compound tires.



Billy
 
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Both billy and I are fans of similar pressures front and rear on track,caveat if your car is ballanced/neutral to begin with.Rather than get all crazy fuzzy with bla bla,do this dave ,once you get to the track bleed your tires to 32 cold front and 30 rear, after a good session say 20-30 minutes come in and park the car and as quickly as you can get your pressure hot.with the stock tires shoot for a baseline of 38-40 psi hot.You then need to feel how the car is doing(handling) and adjust as needed.
 
You will get many feedback on this but overall, start with a conservative baseline and adjust after each session's experience "if" need be. If your tires have good tread on them like 8/32, with 90F ambient temps and no diet to bring the car weight down, you will indeed easily get 8-10 psi with heat in them if you are pushing the car.

For OEM street tires at the track, I have found the 33F and 40R hot to work well. This means cold back out about 4-6 psi on each in the morning - depending how quickly you get them hot. By noon you may found yourself having bled them another 4 psi.

Not sure about 36-38 on the fronts as that would indeed further accentuate the understeer and your power steering will feel quite loose. With track tires - like R compounds, I seem to like 36-38max.

YMMV.
 
docjohn said:
Both billy and I are fans of similar pressures front and rear on track,caveat if your car is ballanced/neutral to begin with.Rather than get all crazy fuzzy with bla bla,do this dave ,once you get to the track bleed your tires to 32 cold front and 30 rear, after a good session say 20-30 minutes come in and park the car and as quickly as you can get your pressure hot.with the stock tires shoot for a baseline of 38-40 psi hot.You then need to feel how the car is doing(handling) and adjust as needed.
Click to expand...
In a NSX with similar pressures F&R, the handling should go towards a safer UNDERSTEER (due to the smaller front tire relative to rear) rather than a setup with a already high rear cold pressure -which would make the car oversteer more and be less forgiving.

For most drivers, understeer is safer and more forgiving, especially in our mid engine platform. I rarely hear people (especially beginning drivers) complaining about understeer.


For the record, I love oversteer
 
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Hrant good points but I'd rather have him push a little around lrp. he can always bleed the front off from 38 if he can't get the front to turn in crisply,safer that way.I see Billy chimed in so get that pyrometer dave!
 
stuntman said:
In a NSX with similar pressures F&R, the handling should go towards a safer UNDERSTEER (due to the smaller front tire relative to rear) rather than a setup with a already high rear cold pressure -which would make the car oversteer more and be less forgiving.

For most drivers, understeer is safer and more forgiving, especially in our mid engine platform. I rarely hear people (especially beginning drivers) complaining about understeer.


For the record, I love oversteer
Click to expand...

I know you love it:cool: your a pro and you love to drift.:wink:
 
So I guess I won't stay until I see the flag thrown? The tires cool that fast that a cool down lap will change them even if they are still rolling on hot asphalt? I am surprised.

Where do I get a temp probe?

Is this thing good? it monitors pressure and temperature. Looks cool but probably more than what I need now although it would make monitoring easy.

http://www.amazon.com/Pacific-Dualies-90000-PressurePlus-Temperature/dp/B003GCLJZO
 
TURBO2GO said:
Is this thing good? it monitors pressure and temperature. Looks cool but probably more than what I need now although it would make monitoring easy.

http://www.amazon.com/Pacific-Dualies-90000-PressurePlus-Temperature/dp/B003GCLJZO
Click to expand...


NO!

31sSNo0Y1QL._SL500_AA300_.jpg

http://www.amazon.com/gp/product/B0..._m=ATVPDKIKX0DER&pf_rd_r=15QD86W14QSA2H8CC6BT

41Uiz%2BIAmhL._SL500_AA300_.jpg

http://www.amazon.com/Longacre-Memo..._8?ie=UTF8&s=automotive&qid=1278704971&sr=8-8

And yes the tires (surface temp) cool down dramatically very quickly. If you pull off the track with out a cool down and check them and then check them again a minute later you will see the temps dropping like a rock. If you do a cool down lap and then wait until you pull in to the paddock and take the temps the info is worthless.
 
