Another Speedo error thread.

[wallymn]

I spent 1100 miles in the car yesterday, Lots of time to kill,

So with winter tires on, my speedo is off 5 MPH at 70. (reads 70, actual is 65).

GPS reports 65-66 at indicated 70...

So I figured the Odometer should be off, But comparing to sign posts and GPS, it wasn't. (over 20 miles of flat straight road the GPS, sign posts and Odo were only off by 1/10th mile, or about 0.05%)

So then I used the "average MPH" from the trip computer. It reports the correct Speed (about 1 MPH less than the GPS reports). Correct being a guestimate based on sign post, I set the Cruise at 65, GPS reports 61 over 10 miles of flat road, Ave speed in trip computer is 60. I covered 10 miles in 10 minutes 3 seconds....

So, The trip computer knows the correct speed, and isn't getting it from the GPS, but then the SPEEDO is off by 5 MPH.

So the Speedo must be off on purpose?

 

[ASHDUMP]

I've noticed a difference in my speedo as well with my Falken Euro winter tires. My PSI is around 29 to 30..... I haven't done any detailed calculation like you have, but I've noticed a difference. I'm not completely sure if I like it the way it is. I usually set my speedo cruise at 70 knowing I'm around the posted speed limit of 65.