Steel Frame for the ZX636

The 03–04 Kawasaki 636 is the most popular motorcycle for stunt riding. The 05–06 version is also very common. There are many reasons: a powerful engine, relatively low weight, good handling and weight distribution, and price (in the USA it is the cheapest sport bike in its class, along with the F4i; here the motorcycle is expensive). Everything is great, but there is one drawback: the frame. The 636 frame is rather weak. Practically everyone who rides this motorcycle seriously has had problems with it. For professionals it's a disaster, since repairs take precious time. The frame usually cracks at the engine mount or breaks in half.

The first thing that came to mind was welding over the weak areas. Such a modification isn't very effective. Reinforce it in one place, and it breaks in another. It's hard to say exactly what the cause is. Probably the metal, the wall thickness and the geometry as a whole are all weak.

Given the motorcycle's popularity, pro riders made steel frames. Obviously, making such a structure is complex work that requires high precision. The guys from StaticMoto were the first to make such a frame, in 2009. The solution turned out to be very successful: such a frame is practically impossible to break. Now other manufacturers have appeared, and many make frames for themselves. The only drawback is weight, but even that can be offset with smart geometry. There are two types of steel frames:

All-steel

The frames are made from steel tubes. Very strong. Of course, such frames are heavier than stock, but the guarantee of indestructibility is the key factor when fitting one. All-steel frames are often made as a set with a subframe, which makes the motorcycle super strong.

Hybrid

Only the front part of the frame (the most fragile) is made. The steel part is rigidly bolted to the aluminum part. To do this, the stock frame must be cut and a seat made to join it to the steel part. A hybrid frame is the optimal solution. More and more pro riders fit them instead of stock frames.

Such a frame is lighter, cheaper and strong enough, since the fragile part is completely replaced.

In conclusion, it's worth noting that the cage has a huge effect on the frame's durability. If the cage has poor geometry, no frame will withstand the loads. If the cage is well thought out, even a 636 frame can handle serious crashes.