How big a difference can ambient temperature make on laptimes?

[skyline23]

About a month ago I was at Thunderhill and was lapping between 2:08 to 2:10, with a best of 2:07. The weather was a cool 55-60 degrees F. Since then, I replaced my koni/spring combo with Kw V3s, and got comptech sway bars, and went back to thunderhill this weekend,excited to see what the effect would be on my laptimes...While I felt I was driving "better" with more solid lines,braking points,steady state cornering, etc, my best was still only a 2:07. However, it was about 90 degrees F this time, and my tires had about 4 more track days on them since my last time at thunderhill...So basically what I am trying to figure out is if I was actually driving better and it was the heat of the day and wear of the tires that prevented my improvements from showing through in laptimes?

anyway, just curious if the ambient temperature can make a big difference, or not really..I definitely felt that the track surface seemed much more slippery and harder to find grip, and my car (supercharged) definitely felt down on power, or maybe I am just trying to convince myself of this so I feel better about my suspension purchases.

on another related note, how many track days do you guys get out of a set of good high performance street tires such as Dunlup Star specs or Yokohama Ad08s? Do they heat cycle and degrade after each session or do they perform consistently until tread is close to worn out?

 

[illwillem]

Ill get about 10 days out of a rear set of NT01's and maybe 18 out of the front with stock power. Temp plays a HUGE difference in lap time down south of you in the dead of summer I can expect to run a second/second and a half off my personal best and also typically set my fastest time of the day on the very first session and the very last session when the track temp is coolest. My car also feels lazy when revving in anything hotter than 85 degree weather and I only do about 5-6 laps before I come back in. You can get around some of the slipperiness by changing pressures and what not but yeah, in generally its slower.

 

[Coz]

Heat is always a power killer...
The hotter the ambient temp the quicker the motor gets heat soaked and then from then on you are losing HP.
If you notice, most best lap times are usually run in the mornings when the ambient temp is cool outside. As the day progresses, the lap times usually go up.
I also continue to reduce tire pressures as the day goes on and the track surface continues to heat up.
Buy the end of a day, I usually have right around 24 lbs in my tires when they cool completely off.
Hot I look for 32 to 33 lbs. and 200 degrees across the tires and adjust from there.

William,Thats sounds about right, I get right at 10 hard track days out of a set of NT01's before they cord. (5 Weekend Events)
I usually run 2 TTU sessions each day and the Time Attack on the Second day. Thats 5 hard sessions a weekend. Then of course there is the 3-4 ride alongs with students over a weekend, but I'm not pushing the tires for those. I also drive the NSX on the street as well here and there between events.
I find the NT01's are very consistent right up until they cord.

I tend to burn up the fronts and rears equally due to how I have my car set up. But I track temps across and pressures religiously on all 4 to make sure I'm getting even wear and full tire patch on the ground.

If your slipping and sliding, it may feel fast but in all reality all your doing is burning up tires and producing slower laps times since you are continually scrubbing off speed.
I've learned to really watch and take care of my tires since the are not cheap by any means.

 

[docjohn]

what tires are you running? and at what hot pressures?

 

[Hrant]

The comments above are right on the money re ambient temp, tire pressure, loss of power (heat soak in the CTSC), and slippery track. Thunderhill is known to play games with one's psyche and zap time. It is also one of the track when the ambient temp reaches 90+ many OEM NSXs start to overheat if shifting at red line.

 

[skyline23]

what tires are you running? and at what hot pressures?

I am running Yokohama AD08s, and was shooting for 36ish front and 38ish rear..I think i started the day cold around 31fr 33rear, and at the end of each session would measure hot temps and reduce down a bit to the temps I was hoping for (seemed to end my sessions around 38-40ish or a little less

 

[Coz]

Too high....

 

[skyline23]

What should I be shooting for? from my searches on Prime that 36-38 seemed to be the recommended hot temps, but I am all for trying others if you have suggestions.

Too high....

 

[Ponyboy]

Man, I've seen lap times vary by +/- 3 seconds depending on ambient heat.

However, I've seen it vary more with a dusty track. Not many consider that independent variable.

 

[docjohn]

What should I be shooting for? from my searches on Prime that 36-38 seemed to be the recommended hot temps, but I am all for trying others if you have suggestions.

what was your car doing? loose ,push ect....

 

[illwillem]

Ive always found that 38 is too high, I adjust accordingly but im usually around 34-35 in NT01s

 

[Hrant]

Driving style and suspension do play with what tire psi you want to be "comfortable" with - the operative word.

