During my holiday road trip to visit relatives, I experienced my first ever flat tire on my '08 ML550. We're driving down the interstate and POW! Front driver's side tire, which was only about 2 months old.. Luckily, and perhaps due to the height of the tire sidewall (50 series profile), the rim just sat down on to the tire and kept rolling at 75 mph. It almost didn't feel flat, but the TPMS light had illuminated, so I knew something was up. There was a big puncture hole in the middle of the tread, but I have no idea what I ran over. With incredibly good luck, a roadside rest stop was only two miles ahead, so I managed to pull in there before the sidewalls of the tire self destructed and had me rolling on the wheel itself.

The jack, tools, and shorter bolts, along with a brand new space-saver sized spare tire were all where they were supposed to be in the space beneath the rear storage space. The spare felt firm to the touch, but once it was mounted, it was very obvious that it hadn't been re-inflated since it rolled off the factory assembly line. When I lowered the vehicle down on to the tire, it looked no more than half inflated, probably less. A quick search revealed there was a Discount Tire store only 4 miles further down the interstate. I put the flashers on and limped that 4 miles at about 40 mph, knowing that my front spare barely had enough air in it.

I agreed with the service writer that the sidewalls of the flat tire were very suspect and likely ruined after having been driven on, so I chose to purchase a new tire in order to feel safe over the last 700 miles of my trip home. Of course, they didn't have a tire that matched what is on my ML, so I now have a new one of those on order so I will once again have the same make and model of tire at all four corners. We got the new tire mounted, inflated the spare, repacked all of the stuff that had to be moved to access the spare and jack, and made the rest of the drive home uneventfully.

But this experience was a great reminder that it's always an excellent practice to regularly check the inflation of the spare tire, which should be 60 psi. When I got home, I check the spare in my wife's 2014 ML, and it was at 26 psi - it too obviously had never been inflated since leaving the factory. Needless to say, I added air to bring its inflation up to spec. I was just extremely luck I got my flat where I did. I could have been stuck in some remote location and it would have been a real disaster. So, if you haven't checked the air pressure in your spare tire recently, I urge you to do so. You really don't want to get a flat only to find out your spare is nearly flat too!!!!

 

It's also good to know that the air valve for the spare tire is a special item you can only get from a Mercedes dealer. I carry a spare in case this one fails or is damaged.

 

Also be aware that the spare tire takes a Short stem air valve. The dealer gave me a long stem by mistake. I placed the spare, valve stem down as required, and then later discovered that it was being bent by the position and cracked at the base resulting in a leak. :^(