Tire pressure question [Archive] - Dodge Charger Forums

: Tire pressure question


Murunga
07-26-2005, 05:19 PM
After looking at my new Charger for one day, the tires looked low on air. There is a sticker just inside the drivers door that says tire pressure should be 32 lbs. But when I checked the tires they said max pressure 44 lbs. I checked the manual and it really didn't say anything more than keep your tires properly inflated. Well, since they looked low, I blew em up to 44 lbs and they now look perfect. I went back to the dealer and asked the salesman at the dealer and he said that 44 lbs was a max pressure and it was ok to run them under. Another salesman there said he would run them at 32 but when we walked over to look at another charger that came in with mine, he admitted they looked low just as mine had looked. I said I trusted the tire manufacturer (at 44 lbs) more than the vehicle manufacturer (32 lbs). The salesman said the manufacturer knows more about the cars weight and handling in relation to the tires. Anyway, at this point I'm considering taking them down to 40 lbs and see how they look, but I'd really like to know what the proper pressure should be. I'm also betting many Chargers only have 30 lbs from the factory and are severly under inflated just as mine were.

Tires are 18" Michelins V rated Pilot HXMXM4

Thanks for any help in advance.

Murunga

GLHS837
07-26-2005, 05:34 PM
The max rating is just that, the max pressure the tire can be used at, and here's the crucial part, depending on application Some applications might indeed call for higher pressures, evidently, the Charger does not.

You should really run them at the door sticker pressure. And NEVER, NEVER, EVER, ask a salesman ANYTHING about the care and feeding of your car. While he may be that rare creature, the gearhead salesguy, the odds are wildly against it.

Tell you what, you want expert, try the Tire Rack. Those guys are indeed experts on tires, not just salesmen. I spent 20 minutes on the phone with one guy figuring out which tire was right for my SRT-4, he knew his stuff.

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=38

There's a drop down menu that leads to more knowledge about tires than most folk ever want. Me, I drive hard, and those four small patches of rubber are all I have, so I've studied tires a bunch.

DAYTONA_R/T
07-26-2005, 05:45 PM
The max rating is just that, the max pressure the tire can be used at, and here's the crucial part, depending on application Some applications might indeed call for higher pressures, evidently, the Charger does not.

You should really run them at the door sticker pressure.

I concur 100%.... run as per the door sticker, the max is just that... the max... not optimum pressure... the manufacturer has figured out the optimum pressure for you...

if you want to figure out the best pressure with disregard for what the car maker says.... run a line of chalk across the width of the tread.... then drive a few yards... see if the chalk wore off evenly or not

chalk wore off only on the outsides? tire is under inflated, chalk wore off only on the middle? tire is over inflated....

Murunga
07-26-2005, 06:15 PM
I concur 100%.... run as per the door sticker, the max is just that... the max... not optimum pressure... the manufacturer has figured out the optimum pressure for you...

Ok, the door sticker says 32lbs, but it really looks low. I mean the side walls were bulging out. Is a tire supposed to look like that these days? What are you guys running these Michelins at?

Murunga

DAYTONA_R/T
07-26-2005, 06:18 PM
Ok, the door sticker says 32lbs, but it really looks low. I mean the side walls were bulging out. Is a tire supposed to look like that these days? What are you guys running these Michelins at?

Murunga


it may look low... but trust me... it is fine...

On my Avalanche I am running 325/60-18 Nitto's at 35PSI, they look low... but in 20k miles they are wearing perfectly even....

dont go by the "look" go by an air gauge

chargin06
07-26-2005, 06:26 PM
Checked the P225 60/R18 for the R/T's (Continental ContiContactTouring)

Tire states MAX PSI = 51lbs

Door states PSI = 30lbs

21lb difference. I do not have a gauge at the moment to see what they are set at, I have not modified the pressure, but they look fine to me.

Related Question:

My window sticker states the R/T's have a tire pressure monitoring system (sensors). Is this correct? If so it must be configurable. I will look more into that.

epoch
07-26-2005, 10:38 PM
Ok, the door sticker says 32lbs, but it really looks low. I mean the side walls were bulging out. Is a tire supposed to look like that these days? What are you guys running these Michelins at?

Murunga

Michelins? Do you have the Road & Track package or something?

Murunga
07-27-2005, 04:19 PM
Michelins? Do you have the Road & Track package or something?

I have the Daytona package.

Murunga

Murunga
07-27-2005, 04:23 PM
Checked the P225 60/R18 for the R/T's (Continental ContiContactTouring)

Tire states MAX PSI = 51lbs

Door states PSI = 30lbs

21lb difference. I do not have a gauge at the moment to see what they are set at, I have not modified the pressure, but they look fine to me.

