centflatsx

Is it ok if the PSI goes to 37 or 38 when the temps are in the 60's or 70's? I realize that cold PSI is the reading when the car is parked overnight and that is the lowest reading they will get and they do go up on warmer days and after driving a bit. I don't remember mine being that high before. I went to dealer service over the weekend and I saw they were that high late this afternoon. Basically, the PSI should be 33 like it shows on the door label when you check the reading after the car has been parked for several hours, correct?

Thanks!

ed_423

thatseems a tad bit high, i'll just hold out for a few days and see if it goes back down, if not just release some air lol

cmalberto

You definitely want to adjust tire pressure when they are cold. Yes they will rise a little when they warm up. Perhaps not the extremes you show there. Cross with a good gauge. Running that high actually lowers the rolling resistance but causes un-even tread wear through the center as the edges touch less. I ran 40 in my Prius for even better mileage. You want notice anything in the TSX and more than likely will lose handling characteristics =bad.

How many miles do you have on the TPMS? They can be re-calibrated I believe once you get them lined out.

--Mickey

centflatsx

Thanks for the suggestions. I will see how they are tomorrow. We've had some cool nights here and that lowers the pressure a bit. I think if they are at 33 or 34 at the start of the day that's not bad. I'm thinking the tech put air in thinking they would be low. Yep, I can let out some air easily. It's easier to let air out then put air in...ha

PyroDave

i like my cold start to be at 32, and go up to 34-35 while driving. i actually have to add some because of the temp drop. im down to 29ish. its just hard keeping up with the mood swing temps. goes from 60 degrees to 20. and thats like 2-3+ PSI drop lmao

ceb

The amount of technical incompetence is sometimes staggering. Not from the people asking the question but from the people giving the answers.

Tire pressure is meant to be checked cold.
Tire pressure varies by car weight and by loading. Just because 40psi was fine in a Prius doesn't mean anything for any other car.
Tire pressure varies by speed. Higher speed driving requires more air pressure
You lose tire pressure with time

Finally

The freaking engineers know that tire pressure increases once tires have been driven and have taken that into their "check when cold" calculation.

Set your pressure when cold, check it once a month and adjust as required. I'd bet you never need to let air out.

Oh - a psi or two or three will not make a significant difference one way or the other but you never want to run your car with pressure being about 15-20% lower than indicated for your car. That is dangerous and will lead to excessive wear.

In my 40 years of driving I have never had to reduce the psi of any tire once they were set properly - I just had to add air periodically.

Oh - and always use the same gauge to measure. None are calibrated the same so a 2-3 psi variance is quite normal. Tire dealer and gas station gauges are notoriously bad. The get beat up and thrown around and should only be used as a guesstimate.

PyroDave

being a bit harsh there buddy? no one said anything that varied drastically from that...

ceb

yeah - probably. I've come down with bursitis last night and I'm pretty grumpy right now. Hopefully I'll be in a better mood after I see the doc.

What annoyed me was the immediate "that is not right, you need to adjust it" when in fact it is nothing to worry about.

Psi will fluctuate significantly while driving - as such as 10psi or so and an underinflated tire will fluctuate more

From the cold of morning (when you check) the temps throughout the day may rise 30 or 40 degrees - each 10 degrees is equal to 1psi. Driving heats up the tires which heats the air. An underinflated tire heats up more so there is even more heat transfer.

Checking your tires at 20 degrees, then going for a spirited drive for a few hours and checking the tires thereafter at 3pm will often show you a 10 to 15 psi difference. All normal and no need for any changes

Sorry for my little outburst but please don't provide incorrect or incomplete answers that would mislead the OP (in this or any other thread) to take unneeded actions.

LaCostaRacer

I have a TL with the Michelin Pilot AS tires and run 36PSI cold and the tires usually read 37 after a 10 mile drive so the pressure doesn't go up a bunch at least at 60 degrees. If you have Michelin tires, check the max pressure and subtract 10% and you'll be good. My tires have a 50 PSI max so I could go up to 45 with that formula but I might suffer in ride quality- looks like 37-40 is where I'll run now.

