speedometer W value to gear ratio

[subforry]

Since I spent quite a bit of time researching the W number of the back of speedometers, I thought I should share my findings.


This info may only apply to W114/5 and W108/9 cars.


The W number is the RPM of the speedometer input to read 60mph. The digits past the comma are not fully represented. For example W = 1,5 is actually 1,500 RPM.


Here are some W values matched to rear axle ratios.
1500 -> 4.08
1440 -> 3.92
1275 -> 3.46
1190 -> 3.23


From here you should be able to extrapolate other gear ratios. Of course tire size effects speedometer accuracy, which can be fined tuned by changing gears in the speedometer. Unfortunately using a driveshaft calculator doesn't work because the transmission has gear ratio between the output shaft and the speedo cable. I think this ratio is the same across generations of transmissions, but I am not sure.



Finally, when shopping for a replacement speedometer, look at the shift point markings on the dial. They should match the number of gears and Mercedes listed max speed shift points.