Does Speedo off equal Odometer off?

I noticed when I had my GPS in the Tacoma the other day that my speedo is off by about 4-5 mph at 75, so I was actually only doing about 70. Since I know this now I don't really care enough to spend money to fix it unles my odometer is also spinning faster than I'm actually going.

What do you think? I called a dealership, but of course they haven't called me back with an answer. Thanks in advance.

 

No it does not.

 

That is the response I was hoping for!

So the odometer uses a different system than the speedo? So what happens if I decide to do bigger wheels and tires? Is the odometer system something that can be adjusted to account for changes in wheel and tire size? Thanks again.

 

look here for more info: http://www.tacomaworld.com/forum/technical-chat/39999-new-take-perspecive-speedo-error.html

 

I don't understand how the odometer can be a different system than the speedo? Please explain.

My gps mileage is proportionately off in relation to my odometer in the truck.... same with speed. I get 1.1 miles on the GPS for every 1 mile on the odometer. This same amount can be translated on my speedometer. When I'm doing 60 on the speedo, my gps reads closer to 64.

I've done the math calculations, both are off proportionately by 1.07 or so.

I think you read that wrong.

 

I am pretty sure that there is no fix here. The reported problems ( do a search here ) are too random.

For example, my '09 TRD/OR AC ; the speedo needle is dead on with my GPS, but the odometer is slow by about 4.XX % ie: 104 on the GPS is 100 on the odometer.

The analog needle is error prone just becasuse it is a digital to anlog conversion; also, if you pay close attention at verious speeds you will see it is not a linear error; even more difficult to mitigate.
The odometer is a seperate circuit which probably has a differant set of operationsl specs then the speedo.

The speedo and the odometer are not taken from the same data set as it used to be when there was only a cable from the trans. ( or right front wheel, early VW ) to the speedo head and a set of gears drove everything.

 

If your speedo is off the odometer is also off. It shows you going faster then you actually are, so it thinks you're covering more road then you really are.

 

Here is an answer from Chris from another thread;

 

If you search "speedometer" along with "odometer" you will get two pages of threads on this. Should be some good reading but some threads have more info than others.

There is a tire calculator to figure out the speedo differences as well; http://www.tacomaworld.com/forum/tirecalc.php

have fun

 

Hmmmmpph... I give up.... I'm content in knowing that my odometer spins slower because of my larger tires, so I sleep better at night.

 

Also keep in mind that no matter what GPS you are using there is a +/- of error when it comes to speed, distance traveled, elevation, as well as where you are in reference to 6 8 and 10 digit grids...also didnt i hear somewhere on these threads that if you get bigger tires your odometer will be affected and you will be traveling more miles than what it reads? correct me if im wrong but i know i read that here somewhere.

 

Not necessarily. The magnetic sensor in the transmission detects output shaft revolutions and sends pulses to the computer which it uses to calculate speed & distance. It then sends this data in the form of a digital signal to both the speedometer where it is converted into the analog movement of the speedometer needle, and to the odometer where it is directly displayed. It's possible for the digital-analog conversion at the speedometer to be inaccurate while the odometer is accurate.

It's easy enough to test with a GPS - and/or by using interstate mile markers & a stopwatch (or a watch that displays seconds). Drive an indicated 60 MPH (one mile per minute) and when you pass a mile marker, reset your trip meter (or make a mental note of what it's reading) and start your watch at the same time. Hold your speed at exactly 60 MPH indicated and you should hit the next mile marker in exactly one minute - and your odometer should click off a mile at exactly that same point. If your watch hits one minute before you get to the next mile marker, your speedo is off... you're going slower than 60 MPH. If you REALLY want to test it, do that for 10 miles. You should hit exactly 10 minutes and 10 miles at the 10th mile marker.

It's very possible for the speedo to be off while the odo is correct though.

 

That's the key point. The speedo & the ODO are coming off the same sensor.

If one of them is off, they're both gonna be off.

People need to realize - the speedometer on the dash (needle) is NOT the actual data. The needle is just a visual for the driver. If the needle isn't calibrated accurately to the numbers on the dash (for a lack of a better way to explain it), then the needle will always be 'off'.

