twigglius

iTrader: (6)

With aftermarket wheels.

I have had the TPMS sensors on my aftermarket wheels since July and they seem to work fine. Today I went to discount and got a tire rotation and I asked the guys while they were working on the car. How much tire pressure was in the car before they did the rotation. The guy told me 35psi. I thought to myself that seems a bit off because my MID reads 32psi. I then asked him how much they were setting the car at and he said 40psi all the way around. I didn't say anything because I wanted to test my MID when I got back in the car. Sure enough the MID read 37-38 on all the wheels. I am at work so I have not had a chance to check it myself but has anyone else noticed this? Do you think it is the TPMS sensor that is off? Could it be a miss reading from the guy at discount? What do you guys think?

bhelsdon

I think you you may be splitting hairs here. There is going to be a small difference between different tire pressure guages(or the person reading it).A couple pound variation between two different guages is normal, I wouldn't worry about it. The purpose of the tpms is to alert the driver if there is a problem with one of the tires. Even if the sensors are off by a couple of pounds the system will still function as it is intended. How to you know if the sensor is right or if the guage is right?

csmeance

How did the guy check the pressure? did he use a digital or old fashioned stick one? Also i think it might depend wherre the TPMS sensor is, some times, it can be nearrthe ground causing a highreading, sometimes it can be at the top causing a lower reading. Did you move the car after checking the TPMS in the TL?
Oh yeah, the don't the sensors take like 20 minutes to register themselves after the tire has been taken off?

IIIII

Temperature also plays a part in determining the exact tire pressure.

ocwill1

I have also noticed that mine are off by about 2-3 psi all the way around, no matter where I park my car .... I just use the air tool that I have from griotsgarage.com and go by that.....

ocwill1

ml3456

??? Top Vs. Bottom pressure diffrence? Don't think so.

Pressure will be the same. Good old stick gauge is better than a cheap digital. I find a 4 pumd difference total on the TPMS system. Trust a tire gauge and use the TPMS to find a low tire or one going flat.

bhelsdon

LOL, I was wondering when someone would say something about the top vs bottom pressure difference.

Will Y.

One more thought: the pressure "gauge" on the commercial air hoses, like that used at gas stations and some tire stores, are sometimes very inaccurate. One way to check your TPMS is to use a certified air pressure gauge, either bought or borrowed, and compare it to the TPMS readings.

I bought a cheap pencil gauge and a certified (to 1 lb) round needle gauge with bleed valve many years ago; both read the same pressure in all circumstances. I later bought another pencil gauge (nice looking, but uncertified) to leave in another car, but the gauge was off by at least 4 lbs compared to the two older gauges.

2 or 3 lbs difference in pressure will be noticeable in handling/ride if you are taking turns hard. Always check the air pressure when the tires are COLD (not driven on for at least 4 hours, or driven less than a mile within 4 hours).

nospleeny

There will be a difference.

The TPMS will tell you the absolute pressure within the tire.

Your good ol' stick gauge will tell you the relative pressure within the tire. This is affected by many factors from barometric pressure to tire rubber temperature.

Both are actually reading the same pressure if you subtract the factors that make up relative pressure.

Shalooby

Sure there is. And when the tire is flat, it's only flat on the bottom !

Will Y.

2evil05

WOW!!! you really think that, don't you?!?!?! if there was any difference, the tire would have to be HUGE, and it would only be like 0.000005 lbs off. you should read more.

Inaccurate

Mine is ALWAYS EXACTLY correct.

Also know that the TPMS will not give an instant readout without the car rolling. In other words, you can not add air, then look at the TPMS display to watch it increase. The TPMS will not sense the new pressure until the car rolls a bit. For me, it varies... Sometime the new reading will be displayed from pulling out of my driveway. Other times, the new presure will not display until I have gone one city block.

And, those tire guys are not anal-type of poeple. When they say 40 psi, they mean "somewhere around 40psi maybe,perhaps, probably, hell who knows where we set the pressure".

EternaLlx

I guess not many people read the service news..... second page..

http://www.in.honda.com/Rjanisis/pubs/SN/B060500.PDF

Its something like what nospleeny said.

Shalooby

Of course not. I guess I should have added a couple of to that. To get really technical about it even a flat tire has 14.7 psi in it. ( Atmospheric pressure ).

Inaccurate

But, only if the car with the flat tire is along the beach.

pohljm

actually if i use a guage when the valve is at the bottom of the wheel and then rotate the wheel so the valve is at the top I get a slight difference that is due to the altitude difference between the two not because the ground is pushing up harder near the bottom!

j/k the honda service bulletin explains it precisely

ndx2

Don't tell me you guys don't know air expands when hot... that's what the pressure gauge will read, hence you don't fill up your tires after hours of highway driving...

nothing to be concerned about as long as all four measure the same, and not under the recommended PSI.

Inaccurate

OMG !!! That's it !!!!



(thanks to ndx2 for suppling the graphics)