Speedometer Error

[conez0]

When I picked up this car (first drive home) it didn't have a lot of gas in it so I drover conservatively. 60mph in a 60mph zone. I noticed that an awful lot of people were whizzing by me. I figured "my, my the tacoma people are in a rush today!"

Then I took out my phone and opened the GPS Speedometer app and found I was going about 5mph below my indicated speed. After some further testing I concluded that its a constant 5mph below.

I've heard this is typical? Is there any way to rectify this other than getting slightly larger diameter tires?

If not I guess I have a "5 over" speedometer.

[mauryc]

Typical? Hmmm.... What is your tire and rim size and is the total diameter equilavent to stock?

[tlister67]

Mine read about 5 mph under when I put wheels/tires from an E39. In your case I am guessing your tire diameter is smaller than spec. I think this happens often due to the original metric wheels.

[conez0]

what is stock tire diameter?

I'll have to double check but I think I have 205/70R14s on there now.

[ldk]

So, if you're actually going 15, your speedometer says 20. If you're going actually going 60, your speedometer says 65.

If that's the case, then your speedometer needle needs to be taken off and replaced 5 mph counterclockwise.

There are lots of posts here and elsewhere on getting the instrument cluster out, mostly about changing the SI batteries or replacing the odometer gears.

[CW6er]

I wouldn't mess with it.

The size of the original rims and tires that came from the factory:

...................................... Rim Width x Diameter - "ET" or Offset (mm) - Tire Size
Stock wheels ('76 to '81) .............. 6" or 6.5" x 14" - ET22 with a 195/70 -14" tire that has a diameter of 24.74"
Stock wheels ('82 on) ................... 6" or 6.5" x 14" - ET22 with a 205/70 -14" tire that has a diameter of 25.30"
TRX (165mm x 390mm) ................. 6.5" x 15-3/8" - ET22 with a 220/55 -390 tire that has a diameter of 24.88"
TRX (195mm x 415mm) (M6) ........ 7.5" x 16-3/8" - ET19 with a 240/45 -415 tire that has a diameter of 24.84"
TRX (210mm x 415mm) (M6)† ... 8.26" x 16-3/8" - ET15 with a 240/45 -415 tire that has a diameter of 24.84" (early "///M" rim)

[conez0]

Thanks,

My error must not be from the tire sizes. I believe mine came with the 14" wheels stock. Even if it did come with the TRX's the speedometer reading would have gone down not up.

I don't want to mickey mouse around with moving the needle. There is no way to calibrate the speedometer since its electronic?

[Bert Poliakoff]

Take it to s speedo shop. They have a machine they put it on see where your speedo is reading at a given 60 mph and then re set the needle!!

[conez0]

Take it to s speedo shop. They have a machine they put it on see where your speedo is reading at a given 60 mph and then re set the needle!!

Is this expensive?

[ldk]

I'll try not to take offense that my solution was described as Mickey Mouse. It would be a perfectly easy thing to do, as the needle just presses on anyway, and you wouldn't ask how expensive it is.

[Bert Poliakoff]

+1. If moving the needle is Mickey Mouse, then all of the speedometer shops must be too, as this is the standard for doing a calibtration.

[conez0]

Not trying to offend anyone, its just a phrase use a lot, maybe too much. Is it really easy to move the needle?

[TJC1]

I'd have to agree with Chris (CW6er), what benefit will you get from going through the trouble of correcting the speedo by 5 MPH? Since you know how far the speedo is off you can certainly mentally correct for it in your every day driving.

As an aside we recently sold our '80 VW Westy and the speedo (not the odo...it was correct!) was reading high by about 12 MPH...from a psychological standpoint it was pretty cool as we could "bury" the 85 MPH speedometer when on the Interstate and could just dismiss everybody else that were passing us as must have been going 100 MPH!!!

[conez0]

I have to admit its not that bad, I just figured if its something that can be corrected with 1-2 hours of work I'd try and do it.

I gotta say I prefer the error being high rather than low. Its a bit of a letdown if you are trying to max out, but for normal driving it helps me be a bit more economical.

My previous car had slightly larger tires on it so the speedometer read about 4mph slower. Had to be careful not to speed too much over the limit on that one...