Tire pressure actuals?

[shortseller]

I have recently noticed that my nitro pressure on all 4 tires when cold read around 28-29 degrees based on my Idrive screen, at current winter temperatures. Door jam sticker recommends cold readings should be at 32 degrees for proper tire wear. They do raise to 32 when warmed. Should I have them inflated to 32 at cold? Or run them as is, 32 when hot?

Just had a recent service and the tech did not adjust them, so I am wondering if the above ranges are acceptable? I realize they will give a better ride and better traction at lower psi but will this greatly effect tread life?

[secretariat]

I'm pretty sure they should be at 32 when cold. I've noticed my tire pressure increases as I drive. My drivers side tires can go up to 34.1 and the passenger side usually 33.4 or 33.5. I also asked my service guy to put the tires at the right pressure but they didn't adjust anything. Good question, if the tires are suppose to be at 32 when warmed up then you have to start at 30.5.

Anybody else that has knowledge of this chime in.

[Vigilant]

Originally Posted by shortseller

I have recently noticed that my nitro pressure on all 4 tires when cold read around 28-29 degrees based on my Idrive screen, at current winter temperatures. Door jam sticker recommends cold readings should be at 32 degrees for proper tire wear. They do raise to 32 when warmed. Should I have them inflated to 32 at cold? Or run them as is, 32 when hot?

Just had a recent service and the tech did not adjust them, so I am wondering if the above ranges are acceptable? I realize they will give a better ride and better traction at lower psi but will this greatly effect tread life?

32 psi all around when cold. If you plan on tracking at elevated speeds close to 100 mph, then inflate 34 to 36 psi before event.

[rsr racer]

Originally Posted by Vigilant

32 psi all around when cold. If you plan on tracking at elevated speeds close to 100 mph, then inflate 34 to 36 psi before event.

who told you that gem, praytell?

almost fell off of my chair when I read that

if you are going to the track with nitro initially, then you should make sure someone has a bottle there. you wont be mixing gases. not a good idea.

only lap times with pit measurements will tell you where you should be while using nitro or air which will be affected by ambient air and track temps as well.

if you can get a friend to do pyrometry and another to do pressures when you come to pit lane; you will be able to gain data to form a index base to work from.

[rz3]

Originally Posted by Vigilant

32 psi all around when cold. If you plan on tracking at elevated speeds close to 100 mph, then inflate 34 to 36 psi before event.

Uh... no.

[Vigilant]

Originally Posted by rsr racer

who told you that gem, praytell?

almost fell off of my chair when I read that

Educate me.

[rsr racer]

Originally Posted by Vigilant

Educate me.

i edited my reply...see above

different temps will cause different rates of expansion. nitro to start will still change but not as significantly. but a back of the envelop hot pressure start with with nitro alone still has to be monitored with pyrometry and pressures and lap times.

I have no hard data with the stock tires for track applications

hopefully someone can offer some. most hpde guys dont get so involved but a club racer will def offer some significant data.

[Vigilant]

Good info...did not realize he was referring to nitrogen instead of O2. The nitro argument is an interesting one. It is true that air pressure may be maintained longer in the span between inflation events. Don't people realize that air is 78% N2 in addition to O2 and other elements? I guess that is another topic altogether.

[rz3]

Good info and it applies to whatever is in your tires. O2 will expand more, which means pressures will get even higher after warm up. A few HPDEs ago I met a guy who explained a lot to me and helped me figure out what pressures to run and how to tell by my tire temps. I lowered the starting pressures a couple of pounds before my runs and found that I was able to run much better. Before that, it was like driving on basketballs feeling every bump and sliding around on the center of the tires.

If you watch racing pros they always start with low pressures so that the tire can come up into its optimum range. If you start too high, the tire will over inflate as it heats and you will have less contact with the road.

[Vigilant]

Originally Posted by rz3

Good info and it applies to whatever is in your tires. O2 will expand more, which means pressures will get even higher after warm up. A few HPDEs ago I met a guy who explained a lot to me and helped me figure out what pressures to run and how to tell by my tire temps. I lowered the starting pressures a couple of pounds before my runs and found that I was able to run much better. Before that, it was like driving on basketballs feeling every bump and sliding around on the center of the tires.

