Drive Train

Chain And Sprockets

Even with today’s technologies the simple chain and sprocket drive train is still the best way to deliver power to the rear wheel especially with dirt bikes that have suspension travel of 10 inches or more. The drive train can affect the handling and the suspension of your bike. Under acceleration the chain forces the rear wheel in to the ground. That’s why landing from a jump with the throttle applied helps the rear suspension from bottoming out. Once the chain and sprockets get worn, corroded, or just packed with mud, it creates more friction which in turn places more load on the engine reducing usable power.

Cleaning And Lubing The Chain

After each ride the chain will need to be cleaned and lubed. Spray the chain and sprockets with a degreaser and rinse with water while scrubbing the chain with a stiff brush to remove all dirt and chain lube. Make sure you clean the teeth of the sprockets to remove any debris. Compressed air can be used to quickly dry the chain but WD-40 could be used to displace the water from the parts. Ideal chain lube should be a spray lube that penetrates the chain’s roller pins and links, but doesn’t fly off or attract dirt.

Chain Types

The two chains that you will come across are conventional and o-ring chains. Conventional chains use steel pins with a press fit with softer metal bushings to form each link. These chains have minimal clearances between the rollers and links to provide a mechanical seal. O-ring chains use o-rings to seal lubrication inside the link and keep water and dirt out. Conventional chains require more cleaning and lubing then o-ring chains. O-ring chains are great for off-road riders due to the chain requiring less maintenance.

Sprockets


Sprockets are mostly made of steel and aluminum. Steel sprockets are cheaper and have better longevity but heavier. Aluminum sprockets are lighter and more expensive and may not offer much advantage to the average rider. The rear sprocket is bolted to the rear wheel hub with tapered head type bolts. Every few rides check the bolts for proper torque. Loose sprockets bolts will destroy the hub; and hubs are expensive to replace. Using Loctite on the threads will help ensure they don’t come loose. Once the teeth of the sprockets are worn in to a wave like pattern it’s time to replace the sprockets. I prefer to replace chains and sprockets as a set.

Gearing

Depending on the type of track or off-road terrain your riding you may need to change the gearing of your dirt bike. If your track has steep hills, tight turns, etc you’ll need to change to a higher final drive ratio (gearing the bike down). If you’re riding a track that has long straights, flat overall terrain then you’ll need a lower final drive ratio (gearing the bike up). Basically this is a simple rule; for more top speed switch to a counter shaft sprocket with one more tooth count than stock; for better acceleration switch the rear sprocket for one that has two more teeth count than stock.

Gear Ratio Chart
  12 13 14
49 4.08 3.76 3.50
50 4.16 3.84 3.57
51 4.25 3.92 3.64
52 4.33 4.00 3.71
53 4.41 4.07 3.78

*Numbers across the top are front sprocket size.
*Numbers down the left hand side are rear sprocket size.