How accurate are the speedo's in these things? Just curious if I actually was going as fast as the speedo claims......lets just say it was up there a bit.....

Just curious....

How accurate are the speedo's in these things? Just curious if I actually was going as fast as the speedo claims......lets just say it was up there a bit.....

Just curious....
$tealer told me speedo reads fast 3-4mph. You can check yours using the 'speed limit' function. Set for 100-your speedo should read 104. Or?? John.

I have my limiter set to 85 and the gong sounds at an indicated 89-90, so I'd have to agree with the 4-5mph fast comment.

I also recall an article in Car & Driver a few years back that found the same thing for the BMWs that they tested. I believe they also mentioned that if the tire/rim combination was changed from say 16" to 18" or more, the variance be less (??)

I believe they also mentioned that if the tire/rim combination was changed from say 16" to 18" or more, the variance be less (??)

There would only be a varience if the overall wheel/tire diameter changed. This is totally dependent on the tire you choose. There are several calculators available - I believe one is at http://www.miata.net/garage/tirecalc.html .

In my experience, the OBC is correct and the speedo tends to read high. I know Mark Wong (a fellow Seattle 7 and police officer) did a radar test at various speeds. When he reset the OBC, it read about 3 MPH slower than his speedo at cruising speeds. The radar gun test confirmed that the OBC was right on and the speedo was slightly high... However, not enough to make much of a difference. This is consistent across all BMWs. One theory is that German law is tough when speedos read lower than actual speed... I'm not sure if this is accurate.

Cheers,

In my experience, the OBC is correct and the speedo tends to read high.

Yes, I think Jack's speedo shows 145 when he is really only going 141, according to his OBC...

I'll have to check out the OBC limit alarm. I ran mine upto the 14x range. Couldn't believe how smoothly and quickly it got there. Wasn't sure I was really going that fast. The Old car ran steady at those speeds...and above....but you knew you were there. This thing is just so dang smooth.

Yes, it is built into the gauge to read faster than you are actually going, you can probably thank some lawyer for that. The actual mileage accumulation is correct though for all you "leasers" out there.