Replacement of Wheels

It can be done...but it isn't necessarily straightforward.

Your sketch is what most people usually start with when thinking about tracks. I'll hit the high points of what needs to be thought about when you are going to retrofit tracks onto a wheel tractor.

Most of this knowlege comes from experience--I built a steel tracked "garden tractor" when I was 14, and have been interested in tracked equipment since then, 40 years later. Interested enough to become a mechanical engineer.

1. The steering system has to be changed from the wheel setup--this involves modifying the tractor wheel drive system to be able to vary the wheel speeds independently on each side. If your tractor has a differential, it can be crudely done by simply applying the brakes on one side of the machine and forcing the power to go to the opposite side. This never works very good since a standard differential is not usually sized to handle this kind of loading. Also, a standard differential will cause the speed of the unbraked track to double if you lock the brake on one side. Many tracked machines use hydraulic drive with independent motors on each side.

2. You will probably have trouble with the tractor final drive gears as well, since wheel tractors don't have the traction a tracked machine has, and therefore final drives need to be stronger.

3. Each track will have to be built as a unit, called a "track frame". This frame will contain a heavy spring to allow debris that gets into the track to go around a sprocket without breaking anything. Usually the front idler has the spring and an arrangement to allow it to slide rearward if something gets in the track.

4. The track frame usually has several rollers supporting the track on the bottom side--if this is not done, the front and rear sprockets can see huge forces pulling them together: Imagine running over a big rock with the track with no rollers supporting it. The rollers also serve to guide the chain, reducing the chance for the track running off the sprockets.

5. The front sprocket is not usually a sprocket--it is a wheel with a central raised rim that engages the track chain. Sprocket teeth are only used where they are necessary: on the drive sprocket. Anywhere else they are just invite problems with trash.

6. Sprocket teeth: They look like standard roller chain sprockets--NO,NO!! You need to use "double pitch" chain and sprockets made for a chain of half that pitch. Why? Because you need to maximize the ability for the sprocket to clear trash in the tooth pocket in the chain. Imagine a chain that is full of dirt approaching a sprocket that is the same pitch as the chain: The sprocket tooth is made to fill the gap in the chain, but it is already full of dirt. Something has to give! Now imagine a double pitch chain approaching the same sprocket. What fills the gap in the chain is two sprocket teeth and the gap between the sprocket teeth. That gap is important to allow room for trash and it works. All of the above is assuming that you are using track shoes that are solid, without any holes cut in them to allow trash to push through the chain. Most modern crawlers don't have holes in their track pads but sometimes soil conditions are just right and tracks will pack tight with dirt so they have to have relief holes. Its just that cutting the relief holes weakens the track pads.

7 You will have some challenges in finding a commercial chain that fits the requirements of tracked vehicle chain. I've used material conveying chains because they were tough and not as costly as heavy roller chain. I could also weld track plates to the sidebars, where roller chain usually has too much carbon in the steel to make a decent weld. Oh, and roller chain needs to be the "straight sidebar" type so the track rollers can have something smooth to roll on. I found that most commercial chains don't have much distance between the roller OD and the "height" or "thickness of the chain. A crawler chain should have some distance between the roller OD and the inner side of the chain to allow the front idler rim and track roller rims to ride in without their inner rims contacting the track rollers. This of course, helps guide the chain.

8. There are a lot more details to track design than the above 7 I have noted....one example is the track pads you have drawn. With pads that simply sit close together, they can be very dangerous to an operator when working areas with many small trees, like willow trees, with trunks small enough to get between the pads where they are open wide, going around the front and rear sprockets. When the pads close up again, they pinch anything that is between them and whip it around violently. If you look at track pads on modern crawlers, the pads are arranged so they are overlapping even as they go around a sprocket so trash cannot be "grabbed" by the track.

I don't mean to be negative--its just a huge topic and you could spend a lot of time re-inventing the wheel, er, track!

Jon.