Is this okay

[lincpimp]

I would say that the motor should make plenty of torque, just gear it up until something gets too hot! Keep an eye on the temps and you should be ok. I see no reason why 18/36 will give you any issues. You just have to make up for the lower motor speed with higher gearing. Not the best way, but most certainly cheaper than a new esc and batteries. Now if you were trying to get 50mph out of that setup you may have issues, but 40mph sounds realistic and definately do-able.