Tire PSI

[RHAGEL]

I was just curious to see how people fill their tires. I have stock 17 Goodyear RSA's. The recommended pressure is 32. I fill mine to 35. I found that I:
1. Get better gas mileage
2. Less body roll
3. Better steering response
4. Better tire wear
5. No noticeable degrade in ride quality

Other that the fact that they want your tires to wear out quicker, grip would be the only reason to fill them to the reccomended pressure. I wouldn't actually know since have never tested max grip in the car.

I just want to see if anyone else has any insight.

[Tengo]

i need to get mine checked out and filled correctly. i have like 20-25 psi on front tires and right rear is like 13 psi (lmao) and other side like like in the high 20's. so 35 psi is a good rate for all four tires? i want better gas mileage and good tire wear.

[tsunami]

dear lord 13psi... is that a drag slick?

i ran 36psi all around when i had the rsa found 34 seems good on the 18" runnin with kumho mx (http://www.tirerack.com/tires/tires.jsp?tireMake=Kumho&tireModel=ECSTA+MX) road noise is quite loud but the grip is much improved

[Tengo]

i dont know how it got that low?

[BlueMonsta]

tires leak air on its on,
its a good practice to check ur tire pressure once a week.
I do mine monthly cause im lazy.

during the summer, I ran 32psi on cold tires (17'' RS-As).
I tried 35, ride got to bouncy. I'll try it this coming summer since the suspension is more worn now.

winter I ran 40psi on warm tires (not cold), at 7 degrees C.
I need to check it again since its -10 degrees C now.

please note: psi will increase with increase of temperature, and vice versa. also note the max psi stated on your tire's side wall.

[Tengo]

im going to go to the gas station and put 32 psi on all my tires

[Olestra]

Sry, couldn't help but laugh out loud at the 13 Psi...

32 is good if you're not sure if going with higher will affect your tire wear.

Couple things:
-Fill your tires when they're cold - driven less than 2 km. Best to do right in the morning after the car has sat overnight.
-General rule is 10 degree temperature drop = 1 psi pressure drop.

So if you filled your tires in the summer at 32, and it's winter now (like -30 C last week for me) then you can easily find yourself at 26 Psi and lower.

Check every week as someone above mentioned, but if you even check once every 2 weeks or month, you're still probably fine. Takes 2 seconds to put a guage from your glove box onto the tire. I usually just check one tire if I'm just trying to get an idea of what my pressure is b/c I'm lazy too =)

I put 36 PSI on my winters to see how it would go on a -15 C day thinking that the weather was gonna stay cold. It has warmed up to about -5 C and seeing this thread has made me realize I'm probably over inflated...

As for gas mileage, I did see a bit of improvement. Ever since we had snow, my gas mileage has visibly been declining according to the trip computer. I went from 9.1 L/100KM (Cdn, below the 9.2 avg) to now at 9.6. But it hasn't moved since I inflated my tires to a higher Psi. So my decrease is probably due to the fact that I was trying to keep 32 Psi and also b/c I have my heater on all the time (I heard if you have it on the floor setting and anything to the right, it uses the A/C automatically? I heard this for the 05, is this true for 06 M3?)

[xeryusdvirus]

I was told that using or filling tires with Nitrogen mixed air from tire centers would prevent air loss (or slow down the process). I just keep my tires inflated to specs. When I buy new tires, I would look into places that fill it with nitro.

[tsunami]

yeah its true if you use your heat at the floor (12'o clock) or to the right it automaticaly uses the ac... so your loss in milleage could be accounted for there i would think

[Brian MP5T]

If the company recomends 32, it's more than likely better to use that. The traction diferences are noticable between the two... Ye don't want to look like an ass trying to save $12.00 a year in gas, just to smack the back of a guy on a mortorcycle and accumulate $1,000000 in Hospital bills?

[RHAGEL]

If the company recomends 32, it's more than likely better to use that. The traction diferences are noticable between the two... Ye don't want to look like an ass trying to save $12.00 a year in gas, just to smack the back of a guy on a mortorcycle and accumulate $1,000000 in Hospital bills? Traction and grip is not an issue unless you are pushing the car to its full potential. I have been slightly overinflating my tires for years with no problems. I drive a windy mountain road everyday and don't even get my tires to squeal. I agree though, if you are making turns at 60, then you may want to rethink that. But then again, if you are making turns at 60, your traffic tickets will be outrageous.

