Have you ever noticed the swingarms of your bikes and checked as though why they are made rectangular and box type and not circular or tubular or even oval for that matter? To say the least, there is a very good reason for it which we are going to discuss here today. Check out any bike you wish to ranging from entry level sportsbike to a superbike and you will notice that though the shape and style may vary a bit, but the swingarms for all these bikes are always made in a rectangular box type pattern. And not just that but in case they are made out of tubes, multiple parallel tubes are used to ultimately form something rectangular when put together.RELATED ARTICLE: Motorcycle Swingarm And Its Importance Explained
If you ever went through the Ducati Desmoquattro Performance Handbook by Ian Falloon, you will know what I am talking about. Back in the day when Ducati was still using the Bevel Gear drive on their bikes along with the dual suspension setup, they were using tubular steel swingarms, but it did not provide them the kind of handling and performance from their bikes. It was later in the 1980s when the Italian marquee shifted to the mono-suspension setup was when they finally decided to go for the rectangular box type swingarms and though the performance was not affected as much, the handling of the bikes improved drastically.
So to put it all in short, it all depended on the strength provided along with the flexibility of the rectangular box type swingarms is what gives it the edge. The rectangular swingarms always have the wider section of the area in a vertical position and the smaller in horizontal position. If you observe the movement of the swingarm and the way it manages the load, you will notice that the vertical longer section is the one which manages all the heavy stuff and takes up the stress. The longer section manages in the stress handling better.
Consider the same in case of tubular swingarms, the stress taken is pretty much equal from all ends and hence the swingarms will not function as properly due to the low stress handling capability of the tubes. Hence multiple tubes are used here so provide it the required rigidity. So rectangular box type swingarms are always preferred in this case. Also when considering in the corners, the overall strength provided by the rectangular swingarms is more due to the diagonal stress taking capability of the rectangular swingarms compared to tubular ones.There are also arguments about the material used for the swingarms and also the thickness of the materials used. But even then considering that the thickness of the material is less for the rectangular than tubular with the material for both being the same, the same stress principle applies and makes the rectangular swingarm better, but only up to a certain limit until it is going to crack.
So next time if you plan to change the swingarms of your bike and modify it for something cool, remember the purpose for why it is that and even if it might look not to cool. A better option would be to simply wrap it with something or add stickers to it to make it attractive, but never go on to modify it without proper technical knowledge.
By: Pratik Patole