Speedometer error (says faster than real speed)

Bought an 08 Tacoma base model used. 4 WD, 4 Cyl, Manual transmission. Quickly discovered that when going (what I thought was) 65 MPH I was actually going 59.7 MPH. So I did quite a few time trials and determined my speedo was off. WAY off. And not consistently off by any given percentage. If it were 3% it would be 3% at 10 MPH, 20 MPH, 60 MPH - heck, it'd be off 3% at 100 MPH. But that's not the case.

Checked ring & pinion; factory 4.10-1. No after market electronic devices installed anywhere along the wire harness.

Here's what I found in time trials: When going 45 MPH (according to the speedo) I was actually going 41.3 MPH. An error of 9%. At 50, 46.2, 8.2% error. @ 55, 51.4, 6.9% error. @ 60, 54.97, 9.15%. @ 65, 59.7, 8.8%. @70, 64.9, 7.8%. @75, 69.7, 7.6%. To recap the percentages; 9%, 8.2%, 6.9%, 9.15%, 8.8%, 7.8%, 7.6%. Error goes up and down (and back up again with later higher speed trials).

I did these tests over 100 miles of mile markers using a stop watch and a calculator. Actually I drove (with cruise control) while my wife took the time measurements and did the calc's. There were approximately 10 miles per speed range test and I had to go on different roads to safely achieve these speeds.

On the way home I noticed that for every 23 miles I went (approximately) the odometer would read out an extra mile.

I've repeated the tests using a dash cam with GPS speed so you can observe the actual speed and the actual speedometer reading and clearly see they are way way off.

I just put new tires on (OEM 245 75R16) but there has been virtually no change. Perhaps a half a percent due to worn tires before.

I've seen many people say "Yeah, I have that problem too". Great. But what I want is a solution to the problem. The first thing I would want (under warranty) is a new speedo since mine is all over the place (percentage wise). I also understand you can't re-flash the computer to a different tire size, but I thought I heard someone say there's a chip you can change or something.

Before I go tearing things apart I'd like to know more and more certainly what to do and how to go about doing it.

So I need your help. If you know of a solution, please share it with me.

Thanks.

Tony.

")

 

Get a GPS or scan gauge or ultra gauge and use them. My speedo is off, and according to Toyota, they can be a % off.

 

They all do that and there is no solution.

Check your odometer over 100 miles against a GPS, you'll likely find that the error is about half the speedometer error... not significant enough to have an impact on resale or the warranty period.
Japanese motorcycles are even worse, being off by as much as 15% on speed and 7% on the odometer.

Federal law allows for an error of as much as 15% on the "high" side. European standards allow NO leeway the other direction... the speedo must read actual speed or higher.

 

@ Impulse:

Thanks, but that's not the solution I'm looking for. I want to make my speedo work correctly. Otherwise I'm afraid I'll end up looking like a Delorian with a flux capacitor mounted on the back, and a long pole to catch lightning.

 

Get bigger tires

 

Pretty much every vehicle I have owned has been off on the fast side like you. Normally only just 2-3 mph off though.

 

Ya... My '03 Tundra was dead-on, but my '08 Taco is about 5mph high at 70.

 

@ Impulse:

I'd have to get WAY bigger tires to cover a 9% error. That would cost me a couple thousand bucks. Got any money laying around you're not using? We're not just talking tires, there's rims included because the standard 16 inch rim won't support a tire that big. And you have to consider wheel well clearances too. And no, I don't want to start doing major body work.

If you have nothing helpful to say, please enjoy the music.

 

You wanted ways to get your speedo accurate. Different size tires is one way.

 

@ Impulse:

''/

 

yup. your getting free help from people that have full lives outside of this forum. they are not responsible for searching and finding you the correct answer. without an offer for compensation, im going to still go out of my way and give you whats on top of my head.

265/75 gives you about a 3% increase and fits nicely in the wheel well.

respect the people, respect the answers, and put a little effort in yourself once in a while. otherwise, just enjoy the music

 

I do appreciate your research and math. I also share your concern about this. no wonder Toyotas last so long right, the damn things are liars!

na they are good trucks. running 265/75 brought me up to traffic speed with 70mph under the needle. that's about what people run around here without getting tickets so im a happy camper

 

You sure? Cause my Daytona 675 SE (Made in GB) has a significant speedo error.

 

@92DLXMAN:

I don't expect people to solve my problems, I'm asking of someone who has encountered the problem and knows of a way to fix it. Seems like some people merely read the title and come up with an answer without reading any of the particulars.

