So if it were you (or me), a 5-11, 162-ish driver racing Yamaha spec pipe / can, would you take out the middle bearing or leave it in?
When I got the kart, I took it out, but my racing friends tell me to put it back in. Their argument is that having it in gives me more tuning options. My counter to that is if I want to tighten up the rear, I can
1. narrow the rear track
2. tighten the bolts to my rear bumper
3. install my rear torsion bar
Well option 3 should be the very last resort on any kart. 99% of people throw out their rear torsion bars.
I like having it in because it’s a quick little adjustment to see if you need to go stiffer on the axle. Put the bolts in and see if the slight stiffening helps the kart.
Options 2 and 3 on your list involve stiffening the actual frame from tube to tube. I like to have an option to stiffen the axle too, as that can have a different effect to stiffening the actual frame.
I haven’t flipped, but I will say that my local track has a hairpin-ish turn, and I swapped ends three times this past weekend. The kart didn’t swap ends on initial braking, but late in the zone, just before turn in.
Now, perhaps this was because I may have started the turn before my kart had slowed enough, but I’ve driven this track for eight years and have rarely had this much trouble.
Maybe the middle bearing, even just zip tied, provides a bit more stability under braking, no?