I have two boys ages 10 and 8, they are 90 and 70 pounds respectively. I want to get one used bike for them to share and check out their interest/skill level. The 8 year is a very aggressive and daredevil type rider on bicycles, scooters, and anything else he gets on and usually outrides the 10 year old. So whatever would work for a beginning 10 year old I would feel comfortable putting my 8 year old on. I'd rather spend 1K now to see where they stand and then go spend the 3k apiece than put all the money up front just to find I got the wrong stuff for them. Any suggestions would be appreciated.