I have at times a 6.9% error and at other times a 9.2% error. Clearly this is not a mechanical issue, as I've contacted a shop that claims to be able to fix these. This guy wanted to bend my needle (basically) for $99.00. But that would mean that I'd have to be going 15 MPH before my needle would move off the peg. Getting tires of any size still doesn't correct the problem with the gage. And I agree with you, the truck hasn't gone as far as the odometer says it has. Probably two reasons behind that. First, you burn up the warranty faster, and second, as you eluded to, they appear to go farther.

This all makes calculating gas mileage a bit tricky too because it not only depends on the speed you travel it also depends on what the odometer is thinking.

I've heard something about changing a chip in the gage cluster. Wish I knew more about it but as a general habit, when I don't know - I ask. And when I ask for solutions I don't mean that (example) if the house is leaning to the left you just need to tilt the ground to the right. That's NOT a solution. And in my case, tires would have to be 295 75R16 in order to accommodate an 8.85% change in ratio to nearly completely zero in on an accurate speed. The next best size tire (and rim) would be a 265 75R18 (if they make such a size). But now it's a tire AND rim. 265 80R16 would give me 6.8% correction, closer, maybe even close enough, but a sidewall that tall would be flimsy as all get-go. It would be like riding a bicycle with rubber-bands for spokes. Steering would be impossible. And imagine what would happen in a good cross-wind. You'd be all over the place.

No, taller tires is an easy solution but it is not the right one. When your leg is broken you don't get an extra arm to compensate. You fix the problem. This case, the problem is the speedo. I'd get a new speedo but two things, first, they're $800.00. Second, I've paid for a warranty and the dealership doesn't want to honor it. So I'm thinking about legal action.

Unless I can find an easier solution. Fixing the speedo is what I'm after. Not taller tires, not a lower, more aerodynamic roof line, not a spoiler on the tailgate, the speedo.

Is that so hard to ask for? Help from someone who KNOWS how to deal with this?

 

If it is actually the cluster with the issue what about a used gauge cluster off eBay? Cost ~$200 give or take $100 or so.

Not speaking from experience though.

 

ok, the problem so far then is that of the people who have posted, none of us know.

what I know is that Toyotas are known for this. my truck, dads truck, moms runner, and numerous other people on this forum have encountered this problem. non of us have done the math to see if there is a fluctuation in percent-error. that is a problem far beyond my abilities to understand.

im not sure but I imagine speed is picked up by either a magnetic signal generator at tailshaft or a small gear on the tailshaft. obviously, either way that signal is then translated into something the speedo can understand. so your problem is in software, or maybe even the speedo motor itself. it is a margin of error inherent to the system.

now that im really thinking about it, im almost sure the signal is generated via gear. let me see if I can find you one with a different tooth number. that will however, not fix your varying percent-error, unless you are a hair off with your math. lets see if we can find you an 8% gear as that looks like a good median number

 

http://www.rocksolidtoys.com/forum/showthread.php?t=191

there you go. amazing what a bit of google does

 

My speedo is off 4mph on the high side, give or take. I haven't done the math. Just compared to what my GPS says. I thought it was my GPS, but 2 GPS's and my phone all say the same. Not too big of a deal to me but interested in the solution...

 

Great you guys. Thanks for the Dakota Digital. Not sure that's what I heard of before, but it should bring me much closer (and cheaper than tires and rims). I still wish Larry H Miller Toyota of Murray (UT) would agree there's a problem but they say I'm only off by two miles per hour. They're plugging their computer into my computer which is getting corrupted data from my speedometer, so how accurate can they be?

Nevertheless, it looks like the Dakota Digital will compensate for the error. As for the fluctuation - I guess I'll just have to wait for the cluster to completely fail.

Thanks. An answer at last.

")

QUICK COMMENT ON THE SPEED PICKUP: It's a magnetic switch located on the tail shaft. It's common to standard transmissions, and mine has been replaced already. Bout a couple months ago. Did nothing to fix the problem, and there are no different ring gears or sizes to compensate for tire sizes. Automatic transmission vehicles - the speed is calculated in part from a tail shaft but mostly from the speed sensed at the Anti-Lock Brake rotor sensors. If there is a disparity between the wheels and the transmission the computer SHOULD throw a code (or so I hear). Since mine is manual, there is a red wire coming from the sensor to the gage cluster directly. Not to the ECU. The ECU only gets what the Gage Cluster tells it. So corrupt data in - corrupt data out.

Thanks again.

")

 

cool let us know how it works out if you buy it. I didn't know it existed before today. . .

be a nice thing around here as a lot of us are under and even some guys are over-geared.