How far off is your spedometer?
04-16-2005, 10:08 AM
#1
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How far off is your spedometer?
I found this post on one of my other forums I hang out on, thought you guys might like to read it, I know I am going to try it out.
Everything looks good to me (math wise) I just need a chance to test it out.
lately my car has been showing 74mph on the speedometer @ 3000 RPMs
I used the formula
MPH= (tire dia in inches * RPMs) / (336 * diff ratio * 4th gear ratio)
this is where I found this formula
MPH =(24.8" * 3000RPMs) / (336 * 2.74 * .98)
MPH= 82.5
I made five one mile runs. timed with a stop watch. my cruise was set at 60mph on the speedometer the adverage time was 55 seconds per mile
60mph/60min = 1mile per minute @ 60mph
1 hours is 3600 seconds so 55sec / 3600sec = 0.0153 hrs
use the distance formula D=RT leaving R as the unknown R= D / T
R=1mile / 0.0153 hrs
R=65.4mph
so my speedometer is 5.4mph off. dry.gif
Percent Error = (math value - speedomete value) / speedometer value x 100%
PE = 9% off for the speedometer
percent error for the car over all
so if I go back and add 5.4mph to 74mph its 79.4mph at 3000RPMs
PE = (82.5 - 79.4) / 79.4 x 100%
PE = 3.90%
so my car is within 4% of where it should be at a certain RPM. I guess thats not soo bad on a 123000+ mile car.
I used the formula
MPH= (tire dia in inches * RPMs) / (336 * diff ratio * 4th gear ratio)
this is where I found this formula
MPH =(24.8" * 3000RPMs) / (336 * 2.74 * .98)
MPH= 82.5
I made five one mile runs. timed with a stop watch. my cruise was set at 60mph on the speedometer the adverage time was 55 seconds per mile
60mph/60min = 1mile per minute @ 60mph
1 hours is 3600 seconds so 55sec / 3600sec = 0.0153 hrs
use the distance formula D=RT leaving R as the unknown R= D / T
R=1mile / 0.0153 hrs
R=65.4mph
so my speedometer is 5.4mph off. dry.gif
Percent Error = (math value - speedomete value) / speedometer value x 100%
PE = 9% off for the speedometer
percent error for the car over all
so if I go back and add 5.4mph to 74mph its 79.4mph at 3000RPMs
PE = (82.5 - 79.4) / 79.4 x 100%
PE = 3.90%
so my car is within 4% of where it should be at a certain RPM. I guess thats not soo bad on a 123000+ mile car.
04-16-2005, 10:17 AM
#2
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all that math makes my brain hurt. but is cool and would be nice to try out if you had the means and wanted to know the deal. especially if you have different size rims than factory.
04-16-2005, 11:09 AM
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I want to go try it out, but I need the differential and 4th gear ratios, anyone know where to find them?
http://www.internetautoguide.com/car...1997/acura/tl/ Differential ratio is 3.133:1 correct?
http://www.hondanews.com/CatID3015?m...&archives=1998 Fourth gear ratio is 0.654 correct?
http://www.internetautoguide.com/car...1997/acura/tl/ Differential ratio is 3.133:1 correct?
http://www.hondanews.com/CatID3015?m...&archives=1998 Fourth gear ratio is 0.654 correct?
04-16-2005, 02:36 PM
#4
TL no more!
I track my speed with my GPS. When the speedo shows I'm going 74, the GPS shows that I'm actually going 70. But at lower speeds, our speedos are pretty accurate.
04-16-2005, 03:42 PM
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My speedo is accurate up to 85 (at least)
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