Move Wheel on Ground by Curve

First vex is the anim by curve - move along curveu:

f@pos = chf("curveu");
float u = @pos;
int prim = 0;


vector pcurve = primuv(1, "P", 0, set(u,0, 0));
@P.z = pcurve.z;

 

Then the rototion vex:

float pi = 3.14159;
float curve_length = prim(1, "perimeter", 0);
float position_along = point(0, "pos", 0);
float wheel_radius = 1.0;
@wheel_rot = 360 / (2*pi*wheel_radius) * (curve_length * position_along);