I use to run 33-35 and my tires were wearing on the outside so I'm bumping the pressure now to see if things improve.

centflatsx

I didn't want to see anyone get all upset over my question..lol
I think the techs at Acura really don't know what the correct pressure should be. I've been driving with 33 or 34 with warm PSI and when it got cool out I went below 30 and that's when the light came on. I put air in a couple weeks ago and then they must've put more air in over the weekend when I went to Acura. I believe anything from 33psi to 37psi would be fine after some driving. I think starting at 33 or 32psi is good. In summer it gets very warm here in FL of course so 37 or 38psi is probably pretty common.

ceb

Among other things, proper pressure is a function of load. The max pressure printed on the tire has nothing to do with the pressure you should be running. That number is the maximum safe pressure for that tire - kind of like the maximum amount of air you can put into a balloon before it pops.

Your owner's manual and door jamb gives you the appropriate pressure for your car. Use that as a guideline and adjust from there according to your preferences.

This is the type of bad advice I was referring to. If you don't know what you are talking about then please don't post.

centflatsx

The label inside the door says max cold psi of 33. If that's cold before driving and when you drive of course air expands and heats up then your reading will go up to 35, 36...
If max is 33 at any time (no driving in 12 hours..or driving 70mph for an hour). then we should see below 30 psi before driving to allow for the psi to increase, however we know that's too low to start off with. So there are varied answers so lets say that we should stay within the 31-36psi rang will will allow for some variance with driving conditions/load.

ceb

Of course Acura knows what they are doing - the individual dealerships just don't care.

Engineers have to walk a fine line between handling, safety and comfort - a kind of 3d line. More air and handling improves but comfort suffers. Less air and the ride improves but handling suffers and safety could be compromised.

Assuming normal loading (2 people) and normal US speeds (under 100) then the door sticker is the proper pressure for that happy medium. Adding a few psi will sharpen handling while dropping a few psi will make the ride smoother.

The TPMS will alert once the pressure drops by about 25% - at that point you are wearing tires rapidly and are getting close to dangerously low pressure.

ceb

No. The psi listed for the car is the cold pressure . Don't worry about warm pressure as the engineers have taken that into consideration.

You are way overthinking this. a psi or two won't make a difference. Your gauge probably isn't calibrated properly anyway - the reason to use you own gauge all the time.

PyroDave

the door jamb lists the cold psi. would as said, should be as close as possible to 33. as the tires heat, handling will improve, until a certain point. as i said, somewhere about 40, the handling begins to rapidly deteriorate. the center of the tire bulges out, and you run on the bottom curve of the tire, instead of a more flattened curve shape. when you go too low, the tire cannot maintain the proper pressure to stay on the rim firmly, and to support the rim. low enough, your rim is riding on rubber, instead of air, and it will slice a hole through your tire

ceb

Correct, but specific over and underinflation pressures vary due to a multitude of reasons.

In general, 20% underinflation will start to affect wear and 25% starts the slippery slope to safety issues, while 25% overinflation will start uneven wear in the center of the tire. Overinflation is seldom a real safety issue until the tire starts to exceed 30-35% over label pressure or when it starts coming close to the max rating of the tire.

For most consumers, overinflation will never be an issue.

LaCostaRacer

Oh but I do know what I'm writing about- that's where you seem a little off IMHO. 1) The tire max pressure rating on the tire specifies COLD PRESSURE and not HOT. 2)All you need to do is read your Owner's Manual and you'll see that increasing the PSI is not so bad. 3)You'll see that the tire increases in pressure about 4-6 pounds when 'hot' versus 'cold' so a 10-15% allowance of the max pressure is well within the operational specs of the tire in question.

I followed Acura's recommended pressures and guess what: I need new tires after 25k miles when they should last 45k miles. The car had an alignment when I got these tires and they have been rotated but yet my tires need replacement. I had the same problem with the OEM Michelins too. 4)Wear on the outer edges is a classic indication of under-inflation when I had 32-34 PSI in the tires at all times during their life.

If you read the owners manual, you'll see a reference about 'high speed' driving and how you actually need to increase your PSI about 8 pounds to account for the increase speeds. I tend to drive 80mph a lot so having a few extra pounds over the sticker is not a bad idea for people that drive fast.

Since people use different brand tires, I suggest you check the actual tires Max Pressure and use it accordingly instead of blindly following a sticker on the door jam in all cases. That sticker factors in other concerns (ride comfort being one) that have nothing to do with actual safety or tire performance.

