Is the speedo accurate..??

[bobbyboy]

The only reason I ask, is that after dropping my sons girlfriend off at home I have a 3/4 mile run along a dual carrageway...Bieng in a bit of a rush to get home last night I was a bit heavy with the right foot........traffic lights looming ahead, I think ...hmmm....going a bit quicker than normal..looks at the speedo....... 110 mph.... ..looks at my son....big cheesy grin... ...

whoa neddy.....but I cant help but feel impressed that the car seemed to get there effortlessly and quickly.... ...

IF it was actually going that fast......

my son now thinks im a speed demon and it seems I am a little bit cool for an "old un".... ..

(I will relish this for a few days...before I start lecturing him on the effects of excess speed and I "only did it try try and frighten him" leaving out the bit that i didnt even know!!!!....)

[Maddog1974]

My actual speedo seems the read 3-4mph high but you were still going pretty well your another one who owns a private road i guess

By the way i'm comparing to a fitted nav using gps & speed pulse info!

[VectraV6CDTi]

You know if its accurate - when you get a big white car with stickers down the side and a flashing blue light on top chasing you

[Gsi3.2]

100mph on my speedo is 94mph on GPS..

all done on private land of course..

[Elite2.2DTi]

My GPS readings are always a few mph different to the speedo, as said my mark above.

[TechWolf]

Mine shows 4-5km/h high all the way ...

[leeds vectra]

I have noticed this in all Vauxhall's i have owned since having stand alone gps. Even at work the truck I drive reads 2-3mph more than what gps is showing.

[bobbyboy]

I have noticed this on the motors at work...4-5 mph difference..I wonder which is correct...???? hmmmm....

[Ste]

I would think that the GPS is more accurate then the speedo, as the speedo measures the rotational speed of one of the front wheels, actual forward speed can change but still have the same speedo reading as the rolling radius of the tyre changes by tyre wear, inflation etc etc.

[Duncan]

It's normal practice for speedos to over read by a few mph. A speedo can over read by up to 10% iirc, but it can never under read. e.g. it can show 70mph and you're actually doing 65mph - that's okay. But it can't show 69 mph and you're actually doing 70mph.

So manufacturers just have them set to over read slightly to avoid that possibility.

D