: Speedometer accuracy



mrk4543
03-29-12, 06:36 PM
Has anyone had their speedometer checked for accuracy? Mine seems to be reading high when going by the highway radar displays...such as an indicated 70 shows as 63 on the radar display. I did have the diff replaced not too long ago and wondering if there was a ratio change. Going to check elapsed time on interstate with mileage markers in the next few days.

Marty

GM-4-LIFE
03-29-12, 08:10 PM
I show a 1 MPH discrepancy on my speedo vs. the radar display signs. Radar signs show 1 MPH less than what the car shows.

Marcuse12
03-30-12, 12:22 AM
I've noticed a 3mph difference between the digital speedo and the analog one. Wonder which one is right.

khoeysr
03-30-12, 09:48 AM
Occasionally there is a 1 mph diff (car higher) vs. my GPS enabled Escort radar detector. Found this in both my '11 and my new '12.

V Wagon
03-30-12, 12:02 PM
Has anyone had their speedometer checked for accuracy? Mine seems to be reading high when going by the highway radar displays...such as an indicated 70 shows as 63 on the radar display. I did have the diff replaced not too long ago and wondering if there was a ratio change. Going to check elapsed time on interstate with mileage markers in the next few days.

Marty

Do you have an automatic car? 63/70=.9. 3.27 (that's the auto rear ratio right?)/3.73 (manual rear ratio) = .8766

It seems very possible that you ended up witht he wrong rear end.

mrk4543
03-30-12, 02:29 PM
My car is an automatic....I am going to check the time/distance this weekend over a measured mile and see what transpires......

Marty

neuronbob
03-31-12, 04:05 AM
^^^^
A good idea. Around here, there is a road that has a measured mile that would serve that purpose. (For Cleveland locals, it's Rockside Rd. in Garfield Heights/Valley View if the AAA signs are still up. Will have to look this weekend.)

Couldn't it also be that the radar sign is busted and is throwing out the wrong speed?

mrk4543
03-31-12, 07:46 AM
It is quite possible the radar display was broken....wouldn't surprise me at all since it belongs to the Highway Department of the State of Disrepair (Florida)....that is why I am going to check it on measured mile. The interstate mileage markers should be good enough for this type of check....of course, they are administered by the Feds...what could possibly be incorrect?

Marty

h8-2goslow
03-31-12, 09:22 AM
I've noticed that my analog speedometer is about 2 mph higher than the digital one.

mrk4543
04-05-12, 11:01 AM
It would appear that the mileage paddle markers on the interstate are no where near being properly placed.....checked out the paper work on the diff replacement with the car's build sheet and the part numbers etc. seem to be proper. Not too much else to do until I can get to a measured mile or get to a shop to have the speedometer calibration checked. Life goes on....

Marty