bign1497

I'm getting a used superchip tuner. It doesn't have the ability to change tire sizes for my 2011 3.7L . I can change gear ratios but I'm confused as which way to go higher or lower. I know that putting higher ratio gears in the rear end makes up for bigger tires. Can I do this to "fool" computer to make up for 10% increase in circumference? If so do I enter a lower ratio or higher?

1994Vmax

You can try it and see how close you get. If you increase tire size it's like losing mechanical advantage in the rear end and if you decrease tire size it's like you increase. So adding larger rubber to a 3.73 truck makes it like a 3.55, 3.31 etc. Ford screwed up my XLT's strategy code from day one and it was about 5% off. They had it programmed as if the truck has 3.73 when it actually has 3.55. So being you are a 3.7 that likely has 3.73 input the 3.55 ratio and see how close it gets you...... provided it takes. I know I have entered 3.55 in my truck multiple times with SCT and it never fixes the speedo...... had to fake a tire size change to get it correct.


If you go 3.55 that is 5% from 3.73 and if you go 3.31 that's 12%. Your choice.

bign1497

Appreciate the info Vmax

techrep

iTrader: (1)

I would not do this... and I would buy a tuner that was able to input current tire size... telling your truck you have something you do not is not always good..

1994Vmax

It's going to be fine...... Ford told my truck it has 3.73 from the factory and it actually has 3.55.... and other than the speedo being off the truck drove no differently than it does now. Tire size or axle ratio will essentially do the same thing. In fact either tire size or axle ratio may alter the shift points enough it drives like it has 3.31 gears as an example.... because now it effectively does.

bign1497

It will correct for tire sizes for 2012 on up but not for 2011. Plus it gives a 37hp increase for my 3.7 compared to SCT 's 15 hp. Not bad for canned tune. I don't think the vehicles computer knows if I have lower ratio gears or bigger tires. I just need to get Speedo and shift points corrected. Damn Vmax we almost said the same thing

bign1497

Well I got my tuner, updated it, and installed 87oct. I did an advanced tune adjusting tire size to 33". It ran better but not much. Then I changed the gear ratio input from stock .355 to .315 and voilą! the Speedo is off only 1or2 mph and shift points changed dramatically. Can't wait for empty so I can fill with 93oct. and run performance tune.