LaCostaRacer

Here's an eHow link that seems to jive with what I was writing on this subject and seems very clear too: http://www.ehow.com/how_4576170_dete...ssure-car.html

ceb

It is obvious that you either didn't read my response or you had difficulty comprehending it.

Many people - you included apparently - believe that a random eHow article makes them a tire expert. Your response is a prime example about how a little bit of knowledge can be a very bad thing.

First and foremost, let me make one thing perfectly clear. The maximum psi listed on the sidewall has nothing to do with the amount of air you should put into the tire. It is a "don't ever put more air than this into the tire or they may be damaged - as in catastrophic failure."

The amount of pressure to put into a tire is set only by the car manufacturer and the tire brand is immaterial.

The manufacturer calculates the load on each tire per corner, determines approximate payload and sets a pressure based on the desired handling/comfort balance I mentioned before.

That baseline (often a few different numbers depending on load and expected constant speed) is appropriate for most owners.

Now, as to your tire wear, that can have many reasons. How do you know that you had the correct tire pressure? How often did you check it? Was the wear on the outside or the inside of the tires? Did the front and rear wear evenly? Are you an aggressive driver? What types of tires were they (summer performance, all-season or winter?) What car were they on and why did you expect to get 45k miles on them? How often did you get an alignment? How badly out of spec was the car when you got an alignment?

Quite simply, a few psi one way or the other will not increase wear dramatically but alignment issues and driving style will. If you only got 25k miles from an all-season tire were you expected to get 45k then you were either running extremely low pressure (in excess of 20% low) or you had an alignment issue or a very aggressive driving style. maybe your radar detector and rear sway bar are an indication of your driving style - which would easily account for increased tire wear.

Professor

It's weird. I have always had to put air in the 2005 17in. RL tires when it gets cold. The cold reading is usually 25 psi.

With the 18in TSX wheels, I didn't have to add air this year.

FWIW, I have one of the cigarette pumps to keep things in check. I like 36 psi around on a warm tire.

And BTW, an alignment is way overrated on a FWD car, because there are certain things you can not adjust. I've never had an alignment on my 1997 Honda Accord Coupe with over 250K miles. The tires wear even and no pull.

LaCostaRacer

^ceb: Like I already wrote, I ran 33 PSI and the tires were by no means under-inflated if you go by the door sticker (your point) but definitely under-inflated if you go by the max pressure for the tire minus an allowance (my point). I found it telling that there was an eHow article on precisely my original point though- and I did not author this article by the way. This is by no means a novel idea.

My original tire pressure guidance came from my Father and I dared to differ with the TL and didn't really notice what the max pressure really was on the Michelins since the print is very small- it's not obvious with those tires. I simply thought the OEM Michelins were crap and bought the Pilot AS Plus (all season) tires for my next set which happened to have a 45k warranty. When I saw those tires wear (again) I took it to a tire shop (Goodyear) and they said the tires appear under-inflated eventhough that have alrways had 32-34 PSI in them. How do I know? Well I happen to have a TPS system in my TL that tells me the pressure of each tire so it's a simple button push to get this reading and it confirms with a guage reading too.

Logic would dictate that a tire manufacturer's pressure rating would have much more merit than a car manufacturers recommendation since people change tires and the tire technology changes. You have a much higher chance of a blowout running low pressures than high anyway for many reasons: excessive heat buildup, and losing the bead on a hard cornering,

Anyway, the original question was about cold .vs. hot pressure readings and I still think the owner's manual does a decent job in saying there is a 4-6 PSI difference. It also says that a tire would be considered 'cold' if you have travelled less than a mile so the car does not have to sit for long periods of time to be considered cold. A wait of about an hour would work equally well.

^professor- my guess is this has a lot to do with the profile of the tires. The 17s have more air volume than the 18s hence the difference- there is more variability when the temperatures drop when you have less air to begin with.

ceb

Let me try to explain this in a way that you can try to understand it.

Take one of those medicine balls you sit on.

You pump it up and at some point it explodes - that a hair above max pressure.

If you pump it up so that your 100lb girlfriend can sit on it, the guy's 300lb ass will put a good size dent in it and you have to add more air. The max psi of the ball is immaterial and would be much too hard for your girlfriend and for your 300lbs.

The same with tires. A heavier car requires more air in the tires to achieve the same desired handling/comfort.

