Basically, you set your rig up as you NORMALLY would for a trail ride. If you only go down to 15psi, than that is how you should ramp it.
If you disconnect swaybars, than go do it for ramping.
If you have no trackbar, than no need to get one
If you want to see the difference airing down makes, give it an "unofficial" try at lower psi, about 10psi would probablly score about 2-300 higher than 15psi. And when you see the difference, you may even try a trail at that psi to see how much more performance you may gain :wink: And next year you can ramp it "officially" at 10psi :lol:
The biggest advantage you can get is letting air out of the front driver and rear passanger, this will produce the highest score.
The measurement is taken at the point that the rear driver tire starts to get "air". Have the competitor back down a "tad" to get the proper measurement with all tires making contact with ramp or ground.
We have always used the centre of the rim to the centre of the rear rim to get our wheelbase. It just has to be "close" when you measure.
Of course if this ramping is entirely for fun with no prizes and no bragging rights, than do whatever you want:D