Hi all. I'm working on building a go kart, and it's been a very long time since my college trig based physics classes. I'm having trouble figuring out the proper stiffness and length of spring to buy for the suspension. In short I need to know the vertical force generated by a wheel and attached suspension encountering an obstacle. I can understand simple physics, but impact centripetal physics seem to be beyond the capabilities of this cobwebbed brain. Forward velocity = 18 m/s Obstacle = .05 m high Acceleration (linear degradation) = 0 m/s2 @ 18 m/s, 4.5 m/s2 @ 0 m/s Vehicle weight = 113.5 kg Front wheel diameter = .10 m Front tire diameter = .26 m Front Tire & Wheel weight (ea) = .91 kg Front unsprung weight (each side including tire/wheel) = 2.8 kg Rear wheel diameter = .15 m Rear tire diameter = .37 m Rear tire and wheel weight (ea) = 4.1 kg Rear unsprung weight (each side including tire/wheel) = 14.79 kg Sorry I don't know the compression rate for the tires. Each tire is inflated to 27.6 kPa. If it makes a difference they are pretty simple 2 ply tires. Here's what I've tried. Speed equilateral right triangle, hypotenuse 17.88 gives Vx=Vy=12.64 m/s Obstacle equilateral right triangle, sides .05m, hypotenuse .0707/17.88 = t = .004s Since Vy = 0 to start, ay = 3160 m/s2 Using F = ma, forward force exerted on bottom of spring is 8848 N, rear 46736 N These seem high to me, even considering the impact speed. I'm sure that the low pressure tire absorbs partial impact, more force is lost since the tire rolls over the object instead of point impact. Obviously I've not found a reasonable spring which can accommodate this, which is why I need someone who can understand this better than I can. Thanks for the help.