I'm sorry that you (and that eHow article) don't want to understand the fundamentals of air pressure and tire technology, but please don't try to pass wrong information to board members - even if you got that wrong info from papa.

ed_423

major knowledge has been dropped here, thank guys...keep it friendly

LaCostaRacer

^ceb- I do understand. Your points are and have been simple all along that even somebody as dumb as myself can clearly understand then. You need more tire pressure when you have more weight, the car manufacturer recommends a pressure, the pressure goes up as tires heat up, etc- UNDERSTOOD. Since my TL is a 5 passenger vehicle there is a load already factored in for making this recommended PSI, but you're missing a point that NVH is also a component in the manufacturer making this recommendation. If you run a lower pressure tire, the car will ride better and things will not rattle or vibrate as much.

But lets make sure you understand a thing or two as well where I'm coming from. I follow the recommended tire pressure for the car 33/32 PSI, rotate the tires every 7k, and my rear tires wear on the outside edges (a classic sign of under inflation). The pressure is monitored via a TPS system as well as a gauge monthly so that's not the problem.

I equate the first set as an issue with rear alignment and got a 4 wheel alignment along with a camber kit to bring the rear to spec the day after my next set of new tires. Again, I use the recommended tire pressures and notice my second set of same branded tires develop the same wear pattern. The car is in excellent shape but likes to chew threw tires apparently. I have no reason to think there's a fault with the car- in fact many owners have the same issue based on a Google search and many have Michelin tires. These tires are designed for the Autobahn speeds so I don't think driving my car 70-80 is the reason for my wear.

I then do a Google on this along with hearing from a trusted tire guy that I need to actually bump up the pressure more than recommendation to eliminate this issue. I use a 37 PSI (only 4 pounds higher) as a starting point which is well below the 50 PSI maximum stated on the tire. You're essentially warning me that my tires are going to blow up even though the Owner's Manual recommends a 39 PSI setting for high speed mode (110 MPH) with a tire with a load factor well above the actual car requirements. I think you're being a bit of an alarmist- my tires are not going to blow up even with 45 PSI that you're disputing me on the (Max - 10% rule of thumb) .

My car still handles very well, brakes well, rides well, and my MPG ticked up a little bit too by a whopping 1 MPG so all those things don't seem so bad now do they? No I have not tried a skid pad to see if I adversely affected my lateral grip but my seat of the pants test seems the same and possibly better even.

What I can't yet tell you is if my ultimate goal will be met which is extending the life of my $900 set of tires that have good tread like along the 80% of the middle of the tread. That will take some time and I'll probably need to get the next set to really know the answer since the damage is already done with my current set.

My guess is there are other folks with Michelins that might have experienced this same issue and trying to help them and not necessarily you ceb.


So again back to the original point, the 'cold' tire pressure changes about 1 PSI for every increase in 10 degree F. So you need to adjust your tires a number of times during the year just to account for the ambient temperature changes- in particular with cold winters. I'm fortunate because my locales ambient only changes maybe 40-50 degrees or 4-5PSI but deserts might have a 100 degree change and need a +/- of 10 PSI for the tires between Summer and Winter.

ohsixMTee

iTrader: (2)

I'm surely no rocket scientist just an industrial printer but I'd like to add my .02....

I like keeping my rear tires approx 2 psi or so lower than the fronts to compensate for the lack of weight as opposed to the fronts that bear the engine's mass.

I don't know....just find what works for you and your tires.

I will also add that when I purchased the car the cold pressure was approx 32 all around, I found the car was unpredictable at highway speeds when the suspension reacted to the uneven PA roads. All around the ride was just too soft and bouncy. I prefer being a few psi higher than what the NASA scientists recommend for the TL. lol

ceb

Well, it seems like you finally got it.

Like I said all along, the door jamb values are a starting point and designed for the average driver. That average driver doesn't have excessive wear at those values.

With suspension mods and/or aggressive driving, you'll need to increase the pressure in your tires until you get the handling/comfort/wear characteristics that you want as long as you don't exceed the max value of that particular tire.

Your prior fixation with using the max value as some sort of a guideline to set pressure is what was wrong. That only comes i to play once you've radically increased pressure. You'll want to assure that you never exceed that max pressure. in reality it is unlikely that you ever would as the car would handle poorly in anything ut the best conditions and driving over a pebble would feel like a harsh impact.

