[NA]Car tire pressure[NA]

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Let'sgoflying!

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Dave Taylor
Tire sidewall say x psi, car doorpost says y psi.

Is it like the aircraft tire v the aircraft service manual issue; the aircraft manufacturer wins?

(installer put 55psi into my Tundra Hankooks, that's what the sidewall says; the truck was dancing all over the road til I reduced them to 30psi. Now I'm worried about edge wear)
 
I always go with the vehicle manual/door sticker myself. Seems to me like the best way to handle it.
 
Door post.

Scary the tire shop didn’t know that, but looking at some of the cars they crimp weights on vs using sticky weights, and watching them take a impact gun to aluminum wheels, not a huge surprise I guess
 
Funny, I actually just ran into this on Monday. Dad and I did an oil change on Sunday and we also checked the tire pressures. After just putting in a couple of lbs on Sunday, my tire pressure light illuminated on Monday morning. I checked each tire and they all read the same at about 42psi, which is what they’ve been at since I’ve owned the car.

The tire wall says 50psi max, but the doorjam sticker says 37psi on all four, so I let out 5lbs and reset my tire gauge on the car and it hasn’t come back on since. So I’d also say to go with the door sticker.
 
I run my car tires at 40 psi cold. Best handling, best mileage, best longevity. When the oil change place deflates my tires and puts in 32 like the manual suggests, it handles like a turd and steers like a truck.
 
Ryanb said:
Funny, I actually just ran into this on Monday. Dad and I did an oil change on Sunday and we also checked the tire pressures. After just putting in a couple of lbs on Sunday, my tire pressure light illuminated on Monday morning. I checked each tire and they all read the same at about 42psi, which is what they’ve been at since I’ve owned the car.

The tire wall says 50psi max, but the doorjam sticker says 37psi on all four, so I let out 5lbs and reset my tire gauge on the car and it hasn’t come back on since. So I’d also say to go with the door sticker.
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Your GTI has a passive differential TPMS system. It only detects when 1-3 tires go lower than the remainder based on wheel RPMs that the ABS reports. It's not a direct reading TPMS with sensors inside the tires that would know the real pressure of each tire. (GM and BMW are two makers that use direct reading. Subaru too, I think)

For that reason, you need to manually reset the TPMS system each time you add/subtract air from any of the tires.
 
asicer said:
Your GTI has a passive differential TPMS system. It only detects when 1-3 tires go lower than the remainder based on wheel RPMs that the ABS reports. It's not a direct reading TPMS with sensors inside the tires that would know the real pressure of each tire. (GM and BMW are two makers that use direct reading. Subaru too, I think)

For that reason, you need to manually reset the TPMS system each time you add/subtract air from any of the tires.
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Right. The tires have remained right around 42lbs since I’ve owned it. Due to the fact that we added a couple lbs it threw off a few of the others. I reduced pressure down to the doorjam recommendation of 37lbs and reset the tire pressures to that value, so if they fall below or rise above that value, it’ll throw off the sensor again.
 
The number on the sidewall is mostly useless. It's there only to tell you the maximum tire pressure that this tire can take. So don't go over that ever but otherwise don't pay attention to it. Technically, the number on the door is for the original tires and for the "best" "performance/wear/handling/economy/whatever" the manufacturer deems important(you may feel differently about what is important to you). It's a good starting point. Different tire, vehicle load(weight), driving style, road type, and outside temperatures will dictate different pressures. In the summer, I run my summer tires at around what the door says. In the winter, my winter tires are at about 8lb higher pressure normally, otherwise they are way too soft and car handles like crap. Off roading, people take pressure down to under 20lb.
 
I always figured the sticker is the number the mfg found that gave them the best balance of "comfort vs mileage" for the original OEM tires. After that, you are on your own. The sidewall is the max that tire is rated to take. I like to air up a few PSI above the door sticker. It gives me a little stiffer ride, but I can see one or two more miles per gallon.
 
I inflate them so that the tread and sidewall are equally warm when I pull off the highway.

Overinflated, the tread will be warmer; underinflated, the sidewall will be warmer.
 
I run each vehicle at different pressures depending on what I feel is best. I generally run my truck tires between 35-40psi, depending on time of year and whether I’m towing/hauling anything if significant weight. I run my sports sedan at around 35psi year round because the low profile tires start getting rock hard after that, which makes the ride a bit stiff for everyday driving. Trailer tires I almost always keep within 5psi of max psi to avoid them heating up.
 
The sticker on the door post is for the cheap, 40,000 mile tires that the manufacturer puts on.

The tire manufacturer puts the maximum pressure for a loaded vehicle on the tire.

Depends if you want ride comfort, handling or load bearing.

The original tires on my wife's Subaru calls for 40 lbs PSI max. But she likes the ride when I set them at 33. For driving around town that will allow the tires to warm up. When we go on a road trip I bump them up to 40 to make me happy. But it gets new Michelins this Saturday so I will have to start all over to find our happy pressures....

