I've been noticing something weird with the speedometer and the attached picture shows it pretty nicely. When setting cruise to any speed over about 30MPH, the displayed speed shows 1MPH less than the setting. You would think they'd be using the same reference, so match. Even weirder is that the speed indicator shows red even though the displayed speed is "correct". I can see this being rounding error o r something, but you would think they'd handle that a bit more gracefully. Is this maybe just my car? Do others see this too? If the cruise control and speed limit indicator agree, but the speedometer doesn't makes you wonder who is right? Fun side note: Note the miles and gas tank, I was still on the dealership's initial fill at that point! This was my second 200-mile mountain trip, so almost used up the first tank. will
What is weird is your temperature gauge! Mine read 88 degrees yesterday. I thought those red speed limit signs were the only color they had. If I go under 50 in a 45mph zone someone always honks at me as they take off my tail doing 55 or more.
Have noticed the same thing, displayed MPH is frequently one less than the cruise control target, even on open road when no one is around. Same model/trim.
Ditto. I've taken to automatically setting my cruise 1mph higher. It seems to be a "safety" feature so that the car has a little leeway with the speed but never exceeds the set speed. I've noticed it will reach the set speed after clearing a hill or during a downhill coast.
Tovli, Ken2023, and Hammersmith: OK, looks to be systemic then. As you can tell, I'm just setting to 1MPH higher. On decent hills there is an expected delta as you point out. Tovli: Yea, that temperature surprised me too! It was up in the mountains above 8000 feet. This is the first car with that kind of ice warning too, so was a double-surprise to see it (temperature and the warning)! Winter is coming. In a couple weeks is a trip to Keystone, CO, so up to 11,000 feet through the Eisenhower tunnels. The approaches on either side were battery drainers for my older Prii, so will be interesting to see how the Gen5 handles that. I'll report on it after the trip. I've never been able to keep up with the speed limit (75MPH) for the entire climb. will
I am experiencing the same thing when I use DRCC in my 2023 Prime SE, many times the car maintains a speed of 1mph under what I set.
Trollbait: I agree there is rounding error involved, but all three systems (DRCC, speedometer, and speed warning) should be using the same reference! I'm used to seeing different speeds between the car's speedometer and my standalone GPS as they used different sources of information, but here I'd hope they are all three systems are using the same reference in the car. Kinda weird to have three different systems are computing the speed independently and even differently from the same wheel sensors. Even if there was some different rounding, that is something a decent user interface could/should hide. BTW, for reference, whenever the car and GPS disagreed, I was pretty sure the GPS was more accurate as it was spec'd to <0.1MPH accuracy over any reasonable speed with a good lock. Way too many variables with wheel sensors to be that accurate. It boggles my mind that some RF receiver picking up microwatt (nanowatt?) signals from satellites in orbit was an order of magnitude more accurate than something touching the road! will
Not anywhere near micro-watt or nano-watt. Not even pico-watt. How does sub-femto-watt sound? "The GPS receiver receives GPS signals at 1575.42 MHz (L1 frequency) at a power level of -125 dBm (about 0.1 fWatt)." A couple other sources mention -130 dBm.
It is the same thing in Gen 4 with TSS 2.0. Cruise control controls the speed within ±1 mph, not ±0.1 mph. It is more often −1 mph than +1 mph. Moreover, on my Gen 4, the speedometer intentionally displays 2 mph higher than the actual speed at all speeds. You can check it with the Google Maps navigation. As for the red road sign, that is strange. Could it be because you set the cruise control above the speed limit? That would be my guess.
Speedometer wil always read 1-2% high on any vehicle. Manufacturers (Lawyers) don't want to be liable for speeding tickets. See Section 5.3 of the attached.
Same reference source doesn't mean they have to use the same display rules, such as how to round the decimal, which the computer knows. Most likely, it is the legal reason that has been pointed out. There are regulations dictating the accuracy of the speedometer, with CYA leading the manufacturer to having it read on the higher than actual. The cruise setting isn't has constrained. Between the sensor and the road is a soft material that wears with miles, and the inflation of which changes with temperature. All of which leads to changes in the distance traveled from each revolution of the sensor.
I'm pretty sure it's the rounding. I think the red is triggered by anything at all over the speed limit. So if the speed limit is 50mph, then 50.0001mpg triggers a red sign even though the speedometer will continue to read 50 until the actual speed reaches 50.5 or 50.5001. Different teams working on different functions over many years.
A 'your current speed' sign in my town is like that. Does the flashing while displaying the legal speed. Trains you to just ignore it in my experience.
I've found (on our gen 3), regardless of plus/minus vagaries in speed on cruise, say 1~2 kmh to either side, if I set it to a speed, it'll settle back to that speed, not one under. Could be something a software update would fix?
The systems could be working in kilometers, and the displays are rounding the miles conversion slightly different.
Yes, that is exactly what I meant by "intentional." However, in the case of Prius's digital speedometer, it is not a percentage. As I asid, it is +2 mph regardless of speed. So, if you are at low speeds, it is a lot more than 2%. My 1985 Corolla's "intentional" calibration for its analog speedometer had a much higher difference from the actual speed, and it was more like a percentage.
My gen3 Prius v display is more like 3% high compared to its own real speed accessible via obd2. At low speeds the difference is small as you would expect with a percent factor. In fact I monitor real speed and coolant temp in realtime and have for years. This P10 device also has configurable alarms.
I see. It is a constant difference of +2 mph in my Gen 4. In your case, there could also be a problem with your tires' "revolutions per mile" spec; so, it may not be an intentional-calibration issue—rather an unintentional one. I am surprised that my Gen 4 is so accurate at all speeds other than the constant 2-mph intentional addition.
