TPMS

[Robin Cox]

Well now I have had another tire dealer tell me that they can reset the Tpms sensors, and again they were wrong!!!!! They had some young kid come out and look at it and check the air pressure on the tires and wheels that I had put on, the tires were hot from a 70 mile trip I had just taken and they read 36psi, he reduced the psi to 32 and had the nerve to tell me that too much pressure will set the tpms off....what a laugh....DA.....anyway thanks to some of you guys telling us about the Ford tpms reset tool, I got one off of e-bay for $35, granted it did not have the instructions, but I was able to get the instructioins on line, I would have done this myself with this tool but I had strained my back the week before and did not want to attempt to change the wheels and tires myself....anyway...the Ford tool did Greeeaat!!!!! Thanks to all of you that reported this on this site, you saved me a trip to the dealer to get it done again. Also checked my air pressure yesterday when the tires were cold, and yes, they were at 28psi.....imcompetence at best........

 

[Todd Z]

:banana::banana:

 

[EddieS'04]

There is no way to acurately adjust pressure in a hot tire..what a dip.

 

[Bill Koonce]

Somewhere on the Internet I found a handy chart showing what tire pressure to use if you keep your car garaged at one temperature, and the outside temperature is different. I was surprised by the wide variation! I wish I had bookmarked it.



Here in Madison, WI the ambient air temperature is 10 (F). In my garage it's more like 60. So if I'm going to go out driving for any amount of time, I should pump my tires up to 38 PSI with 60 degree air, so that when Mother Nature sucks all of the heat out of those tires, I'll end up with the proper 32 PSI inflation. That's the general idea in a nutshell.



I've been doing a lot more highway driving, and have been taking measurements at rest stops to see if and how much the tire pressures vary after driving at highway speeds. One thing that became immediately clear was that any heat from friction between the tires and the road, or from the brakes made no measurable difference in tire pressure.



The other really obvious clue was that the sun's radiant head did have a major effect on tire pressure! When I checked my pressures before leaving on a trip, the side that had been exposed to the sun was 2-4 PSI higher than when I measured the night before, and higher than the shaded side.



During this cold winter, I'm keeping my inside pressure at 35 PSI. After being out for an hour or two in 0-20 degree temperatures, I might be down below 30 PSI, but it's enough for around town, low speed driving. When I go on a road trip, I let the tires cold soak while I load up, and typically check the pressure at the gas station right before I hit the highway. I might double check if I make a pit stop, but in general this practice has worked for me.



The only exception has been the several times when the outside temperature has changed a lot in a short period of time. In one case I left Madison in single digits and arrived in Chicago in the high 40s. In that case I had to bleed off excess pressure to bring it down to the 35 PSI max rating.



I've never had any TPMS issues with my ST. I've had the TPMS light come on in rental cars.