Just for ****s and giggles I down loaded a few of the gps speedo apps for the iPhone. I installed the 3 highest rated free apps so I could compare them to each other. Two out of the three showed the same speed and one varied by 1mph. As a control I tested them all with my cruise control 45 mph.

I was curious on how much my speedo would be off going from stock tires to 31's. To my surprise all three read either 45 or 46 mph. Virtually exactly what the speedo in the dash showed!

Is it possible that in stock form the speedo was that far off?

 

I have 31's and my speedo is pretty much accurate. I've tested on the radar trailers parked on the sides of streets and actual miles.

 

i've checked mine auto with 31s is about 4 miles off @55mph. at 45 it's less than 3 miles off. at 35 it reads the same.
my 5 speed is dead on with 30" tires at all speeds.

 

Thanks for the input, my Tacoma was the same way. Dead accurate going from 31 to 33" tires. I guess I wasn't getting nearly as good of gas milage as I thought when it was stock!

 

Try a higher speed, like 65. The difference will show more then

 

Yeah, I checked my Ford F150 with the tires that came on it (size 235x65r17) and the GPS said it was doing 60 and some tenths at 65. After I put a set of 265x75r17s on, the GPS said I was doing 64.9 when the speedometer read 65.

 

well mainly because 1-2mph off at 45 could be 5-6 mph off at 60

 

I will check it at faster speeds on the freeway in the morning. If its anywhere close to acurate, within a mph or 2 im not gonna mess with it!

 

we did the gps on my jeep after i lifted it and it showed that when my speedo was at 70 we were doin 87 so im suprised urs was right on, i had 29s on before the lift and it threw mine off by one mark... weird

 

Accurate within 1-2 mph at 70mph, I'm surprised at the results, speedo is way of is stock trim!

 

That is surprising. I'm on 31's and am off about 8 miles an hour at 70. 70 on the speedo = 78 actual speed.

 

Who knows what the previos owners had done to it before I got it!

 

Odd, if it was off by 1-2 mph at 45, it should be off by more at 70

 

That's about normal

 

It varied from app to app, 2 of them were spot on at 45, I just tried again with a garmin gps and it was 2 mph off at 70, I'm showing 70 gps verified at 72!