Tire upgrade and pressure sensor question

[Dr Ed]

I'm going to swap OEM tires for GY Comfortreads, same size. Do the pressure sensors need to be recalibrated if moved to another same size tire? Thanks.

[FL_Prius_Driver]

<div class='quotetop'>QUOTE(Dr Ed @ Jul 29 2007, 12:54 AM) [snapback]486950[/snapback]</div>

I'm going to swap OEM tires for GY Comfortreads, same size. Do the pressure sensors need to be recalibrated if moved to another same size tire? Thanks.
[/b]

No, but the car has a recalibrate button under the steering wheel that "MAY" need to be pushed depending on the tire pressure you want to inflate the new tires to. For details the owners manual has the info, but with a contorted description. Seach this site using TMPS as the search entry.

[David Beale]

The tire size has no effect on sensor calibration. The tire sensor measures pressure inside the tire, and compares it to the setting you make once in a while when you press the button (after you check and inflate/deflate appropriately). So once you have the new tires on the car, inflated correctly to your choice of pressure, press the button.

[jonjonbear]

<div class='quotetop'>QUOTE(David Beale @ Jul 29 2007, 12:23 PM) [snapback]487106[/snapback]</div>

The tire size has no effect on sensor calibration. The tire sensor measures pressure inside the tire, and compares it to the setting you make once in a while when you press the button (after you check and inflate/deflate appropriately). So once you have the new tires on the car, inflated correctly to your choice of pressure, press the button.
[/b]

How do these sensors work? do you have to replace batteries on occasion or the whole unit? I wonder how long they last? I saw them online somewhere for over 100.00 each..yikes! Just thinking that if they are battery powered, they won't last long but maybe they have lithium batteries?

Thanks!
John

[David Beale]

They have a lithium primary battery (not chargeable) and it's not replaceable. Five to ten year life is my guess. Probably you would want to replace them by that time, as the valve stem would have started looking a little the worse for wear, and it's part of the sensor.

Or just live without them. They are there as a "cover your ass" idea from politicians/bureaucrats. They aren't really needed if you look after your car and check tire pressures once a month, like you're supposed to.

[Doc Willie]

As I recall from a previous discussion, the tire pressure sensors only activate when one has lost 10 pounds of pressure or something like that. SO-O-O-O, could one sensitize the sensor system by inflating one's tires all the way to their maximum (or beyond if you dare), pushing the reset button, and then deflating the tires to the operating pressure? These things are still crude, but it seems to me that this would increase the sensitivity.

[Bill Merchant]

They report a differential pressure change of 25%; that is, when the pressure has decreased by 25% from the pressure at which the button was pressed, the warning light comes on. The recommended 2 psi pressure difference between the front and rear tires has no effect since TPMS measures each tire's pressure. If you want less than a 25% drop warning, increase your tire pressure, reset the TPMS, deflate your tires to your running pressure. The difference between set pressure and running pressure will come out of the 25% and you'll get an earlier warning if your pressure drops.

[apriusfan]

<div class='quotetop'>QUOTE(David Beale @ Aug 15 2007, 09:13 AM) [snapback]496174[/snapback]</div>

...Or just live without them. They are there as a "cover your ass" idea from politicians/bureaucrats. They aren't really needed if you look after your car and check tire pressures once a month, like you're supposed to.[/b]

The only problem with the live without them alternative is that you will get a TPMS light illuminate on the dash. After a while, it gets annoying. You could then put a piece of black electrician's tape over the TPMS indicator, which may or may not be an acceptable alternative.

[FL_Prius_Driver]

<div class='quotetop'>QUOTE(apriusfan @ Aug 17 2007, 12:09 PM) [snapback]497862[/snapback]</div>

The only problem with the live without them alternative is that you will get a TPMS light illuminate on the dash. After a while, it gets annoying. You could then put a piece of black electrician's tape over the TPMS indicator, which may or may not be an acceptable alternative.
[/b]

I'm already annoyed at the passenger airbag light. It's just plain bad design to have an indicator permanently on in a color that indicates a problem. (This is not Toyota's blunder, it is an US blunder.)

[apriusfan]

<div class='quotetop'>QUOTE(FL_Prius_Driver @ Aug 17 2007, 03:21 PM) [snapback]498051[/snapback]</div>

I'm already annoyed at the passenger airbag light. It's just plain bad design to have an indicator permanently on in a color that indicates a problem. (This is not Toyota's blunder, it is an US blunder.)
[/b]

The only saving grace about the airbag indicator is that it is sort of out the normal field of view. The TPMS light is not (out of the normal field of view).