so, i checked my air pressure again Tuesday as its gotten really cold here lately. my tires were at 28psi all the way around so i decided to top them all off. this is when it hit me that i'm a complete noob when it comes to tires and all things wheel related. am i supposed to be reading 32psi when i go out to the car in the AM and the tires are cold from sitting around and the pressure is at its lowest or am i supposed to be reading 32 psi after a nice spirited drive when the tires have been brought up to operating temperature?

sorry if this belongs in the tires/wheels/suspension area, but i didn't know if the answer would change depending on which car's manual you are reading... i didn't see anything about that in the manual, but honestly, it was dark out and cold, so i didn't read anything other than the numbers.

 

read howard coleman's posts...
John

 

ah... see... i figured i was such a moron that this had never been posted before... my bad guys... sorry.

 

it is actually a good question.... (whether to check hot or cold) the answer is to just pick one or the other. the primary mistake is to assume that you are looking for the same pressure hot or cold.

tire pressure is perhaps the most overlooked factor as to chassis tuning which is ironic as it is one of the single greatest influences as to handling.

tires, by their compliance, function as springs. more air creates a stiffer spring rate. less air, less spring rate. for instance if you want to judge how your car will handle w those 800 pound/inch springs that come w the Tein RA coil overs just air up your tires to 60 pounds and go for a drive. it won't be pretty and it won't be fast.

tires of course have a lateral contact patch.... the wider the better. with too much air pressure that patch rounds like any balloon robbing you of contact area. too little air pressure and the center of the tire is insufficiently supported making the edges of the patch have to support more of the load. the way to determine ideal tire pressure is to go for a drive to get your tires up to temperature and then check their contact patch with a pyrometer. too hot in the middle, lower the air pressure. too hot on the edges, add air.

the FD is a front engine rear drive platform and as such the primary challenge is to make the rear stick. since the stiffest end of the car slides first the rear needs to be softer than the front.... both with springs and tire pressure.

i recommend 30 front and 27-28 rear set cold. at the track i generally will bleed down built up air pressure based on the tire's heat measurements.

please don't neglect your tire's air pressure.

howard coleman

 

Howard, I agree with everthing you said, but I'd like to add a couple of things:

Since rubber has a higher friction coefficient at lower contact pressure, increasing the size of the contact patch (assuming it doesn't deform too much) will give more grip (cornering force). Lowering the inflation pressure increases the size of the contact patch. This works along with the reduced spring rate in producing more grip.
The limit in how low you can go in inflation pressure (especially in radial tires) is determined either by:
1) when the sidewall starts to roll over and/or the footprint becomes distorted, or
2) durability issues (low pressure means more heat generation and possible tire failure)

 

Published tire pressures for street tires are always cold. That means you check the pressures before you drive the car.

 

thanks Howard you gave me the exact type of info i was asking for now, for the next stupid question, does that go for ALL sized tires for the FD? i'm planning on upgraded to an 18x9 rear wheel eventually... would you still recommend the 27-28psi? i think i'm gonna try that little pyrometer trick someday, it sounds fun.

 

Howard knows a lot more about making a car fast than me, but I really don't like lower pressures. I like to keep cold pressures right at 32 or so. The car feels a little "sluggish" to me with lower pressures.

 

i run 18X10 rear wheels and 27 psi cold in the rear. i do think it works well generally through a broad range of tires/wheels.

others may prefer a bit more tire pressure... within a fairly small range it is a matter of preference.

howard coleman

 

I thought you were supposed to let all of the summer air out, and then fill the tires back up with winter air. I also take the time to top off my blinker fluid when I do this.

 

27? 30? 32? Wow...I'm guessing those are stock tires? (225s?) I have 245/35/18s in the front (on 8.5s), and 285/30/18s in the rear (on 10s) (thanks Rynberg ) and Falken publishes is max cold psi for both sizes as being 51!! http://www.falkentire.com/tires_451_sizes.htm I usually have all 4 set at 47 or 48, both to help increase the contact patch a bit, since they have real stiff sidewalls, and to reduce the possibility of a blowout from a real hard run.

