99alta

How much error are you guys seeing when comparing the cars tire pressure indication vs measuring each tire with a calibrated gauge?

My car is reading about 2-3 PSI lower than the actual tire pressure. That is about a 10% error which seems a little on the high side.
The sensors seem to work fine as when I get on the highway they all register about 2 PSI higher, which seems normal.
Original tires and sensors.

dchar

Keep in mind, tire pressure will be slightly higher when the tires are warmed up like when driving on the freeway. 10% error sounds about right.

99alta

Curious if you and others have checked their cars pressure indication against a dedicated gauge?
In industry a +/- 3% deviation between an indication and actual (error) is acceptable. But 10% seems a little on the high side.

rominl

iTrader: (4)

i am not exactly sure how the tpms on the latest lexus works. but the way it used to be, you have to sync between the system and the tpms. what it means is when you press the reset, it will register whatever the tire pressure is in the tire as the default, say 32psi. so if all the tires are 34psi when you press reset, the dash will show 32psi but actual pressure is 34psi.

again not sure if that's how it works on the gs but that's my prior understanding of how tpms works, it's been years so things could have changed

bclexus

All four of my TPMS readings are accurate to within a fraction psi. How do I know? I have three different digital psi gauges, two register in 1/2 psi amounts and one registers in 1/10 psi amounts, and all register the exact same readings. I also have two gauges that are calibrated with certification...and the digital gauges match the certified gauges exactly. I even take into account the fractional psi that is lost whenever the valve is depressed while taking a reading...

I am very picky about my tires' air pressure being the same - to the point of being a fanatic about it. When the time of year dictates (going into cooler weather or going into warmer weather) I'll adjust my tires' air pressure. What I do is - I'll add a couple more psi than I need and then tweak the tire pressure down to what I really want after the car sits overnight in a dark garage. I take the garage's temperature into account, and also whether (based on the time of year) the outside driving temperatures will be increasing or decreasing from what the garage temperature is. I like to have the psi of all four tires change within a minute of one another (typically driving 1/4-1/2 mile at most) on a cloudy day or night time when the sun's radiant heat affects are not a factor. I even go as far as releasing the tiniest (minuscule) puff of air in order to match the air pressure in all four tires. It's almost like a game to me. Call me strange, but...

PS - I was somewhat surprised to see that all four TPMS units are as accurate as they are.

Joe166

My TPMS is accurate within a half pound based on a couple of digital tire gauges.

I do not think that you can influence the PSI shown on the dash by setting it at any particular "normal" tire pressure. I routinely run my tires a couple of pounds above the door jamb pressure and the pressure shown is the pressure I set it at (at least for a while, some air seems to leak out after a few months, but evenly).

AJLex19

Agreed with bclexus and Joe166 on the accuracy - the TPMS is very accurate in my experience. I recently replaced my tires and the shop over inflated all tires to around 45PSI. When I got in, the TPMS readout was showing 45-46PSI all around.

I got out of my car, removed about 10lbs of air, checked them with a non-digital, old school Milton made in the US pencil type gauge to make sure they were at around 35-36.

When I got back in my car, drove about a block, shut the car off and back on, all tires were showing 36lbs as expected on the LCD driver readout.

rominl

iTrader: (4)

but have you tried to reset the tpms system when the tire pressure is say at 40psi? again newer system can be working differently now i don't know

99alta

Thanks for the replies guys, something is wonky on my car.

As an aside I once asked here if there was an absolute value that brings in the TPMS warning light.
Then I remembered I had asked Lexus Service to record my TPMS sensor data before they switched back to my summer tires. They did an ECU print out and there it was in black and white. The absolute value for the TPMS alarm was 10 PSI lower than the current set pressure of 36 PSI.

bclexus

It's my understanding that the TPMS warning light turns On when tire pressure is below 20% of what the vehicle manufacturer recommends. So, if the recommended tire pressure is [say] 33 psi the warning light will come On when any tire falls to 26 psi.

