Considering some kart shops will sell individual
tires. Has anyone ever replaced 2 tires at a time rather than 4? If so, which do you go for, 2 fronts, 2 rears, or the 2 outsides (if the track has more rights/lefts)?
Anyway to minimize the drop off after the first run on a fresh set? Does anyone make changes to add in more overall grip after the first/second run. It’s hard to understand how some brands of new tires are whole second faster.
Every kart and brand of tire is different. Every driver is different. Generally tires will ‘fall off’ after the first session. How much and at what rate is variable.
Some people will wrap tires in Saran Wrap after the first session to preserve oils, but that’s a controversial take (good for storage).
In general I would avoid changing just 2 tires or individual tires on a kart.
I’ve seen shifter drivers at our local track change out just the two rears (as the rears wear quicker), essentially going through two sets of rears for every set of fronts. I’ve you’re a mid-level club racer looking to save $$$ then there’s not any harm in this approach. I would avoid changing just one side.
As for my personal approach, I’m with Eric in that if I’m changing tires I’m changing all 4. Always.
FYI, with a heavy weight class, low hp, “medium” grip tires, we do the opposite of high hp karts. We will sometimes put new(er) fronts on twice as often as rears.
I’ve only ever seen someone try right sides once. It caused balance issues and actually slowed the kart down so I wrote it off forever.
Sounds like you need to move your seat forward 
Evan means well. He doesn’t know I’m a shrek like ogre.
Thank you all, I’ll try changing rears only and see how it goes.
We have done it several times, we tend to on some tracks to wear down the rears quite fast, so we have changing rears only, its not perfect but its minute what we gain by changing the fronts compared to the rears.