Howard, according to your recommendations for tire pressure, should I be running 49 front, and 47 rear? (or something in that ballpark)? Or am I wayyy off? Cuz 27 vs. 47 is a BIG difference...

 

"Max cold psi" is just that; maximum. That is the highest pressure the manufacturer recommends assuming the tire's size and load rating. The max psi listed on the side of the tire has absolutely nothing to do with what pressure you should actually run day to day.

http://www.tirerack.com/tires/tirete...l/pressure.jsp

http://www.tirerack.com/tires/tirete...vs_dryperf.jsp

http://www.tirerack.com/tires/tirete...vs_wetperf.jsp

http://www.tirerack.com/tires/tirete...k_pressure.jsp

 

I empathize with your quest for good information about tire pressure.

The tire manufacturer specifies maximum cold pressure. What you run must always be less than that, usually much less. The actual optimum pressure depends on two things: gross vehicle weight and desired handling/tire wear/etc characteristics. Tires are designed to run in a slightly deformed shape, and this shape is provided by proper pressure. This shape ensures the best contact patch possible, as well as reducing stresses in the tire and improving grip. Underinflation or overinflation will distort the tire shape to reduce contact patch, and also overstress the tire. Falken can't tell you what tire pressure to use since you might mount it on a Lotus or a VR4. So they just specify a max.

Sideline: This is why Firestone tires blew out often on Explorers: Ford specified a lower pressure than is customary (to improve comfort and rollover risk), and ignorant drivers then had less margin against underinflation. The overstress caused by high speed driving with underinflated tires, coupled with the reduced strength of some tires manufacturing errors, caused blowouts at highway speed. As far as I've read, inattentive drivers on grossly underinflated were a factor in all of the failures.

So tire pressure it depends mostly on the car, followed by a tweaking based on handling. In a nutshell, for street driving, run at 32psi recommended by Mazda. Plus/minus a few PSI per your taste. (My dd maxima likes a few extra psi in the front since it's a front heavy car. For the FD, the weight is closer to 50-50 and so any front/rear difference in pressure is done to influence handling, as others have recommended).

Upper 40s is very firm and probably not good for tire wear, grip, or comfort. I suggest you bleed them down to 30-32psi cold before your fillings fall out.

Dave

 

Not to mention that when they heat up, they're probably exceeding the manufacturer's maximum rating, and (no offense) Falkens aren't exactly the highest quality tires on the market...

 

Damon, I'm gonna make sure I give those links a good read in a few. Thanks

Dave, thanks for the info. I understand the PSI they set is a MAX, but I also figured that normally you should run your tires close to the max (ie fully inflated), not a good bit below it - esp. not nearly half below the max! But I believe you guys, although running my tires at 32 psi comes as a shock to me lol. I thought the higher psi was for larger tires, so you no longer stick w/ the stock 32. But hey, you guys obviously know more than I do, so I'm gonna try it, and I'm sure I'll be happy w/ the results

On that note Dave, we also have a '98 Maxima...max psi rating on the tires (factory size) is 35psi IIRC. What psi are you running? I think the tires are 205s, right?

Jim, no offense taken, but on the same token, I don't think they're el-cheapo POS tires either. I think they're the best tires for the money, given that my 285/30/18s ran me $189 a pop, vs. Pirelli PZeros that run $289 a pop, and last a whopping what, 7K miles? lol. The Falkens have great traction, stiff sidewalls, and have LONG treadlife. That's why I got 'em. If there's something about them I'm not aware of that would make you shy away from 'em, plz lemme know. But I'm just not looking to buy $300 tires that'll last me only a few thousand miles, that's all.

 

Damn Rami, your tires are going to be tread-bare in the middles and completely unworn on the edges....lower those suckers to 32 psi or so! The steering will feel heavier at first, most likely, but I bet you experience greater stability and more grip.

 

I run my 97 Maxima SE at 32psi front, 30psi rear. A lot of folks have recommended that +2psi differential for FWD cars. Just last month I adjusted them back up to 35psi, knowing that the weather hadn't cooled fully for winter and by February they'll probably be in the 30-32 range. I think the SEs came with 215/55R16, and I'm running 225/55R16 now.

