When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
yes, that was my point... that 1psi the next time you visit a track, might be a different track too,and you could still see that 1psi variation . with or without Nitrogen. but you are right, if you live in a high humidity area, this can be a variable that can make the differences even more dramatic. 2psi or even 3psi. but again, on a given day, you can adjust .. some would say its worth the more consistent pressure predictions, to use Nitrogen, but to the OP, i dont think we think its worth the effort. but , it certainly cant hurt, but its not required to get control of pressures over a given track day.
Look, maybe you like showing up at the track and having any data you have collected previously be basically worthless. I, and others here, obviously don't.
When I race with NASA, I get three sessions each day. I can't really afford to have the first session be wasted if my cold tire pressure guess is way off. There is not enough time to come in, check pressures, adjust, and then get back out. Well, not enough time if you don't hire a crew. Maybe you don't care if your guess is off. I do.......
2) Regarding the water vapor in the tire with plain air, granted that the vapor causes much more change in tire pressure for a given level of tire heat than for an N2-filled tire, how meaningful is this in real life? Does a tire's gas-fill attain a pretty steady temp during a session or does it fluctuate significantly, thus causing appreciable pressure change, in which case the N2 would be the way to go due to there being no water vapor in it.
I don't run external tire temp sensors or pressure transmitters like others, but here's a datapoint based upon my circumstances for you to determine if dealing w/ N2 is worth it for you.
With normal, undried air from my compressor in the summer months, I normally see ~8 psi increase from cold pressures to hot. Using nitrogen and filling/deflating the tire a few times, that increase is ~5 psi. These are cold-to-hot pressures taken after a run, not changes during the run, so using N2, for me at least, does allow me to better achieve target hot pressures due to reduced pressure increases. Just my $0.02.
Look, maybe you like showing up at the track and having any data you have collected previously be basically worthless. I, and others here, obviously don't.
When I race with NASA, I get three sessions each day. I can't really afford to have the first session be wasted if my cold tire pressure guess is way off. There is not enough time to come in, check pressures, adjust, and then get back out. Well, not enough time if you don't hire a crew. Maybe you don't care if your guess is off. I do.......
Don't confuse preference with correctness.
Winders that a great point, and sorry if you took what i was advising as being advice to you. i thought i made it clear that you need to sacrifice the first session, at the risk of being "off" on your pressures by up to 1-2 psi is not a big deal for me.... it might be to you and, certainly, using Nitrogen and being more accurate is better. my preference is not incorrect, as i take the humidity into accounnt. i cant remember when ive measured a tire pressure and was surprised. im usually not off by more than 1 psi from goals.
Let me be as clear as possible, and reference what you and others have said. (the following post says this too) that nitrogen vs air can be near 3psi difference.. cold vs hot. BUT, if you account for that , you should only be off in the 1psi ball park....... thats all im saying.
what this means is that you can go out there and know the humidity factor will not change your projections, after all, you still need to take into account outside temps ,even with Nitrogen.
Here is the bottomline........ Yes, Nitrogen is a way to more accurately predict final pressure rises. Ive been able to do this as well with air.. ( 95% humidity day vs a dry day in Nor Cal, il make a 1-2 psi adjustment and it seems to work) ive been doing this , as others for 20 + years and it seems to work
IF you go to any club racing weekend, NASA, SCCA and the SCCA runnoffs, i can confidently say that most all tires on the race cars are filled with air. ever see how busy those tire guys from Goodyear, or Hoosier are? they are not filling the tires with nitrogen. now, go to a cup car race, and the percentage is much greater. the funny thing is , this is a similar argument to what measuring device you use for pressure... ive seen a 3psi difference between gauges.
so, for the OP, sure its better to use dry air or nitrogen if you want control pressures, but air is fine too, when you finally arrive at you pressure goals. and remember what the delta is on a given day.
Originally Posted by jerome951
I don't run external tire temp sensors or pressure transmitters like others, but here's a datapoint based upon my circumstances for you to determine if dealing w/ N2 is worth it for you.
