Speedo reading 17 mph when stationary

[Phil the Brit]

Can anyone tell me why speedo reads 17mph when my car is stationary. Someone told me they all do.
Can someone throw any light on this for me please.

 

[Grinzzz]

NO idea WHY they chose to do it, but if you look carefully theres a little pin in the speedo that stops the needle dropping below it.

 

[rossyl]

It's styled to look like it's moving even when it is stationary. Italian design.

 

[allandwf]

Innaccuracy at bottom of range probably.

 

[2b1ask1]

I agree with the above but it is possibly also the slowest speed the clutch is 100% engaged on the CC so accuracy can be assured... Just a thought

 

[CatmanV2]

I' amazed people asking this question. I have *never* had a car that read zero on the speedo.

Every one had a rest that was > 0

C

 

[karatemaserati]

^^^^^ thats an interesting theory

 

[CatmanV2]

I agree with the above but it is possibly also the slowest speed the clutch is 100% engaged on the CC so accuracy can be assured... Just a thought

You might want to think a bit more? Not *sure* but I suspect there's something of an error in your logic there.

C

 

[2b1ask1]

You might want to think a bit more? Not *sure* but I suspect there's something of an error in your logic there.

C

Ok, I am assuming it is an electronic speedo not a cable driven mechanical one like the old days. If this is the case then it would be driven by the ECU, as the clutch and gearbox are separately controlled but feed their parameter information back to the ECU I am just premising that the speedometer cannot be fed accurate speed information until clutch slip can be eliminated from the equation. Basing my thoughts on that logic it is not unreasonable to say this is the sort of speed necessary for 100% engaged drive.

Discuss...

 

[2b1ask1]

Ok, adding to this; I am fully aware that pulling both paddles at any speed will find a neutral and the speedo does keep displaying...

 

[Phil the Brit]

NO idea WHY they chose to do it, but if you look carefully theres a little pin in the speedo that stops the needle dropping below it.

Yes, I spotted that the pin stops it. I wondered if there was any historical relevance, you know some very interesting fact about the figure 17. If there isn't I'll just make it up and lie when I tell friends why all Maserati's stop at 17.

 

[Grinzzz]

Ok, adding to this; I am fully aware that pulling both paddles at any speed will find a neutral and the speedo does keep displaying...

MOdern practice tends to be that the speedo runs off the ABS sensors. Even on older cars it used to run off the output side of the gearbox, otherwise it would be a rev counter!

 

[2b1ask1]

Yep, that makes sense Grinzzz; ABS is witchcraft to me though

 

[CatmanV2]

MOdern practice tends to be that the speedo runs off the ABS sensors. Even on older cars it used to run off the output side of the gearbox, otherwise it would be a rev counter!

Indeed, really does need to be from somewhere there is a fixed ratio to the wheels, or it's all just guessing, really

C

 

[Emtee]

After a bit of internet research... it may be that these are electronic pulse driven speedometers. A signal (magnetic pulse I think) is generated from the output side of the gearbox (don't ask me where, as I have no clue).

The pulse generator, in order to code the fullest possible speed range of the car, works off an electronic switch system. The differing pulse rates (speeds) are coded to different combinations of switches in either on or off positions.

I think 17mph is the minimum switch combination in order to leave enough switch combinations available to code the top end speeds.

 

[BennyD]

It seems to work as mine reads about 2 mph fast at 165 (compared to GPS).

 

[Emtee]

Yes I've noticed a slight speed difference when compared to a GPS. Apparently you can get GSP speedometer modules that feed a much more accurate pulse to the speedo dial and obviously aren't affected by tyre choice.

 

[Grinzzz]

Its odd, dont know why maserati choose to do it. Our discovery is fully electronic dash and so works off pulses from a magnetic switch (probably the ABS system since there arent any other speed sensors). It has no problem reading as low as 5mph and it's pretty accurate (within 1mph) according to our handheld GPS (which being older than most doesnt have much clever software in it and hence is quite accurate too) at most speeds.

I've not noticed any modern car I've driven NOT reading down to zero. But then again it's not something I tend to look for.

Wouldnt trust GPS speedometers. Ok in a boat, but have you looked at the raw GPS signals in a city! The amount of time you only have one satellite is quite frequent. Modern Satnav systems compensate by "guessing" for any short gaps in coverage. Not much use for a speedo!

I'll go with the "it looks fast when it's standing still" explanation - much more interesting!

 

[Emtee]

What's the top speed on the Disco' Grinzzz? Apparently it's catering for 170(ish)mph and above that lifts the minimum code-able speed.

 

[dunnah01]

Not sure that a speedo would work very well triggered off an ABS sensor which measures wheel rotation (or lack of it) - if you light up the rears (this option is only available on a 3200 obviously) your speedo would say your doing 174mph when your only doing 20mph?