Thanks for that link. I've certainly checked the accuracy of the speedos in the cars I've owned in the past against my GPS, but never thought too much about calibrating the odos. Has anyone ever thought to cal the speedo/odo at different speeds? I know the speedo in my Explorer reads pretty consistently 3 miles per hour high at all speeds from 20 to 70, which is to say, the percent-error varies greatly. Haven't done it yet for the new Lexus, but will when I get a chance and will report back.

A couple other points on highway mileage markers --

o Years ago, (does it still continue?) California's markers showed mileage to the 1/100th. E.g. a marker placed at "So-n-so's Creek Bridge 283.47 miles." At the time, I assumed it meant the markers had something at least approaching that accuracy. Maybe it just meant it was ~ halfway between the 283 and 284 markers, which were placed with their own errors...

o 30 years ago, I was pulled over by a cop for speeding in the Columbia gorge. I was driving on a permit with my mum in the right-seat. Cop said I was going 65, but I said I was going 60 tops. He said, "Check your odo against the mileage markers in this upcoming stretch. They're placed pretty accurately through here." (Implies they're not placed accurately other places, I think.) I verified the odo in that car read 5 miles per hour *low*, wrote a letter to the judge, had my mum sign it, and got most or all the fine knocked off.

Benton 8may08

I did technique like Mr Kite, and found I drove about 3% further than odo. However its 6 months and 17k miles later, tires should have worn slightly and I probably need to check calibration again.

I have seen the cars estimated MPG be off in either direction. Seems to depend on driving techniques used. As my mileage has gotten more extreme, the car underestimates more and more. When I first started it tended to overestimate.

Somewhat related, the low gas light comes on way too soon. I'm figuring about 3 to 3.5 gallons left. That would make since to come on that soon in a 15mpg car, but at 25/35mpg, it really could wait a while longer. I'm very sad I don't have an estimated-miles-remaining. I think its availabe on the cars with nav. Is it accurate or does it show zero miles too soon?