Speedometer off by five miles Civic EX '00

[Machin19dXvida]

Hello,

I drive a Honda Civic 2000 EX, everything is stock, the car has not giving me problems.

I have noticed on road trips that as I go 70mph on the freeway the car actually goes 65mph so I always now go 75mph so that the car actually goes on the speed limit of 70mph.

How can this be fixed? Why does this happen?

I feel this is dangerous and/or risky since I want to know my speed to not get a ticket or miscalculate my speed

Thanks all for the help in advance.

[theholycow]

If it's truly off by 5mph, then take it apart and adjust the needle.

More likely, it's off by ~10%, which would be a result of using the wrong tire size or changing the final gear.

[RITmusic2k]

To elaborate on what theholycow said*:

It's either a scaling error or a positioning error. If the speedo says you're doing 5mph when the car is stopped, then the position of the needle just has to be adjusted. If it starts at zero and is ~2.5mph fast at 35mph, 5mph fast at 70, and so on, then it's scaled incorrectly.

There's a little % error to be expected in all cars, but yours does sound a little too far off. Most likely your tires are smaller than what came from the factory. You might be able to get it adjusted electronically if a local Honda mechanic has the computer needed to interface with your car. Often times these days, your car's ECU comes equipped with a few different speedo scaling factors to account for the different wheel/tire options provided with different trim levels for the car. Maybe one of those will match your current setup more closely.



* - because I'm good at saying in many words what so many others are good at saying in many fewer words

[theholycow]

* - because I'm good at saying in many words what so many others are good at saying in many fewer words

Hey, that's my job! I'm usually the one spouting endless hot air!

[Machin19dXvida]

I see. Well more than likely is probably adjusted incorrectly since the neddle marks zero when the car is stopped and not five. Do you think by switching to correct tire size the car will fix itself?

I dont know how to take car parts apart. Is there a better and cheaper method than going to the mechanic?

Or is that the only option?

Where could I get more in detail information on this issue?

Thanks

[LHOswald]

you could get more detail about this issue from a honda dealership, or a honda forum.

[VTECaddict]

well, do you have the correct tire size on there right now or not?

mine reads high too, but it's by design apparently.

[LHOswald]

so you feel like your going super speedz?

[theholycow]

What size tires are on the car? Tire Rack says it should have 185/65-14. Post the complete set of numbers like that, not just one of the numbers.

If you want to stay with your current tire size, the appropriate way to adjust the speedometer is probably with a custom computer tune. With the popularity of modifying models like yours, there may be cheaper alternatives and well-documented hacks, but you'll have to google Honda forums to find them. You'd have to do that anyway to find out what downloader you should buy or custom tuner you should hire.

[FDSpirit]

I sent you a couple of links in one of your earlier topics in a different section. I suggest downloading that manual and seeing if it says anything.

[LHOswald]

wait how do you even know your speedometers off? did you have someone track your speed with a laser radar gun? because thats the only way to get it down within a tenth of a mph

[vedran]

wait how do you even know your speedometers off? did you have someone track your speed with a laser radar gun? because thats the only way to get it down within a tenth of a mph

probably via GPS

its most likely your tires. my speedo is off by 5-7% too

[carsncars]

I know for European cars, speedometers are regularly set 5% above on purpose--EU law levies heavy fines on "too slow" speedometers, but the margin of error allowed for "too fast" speedometers is bigger. Thus manufacturers target it slightly fast.

That said my '98 Civic (which is the same basic model as yours) reports its speed spot on. So there's something up there.

[Rope-Pusher]

take a felt-tipped pen and write a new set of numbers on your speedo gage bezel, in the positions you have previously determined to be correct for each speed value.

[AHTOXA]

Up to 10% margin of error is considered normal for car manufacturers and is not likely to be replaced as defectve. Many cars suffer from that and most owners do not even know about it.