[RHAGEL]

I was told that using or filling tires with Nitrogen mixed air from tire centers would prevent air loss (or slow down the process). I just keep my tires inflated to specs. When I buy new tires, I would look into places that fill it with nitro. The reason why is that nitrogen particles are larger than air particles, so then don't leak through the tires as easy. Not only that, but nitrogen is lighter than air and does not condensate so you wheels will be lighter, (maybe a pound or so). I do know that Costco uses nitrogen in their tire department.

[jacen]

Air is 79-80% nitrogen, most of the rest is oxygen, then a small amount C, H, and O compounds, so nitrogen isn't really bigger than air particles. Nitrogen fill is drier, as you mentioned, which helps reduce expansion. Their is some talk of better tire life without the oxygen on the inside, i think this is mostly for car who get the tires pretty hot for extended time periods, like road course driving. I would use nitrogen if it was easily available around me, but I haven't found an easy source.

Oh, and I tend to run higher tire PSI than 32 on the street.

[Olestra]

If the company recomends 32, it's more than likely better to use that. The traction diferences are noticable between the two... Ye don't want to look like an ass trying to save $12.00 a year in gas, just to smack the back of a guy on a mortorcycle and accumulate $1,000000 in Hospital bills?

Yeah - Mazda 3's manufacturer recommended PSI is 32. I have been trying to keep that, but when the temp went down 20-25 degrees here in Canada, my PSI went down with it. So I overinflated a bit as an experimentation and also in anticipation for the cold weather.

Well this week it was warm, around 0 degrees C. I checked my tire yesterday finally(been lazy) and it was at a ridiculous 40 PSI. I thought that a bit of air would have leaked out and maybe I would be sitting at 36, 38 tops. So I of course let the air out until I was back down to 34 PSI. So that goes to show that you should probably check your pressure every week especially if your weather is tempermental like here in Edmonton.

PS. I don't know why you think inflating a little past 32 would cause my car to lose control and kill someone? That's absurd unless I somehow go past the 44 PSI rating on the tire and it blows up.

[MightyMouse]

The reason why is that nitrogen particles are larger than air particles, so then don't leak through the tires as easy. Not only that, but nitrogen is lighter than air and does not condensate so you wheels will be lighter, (maybe a pound or so). I do know that Costco uses nitrogen in their tire department.

Wow, did Costco ever do a sales pitch on you! LOL :)

Air is 78% Nitrogen, so, the "particle size" is pretty much going to be the same. So, from that, you can figure your tires are not going to be any "lighter" either (1 lb lighter? How much do you think the air in your tires weighs?)

The only benifit to using Nitrogen over air is that pure nitrogen has no MOISTURE in it, which can affect the longevity of the tire (but who keeps tires for 10 years anyways) and how much the tire pressure increases as the tire goes above the boiling point of water (100 deg C). No water in the nitrogen, so the pressure does not increase quite as much (only makes a 2 or 3 pound diff) (We use nitrogen in race cars because we need extremely stable tire pressures mainly in the 170-240 deg F range where water content makes the biggest diff, almost nobody in a street car ever gets their tires this hot unless they are out of balance) Although, if you use completely dry air (which can be purchased) it is pretty much the same as using nitrogen. Or, just fill up your tires on a very low humidity day for free.

A side note about tire pressures. The size of your contact patch is directly related to tire pressure. Double the pressure, and you cut the size of your contact patch in half. Therefor, if you increase your tire pressure over stock, you are reducing the contact patch, and therefor you are reducing the amount of traction the car has. And when it comes to an emergency panic stop, every square mm of contact patch matters. Plus, any savings from fuel economy you get from running an overinflated tire are greatly offset by increased tire costs because the center portion of the tire will wear out a lot faster...hmm..... get an extra 20 miles to a tank and buy a $800 set of tires twice as often....good savings (doh)

I have learned a lot about tire pressures first from being a class "A" technician, but also from racing, where every 0.5 PSI difference can make a huge difference to tire longevity, cornering ability, braking traction and tire temps.