And I put nitrogen in the tires..... :popcorn:
 
asicer said:
Your GTI has a passive differential TPMS system. It only detects when 1-3 tires go lower than the remainder based on wheel RPMs that the ABS reports. It's not a direct reading TPMS with sensors inside the tires that would know the real pressure of each tire. (GM and BMW are two makers that use direct reading. Subaru too, I think)

For that reason, you need to manually reset the TPMS system each time you add/subtract air from any of the tires.
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My ND Miata (2016) has the passive system. So nice that you don't have to fuss with TPMS sensors when you change over to track/autocross wheels & tires, or replace a sensor when it or its battery goes bad.

Perhaps not as accurate as direct sensing, but I like when you can take hardware that already exists and simply tweak software to get more functionality.
 
SoCal RV Flyer said:
My ND Miata (2016) has the passive system. So nice that you don't have to fuss with TPMS sensors when you change over to track/autocross wheels & tires, or replace a sensor when it or its battery goes bad.

Perhaps not as accurate as direct sensing, but I like when you can take hardware that already exists and simply tweak software to get more functionality.
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Yes, each system has it's pluses and minuses. In exchange for fussing with remote sensors, it's nice to be able to push a button and get a numerical PSI reading on all 4 tires. And theoretically, a passive system wouldn't detect a pressure loss that happened to all 4 tires simultaneously and at the same rate (yes, such an occurrence is very unlikely).
 
asicer said:
Yes, each system has it's pluses and minuses. In exchange for fussing with remote sensors, it's nice to be able to push a button and get a numerical PSI reading on all 4 tires. And theoretically, a passive system wouldn't detect a pressure loss that happened to all 4 tires simultaneously and at the same rate (yes, such an occurrence is very unlikely).
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More likely than you think. Winter. I have love/hate relationship with TPMS sensors. I love having them, I hate dealing with them.
 
The tire stamping is a MAXIMUM operating pressure. The Manufacturer recommended pressure should not exceed this (If it did, I suspect you're not using the right tires to begin with).
 
I start with door post recommendations, and depending on car tweak it a bit. If the car has understeer (most cars), I increase the front pressures some to alleviate. If the car oversteers (rare), do the opposite, start increasing rear pressures. One caution: I've found on some cars that once I add enough air to the front tires to balance them in the dry, they get VERY tail happy in the wet[1], so it's all a compromise.

As for checking, I check the tires on all three cars the first Saturday of each month, and always before any long trip.

[1] The 2001 F-150 SuperCrew I owned had door post pressures of 30F/35R. I found the dry handling MUCH better at 35/35, but at those pressures the rear wanted to pass the front in the rain.
 
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Sac Arrow said:
I run my car tires at 40 psi cold. Best handling, best mileage, best longevity. When the oil change place deflates my tires and puts in 32 like the manual suggests, it handles like a turd and steers like a truck.
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I use the vehicle mfr's psi which is about 5 psi over whatever manual the shop book has. Every time I bring my truck home from an oil change I see where the shop has deflated them and it irks me to no end. But I never remember to tell the shop to leave the tires alone when I go in for an oil change. The bright side is that I can tell right off the bat what they've done because they look half flat.

What's weird is the tires on my wife's car. Once or twice she's had a problem and I'll see where a tire looks only slightly low and put the gauge to it and it'll blow 15 psi or less.
 
genna said:
The number on the sidewall is mostly useless. It's there only to tell you the maximum tire pressure that this tire can take. So don't go over that ever but otherwise don't pay attention to it. Technically, the number on the door is for the original tires and for the "best" "performance/wear/handling/economy/whatever" the manufacturer deems important(you may feel differently about what is important to you). It's a good starting point. Different tire, vehicle load(weight), driving style, road type, and outside temperatures will dictate different pressures. In the summer, I run my summer tires at around what the door says. In the winter, my winter tires are at about 8lb higher pressure normally, otherwise they are way too soft and car handles like crap. Off roading, people take pressure down to under 20lb.
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I was gonna say mostly that, til you did. Otherwise, I’ll just add that serious Jeeoers are running single digit air pressures off-road, mounted in bead lock wheels. ;) The specificities tire, wheel, vehicle configuration, and mission all factor in. For the remaining part of the population that typically engages with a vehicle in this manner: Key, brake, D, gas brake gas brake gas brake, P, key... well, I guess they have other people change their oil and only use their cars for hauling groceries and lattés, so whatever air is in their tires is fine. :)
 
The best place to start is with the numbers on the door jam. The number on the sidewall is the limit, and the numbers on the door jam are what the manufacturer has found work the best in that vehicle. Running 55 in a street car that's spec'd for 37 is going to be a pretty bad ride and I would expect it to go all over the road. Semi trucks and busses run around 100 psi, my Ram runs about 75-80 psi (keep in mind those are Load E tires). As @Bill Jennings said, you can get some performance optimized by varying a bit. I wouldn't worry about increased tire wear either.
 
Sac Arrow said:
I run my car tires at 40 psi cold. Best handling, best mileage, best longevity. When the oil change place deflates my tires and puts in 32 like the manual suggests, it handles like a turd and steers like a truck.
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Same here..

