Many Cinq Sporting owners on standard tyres have noticed that the speedo reads faster than the real speed.

By chance I've found the reason: in fact it's not the speedo as such, it's the markings on the mph speedo which create the problem!

Here's a picture of my instrument panel:



And here's a picture of a kph speedo:



Notice for example where the MPH speedo is marked 60, the KPH is marked 90... but 90 kph is 56 mph.. :bang:

I live in France where the standard speed limit is 90 kph.. With a satnav to confirm the speed, the needle is exactly vertical, so would be spot-on with a kph speedo!

The difference is about 6%. I've just fitted 175/60R13 Toyo Proxes CF2 tyres (a post on why, etc, to follow) which are... 6% bigger in diameter! So with my MPH speedo, it is now near-enough dead accurate

There is also a legal issue about over reading speedos.

They are only gauges, not instruments.

D

I noticed something too, not quite Cinq, but still Fiat group.

The Alfa Romeo 145 Cloverleaf and the "lesser" models have the same speedo and speedo drive, but the lesser models have slightly smaller tyres, about 2%

Is this a cheap method of ensuring the "Sports" model appears quicker? For the same apparent speedo reading, it'll be going faster.


With Cloverleaf rims and tyres on my 145 TD, the speedo is dead on.

manxfrance said:

Many Cinq Sporting owners on standard tyres have noticed that the speedo reads faster than the real speed.

By chance I've found the reason: in fact it's not the speedo as such, it's the markings on the mph speedo which create the problem!

Here's a picture of my instrument panel:


And here's a picture of a kph speedo:



Notice for example where the MPH speedo is marked 60, the KPH is marked 90... but 90 kph is 56 mph.. :bang:

I live in France where the standard speed limit is 90 kph.. With a satnav to confirm the speed, the needle is exactly vertical, so would be spot-on with a kph speedo!

The difference is about 6%. I've just fitted 175/60R13 Toyo Proxes CF2 tyres (a post on why, etc, to follow) which are... 6% bigger in diameter! So with my MPH speedo, it is now near-enough dead accurate

Click to expand...

Your "UK" speedo is correctly marked, note the yellow 100kph mark at 62mph. The pointer position is diffeent on the two speedos for the same speed. The error is tyre size and deliberate over-reading calibration. The regulations (and/or lawyers) do not allow for an under-reading speedo.

Robert G8RPI.

So this is why driving a Cinq feels like a Ferrari!!!
?

Steve145 said:

I noticed something too, not quite Cinq, but still Fiat group.

The Alfa Romeo 145 Cloverleaf and the "lesser" models have the same speedo and speedo drive, but the lesser models have slightly smaller tyres, about 2%

Is this a cheap method of ensuring the "Sports" model appears quicker? For the same apparent speedo reading, it'll be going faster.


With Cloverleaf rims and tyres on my 145 TD, the speedo is dead on.

Click to expand...

The legislation requires that any speedometer reads the correct speed, or up to 10% higher than actual.
Years ago manufacturers would specify different speedo drives for models with alloy wheels, but these days, they try to specify from the cheapest with steels to the highest spec alloys all within 10% rolling diameter. That is also taking into account the max wear on the smallest diameter, which would give the fastest reading. Cheaper that way, as just one speed signal to calibrate.
Many these days also do not have a separate speed sensor, taking a reading of the average from the ABS sensors.

Speedometers were calibrated to the gearbox that originally appeared on the Fiat Panda 999ie and 1100. Those cars used 145-70-13 tyres and the Cinquecento Sporting uses 155-55-13 tyres.

I always thought it was the difference in overall circumference that generates the false reading.

g8rpi said:

Your "UK" speedo is correctly marked, note the yellow 100kph mark at 62mph. The pointer position is diffeent on the two speedos for the same speed. The error is tyre size and deliberate over-reading calibration. The regulations (and/or lawyers) do not allow for an under-reading speedo.

Robert G8RPI.

Click to expand...

60 mph does not equal 90 kph. The 100 kph mark on the kph speedo is visibly 'to the right' of the 100 kph mark on the mph speedo. UK and European Sportings have the same tyres as standard. Is it documented that UK speedos are deliberately calibrated to over-read? Why would Europeans not want the thrill of imagining they were going faster than they really were? To me it seems more than a coincidence that on standard tyres the speedo reads accurately on the kph speedo. The over-reading on the mph speedo, whether it is a fluke created by the designer wanting the mph speed markings to be symmetrically arranged around the dial, with 60 at the top, or a deliberate wheeze to impress UK buyers, is surely achieved just on the dial, don't you think?

Hi,
I did not say that 60mph was 90kph. The Speedo clearly is marked as 100kph = 62mph. This is correct. The UK instrument is correctly marked.

Robert G8RPI.