TPMS quite useless!

[yyalb]

It's been under 10F in south Michigan recently. I noticed a significant drop in MPG, so I checked my tire with my pressure gauge yesterday. The pressure for all 4 tires dropped to 27-28 psi, while the standard one should be 33 front and 32 rear. The problem is that TPMS never shoot any warning! After inflating all tires to the standard pressure, the car feels more responsible and agile, and the MPG become comparable to it used was, around 35-36 around town and 38-40 on the highway.

I just want to point out that the TMPS our civic has does not measure tire pressure directly. It is just a byproduct of wheelspeed sensor for ABS and ESC, etc, which measure the difference of wheelspeed of all wheels to detect anomally with one or two tires. When all four tires are in low due to cold weather, it is useless!
Please do check your tire pressure regularly even though you have TPMS. It is quite dangerous to run on low-pressure tires!

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[Chief 08]

Good to know, thanks.

 

[mzubb]

Same here. All 4 tires 28-28.5. Not unexpected in very cold weather, but it would have been nice to get a warning from the TPMS system. But on this car it’s just software watching for rotational differences in the tires.

A real TPMS would have alerted us.

 

[zroger73]

I'm surprised the indirect system is permitted since it can't detect equal amounts of underinflation that occurs over time and due to seasonal changes.

I guess someone thought four tires with only 5 PSI was safer than one tire deflated to 20 PSI.

Sadly, most people I know have no clue what their tire pressures are or are supposed to be. They typically get checked or adjusted only when:

• The vehicle goes in for maintenance or repairs and tire pressure is an inspection item.
• One or more tires are obviously low and the driver has enough intelligence to address the issue (this is rare - I've about given up on humanity).
• The state inspector visually notices a low tire (though an actual pressure check isn't required).

I suppose indirect systems are better than nothing, even though they aren't effective for normal, common causes of equal underinflation.

EDIT: This is incorrect. The system measures not only the rotational speed of each wheel, but also the peak resonance frequency of the front wheels to issue a low tire pressure warning if all four tires become equally low.

 

[Chief 08]

I'm surprised the indirect system is permitted since it can't detect equal amounts of underinflation that occurs over time and due to seasonal changes.

I guess someone thought four tires with only 5 PSI was safer than one tire deflated to 20 PSI.

Sadly, most people I know have no clue what their tire pressures are or are supposed to be. They typically get checked or adjusted only when:

The vehicle goes in for maintenance or repairs and tire pressure is an inspection item.
One or more tires are obviously low and the driver has enough intelligence to address the issue (this is rare - I've about given up on humanity).
The state inspector visually notices a low tire (though an actual pressure check isn't required).

I suppose indirect systems are better than nothing, even though they aren't effective for normal, common causes of equal underinflation.

It's funny because it's true.

 

[tacthecat]

TPMS is to detect a very low tire pressure that would be dangerous to drive on for any period - it's not for telling you to air up for seasonal changes.
The "old" system on our '12 Si triggers at about 4 psi low (32 normal had trigger at 25 during seasonal change from 70 deg to 20 deg F the first year we had the car).

 

[NoelPR]

Someone at HondaHQ must be saying after reading this thread.

"You can never make people happy. If the alarm threshold is too high they complain, if is too low they complain too."

 

[gtman]

While I prefer the more traditional TPMS sensors, this Honda system has one big side benefit. If you upgrade your wheels, you don't need to purchase and install 4 new TPMS sensors which can be fairly costly.

 

[grumpyguy6]

I got so used to having a real TPMS and now that I don't have it, I realize how useful it was.
Thinking about getting something like this:
https://www.amazon.com/gp/product/B074WKVG6J/ref=s9_acsd_topr_hd_bw_b2P0Net_c_x_w

Anyone tried something similar?

 

[charleswrivers]

While I prefer the more traditional TPMS sensors, this Honda system has one big side benefit. If you upgrade your wheels, you don't need to purchase and install 4 new TPMS sensors which can be fairly costly.

This. I'm actually very happy with this system. I check my tire pressure regularly after a temp change. Not having to go through that TPMS sensor BS over the life of a car is a big up check to me. It still performs it's safety function if you have one tire go down. Since TPMS never quantified the amount you were low or what tire was low, I always found it kinda worthless to maintaining pressure due to temp changes.

 

[jakabony]

I just got around to checking my tire pressures. 27 in the front and 25 in the back. I only drive mine once or twice a week. I find it odd that my beater Accord hasn't lost any pressure. You would think that you would lose more pressure by driving. Guess not.

 

[tacthecat]

I just got around to checking my tire pressures. 27 in the front and 25 in the back. I only drive mine once or twice a week. I find it odd that my beater Accord hasn't lost any pressure. You would think that you would lose more pressure by driving. Guess not.

Some tires/wheels loose a pound (psi) or more a month in static conditions. In supercold weather it's not uncommon to actually have them go flat.

 

[Monocacy]

You can calculate how tire pressure changes with temperature. The formula is as follows:

P2 = P1*T2/T1

Where P = pressure and T = absolute temperature in degrees Kelvin
To find absolute temperature, take the temperature in degrees Celsius and add 273.

Example:

P1 = 32 psi

T1 = 282K (48F or 9C)

T2 = 273K (32F or 0C)

P2 = (32psi)(273K)/282K = 31psi


So a temperature drop of 16F (9C) will lower tire pressure by about 1 psi

 

[Monocacy]

One more example. Tires filled on a hot summer and not checked until winter (assuming no loss of air):

P1 = 32 psi

T1 =308K (95F or 35C)

T2 = 273K (32F or 0C)

P2 = (32 psi)(273K)/308K = 28 psi

Loss of 4 psi with a temperature drop of 63F (35C).

 

[ClemsonPatriot]

Yeah it's not as effective as a traditional TPMS setup with the actual pressure sensors. However, I check my air pressure on occasion out of habit (takes 2 minutes) when the seasons change or montly; whichever comes first. I trust myself over any on-board system too.

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