Yeah it's hard to keep down. For consistent starts you need to stretch it. That's a given. I can sit nearly on the tank and launch decent but until mid 3rd gear, im fighting with the bike to keep it strait. My bike is set up to launch in 1st, not the usual 2nd. If you listen to the vids, i just shift up 4 times.
However it provides awesome traction for my riding areas. Plus they grow from 22" to 25" over 50mph i believe. Perfect since i dont have 6th gear. I refuse to stretch my bike. It's a play bike, not a drag race bike.
go on FAST's website. He sells(i think, havent been there in a while) pro wedge two's mounted on light weight wheels.