Speedo error

[richj11]

Well, I finally got the GPS in the 80 to check my speedo. After reading many posts about speedo correction, I was expecting to see some kind of percentage (X %) error in mine.

What I did see was an 8 MPH error straight across the board. When the speedo read 20, the GPS said 28. When the speedo read 70, the GPS said 78.

I have 31's on currently, when I measured the diameter, it was just shy of 31". I'm not sure what would have been stock size tires on a 91 FJ80. When everyone else is talking about a percentage error, I'm reading the same error all around.

Does this make sense? I guess I'm just a little confused by everything I've read. I'm doing a little more digging in the FSM now...

 

[landtank]

so when you were parked you were going 8 mph.

 

[richj11]

Now that is FUNNY! Doh! I had to run out and check, but, it is sitting at 0 when parked...

 

[MoJ]

8 MPH is quite a difference given the tire size you mentioned and it doesn't make sense that it would be a linear 8 mph. For instance, with a 2" difference in tire size my speedo reads 5 mph low vs GPS at 70 mph (speedo says 65, GPS says 70 and radar signs on the highway agree with the GPS). I'm speedo gear corrected for 33" tires but running 34.9" tires.

I believe your GPS is to blame.

 

[richj11]

Really? I maintained the speed long enough to verify the GPS had a good speed reading....

I don't know the full history of the vehicle, maybe a PO could have tried a correction, or maybe the speedo is just wacked.

 

[Beetleman]

31" tires are the stock size for 80 series FJ. It doesn't make any sense that your speed difference is the constant/same at all speeds. The difference in tire diameter results in different speed readings, and it will be a percentage difference.

Here's is another way for you to test both your speedo and GPS. Drive on an interstate hwy with mileage markers. If you go 60mph, you should hit the next mile marker after exactly 60 seconds. I suspect you'll find your GPS is incorrect.

 

[rgsiii]

On my trip out west, my GPS proved that either:
1)I own the land speed record for the 80 series
2)When I got sleepy, I drove off an overpass
3)when I went to sleep at a rest area, I was victim of an alien abduction
4)GPS' can have errors

Maximum speed 119 MPH--yeah.