125 shifter w sticky tires BTW. I ran a Ribtect Large Tall. I’m 5’11 and 170 lbs. With a rib vest. It hurt my ribs. Granted I was nursing rib pain from a TaG with no rib vest (we all have to go drive around until we can’t stand it the first time we get in a real kart is appears), but this seat hurt me. I worked with a long time karter to mod the seat. We used a spreader jack and a heat gun and opened it up some, flaring the sides out more. It became comfortable and my ribs healed.
You need about a finger’s width of play on the sides, with our without the rib vest. Too tight and it will hurt you.
I let that seat get away and ran the stock CRG seat in a new shifter chassis. After a long few days (10 test n tune sessions and a race day), I almost could not move. Added some pads to the seat over the bolts, change seat position so I was not bouncing forward and the shallow sides hitting me. Still chased rib injury and pain.
Quit driving the shifter. 206 kart w rib protector, stock Arrow seat (EMAF?), life is good and ribs heal up. That is, until I get in a CRG seat in a shifter. Once the tires warm up I can feel my ribs folding over the top of the seat and the injury/pain comes right back.
I need a taller deeper seat that fits me if I am to drive a TaG or shifter. It may not be a chicom flexy flier like the stock CRG seat, but it is either get a different seat or don’t drive at all, regardless of what it does to the tuning of the chassis.
When researching this before, I found some posts about a top S4 driver that went Ribtect in a CRG chassis and he said he had no issues tuning around the seat.
Brand alone is not the resolution – it has to fit right, and you need to pad over the bolt heads, use flatter bolt heads, come up w your own flat bolt heads, etc. to go along with it. The Ribtect flat heads are cool but expensive and only have a few threads in them. They tend to fail in my experience.