Not to get off track maybe falls in with speed tickets arguments if radar gun not calibrated.
Also understand there is +- % acceptability range for OEM
There is an Internationally Agreed allowance for OEM Speedo/Odo variations, but it's not a 'plus/minus %' thing - it's
JUST a plus!! OEM Speedo/odo's can read up to 10%
OVER the vehicle's true/accurate speed, but they're not allowed to read
UNDER at all! :lecturef_smilie: And given that most manufacturers really don't want to get caught up in the litigation that would surely follow if people relied on their speedo/odo's to avoid speeding tickets, only to find their speedo was telling them they were under the speed limit only they weren't really, almost every speedo leaves the factory reading something faster than the true/accurate speed & usually their odo's also read that they've travelled more miles than is strictly accurate... both often by something close to 10%! :gaah:
So Joe Bloggs in his Bowling hat & shirt tooling along happily in his brand new car on its standard sized tires at what he thinks is a reasonable 60 mph & not giving a crap about making it easy for anyone caught behind to get past is far more likely to be doing something closer to 54mph than he is to be doing 60 mph! :banghead:
That might not seem to be a biggie in the overall scheme of things
for him, especially if he's only driving the 2-5 or maybe even 30 miles or so to the Bowling Alley; it might not be too bad for anyone caught behind him who's only travelling the same sort of distances or who has no time constraints on their travel; but for those who drive for a living &/or work/drive/live on a tight schedule, or for anyone who's got 600 or maybe even as much as a 1000 miles to travel
today, all they need is a few 'Joe Bloggs' holding them up and suddenly their schedule's blown out the window or their day became a few hours longer - and if they have a limit on the number of hours per day that they're permitted to travel before risking massive fines (like the truckies do here in Oz!) that could mean the difference between making ends meet or losing money &/or business if not their livelihood!! :gaah: Besides, you never know if that other driver who is trying to get past is a Doctor racing to save a life; a parent racing a sick child to hospital; or someone with another perfectly valid reason for them to be trying to travel closer to (or over??) the speed limit than your deliberately inaccurate OEM speedo suggests is the speed limit - so it's really only common courtesy to let them past at the first safe opportunity
and if they're just speeding for the heck of it, as some might do (
pps: ) surely it's better to have them pass & get out of your way as quickly as they see fit instead of risking you becoming their bonnet ornament?!?
Btw, due to the way these speedo/odo's &/or dash modules are manufactured & driven (& Mike
is right about them usually being linked & driven by the same things!
)
generally both the speedo & the odo in any one dash will read both faster mph's & more miles travelled than is strictly true/accurate, but they won't necessarily have the
same discrepancy - they
might, but that's usually a coincidence! So if you change tire sizes to change one/make one reading more accurate, you'll usually change them both by the same percent. Similarly, if you do anything to change the sender/sensor signal, their proportional error will generally remain the same if/when any correction is applied, unless you change the programming on one & not the other, which isn't easy!
And it's also pretty rare for any two vehicles to have
exactly the
same discrepancy/s too, so however much
YOUR speedo/odo is out doesn't necessarily mean that anyone else's speedo/odo will have
exactly the same discrepancy - and then there's the differences introduced by varying tire sizes, tire pressures, road surfaces, rolling resistance, and a bunch more besides!! But at least in these days of electronic instruments & dash units, senders, sensors etc, the variation/errors between speedo/odo's on different vehicles are usually reasonably similar & relatively easily corrected, be it by re-programming, changing tire sizes, or intercepting & modifying the signal!
hyea:
Just Sayin' :thumbup:
I don't see why I would care that my dashboard speedo is 2mph faster than my mounted Garman GPS(??) I kind of like that fact. It keeps me from going over the posted speed limits in "speed trap zones, etc. 
