speedo issues

[nitricacid]

So the speedo is off by 3mph> gps checked> all factory with the 16" bf longtrails?....

is that wiithin nissan specs?
would thatmean my miles are real less than whats stated?

[KamyKazyTommy]

I also noticed that I run approximately 2-3 miles per hour slower than what the speedo actually reads everytime I drive past a radar sign. Therefore, I run with the cruise on at 10 over the speed limit all the time and never get looked at. Perhaps this is a good thing.

[GolfTango]

Yes, the speedo is 3-4 mph faster than your actual speed.

[bigdog]

get bigger tires and it will flip on ya. My guess is that the speedo must have been tuned to the 32" tires

[nissankidd]

Yes that is within nissan standards it is allow to display faster up to 3-4% but not a bit slower than actual speed

[Mainerunr]

3mph at what speed? usually they're off by a percentage so the mph difference changes depending on how fast you're going. (mine was reading 1% high, now it reads 6% low so when it reads 70, I know I'm going 74).

[KamyKazyTommy]

Originally Posted by Mainerunr

3mph at what speed? usually they're off by a percentage so the mph difference changes depending on how fast you're going. (mine was reading 1% high, now it reads 6% low so when it reads 70, I know I'm going 74).

75 ish. I agree that it is a percentage, and have thought about the bigger tires as well!

[nitricacid]

Originally Posted by Mainerunr

3mph at what speed? usually they're off by a percentage so the mph difference changes depending on how fast you're going. (mine was reading 1% high, now it reads 6% low so when it reads 70, I know I'm going 74).

70mph on speedo = 67mph actual
80mph on speedo = 77mph actual

[Mainerunr]

keep in mind that every instrument has a level of accuracy when it is built. The tolerance may be that it reads +5%, -0% or something similar because if it reads low, you could end up with legal problems, if it reads high, not so much. Now, I have no idea what the acceptable tolerance on a speedometer is but I doubt that they are required to be more accurate than say +/- 2%. The more accurate the instrument, the more expensive it is as well.

Also, just because the vast majority seem to read +3-4mph does not mean that all are like that (as I said, mine was off by 1% before I got new tires).

One other comment that goes back to the days when I was running. I used to clock my loops with my car but I would always round the mileage down because it's pretty well known that vehicle odometers tend to read high (every car I've ever owned has read high). I actually wheel measured a couple loops and always found them to be 3-5% shorter than what the odometer had said (for those who dont know, wheel measuring is extremely accurate, nothing more than a wheel with a very accurate circumference and a rotation counter).

And one last thing. Your if your speedo/odo read high now, they will be off by more when your tires are worn since your tire diameter will be smaller. tread wear alone can result in 2-3% variance in readings between new and worn tires.