do older car speedometers read more than actual speed?

[jon-]

All cars are calibrated slightly over, old or new.

The amount varies from model to model.

[kambites]

In my experience, most cars are calibrated to over-read by roughly 5% (the middle of the permissible range).

Modern speedometers are fairly precise (assuming the right tyre pressures), but not very accurate.

[Martin_Hx]

Some of those flashing things flash even under 30! More of a reminder not a warning I suppose

[DKS]

At that age it still likely electronic, so if it works at all its most likely reading the same as when it first rolled out the factory.

[Shaw Tarse]

The speedometer on my XR3i was very optimistic

[CrutyRammers]

Yes, as above. A speedo may overread to an extend, but must not underread. Thus manufacturers will make them read over by a comfortable amount to account for variances in production.

On my Dax, I callibrated it to 1mph over on the rolling road. The VOSA tester said he found it very hard to check because it was so close, he had to hold his speed very accurately

[A900ss]

The speedo on my TVR is unbelievably accurate. 80 mph on speedo corresponds to a true 79mph from the sat nav.

It holds that accuracy all through the speedo range. My modern BMW is going 77MPH at an indicated 80Mph

[Captain Muppet]

jon- said:

All cars are calibrated slightly over, old or new.

The amount varies from model to model.

Also the speed limit flashy signs aren't calibrated precisely, and the amount varies from sign to sign.

I pass through three in a row once a week, and they go off a different speeds.

[Kev T360]

I read once ( in PBMW mag I think) that in a bmw to do a true 155mph the speado will have to read 168mph. I might be wrong though.

[Johnnytheboy]

Those speed activated signs seem to lie a bit, my road angel will be reading 30 and they'll be showing 32.

[Captainawesome]

if you go past those signs at 100 you just get 3 lines instead of a speed.

[sandman77]

The signs can be programmed to come on at any set speed. They can also be programmed not flash at all if you are above a certain speed (to stop people competing for the highest reading).

[McSam]

kambites said:

Modern speedometers are fairly precise (assuming the right tyre pressures), but not very accurate.

Exactly this.

[Matt UK]

Neither your car nor the road-side sign will have NASA levels of precision calibration.

[Dave Hedgehog]

A900ss said:

The speedo on my TVR is unbelievably accurate. 80 mph on speedo corresponds to a true 79mph from the sat nav.

It holds that accuracy all through the speedo range. My modern BMW is going 77MPH at an indicated 80Mph

many modern audi's i have tested have been bang on as well

[JDMDrifter]

See in my car ive noticed it reads say 70mph but a satnav read about 76mph? Either one of them is wrong or they're both fluffed

[GroundEffect]

JDMDrifter said:

See in my car ive noticed it reads say 70mph but a satnav read about 76mph? Either one of them is wrong or they're both fluffed

Your speedo, by law, is not allowed to read less than the 'real' speed, therefore they run them with a bit of discrepancy. If you're that much over you probably either have bald tyres or they're under-inflated.

[dbdb]

Does your car have its original wheels? If it does not, then they may not be the same size. If so, this will affect the accuracy of the speedometer.