Related Question:

My window sticker states the R/T's have a tire pressure monitoring system (sensors). Is this correct? If so it must be configurable. I will look more into that.

The Continental tires I saw at the lot looked like they were propoerly inflated, they sat right. Its the Michelins that looked really low.
My manual shows that I have a tire pressure monitering system, but it never lit because it probably thinks that 32lbs is just fine, and maybe it is.

I droped the tires back to 40 lbs last night and they still look good. I still think 32 lbs is wrong, but this is probably just me being hard headed and stubborn, lol : ). I'd like to hear from soemone else with these tires.

Thanks for all your help guys.

Murunga

GLHS837
07-27-2005, 04:31 PM
The Tire pressure monitorig system is not a convenience thing. It's really more of a safety thing, so it's values are really low. I don't know what they are, I'll dig that up later, my guess is somewhere under 15 psi.

Try googling "judging inflation by eye", I haven't tried it, but I'm pretty sure you will get some good info. Also try tire maker websites, more to be had there, especially Firestone:)

DAYTONA_R/T
07-27-2005, 04:37 PM
The Tire pressure monitorig system is not a convenience thing. It's really more of a safety thing, so it's values are really low. I don't know what they are, I'll dig that up later, my guess is somewhere under 15 psi.

Try googling "judging inflation by eye", I haven't tried it, but I'm pretty sure you will get some good info. Also try tire maker websites, more to be had there, especially Firestone:)


tire pressure monitors in general come on when tire pressure is 5psi lower then recommended

as far as running your tires at 40PSI... your gas milage will go up, but your tread wear will suffer....

oh... in case you think that the recommended is wrong... remember... they pay engineers to figure this stuff out... not rednecks saying... "ahh... 32psi is all you need to keep the rim off the ground"

chargershed
07-27-2005, 05:19 PM
Something I'll have to check out is the air pressure placard on the Charger... the new rules say there should be 2 air pressures, one for normal drving and one for fully loaded vehicle...now it is possible that on the Charger they are the same. Run the pressure at the stated pressure by the manufacturer of the vehicle, the car is engineered to ride and handle a certain way. The air pressure is also set when the tires are cold, as you drive the tires warm up and the air pressure in the tires increase 4-5 psi, running the tires over inflated could alter the handling ( higher inflation pressures narrow the contact patch) and lengthen stopping distances, reduce wet handling etc.. Michelins sidewall technology alows them to "pooch" out a little more than most tires to improve ride ( but not handling). Hope this helps, p.s. the first thing I would do to improve the handling of the Charcer is to ditch the Michelins for something more sport tuned, like a pirelli or a yokohama...just my .02 after 12 years in the tire biz...

GLHS837
07-27-2005, 05:32 PM
Keeping in mind, of course that each brand does have performance tires. Actually, the Yokos on my SRT-4 are the lowest performance (but longest lasting:)) tires she's worn.
While the Michelin Pilot Sports and Bridgestone Potenza SO3 Pole Positions were great, but only lasted about 20K.

Tires have a lot of tech wrapped up in them. And a proper choice is going to be a careful weighing of factors. Maybe later I'll take a look at the 'rack to see what the choices are. I've kinda blown it off becuase the -8 is going to be it's own very exspensive baby, with it's own choices to be made.

Murunga
07-31-2005, 07:11 AM
To qoute-
"oh... in case you think that the recommended is wrong... remember... they pay engineers to figure this stuff out... not rednecks saying... "ahh... 32psi is all you need to keep the rim off the ground"

Ok, I believe the engineers spend alot of time and money on this and I'm sure are very competent (I hope). But here's one thing I really have to wonder about-
How is it that the Continental tires on 17" rims use the exact same air pressure as the Michelin pilots on 18" rims? Is it due to the weight of the vehicle? Is it coincidence? Is it possible that the engineering was done with Continentals (which look right at 32 lbs) and they just put the same placard on the cars with the Michelins?

I know, I should just trust the placard as everyone says, but I do tend question what just doesn't look right to me. I'm going to a tire dealer today (Bell Tire) and get a professional opinion. I'll let you know what they say but I think I already know-
"The proper pressure is what the vehicle manufacturer says on the placard", lol. : )

Murunga
ps, they run great and look right at 40 lbs.

chargershed
07-31-2005, 11:43 PM
It is because the weight carrying capacity of a given tire at a specific psi... most likely, the Michelins matched the conti's ( or was very close to) load capacity at 32 psi, which saved DCx money on the placards. When you go visit your favorite tire shop, ask the if they have a michelin tire data book or "mast" book. In the front are all maners of pages full of diffrent types of data concerning tires. There is a section where it shows what tire size will hold what ammount of weight at any psi, which is valuable if you plan on upsizing rims and tires.