[Fuchs]

Guys...

go outside, open your drivers side door, and look at the sticker titled "Tire and Loading Information". It will tell you what is recommended ;)

It's in your door jam.

[RHAGEL]

Wow, did Costco ever do a sales pitch on you! LOL :)

Air is 78% Nitrogen, so, the "particle size" is pretty much going to be the same. So, from that, you can figure your tires are not going to be any "lighter" either (1 lb lighter? How much do you think the air in your tires weighs?)

The only benifit to using Nitrogen over air is that pure nitrogen has no MOISTURE in it, which can affect the longevity of the tire (but who keeps tires for 10 years anyways) and how much the tire pressure increases as the tire goes above the boiling point of water (100 deg C). No water in the nitrogen, so the pressure does not increase quite as much (only makes a 2 or 3 pound diff) (We use nitrogen in race cars because we need extremely stable tire pressures mainly in the 170-240 deg F range where water content makes the biggest diff, almost nobody in a street car ever gets their tires this hot unless they are out of balance) Although, if you use completely dry air (which can be purchased) it is pretty much the same as using nitrogen. Or, just fill up your tires on a very low humidity day for free.

A side note about tire pressures. The size of your contact patch is directly related to tire pressure. Double the pressure, and you cut the size of your contact patch in half. Therefor, if you increase your tire pressure over stock, you are reducing the contact patch, and therefor you are reducing the amount of traction the car has. And when it comes to an emergency panic stop, every square mm of contact patch matters. Plus, any savings from fuel economy you get from running an overinflated tire are greatly offset by increased tire costs because the center portion of the tire will wear out a lot faster...hmm..... get an extra 20 miles to a tank and buy a $800 set of tires twice as often....good savings (doh)

I have learned a lot about tire pressures first from being a class "A" technician, but also from racing, where every 0.5 PSI difference can make a huge difference to tire longevity, cornering ability, braking traction and tire temps.

I hope you feel a little better about yourself trying to be Mr. Fucking Smart Ass. You basically re-iterated everything I said. I have never bought tires from Costco, I just said that I know they use nitrogen. And I also, said that I realized that over inflated tires can reduced grip but I havent seen any adverse effects for over inlating 2 psi. And so what if your tires are 1 lb. lighter? I was just noting that it "might" be a positive. So next time shut your fucking mouth (figuratively speaking) and stop trying to make yourself look better by putting other people down...jackoff.

[MightyMouse]

I hope you feel a little better about yourself trying to be Mr. Fucking Smart Ass. You basically re-iterated everything I said.

Actually, I was correcting some of the missinformation you were spreading.

I have never bought tires from Costco

I'm not sure why you have the need to mention this, but, um, OK.

I just said that I know they use nitrogen. And I also, said that I realized that over inflated tires can reduced grip but I havent seen any adverse effects for over inlating 2 psi. And so what if your tires are 1 lb. lighter? I was just noting that it "might" be a positive. .

Please re-read what I wrote, and you will see why it is impossible to make your tires any lighter by using nitrogen.

So next time shut your fucking mouth (figuratively speaking) and stop trying to make yourself look better by putting other people down...jackoff.

Wow, somebody pissed in your cornflakes this morning eh?

I am just trying to put an end to some of the misinformation in this thread. There seems to be lots.

I just want to see if anyone else has any insight.

You asked for comments.......just because they don't agree with what you said, don't get all pissy.

[RHAGEL]

Actually, I was correcting some of the missinformation you were spreading.



I'm not sure why you have the need to mention this, but, um, OK.



Please re-read what I wrote, and you will see why it is impossible to make your tires any lighter by using nitrogen.



Wow, somebody pissed in your cornflakes this morning eh?

I am just trying to put an end to some of the misinformation in this thread. There seems to be lots.



You asked for comments.......just because they don't agree with what you said, don't get all pissy.

