4th Gen 4Runner Speedo/Odo/Computer Error tested....

[Duc Hunter]

I recently took a road trip and thought it would be fun to really test out the whole Odometer, speedometer, computer MPG calculation errors. What I discovered was quite surprising.

My vehicle is a 04 Limited V8 with a 4 inch lift, 265/70/17 Revo

 

[live4swell]

Very interesting find...I always wondered if mine would be off after I installed my daystar lift and 265/70-17 Revos. Good job with the data

 

[cmj685]

My question is, should you accept the GPS mileage as the gospel, and assume that it is the odometer that is wrong? If so, why? Is it the illusion that the GPS is higher tech and therefore must be right? I run GPS on all my trips(last one was 3500 miles in April) from the navigator seat where I monitor the various onboard, added and modified instruments carefully and don't have to worry about driving at the same time. There is always some discrepancy between the GPS and the odometer, and in some cases, I know it was the GPS which was wrong--didn't get reception at some point along the way (under thick tree canopy for example, or in canyons or in the mountains), or didn't locate satellites quickly as we drove off, or I forgot to turn the GPS on immediately or any number of other reasons.... My view is that it is every bit as likely that the GPS may be off a little bit as that the odometer is. After all, which is more likely to be right: estimating a distance from a thousand miles away, or laying a ruler down right on the road?

 

[The Razor]

For me I will be buying a Yellow Box to correct this and I will set it so that the ODO is dead on.

What exactly is this yellow box? Is it a tool to correct the speedo due to different wheel and tire combo's? If so please let me know where I can pick one of these up.

Thanks,
George.

 

[boston_kevin]

My question is, should you accept the GPS mileage as the gospel, and assume that it is the odometer that is wrong? If so, why? I

I don't think it has anything to do with the technology involved. He added larger diameter tires which, unless you reprogram the computer with the new diameter, will be off because the computer in the truck thinks the tires are the same size it was equipped with. GPS is extremely accurate, but it depends on how you set it up and how often you take measurements (it is not always beaming information back and forth), so some amount of error is expected when calculating distances along non-straight and non-level paths, but this can be minimized with an aggressive polling cycle of the satelites.

I have not upgraded my tires yet, but my GPS is setup to take measurements every 10 seconds when it is plugged into the car, and it is very accurate (a measured mile is exactly 1 mile according to the GPS).

 

[Bobby]

I've been playing with a Magellan eXplorist 600 for a few weeks now and I've seen the same speedo difference. About 1mph higher than indicated @ 60mph with a 2.5" Daystar lift and 265/70 Revos. I didn't go into detail like DucHunter but I would think he's just about right with his calculations. I'm just too lazy to do everything he just did .

 

[TeryT]

Has anyone done a good gps check of the stock tires with odometer & trip computer? By comparing the two I consistantly get about 10% error in that that the trip computer is too optimistic on the milage (which everyone knows).

 

[boston_kevin]

I did a comparison, but not against the trip computer. Once in a blue moon that will be close, but I consider it a toy. All of my passengers get in and see the average MPG reading at 26.5 +/- 0.5 and tell me they love this SUV. (I'm actually getting around 24 MPG, but I'm not telling them)

 

[TeryT]

I did a comparison, but not against the trip computer. Once in a blue moon that will be close, but I consider it a toy. All of my passengers get in and see the average MPG reading at 26.5 +/- 0.5 and tell me they love this SUV. (I'm actually getting around 24 MPG, but I'm not telling them)

24 MPG!!?? I hate you V6 guys! So if you tested it, how accurate was the speedometer & odo?

 

[boston_kevin]

Odometer was dead on (to the .1 mile which is as accurate as it gets). Speedo also matched (as close as I could tell) GPS. I am going to test the GPS with a State trooper friend who has a laser. We should be able to verify the GPS to 0.1 MPH, speedo will be almost impossible to verify to any accuracy greater than 1-2 MPH due to needle position and perceived location on the gauge.

 

[khaug]

Duc:

I checked the speedo and odo accuracy of our unmodified '03 Limited using both GPS and Interstate mile markers. The speedo was dead accurate, while the odo under-reported mileage by 2.5%. The results from GPS and mile marker checks exactly matched each other, so I think they were probably accurate.

