Speedo off 2MPH -- anyone else?

[sammyb]

I drove my wife's Genesis 4.6 for its first longer trip (240 miles round trip) and I noticed that with the adaptive laser-guided cruise control set at 70 the speedometer needle pointed to 72. (It was well past the line for 70.)

I took out my iPhone speedo ap (which I use for classic cars with non-functioning or Italian-made speedos) and the application confirmed the cruise was correct at 70.

Anyone else have this problem? I know that my '02 Corvette's problem (1mph between the needle and the heads-up display) is shared with all C5 Corvettes, but this is the first time in decades that I've seen such speedo error in a modern sedan between cruise control and needle display!

 

[Mark_888]

I think everyone has noticed about the same difference with the speedometer (not many members have the adaptive cruise control). My speedometer is off by about 1.5 mph per my Garmin GPS.

 

[flyboy2]

How many satellites does the I-phone gps pick up? It's margin of error? The i-phone GPS is one of the inaccurate gps's in the world.

Your scientific conclusion is making you look bad as a journalist.

 

[huksa]

In fact, speedo off by 2 mph is better than many cars around. My Touareg is off almost by 5, and M5 I used to own had very optimistic speedometer.

Some claim that manufacturers intentionally calibrate speedometers that way... Personally, I am not racing against clock, so 5 mph is no big deal.

 

[sammyb]

How many satellites does the I-phone gps pick up? It's margin of error? The i-phone GPS is one of the inaccurate gps's in the world.

Your scientific conclusion is making you look bad as a journalist.

Flyboy,
The fact that the needle is off from the cruise control is the indication that at least one of the displays in the vehicle is not accurate. So either the cruise is off or the speedometer is off. Has to be one or the other -- or both. Not hard scientific principles.

I am extremely aware of the margin of error of GPS, but considering the rate and consistency of travel (stable high rate of speed),and the fact that it showed exactly the same speed as the cruise control setting. it's not a stretch to be confident that the display for the speedometer needle is off.

If you'd like to discuss the history of speedometer error from the practice of testing with every review of an automobile by the likes of Road & Track to comparing the accuracy of Smiths/Jaeger, Veglia, VDO, or domestics in various makes and models, I'd be happy. I even have plenty of experience with performance meters like the G-Tech and Passport G-Timer and can go a few rounds on the accuracy of those units...

...or you might just want to re-read the original post before throwing a bomb like questioning if I might look bad.

As for margin of error in cars such as BMW, this is a different issue entirely, because while BMW speedometers have been extremely optimistic in the last decade, the speedometer and cruise control show the same speed. The problem here is the disconnect between the speedo and the cruise control which show a 2mph difference.

 

[BacktoHyundaibychoice]

This is a problem because? Many people have commented on the same issue, usually reporting a 1-3 MPH difference. You're the first I can reecall using the exclamation point for emphasis.

 

[sammyb]

It's a problem, because it's very, very, very unusual to have a speedo off from the cruise control.

 

[GripperDon]

Problem IMO Schroblem.

 

[esulto]

He,(Sammy B)sounds like an, egotisical "show off" to me, with all his fifty cylinders

 

[flyboy2]

I drove my wife's Genesis 4.6 for its first longer trip (240 miles round trip) and I noticed that with the adaptive laser-guided cruise control set at 70...

How do you set your cruise control at 70?

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[BocaDave]

My Avalon was 3 MPH too low at 70 MPH, and was the only car I ever owned that was conservative in its mileage/speed readings.

My Genesis 3.8 is high by 2-3 MPH at 70, with brand new tires. That difference will only increase as the tires wear down (due to more revs per mile with the smaller circumference tires).

I know of no way to tune the speedometer or trip computer, so I'll just live with it.

Compared to starvation in Africa and Haiti, this doesn't seem like one of the worst problems in the world.

 

[Disaster]

My Avalon was 3 MPH too low at 70 MPH, and was the only car I ever owned that was conservative in its mileage/speed readings.

My Genesis 3.8 is high by 2-3 MPH at 70, with brand new tires. That difference will only increase as the tires wear down (due to more revs per mile with the smaller circumference tires).

My 3.8L is off a similar 4% or so. I wish I had bought slightly bigger winter tires to make up some of the difference, however, 4% is a big number to make up. The next higher profile gains only about 3%.

 

[Sayantsi]

Yes, its pretty common knowledge that speedos are off, anywhere from 2-6%. I remember a car mag did a test a number of years back, and found the German cars to be the most "optimistic" in terms of reported vs actual speed. I think the issue is, odometers and speedometers are tied to the same sensors, and only one can be ~100% accurate, so automakers set odometers to be accurate at the expense of speed accuracy.

