Speedo Accuracy

I got exactly the same difference between 40-90 MPH on my 456 GT '95.

Did this against FIVE/5 radars posted along side the roads between Santa Rosa and Ukiah on a 50 mile drive, July 17th. Made it a point to check. Of course the RADARS can be defect or mis-calibrated

greatest thing about a Ferrari: your going 10MPH standing still

 

On my 575 the speedo reads 8-10% high across the board. I believe they are designed this way.

 

I believe that most EU countries require speedos to be optimistic by at least 2%. Switzerland requires an error rate of at least 4% to the positive.

 

Funny you post this. On my new to me '95 456, I have noticed that the speedo seems to read fast (everyone is passing me like I'm going backwards at an indicated 70 mph, they drive fast in CA, but not that fast). I was intending to take out my GPS to see what the actual speed is, and although I will check anyway, it seems like I have my answer (5 mph to high).

Alberto

 

Same here

 

my 355 idles at 10 mph

does anyone know if the odometer is affected by the speedometer being off?

 

I would say yes, since it is a sensor type that works on the revolutions of [I think] either the crank or ??

so, if speed is off, so should the mileage.

anyone see this differently?

 

if this is true, shouldn't my odometer increase as i'm idling at 10mph?

 

Well, I finally did the same experiment with the same results up to about 70 mph (closed circuit, non-public street test); 5 to 7 mph too high.

Does anyone know if these are somehow adjustable somehow? I'd like to get mine more accurate if possible.

Thanks.

 

yeah my BMW is about 7% off. I wont complain though because it reads fast so when I pass an officer at 80 its probably more like 74

 

Speed is measured at the wheels (or on some part rotating the same speed as the wheels), as you can't tell by the rpm of the crank how fast you are, it depends on the gear (-> 4000rpm crank in 1st gear is a bit slower than 4000rpm in fifth gear). Interesting question though, I think they might have kind of a 'system' (however that might look, either mechanical or electronic) to reverse the speedo error. Or otherwise, the odometer works accurate but the 5-10% tolerance (which aren't due to some inaccurate sensor but, as stated, partly forced by law) occur only on the speedo itself.

 

Yes, I've heard that Mercedes are plagued with electronic glitches and their quality index has steadily declined.

 

Just to confirm, both of my BMW's read about 4-5 MPH fast too. Now that I know that, I account for it so I would rather it be accurate. I haven't tested it on my 328 yet.

Has anyone ever used the "My speedo reads 10 MPH high so I didn't realize that I was speeding officer." Hopefully I'll never have to try it, but if the situation arises, I will give it a shot.

Gene

 

Checked the speedo again this morning --via wife who drove the Mondial T-- against five/5 stationary RADAR dectectors on HW 101 between Santa Rosa and Ukiah. VERDICT: 4 radars = 5 MPH over limit and remaining Radar/#5 = 10MPH over speedo.

I am finding this all over, BUT what I don't know is if those RADARs are calibrated. But, predict since this is a common value all about, that such is the case: min. of 5MPH over speedo shown.

 

My '89 328 reads high as well. It's showing 65 mph on the speedo when doing 60. I have also checked the odometer against 10 consecutive mile markers. When 10 miles were driven, the odometer registered 10.8 miles. I think that difference is enough to establish that the odometer reads too fast since I doubt highway mile markers would be off by 8% over 10 miles.

 

My 550 reads approx 8% faster then actual, have concluded that the mileage on the car is actually 8% lower then read