Other S80 Problem: Speedo not reading correctly

[sparkeysteve]

i've noticed that the speedo is really out.
speedo tom tom
80...........71
70...........62
30...........24

now i know speedo's arnt spot on but this is way out
any idea's why and how to sort it out?

[wise old monkey]

have you changed your tyres or wheels, but that difference is quite normal, unless you have a expolice car which is caliberated, my tomtom is the same as my speedo

[harveys]

My van is pretty much the same difference , you have a margin not to get caught speeding.

[davebb]

Hi what is strange , if you reed the speed with vida or any obd2 programme or reader the speed will be the same as the gps
Dave

[Darlo 1]

No that is not normal that's friggin miles out.

[Rossi-fan]

I think you'll find most speedometer's show a higher speed than you're actually travelling at, it should never be the other way round. Mine is nearly 10% fast, but I can live with that tbh.

[petey]

Recently, I had a front abs sensor and ring failure. Whilst this issue was developing, there was a very subtle cyclic surge when using cruise control that wasn't there when using the throttle pedal for the same speed, so I assume that the vehicle gets a speed signal from the aggregate value of each wheel. Certainly, a code reader gave me 5 speed outputs. Potentially you could have a speed signal from one of the wheels thats woefully out?
Either that or it's on a wheel tyre combination that it's not expecting.

[Joe Harding]

Sat navs I've used always read low. Typical figures might be 70 on the speedo and 65 on the sat nav.

But try going up to one of those speed warning signs that tell you your approach speed. I've found those agree exactly with my car speedo.

Don't trust the sat nav. The grumpy guy in the fast car with blue flashing lights won't be impressed.

[GreenBrick]

My v70 speedo overreads to my GPS quite a lot.
I would prefer it to be accurate and let me decide what is right and wrong!

[Clan]

Originally Posted by sparkeysteve

i've noticed that the speedo is really out.
speedo tom tom
80...........71
70...........62
30...........24

now i know speedo's arnt spot on but this is way out
any idea's why and how to sort it out?

These people will calibrate it for you , they have been doing the police volvo speedos going right back to the 850 T5 days ...

http://www.irs-gb.com/police-en.html

There is also a limited amount you can do in the DIM with VIDA you could change tyre sizes to optimise it or it may not match the tyres you have on ..

GPS is only correct on a FLAT and Straight road ...
if you were going up a 45% hill it would read half ...

Likewise it would read slow on a bend as it calculates speed between two fixed points and it cuts the corner with a straight line when getting it's coordinates it gets worse the faster you go around a bend .

The speedo has the ability to read exactly correct with the technology in the car but volvos and most cars seem to read about 8% high to give a margin of safety for speed cameras etc .