I have been semi lazy about checking tire pressures for about a month. I run at 42/40. I went to costco tonight, and I was at 38 and 35 up front, and 30's in the back! How I've been staying above 50mpg is beyond me. So just a friendly reminder to check your pressures. Side note: Costco guy said he gets a LOT of Prius owners asking for CRAZY pressures above the max PSI. He made sure to check my tires to see that 42/40 was below the 44 max psi. I asked him to define "crazy". He said 60 to 70 psi on 44 max.
60-70 is nuts. 60psi is what the spare tyre is stored at. Also, a 35psi tyre checked at an underground heated garage = 30psi out in -30°C temps with literally no chance for the tyres to warm up unless you're travelling at 100km/h for 20 mins. I forgot to take into account the temperature differences!
If your back tires were down to the 30s, why didn't your TPMS light come on? You might want to reset it after you get your tires pumped back up.
I usually stop at either the Discount Tire Co and have them fill my tires or I do it myself at a gas station. I always have them overfilled to 40 all around and adjust them the next morning to factory specifications (found on the label in the drivers door ledge). That way I adjust the tires when they're cold, if you set them to desired pressure when they're warmed up from driving (driving to the tire place to get them filled) then the pressure will drop when the car sits, especially ouside in the cold. Tire pressures are supposed to be measured when cold, therefore you are probably not running quite as high of a pressure as you may think you are. I noticed last year when the first cold of winter hit my low tire pressure light came on and when I checked them they were all exactly 5 psi low each just from the outside drop in temps.
It is my understanding the TPMS is designed to alert you when pressures fall 5-8lbs below where it is set. So, if you're going to run your tires higher than recommended (40lbs), then reset the TPMS at that new pressure and it alert you when they fall to 32-35lbs. Reset is easy. After filling the tires, put the vehicle in ready mode, depress and hold the brake pedal and press and hold the TPMS button at the bottom of the dash until the indicator on the dash blinks then goes steady. Release the button and the brake pedal but keep the vehicle on for a few minutes to allow the TPMS to read and memorize all 4 wheels.
