2012 Accurate Speedometer

[Midnightsun]

They have definitely changed the way the speedometer gets its speed readings and I am quite sure it is not from tire rotation as with almost all cars today that I know of.

I am the type of driver who likes to drive on the limit of being legal and correct speed is imperative or I will get a ticket. (Have no ticket in the last 7 years) I always check to see what the true speed is by comparing to my gps readings and on the genesis it is pretty much dead on, at least is is on my 2012 Rspec. My previous 2010 4.6 was about 1 mph slow however that is pretty close to accurate. Here is the kicker, I use snow tires all around and these were chosen to be the same size however on 17" rims so obviously not as low profile as the stock 18". After installation I checked with my gps and found they these tires were reading 3mph off. I called my friend at the tire shop and sure enough this was normal so to say.

Skip forward to my 2012 Rspec. My speedo is dead on and last week I installed my 17" wheels left over from my 2010 4.6. I was shocked when I put them side by side (19" stock vs 17" winters 225/55R17) as the stockers were at least an inch probably 1 1/2" taller. I was sure the speedo would be off substantially but the gps confirmed cruise set speed and speedometer speed to again be dead on.

Based on these finding I have to conclude speed is taken from the gps and even if I were to put on tires half the height the speedo would be accurate. This was not the case on the 2010 so somewhere after a change was made.

 

[brfatal]

There is no way your speedometer is streaming GPS data. If that were the case your speedometer would not work after start up until the connection is made or if you have poor reception (ie in tunnels or on mountains) Your GPS itself may track it in the head unit, but your gauge cluster is completely independent and in no way connected to the GPS antenna.

 

[Midnightsun]

There is no way your speedometer is streaming GPS data. If that were the case your speedometer would not work after start up until the connection is made or if you have poor reception (ie in tunnels or on mountains) Your GPS itself may track it in the head unit, but your gauge cluster is completely independent and in no way connected to the GPS antenna.

Maybe it is not but then can someone explain how come my speedo readings are identical match when I have different size tires? There was a rather large difference on the 2010 4.6 as I mentioned and nothing on the 2012. I can't figure this out either and assumed it was gps. I can however say that wheel/tire diameter differences do not affect the readings on the speedo. Lets try to figure this one out.

 

[Southern Boy]

Try going to this site to compare tire size to odometer readings.

http://www.miata.net/garage/tirecalc.html

 

[CanukV6]

I'm not sure if the Speedo uses GPS to correct for Tire Size etc, but like Midnightsun, I have definitely noticed that my speedo is far more accurate in my 2012 than it was in my 2009 (based on GPS data). I also used to see a difference when I fitted my winter tires on my 2009 but not any longer. Since the Speedo is completely electronic, there is no reason why the GPS could not be used to correct a reading taken from the ABS sensors.

 

[427435]

Your speedometer is calibrated to the rpms/mile of your OE tires. If your speedometer is now reading incorrectly with winter tires, there rpms/mile is different. Go to tire rack and look up the specs for rpm/mile for your particular tires.

 

[CanukV6]

Ummmm.... I don't think you have read the thread correctly, we are saying that the Speedometer is quite accurate, despite fitting different tires.

 

[geoffc]

How did you get 17" on the R-Spec? I wanted to go 17"s on mine for snow tires, severe clearance issuses with front calipers. Are factory 17" shaped differently inside the wheel for clearance? No luck finding aftermarket 17" to fit the R-Spec, my after market 18" barely clear with 40mm offset. Do 17" have larger offset?

 

[brfatal]

Offset has nothing to do with brake clearance. It's 100% up to the wheel design. An 17x8 +20 wheel may not clear while an 18x8 +40 wheel will.

 

[Midnightsun]

How did you get 17" on the R-Spec? I wanted to go 17"s on mine for snow tires, severe clearance issuses with front calipers. Are factory 17" shaped differently inside the wheel for clearance? No luck finding aftermarket 17" to fit the R-Spec, my after market 18" barely clear with 40mm offset. Do 17" have larger offset?

