nightfeng

Hi guys, I have a 2013 GLK 350 4Matic, and today I went to check the tire pressure of the tires at the gas station and noticed all of them are around 20 psi. After looking at the normal psi on the fuel door( the gas lid thing), I pumped the tires up to that normal value (NOT MAX, just the normal) , which is 35 front and 38 back. And then i told my friend about this and he said i shouldn't have pumped them because it's winter(I am in Toronto, so temperature can get quite low during winter), so the tire pressures are supposed to be lower, and when it gets warm it'll cause damage to the tires.

I am not an expert on cars, so I am just asking should i not have pumped the tires instead? What should I do now?

JohnMichael

You did fine. Tire pressure goes down about One lb for each 10 degree temp drop so if you had not checked pressure since summer you can see why they were low. Also goes up when it gets warmer. Just always check tires when you first start out and tires are ambient temperature not after you have driven. The Mercedes recommended pressure should always be used. If you have pressure monitors you will see pressure rises as tires heat up and that is all ok as. Tires are designed for this. Just be sure as I said you check tires before you start driving. Tire pressure determines foot print or rubber contacting road and this is set by engineers and extremely important for correct braking, traction control etc. you start varying tire pressure from recommended and you jeopardize safety and handling.

Rdub

Essentially you have been running WAY UNDER inflated !!! This is DANGEROUS, given you have no special purpose in mind or that you have stated !! Even at that, you have risk levels, aka, you are willing to accept ! One should run PSI @ @ the least the recommended oem PSI, door post placard, as you state- 35F/38 R @ the temperature range you will most likely encounter. So IF it is 36 degrees F in Toronto right now, pump those babies up to 35/38 PSI !!! When the ambient temperature situation gets UP/DOWN appreciably and is within the AVERAGE temp you are operating in, you can always readjust the PSI.

So given MSG # 2's, 1# for each 10 degree F, you would need 150 degrees F CHANGE to get the TP up to 35 PSI !!!!!

nightfeng

thank you so much for your help guys! Glad i did the right thing! Ill make sure to keep an eye on the tire pressures monthly!

rmfnla

20 psi?!

Do you not have tire pressure sensors?

They should have sent a warning well before now...

koalatm

The OP might have a Canadian GLK, which means no sensors. Our sensor is different, it just detects if one wheel is rotating at a different speed than the rest, but if all four tires are approx the same pressure, I don't think that would trigger this type of sensor.

I try to check tire pressures at least once a month and I adapt the pressures to the environment. So yes, warmer weather heats them up, but the differences are fairly small.

rmfnla

I'd love to hear MB's reasoning for this...

LesF

I adjust pressure on a regular basis on my 250BT depending on load and temperature.

Normally cold inflation, regardless of season, is 33psi x4 for everyday use but highway will be 38-42psi rear, and front at 35psi under load

Rdub

That is how it really should be !!

The attitude that SEEMS to affect the issue for most people, is (like the RONCO TV oven :Set IT and FORGET It !!!

The truth is more fluid to variable than that.

koalatm

The reasoning is that TPMS isn't federally mandated in Canada. It isn't much more complicated than that!

rmfnla

I didn't realize they were mandated here; thanks...