For street tires on OEM wheels, I have found the range +/- 33 front 38 rear hot to be balanced. For track tires, yes the range is more 36f/38r. As Coz said, 38f is too high, and 40r on a hot track would be marginally slippery.

YMMV

 

[skyline23]

It was doing a few things...early on in each session the tires felt mushy and would push corner entry and mid-corner in long sweepers..I was able to control the corner entry understeer by trail breaking and adjusting my inputs a bit, but mid corner it just wanted to push kind of regardless of what I did....but then towards the end of the session the car would get fairly slippery. Not uncontrollable slippery but definitely wasn't holding the same speed I was used to be able to during the long sweepers without wanting to slide out (more neutral 4 wheel slide, not so much under or oversteering)..

there were a few laps in the middle of each session where it felt pretty good though.

what was your car doing? loose ,push ect....

 

[docjohn]

well you have to take it piece by piece.In general your tires will go through various performance levels in a session.I like to keep my front and rear tire pressures the same...my feeling is that the tire grips and holds best at a uniform pressure regardless of front/rear.....next is the kw.these are new to you..what settings did you have the shocks at?

 

[Coz]

Have you had the car corner balanced since putting the KW's on ?
Thats the first thing you need to do !

Here is a oversteer and understeer flow chart to give you some basic's as a guide to set up.

- - - Updated - - -

I'm right at 33-34 hot as well with NT01's. I run the same tire pressures front and rear.
I start off cold some where between 24-26 depending on the ambient temp.
I usually get a 8 pound difference from Cold to Hot on track.

Ive always found that 38 is too high, I adjust accordingly but im usually around 34-35 in NT01s

 

[RYU]

I once saw a 10-12psi increase from cold to hot. I then realized it was all the water molecules causing such a big variance. I hadn't emptied out the water in my compressor for years. doh!

 

[ryneen]

I've been running NT01's for a few years. With my setup I run 36lb front and rear. I average about 24 full tilt sessions before they cord (I shave them, but it's not really necessary). They are quick to the end. I also drive them to and from the track and occasionally to work. I used to swap tires, but now I'm too lazy. I use nitrogen so the tire pressures don't go up as much as regular air.

With your scenario of changing suspension components, it's tough to say why your lap times are still the same. I've found out that a good setup is critical to quick lap times. Everything else is secondary.

 

[CB72]

I experienced exactly the same as you did: disappointing lap times after improvements to the car but...the outside temperature was way higher.
The problem was easily spotted when a normally aspirated NSX I normally pass easily stayed with me for a long time:redface:
I had a CTSC in those days and the heat soak is such that I lost a minimum of 3 seconds per lap...
In my view superchargers are no good for track use!
Today, I run with a LoveFab stage 2 at 8 psi and it's a world of a difference:smile:

 

[1K2GO]

Heat is the enemy of peak horsepower & peak brainpower. At my last track day my car was able to last much longer than me especially in the hot afternoon sessions when fatigue is setting in.

 

[R13]

First, and I'm surprised I'm the first to say it: Given the same power and tires, I wouldn't expect big improvements in lap times purely from coilovers and swaybars....maybe more consistency since you could feel the car better, but not in outright fast time. The big gain with an adjustable setup is the ability to fix any bad handling characteristics you can't drive around (e.g. intrinsic to the car), vs. the raw time gains from stickier tires or adding power (the latter only up to a point).

That said, yeah the temperature makes a big difference, particularly on a track where power is important (long straights, or slow point/shoot corners). I'd definitely wait for another ~60 degree day before resigning yourself to buyers remorse

Lastly, my $.02 on the tire thing: an NT01 is not the same as an AD08, etc. I haven't run the Yokos, but I know my Star Specs were happiest ~34-35 hot, and my NT05s like 37 hot all-around. I spent a couple of weekends playing with a pyrometer at CMP and Road Atlanta and that's where the temps evened out across the tire section, which coincided to my quickest sessions of the weekend.

That's obviously going to vary a little between tires given the minor differences in compound and construction, but you're in the ballpark. You might reduce by a pound and see if it's better/worse and go from there.

 

[WasianNSX]

Personally I think that track temp makes a lot of difference. From my experience colder is always better, to an extent. I have raced on very hot days at WSIR and Buttonwillow and not only are the tires a lot slicker, it's the heat getting to the driver. Temps inside my RX7 easily reach 115f+ on a hot day, with the addition of wearing a full suit and helmet it gets unbearably hot, not letting me fully concentrate on driving. Tires im running are usually Hoosie R6's (a very good tire for the track, not so much on the street)