Si: Not 100% sure about the wheels. The £5 sack truck wheels from northern tool seem like the ovbious choice though im a little concerned the small 10 diameter might reduce my top speed too much.

(That is assuming that the wheel diameter affects the speed in a gravity kart in the same way it would a powered one)

Rob - Tried the skid steer idea last year on the grounds of minimal moving parts and maximum simplicity but it didnt work!. When one wheel stopped all 3 others did too.

Im thinking the lever on the tyre might be the better appoach ..the more I look into it the more I realise discs are complicated and expensive.

As for calling constrictor a rotten; how dare you! :P Ill remove it if you remove the rotten carrot from yours.

I actually have nothing to show right now as everyting is just in my head or scribbled on paper. Once ive made some progress ill share some photos.