speedo way off

I have stock tires on my 07 that match the door sticker and my speedo is off by a good margin. 65 mph (gps) indicates 71 mph on the speedo. Whats up?

 

That is a greater difference than most, but it isn't unusual for the speedometer not to be accurate. In fact it is impossible for them to be accurate 100% of the time with today's technology. We just never knew it before GPS.

Most people, including myself found the speedometer to be more accurate after we upsized to 1 size larger tire. It's almost as if Toyota expected owners to go to a bigger tire.

But tires get smaller in diameter as they wear down. If you were to get everything calibrated to be accurate with new tires the speedometer, and odometer would slowly change as your tires wear down and get smaller. By the time you've worn the tires to the point where they need to be replaced you are effectively one size smaller than you started with and the speedometer will show you 2-3 mph faster than your GPS.

I'm betting that your current tires are worn and are needing replacing soon. From the factory most Tacoma's show you 2-3 mph faster than a GPS. Add another 2-3 mph due to worn tires and that would explain the 6 mph difference.

 

Tires are brand new with less than 5k on them. Old tires that came off indicated the same reading. I’ve just learned what speed I’m actually going at what’s indicated and adjust accordingly

 

Maybe it was regeared or someone put the wrong ratio rear axle in it.

 

I wouldn’t like the fact that you are racking many more miles on the odometer than it really has…

 

My point exactly. Axle differences are possible but unlikely. Plus calculating MPG is nearly impossible. Now, whats the fix?

 

Do you have a scan tool that can read live data so you can see if it's actually reading wrong or if the gauge is just off?

 

Have access to one
I’ll try that

 

Here's a spec to look up. e393.82 Speedometer error.
It states: "The speedometer must be accurate to within plus or minus 8 km/hr (5 mph) at a speed of 80 km/hr (50 mph)."
That is 10%, so I assume at 70 mph it could be off 7 mph. I doubt if manufacturers are ever off on the plus side as they wouldn't want consumers suing them for getting caught speeding. It's another reason you don't drive in the left lane unless you're passing slower traffic. The drive could have a more accurate speedometer. I have found my vehicles to read about 2 - 3 mph slower at 70 mph and much closer to the actual speed limit at 30 mph.

 

Thanks folks. All good info

 

1. All tires are not made the same
2. That is inside the margin for manufacturers specs though it is on the high side
3. I've never had a car speedo that didn't read on the lower than actual.

 

Speedo is measured off the wheel sensor as it is not affected by axle ratio.

Did you put 245s on instead of 265s or something? Might have both sizes listed on the sticker.

 

I use this Hypertech speedometer calibrater. It installed between the ribbon cable running to the back of your instrument cluster so you'll have to disassemble your dash a bit to install it. If you run a longer USB cable down and let it hang below the dash, you can hook up a thumb drive to that to flash the module without needing to take apart the dash again which would be helpful if you are trying to tweak the tire settings. Yes, I understand that you are running stock tires so there shouldn't be a reason to tweak the tire size on the computer, but if you want to play with the numbers on the program you can dial in a closer speedometer reading. The thing is, if you're using an OBDII reader, the computer will be reading one speed while your dash will read another. It may be a bit overkill for your use though.

-J