I am also happy to see that you've validated my other points of more pressure (within limits) increasing handling and adding the point I failed to mention that the resulting lower rolling resistance will increase gas mileage.

Recognizing that most consumer cars are biased a bit towards comfort, I generally start by adding a couple of psi right from the start and adjust pressure from there over the next couple of weeks - remembering that you have to wait until a new tire is broken in before you can really determine any real handling/comfort features of a tire - usually after about 500miles.

Getting back to the topic at hand. The average (non track) user never has to worry about anything but cold psi levels. Set your pressure when the tire is cold (having been driven on less than a mile after resting 8 hours or so - with adequate pressure of course) and adjust (only when cold) to get the handling/comfort you want.

its rayden

you're both right. just bad communication. i didn't understand what lacostaracer was trying to say until his last post. i thought he was saying to fill to max pressure as stated by the tire manufacturer, which is very dumb indeed.

there's one thing you guys havent mentioned at all. the load rating of the tire is also a factor in how much PSI you should be at. the lower the load rating, the higher you would need to bump up the PSI.

ceb

Right. That's the same thing that I thought.

The load rating of a tire (XL for example) is something that the car manufacturer takes into consideration as they spec out a tire and, if the car comes with xl rated tires, you really shouldn't replace those with non load rated tires.

While important, this really isn't anything the average consumer needs to worry about. The "set it and forget it" to the door jamb pressures method works quite well if you "set it and forget it" about once a month.

ceb

While I would not go a youtube video, answers.com or eHow to get definitive information about tires, I would go to the known tire experts for advice. Tirerack has an extensive library of tech articles about things relating to tires.

Here is what they have to say about proper inflation.

They also have some very nice videos showing the advantages of winter tires. I would recommend that anyone with tire related questions review their tech section.

dallison

What ceb said. Just keep your cold pressure as close to manufacturer spec as possible. You can adjust a couple psi to taylor to your needs or whatever.

tvac

Use nitrogen if you want significantly less pressure fluctation due to temperature variation.

Professor

^ Isn't like 78% of "regular air" already nitrogen?

ohsixMTee

iTrader: (2)

Most would argue that same point. It's sort of like opinions on oil, you just need to see if whatever works for you.

ceb

No. The extra 22% nitrogen in 'pure' nitrogen expand and contract just like the 21%oxygen (and 1% other gas) in ''normal' air.

There is no advantage to consumer use of nitrogen.

ceb

Yep. Like you, I prefer to use a nitrogen blend to fill my tires.

tvac

ceb, I stick by my statement. However, I do agree with your statement concerning the expansion and contraction of gases at a fundamental level. It's physics. But it doesn't go far enough.

The fact that a volume filled with pure nitrogen will experience less pressure variation due to temperature fluctuation, actually has little to do with the properties of the nitrogen gas itself. The improved pressure stability results primarily from displacing the percentage of oxygen, water vapor and other gases in a tire from 22% to 7% or lower. Sure nitrogen fluctuates with temperature change, but it does so much less than when water vapor is present.

Ambient air contains moisture, nitrogen does not. Moisture contributes to a greater change in pressure because at lower temperatures water condenses to become a liquid. Water, in its liquid form occupies very little volume and contributes negligible pressure to the tire. But when temperatures increase, like in a running tire, water evaporates inside the tire and becomes a gas increasing pressure in the tire.

That's why NASCAR teams use nitrogen, so they can more accurately predict tire pressure fluctuation. Drivers claim to feel handling differences with very small tire pressure changes. On my motorcycle, I can feel marked differences in handling when tire pressure is off by several pounds. So, getting the water vapor out of the tire might make a difference in handling. Whether or not these are changes that will be noticed in lesser performance vehicles like SUVs or minivans is debatable.

It's also worth noting that nitrogen, being a larger molecule than oxygen and most of the other trace gases, will not permeate the tire rubber at as great a rate as plain 'ole air, minimizing pressure loss due to out-gassing. So, while you can argue the overall merit of nitrogen filled tires there can be no doubt that pressure fluctuation due temperature variation will be less in a tire filled with nitrogen than one filled with plain 'ole air.

its rayden

who does this guy think he is, coming in here with science and crap...

ceb

And I'll stick by my statement as well. Nitrogen brings no benefit to the consumer.

tvac

I'll dumb it down for you next time.