I got caught out....

Yeah, pretty much. I even told the service people not to mess with the pressure and they did anyway.

 

Ditto!

 

Yup, told dealer not to adjust the tire pressures, he said alright and wrote it down, got the car back and drove home and once i pulled into the garage noticed they didnt look right, almost flat. 30 front 32 rear....Wth?

 

happened to me too... took it for an oil change and they bled out my tires and did not reset the oil light. yay.

 

Same thing happened to me with Honda dealership, just a few years back. At least they were very flexible, quickly raised the pressures when I caught it, before leaving. If there's anything worse than someone undoing your preferences, it's getting a sermon as well...

 

My guess is that they did reduce it to the recommended spec, while tires were HOT. Once they cool to room temp, you know the rest...

 

Just what is the recommended PSI for our tires? Mine was 30 PSI over the weekend, I decided to get pump it to 40 PSI, I read on the tire it says the max input was 44 PSI so.... I wonder if this is ok.

 

You are fine at 40 PSI no matter how you fill it.

If you want to go higher with the PSI then you need to make sure you have an accurate gage and you pay attention to outside tempature and how long since the car was driven before checking the pressure.

You might want to keep the rear tires 2-3 PSI lower than the front though instead of doing 40 all the way around consider 42 front/40 rear or 40 front/38 rear.

 

Sorry, don't know what caused the anomaly, It must have been Dracula intervening. Sorry

 

What is the reason for lower pressure on the rear tires? Better traction control?

I also realized mine was always at 30 PSI, but I didn't do anything til I read up on increase MPG by increase the tire pressures.

 

Balance of the car. I believe the front tires are inflated by 2 PSI more than the rears to compensate for the extra front weight of the car.

You'll get more even wear and much better MPG's with your tires near the max PSI than at 30 PSI.

 

That would be quite a temperature difference to get those numbers.

Ideal gas law = PV = nRT where P = Pressure and T = Temperature in Kelvin (Celcius + 273).

P1 = T1
P2 =T2

For this exercise (and my errors will be pointed out and corrected) lets assume that V, n, and R are constant and equal 1. Let's assume they did set to 36 PSI @ unknown temp and you found it at 30 PSI at 59F (15C = 288Kelvin)

Thus, For a 6 PSI change

36/30 = x/288 Kelvin. 36 PSI(288 Kelvin)/30 PSI= x = 345.6 Kelvin = 67.6C (154F).

That would take a 100 degree farenheit change. I don't think the tires get that warm......

 

In the Uk it is illegal to have tyre pressures that are more or less than 10% of the manufacturers recommended pressures.

 

I do. There's a signifciant change. Recommended is 34, so it only takes tire temperature that'd raise it by 4 for them to mess it up. I got caught out the same way when I had my new tires installed.

They might not have been off by 4: part of the effect could have been additional autumn temperature drop.

 

Interesting, I didn't know that. How/when do they confirm this?

But even still, it doesn't impact Jin (who is in Maryland).