Mounting used tires and scuffs

Yep! Its the pits I know too well!!! Having a few extra rims and more than one car in a shop helps too! As we run 2s everywhere but left rear (3) with no room for spacers, it is more easily a decision to mount! Air pressure of 50 lbs. over night or letting it back down through the week helps us keep roll out under control. The right rear tends to gain as run, having more heat and flex !  Just having more pressure threw the weak will help keep what you want or letting it down to keep from stretching!! Keeping a close check on air pressures and roll out helps to hold your setup in check! A 1/2 inch is all we run on our metric cars and keeping that is just as hard as finding more for the front! (1-1.5) Our left ft. is the most sensitive spot on our cars as changes goes! It is loaded the most and with caster throwing the weight around as you steer, it does control most of the handling making ft roll out just as important as rear if not more when you consider all it changes (the big 20) with any alterations! Most used tires need to set over night with more air than run to stretch back into a norm before letting them down to running pressure before doing a roll out test! Always use your own gauge and never loan or barrow, as most vary! Most tires are seldom as marked anyways with rim differences in  bead locks or not! A half inch shorter if mounting on a bead lock is a good rule of thumb! Trying is almost like succeeding when searching for stagger and then air pressure has to do the rest! Bite location of the tread hitting the ground does change with tire pressure as well as spring tensions of tire spring to change your whole set-up! Keeping things in check allows you to change others to the good to perfect those other settings! The Big Twenty as I call them! Most of which are vary allusive and changing constantly but not beyond our control with variations in extra caster and placement of springs, shocks, lean, and bar angles! You always need a shorter or taller set of tires for gear changes too if wanting a bit more ump in the heat with more roll out on a tacky track or just drop one pound of air on both sides and try that! It loosens the right rear and tightens left rear and gives more bite if wet while driving the same on my set-up! Air pressure is like a spring under your springs and it changes total rates faster if stiffer! Which one gives first? The tire or your spring? A set up night mare if not controlled to perfection by weight placement during roll! A one or two pound gain can change you setup during the race to crap if not compensated for into the working range of tensions in compressed heights! Checking pressures and roll outs quickly after a race will help you understand your set up! Even when working correctly! Setting static pressure by weight applied is good but don't forget about the transferred weight too when setting pressures and thinking roll out as a low rt. rr. tire is shorter and may reverse roll out causing a push or roll under causing a loose condition! You have to set the air per car, per set up, per transfer, per driver, per roll out desired when rolled! Have a nice Day! This is every-ones Quest!