8th Generation Honda Civic Forum - View Single Post

Thunder · 06-26-2009, 10:35 AM

I took a good trip (300 miles or so) in an '01 Jetta I used to own... and had an aviation certified GPS along. I found that my speed was indicating significantly high - enough so that over the course of my lease of the car, I would be buying over 1000 miles I wouldn't actually get.

Then, I clocked out the odometer... and found it dead on. Turns out that the speedometer can be off by a significant percentage *reading high*, but cannot be low at all. Therefore, manufacturers fudge the internals such that they are at no risk for reading low, even if the maximum tolerance in the part is reached.

My Civic reads 66 to go my usual cruising speed of 64, and I settle in on 77 for an actual 74-75. Occasionally, I'll go up to 78 and the (Uniden GPSRD) GPS will still show actual groundspeed of 75.

I, too, wouldn't worry about a few tenths of a mile here or there in a thirty-odd-mile (or kilometer) trip.

06-26-2009, 10:35 AM	#11 (permalink)
Thunder Senior Member Join Date: Jul 2008 Location: Raleigh, NC Posts: 300 Dan	I took a good trip (300 miles or so) in an '01 Jetta I used to own... and had an aviation certified GPS along. I found that my speed was indicating significantly high - enough so that over the course of my lease of the car, I would be buying over 1000 miles I wouldn't actually get. Then, I clocked out the odometer... and found it dead on. Turns out that the speedometer can be off by a significant percentage reading high, but cannot be low at all. Therefore, manufacturers fudge the internals such that they are at no risk for reading low, even if the maximum tolerance in the part is reached. My Civic reads 66 to go my usual cruising speed of 64, and I settle in on 77 for an actual 74-75. Occasionally, I'll go up to 78 and the (Uniden GPSRD) GPS will still show actual groundspeed of 75. I, too, wouldn't worry about a few tenths of a mile here or there in a thirty-odd-mile (or kilometer) trip.