Also, the 18 inch tires and wheels are the same diameter as the 17 inch tires and wheels, which means you have a half-inch less sidewall to look at on the michelins than on the cont's...which could be why they look "flatter" to you. One other thing, Michelin's in general are more "squatty" in shape than other tires... Ask your tire store to show you two tires with the exact same size, one Michelin and one some other brand. Be prepared to be shocked to see how much diffrent the tires are in overall hight and width, It's a real eye opener, and also why I would never-ever change tires 2 at a time!

chargin06
08-01-2005, 06:53 AM
I have the Conti's, the placard states 30PSI... I tested mine with a nice gauge type system, and all 4 are sitting at 28psi... They look fine and properly inflated. I am thinking of bumping them to 30. The tires state Max Air of 51psi...

I will try the chalk test on these sometime soon...

ANTMAG06
08-01-2005, 09:59 AM
I have the Conti's, the placard states 30PSI... I tested mine with a nice gauge type system, and all 4 are sitting at 28psi... They look fine and properly inflated. I am thinking of bumping them to 30. The tires state Max Air of 51psi...

I will try the chalk test on these sometime soon...

28PSI and your low tire pressure light did'nt come on? I got a nail in my tire 4 days after I bought it. I had to have the wife look up the indicator in the manual while we were driving. Pulled into a gas station and my PSI was at 30 in that tire. When I put air in them the light did'nt go out until the PSI was at 32.

chargin06
08-01-2005, 10:02 AM
I guess the jury is out on this, I have no idea when the light is supposed to come on. These are definitely at 28 and no problems yet...

miamiyogi
08-29-2005, 04:08 PM
DO NOT RUN YOUR TIRES AT MAX PRESSURE. That pressure is the max. the car can tolerate under fully loaded conditions.

Always TRUST the placard in the driver door jamb. You should be at 30psi. Remember that after an hour of driving your tires will warm up and gain 1-2 psi. Drastic changes in the barometer will also affect psi....read further for proof.

The R/T has a tire monitoring system. I don't know what the alarm is set for. However, my car has been at 30 psi and is checked monthly. The saleshole from PLANET DODGE (y'all stink) NEVER MENTIONED ANY FRIGGIN' features (then yelled at me on the phone for giving him a poor review on my sales survey). After hurricane Katrina hit Miami I went to work the next day...a funny yellow light came on the insturment cluster so I pulled over to look it up. BEHOLD! I have tire pressure monitoring (saleshole!!) so I check and sure as anything I was 5 pounds low....had been checked days b4.

Planet....u stink!

vibrosrv
02-27-2006, 09:39 PM
Checked the P225 60/R18 for the R/T's (Continental ContiContactTouring)

Tire states MAX PSI = 51lbs

Door states PSI = 30lbs

21lb difference. I do not have a gauge at the moment to see what they are set at, I have not modified the pressure, but they look fine to me.

Related Question:

My window sticker states the R/T's have a tire pressure monitoring system (sensors). Is this correct? If so it must be configurable. I will look more into that.


I too have these tires and they say on the tire that 51 PSI is the max. However, while driving it home to Texas from North Carolina I thought the handling was a little loose.......kinda mushy. So, I bumped them all up to 40 PSI and my handling impoved greatly plus I got about 2 miles a gallon better fuel miliage.
I like running 40 PSI for the reasons previously stated and unless anyone can convince me that this is a very bad thing, I don't see any problem in doing this. Yes, the ride is a little more bumpy, but the tires don't squat out anymore and the handling is much better, plus better fuel economy.

Any major problems with this?

arfur
02-27-2006, 09:56 PM
I too have these tires and they say on the tire that 51 PSI is the max. However, while driving it home to Texas from North Carolina I thought the handling was a little loose.......kinda mushy. So, I bumped them all up to 40 PSI and my handling impoved greatly plus I got about 2 miles a gallon better fuel miliage.
I like running 40 PSI for the reasons previously stated and unless anyone can convince me that this is a very bad thing, I don't see any problem in doing this. Yes, the ride is a little more bumpy, but the tires don't squat out anymore and the handling is much better, plus better fuel economy.

Any major problems with this?
The maximum pressure stamped on the tyre speaks for itself.

