Speedo Error

[jkronq]

I was wondering if anyone else has noticed an error in what your speedometer shows your speed to be vs. your actual speed. I have a 5 MPH differance! My GPS shows actual speed. When my speedometer shows 75 the GPS shows 70. I double checked this by haveing a friend follow me. Again, myspeedo showed 75 the GPS 70 and my friends speedo in his car 71. Is this a common thing?

 

[Big Daddy]

All speedometers are imperfect. I am not sure what the allowable spread is but that does not sound too far off. It should vary with speed. Have you changed wheel or tire sizes?

 

[nadroj]

on my e30 318is its about 10 mph off at certen speeds.

 

[William330]

I was going to ask what Big Daddy asked, because changing your tire
size / wheel size can not only throw off your speedometer, it can throw
off your gearing ratios.

 

[Big Daddy]

10 MPH off is pretty excessive, I'd have the speedo sensor checked. Also, at least where I worked we would check your speed with radar or lidar if we were available and you requested it. You might ask your friendly local police department if they are willing.

 

[jkronq]

I have not tire size. I am still running the original tires that came with the car. I do have the optional 19" rims. Maybe the car was set up for the stock 18's and by going to the 19's that is what is causing the error's.

 

[Big Daddy]

That could be the problem. I would have that checked.

 

[nadroj]

10 MPH off is pretty excessive, I'd have the speedo sensor checked. Also, at least where I worked we would check your speed with radar or lidar if we were available and you requested it. You might ask your friendly local police department if they are willing.

The tires on my car are a little lower profile than stock. they are 195/60. stock is 195/65. also im not to worried about it. i hardly driver her any more. some one hit it about a month ago too