Regarding the change in pressure for moving to a low profile tire, I can't think of any reason why it's necessary. The real test is to take it to a skidpad and use a penetrating pyrometer to figure out what pressure creates the even temperature (loading) distribution across the width of the tire. Maybe someone who has road or autox'd on stock and low-pro tires could enlighten with some hard numbers on that point.

Dave

 

I didn't say that, but you are getting a little more than just a name when you pay for high-end brand name tires. They have more R&D, more than likely have better quality control, and even the materials they use in their tires may be superior to those of cheaper brands.

That has nothing to do with the quality of the tire, of course. Look at the tread wear rating of the two tires. I doubt your Falkens are as soft as the Pirellis, and therefore they wear longer. You can get a 100,000 mile tire if you want. You just aren't going to get great traction from them because they wear like iron.

Your Falkens are rated 280 for tread wear and AA for traction. My S-03 Pole Positions are rated 220 AA. Yours will last longer, but mine will provide better grip, despite their both having an AA rating. AA just means above 0.54 g for asphalt and above 0.41 for concrete, but it's open ended and tires may exceed the AA rating by varying degrees.

BTW, my S-03s averaged about $250 ea., and that's for 19s.

I look for good wet and dry traction and low road noise. It doesn't matter to me if I get 30k miles out them. It's a performance car, so you're going to go through tires more quickly than a passenger car. I'm not looking for a tire that I can get the maximum number of miles out of, but have to compromise on performance during that entire time to do it.

Regardless, they'll last longer if you don't over-inflate them.

 

Tyler, what can I say? That's the price of ignorance lol. I just didn't know any better... The good news is I've only had the tires on for mabe 3K miles tops. I'll def. bring 'em down to 32 psi, then start playing around w/ the rears, see how 30 - 27 in the rears feels. Man I love the forum

 

You know, we don't really need to know how it feels in the rears. Good luck with your tires tho.

Dave

 

Just set them all at 30-32 psi cold and you'll be fine.

 

Don't take this the wrong way, Ramy, but if you're as good a driver as you say you are, then you should fork out the extra $$ for some serious tires and discover just what "great traction" really is. And to tell you the truth, all 18-inch 30-35 series profile tires have a "stiff sidewall"; they have to, not only in order to keep your rims from getting smashed when you hit a pothole at speed (although that may happen anyway), but also to prevent such a short sidewall from bursting when you hit said pothole, resulting in catastrophic failure/deflation.

 

Hmmm...I didn't know that (yea I know there's a lot I don't know lol)

Yea I'm looking for excellent wet & dry traction, but I don't care about road noise. Never really hear anything over my exhaust anyways And you have a point w/ respect to grip vs. miles. I guess I'd like to get (closest to) the best of both worlds. I'll read up some in the Suspension/Tire section, see what way to go w/ my new tires (when the time comes)

Yea yea...got that point already. No need to rub it in lol

Huh?

31 all around, and I'm good to go

Kento, I'm not taking it the wrong way, but I don't think I've claimed to be an incredible driver. I think I'm considerably above average, but I don't have anything over someone like Tyler, who autocrosses regularly, or Damian, who hits the roadcourses like twice a day lol. Those opportunities come my way far and few in between due to time constraints, but when they do, yea, I hold my own pretty well.

Got your point about the stiff sidewall w/ such a low profile. As for $$, what can I say...owning an FD has continually expanded my working budget (by force), and I bought the tires at a time when being economical was very important. Seeing that my iron tires have a million more miles to them it might be a while before I spring for new tires, esp. given the upcoming much larger expenses. But in short, you're right. Grip isn't an area I wanna skimp in. I've learned my lesson

BTW, Kento, I PMed ya.

 

Hey Guys Well For Me I Take Mine All The Way Up To 42 Psi I Dont Want What Happend To Me A Yr Ago To Happen Again, I Was Doing Like 90 And All Of A Sudden My Rear Driver Side Tire Went Flat And I Check The Other Side And It Had Like 14 Psi
But It Didnt Look Low So I Take It Up To 42 Now But No More Hope This Helps Others

 

Hmm, you could just try checking it more often. Speaking nicely, your approach is poor at best..