However, increasing the pressure above that stated in the handbook (but below the maximum rating) does change the dynamics somewhat. Your mpg figure will most certainly increase, as increasing the pressure in the tyre results in a reduction in rolling resistance (the tyre is firmer and less energy is needed to rotate it for a given load - you get less deformation as the tyre rotates). However, as with just about everything, it is not all give and there will be some take. For instance, you will end up with uneven tread wear - greater pressure will result in the centre of the tread wearing far more rapidly than the edges, so eventually you will end up with oodles of tread either side of the tyre tread, but it will be nearly bald towards the centre (the severity of this will depend on the deviation of the maximum pressure from the figure stated - the higher the pressure, the worse the wear). The net result is that the tyre life will be reduced!

Another issue, is the fact that braking efficiency of the tyre starts to degrade the higher the internal pressure, as the footprint under braking loading is reduced. This is magnified when braking in the wet! There are also changes to the cornering efficiency of the tyre.

Basically, increasing the pressure will give you a little gas mileage, but will increase the wear at the centre of the tread and will effect dynamic handling and braking efficiency - especially in the wet!

(I am not going to go into the increased loading of the suspension components and potential for increased wear in the dampers).

Choice is yours! :)

HoosierHemi
02-28-2006, 02:01 AM
[QUOTE=Murunga]The Continental tires I saw at the lot looked like they were propoerly inflated, they sat right. Its the Michelins that looked really low.
My manual shows that I have a tire pressure monitering system, but it never lit because it probably thinks that 32lbs is just fine, and maybe it is.

I droped the tires back to 40 lbs last night and they still look good. I still think 32 lbs is wrong, but this is probably just me being hard headed and stubborn, lol : ). I'd like to hear from soemone else with these tires.

Thanks for all your help guys.


Definately use 32 lbs!!! You will ruin your tires in 6000-8000 miles at 40 PSI. When I was younger and dumber, I ruined the tires on my 1990 Mitsubishi GSX by running at 40 psi or better. That rating is if you have 5 fatboys in the car, a trunk completely loaded down, and a trailer on the back end. In other words, 5500+ lbs. I have a Daytona, it's weight is 4030 (without me in it). I even tried to get warranty replacement but the abuse was obvious I guess. I'll never go over 36 psi. Been there, done that!

teros
02-28-2006, 04:54 AM
Pirelli (http://www.tirerack.com/tires/tires.jsp?tireMake=Pirelli&tireModel=PZero+System+Asimmetrico) I say go to max and when those 'grandpa going to church' Michelins wear out get you some Pirellis, I had some of those an a Grand Marquis I used to own and it handled like a ricer on 20's! Pirelli is probably my next tire for this Charger, even on the RT rims. And sure I know I am old school and there is probably some Yokajujitsu tire that may be better this week, but I think Pirelli has proven its worth on the racing circuit.

Me likes these:

Pirelli (http://www.tirerack.com/tires/tires.jsp?tireMake=Pirelli&tireModel=PZero+System+Asimmetrico)

daytona0231
02-28-2006, 05:14 AM
The tire pressure sensors go buy the amount of air pressure the car needs to safely ride with the current load. At 28 psi my car was fine until I picked up my firend from the airport with all those bags and suddenly 28psi was low tire pressure. The car tech. works, if you dont understand it just research it before taking it in your own hands.

3996 Daytona
02-28-2006, 05:52 AM
My tire pressure light came on the other day also. With me out of the car measuring I had 32 lbs in 3 tires and 30 in the left front. I added a couple psi and the light went out.

Does the tire low indicator work on an average? In other words the difference from one to the other. 35 on three and 30 on one will set it off, maybe? I don't know. I know my Ford tire pressure warning can be calibrated by me for what ever pressure I have the tires at. I didn't see any mention of that in the Charger handbook.

Blkout
02-28-2006, 10:30 AM
A good rule of thumb for me has always been 32-34psi cold pressure for a car, SUV's and trucks are different. Keep in mind though that when the tires heat up, the air pressure goes up too which is why you want to stay away from the MAX tire pressure since that allows some room for the pressure change. The sticker on the inside of the door will tell what pressure to run your tires based on the factory installed tire and you should stick to that suggestion. If you install a different brand of tire than what was originally installed on your vehicle, the tire pressure recommendation could change, but to be honest, in all my years I've found that its usually pretty close to the same, I can live with 2-3psi difference one way or the other. Also keep in mind that the more pressure you run, the stiffer the car rides which can also be very undesirable.

