WHAT DRIVES YOUR MOTORCYCLE?Posted On: December 24, 2018 By : AutoLife Team
Hello again auto enthusiasts, this month I’ll be giving you an insight into your motorcycle’s final drive mechanism. The reason it is called the final drive mechanism is because it is responsible for transferring the energy produced by the engine to the tyres and eventually to the ground, propelling you forward. There are three commonly used mechanisms on motorcycles; chain drive, belt drive and shaft drive. Let’s see why and where these three mechanisms are used and its advantages and disadvantages.
Chain driven motorcycles, as we’ve seen it is the most common drive mechanism, use two sprockets and a chain. A smaller sprocket is connected to the transmission shaft on the engine and a larger sprocket is connected to the hub of the rear wheel which are both connected by a chain. When the clutch is engaged and the transmission shaft turns the smaller sprocket, also known as the driving sprocket, it pulls on the chain and in turn rotates the rear sprocket or the driven sprocket. Chain drives are most common because it is very inexpensive and also because the maintenance on it is very simple. Although its biggest advantage is cost and simplicity in maintenance, its biggest disadvantage compared to the other drive mechanisms is it requires the most frequent maintenance. It needs to be lubricated and tensioned frequently and the whole mechanism needs replacement at frequent intervals. Riders can, however, change the gearing of their motorcycles quite easily by just swapping out different sized sprockets either at the front, rear or both, to give their motorcycles a different gearing ratio, which done with proper calculations will make the motorcycle perform a whole lot differently. That in itself is a topic of discussion for a future article.
Belt driven motorcycles are not fairly common in Nepal aside from a few Harley Davidson motorcycles we see now and then, but are used in all commuter scooters we find here. Belt drives are a little more expensive than chain drives but their biggest advantage is that it requires fairly no maintenance at all. Once the belt wears out, the only maintenance for it is to replace it. it has almost no customisability for people wanting to change their drive ratios like that available on chain drives but what it offers is a reliable problem free riding experience. The belts are similar to the timing belts found on four wheelers, which is made of rubber and Kevlar strands. This unique composition brings flexibility and strength to the belt which offers a longer life than the chain drives.
A shaft driven motorcycle is the most maintenance free option of the three mechanisms, which transfers the energy of the engine through a metal rod all the way to the rear wheel. Its biggest advantage is that there is virtually no maintenance required and it offers the smoothest riding experience. This mechanism is widely common on rear wheel driven four wheelers. On motorcycles, this is mostly used on cruisers and adventure touring motorcycles like the BMW R1200GS. Since these motorcycles are used for long distance travels, this mechanism makes it more feasible for cruisers and adventure tourers. The biggest disadvantage is that it is very expensive, very heavy and offers no customisability.
Now that we’ve seen the differences of these three mechanisms, let’s talk a little about how efficient these three systems are. The shaft driven motorcycle is the most reliable form of drive mechanism, which is treated nicely will last as long as the motorcycle itself. But due to the way it operates, having to convert the engines torque 90° once from the engine and once at the wheel causes a massive energy loss, so although they are the most reliable, they are also the most inefficient with power loss of up to 25%.
Belt driven motorcycles have a fairly lower power loss compared to the shaft driven ones, at 9% but it needs frequent maintenance at around 25,000-65,000 km depending on the quality of the belt. The replacement of these belts on motorcycles is fairly difficult and time consuming, which requires the removal of the entire swing arm from the frame. They also require bigger pulleys as belts aren’t as flexible as chains and due to this reason it isn’t that feasible on smaller motorcycles as space is a big constraint.
Chain drives are very maintenance heavy but they are very efficient. Their power losses are calculated to be around less than 4%. This is the reason that we see this mechanism used on sport bikes, drag bikes, dirt bikes, etc. where the rider requires maximum power transfer to the wheel. It also fits in a more compact package. But it requires maintenance every few hundred kilometres and the whole setup needs replacement at around 20,000 to 40,000 km.
Now that you have a better understanding of how and why different drive mechanisms exist, choose what best suits your needs and always perform a thorough inspection before heading out for a ride. If you take care of your vehicle, it will take care of you and won’t leave you stranded in the middle of the road. Adios and safe riding, everyone.