108 speedometer error
 

Yesterday I checked my speedo error using a GPS for actual SOG and came up with an error of -9% from 20 to 50 MPH. It is a linear error so I suspect it is not a malfunction speedo. I did not check the acuracy of the odometer......that is next on my list.

My tires are 205/70/R14 and that is the size I intend to stay with so my question is: "can the error be adjusted out either by a DIY action or by a speed/tach shop.

tks all and Merry Christmas

By -9% do you mean that the speedometer is underindicating speed, or actual speed is 9% less? In other words, it says 50, but you're doing 54.5 or 45.5?

Opps, I mean that true speed is - 9%. At 45 indicated I am doing 41.3 true. Also, I am rounding a bit.

The speedo just needs calibration.

It doesn't really bother me much, but mine is way off. At '80' (fake 80) the car is actually going 68. The faster you go, the more inaccurate it is, on my car anyway. One day when I'm not lazy, I'll go somewhere to have it fixed. Is it true that AAA has special days where they do this for members?

Sounds to me like your speedo has been changed before. I had the same issue in my '70 280s when I got it. It "claimed" to be doing 80 while most traffic was just flying right past me. When I bought it there was another instrument cluster in the trunk. Upon inspection I found the odometer was not working on the "spare". I reasoned that this was the original (top speed 140) so I repaired it and then replaced it with the "operating" one (top speed 160). Now the speed is more accurate, i.e. at 80 I'm the one flying past everyone else! :D