My advice for all you with Chargers or other passenger cars, 32-34psi cold pressure is a good safe bet and you will probably never go wrong with that number.

arfur
02-28-2006, 06:52 PM
A good rule of thumb for me has always been 32-34psi cold pressure for a car, SUV's and trucks are different. Keep in mind though that when the tires heat up, the air pressure goes up too which is why you want to stay away from the MAX tire pressure since that allows some room for the pressure change. The sticker on the inside of the door will tell what pressure to run your tires based on the factory installed tire and you should stick to that suggestion. If you install a different brand of tire than what was originally installed on your vehicle, the tire pressure recommendation could change, but to be honest, in all my years I've found that its usually pretty close to the same, I can live with 2-3psi difference one way or the other. Also keep in mind that the more pressure you run, the stiffer the car rides which can also be very undesirable.

My advice for all you with Chargers or other passenger cars, 32-34psi cold pressure is a good safe bet and you will probably never go wrong with that number.

Couldn't have put it better meself.

Oh - and as an aside and something that I forgot to mention yesterday - increasing the pressure of your tyres from 32psi to 40psi increases the energy within the tyre a great deal. That is an increase of 8 pounds 'per square inch' on the tyre inner wall. This is about the same pressure as is seen on the inside of a commercial airliner when pressurised and flying at 37,000 ft. Any guesses what happens if the aircraft structure loses its integrity in this situation.......? Basically, if the tyre gets damaged, there is a greater chance of an impressive blow-out - which would be far greater in its ferocity than at the normal advised pressure! (or something that might have just caused a rapid deflation results in an explosion - if you see what I mean. :beat:

Blkout
02-28-2006, 10:19 PM
Couldn't have put it better meself.

Oh - and as an aside and something that I forgot to mention yesterday - increasing the pressure of your tyres from 32psi to 40psi increases the energy within the tyre a great deal. That is an increase of 8 pounds 'per square inch' on the tyre inner wall. This is about the same pressure as is seen on the inside of a commercial airliner when pressurised and flying at 37,000 ft. Any guesses what happens if the aircraft structure loses its integrity in this situation.......? Basically, if the tyre gets damaged, there is a greater chance of an impressive blow-out - which would be far greater in its ferocity than at the normal advised pressure! (or something that might have just caused a rapid deflation results in an explosion - if you see what I mean. :beat:

This is true too.

Dutch
03-02-2006, 10:47 PM
Is a tire supposed to look like that these days?

Yes. What, did your old car have bias-ply tires?

Black One
03-03-2006, 12:40 AM
There is one fool proof method of figuring out the proper tire pressure.

1) Read the owner's manual and it will tell you the proper psi.
2) Remove the cap from the valve stem and check the air in the tires with the appropriate tool.
3) If there is too much air in the tires, let some out.
4) If there is not enough air in the tires, put some in.
5) Put cap back on valve stem and drive like hell.

OGB
03-03-2006, 09:59 PM
The door sticker is there for one reason,YOU!!

arfur
03-03-2006, 10:39 PM
The door sticker is there for one reason,YOU!!

Won't stop some tho.....

Crow
03-03-2006, 11:14 PM
I have the 18" Michelins and it states 32 PSI on the door pillar. You have to remember, tires are not exclusive to one car, and therefore you have many different applications for the tire, with a maximum load capacity of 42 PSI. Dodge Charger is not one of those 42 PSI applications.

Obviously, 32 PSI is what the CDX engineers have come up with all the testing on handling/speed rating/ etc... They don't pull these numbers out of a hat. There are reasons for not exceeding the recommended pressure.

You shouldn't really go above what is recommended, regardless of what the tire says it can handle.

Another tip, if you can locate some, use nitrogen rather than regular air to inflate your tires.

1) Nitrogen does not expand nor contract like air. This gives you a more constant air pressure while driving hot or cold.

2) Nitrogen molecules are bigger than air, thus it does not escape through he rubber as quickly. Maintains correct tire pressure for longer periods of time.

Some pro shops will usually have it or know where you might get it.

Sam
03-05-2006, 10:25 PM
Exceeding the car (not tire) manufacturer specs for air pressure can also make your car ride unnecessarily harsh. The Chrysler specifications are not arbitrary.

If you anticipate carrying a very heavy load (not exceeding the overall weight limit) you can safely go 5 psi over.

Radial tires are normally supposed to bulge some at the sides, even when properly inflated and you can't really tell by looking unless you're maybe 15 psi down or more.

Use a quality tire gauge. Always worth the money.

Respect your tires, they are the most important part of your car. "Brakes stop the wheel, the tires stop the car."

