StephenK

Can anyone tell me what the various numbers and letters mean on these tires??

Front Michelin Pilot Sport 255/40 ZR 18 95Y
Rear Michelin Pilot Sport 285/35 ZR 18 97Y

Gregs210

But so long as I'm here...

The first number is the width of the tire in millimeters.

The two-digit number after the slash or dash (40 and 35 in your examples) is the profile or aspect ratio. Basically it's an expression of the width of one sidewall as a percentage of the tire width, so one sidewall on the first tire would be .40 x 255 or 102 mm "tall".

The letter (Z in this case) is the speed rating of the tire and the last two-digit number is the diameter of the wheel the tire is designed to fit.

You can find all this -- and more -- at tirerack.com. They have a lot of useful info there.

If you want to play with different tire widths, aspect ratios and diameters, the boys at miata.net have a great little java toy: www.miata.net/garage/tirecalc.html

Enjoy the ride,
Greg

RadSteve

I'd have told ya, but thought you knew, and after the post before this, now you certainly do! the tirerack site is very good for this sort of info. Have fun with your new car!!! (I know I am...break in is OVER)

Steve

vraa

What Rad said, I wouldn't mess with going different sizes unless you can find it on Tirerack.com . I use them for almost everything except finding a date for Saturday.

I have Clublexus for that..

StephenK

http://www.michelinman.com/assets/pd...pilotsport.pdf

Check out the Michelin PDF, in reference to rear tires

285/35 ZR18's

Which one would you pick 97W or 97Y.

It seems on our cars you get 97Y but they lick 97W as original equipment. Does it make a difference????

RJC

You should be able to order the Pilots with the MO designation, this means its specs have been approved as original equipment by MB; I've been told there is no difference (who knows) but the stock tires all carry this marking and if you're a perfectionist like me, you'll want it on yours...

tiggerfink

It depends on how fast you go. Y rated tires can go faster than w rated tires. Also Y rated tires can handle more load at faster speeds.

97 is the load index. I was depressed when Michline stop making pilotsport with a load index of 91 for my SLK. My SLK came with pilotsport with a load index of 91. The new pilotsport only supports 87. I had to get a different tire for my SLK.

The test results below are from tire tests perfrom for an hour.

W-Speed Rated Sizes:
Maximum Speed (mph).....118..124..130..136..143..149..155..161.. 168
Inflation Increase (psi)........0..1.5...3.0..4.5...6.0...7.5...7.5.. 7.5..7.5
Load Capacity (% of max).100.100..100..100..100..100....95...90...85

Y-Speed Rated Sizes:
Maximum Speed (mph)......118.124.130.136.143.149.155.161.168.174 .180.186
Inflation Increase (psi) ........0....0....0....0..1.5....3..4.5....6..7.5. 7.5..7.5.7.5
Load Capacity (% of max) 100.100.100.100.100.100.100..100.100..95..90..85

StephenK

I thought it was strange that the W-rated Tires are listed as original mercedes equipment when it is actually the Y-rated tire that comes on the car with the sport package.

tiggerfink

W rated tires are cheaper than y rated tires. Y rated tires are the better tires.