Yes, I'm fully well aware of having access to the TWO adjustments as in gear ratio and revs/mile (tire size) As for the X-4? there is no third option for adjusting actual tire size Ex 235/55R17 At any rate, I clearly stated in my previous post that I set the gear ratio and selected 3:55 in which I also had installed by a custom shop, therefore the pinion depth and backlash were set correctly. I also clearly stated that I made adjustments several times by fine-tuning the speedo with revs per mile setting. However, as also mentioned in the previous post, despite all the adjustment changes made thru the X4, my speedometer is still off between 5-8 MPH slower when compared to my actual speed from my GPS. So once again as also previously mentioned, I was told by someone from SCT tech support that if the X4 has a custom tune file? the end user is required to have the custom tune vendor provide a revised tune file with the new gear ratio, as the SCT tech rep claims that even if the custom tuning vendor provides the end user with the ability to make parameter adjustments? they will NOT function accurately nor properly when uploaded into the vehicle from the X4 device. In other words, the SCT tech support rep is claiming that parameter changes can only be made by the end user with their preloaded X4 tuning files. That being said, is this SCT tech support rep I spoke with right about this or is he full of fucking shit and has no idea as to what he's talking about!