speedo accuracy

[Colin P]

Hi all, while following my wife who sticks to speed limits religeously i noticed in the 30mph zones my speedo was showing app 35mph. I then got her to flash her hazard lights at exactly 30mph and sure enough i was showing 35mph. Is this normal for my 75 club se cdt or do i have a fault somewhere.
Thanks
Colin.

[macafee2]

all I can say is that recently I was showing 30mph when a digital sign flashed up that I was doing 27mph.
macafee2

[stevenkeyte]

The speedo on all the 75's I've owned read slow, typically reading 70mph against an actual speed of 65mph (as indicated by a satnav) and when the speedo reads about 33 / 34 the actual speed is 30 mph

Steve

[IverRover]

I noticed exactly the same thing during our holiday drive to Devon. Towing a caravan and travelling along the M4 the cars speedo said we were travelling at 60 mph but sat nav said no no no.....you're only doing 55.

Digital speed sign near home in Uxbridge said I was doing 26 when speedo showed 30

In my previous job demonstrating new cars around the UK, almost all cars speedos were out by about 3 mph but around 5 seems a bit excessive. Tyres are all brand new on my car so not down to tyre wear, so it would seem it is a particular fault to the 75's.

Will be interested to see if anyone of our clubs more technically gifted members has looked into this and come up with any solutions.

[ako2k7]

Originally Posted by IverRover

I noticed exactly the same thing during our holiday drive to Devon. Towing a caravan and travelling along the M4 the cars speedo said we were travelling at 60 mph but sat nav said no no no.....you're only doing 55.

Digital speed sign near home in Uxbridge said I was doing 26 when speedo showed 30

In my previous job demonstrating new cars around the UK, almost all cars speedos were out by about 3 mph but around 5 seems a bit excessive. Tyres are all brand new on my car so not down to tyre wear, so it would seem it is a particular fault to the 75's.

Will be interested to see if anyone of our clubs more technically gifted members has looked into this and come up with any solutions.

Yeah, id agree with this. My car is roughly 3mph out at 30mph, my mate has an astra and a transit van and they both do this too

[Mike24]

I have the digital speedo enabled on the IPK; when the main speedo is showing 68mph the IPK is showing 65mph. However, GPS says the actual speed is nearer 62mph - this would mean that the speedo is over-reading by about 10%, so 3mph at 30 - 4mph at 40 etc. I have read in other threads that the main speedo over-reads by between 5% and 10%, but I'm not sure whether the gps on my phone can be trusted - perhaps others who know more about GPS could comment?

[Mike24]

Hi IverRover; you must be one of my nearest neighbours on the forum!

[Colin P]

Thanks guys feel a bit better knowing its not just my car and seems to be a common fault.

[IverRover]

Originally Posted by Mike24

Hi IverRover; you must be one of my nearest neighbours on the forum!

Hi Mike24. Yep only just down the road but you'd be surprised just how many club members there are about locally, some of which I got the chance to meet up with towards the end of last year at a group meeting held near Blackwater. All welcoming and helpful.

[IverRover]

Originally Posted by Colin P

Thanks guys feel a bit better knowing its not just my car and seems to be a common fault.

I wasn't aware you could have a digital readout enabled on the ipk but as it would appear this gives a different reading to the speedo, I wonder if this 'common fault' is due to the mechanism that drives the speedo? Is is electronic or as in days of old, a worm drive in the gearbox on the end of a cable between the two (gearbox and speedo), and the drive wearing with age or just purely poorly designed.