Speedo accuracy in '99 Z3M

[classicwhaler]

Just stumbled upon and happily acquired a '99 Z3M with only 15k miles and in like new condition. But it seems the speedometer is about 4 or 5 mph too fast at 70. Actual speed is about 66 according to the GPS and and an accompanying vehicle. Tires are original size. No mods of any kind. Any thoughts? Thanks!

[Numark318i]

i do believe BMW does this on purpose. Its off a few mph to save you ass? something about speeding tickets and the autobahn?

anyone confirm this?

[witeshark]

Yeah I have heard the same thing.

[denyo77]

I can confirm this at least for all European cars.
It's ok.
Saves your ass.

[darreldore]

German law allows manufacturers to have speedometer that read too fast, but the law prohibits ANY error on the slow side. My 2000 Z3 reads about 6% fast thru the entire range BUT the real impact is that all service is increased by the 6% factor. The worst speedometer/odometer error I ever had was in a 1971 Porsche 911T that read 12% fast. That meant that the already expensive Porsche service was increased by 12%!

[denyo77]

mine shows about 60 kph when I drive 50
which is why I don't get teh tickets

btw it's been a ticket week for my family, tho:
my bro: 3 tickets, one with 58 kph too much (will lose his license for some months)
dad 1 ticket, mom 1 ticket.
And I'm faster and don't get caught

[///M Power]

I believe the error margin should be no more than 2-4%, but this is supposed to increase with speed up to the 4% max. You should probably get your speed sensor checked out. To be perfectly honest i've never heard anyone with such a large speed error at only 70 mph.

[Teh Prof]

Originally Posted by ///M Power

I believe the error margin should be no more than 2-4%, but this is supposed to increase with speed up to the 4% max. You should probably get your speed sensor checked out. To be perfectly honest i've never heard anyone with such a large speed error at only 70 mph.

Both of my E39's had about the same error as his. My M3 had a much lower error.

[dudex]

i saw this topic yesterday and tried to give it a test,
i brought my portable GPS and went in a jeep and altema and then my z3
all of those cars where at 100km and the GPS where from 93 to 96Km

problem solved,
Thanks