My 2020 Advance is slow by 2 mph when checked against the gps speed display on my radar detector and an app on my iPhone.

just wondering about yours...

 

I'm not sure my tired old eyes are calibrated that well for the analog gauge. Are you using the HUD on an Advance? ( I have it but don't use it ).

Are your tires stock, and inflated to the recommended pressure? Slightly oversize or overinflated tires would cause the speedo to read low.

 

I don't know about your radar detector (mine are Uniden R3 and R7) but Uniden specifically says not to use any of their speed related messages basically 'as gospel' because they are not designed for that level of accuracy.

 

My R7 always reads 1mph faster then my gauges, I’m betting on my gauges being the accurate one

 

My RDX is only a couple of weeks old, and is a stock Advance package. My radar detector is an Escort Max 360 and calibrates perfectly with the Speedometer app on my iPhone. My last car was a 2011 Subaru Outback and it was 2 mph faster than my detector and phone app. This seemed very common among other Outback owners. I am comparing them to the digital speed on my HUD. I can't verify for sure if the digital speed on the HUD is perfectly matched to my speedometer, but as best I can tell they are the same.

I'm curious how the A-Spec lines up with the 20 inch wheels. If I had to choose which was correct, my money would be on my radar detector and iPhone app over the vehicle.

 

MPH can be affected by things like tire inflation and other factors. After a few scandals, which were mostly related to miles-traveled, automakers tend to be more conservative with MPH figures. So yeah, there's going to be a difference between the mechanical measurement and the sat-based one. Just be happy that your mechanical one is the legal measurement, because it's probably lower than the actual.

 

The mechanical odometer measurement may be the "legal measurement", but AFAIK the cop's radar gun measurement is the legal speed measurement.

 

OTOH, no self respecting officer of the law would write you up for going less than 10 over the limit.

As a natural born American, it is my God-given right to do 10 over on any highway in the US of A, presuming I am not weaving all over the road. In about a millyun miles of driving and over 40 years of doing so, I have never been written up for such.

(I double checked, and it is not in the Constitution, per se, but the Fourth Amendment against unreasonable search comes to mind.)

 

I think it depends on where you are. When I lived in NC about 20 years ago, the cops in VA were notorious for pulling over people doing 70+ in a 65.

 

Yeah. Va. is notorious. I stay within 5 when I pass through there. Them cops have no self respect, for sure, and everyone knows it. Plus, even worse, they are hard, or even harder, on their own drivers. You get further South, and no Carolinian Cop would ticket a fellow Carolinian for 15 over if he can get a New Englander for 10.

 

Tell that one to the TSA. Talk about no respect...

 

we have Global Entry and just skip all them guys. A mere wave of the hand, say “we are not the smugglers you are looking for” and away we go.

 

i used to travel a lot when programs like TSA Pre were not available. I absolutely hated it and have a PTSD style reaction when I think of flying now.

 

My 2020 is pretty spot on as compared to Waze, etc.

 

which model do you have? A-Spec with 20” tires or the others with 19” tires?

 

My dashboard gage runs about 2 mph slower than the digital HUD. The HUD tends to agree with the target speed setting of the adaptive cruise control when there's nothing to slow me down.

 

That's weird that they're different but if I had to guess, it's because the HUD is linked to the Nav which has GPS-based speed, while the dial is fed by a mechanical system measured at the driveshaft.

It's worth noting that most cars are a little high on MPH at the gauge. This is the result of being overly cautious after there were some scandals a few years ago, especially Honda, where speedometers and odometers were found to be inflated so that owners (especially those on lease) had higher miles than they should have had, and had to pay higher end-of-lease fees as a result.

 

My 2019 Aspec is the same as Waze at 80mph.

 

The dashboard meter assembly is completely digital. No physical speedometer cable like cars of yore.

But the system is well aware of crankshaft position at any millisecond in time, because that's how it times fuel injection pulses and spark plug ignition. And it knows about wheel rotation from the ABS and stability assist systems. Which isn't to say there may not be a problem with translating speed data into physical movement of the speedometer meter needle. And there is still the issue of effective tire diameter, or "rollout distance".

But don't neglect the parallax effect.

If you are reading the analog gauge from an angle, rather than straight down its central axis, and there is any distance between the needle and the markings on the dial face, you will get a false reading. I can easily observe this affect on this gauge.

 

I would say fairly accurate based on the speeding ticket I got 2 weeks after I picked it up 😂

 

you can argue in court that you thought you were going the speed limit, but that your speedometer was mid-calibrated...

 

I noticed last week that my speedometer differs from my cruise control speed by about 2mph.