I'm giving my old x cal 2 to my cousin for her 04 XLT with the 3v 5.4 any way she bought a new tune from 5 star for it and she has some take off 20's from a 13 xlt on it with the 275/55/20 pirelli ATR's, the original size was 255/65/17. I need to adjust for the new tires and I don't remember if the x-2 goes by revs per mile or circumference in mm? And what is a good starting point? She will be here in about an hour and a half so I can load the tune and adjust the speedo. Oh and I used live link to unlock it and erase the old troyer tunes and load the new 5 star tune that is written for her truck.

 

I'm pretty sure all of the SCT's use Revs per/mile. At least starting with the X2. And according to Discount Tire's website, 275/55R20 would be 632.04 revs/mile.

 

Ok, thanks I guess I'll start off with 630, cause IIRC you can only go up or down in increments of 5 then take it out and compare it with my gps app on my phone.

 

My SCT uses revs/miles (I just checked last week). I don't know if I need to do the math for the tire size on paper, or what it actually measures out to. I'm gonna do the same trial and error as you though when I put the 35s on.

 

Tire rack says the pirelli ATR has a revs per mile of 651, so maybe I'll start with 650 and see how close I am.

 

UPDATE; well it's loaded on her truck now and I started with 635 revs and it was close. At 70 mph the gps read 71, so I tweaked it again and set it to 630 revs and now its perfect. At 70 mph the gps read 70. So if any one is upgrading to the stock 20" pirellis try starting with 630 revs per mile and you should be real close if not perfect.

KMAC, try going to the tire manufactures site and look up your tires, they should have a revs per mile listed. It's a good starting point, that will get you in the ballpark. Then you can tweak as needed.

 

Glad to hear you got it all adjusted perfectly!

Thanks, I honestly never even thought about the revs/mile being listed anywhere. Great tip that I'm sure will save me a lot of time.

 

The listed revs per mile is with the tire unloaded, the manufacturer can't possibly know the exact application the tire will be used on. Vehicle weight and tire pressure will effect the actual revs per mile. That's why the listed revs are only a ballpark figure.

When I had 35's on my 07, IIRC I used somewhere around 580 revs to get the speedo right. The tires were 35 x 12.50 x 20 trail grapplers and nitto lists them at 35.04" tall.

 

I'll keep that in mind, cause those are the exact tires and size I have waiting to go on. Mine, interestingly enough, are only 34.50" tall mounted on the wheels with 40 PSI in them. So I'm expecting them to stand 34" tall once they're on the truck.