I am currently building a custom large scale monster truck. So far I have a basic frame(30" long wheel base) and an engine. I plan on setting it up for a chain drive 4x4. What I am not sure about is the tire size I want to use. I have found some tires off of a roto tiller, the ones that look like monster truck tires , they are 13 inch out diameter and 5 inches wide, I have aluminium Go Kart rims to mount them on. The question I have is... do you think that a 30cc chainsaw motor could handle them? I am also just using the stock centrifugle clutch. I have heard of people using a 30cc to power gas scooters and bicycles, and I figure if it could pull 100+ lbs @ 20-30mph, that it can drive a 40 or less lb truck at that speed. If all else fails I can chop the frame and lessen the scale. Any advice would be very helpful... especialy for steering those big tires .

30" long wheel base is to long. It should be 27" because if you buy a body it won't fit your old origional size. The tires are extreme and heavy. the size is ok but you want wider tires and lighter. The motor will work, but you will need to build a main gear reduction and one at the rear wheels total gear reduction should be 30:1. You will have problems with the steering if you want 4x4. The main problem with chain drive is fitting it in a small space and to get the right gear ratio(use 25 pitch chain).You won't be able to make a quick sprocket change to ajdust the trucks speed and power. You will need to make a plate chassis if you want independent wheel suspension