how much do stock seats weight?
 

??

About 28 lbs. ea. without the rails, according to my information.

Is that for R1 seats or the leather seats?

That weight is for base model cloth seats, IIRC.

Jeff Hoskinson weighed a leather seat (with rails) and came up with ~38 lbs. I haven't weighed my R2 seats, but I'd assume they're in the 35 lb. range with rails.

So what do aftermarket seats weigh?? Are they much less?

the weight of aftermarket seats range depending on if there reclinable or not,brand and ect. i have seen bride racing seats they weigh around 5 pounds per seat