Speedometer miscalibrated?

[DannyvanDelft]

Speedometers are required by law to read higher than you're actually going. That way if you get a ticket for speeding, you can't blame the manufacturer that your car was saying you were going the speed limit. Every speedometer is off by a little.

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[spyder40]

do measured mile testing,

you'll likely find the odometer is not cheating you.

mph is ~2 off but odometer on my rav4 and 4runner is giving me free tenths
over 5 miles, so no, my 36,000 miles displayed is not occurring at
less than 36,000 miles. I got bigger tires to fix the displayed MPH and
now I get even more 'free tenths ' on odometer

Since the odometer doesn't do tenths I should probably try like a 10 mile test so it's a little better attempt

 

[127.0.0.1]

Since the odometer doesn't do tenths I should probably try like a 10 mile test so it's a little better attempt

have you seen the trip meter ?

 

[spyder40]

Doh

have you seen the trip meter ?

Doh.....yeah. Forgot it's in tenths Still thinking do a 10 mile test so it's a little more accurate

 

[Gumpus]

Speedometers are required by law to read higher than you're actually going. That way if you get a ticket for speeding, you can't blame the manufacturer that your car was saying you were going the speed limit. Every speedometer is off by a little.

Yes. According to the Michigan State Police my Volvo was only doing 86 when I thought I was doing 90. I was still happy to get off with a warning.

 

[NotApplicable]

Speedometers are required by law to read higher than you're actually going.

This sounds like a myth. Manufacturers likely do this for liability purposes but not because a law exists that forces them to. I suspect the law simply states that an odometer can’t read under the actual speed, but that they are free to read over the actual speed.

 

[127.0.0.1]

This sounds like a myth. Manufacturers likely do this for liability purposes but not because a law exists that forces them to. I suspect the law simply states that an odometer can’t read under the actual speed, but that they are free to read over the actual speed.

strange thing is my '99 4runner, 2010 yaris, 2013 tacoma are dead on accurate on OEM tires

only my 2022 rav4 and 2025 4runner have this ~2mph deviation. for whatever reason.

so I did some tire calcs and installed bigger meats to get close to accurate

 

[Nodak]

also federal CFR rules give oem's a big leeway to fall within specs.

speedometer must be accurate to within plus or minus 8 km/hr (5 mph) at a speed of 80 km/hr (50 mph)

so they can be as far as 5 mph lower than displayed speed, they usually dont do higher due to liability lawyers.

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