Bully Dog 40420 gauge GT tuner - Manual (Page 14)

GT
DIESEL
13
Driving Coach Setup (continued)
Checking Speedometer Accuracy
First: Change the Gauge Setup to have the Speed displayed on the main display screen. See page 9 for more information about changing the
information displayed on the main display screen.
Next: Go to a safe place with little to no traffic where you can perform a speed test. Make sure the speed limit is at least 60 mph. Here are two different
ways to find out your vehicle’s actual speed:
Method 1: GPS
1. Use a GPS device to compare your actual speed and the speed displayed on the Bully Dog.
2. Calculate the Percent Difference by using
this formula:
Method 2: Stopwatch
1. Use a Stop Watch to measure how long it takes to travel one mile while traveling at 60 mph according to the GT.
Accelerate up to a speed of 60 mph (as shown on the GT)
While traveling at that constant speed, record the amount of time in seconds that it takes to travel exactly one mile.
*Use highway mile markers to ensure that your one mile measurement is correct.
2. Record the time.
3. Calculate the Percent Difference.
If it takes 60 seconds to travel one mile
at 60 mph, then the GT is accurately
reading your vehicle speed.
If it takes 2 seconds more or less than
60 seconds to travel one mile, then use
the formula to the right to calculate the
Percent Difference.
Once you have calculated the Percent Differ-
ence, you can use that information to adjust
the speed display as described below
Adjusting the Speed Display
1. Use one of the methods described in the previous section to determine the exact percentage difference between the GT and your actual speed.
2. Choose the opposite percentage in the Adjust Speed Display menu.
For example, if the difference between your actual speed and the speed displayed on the GT was 5%, you should choose -5% (negative five percent).
To calculate the percent difference use this formula:
Recorded Time - 60 seconds
60 seconds
Example 1: Using a stop watch the actual time it took to drive one mile while traveling at
60 mph according to the GT was 63 seconds.
63 - 60
60
3
60
.05 or 5.0%
Percent difference =
Step 1. Percent difference =
Step 2. Percent difference =
Step 3. Percent difference =
GT speed - GPS Speed
GPS Speed
Example 1: A GPS device reads 65 mph and the GT reads 62 mph for one single moment.
62 - 65
65
-3
65
Step 3. Percent difference = .046 or 4.6% then round up 5%
Percent difference =
Step 1. Percent difference =
Step 2. Percent difference =