wheel size vs speedometer

[jr811]

I have 15" wheels on my 1979 450SL (orginal 14")
At a true 55 mph my speedomete is reading around 65mph

Is there any type of adjustment I can made to correct this.
On some american car you can change size of gear on tramsmission housing.

[revray]

Aloha Jim,

Cannot help on a possible machanical fix for you problem. Sorry. Can suggest that when you get ready for a new set of tires, you consider a size that more closely replicates the original diameter. That may get you the speedometer accuracy you're looking for. Both of my cars started out with stock 14" rims. Presently have 16's on my sedan, and 18's on my coupe, with the speedo accuracy to within 1 mile. Whatever you decide, good luck!

[DJChillfit]

This might not be any better a solution, but for $100 you can get an eTrex GPS unit that can tell you your true speed with a high degree of accuracy.

The bad news is that you're putting 10% more miles on the odometer. I just had to have mine recalibrated, though not due to wheel size. (My guy sent it to Germany--cost a couple of hundred bucks.) I imagine they can recalibrate for variations in wheel diameter.