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Dave I use longacre needle probe.
 
docjohn said:
Hrant good points but I'd rather have him push a little around lrp. he can always bleed the front off from 38 if he can't get the front to turn in crisply,safer that way.I see Billy chimed in so get that pyrometer dave!
Click to expand...


Good point. I just want him to experience the four wheel drift before it gets to the snap "O" ..... :eek::tongue:
 
stuntman said:
My baseline setting is to target 38psi hot all around and adjust from there. On a cold day, I might start off at 34psi hot then bleed the pressures down to 38psi immediately after I get off the track (with no cooldown lap).
Click to expand...
I'm guessing you meant to say that you might start off at 34 psi cold then bleed the pressures down to 38 psi...
 
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TURBO2GO said:
So I guess I won't stay until I see the flag thrown? The tires cool that fast that a cool down lap will change them even if they are still rolling on hot asphalt? I am surprised.
Click to expand...
CL65 Captain said:
And yes the tires (surface temp) cool down dramatically very quickly. If you pull off the track with out a cool down and check them and then check them again a minute later you will see the temps dropping like a rock. If you do a cool down lap and then wait until you pull in to the paddock and take the temps the info is worthless.
Click to expand...
The ideal 'cooldown lap' is where you go around the track as fast as possible with using minimal to no braking. You should be cornering at speed (which keeps the tires at operating temps) so you can have a more accurate reading when you check them. Not only do tires cool down a minute later, you have to check your temps quickly because the tire temps would have dropped a little by the time you get around to checking your 4th tire.

*You want to check (and record) your tire temps in 3 locations per tire (outside, middle, inside - IN THAT ORDER) measuring about ~1-1.5" from the shoulder of the tire (for outer and inner measurement) and in the middle of the tread blocks, away from any corner of a tread block. The ideal location will depend on the tread design, but staying far away from the shoulders of the tire and the edge of a tread block will yield more consistent numbers.

Operating temps of tires varies on many factors but generally speaking you don't want to see under 150*F or over 220*F -and a 20*F spread from inside to outside is a good rule of thumb to determine tire pressure and camber. EX: 178-189-202 (outside-middle-inside).

nsxtasy said:
I'm guessing you meant to say that you might start off at 34 psi cold then bleed the pressures down to 38 psi...
Click to expand...
Yes, you are right! Thank you for catching my error :)


I will edit my post.
 
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Billy, my inside temps are usually dramatically higher than the middle/out and I have always been under the impression that was due to toe which causes them to heat up when going down the straights and thus skews the data for the inside.

????
 
CL65 Captain said:
Billy, my inside temps are usually dramatically higher than the middle/out and I have always been under the impression that was due to toe which causes them to heat up when going down the straights and thus skews the data for the inside.

????
Click to expand...

front ,rear,both?
 
what are your alignment specs? and what are your hot tire pressures?
 
docjohn said:
what are your alignment specs? and what are your hot tire pressures?
Click to expand...

2.8 camber/2.5 camber - 3mm toe out
3.2 camber/3.0 camber - 4mm toe in

(why the stagger in camber L/R ? - my home track has 8 right turns and 2 left :wink:)

38/38 hot Dunlop Z1

PS: Car handles great! My student who went for a ride today said, "I can not believe how well this thing sticks with street tires." :tongue:
 
CL65 Captain said:
2.8 camber/2.5 camber - 3mm toe out
3.2 camber/3.0 camber - 4mm toe in

(why the stagger in camber L/R ? - my home track has 8 right turns and 2 left :wink:)

38/38 hot Dunlop Z1

PS: Car handles great! My student who went for a ride today said, "I can not believe how well this thing sticks with street tires." :tongue:
Click to expand...
What are your hot temps?
 
well capt....I have always had a nice gradient across the tires like Billy mentioned,but these are ra1...maybe the combo of camber and toe coupled with your driving style and the fact that they are still street tires is cooking the inner tread blocks:confused: btw what is the utog on those tires?
 

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