If you watch racing pros they always start with low pressures so that the tire can come up into its optimum range. If you start too high, the tire will over inflate as it heats and you will have less contact with the road.

Probably contact patch is reduced with higher psi...makes sense.

[shortseller]

Just got a response back from my SA, they recommend 32 at cold start up. Want me in for a top off asap.

[MaynardZed]

Tire pressures for the track much different than for regular driving. I shoot for 36psi hot at the track, which ended up being 23psi the next morning when everything cooled off. Start with 30 psi all around and check them when you come off and adjust them when they're hot. The left tires will heat up more on CW track and vice versa.

Increasing tire pressures for the track seems to be a common error for new drivers. Took awhile to convince a guy this past weekend that driving his Viper with 50psi tires was not a good idea. Don't feel bad, I think tirerack.com has this information backwards on its website.

For the street the tires might go up a couple psi from cold to hot, just set them to your personal preference.

[Vigilant]

Originally Posted by MaynardZed

Tire pressures for the track much different than for regular driving. I shoot for 36psi hot at the track, which ended up being 23psi the next morning when everything cooled off. Start with 30 psi all around and check them when you come off and adjust them when they're hot. The left tires will heat up more on CW track and vice versa.

Increasing tire pressures for the track seems to be a common error for new drivers. Took awhile to convince a guy this past weekend that driving his Viper with 50psi tires was not a good idea. Don't feel bad, I think tirerack.com has this information backwards on its website.

For the street the tires might go up a couple psi from cold to hot, just set them to your personal preference.

A reasonable and informative response.

[jadatis]

Tire-pressure is to give the tire a deflection for the load it is calculated for , so sertain rings of the tire dont get to hot by driving and get damaged because to much sulfur bridges are created, wich harden the rubber and so get damaged at next bendings ( deflections) of the rubber.

The heat produced there is given over to the inside air wich transports it to the rimm and tire and there given over to the outside air with a sertain isolation.

Tire makers use this as goal to calculate the maximum load of a tire.
Those sertain rings ( heel mostly , where sidewall goes over to treath)must stay below a sertain temp.
In this formula they put in demensions of the tire and needed pressure , wich is for standard-load tires of American make always 35 psi ( Europe 36 with exeptions to lower).

This calculation is made for 160km/99m/h and 18 degr C/65degr F .
When riding the tire inside air gets warm by the heat produced by the bending of the rubber and goes normally to about 45 degr C/112degr F .
When measuring at lower outside temperature the tire has lower cold pressure, and by that more deflection so more heat production by driving .
But by warming up when driving the pressure rises so deflection gets less and so heatproduction gets less.
At a sertain point there is a balance.

At higher speed the tire makes more cycles a second so more bendings of the rubber so more heat production, so needs lesser deflection to give the same heatproduction the tire can cool down and transported by the inside air to the places it can be transported to the outside air, wich is the rubber of the tire and more the metal of the rimm.


So the pressure advice is given for 65degrF and you dont have to worry what it will get when other temps.

I made a spreadsheet to play with the temperatures and pressures.
placed it on my one-drive in the motorhome-tire pressure calculator map and call it pressurecalculationwithtemp.
Its an older spreadsheet and made it for races where I read that the inside tire temp gets 190dgrF and .
planning to review it because for normal road use this would give tire damage if you follow that advice.

https://onedrive.live.com/?cid=A526E...E092E6DC%21793

Can tell you much more about tire pressure , call myself tire-pressure specialist nowadays. Can calculate the needed pressure for your Jeep if you can produce weights on axles or better seperate wheels, and of tire maximum load and tire kind to determine AT-pressure and speedcode.
Also want to know if they are off road tires with large profile blocks that cover a part of the sidewall, because then maximum load is given to high by the tire maker because lesser sidewall to deflect then a normal road tire.

From the link you can navigate my complete public map like in a forum.
75% about tires and tire-pressure.

Greatings from a Dutch self declared tire pressure specialist, who makes his story's to long mostly.