Sam

Blkout
03-07-2006, 05:39 PM
I have the 18" Michelins and it states 32 PSI on the door pillar. You have to remember, tires are not exclusive to one car, and therefore you have many different applications for the tire, with a maximum load capacity of 42 PSI. Dodge Charger is not one of those 42 PSI applications.

Obviously, 32 PSI is what the CDX engineers have come up with all the testing on handling/speed rating/ etc... They don't pull these numbers out of a hat. There are reasons for not exceeding the recommended pressure.

You shouldn't really go above what is recommended, regardless of what the tire says it can handle.

Another tip, if you can locate some, use nitrogen rather than regular air to inflate your tires.

1) Nitrogen does not expand nor contract like air. This gives you a more constant air pressure while driving hot or cold.

2) Nitrogen molecules are bigger than air, thus it does not escape through he rubber as quickly. Maintains correct tire pressure for longer periods of time.

Some pro shops will usually have it or know where you might get it.

Interesting thought on Nitrogen, never heard that before.

I think I would like to try Helium though. Less drag for faster E/T's.

arfur
03-07-2006, 05:59 PM
I

1) Nitrogen does not expand nor contract like air. This gives you a more constant air pressure while driving hot or cold.

.

Dude - somebody is pulling your leg. I can tell you from first hand experiance that the pressure in aircraft tyres does increase as temperature increases (and the inverse). Do you wanna guess what gas they're filled with....? :)

(all gasses, fluids and materials expand and contract with fluctuations in heat energy - it's physics Jim!)

For example.

"You cannot easily observe the effects of temperature change on gases unless the

gas is sealed in a container. The gases of the atmosphere are free to move when

expanding or contracting. However, experimentation has shown that unlike solids

and liquids, all gases expand and contract to the same extent with a change in

temperature. That is, all gases have the same coefficient of expansion or contraction."


http://www.sciencebyjones.com/expansion-contraction.htm


Gases also exhibit thermal expansion. The coefficient of expansion is about the same for all the common gases at ordinary temperatures; it is 1/273 of the volume at 0C per degree rise in temperature.

http://www.encyclopedia.com/html/e1/expansio.asp

SUPER BEE
03-07-2006, 05:59 PM
here's something to think about also, get yourself a good tire gauge. i've put cheaper gauges against mine and they have been "off" by 5lbs.

Blkout
03-07-2006, 06:05 PM
Dude - somebody is pulling your leg. I can tell you from first hand experiance that the pressure in aircraft tyres does increase as temperature increases (and the inverse). Do you wanna guess what gas they're filled with....? :)

(all gasses, fluids and materials expand and contract with fluctuations in heat energy - it's physics Jim!)

For example.

"You cannot easily observe the effects of temperature change on gases unless the

gas is sealed in a container. The gases of the atmosphere are free to move when

expanding or contracting. However, experimentation has shown that unlike solids

and liquids, all gases expand and contract to the same extent with a change in

temperature. That is, all gases have the same coefficient of expansion or contraction."


http://www.sciencebyjones.com/expansion-contraction.htm


Gases also exhibit thermal expansion. The coefficient of expansion is about the same for all the common gases at ordinary temperatures; it is 1/273 of the volume at 0C per degree rise in temperature.

http://www.encyclopedia.com/html/e1/expansio.asp

Maybe nitrogen is more resistant to expansion in the temperature range that our tires normally see. Just a thought, don't know for sure, but maybe that's where he got it from.

arfur
03-07-2006, 06:34 PM
Maybe nitrogen is more resistant to expansion in the temperature range that our tires normally see. Just a thought, don't know for sure, but maybe that's where he got it from.

It could be...

I don't really know 100% - I have never studied it TBH, but even in the case of aircraft application, it is purely (IIRC) on the basis of being an inert gas - it does not aid combustion.

I dunno - I might do a search and see if I can find some scientific explanation. :)

arfur
03-07-2006, 06:40 PM
Nitrogen Inflation

For the majority of motorists, the benefits of nitrogen are unlikely to outweigh the costs involved.

What is Nitrogen?

Colourless, odourless, tasteless, and non-toxic, Nitrogen exists as a non-flammable gas at atmospheric temperatures and pressures. It is one of the basic elements. Normal, compressed, air consists of approximately 78% nitrogen gas, with most of the remainder being made up of oxygen.

What effect can Nitrogen have on tyres?

Under ideal conditions, Nitrogen will run cooler than normal compressed air, will exhibit slower leakage, have no oxidation, and be virtually non combustible.

