Nitrogen tire pressures

[Doug H]

My left rear got lose on me recently at the track and I could really feel it in a long high speed sweeping right turn. I got off the track, checked the pressure and had a reading of 40. The tire was at 28 cold and returned to about 30 in 15 minutes.

I have another track event this weekend and am going to use nitrogen. My tires are the stock AD07s. What pressure should I run with nitrogen for both front and rear?

[choi0706]

I use 20/22 warm on ad07s haven't tracked it much to determine if it's optimal but 28 cold seems a bit high.. higher than the factory's recommendation..

[MyElise]

You don't need to use nitrogen. You just need to set the cold temps such that they will reach the appropriate operating temperature when hot and do a couple of easier laps to get them there.

[Doug H]

Originally Posted by MyElise

You don't need to use nitrogen. You just need to set the cold temps such that they will reach the appropriate operating temperature when hot and do a couple of easier laps to get them there.

Haha, that is why I put the information above. My left rear went from 28 cold to 40 under very hard laps in a just a 30 minute run. The right rear never went above 32. At that rate, I would have to drop my left rear to about 20 cold temp making my car a mess until the left rear heated up and everything got even.

I have run nitrogen with good success on my track cars back when I used to club race and be into this more. The pressue with nitrogen can still fluctuate a little, but no more than maybe 2 pounds. I can deal with 2 pounds, but 12 pounds on the left rear while the right rear went up only 4 degree to 32 is not good.

The car felt pretty good when the rears were between 30 and 32. Should I run 28, 29, or 30 if my target hot temp is 30 with the ADO7s and such low starting tire pressures.

[fishguy]

from my experience, you should use air, AND a pyrometer, the probe type.
check the temps across the surface of the tire, and make the surfacetemp of the tire even by setting air pressures to do so. if your tracking w/o a pyrometer, your not going to be able to set pressures correctly. i tried to do so w/o, and with.............. night and day difference in ease and tires performance.
Fish

[Doug H]

Fish:

Thanks. I may be using air again soon enough. I am switching suspensions, wheels and tires before my next event October 28 - 30. I just need to get another weekend out of these AD07s and, after 3 track events with air and a lose rear end when really hot, I want to try nitrogen. It may be a waste of a few dollars, but I don't care. I know it probably ain't necessary and . . ., but having a lose rear due to a hot tire is less fun.

I am really just looking for: (1) advise about tire pressures for these AD07s; and (2) how much expansion I can expect with nitrogen with AD07s and starting at such a low pressure to begin with. Does anyone else agree that the AD07s seem best at about 30 to 32 hot.

[Buz]

Since you are running clockwise around the track both left tires should have lower cold pressure than the rights. The pyrometer will show you what you need.

[fishguy]

doug, i think whether you use nitrogen or oxygen, you still need a pyrometer. my experience was even 1/2 lbs psi made a BIG difference in contact patch. if you dont know how to use the pyrometer, PM me and I will tell you how I used mine . it was , for me at least, impossible to set the tires correctly w/o it.
fish

[FlyLo]

Originally Posted by Doug H

The pressue with nitrogen can still fluctuate a little, but no more than maybe 2 pounds.

I don't believe this. Air is 80% nitrogen. pv=nRT for all gasses.

Unless your air supply is full of water, there's no way you see this much difference between air and nitrogen.

[Series 2 Elite]

Originally Posted by FlyLo

I don't believe this. Air is 80% nitrogen. pv=nRT for all gasses.

Unless your air supply is full of water, there's no way you see this much difference between air and nitrogen.

Correct. For example, the density of nitrogen at 400K is 74.8% of its value at 300K (both at one atmosphere). The density of air at 400K is 75.0% of its value at 300K, again at one atmosphere.

[Doug H]

Originally Posted by FlyLo

I don't believe this. Air is 80% nitrogen. pv=nRT for all gasses.

Unless your air supply is full of water, there's no way you see this much difference between air and nitrogen.

Haha, I will let you guys know after this weekend. Filled them with nitrogen this morning. Running 26 front and 29 rear. I am hoping that I will only see about 30 to 32 rear and 28 or 29 front when hot and would like to avoid 35 to 40 left side readings if at possible.

I candidly have no stake whatsoever in whether nitrogen will alleviate those high readings so I will let you guys know how it went.

Out of all of these posts, only one recommended pressures and those seem a little off to me. I was seriously not trying to debate the merits of nitrogen, nor do I care to change any one's mind about nitrogen. A post relating to pressures (hot or cold) would have been helpful.

