My Mark LT has a 33" inches tires, the stock tires were 31.9" and i just install 4.56 gears , stock were 3.75. So it means that right now i have a 1.1" inch higher tires and 4.56 gears instead of 3.75, I don't know if i am crazy but my speedometer seems to be at least 15-20 miles off. When the speedometer shows 80mph the truck seems to be at 60mph. Is there any way that i can calculate the real speed ?? And the other question is, will the Xcal2 correct 100% the speedometer ? Thanks a lot guys.

 

I'll give this a try. Anyone who finds a problem with my math below please feel free to jump in.

The effect of the tire change on your speedometer can be determined by dividing the circumference of the stock tires by the circumference of the new tires. This ratio will be 31.9/33 = 0.9667, meaning your speedometer is reading low (i.e., true speed = speedometer reading divided by 0.9667.)

The effect of the gear ratio change will be to make your speedometer read higher than actual. In this case, 4.56/3.73 = 1.2225, so your true speed = 1.2225 times speedometer reading.

Now, putting the two together: 1.2225 / 0.9667 = 1.265. So your true speed is calculated by dividing your speedometer reading by 1.265. (This is equivalent to multiplying your speedometer reading by approximately 0.80).

If you are reading 80 MPH on your speedometer, the above would mean you are actually going 63.2 MPH, so it appears your initial guess at your actual speed was close!

I do not own the XCal2, but from the posts I have read on this forum, the XCal2 *can* be programmed to correct your speedometer. I do, however, own the new Edge unit--this device will also correct your speedometer.

Isn't math fun? Good luck!

 

Xcal2 and most any other prog. will adjust for gears and tire changes!


C-17 Pilot- Great info

 

i agree

 

I don't know that they are setup yet for the 06 models on the programmers though. I know that the predator isn't even out for some 05's yet.

And, when it comes right down to it, linclon is the last one they worry about. There aren't many of us Lincoln boys out there changing what Lincoln does from the line.