With normal, undried air from my compressor in the summer months, I normally see ~8 psi increase from cold pressures to hot. Using nitrogen and filling/deflating the tire a few times, that increase is ~5 psi. These are cold-to-hot pressures taken after a run, not changes during the run, so using N2, for me at least, does allow me to better achieve target hot pressures due to reduced pressure increases. Just my $0.02.
you are doing it the way it should be done to get the benefit of nitrogen. my question to you, is if you know you have a 8psi change with air, why not account for it and just go off that delta pressure change.. after all, if your target pressures are 30psi for example, it doesnt matter if its done with air or Nitrogen. the pressures vs temps will stay consistent in the higher temp range as well. (not from cold to hot, but in the operational tire temp rang).
and if the range is 3psi, and you account for it, and you get a 50% humidy day vs the 80% humidity days you have been running, , you can account for it. after all the most you can be is 1-2 psi off..... for someone doing a DE is this really a problem?
one of the BIGGEST advantages of using Nitrogen is the use in real slicks (DOTs are not as sensitive ) this is because you need to run the slicks at generally lower pressures at temp than a DOT tire, this means you need to start out at a 8psi lower pressure vs 5psi lower pressure witih Nitrogen...this also means that the tire is not running and being urged to tempurature with extra low tire pressure, which can damage the tire.
(eg pirelli DH wants 28psi hot temps, so you need to go out at 20psi with air vs 23psi with nitrogen.) this is a big benefit for those racing on slicks.
I asked a question about what everyone thought about how it takes for tire temps to decrease after you measure them in the Hot Pits. i did a recent test last race weekend after qualifying. the results may surprise many. ( VR was one that made fun of this in an earlier discussion)
as i had mentioned, tire pressure doesnt decay as much as most would think..here pictured vs a clock is the pressure in the hot pits vs pressure near 5 mins later. IR readings do change very quickly, as Matt and his dynamic heat sensors show, but pressures do not..... i figure this is because the tire is heated not only by the tread and its friction battle, but the rims that are heated mostly by braking... often we can see the rim temps at over 250F at the centers and the rim edges (or barrels) due to 350 to 400F post session temps of the rotors . they take a while to cool down and provide a heat source for the air in the tire
notice the temps vs the time.. (by the way, it took me a 1min or so to figure out how to hold the pressure gauge and take the picture) so it was a few mins longer........... but you get the point. pressure decay is pretty slow to react. starting pressure was 24psi cold on this day.
Can we go through all the noble gases? If this thread doesn't reach 15 pages everyone is not trying hard enough.
Argon is as high as you need to go. Readily available and does what you all want. You don't just go to the industrial gas supply store and get Krypton and Xenon. Before I get another graph request, thermal conductivity is a discrete value. Argon is about 2/3 of air. That is why drysuit divers use it to fill their suits in cold water. So, just order order it with the lowest available dew point.
Mark Kibort's time-delay tire pressure info is interesting for at least 2 reasons:
1) We learn that there is great stability in the pressure value -- it doesn't decay rapidly between sessions. Mark's observation about the 'heat-sink' effect of the hot metal wheels is also very meaningful, and it suggests that the value won't fluctuate much during track sessions after the tire temps have reached equilibrium.
2) There is lots of data to be had without fancy measuring gear. (As example, I tell my students to select a reference point on the straight shortly after certain key corners and note the rpm or speed. Then use that as a reference for future laps. Absolutely zero-cost high-quality data, available in every vehicle!)
I have found that tire tens decay at varying rates depending on vehicle, aero, environmental conditions, etc.
I think you meant to say, "temp". The test I did , was done on a few other cars this day..... the main difference and purpose for the test I was doing, was the decay of pressure based on time from hot pit to paddock.... (main point is to rush to take IR readings , but no rush for pressure). which doesn't rely on "aero "or any other dynamic factors
as my test showed, 5 mins later and there wasn't even a pressure drop of 1psi. this is more rim related and how it is heat sunk to the hub and rotor.
a curious test would be to see if pressure rise and fall is different for a wheel with more thermal isolation to the barrels..... or is most of the heat transferred from the inside of the rubber to the air, and heats the barrels.
but yes, lots of factors for how tread temps changes on the track
11-23-2016, 03:46 AM