I'm just tired of all the people always making smart ass, know it all comments. If you have a comment, make it. Just don't put people down because you think know something that others may not. This was never meant to be about nitrogen. I had a comment to make about tire pressure that is legitiment and was trying to spark some new conversation. Thats it, maybe I overreacted a bit...my apologies.

[MightyMouse]

I'm just tired of all the people always making smart ass, know it all comments. If you have a comment, make it. Just don't put people down because you think know something that others may not. This was never meant to be about nitrogen. I had a comment to make about tire pressure that is legitiment and was trying to spark some new conversation. Thats it, maybe I overreacted a bit...my apologies.

Hey, NP. Well, you really got some conversation going....:)

[thabigo]

wow i was just reading this thread and i checked my Tire Pressure this Morning before i went to work. After sitting over night my Tire Pressure was at 47 psi!!!! It was 32 degrees this morning as well!!. I immeadately took my gauge and lowered it to around 38 PSI on each tire. Man the dealer must have giving me the car with the tires way over inflatted. I have been driving like this for a week now. Im ussing one of those pretty Accurate gauges as well from Advanced auto parts. Im going to confirm tire pressure later on today to make sure that my Gauge isn't off. I mean 47 psi that was crazy. If my gague is accurate im def. complaining to that dealership.

Thanks,

Orlando

[dread]

mine was 50.5 psi, so I am not surprised, took it down to 32 and the ride is much better now.

[StreteSpd]

Traction and grip is not an issue unless you are pushing the car to its full potential. I have been slightly overinflating my tires for years with no problems. I drive a windy mountain road everyday and don't even get my tires to squeal. I agree though, if you are making turns at 60, then you may want to rethink that. But then again, if you are making turns at 60, your traffic tickets will be outrageous.

Not that I don't think the tire pressure could be up'd by a point or two, but I'm going to agree with Brian_MP5T, not just because it makes sense, not just because manufactures stand to gain nothing if our tires just wear constantly since they aren't making money they can count on from it and thus probably aren't leading you on, but because I used to have a light quick (not fast) car that was fun to drive at the limit, and it was WELL BELOW the limit, when I was fully comfortable with my 4.5lbs-over-inflated tires that I went to turn a 60km bend at 40 in the rain and the car just never turned, sliding me off the road, readily cutting down both front tires, and narrowly missing a tree. My Car was lowered, so guess how much extra damage it did.

It's true that increasing tire pressure has some benefits, but don't forget that in inclement weather, the benefits are few, and in addition to that, the tires are wearing with use. This means that when they are new, you're probably fairly safe even over inflated, but as those tires wear, the unsafe-factor increases exponentially instead of gradually (the way they would if you had them at recommended tire pressure) ..which is what allows ppl to drive on the tires long beyond the recommended switch-frame and still get away with it.

The gains in fuel economy and steering feel are great, but car control decreases, and with wear, the chances of unexpected occurrences ramp up fully. There are a ton of other methods and techniques to save on gas where if you get them wrong, you'll be safe to try again. Over-inflating tires isn't one of them.

Imagine this, it might be a sweet race strategy to overinflate the tires a bit and run longer than everyone else..walking to the checkered flag... yet there's a reason that this is never done. Safety first right?

Like I said, likely no harm in going over by a couple.. but there isn't a lot of benefit that comes from a couple over... the big benefit comes typiclally from +4 and up... i used to do this. (peep)

[Rotus8]

In my opinion, the best place to start on tire pressure is the manufacturer's reccomendation. Then adjust based on real data. Real data can be obtained by measureing the temperature of the tread after a drive using a pyrometer. A reasonably priced one can be had from Summit racing http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2DG1054&N=700+115&autoview=sku.

The technique is to drive for at least 20 minutes using a style that you want to optimise for. Then stop and quickly measure the temperature of the tread in three places, the inside corner, middle, and outside corner of all four tires. If the center is hotter than the edges, you need less pressure. If it is colder, you need more. This also tells you about your camber setting; if the tire is hotter on the outside you need more negative camber.

A seat of the pants dyno is often misleading. Real data is the only way to make meaningful adjustments. Keep a log with the cold pressures of all four tires at the beginning of a drive and the temps at the end. A few commute days and you will have it perfect.

