Tire PSI Question
01-30-15, 09:10 AM
#1
Pole Position
Thread Starter
Tire PSI Question
Notice tires should be 36psi "cold". Been driving around for a week with tires hovering around 32-33 PSI but I have not had my tpms light come one.
Any suggestions as to how the computer interprets low PSI and when the light comes on. Also, even though the light isn't on, would it be beneficial to add a few pounds at all 4 corners.
Weather has been low 40 high around 75.
Any suggestions as to how the computer interprets low PSI and when the light comes on. Also, even though the light isn't on, would it be beneficial to add a few pounds at all 4 corners.
Weather has been low 40 high around 75.
01-30-15, 09:16 AM
#2
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Did you check the manual to see if it lists what the low PSI is?
Been drivng it for 1 month now since I got the car. Mine is currently around 37, but I remember that it was 39 psi when I first got it. 39 sounds high, but I'm not sure.
Been drivng it for 1 month now since I got the car. Mine is currently around 37, but I remember that it was 39 psi when I first got it. 39 sounds high, but I'm not sure.
01-30-15, 09:21 AM
#3
The TPMS light is going to be more sensitive to changes in any one single tire pressure in reference to the others. Meaning if you have one tire at 32psi and all the rest at 38psi it will trigger a light. When all tires are low it doesnt trigger until around 29psi if I recall correctly.
Mike
Mike
01-30-15, 09:34 AM
#4
Pole Position
Thread Starter
The TPMS light is going to be more sensitive to changes in any one single tire pressure in reference to the others. Meaning if you have one tire at 32psi and all the rest at 38psi it will trigger a light. When all tires are low it doesnt trigger until around 29psi if I recall correctly.
Mike
Mike
01-30-15, 09:45 AM
#5
01-30-15, 09:49 AM
#6
Lexus Test Driver
Thats not true. Tire pressure sensors are built to a trigger point. For a tire made for 32-34psi, the trigger point is 26psi.
The reason this is done to account for temperature changes in colder climates. Because if you have a tire at 34psi at 70 degrees, and it drops to 10 degrees, your tire pressure is going to drop to 30psi (all other variables held constant), and they want to give enough range so that you don't get a light during normal acceptable density changes.
The sensors don't care what is "relative" to the others, they care what the single sensor says. lmao
OP...go to a single tire, put a tire pressure gauge to it and bleed out about 8 more lbs, $10 says your light comes on....
The reason this is done to account for temperature changes in colder climates. Because if you have a tire at 34psi at 70 degrees, and it drops to 10 degrees, your tire pressure is going to drop to 30psi (all other variables held constant), and they want to give enough range so that you don't get a light during normal acceptable density changes.
The sensors don't care what is "relative" to the others, they care what the single sensor says. lmao
OP...go to a single tire, put a tire pressure gauge to it and bleed out about 8 more lbs, $10 says your light comes on....
01-30-15, 10:16 AM
#7
Won't that actually prove the whole "single tire being different than the rest" theory? All good points btw.
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01-30-15, 10:56 AM
#8
Thats not true. Tire pressure sensors are built to a trigger point. For a tire made for 32-34psi, the trigger point is 26psi.
The reason this is done to account for temperature changes in colder climates. Because if you have a tire at 34psi at 70 degrees, and it drops to 10 degrees, your tire pressure is going to drop to 30psi (all other variables held constant), and they want to give enough range so that you don't get a light during normal acceptable density changes.
The sensors don't care what is "relative" to the others, they care what the single sensor says. lmao
OP...go to a single tire, put a tire pressure gauge to it and bleed out about 8 more lbs, $10 says your light comes on....
The reason this is done to account for temperature changes in colder climates. Because if you have a tire at 34psi at 70 degrees, and it drops to 10 degrees, your tire pressure is going to drop to 30psi (all other variables held constant), and they want to give enough range so that you don't get a light during normal acceptable density changes.
The sensors don't care what is "relative" to the others, they care what the single sensor says. lmao
OP...go to a single tire, put a tire pressure gauge to it and bleed out about 8 more lbs, $10 says your light comes on....
Tire sensors are not built to a "trigger point". These sensors do not act as on/off triggers.
They provide pressure data to the TPMS system receiver. We have active sensors that provide exact pressure. They do not act as passive triggers that "go off" at a certain point. The sensors send the data to onboard receivers in the car. It is this receiver or computer that has settings to determine the point to illuminate the indicator light. By law it has to be at the very least when the TPMS readings are 15% below the certified tire pressure found in the door jam.
In the older indirect TPMS systems, the tire pressure was monitored by ABS wheels speed sensors and in those systems they could only measure the relative difference in sensor data so if inflation was lost in all 4 tires (ie, from weather) it would not trigger a light.
Bottom line is that the TPMS system in our cars is set to trigger at whatever point lexus programmed it to trigger.
