Tire Heiroglyphics – Cracking the Secret Code of the Sidewall
The Valley of the Kings, Egypt, 1922: Torch in hand, intrepid archaeologist Howard Carter enters King Tut’s tomb and … sees walls covered in indecipherable hieroglyphics. This is pretty much what most of us see when we try to understand the coded information on the sidewall of a modern automobile tire.
Driving in an F1 race, winning the Indianapolis 500, or stopping safely in the rain – all require the right tire. I’m here to act as your personal Rosetta Stone to the mysteries of tire sidewalls. Adjust your pith helmets, and let’s begin.
To demonstrate, I’ll use the OEM tires for Mercedes’s highest volume seller, the GLC300. It comes fitted with Pirelli’s Scorpion Verde, All Season 235/60 R18 tires.
First, 235 millimeters (1): Why? John Dunlop, 19th-century Scottish veterinary surgeon and inventor, invented pneumatic “tyres” for his daughter’s tricycle. Thus, tires were created using the Queen’s metrics: 235mm is the width of the tread and 60 is the percentage of the tread width for sidewall height. Doing the math, 235x.60 = 141mm tall sidewall. Now you know a quick method to find the height of any tire. Yay, math!
Next, R (2): R stands for “radial.” Radial means the plies (cords) under the tread are perpendicular to the tire’s centerline and bead. The centerline is, well, the centerline. The bead is the part of the tire shaped to fit the rim and is what holds the tire to the wheel. Don’t hurt your brain trying to picture the geometry. Just trust me on this one.
Followed by 18 (3): The 18 of R18 is inches. Yes, 18 inches of inner-tire diameter. Why inches and not millimeters? Because wheels made for American cars have their diameters in inches like God intended!
And 103H (4): This grouping describes tire load and speed rating; 103 means each tire can carry a load of 1,929 pounds. The “H” means you can safely cruise at a sustained speed of 130 mph on American interstates. Uh … I meant the Autobahn. To learn more, you can research load and speed ratings at www.TireRack.com, keywords “load rating.” For the rest of you, just hang in there.
M+S (5): These letters mean Mud & Snow. “All Season” just wasn’t engineery enough for the slide rules at Stuttgart. So, engineers at Mercedes insisted Pirelli put M+S. It helps the engineers sleep better at Nacht.
Now, the big three (6): The big three are treadware, traction and temperature, 600, A and A respectively. “TREADWEAR 600” is internal to Pirelli and means these tires last six times longer than Pirelli’s quickest-wearing tire. “TRACTION A” means the wheels fall into a category occupied by 77 percent of all tires for stopping ability in a straight line in wet conditions. “TEMPERATURE A” means these tires meet the highest standard for heat resistance – which they’d better, since they’re named Scorpion Verdes!
Hey, we’re almost done, and I promise there won’t be a test at the end.
Introducing MOE (7): Is MOE one of the Three Stooges? Sure, but in this case, MOE means Pirelli manufactured the tire specifically for Mercedes-Benz; the “E” means Extended. MOExtended tires will run flat for 50 miles. You can “see the MO difference” by searching “Mercedes-Benz tire types.” You’ll be treated to a hilarious video about how choosing the right tire for your Mercedes-Benz is like choosing the right track shoe. Evidently, it’s hard to run in flippers!
Now for some final glyphs (8): Let’s bring this rubber-infused mental expedition to a close by holding the light up to a few remaining glyphs. DOT – the tire meets Department of Transportation safety standards for road use. 93 – the Pirelli manufacturing plant. K3 – Pirelli’s internal size code. T899 – Mercedes internal code for tire brand and characteristics. 0219 – the tire was manufactured the 2nd week of 2019. This information is for recall purposes and so the car’s owner will know when the tires should be replaced.
Tut, tut! Now that wasn’t so bad was it? Like Carter, whose lectures ignited the American Egyptomania craze, you can now speak knowledgeably at Cars & Coffee and start American Tiremania! Or, ply your significant other with this newfound knowledge to help lull them into a good Nacht’s sleep.