'94 Mercedes C200 speedo exaggerates speed by 5%
TE Cheah
( 195/65R14 Michelin ). Has any1 here noticed this difference ?
My gps reading is correct ; [i] my 2 cars ( Proton & Honda ) use
taller tyres than original, & this receiver correctly reports the
proportionately higher readings than speedos'. [ii] from gear ratios
& axle heights & zero toe-in, I can calculate speed @ different
engine rpm.
Roland Franzius
The speedo is not allowed to show less than the physical exact speed. So
for convenience (and a bit of exaggeration) they typically show +3% up
to +5%.
The radial difference of 6mm/300mm for new tires compared to old counts
for 2%.
The MB navigation system has a setting for age of the tires. In this way
exact distances can be read off the wheels rotation in case the
satellite contact is bad for more than lets say 100 m.
--
Roland Franzius
Kev
> : shows 105 kph when gps shows 100 kph. Tyre size was standard
> ( 195/65R14 Michelin ). Has any1 here noticed this difference ?
>
> taller tyres than original,& this receiver correctly reports the
> proportionately higher readings than speedos'. [ii] from gear ratios
> engine rpm.
>
>
you'd be hard pressed to find any car these days that doesn't read fast
In Australia the old design rules stated a speedo must be accurate to
within 10% +/- but around 2002 they changed it to be just 10% -/0
all my cars read around 5kph fast, changing my Landcruiser tyres from 31
inch to 33 inch made the speedo read true
This of course led the way for the Govt to make laws that make it
possible to be booked for speeding by 1kph over the speed limit and
arguing speedo error won't hold up
Our Trucks must be speed limited to 100KPH, but this speed limiting is
tested on Dynos not the off the vehicle's speedo, therefore you have a
truck driving along at 100kph and passing cars doing just 90-95kph. Then
these car drivers would call the Police and complain about all the
speeding trucks not realising that their speedo was at fault not the
truck drivers
Kev