That's another benefit to owning a Scangauge - you see the actual data from the computer. On my truck, the needle is 2mph slower. My GPS & the Scangauge MPH data matches.

 

Well my truck does what I see the majority of other Tacoma trucks do, the speed reads a little high (by the way almost all cars do) by 1-2 MPH over the 25-70 MPH range. The Odometer is always the same, reads .1 miles less than actual mileage for just under a 10 mile strech.

What does this mean:
1) Your ODO will reflect less mileage than you actually drive on new tires but as your tread wears I suspect it will be close to actuale miles driven.

2) Like so many other cars on the road, the speedometer does not read true speed, most actually say you are going faster than you are. I don't know of a mechanical reason this occurs unless they factor in you could use a larger tire, but I doubt that. I like to think it's a way to keep you under the speed limit, even when you think you are speeding.

I think we answered the thread starters question.

For the few of you saying you have the opposite problems, I strongly suggest you use a different GPS and double check your facts. If you have a problem you should clearly contact the dealership about it.

A little history... Honda had a problem in thier 2002 Accord (could be more but that was all that affected me) line where the ODO recorded more than actual mileage and a law suit occured. The result was the warrentee was extended by 5000 miles.

-Joe

 

I think we agree... but I'm confused by your statement that "If one of them is off, they're both gonna be off." That's not true. The computer can be calculating the speed & distance correctly based on input from the transmission (as long as you're running stock-size tires) and sending that correct data to both the speedo and the odo, but, like you explained, if the analog speedometer is not displaying that speed accurately due to a calibration problem or whatever, it's possible for it to be off, while the odometer displays the data correctly and counts off the miles accurately.

At any rate... it's easy enough to check.

 

People were thinking the two (speedo & odo) were two different systems.

They're the same and the info comes off the same sensor.

I was simply trying to say, if one of them is inaccurate...the other one will be inaccurate also (and I'm only talking about actual data in the ECU). I keep forgetting that people only have the needle to use as a reference to compare to. In most cases, that needles isn't accurate to the data in the ECU.

 

It's probably a manufacturer decision to have the needle indicate higher than the true speed as a liability protection. If it were set too low, they could be held liable for any speeding tickets issued. If they have it set 2-5 mph high, you can't really claim it's their fault for a speeding ticket. My guess is most manufacturers would do that to protect themselves.

Plus it may be something that helps customers get closer to the indicated mpg ratings (if you're driving slower, you'll get better mpg).

 

When using my Acutron Scan Tool I can read the ECU data and the MPH data and the needle does not match. In my perticular case, the ODO reads .1 miles less over ~10 miles (a good thing). The needle does indicates faster MPH. These are inverse values. The needle is off and it could be in the D/A circuitry. Just because the needle is off does not mean the ODO is off or even off in the same direction.

Your statement about if one is off, the other will be as well is inaccurate and you're not stating facts but it sounds like you're making up facts.

I'm not trying to offend you but when reading these forums, people don't need others making up facts. If it's an opinion then make it clear.

Now I do agree that most people probably do not have a way to read the ECU so the needle is thier main guide, but the ODO is there too and they can use a GPS or miles markers over a long drive to get an idea of the ODO accuracy.

I also agree the needles are not accurate in most cases but I cannot state a fact they all are.

-Joe
P.S. Damn, you have some nice cars on your website! Wish I could afford the vetts.

 

Analog can be inaccurate due to your line of sight on the guage, just because its an 'analog' meter....its still fed by a digital signal. Sure, the needle can be off, or miscalibrated, but in the end its ONE signal.... we've all agreed on that I believe.

Honestly, you guys are reading wayyyy to deep into this. I've personally done my math, and some of your research only backed up my findings. My speedometer is accurate to my odometer.... why? Because I traveled a whole damn tank of gas and compared the simple math between the two. The 'error' is the same between the two. 107/100 is my error (gps to odo/speedo). If your needle is off, thats a whole 'nother issue that you should get resolved at your dealership. It won't be caused by tires. Am I reaching anyone here?

Probably not.... I suck at explaining things.



ONE INPUT....

TWO OUTPUTS.... simple as that.


Also please keep in mind, my 'error' is not going to be the same as everyone elses, I'm running 285's.