Seems small: I checked the psi on my spare, it had 18psi! What good is a spare if you cant use it. Checked my Merc's spare (first time ever) it didn't even register any air and it is supposed to have 61psi! Good advice, check the spare.

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'03 Black BMW E53 3.0i 110,000+ miles
'03 Black Mercedes-Benz W211 125,000+ miles
'13 White Mercedes-Benz W2o4 New