If the tire temperature is even across the tire it means you are getting equal traction and equal wear, utilizing the rubber across the whole tire to the maximum.

Edit: The maximum pressure on the tire sidewall is just that, the maximum. It is never the correct inflation pressure!

[slammie]

OK, I think you've all beaten the horse to death and then some. Rhagel and Mighty Mouse thanks for the good laugh...I needed that.

[Red Ace55]

For those of you looking for the real benefits of using N2 in your tires, please refer to the paper attached...

[Olestra]

I am wondering - what is the recommended pressure on the MS3? What does it say on the door jamb, if anyone can check? I would imagine it's higher than the reg 3 b/c MS3 is a heavier car with larger tires.

Not that I don't think the tire pressure could be up'd by a point or two, but I'm going to agree with Brian_MP5T, not just because it makes sense, not just because manufactures stand to gain nothing if our tires just wear constantly since they aren't making money they can count on from it and thus probably aren't leading you on, but because I used to have a light quick (not fast) car that was fun to drive at the limit, and it was WELL BELOW the limit, when I was fully comfortable with my 4.5lbs-over-inflated tires that I went to turn a 60km bend at 40 in the rain and the car just never turned, sliding me off the road, readily cutting down both front tires, and narrowly missing a tree. My Car was lowered, so guess how much extra damage it did.

It's true that increasing tire pressure has some benefits, but don't forget that in inclement weather, the benefits are few, and in addition to that, the tires are wearing with use. This means that when they are new, you're probably fairly safe even over inflated, but as those tires wear, the unsafe-factor increases exponentially instead of gradually (the way they would if you had them at recommended tire pressure) ..which is what allows ppl to drive on the tires long beyond the recommended switch-frame and still get away with it.

The gains in fuel economy and steering feel are great, but car control decreases, and with wear, the chances of unexpected occurrences ramp up fully. There are a ton of other methods and techniques to save on gas where if you get them wrong, you'll be safe to try again. Over-inflating tires isn't one of them.

Imagine this, it might be a sweet race strategy to overinflate the tires a bit and run longer than everyone else..walking to the checkered flag... yet there's a reason that this is never done. Safety first right?

Like I said, likely no harm in going over by a couple.. but there isn't a lot of benefit that comes from a couple over... the big benefit comes typiclally from +4 and up... i used to do this. (peep)

Alot of misinformation in there... Where you find that "unsafe factor" increases exponentially. Do you have a graph or some sort of proof? You're right in saying that a new tire will do better than an old, only because the tread is not as worn out. Having the correct pressure maximizes the surface area of contact between your tires an the road, which will maximize car's handling capabilities. Having a slight over inflation will cause the outsides to lift off the road a little and with less contact surface, you get less friction which is probably why you get better fuel econ (if any at all, it's probably negligeable) but worse handling. Underinflation will cause the edges to bow out and the middle to lift off the road, again giving you less surface. As well, this is extremely dangerous because now you're susceptible to tire roll, which is when turning, the tire rolls onto it's side and affects your handling and can create a loss in traction (probably what happened to your car).

Edit: I see autoX drivers do overinflate-mybad

I did a couple over recommended not because I thought there was a huge benefit in doing this but because I wanted to see if there actually was any difference and also b/c I'm lazy and figured that since pressure will decrease in a few weeks, then by the next time I check, it'll have gone down to 32. I'm probably just better off maintaining 32 by not being lazy.

[BoostedMP3]

should the pressure be more or less in the front for the MP3?

[Rotus8]

should the pressure be more or less in the front for the MP3?
Take a look at the sticker on the driver's side door post. Reccomeded tire pressures are there.

[wealas]

Interesting post, when I went to autox school the guy told us that manufacturers will usually recommend lower tire pressures to improve the ride of the car without actually considering the effect on traction or handling. He even mentioned that Ford had some problems with underinflated tires blowing on some of their SUVs. I wonder if the recommended tire pressure is a good start or not? I guess measuring the tire temp in different zones is really the only way to go...

[BlackJack]

I would go for the suggested PSIs. Lowering the PSI is great for the track/autocross, but it also lowers the MPG. But it's up to you.