In particular circumstances, pure Nitrogen is used as the inflation medium in earthmover, racing, and aviation tyres to where they are required to perform under conditions of high stress and in critical environments, generating higher than usual temperatures. Examples are:


Where exceptionally high loads are carried by the vehicle,
High-speed travel,
Where high pressure must be maintained.
Also, in some instances, the tyre casing wears better, and to some extent, tyre tread wears more slowly, when Nitrogen is used in these extreme circumstances.

How can Nitrigen affect on-road tyres?

Despite the advantages in specialised tyres subject to extreme conditions, the benefits of Nitrogen inflation for tyres used primarily on ordinary roads in standard driving conditions are not at all clear.

The main arguments put forward for its use of pure Nitrogen in tyres under normal conditions are:


a) Alleged Improved Tread Wear
Unfortunately, little controlled test data exists to support or refute this claim.

Improved tread wear comes from proper tyre maintenance, for example from:


Checking your tyre inflation pressure at least once a month, and preferably fortnightly
Regular rotation and
Correct wheel alignment.
Take care of these, and your tyres will ride more safely and wear better, irrespective of the choice of inflation medium.

b) Casing Durability
When the tyre heats up, moisture in the tyre vaporises and expands. In some circumstances, moisture in the compressed air in a tyre can gradually migrates through the inner lining of a tubeless tyre and into the steel-cord body plies, resulting in rust, which ultimately causes casing degradation.

This applies to truck and bus, and some light truck tyres. Passenger and most light truck tyres are not affected, as they are composed instead of textile body ply material (eg polyester, nylon, rayon, etc).

One of the main claims made by Nitrogen proponents is that compressed Nitrogen contains less moisture than compressed air, thereby reducing the incidence of this moisture migration effect.

The primary aim should be to avoid moisture migration irrespective of the mix of gas used in tyre inflation. Moisture can be introduced into the tyre as a result of poor workshop practices and incorrect or inadequate tyre fitment procedures.

To this end, we encourage proper selection of compressor equipment, air-line routing, the use of air dryers, and other sound workshop and equipment maintenance practices in order to minimise moisture introduction.

This applies both to initial tyre inflation and top-up air.

Poor tyre fitment and workshop standards can also contribute to wheel and rim corrosion. If proper practices and equipment are utilised, moisture migration is minimised. It does not matter so much whether Nitrogen or compressed air is the inflation medium.

If you fill your tyres with Nitrogen, to retain any benefit, you will need to top up with Nitrogen as well. Topping up with Compressed air will negate any benefit.

When you first fill up your tyres, they already have air in them, so they really should be filled then evacuated, then filled again to remove the residual atmospheric air.

c) Susceptibility to Tyre Fires
Ever since the introduction of tubeless radial-ply tyres, the risks of tyre fires and/or self-ignition of tyres due to excessive heat have been rendered virtually nonexistent.

With tubeless radial-ply tyres, there is no 'tube and flap' which could cause friction and, therefore, heat to be generated.

It takes far higher temperatures to ignite steel radial truck and bus tyres, as compared with fabric-reinforced bias-ply tyres.

If properly maintained and used within legal tolerances, air-inflated passenger and light truck radial tyres will rarely, if ever, generate sufficient heat to self-ignite and burn, whether filled with Nitrogen or with ordinary compressed air.

Those motorists who choose to keep their tyres inflated with Nitrogen must bear in mind that Nitrogen inflation is NOT a 'set and forget' option. Regardless of the gas inflated into your tyres, to preserve their safety characteristics and longevity, you must check tyre pressure tyre and condition regularly.


http://www.btc.net.au/tyrecare/nitrogen.asp

arfur
03-07-2006, 06:45 PM
This is interesting....means that using nitrogen in road cars is a waste of time and money!

Tyres that are at risk of coming into contact with extremes of heat are filled with nitrogen, eg: Ralley Car Tyres. This is because the Butyl rubber lining of the tyre at about 200 deg c releases a gas Called Butidyne . this gas is self heating and eventually explodes even afer releasing the air in the tyre. But it needs oxygen, so nitrogen is used or oxyless nitrogen to be precise. Some companys have experimented with the use of nitrogen in there truck tyres with near fatal results to there staff when stripping them in enclosed spaces.

Allevon
03-07-2006, 06:48 PM
NEVER and I mean NEVER run your tire pressure at MAX unless your carrying a very heavy load.

When you inflate the tire this much, your ballooning the tire round and will wear them right down the middle. Secondly the lack of weight and high pressure means, HARD AS HELL RIDE. You'll feel bumps.

I keep mine around 32-36 as this provides enough cushioning yet enough stiffness to handle the curves.

