2009 Genesis 4 door, v-6 sedan's speedo 5 MPH too fast.

[CWP]

The tire size is factory spec. If you set the cruise control at 65 MPH the actual car speed with be 60, Checked this at various speeds and methods and it is right at 5 mph off. Any thoughts?

 

[Mark_888]

Do you mean the car slows down to 60 after you set the cruise control at 65? Or are you comparing the speedometer to a more accurate source, like a GPS that calculates speed, so when the speedometer says 65 the real speed is 60?

 

[EdP]

The tire size is factory spec. If you set the cruise control at 65 MPH the actual car speed with be 60, Checked this at various speeds and methods and it is right at 5 mph off. Any thoughts?

It is within legal limits though a bit more than most.

Each bus, truck, and truck-tractor must be equipped with a speedometer indicating vehicle speed in miles per hour and/or kilometers per hour. The speedometer must be accurate to within plus or minus 8 km/hr (5 mph) at a speed of 80 km/hr (50 mph).

[ 70 FR 48054, Aug. 15, 2005]

You may want to double check with a GPS. They are pretty accurate.

 

[CWP]

Do you mean the car slows down to 60 after you set the cruise control at 65? Or are you comparing the speedometer to a more accurate source, like a GPS that calculates speed, so when the speedometer says 65 the real speed is 60?[/QUOTE
what ever the speedo is reading it is 5 MPH slow. In other words, if speedo is showing 45 actual speed is 40.

 

[Mark_888]

what ever the speedo is reading it is 5 MPH slow. In other words, if speedo is showing 45 actual speed is 40

Normally, a 2009 Genesis era speedometer reads about 1 to 1.5 too high by design. I guess your speedometer is off by more than that, maybe because it is 9 years old.

I assume you checked the actual speed with a GPS unit that you know is fairly accurate.

 

[CWP]

I have not done that with GPS. I have checked with mileage markers and other vehicles. And it seems to be right at 5mph off

 

[Mark_888]

I have not done that with GPS. I have checked with mileage markers and other vehicles. And it seems to be right at 5mph off

If you want to know exactly how far it is off, see if you can borrow a portable Garmin GPS.

If your speedometer is not accurate, I don't know what parts to replace that would fix it, but I am pretty sure it is not worth fixing once you calibrate it to a known source.

BTW, if you have not owned the car since brand new, what trim level do you have (Base, Premium Package, Tech Package). What are your tire sizes.

 

[CWP]

I bought the car used. I did replace the tires to the spec on the door post. I didn't check the size that was on it. I'll see if I can get hold of a GPS and check it out that way. But you are right, likely not worth screwing around with it. I thought that there might be some sort of re-flash that could be done to correct the problem. Thanks for your thoughts.

 

[Mark_888]

The 2009 Genesis V6 had either 17 or 18 inch wheels, depending on trim level. Here are the OEM tire sizes:

• 225/55/R17 - Base Trim Level
• 235/50/R18 - Premium and Tech Packages

Just between those two tire sizes, there is 1.3 MPH difference at 60 MPH. Plus, if there is any wear on the tread, difference could be larger.

 

[dougmcp]

Manufacturers set their speedometers to read slightly low for legal liability reasons and it's the most common complaint on auto forums. Most are fairly close to accurate (+/- 2%) and very rarely do you find them any more than 5% off which is 3.5 mph at 60.

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