NPR - Sat a.m. - Click and Clack, the tappet bros...

....was listening as drink my coffee read the paper when a call came in w/a ?? re: '99 BMW 540i, so naturally I perked up and listened... question was from two genius guys about how they've tested and tested and are determined that the speedo on their 540 is exactly 5.4% fast... theories flowed about conspiracy theories to get drivers to slow down, maybe this is tied into the odometer and our gas mileage is also off... etc. etc...

I learned on this board a long time ago that German law requires the speedos to NOT read any faster than the car is going... so they factor in about 4% error.. showing you're going 4% faster than you really are...

The callers also said they've tested Honda, Toyota, Mazdas with all the same result... thus the conspiracy theory... my guess is those are all "global" auto companies so they probably just make their speedos the same way to avoid headaches of adapting for the markets... as for our Big Three, (US) I haven't a clue....

Happy weekend everyone.. think I'll order those door latch seals today.
Cheers,

mine is 3% fast, tested with GPS this spring.

A few years ago, a co-worker said his Z3 was reading approx. 10 mph above actual. At the time, I couldn't find much on the web about it so I told him to ask the dealer's service department. Their answer: they take a pair of needle nose pliers, pull the speedo needle off the shaft & re-position it -- pretty high-tech, eh? I believe they can be re-calibrated thru the OBC.

Actually its possible. Did they change their tire size and rim? Back in the day I had a subaru GL wagon I put one size larger tires on it and the speedo was off by about 10 mph.

I know that OBDII can be reprogrammed to correct the speedo. Can't remember how. I think there is some option where it says tire size or something like that and it corrects it.

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Originally Posted by 92E34

I know that OBDII can be reprogrammed to correct the speedo. Can't remember how. I think there is some option where it says tire size or something like that and it corrects it.

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I think the speedo reading and the OBC calculation for MPH and odometer can have a different factor, so that the mileage and MPH on the car is as accurate as possible (given the car is using the right tire size... which will throw it off if not...) while the speedo can be 5% off.

Shogun probably has a link to a page that tells you how to reset the multipliers. What time is it in Japan? :)

I love click & clack!

I thought speedos are all set slightly fast by a tad, so that when you get a speeding ticket, you can't sue the car maker.