I just thought about it and with me running my little 245's my speedo is bound to be way off, I guess this is where I would need to re calibrate it using the Revs Per Mile on my SCT, my 245's have 683 rpm so I'll just try to go with 685 and that should take care of my speedo right?
Unfortunately the SCT will not correct your speedometer. I've been told Ford has a flash that corrects it pretty well and it is free. Some customers, because they have tall tires, do not wish to call attention to themselves and don't want to go to the dealer. In that case, I've heard the Tru Speed is pretty good.
The revs per mile for adjusting the speedo are stored in the VID Block. The SCT Currently doesn't write to that location, so it only changes revs per mile for part throttle shifting. The X3 and Livewire have the capability, it's just a firmware update. SCT is supposed to add this in the near future.
Ive been wondering this also, how exactly do you go about setting revs per mile thing. Especially when using the $pa@rtan tunes. Sorry for the threadjack bro.
We have found this calculator to be most accurate:
This is the calculator we use to figure your revolutions per mile: Tire size calculator
It works with the metric system. If you have your tire size in the standard system, please figure the metric values first with this calculator and then go on to determine your revolutions per mile with the above calculator. Metric Tire Conversion Calculator - Red Rock 4x4
We tested the revs from the manufacturers site, as opposed to our calculations with Powerdog and have found the Powerdog feels like better shifts. This is something you can try also.
Always remember if you are going to set your revs per mile, you must also set your gear ratio.
There are two differences when you set it yourself, in the options menu, before you load a tune onto the truck, as opposed to your tuner setting it for you.
1.) You can only set it in increments of 5, i.e., 575, 580, 585 ... Your tuner can set any number.
2.) Every time you load that file you need to reset your gear ratio and revolutions per mile. If it is set in your tune, by your tuner, it is always there and you don't need to reset it.
#1 - The Powerdog has the option to give you the revolutions in both US and Metric units. There is a drop-down list where you can choose either - go with US units (miles).
#2 - Your revs cannot be below 500 in US units.
Thanks,
Vivian
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