Finally got it to work for me. Script never could find all the tires so I modified it very slightly. Changed code is in the section below. Sorry about the formatting, I just can't get it to display properly.
--Build the vehicle
self.vehicle = Vehicle:Create(self.entity)
for n=1,8, 2 do
child[0] = self.entity:FindChild("tire"..tostring(n))
child[1] = self.entity:FindChild("tire"..tostring(n+1))
if child[0]~=nil and child[1]~=nil then
for i=0,1 do
box = self:CalculateTireSize(child[i])
if box~=nil then
tireradius = math.max(box.size.y,box.size.z)*0.5
tirewidth = box.size.x
tirepos = box.center + child[i]:GetPosition(false)
self.vehicle:AddTire(tirepos.x,tirepos.y,tirepos.z,self.tiremass,tireradius,tirewidth,n<2)
table.insert(self.tires,child[i])
end
end
if n>0 then
self.vehicle:AddAxle(self.vehicle:CountTires()-2,self.vehicle:CountTires()-1)
end
end
end
I used the pickup truck body prefab and added the tires manually, setting the truck's tire children like the attached image...
Hope this helps someone
Edit: forgot to mention the tires must be named tire1, tire2, etc.