172 / Cup speedo accuracy

[CUP80Y]

Just read on another thread that the speedos on the 172 / Cup are prone to under-reading???

Is this correct, as I always thought it was approx 10% over-reading, say at a 110 im really doing 100.

I always go through speed cameras just over the limit so if the above is true im about a nats chuff away from getting flashed bearing in mind the sort of leeway they allow.

 

[JAY172]

a speedo will get more inaccurate the faster you get.at low speeds it will be about right but at 100mph it could read 10mph to much.

 

[CUP80Y]

Thats what I mean Jay, itll over read rather than under. At 110 as indicated by the speedo, I am actually doing more like 100, rather than the other way round as this other thread suggests. Just like to know where the limits are!!

 

[JAY172]

i always thought if owt they would overead but i dont risk it through speed camaras.

.

 

[CocoPops]

When my Origin B2 says 70mph, my 172 speedo says 75mph

 

[JAY172]

that what i was saying as you get faster the speedo will start to get inaccurate.5mph not much though is it?

 

[Rich-D]

Speedo error is a percentage, so naturally as you go faster the actual error in terms of mph becomes greater.

Not tested my Cup with GPS, but my mates mk1 172 was showing 100mph on the speedo and reading 98mph actual, and my 306 Rallye was showing 100mph on the speedo and 97mph actual, so quite low and its often more than this.

 

[Tom]

They will NEVER over read.

The ecu actually receives the actual speed of the vehicle.

but the speedo wont show that as its re calculated.

 

[JAY172]

the ecu recives the average speed of all 4 wheel sensors calculated by the abs ecu on the abs system apart from on the cup that has a speed sensor in the gearbox.there is every chance it may overead very slightly.

 

[Tom]

The systems are very accurate jay the ones i was testing today on a fiesta were out by .004mph