Here is a common scenario - vehicle owner has their tire pressure checked mid-day and adjusted to the recommended pressure during summer (e.g. 90+ degrees) after driving the vehicle for a period of time on hot pavement and with the radiant effects of the sun hitting the tires. Driving the vehicle for a period of time will increase the tire pressure 2-3 psi, the 90 degree ambient temperature will increase the tire pressure 1 psi for every 10 degrees or say 2 psi higher than at 70 degrees, and the sun's radiant effects can increase the tire pressure by 2-3 psi. That total could easily add up to 8 psi - or 8 psi higher than a vehicle's tire pressure that has been sitting in a dark 70 degree garage overnight. So, in the case of tires that are recommended to be inflated to 33 psi - if those tires are inflated to [only] 33 psi when the ambient temperature is 90 degrees and after driving the vehicle for a period of time on hot pavement and with the radiant effects of the sun hitting the tires, those same tires will likely only have 25-27 psi after the vehicle has sat overnight, which is referred to as 'cold'. 'Cold' is when the tires should be inflated to the recommended air pressure. And, people wonder why their TPMS warning light comes On when they just had the tire pressure adjusted recently...

AL13NV8D3R

Lol I do the exact same thing you do regards to tire pressure checks. I go one step further and only pump Nitrogen gas into my tires. I have a 125 cuft Nitrogen gas canister in my garage. Lol. I thought I was the only one that is OCD about my tire pressures.

bclexus

..........

bclexus

During the Summer I will set my tire pressure at 33.0 psi cold (cold = car parked overnight in an enclosed garage) at 73 degrees garage temperature. (Note: I'll adjust the set tire pressure by .5 psi for every 5 degrees above or below 73 degrees the garage temperature actually is.) This is based on the outside (ambient) temperature being (getting up to) ~27 degrees higher (or about 100 degrees) than the garage temperature. The tire pressure will increase as much as ~3 psi on daytime high temperature alone reaching as high as 100 degrees, another 1-3 psi increase for traveling on warm/hot pavement and cement vs. asphalt, and another 1-2 psi if the sun is out with a typical Summer UV rating. So, I start out with 33.0 psi on cold tires and my tires will naturally increase (based on above noted factors) by a minimum of 3 psi during morning or evening hours, or if the day is cooler than normal, or if the day is cloudy. I'll have a maximum increase of ~7-8 psi if all factors are at absolute peak, which is rather unlikely. I will usually only see a 5-6 psi maximum increase (to 38-39 psi) in the Summer.

During the Winter I will set my tire pressure at 33.5 psi cold (cold = car parked overnight in an enclosed garage) at 60 degrees garage temperature. (Note: I'll adjust the set tire pressure by .5 psi for every 5 degrees above or below 60 degrees the garage temperature actually is.) This is based on the outside (ambient) temperature being (getting down to) ~27 degrees colder (or about 33 degrees) than the garage temperature. The tire pressure will decrease as much as ~3 psi on outside temperature alone reaching as low as 33 degrees. However, the tires will increase 1-2 psi for traveling on pavement, and possibly increase another 1 psi if the sun is out even though the UV/radiant quality of the sun is much lower during colder months of the year. So, I start out 33.5 psi on cold tires and my tires will drop 0-3 psi based on outside temperature, yet the tires will increase 1-3 psi based on traveling on pavement and maybe increase another 1 psi based on the sun being out, thus all these factors offset one another for a minimal (~0 psi) change in psi compared to when I started out. I'll have a maximum increase of ~1-2 psi if all these factors are at peak (warm Winter day with full sun), which is very common and gives me around 35.5 psi maximum tire pressure. I will usually see a 0 psi drop to a maximum of ~1-2 psi increase (33.5-35.5 psi) in the Winter.





Tire Inflation Pressure Compensation and Adjustment

CottageChz

I haven't checked mine with a handheld gauge, but when I fill my tires at the gas station the TPMS seems to match their digital air pump.

Joe166

Yes, my tires are now set at 39 frt 41 rear. That is what I usually run. The TPMS goes off when it goes low enough. Frankly, I never let it get low enough to set it off unless I run into a road hazard, in which case it drops so far that I can't actually tell you when it went off, only that at 23 PSI it was showing an alert due to a nail in the sidewall which cost me almost $400. I suspect that it is factory set to go off a certain percentage below what it was set at. But there isn't all that much difference in 10% of 40 lbs (4.0) and 10% of 35 lbs (3.5), as long as it takes the pressure you set it at as the normal pressure and if it weren't going to do that, why would they bother to have you reset it when you set your tire pressures? They could set it to go off at 27 or 25 lbs or some other arbitrary pressure and save everyone some aggravation.