Fish: Got one. Kind of know how to use it as Dad uses it for club racing. I am seriously not that worried about 1/2 to 1 psi. My skills are not at that level. I am trying to avoid wild fluctations and keep them in the hot ranges I listed above. If I can stay within those ranges this weekend, I will be happy.

Car is on the trailer and I am off . . .

[FlyLo]

Originally Posted by Doug H

Out of all of these posts, only one recommended pressures and those seem a little off to me. I was seriously not trying to debate the merits of nitrogen, nor do I care to change any one's mind about nitrogen. A post relating to pressures (hot or cold) would have been helpful.

The point was that tire pressures are the same as previously discussed. 26f, 28r, hot. Definitely under 30. If you have to start out with 20 cold, so be it.

[xtn]

Originally Posted by FlyLo

I don't believe this. Air is 80% nitrogen. pv=nRT for all gasses.

Unless your air supply is full of water, there's no way you see this much difference between air and nitrogen.

You're right, but don't discount how much water is in normal air. Depending on the humidity when the tire was filled, it may result in quite an increase in pressure when the tires are hot.

xtn

[FlyLo]

Originally Posted by xtn

You're right, but don't discount how much water is in normal air. Depending on the humidity when the tire was filled, it may result in quite an increase in pressure when the tires are hot.

xtn

Only if you're getting a phase transition. Water vapor is still a gas.

To be fair, I have seen liquid water come out of gas station air pumps.

[MyElise]

Originally Posted by Doug H

Haha, that is why I put the information above. My left rear went from 28 cold to 40 under very hard laps in a just a 30 minute run. The right rear never went above 32. At that rate, I would have to drop my left rear to about 20 cold temp making my car a mess until the left rear heated up and everything got even.

Something is screwed up with your left rear. Water in the tire? It just isn't right. Never experienced that anywhere. I'd pull the tire and check it out.

I typically run 21/24 F/R cold (mid-summer) and it doesn't screw up anything. A bit mushy for the first couple of turns but after a lap or two they are up to temp and pressure.

[Doug H]

Just got back. Will post video tomorrow. Nitrogen seemed to work well. I started out at 26 and 29 cold. My rears stayed between 31 and 32.5. Fronts stayed around 27 to 29. Temps were hotter on inside of outside rear tire and it seemed to get a little lose after about 15 laps. I dropped the outside rear to 27.5 or so cold and it stayed around 30 to 30.5 hot. 30 on the outside tire seemed about PERFECT for these tires on this track which is a fairly fast and demanding track, Gateway.

BTW: My "coach" as he refers to himself had nitrogen in his compressor this weekend. He has been racing professionally for over 30 years and seemed really adament about using it even in his toy hot rod 69 911 with slicks.

Anyone going to Fort Worth this weekend for the Lotus track event?

[fishguy]

Not trying to be rude, but, If you have a "coach" who has been racing for 30 years, dont ask us(the internet), go with what he says.......... he has to know his stuff. AND if he is there at the track, what more can you ask for.
have fun and be safe

[Doug H]

Originally Posted by fishguyAZ

Not trying to be rude, but, If you have a "coach" who has been racing for 30 years, dont ask us(the internet), go with what he says.......... he has to know his stuff. AND if he is there at the track, what more can you ask for.
have fun and be safe

Absolutely. Have fun and be safe is the key. Not many people though, know much about the Eilses, tire pressures for these cars and best set up yet. That is why I came here to learn from you guys with experience.

[fishguy]

take the front shims out, and just dial the car in with the pyrometer. i always write everything down. it makes adjustments much easier. the tires dont do well when run w/ incorrect pressures for a long period of time.
I would usually start out at 24 front/ 26 rear here in AZ, and adjust from there. it will be different per track, time of day/year, and driving styles.
enjoy.
Fish

[codymac]

Originally Posted by Doug H

Anyone going to Fort Worth this weekend for the Lotus track event?

http://www.elisetalk.com/forums/showthread.php?t=28089
http://www.elisetalk.com/forums/showthread.php?t=28771

Originally Posted by fishguyAZ

Not trying to be rude, but, If you have a "coach" who has been racing for 30 years, dont ask us(the internet), go with what he says.......... he has to know his stuff. AND if he is there at the track, what more can you ask for.
have fun and be safe

My motto is ask everybody everything and believe nothing you're told. You can learn a lot of good stuff from useless people and a lot of useless stuff from good people.