Something interesting to know is that on the inside of most ALL factory Mercedes Benz rims there will be a color band that encompasses the entire diameter of the rim. The color of this bad designates the width of the rim.
Green = 7 inch Red = 6.5 inch
You can also find the part number, as well as all of the dimensions of the rim on the back side of the rim. Usually the part number will be separate from the dimensions.
For example one of our rims with the green band reads-
7JX15H2
Cleaning the area where the numbers are can be done with a small wire brush or a pencil eraser. In some cases it can take a bit of work to get the numbers to show.
The original equipment Mercedes-Benz 15 hole rim is without doubt the best to have. I have seen MANY different kinds of knock off rims, and most of the knock offs will not accept a factory center cap.
While its not "Law" or anything, since you could order anything you wanted for a Mercedes when it was new, but I have found the following to be true most of the times
1986-1988 will usually have a 7 inch width rim
1989-1991 will usually have a 6.5 inch width rim
But this is not always true, and some vehicles have had mixed and matched rims by the time we got them. But for the most part it should be considered what to expect.
The SL of our generation does have diffrent rims than the W126, however the SL is not a W126 anyway.
Seems the color band may also be something to keep rim leaks down. This seems like the main reason its on there, since clearly thats where the tire seats. So its a dual action thing. Got to love that sort of thinking.
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What is to give light must endure burning -- Viktor Frankl