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  #1  
Old 03-20-2007
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Speedo Adjustment

Now that I have 30x950x15 BFG ATs on my truck
where I USED to have 225/70/15

with the old tires, it could always run down the hiway at 72MPH
now the best it would do is about 68MPH

It's only a 4 wz a 5 spd, so it seems with the bigger tires I lost some speed, power and MPG

How can I tell what the real speed is on the sppedo since the change??
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Old 03-20-2007
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Convert Metric Tire Sizes to Inches:
http://therangerstation.com/tech_lib...nch_Tires.html

225/27R15 = 27.4 inches diameter

Checking your Speedometer After Changing Tire Sizes:
http://therangerstation.com/tech_lib...rom_Tires.html

Original Tire Diameter: 27.4 inches
New Tire Diameter: 30 inches

At 100mph actual speed is 109.5mph

109.5 / 100 = 1.095

Multiply whatever speed you are traveling by 1.095:

60mph * 1.095 = 65.7mph

Additionally for calculating gas mileage:

1. Fill tank completely
2. Reset Tripmeter
3. Drive until tank is close to empty
4. Fill tank at same pump
5. Take mileage on tripometer and multiply by 1.095
(ex: 200 miles * 1.095 = 219 miles actual distance traveled)
6. Take amount of gasoling required to fill your truck and divide actual distance traveled by amount of gasoline
(ex: 219 miles / 12 gallons = 18.25 mpg)

Taa Daa!
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Old 03-21-2007
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thanks
just the info I needed
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Old 03-21-2007
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if you have an '01+ get a SCT XCalibrator 2.....it will correct your speedo and give you performance tunes...
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Old 03-22-2007
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get a what??
more details please
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Old 03-22-2007
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Superchips programmer. It reprograms your computer to advance timing to accomidate for a higher octane fuel, which generates more power. It also can read diagnostic codes, firm shifting in auto transmissions, reprogram your speedometer for different tire sizes and or gear ratios, etc. Search google for "Bamachips" for more information.
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