When you use any quality GPS device, like an iPhone, you will see the difference. Look at the bright side, it might be saving you from a speeding ticket if you think you're going faster than you are!

 

[Sayantsi]

I drove my wife's Genesis 4.6 for its first longer trip (240 miles round trip) and I noticed that with the adaptive laser-guided cruise control set at 70 the speedometer needle pointed to 72. (It was well past the line for 70.)

That seems like such a small difference - completely in the spec of perspective. 2 mph could be the width of the needle and where you think its pointing. It seems like a really nit picking detail to me.

Besides, afaik there is only one gauge in the car that shows you vehicle speed, how do you know the cruise control is actually set at 70? All CC does is lock in a currently registered speed when you activate it - are you saying the car was going 70 mph and accelerated 2 mph after you activated it?

 

[sammyb]

Guys,
Here's where the disconnect is:

At least on the 2010 Genesis with the Technology Package, the adaptive cruise control has a readout that indicates the speed (as well as the trailing distance from one of three presets) at which one has set the cruise. The driver can increase or decrease the speed by 1mph with a push of the cruise button on the steering wheel. This is the same as the operation of this feature on the Avalon, Mercedes S550/S600 and many other vehicles.

So the little display right next to the speedo can show 70 (or whatever speed you set it at) and the speedo itself shows something 2mph off. It's very clear that the needle is well beyond the mark.

Now does that make a little more sense why I'd be puzzled why one effective speedo is showing one speed while the other shows another speed...when one would assume the source of both is the same speed sensor?


And if you take offense to my signature, I'm happy to take it down. Not trying to brag, it's just that on most forums people seem to want to know what else you drive (and if you're a vertical collector).

 

[Sayantsi]

Guys,
Here's where the disconnect is:

At least on the 2010 Genesis with the Technology Package, the adaptive cruise control has a readout that indicates the speed (as well as the trailing distance from one of three presets) at which one has set the cruise. The driver can increase or decrease the speed by 1mph with a push of the cruise button on the steering wheel.

So the little display right next to the speedo can show 70 (or whatever speed you set it at) and the speedo itself shows something 2mph off. It's very clear that the needle is well beyond the mark.

Now does that make a little more sense why I'd be puzzled why one effective speedo is showing one speed while the other shows another speed...when one would assume the source of both is the same speed sensor?

Aaaahhhhhhhhhh.... that makes sense. You have two ways to see vehicle speed. Obviously, the digital read out will show more precisely than the analogue.. I wouldn't be too worried about this, I noticed the same thing in a 911 I used to drive with the digital and analogue speedos. If it was significntly off, I'd think there is an issue, but 70/72... thats a 1% difference.

If it makes you feel better, my motorcycle's speedo is off by 8-10%, its basically useless at speed.

 

[flyboy2]

Dang Gone it Sam, you got me all confused. Ever since your post the wife and kids won't ride with me and being the scaredy that I am, now wear my motorcycle leathers and helmet when driving the car. You're the first car expert we've had on this site and when you said we had a problem... well I believed you. In fact I was considering trading in the car this week.

Now, for once and for all, is the problem still there? Did you fix it with one of your space age G-Tech meter gismos? Are we still in danger? Just give me the word. (in plain english please and no auto shop double talk)

 

[esulto]

Sammyb....I am also "car crazy" ....I didn't mean to sound condescending. I've had some favorite collectable original American cars myself so I really understand things that bother you...Before I got this 2010 Genesis v/6 premium&tech package,I had a 2007 bmw 335i where the speedo was off 4 miles@65 mph.the car was only doing 61 mph.....It didn't blow my mind,but it did bother me...you sound like a nice guy....all the best!!

 

[sammyb]

esulto -- thanks.

The post was intended specifically not to complain about the problem, but to establish whether this is typical or atypical and needed to be fixed (like the speedo needle had been affixed incorrectly). Afterall, you don't expect the car to be off from itself .

Because most people here evidently don't have the adaptive cruise control, it seemed to be completely misinterpreted and slide into a pissing contest about relative speedo error. Like most of us, I expect some speedo error.

The bottom line is that this is evidently something considered "normal operation". Case closed.

(And yes, BMWs are notorious as of late for wildly optimistic speedos, which I personally think should be addressed. A four or five mph difference in speed can have horrible consequences in traffic flow on populated freeways. Considering that 2.5 mph was the average "off" back in the 1950s, and cars are much heavier with heavier sidewalls-- leading to less spin and change, we should expect more accuracy. Motorcycles get a pass for high-speed inaccuracies, but cars shouldn't.)

 

[nb_mike]

My 2009 3.8 Sedan is off 2 mph versus my Garmin GPS. Speedo is about two miles per hour off. When speedo shows 55 GPS shows 53.