If you want your car to feel its like wagon wheels, buy one of these no meat tires on bicycle rims everybody seems to like these days. You'll get the hard as hell feel of 44 pressure and be able to turn CORNERS at high speeds, but require a new spleen at the end of your long journey.

If you leave your tires too LOW, your going to wear the edges of the tire real fast and only have treads down the center. The walls of the tire will be your ONLY cushioning.

So again, I HIGHLY recommend 32-36 range.

arfur
03-07-2006, 06:48 PM
Also - and I know that most ppl will know this....air is 78% nitrogen anyway....is an extra 22% gonna turn normal tyres into supa-tyres???

dmrowe
03-07-2006, 06:58 PM
Maybe nitrogen is more resistant to expansion in the temperature range that our tires normally see. Just a thought, don't know for sure, but maybe that's where he got it from.

This is something that a group of us starting trying back in 1967. We worked in a film lab and they used nitrogen to aerate the color developer. We heard about the properties of nitrogen and started inflating our motorcycle tires with it. We thought it made us go faster, but I still think it was what we were smoking. However, check out the attached links, very interesting might be something to it.

http://www.wndu.com/16wheels/102005/16wheels_45316.php

http://www.tirelast.com/id15.html

http://www.tcsdaily.com/article.aspx?id=111604D

moparfan
03-07-2006, 07:01 PM
Question:

I had run my tires between 34 - 36 psi and everything seemed fine. Took it to the dealer for an oil change and he pumped them up to 44. I looked at the tires and they stated 50 psi so I thought, ok I've been running them too low.

Now the ride is a bit more harsh but I figured the tech at the Dodge dealer knows what he's doing. Maybe that was the wrong assumption...?!?

Also, my psi varies widely from 40 psi in the "chilly" (FL chilly that is) morning to around 46 psi when heated and on the highway. I guess it's normal for the pressure to increase with the heat, but the question still remains:

What should the psi be for the all-seaon tires on the CHSRT8?

Blkout
03-07-2006, 07:15 PM
Question:

I had run my tires between 34 - 36 psi and everything seemed fine. Took it to the dealer for an oil change and he pumped them up to 44. I looked at the tires and they stated 50 psi so I thought, ok I've been running them too low.

Now the ride is a bit more harsh but I figured the tech at the Dodge dealer knows what he's doing. Maybe that was the wrong assumption...?!?

Also, my psi varies widely from 40 psi in the "chilly" (FL chilly that is) morning to around 46 psi when heated and on the highway. I guess it's normal for the pressure to increase with the heat, but the question still remains:

What should the psi be for the all-seaon tires on the CHSRT8?


32-34psi cold pressure.

moparfan
03-07-2006, 07:20 PM
32-34psi cold pressure.

Thanks man. I'll be deflating in the morning. :shifty:

arfur
03-07-2006, 07:29 PM
This is something that a group of us starting trying back in 1967. We worked in a film lab and they used nitrogen to aerate the color developer. We heard about the properties of nitrogen and started inflating our motorcycle tires with it. We thought it made us go faster, but I still think it was what we were smoking. However, check out the attached links, very interesting might be something to it.

http://www.wndu.com/16wheels/102005/16wheels_45316.php

http://www.tirelast.com/id15.html

http://www.tcsdaily.com/article.aspx?id=111604D

All interesting in their own way....:)

1) An aircraft is not likely to not explode after a crash because nitrogen was in the tyres (I don't know the exact incident - but puuurrllleeease). I'd be more worried about aviation fuel.....

2) So what if it takes 6 times longer for nitrogen to escape - it takes 5 minutes at a gas station to check the pressures....

3) how long is anybody planning to keep tyres on their rims (from this forum - 2 weeks). Yes oxygen attacks rubber and oxidises it, but nobody - even with a bloody snail car - is gonna need to be worried about the oxygen in the air inside their tyres eating them from the inside out!!! Good grief - how you gonna protect the outside of the tyres!!! I have seen tyres stay on cars for 7 years plus - they didn't suddenly disintegrate! And what it anybody gonna do about ultra-violet light rotting the tyres - it's not gonna happen from the inside cos there's no light...but the outsides get bathed in it all the time. Why do you think tyres are generally BLACK and not lots of lovely colours.....?

Not pointed at you dmrowe... :headbang: :)

Sorry these references just make me believe that this is one of those urban/internet myths which has leaked into everyday life.

arfur
03-07-2006, 07:31 PM
Thanks man. I'll be deflating in the morning. :shifty:

Don't worry - you will prolly just have been increasing the wear rate on the centre of the tread. Changing the pressures back will sort that out. :)