This sort of matches your results, in that the odo error is 2.5% worse than the speedo. It looks like your tire size increase has introduced about another 2.5% error. Since the error magnitude is different between the speedo and the odo, I think you'll be able to correct one or the other but not both. I've come to think of my odo error as a free 2.5% extension of my warranty!

I regard the mpg function on the trip computer as pure fantasy and marketing hype. Mine varies between 8 and 15% optimistic, seemingly at random. Since the error is variable, I don't think it'll be correctible.

Regards,

 

[Bluto]

Duc:
The speedo was dead accurate

Same here.

 

[boston_kevin]

strange that the odometer and the speedo are not giving equal results in some cases. Aren't both of these calculated from the same feed from the tranny? The trip computer and all of it's functions (including range) are definitely off, by approx 10% (in my case), but the trip odometer was dead on to the 0.1 mile. Hmmmm.... now you have me wondering about this. I wonder if they are doing the calculation for the odometer somewhere else... Anyone know where the feeds are for the odometer and speedo?

 

[Offroader]

My 2005 T4R has different readings from the speedometer and computer.
I've set the speed on cruise control at 60 kph, reset the computer, and after 10 seconds, the computer reads "52 kph average speed". This makes me wonder about the fuel consumption readings.

 

[TeryT]

My 2005 T4R has different readings from the speedometer and computer.
I've set the speed on cruise control at 60 kph, reset the computer, and after 10 seconds, the computer reads "52 kph average speed". This makes me wonder about the fuel consumption readings.

It's been long established that the trip computer is overly optimistic by around 10%.

(Just saw you had a turbo diesel!? Where can I read about that!?)

 

[jharris2]

Same here.

Same here, but I always wonder how accurate the mile markers are.

 

[khaug]

Same here, but I always wonder how accurate the mile markers are.

We had a neighbor who was a highway engineer for Michigan's Dept of Transportation. I asked him that question and he said that there is a Federal accuracy standard for Interstate highway mile markers. I no longer remember what he told me the standard was, but I do remember being impressed at the time.

Our GPS mileage exactly matches the mileposts on I-69. I ran the check for a full 10 miles, so any discrepancy between the mile markers and GPS would have shown up. I think the mile markers are very accurate.

 

[TeryT]

Ditto - Odo under by 2-3%

Duc:

I checked the speedo and odo accuracy of our unmodified '03 Limited using both GPS and Interstate mile markers. The speedo was dead accurate, while the odo under-reported mileage by 2.5%. The results from GPS and mile marker checks exactly matched each other, so I think they were probably accurate.

This sort of matches your results, in that the odo error is 2.5% worse than the speedo. It looks like your tire size increase has introduced about another 2.5% error. Since the error magnitude is different between the speedo and the odo, I think you'll be able to correct one or the other but not both. I've come to think of my odo error as a free 2.5% extension of my warranty!

I regard the mpg function on the trip computer as pure fantasy and marketing hype. Mine varies between 8 and 15% optimistic, seemingly at random. Since the error is variable, I don't think it'll be correctible.

Regards,

I got roughly the same results on a trip today. With my fully stock set-up, the odometer consistantly under-reported mileage by about 2-4%. In several 10 mile stretches it would read 9.6 or 9.7 when the 10 mile marker came up.

I didn't have the GPS (brother-in-law borrowed it) for the trip, but checked my watch. With the cruise set at 60 MPH it would clip off the miles right at 1 minute. The odo would start to lag after the 1st mile. (BTW - the trip computer consistantly said I was going 59 MPH.)

A couple places I sware the mileage marker installers must have been drunk, because every so often a marker would turn up way early by both my watch & the odo! The GPS would have confirmed this.

I'll have to check again when I get the GPS back next week.

 

[Offroader]

My case is even more RIDICULOUS. :bash:
The 4Runner's own speedometer indicates a constant speed of 60kph, and the computer indicates 48 kph average speed.

 

[Atlanta_man]

I get a kick out of the concept of a Federal accuracy standard. I worked for a year in Tucson a few years ago.

The Interstate that goes South was selected as a Metric Awareness section. Funded by the Feds (of course).
Implemented by AZ.

They put color and font matched stickers over "mph" and "miles" on all the signs. The stickers said kph and kilometers respectively. They did not change the numbers, just the units labels.
It stayed this way the whole time I worked there.

Nobody noticed that 1 mph does not equal 1 kph ? Maybe it was a stealth IQ test of sorts.