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04-28-2009, 10:47 PM
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#1 |
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Out of the carpool lane.
Join Date: Jan 2000
Location: Clark Co, WA
Posts: 5,672
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Math question-speedo mileage
My speedo is currently off by about 3mph at 35mph and I'm going approximately 38mph at 35. What percentage am I off and therefore how would this correlate for figuring mpg's?
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1968 C-10 SWB, 5.7 Vortec/700R4/3.73 posi, Torch Red 1968 Camaro, 250/Powerglide, all original (No, I'm not gonna drop a 350 in it!...Jeez!) 2000 Honda VFR in the faster yellow! 2008 Husqvarna TE-610 1967 C-10 SWB 'Six Appeal'-Gone but not forgotten... Last edited by Brad; 04-28-2009 at 10:48 PM. |
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04-28-2009, 11:05 PM
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#2 |
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Registered User
Join Date: Nov 2007
Location: Central OK
Posts: 396
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Re: Math question-speedo mileage
I would verify what speed your going at 65mph to start with, 35 is a little slow to get an acurate reading.
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04-28-2009, 11:09 PM
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#3 |
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20' Daredevil (Ret)
 
Join Date: May 2003
Location: Jefferson State
Posts: 13,722
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Re: Math question-speedo mileage
^^ I agree -- however, using your numbers....
3 divided by 35 = .0857, so you are off by 8.57% -- let's just say 8 1/2%. As to mpg, you'd need to make sure your odometer is also off, and by an equal percentage. Assuming it is, your odometer will register fewer miles than are actually traveled -- so your actual mpg will be better. Add 8 1/2% to your odometer's reading, then divide by the gallons used.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay Last edited by Stocker; 04-28-2009 at 11:10 PM. |
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04-29-2009, 12:41 PM
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#4 |
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Out of the carpool lane.
Join Date: Jan 2000
Location: Clark Co, WA
Posts: 5,672
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Re: Math question-speedo mileage
Thanks guys!
__________________
1968 C-10 SWB, 5.7 Vortec/700R4/3.73 posi, Torch Red 1968 Camaro, 250/Powerglide, all original (No, I'm not gonna drop a 350 in it!...Jeez!) 2000 Honda VFR in the faster yellow! 2008 Husqvarna TE-610 1967 C-10 SWB 'Six Appeal'-Gone but not forgotten... |
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04-29-2009, 12:57 PM
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#5 |
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Registered User
Join Date: Dec 2006
Location: Porter Ranch, CA
Posts: 978
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Re: Math question-speedo mileage
Also, these speedo's have a habit of not being off by a percentage, but a flat figure. Mine is off by 4 MPH at 30, 40, and 60. What the speedo guy told me is that the gauge was not zero'd properly when it was built. Get a read on it at 2-3 different speeds and see what it's doing.
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04-29-2009, 12:58 PM
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#6 |
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Registered User
Join Date: Dec 2006
Location: Porter Ranch, CA
Posts: 978
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Re: Math question-speedo mileage
Oh yeah, I forgot to add that my odometer reads dead on. That's why you want to really verify what is happening.
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04-29-2009, 01:11 PM
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#7 |
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Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
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Re: Math question-speedo mileage
Good point regarding the odometer versus the speedometer readings...
If the speedometer is off but the odometer is right then the speedometer mechanism is defective. It's basically a magnetic field induced by a rotating magnet which causes the needle to move. |
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