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Old 09-22-2009, 11:59 AM   #16
onshore
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Quote:
Originally Posted by texomawaves
Results from my lunchtime test drive to get a Sonic burger:

7.1% error against the speedometer (75-70)/70 * 100 = 7.1%
2.9% error against the HVAC diagnostic (106-103)/103 * 100 = 2.9%

I am not sure what to conclude from this other than the HVAC diagnostic is closer to the GPS reading than the speedo, duhh. So perhaps my Pirelli Pzero's are too low of a profile. I guess I might consider bigger tires. The ones I currently have are 205/50 ZR-17 on the front, and 255/40 ZR-17 on the back. Perhaps a "taller" tire will shave off a few percentage points on the error.

So guys... what size tires are you running? ...and what error are you getting? Let's compare.

Chris
I'm running the same tires as you but on 16" wheels and my speedo is exactly 5 mph faster than my GPS or the radar guns they use to warn you of your approaching speed. All this time when I was doing 75 and thinking my spoiler was up it wasn't. Dang!
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