As mentioned all that needs to fit are the wheels over the front calipers and you are good to go. I bought cheap Chinese knock offs to get through our terrible salty winters. Went to the local garage and he tried them on for fitment before I bought as yes there is not much room. Here is a sad shot of my totalled 2010 4.6 with those wheels that are now being used on the 2012 Rspec. http://www.genesisowners.com/hyundai-genesis-forum/showthread.php?t=9209&highlight=insurance

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[Midnightsun]

Try going to this site to compare tire size to odometer readings.

http://www.miata.net/garage/tirecalc.html

Went to the link and input my tires and there is a 2.2% differenace which does NOT show up on the speedo. Why is the question. That chart by the way is not even close as they show the height differance to be about 3/8" when in fact compared side by side they are over an inch which should translate to over 7% at least which I saw when comparing the 2 side by side.

Tire Size Comparison

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
225/55-17..... 4.9in..... 13.4in..... 26.7in..... 84.0in..... 754..... 0.0%
235/45-19..... 4.2in..... 13.7in..... 27.3in..... 85.8in..... 738..... 2.2%

 

[Mark_888]

That chart by the way is not even close as they show the height differance to be about 3/8" when in fact compared side by side they are over an inch which should translate to over 7% at least which I saw when comparing the 2 side by side.

I think the difference in your tires must be related to the specific snow tires you purchased, and not generally to tires of that size.

 

[Crusty Old Shellback]

There are GPS based speedos out on the market and have been for several years. So why wouldn't Hyundai use a GPS speedo in the luxury car?

 

[brfatal]

There are GPS based speedos out on the market and have been for several years. So why wouldn't Hyundai use a GPS speedo in the luxury car?

And they are all aftermarket units. No auto manufacturer uses them for the reasons I started previously. If Bentley, Aston Martin, and Mercedes don't use them, why would a budget company like Hyundai?

 

[427435]

Went to the link and input my tires and there is a 2.2% differenace which does NOT show up on the speedo. Why is the question. That chart by the way is not even close as they show the height differance to be about 3/8" when in fact compared side by side they are over an inch which should translate to over 7% at least which I saw when comparing the 2 side by side.

Tire Size Comparison

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
225/55-17..... 4.9in..... 13.4in..... 26.7in..... 84.0in..... 754..... 0.0%
235/45-19..... 4.2in..... 13.7in..... 27.3in..... 85.8in..... 738..... 2.2%

Again, go to Tire Rack and look up the rpms/mile for the specific brand and tire sizes involved.

 

[kev4]

The measurement is from the center of the rim not the total height. Therefore multiply 3/8 inch X 2= 3/4 of an inch. Therefore your 7% would be divided by 2 which would equal a 3.5% difference. So at 60 MPH the difference in speed readings would be 60X3.5=1.87mph.

 

[Midnightsun]

The measurement is from the center of the rim not the total height. Therefore multiply 3/8 inch X 2= 3/4 of an inch. Therefore your 7% would be divided by 2 which would equal a 3.5% difference. So at 60 MPH the difference in speed readings would be 60X3.5=1.87mph.

Which is pretty much dead on with the difference I saw on the speedo of my 2010 genny 4.6however no difference on the speedo on my 2012 Rspec hence why I posted this.

 

[Shawn33]

One thing to consider as well is the tires can have stiffer sidewalls. If the smaller diameter has stiffer sidewalls then the larger diameter there "on car - with weight" final diameters may be a lot closer.

Shawn

 

[427435]

Jeezzz. Tire diameter and rpms/ mile do not necessarily correlate. LOOK UP THE RPMS/MILE ON A SITE LIKE TIRE RACK!!

 

[Midnightsun]

Jeezzz. Tire diameter and rpms/ mile do not necessarily correlate. LOOK UP THE RPMS/MILE ON A SITE LIKE TIRE RACK!!

I looked up the difference in rev/mile and it is 20. (781 vs 761) So why is my speedometer reading dead on with this difference?