[JNoSol]

Start with the manufacturer recommendation and the recommended temp is cold for daily driving. Our cars have nitro filled tires, they won't increase in psi when tire temp raises like regular air so there's no need to compensate when filling. (the guys above are right, don't mix regular air and nitro. It's not going to react violently or anything, it will just reduce the benefit of nitro filled tires)

For track days, have a laser temp gauge handy. After a few laps, take the temp in 3 spots of the tire surface (2 outers, 1 center). If the center is significantly hotter than the 2 outers, then reduce tire pressure. If the outers are significantly hotter than the center, then increase tire pressure. If one side is hotter than the other, you need to adjust camber.

[jadatis]

Its even better to fill with normal air then Nitrogen filling, and I made a ducument for that . Read it and review your opinion about it.
But any gas exspands the same when temperature chanches.
Exception is water because it goes over to liquid in the temperature range of tires. I more see that as an advantage wich keeps your tires at one piece better , described it in the article.

Here a copy .

Filling car tires with normal air is better then with Nitrogen.

A. Oxygen, which makes 21% of normal outside air, in volume absorbs more energy to rise a degree in temperature then Nitrogen.
Difference is only 1% , but in selling argument is sometimes mentioned in energy/ mass so Joule/kg.degr. Kelvin and there Nitrogen wins by 13 % . Tires though are filled with a certain volume so that counts .
This selling argument can be de-myth simply by the fact that its untrue.

B. Water in a tire transports the heat more then dry air or Nitrogen-filling ( which is by its production process free of water).
Not for no reason water is used in central heating and cooling system of cars as main substance.
The tire inside will have lower temperature which is better for cooling down the important spots of the tire wich have to keep a low enough temperature to prevent hardening and damage in next bending of those parts.
When incidentally the tire inside gets hotter ( sunshine on tire or severe braking, or high ambient temperature) more water goes over to gas wich highens the pressure inside the tire more then dry gas. Also then more water as gas in tire so even better cooling.
So advantage of water is 2 ways when needed, better cooling and lesser heat production.
Disadvantages of water as oxidation only happen at outside . Tire specialists will confirm that when they remove a tire of the rim , the rim inside the tire is not corroded.

C. When a Truck, transporting flammable substance, is on fire, the little oxygen in a tire will , when exploding ,probably even kill the fire .
In tunnels experiments where done to kill the fire with air current , and it worked, despite the oxygen in it.

D. A normal car tire up to truck tire is not a race-car tire, for which a constant as high as possible contact area, so best grip , is needed to give half a second better round time.
For that reason they are filled with as dry as possible air or Nitrogen.
That this gives low lifetime is not important, and for a normal car tire it is.
Often blowing tires at racing, is seen there as collateral damage, but we don’t want that for normal car tires.

E. A car tire is also not a airplane- tire in which the water can freeze and when landing this can give misbalance , which can lead to tire-failure or accident, when suddenly going from zero to about 200m/h.
The water in a car tire does not freeze that often, and when it does and the car begins do drive , it begins slow and the misbalance is not a big problem . then pretty soon, certainly when on speed the ice is melted to water and problem will be gone.

F. When filled with normal air the user is aware of checking the tires regularly, which takes better care of a saver tire, because regularly filled up to the right pressure and optical checking of the tire .
The illusion that Nitrogen filling makes the tire to loose almost no pressure, which is often exaggerated to 5 times , while in real a poor 2 times and then only in the very beginning, makes the user less caring .
The tire also looses air when hitting pavement so temporary leak between edge of tire and rim, Filling with whatever gas-combination won’t prevent that.
This idea is even stronger when TMPS is used which is often inaccurate , so the user thinks to maintain the right pressure, while really riding with to low pressure for longer time, which can lead to tire damage. Aftermarket sensors for TMPS when screwed on the valve can give leakage trough hole where valve is placed , because of the bending of the valve by centrifugal forces at speed.

G. Filling with normal air is always possible, even with a bicycle- pump, is only to fill up so won’t take that long. When you keep driving with to low pressure , in order to find a place to fill with Nitrogen, you damage your tires. So just fill up with normal outside air, even when the tire is filled with Nitrogen. Then also you don’t need to have the tire refilled with pure Nitrogen by your tire specialist when at home again, not worth the trouble, and normal air is even better then nitrogen because of the water in it.