Speedometer of California T wrong?

I've noticed going 315 kmh (196mph) the GPS speedometer shows 307kmh (191mph) only.

Why is the speedometer on the California T is not accurate?


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No Ferrari speedometer is accurate. But what you show is very odd - and illegal here in Europe.

A speedometer must not read slower than the actual speed. Also, the primary reason why speedo.eters show high, is to aide in keeping you at or below the limits.

Some Ferraris, like the 458 and some of the previous V12 models were notoriously inaccurate - as much as 7-10 % off.

From what I recall, a speedo in the EU is not allowed to be more than 13% off.

But the fact that yours show wrong the other way, leads me to believe something else is amiss. Have you tested a different GPS?

 

I've had similar experience. GPS is only as accurate as the number of GPS satellites "visible" to the GPS receiver. GPS accuracy is also inherently not that accurate, can be off by anything from 6 to 30 feet. This assumes the GPS device is stationary. Your car is however, moving in 3-dimensional space so GPS speedometer accuracy may be more challenging to achieve even on a highway, as relative directional bearing, sampling rate and synchronizing also matter. So some discrepancy can also be due to your GPS device.

There is also the issue of tire sizes.

The Cali's speedometer is likely based on sensor readings from the rear-drive axle but Ferrari offers at least 2 different sizes of tires for the Cali and their rear diameters differ so I am not sure which tire diameter the Cali's speed sensors (called reluctors) are basing their readings on for an "accurate" vehicle speed. This is important as the traction control and ABS brakes systems rely on reluctors from all four wheels to agree within a certain range. If they consistently disagree, the ECU will assume there is slippage and traction control will engage, sometimes VERY aggressively, which can lead to disaster depending on vehicle speed. To avoid this and since tire traction/slippage and tire size selection (by the owner) can significantly affect speed data from the reluctors, I believe car makers build in a certain amount of tolerance for error. I am not sure if this shows up on the actual speedometer displays but it definitely affects how the ECU calculates wheel speed.

For what it's worth, I often test my car's speedometer readings using the roadside speed warning displays from the Police, the ones that displays your car's speed. My Cali's speedometer is spot-on as is my RAM pickup truck's speedometer. Given the consequences of having the insurance rates of ALL YOUR CARS go up when your car's speedometer is off compared to the Police's; I would say the Police's speedometer reading is the most important one to consider.

 

Impressive either way.


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For the 458, an indicated 340 kph is 330 kph V-Box proofed. At lower speeds (lower than 200 kph, they read some 5 kph more than the actual speed). As you said, it is illegal for a speedo to under-read, at least in the EU. For that reason ALL manufacturers calibrate their speedos to over-read. Modern Ferrari speedos are really accurate in that respect.

To the OP, 307 GPS vs 315 speedo is spot on!

 

He did not say 315 on speedo and 307 on GPS. He said 307 on speedo and 315 on GPS. That's why I said that's illegal here in the EU.

I have first hand experience with a 458 showing 338 on speedo and 314 on both GPS and V-Box. This speed was held for a few minutes, so both the V-Box and GPS got ample time to read. I've seen other 458s that seemed off by about the same albeit at lower speeds.

I don't think you can definitively say how much they are off. Looks like they are all a bit different. Also, if it's off, it's off by a percentage, not a fixed kph/mph. If it's off by 5% it will show 63 mph @ 60 but 126 @ 120 etc. That's just how speedometers tend to work.

I will say that I've noted that the 488 and 812 speedo have gotten more on point than what I've seen in the F12 and 458. I think the worst I've seen was a 599 that was off by about 11%.

 

No, that's not right. It used to be some 40 years ago, when the speedos read from the final drive of the transmission. With modern electronics they read the rotational speed of the wheels, hence they can (and do) keep a constant speed differential and not a percentage one. So, they make the speedos to read 155 when you are doing 150 and 205 when you are doing 200. I stand by my original thesis regarding the 458's speedo. It is really accurate (factory wheel sizes of course) and much more precise than other performance cars I have measured.

PS: You are also wrong regarding the OP. His Ferrari speedo read 315, but the GPS read 307.

 

My mistake on the speedo vs. GPS. It was written in a way so that I initially saw it as 315 on GPS and 307 on speedo.

 

His wording was a bit misleading, but all you have to do is read the V-Max indication on the dashboard of that Ferrari, which says 315...

 

What do you mean by "it's not right"? I was in the car driving it. It had factory wheels and tyres on it, and when I slowed down, we could see it read off the same way in percentages. Are you telling me both the V-Box and handheld GPS we used were off by the same? Not likely. We did this a few times, as we were quite surprised at how off it was. 70 on the speedo was 65,100 on speedo was about 93, 150 became 140 etc. I was there, I drove the car.

 

Saw it with my eyes too, mate.
What I have seen is the same that the OP showed. 315 kph on the speedo, 307 V-Box. The OP and I agree. You seem to disagree. Perhaps something wrong with your V-Box?

 

I simply disagree because I've seen something that contradics what I saw. Nothing personal.

Something wrong with the handheld Garmin GPS at the same time as the V-Box, and on different roads in different areas? I find that very unlikely. I will say it's a big difference, but I have seen other cars where it seemed to be the same, and I've heard from a few 458 owners that they also experienced a significant difference. Let's leave it here, no need beating a dead horse.

At any rate, to the OP, as REALZEUS said, you're speedo is working as it should.

 

Why is this not considered a defect? The car measures the data inaccurately and there’s not a single mention in its documentation about this.


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Seriously? An F car that measures the data inaccurately? Tell me it ain't so! Mine reads the seat heater data inaccurately...so be it. If you consider this a defect you bought the wrong car.

 

Again, the sampling rate of the GPS matters greatly (as does the sampling rate of the Cali speedometer), as well as the tire size of the drive wheels and the stated degree of accuracy of the GPS device, that relies on satellite readings.

There is no time stamp marking on the GPS speed graph so we don’t know how frequently the GPS speed was interpolated. The readout of the Cali is the recorded maximum speed from reluctors whereas the GPS graph is just a display of what the device sampled off the satellites. The Cali is going to sample the reluctant readings much more frequently than the GPS vbox because the traction control ECU needs it to prevent an accident if one or more of the wheels suddenly loses traction, in a split second.

It looks like none of you guys have any formal training in a technical area. BTW my experience with German cars (VW, BMW) was that their speedometers always read 5 kph higher than actual, but that was with German cars.

 

If it worries you that much sell the car and buy one with whose speedo calibration you can accept

Another option might be to get lawyers involved..........

 

Ι guess that you are new to this car ownership thingy. ALL cars under-read; it's not a bug, it's a feature. The margins vary (within the legal limits), but they are all set up this way in order to assist the driver in the eternal Police vs Driver struggle.

 

I don't know if this was intentional, but you sir come across a bit condescending. Anyway, my E92 has a speedo error of 5-7 kph, depending on the speed. At an indicated 260 kph, the GPS, on two different devices, read 253, which is in line with the speed limiter confinement. Translated from mph, to kph, because, let's face it, kph is the international standard.

 

Assuming the worst of couple of seconds, would fixing the sped of Cali T to 250 kmh for about 10 seconds eliminate the sampling frequency issues and get me a reliable results about deviation?

It may be a bit difficult to do it at 300 kmh need to look at the road.