Mike
01-30-15, 11:09 AM
#9
Lexus Test Driver
Tire sensors are not built to a "trigger point". These sensors do not act as on/off triggers.
They provide pressure data to the TPMS system receiver. We have active sensors that provide exact pressure. They do not act as passive triggers that "go off" at a certain point. The sensors send the data to onboard receivers in the car. It is this receiver or computer that has settings to determine the point to illuminate the indicator light. By law it has to be at the very least when the TPMS readings are 15% below the certified tire pressure found in the door jam.
In the older indirect TPMS systems, the tire pressure was monitored by ABS wheels speed sensors and in those systems they could only measure the relative difference in sensor data so if inflation was lost in all 4 tires (ie, from weather) it would not trigger a light.
Bottom line is that the TPMS system in our cars is set to trigger at whatever point lexus programmed it to trigger.
Mike
They provide pressure data to the TPMS system receiver. We have active sensors that provide exact pressure. They do not act as passive triggers that "go off" at a certain point. The sensors send the data to onboard receivers in the car. It is this receiver or computer that has settings to determine the point to illuminate the indicator light. By law it has to be at the very least when the TPMS readings are 15% below the certified tire pressure found in the door jam.
In the older indirect TPMS systems, the tire pressure was monitored by ABS wheels speed sensors and in those systems they could only measure the relative difference in sensor data so if inflation was lost in all 4 tires (ie, from weather) it would not trigger a light.
Bottom line is that the TPMS system in our cars is set to trigger at whatever point lexus programmed it to trigger.
Mike
In the case of an older non-dispaly style, they use rotational motion in order to monitor tire pressure. It would then send an electrical resistance to the car, which ti would use in order to be aware of hte tire pressure. If voltage sent was at a certain range, the car would actuate the light, regardless which tire threw it. That voltage is determined by the car and thus, by the car company. They provide a constant signal to your car, the same reason you got the painful light when one failed because there was no voltage being provided to the car.
The case for display sensors is the same thing. The only nice thing now, is taht you can see the readout. The ECU is STILL using a voltage in order to know what the tire pressure is. Except I think now, it has an internal chip to determine the pressure pushing against it without rotational motion. The car builder then programs, just like before, the voltage (which now you see as a pressure!!) that should trip the light. So when the pressure on yoru screen gets down to that, guess what, it throws the light.
Nothing has changed, just now you get a pretty picture.
01-30-15, 11:34 AM
#10
You do realize that there is no real difference between them, right?
In the case of an older non-dispaly style, they use rotational motion in order to monitor tire pressure. It would then send an electrical resistance to the car, which ti would use in order to be aware of hte tire pressure. If voltage sent was at a certain range, the car would actuate the light, regardless which tire threw it. That voltage is determined by the car and thus, by the car company. They provide a constant signal to your car, the same reason you got the painful light when one failed because there was no voltage being provided to the car.
The case for display sensors is the same thing. The only nice thing now, is taht you can see the readout. The ECU is STILL using a voltage in order to know what the tire pressure is. Except I think now, it has an internal chip to determine the pressure pushing against it without rotational motion. The car builder then programs, just like before, the voltage (which now you see as a pressure!!) that should trip the light. So when the pressure on yoru screen gets down to that, guess what, it throws the light.
Nothing has changed, just now you get a pretty picture.
In the case of an older non-dispaly style, they use rotational motion in order to monitor tire pressure. It would then send an electrical resistance to the car, which ti would use in order to be aware of hte tire pressure. If voltage sent was at a certain range, the car would actuate the light, regardless which tire threw it. That voltage is determined by the car and thus, by the car company. They provide a constant signal to your car, the same reason you got the painful light when one failed because there was no voltage being provided to the car.
The case for display sensors is the same thing. The only nice thing now, is taht you can see the readout. The ECU is STILL using a voltage in order to know what the tire pressure is. Except I think now, it has an internal chip to determine the pressure pushing against it without rotational motion. The car builder then programs, just like before, the voltage (which now you see as a pressure!!) that should trip the light. So when the pressure on yoru screen gets down to that, guess what, it throws the light.
Nothing has changed, just now you get a pretty picture.
The old systems did not rely on voltage at all. They relied on wheel speed. They used the ABS WHEEL SPEED SENSORS. This is the reason they could not measure losses in pressure in all the tires at the same time. You can only measure relative differences in these sensors.
From Tirerack..
Indirect systems use the vehicle's antilock braking system's wheel speed sensors to compare the rotational speed of one tire to that in another position on the vehicle. If one tire is low on pressure, its circumference changes enough to roll at a slightly different number of revolutions per mile than the other three tires.
... and won't warn the driver if all four tires are losing pressure at the same rate (as occurs during the fall and winter months when ambient temperatures get colder).
http://www.tirerack.com/tires/tirete....jsp?techid=44
Mike
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