hey at my local skatepark ppl always ride on the oval with 2 people on there bikes and they seem to go actualy prety fast on grass with the other added wieght of another person and iv seen alot of ppl riding thumpsters with 2 people on them
just go to google.com and type in wat ur looking for in search and ull find a website that is selling one or ask if they sell them were u bought ur bike
go with the thumpstar if u want quality and trustworthy stuff or the proverts coz there prety sik to muck around on and race to dont get the chinese one