Speedo is off?

[Elwood4u]

I had the cruise set last night to 70 on the way home and when I got home my wife asked why I was driving so slow... I did a speedo check vs. my phone on the way to work today and my speedometer shows about 4-5 mph faster than the car is actually going.

Has me really confused since I have stock wheels, same size tires as the car came with (225/55/17). Mine is the base model 2013 sedan. Tires have less than 5K miles on them.

Any ideas what's going on?

 

[JohnRa]

It's usually just a computer setting. You input the actual size of the tires you're running, and the speedometer is calibrated for that per revolution. Sounds like yours has the wrong tire size selected. A quick trip to your dealer should be able to resolve that.

 

[Mark_888]

It's usually just a computer setting. You input the actual size of the tires you're running, and the speedometer is calibrated for that per revolution. Sounds like yours has the wrong tire size selected. A quick trip to your dealer should be able to resolve that.

All of the tire sizes, regardless of wheel size or trim level (Base came with 17" wheels, and other trims had 18" or 19"), should be fairly close to the same diameter. Obviously, it can be off a little when the tread is worn down, or if non-stock tire sizes are used.

 

[Elwood4u]

All of the tire sizes, regardless of wheel size or trim level (Base came with 17" wheels, and other trims had 18" or 19"), should be fairly close to the same diameter. Obviously, it can be off a little when the tread is worn down, or if non-stock tire sizes are used.

yeah that was my understanding as well for 55 series vs. 40 series as you increase rim diameter. I assumed it was all mechanical and wouldn't be computer related but I have no idea on this one. Called the dealer and they didn't have any real explanation if the stock tire circumference is on the car same as factory.

tires are 90% but I bought the car that way so someone replaced them along the way. If it is computer related then perhaps the previous owner had a different set of rims/tires. I believe Dunlop was the stock tire from the factory at that time and they are not Dunlop now.

 

[Mark_888]

yeah that was my understanding as well for 55 series vs. 40 series as you increase rim diameter. I assumed it was all mechanical and wouldn't be computer related but I have no idea on this one. Called the dealer and they didn't have any real explanation if the stock tire circumference is on the car same as factory.

tires are 90% but I bought the car that way so someone replaced them along the way. If it is computer related then perhaps the previous owner had a different set of rims/tires. I believe Dunlop was the stock tire from the factory at that time and they are not Dunlop now.

I am not sure if the speedometer is computer controlled in the way you are thinking. It could be a mechanical speedometer that converts the numbers to digital format on the dash (in addition to the dial). On the vast majority of Genesis cars of that age, the speedometer reads higher than actual speed by about 1 MPH, based on posts of members of this forum back in that time frame (and my own Genesis).

There are a couple of reason for it reading higher than you are actually traveling. From a legal standpoint, if there was anything wrong with a particular speedometer, they want to err on the side of caution (encouraging you to drive slower than you think you are really going) to avoid any lawsuits as a result of an accident or whatever. If there was any error whatsoever for the speedometer in the other direction (if it said you going slower than you are actually going), then personal injury would put Hyundai out of business in very short order.

Another reason that some have pointed out (I can't say if this is true) is that it also causes the miles to accumulate faster than actual, which favors Hyundai on leased cars.

 

[Elwood4u]

I am not sure if the speedometer is computer controlled in the way you are thinking. It could be a mechanical speedometer that converts the numbers to digital format on the dash (in addition to the dial). On the vast majority of Genesis cars of that age, the speedometer reads higher than actual speed by about 1 MPH, based on posts of members of this forum back in that time frame (and my own Genesis).

There are a couple of reason for it reading higher than you are actually traveling. From a legal standpoint, if there was anything wrong with a particular speedometer, they want to err on the side of caution (encouraging you to drive slower than you think you are really going) to avoid any lawsuits as a result of an accident or whatever. If there was any error whatsoever for the speedometer in the other direction (if it said you going slower than you are actually going), then personal injury would put Hyundai out of business in very short order.

Another reason that some have pointed out (I can't say if this is true) is that it also causes the miles to accumulate faster than actual, which favors Hyundai on leased cars.

Interesting thoughts. I have only seen mechanical in my experience but they have always been pretty close to actual. I only have the dial on mine.

I didn't even think about the odometer. After 100K that could be a pretty large discrepancy since I've tested mine to be 4 mph fast at 2 separate trials.

 

[NJTom]

I have a 2009 3.8 with brand new Michelin size 235/50/18. I've always noticed my speedometer is 1-2 miles slower than the gps unit when on the highway. I use the Waze app when taking long trips and if the app say 70 my speedo is about 68-69 mph.
Per tirerack listed specs for the Michelin tires I have, the 235/50/18 tire has an overall diameter of 27.3" and 762 rev per mile. The 225/55/17 tire has an overall diameter of 26.7" and 777 rev per mile. This is a difference of about 2.2% which calculated to the speedo at 70 is actually about 68 mph -- and with an additional 1 or 2 mph loss with the car already, it is possible your car could be 4 mph slower than actual. (website for tire calculator: https://tiresize.com/calculator/)

If choosing a new 17" tire next time, maybe a 225/60/17 tire would offset a bit for the speed and odometer?

I've always thought about a 245/50/18 tire size for my car and tried this time when purchasing through Sam's club, however they will only mount the size their books say. I'm okay with a 1-2 mph loss on the highway.

 

[Elwood4u]

I have a 2009 3.8 with brand new Michelin size 235/50/18. I've always noticed my speedometer is 1-2 miles slower than the gps unit when on the highway. I use the Waze app when taking long trips and if the app say 70 my speedo is about 68-69 mph.
Per tirerack listed specs for the Michelin tires I have, the 235/50/18 tire has an overall diameter of 27.3" and 762 rev per mile. The 225/55/17 tire has an overall diameter of 26.7" and 777 rev per mile. This is a difference of about 2.2% which calculated to the speedo at 70 is actually about 68 mph -- and with an additional 1 or 2 mph loss with the car already, it is possible your car could be 4 mph slower than actual. (website for tire calculator: https://tiresize.com/calculator/)

If choosing a new 17" tire next time, maybe a 225/60/17 tire would offset a bit for the speed and odometer?

I've always thought about a 245/50/18 tire size for my car and tried this time when purchasing through Sam's club, however they will only mount the size their books say. I'm okay with a 1-2 mph loss on the highway.

Thanks for the info, I was using an app myself too as well as what the wife said vs. her car. So I'm pretty confident in the 4 mph.

I already dislike the 55 series slightly both for appearance and performance so I'd rather not go bigger. And then I also don't want to spend more on new bigger wheels... problems.

Just seems odd to have such a large difference at 70 mph.

 

[Buford T Justice]

I have a 2013 base model as well and noticed the speedo is 2-4mph off (depending on how fast you're going, it gets worse the faster you go).

Last summer I upgraded from the stock 17" wheels to 20s and now my speedometer is dead on. I still have 17" winter wheels and the speedo is incorrect with those on.

It's almost as if all the cars are calibrated for the Rspec's 19s (which I'm assuming are a slightly larger diameter) so having the 17s make the speedo a bit off.

 

[dougmcp]

It's a pretty common issue with a variety of vehicles, my previous Mercedes and Passat were both a little off and my current Ford diesel is also off. Most of my inaccuracies have been in the 4% to 6% range. Pretty much every vehicle specific auto forum has complaints about speedo accuracy.

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[Tito]

Same issue; 2-3mph off needle.