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      09-01-2008, 03:52 PM   #1
ZoinksM3
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19" wheels and speedo accuracy

This is a minor annoyance, but the speedometer seems off on my M3. The "analog" readout is a bit high for the given speed. The digital measurement seems accurate when compared to two seperate GPS devices (not BMW NAV).

This a problem? I have the 19" factory setup.

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      09-01-2008, 03:56 PM   #2
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i've noticed the same thing on mine. and when i pass a radar speed sign, it always displays a lower speed on the sign than both of the speedo's in the dash.
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      09-01-2008, 04:04 PM   #3
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Quote:
Originally Posted by blakepilot View Post
i've noticed the same thing on mine. and when i pass a radar speed sign, it always displays a lower speed on the sign than both of the speedo's in the dash.
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      09-01-2008, 04:12 PM   #4
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Some more detail...

I drove up from Austin today and had some time to test it. Once again, the digital readout on the cockpit display looks to be accurate, the "analog" dial is fast. I first noticed it when I set the cruise control, so I switched my Passport 9500i to speed display (great gizmo, btw). Matched the digital readout. I then broke out my trusty Garmin Nuvi, it showed the same.
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      09-01-2008, 04:40 PM   #5
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just for shitzengiggles, i just did a run around area with my 9500i (ftw) set on speed display also. i set cruise on 30, 40, and 50. each time my passport read out 2mph lower than the digital or analog displays in the dash. very strange indeed.
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      09-01-2008, 06:37 PM   #6
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2 to 3 mph difference? thats nothing.
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      09-01-2008, 06:42 PM   #7
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All BMW speedometers are optimistic. In Germany, it is illegal to have a speedometer that reads on the low side (e.g. you are going 83 but the speedo reads 80).

This topic has been talked about A LOT on here.
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      09-01-2008, 07:06 PM   #8
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better err on the safe side.
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      09-01-2008, 07:10 PM   #9
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Using the serect menu, I determined that the digital readout is about 4-5% optimistic.
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      09-01-2008, 08:46 PM   #10
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19" wheels should not make a difference. The 19' tires have the same rolling radius as the 18' tires, give or take a tiny amount, as the profiles are different.
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      09-01-2008, 09:07 PM   #11
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As noted, 19" vs. 18" wheels have absolutely nothing to do with anything.
And it is normal for the analog speedometer to read 4 or 5% over. It is the law in some countries and the manufacturers covering their ass liability wise everywhere else. If you spend any time on car forums you'll see this subject come up on a regular basis.
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