I also appreciate a stiffer ride, better mileage, and the better handling.. so I've always ran my tires in my cars high

I have some proper Load E tires on my FJ and I keep them at 70 PSI.. I love the way it rides. Granted, I also have a series of other modifications so the door post figures are effectively trash at this point
 
Ted DuPuis said:
The best place to start is with the numbers on the door jam. The number on the sidewall is the limit, and the numbers on the door jam are what the manufacturer has found work the best in that vehicle. Running 55 in a street car that's spec'd for 37 is going to be a pretty bad ride and I would expect it to go all over the road. Semi trucks and busses run around 100 psi, my Ram runs about 75-80 psi (keep in mind those are Load E tires). As @Bill Jennings said, you can get some performance optimized by varying a bit. I wouldn't worry about increased tire wear either.
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I had Load E's for a while on my F-150 (A/T tires I got a good deal on). I ran them at 50psi and thought that was fine since I was running around unloaded 90% of the time. I only added air if I had 500lbs+ in the bed or on the hitch. I sure never went above 65psi for sure as it would jar your fillings loose in an F-150.
 
SoonerAviator said:
I had Load E's for a while on my F-150 (A/T tires I got a good deal on). I ran them at 50psi and thought that was fine since I was running around unloaded 90% of the time. I only added air if I had 500lbs+ in the bed or on the hitch. I sure never went above 65psi for sure as it would jar your fillings loose in an F-150.
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I once did lower my tires to about 30 psi to get out of mud. That's the big issue with having pressures that high.

No doubt I'd have a better ride if I kept a lower tire pressure, but probably would also have worse mileage.
 
Manufacturers tend to set the pressures 10-15 pounds below what they could safely be for ride comfort. In any case, you can tell if you are over or under inflating your tires by the tread wear pattern.

For a while, Ford was recommending underinflation pressures for the older models of Explorers to reduce rollover tendency.
 
What I didn't see above is tire sidewall ratings are max LOAD at max PRESSURE ... not just pressure alone ...
 
A rule of thumb: (but requires some dicking around with pressures) - start with the door jamb pressures COLD, after a significant time on road measure PSI HOT. Hot should be 10% higher than cold. If greater than 10% likely too low PSI cold. If less than 10% likely too high PSI cold.
 
Like many, I often use door jamb as a starting point. I also tend to add more to the front than the rear, though on one car, I instead wound up lowering the rear pressure 2-3 psi.

I will also note that in a very general sense, the more gap between sticker and sidewall, the more excess load capacity the tire has. Think I’ve seen 28 on some door stickers for a 7 lb under inflation recommended.

I do have one car that actually has two sets of pressures listed. One for comfort, and a second set for handling.

And for F150 super crew, the 2005 and newer went to 35/35. Then add limited slip. I haven’t found it all that loose on the rear, but excluding one wheel only on ice, if one rear wheel lets go, they both do.
 
Pretty hard to go wrong with 35 psi for a passenger car.
 
42 PSI in car tires is too high and will diminish the cornering and braking ability of the car. My one-ton van runs 45 front and 60 rear per the operator's manual and it still rides smooth because the massive truck tires are designed for those pressures.

If I ran anything above 35-38 PSI in my car, it would skitter right off the road on freeway exits and the tread would be gone in less than 20,00 miles...

Buying expensive a$$ tires every two years is no fun. Done that...
 
IK04 said:
42 PSI in car tires is too high and will diminish the cornering and braking ability of the car. My one-ton van runs 45 front and 60 rear per the operator's manual and it still rides smooth because the massive truck tires are designed for those pressures.

If I ran anything above 35-38 PSI in my car, it would skitter right off the road on freeway exits and the tread would be gone in less than 20,00 miles...

Buying expensive a$$ tires every two years is no fun. Done that...
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One of my cars has a recommended front PSI of 42 PSI for handling, and the tire sidewall has 45 PSI max. Broad generalizations are dangerous. I think most 45 profile tires have rated max pressures over 35 PSI.
 
I start with the doorpost pressure and tweak from there. On most cars and with most tires, what I settle on winds up being about 2-3 psi higher with the "summer" tires and about 4-6 psi higher with the winter tires.

Rich
 
Those must be "Low rolling resistance" tires, like are found on Toyota Prius and Yaris and other horrible little cars...
 
If that was in response to my comment about 45 PSI marked sidewalls, no, these are Pirellis on an 01 Audi TT Roadster.
 
If the tires are a different size or profile from the OEM tires their pressure recommendation is no longer valid.

When I had the Jeep with big offroad tires you'd work out the street pressure by marking an even chalk line across the tires, and drive it straight on smooth pavement for a few hundred feet. If the chalk wore more in the middle the pressure was too high, if it wore more on the ends the pressure was too low. That usually translated to the best street handling, though higher pressures are better for fuel economy. Offroad, of course, we ran as low as necessary for the terrain.
 
RJM62 said:
I start with the doorpost pressure and tweak from there. On most cars and with most tires, what I settle on winds up being about 2-3 psi higher with the "summer" tires and about 4-6 psi higher with the winter tires.

Rich
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I agree with the 2-3 psi higher than the doorpost says.

But what are "winter tires"?
 
depends on the ride you want....comfort or economy? Comfort a few psi less than recommended. Economy...a few (3-5 psi) more.
 
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