Accuracy of 200mph reading on 575 Speedo?

well, my experience is you always need to subract 10mph from any Ferrari speedo

 

I use a garmin gps 72 for my cars the speedo's are off, it is portable hand held or mounted.
DM

 

Mine overreads by 10mph at 100 indicated (against GPS), I suspect the problem grows and it's 20mph out at 200.

I'm interested which circuit you could get up to that speed

 

I ran mine thru radar a couple of times and it's 5mph fast.

 

Hi Mark, the question really is: how accurate is the GPS reading?

To get up to 200mph is easy... the highway between Milan and Modena at 3AM on a weekday is your best bet but then don't tell the boys in blue waiting for you in Modena that it was my idea

 

Over-the-counter GPS's that are typically used in cars give around a +/- 3 metre accuracy on location. Considering the device determines location several times a second, it is very easy to see that the speed calculation will be very accurate, as long as you don't accelerate or decelerate too quickly. For a constant speed, GPS will give you very accurate readings, certainly in the +/- 0.1km/h range. It is a lot more accurate than radar guns.


Onno

 

I took my 550 to Europe this week and found a stretch of deserted motorway.

At a GPS indicated 180 the speedo was touching 200 mph. At an indicated 100 the GPS tells me that the car is doing 93.

So as with all speedos the one in the 550/575 overreads.

BTW this also confirmed to me that the factory quoted top speed of 199mph is unattainable. At a GPS indicated 180 mph the rev counter showed 7150 rpm in 6th. Whilst fresh tyres with a bigger circumference might make a 1 or 2 % difference - my tyres are down to about 3mm tread depth - I would need to have the revs at almost 8,000 to reach 199 and the rev limiter wll cut in before then.

Here's another old thread on th subject:

http://www.ferrarichat.com/forum/showthread.php?t=54561&highlight=top+speed

 

I had heard you start getting some tire slip at really high speeds, so that indicated speed will be higher than true speed. Not sure about that, but there are a lot of forces battling it out at 180+.

 

There are requirements in several European countires that speedos have to be optimistic by some small percentage. In Switzerland the requirement is at least 4%, so I would imagine that Ferrari makes all of their speedos overread by at least that margin.

My 599 reads 75MPH where the tomtom reads 73, especially critical in Scottsdale where the freeways have speed cameras waiting to snap you at 76MPH.

 

don't forget the the diameter of your tire will grow at higher revolutions. The faster you go... the larger your tires will get...

 

The European Union rules state that the speedo must NOT show a slower speed than actual, and as for how much faster than actual, it's 10% + 4km/h. As far as I know, these rules are EU-wide and supersede individual rules previously implemented by member countries.

So if you are going 300km/h, the speedo should show 334km/h.

They relationship must be maintained in real-life tests, which take into account things like tire ballooning and such.

Does Ferrari make a top speed claim on the 550? I am surprised if they do. They are known to lie about horsepower numbers - do they do it about top speed also? I'd think that would be an easy way to open one's self up for a lawsuit!