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Old 08-30-2005, 09:41 AM   #1
02_Forester
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Location: Northern VA
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Sonic Blue

Default Calculating miles traveled vs speedo inaccuracy

My 225/45 18s run about 2mph slower than what the speedo actually indicates. Does this impact the actual miles traveled?

If so, is there a mathmatical calculation I could use to determine the actual miles driven vs what is being displayed?

thanks.
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Old 08-30-2005, 11:17 AM   #2
Howl
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1999 OBS

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Your speedo and odo work off the same gearing. The gearing is set at the factory and is usually a bit fast with OEM tires (speedo and odo read high). How much it's off depends on the size of your tires. Even tire wear can affect your odo/speedo over time. That's why TSD rally people use adjustable odos.

I found that my TS with 195/60-r15's was about 3% off. With 205/55-r16's it's about 0.5% off.

The formula is simply a percentage. If your odo/speedo is fast by 1% and your speedo reads 50mph you are actually travelling at 49.5mph. If your odo says you've travelled 1,000 miles you've actually travelled 990 miles.
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Old 08-30-2005, 11:50 AM   #3
ripvw
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Old 08-30-2005, 03:53 PM   #4
02_Forester
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Thanks guys
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