[Regorider62]

Hopefully I am posting this question in the correct forum?
2018 Boxster GTS, brought home 5 months ago on August 18. Currently has 2725 miles.
This morning got an error message, right front tire has low tire pressure at -4 LBS. I check the online TPMS once in a while and all 4 tires read 33 LBS which is correct.
I check right front tire thinking I may have picked up a nail. No nail and tire (cold) is at 25 LBS??
I have a portable air pump so I bring the tire up to 33 LBS and decide to check the other 3 tires. All 3 are at 27 LBS??
In any event I bring the other 3 tires up to 33 LBS and am now wondering if this is normal or not? On my motorcycles tires lose air on their own and need a weekly check as they are almost always a pound low. Is this the case with this car?
My wife drives the car and is anything but aggressive and the tires look showroom new.
Thanks for any feedback. I don't want to call the dealer until I hear back from a few forum members.
m

 

[autobahn]

How cold is it outside now vs when the tires were filled before?

 

[Viffermike]

This morning got an error message, right front tire has low tire pressure at -4 LBS. I check the online TPMS once in a while and all 4 tires read 33 LBS which is correct.
I check right front tire thinking I may have picked up a nail. No nail and tire (cold) is at 25 LBS??
I have a portable air pump so I bring the tire up to 33 LBS and decide to check the other 3 tires. All 3 are at 27 LBS??
In any event I bring the other 3 tires up to 33 LBS and am now wondering if this is normal or not? On my motorcycles tires lose air on their own and need a weekly check as they are almost always a pound low. Is this the case with this car?
My wife drives the car and is anything but aggressive and the tires look showroom new.
Thanks for any feedback. I don't want to call the dealer until I hear back from a few forum members.
m

TPMS will go off if there is a pressure difference of 4 lbs or more, not matter what the overall pressure levels are. That's what triggered it.

Car tires do lose air like motorcycle tires do -- and at a generally quicker rate because the volume and/or surface area is greater in all areas: air, bead, rubber, etc. But I have a feeling a mitigating circumstance here is ambient air temperature. The colder a fixed amount of air is, the more dense it becomes and, thus, the less volume it wants to take up -- that equals less pressure. Generally, tire pressures should be taken when the tires are dead cold; the effective air pressure goes up 2-3 lbs when the tires are warmed up to operating temperature.

In a nutshell, if 33 lbs is your target pressure: Your tires should be at 33 lbs when cold. They will go up to 36-37 lbs as you drive.

 

[Rob G]

Depending on the ambient temperature and the road surface temperature, air pressure will vary by several pounds. As was stated in the previous response tire pressure should be checked when cold for the most consistent pressure readings. Use/invest in a good tire guage which will provide you with more accurate readings. Tires are not inexpensive so don't use a cheap guage. Road surface temps will heat the tires up; the hotter the surface the greater the influence on the tires to a degree. In the Summer the inflation temps will vary more than in the Winter when the ambient/surface temps don't vary as much. I found that running Nitrogen is much better than regular "air". I spent 2+ years, read several articles and have logged pressure readings and for me Nitrogen is the way to go if you want to spend the least amount of time/effort keeping your tires properly inflated. If you go with Nitrogen make sure they do a good job of evacuating as much air from your tires before you inflate with Nitrogen. The Nitrogen molecule is larger and less influenced by temperature changes. It also "leaks" out less due to the fact that your tires are porus and will loose air over time. Do some research and decide for yourself. I found my TPMS reading is on average 2 psi different than what is actually in the tire. Each TPMS is different and you can establish the difference on your system by inflating to the pressure you want (cold) then as you get rolling (check the manual) the TPMS will read in your system then you can establish the difference. Bottom line, you still have to check the pressure regularly before driving your car to ensure correct pressure throughout the year! Hopefully this gets you in the right direction...

 

[JazzCatGab]

My car is in a heated garage all winter (well, not intentionally heated, but it stays about 60 F most of the year round, dipping a little on the coldest multiple days). In another car manual I have, it says to inflate the tires about 1 F for every degree colder outside, so if the average winter temperature in 30 F, then adding 3 F to each tire will make 30 lbs --> 33 lbs in the garage and 30 lbs outside (for tires that do not heat up so much in the cold under use). Perhaps it is the softer rubber of summer performance tires, but they seem to warm up much more when driven, negating the need to overfill them in the garage. I have not tested this extensively.

 

[Beardy]

For road use using Nitrogen is placebo effect as normal air is 78% nitrogen anyway.
It is a good money spinner for the tyre shops though