Tales of the Front Sprocket
One of the easiest performance changes that a new owner can make is to lower the final drive gear ratio by changing the sprockets. The stock gearing is selected to enable Ducati to reduce exhaust emmisions, but is simply too high for most road use.
Ducati bike models have a wide range of torque output and the size of the chain and Ducati’s selection of sprockets reflect this range of outputs. All Ducati current models, except the 748 and 749, come with 15-tooth front sprockets. The more powerfull 749R is 15T.
The 748 and 749 series (with the exception of the 749R) all have torque outputs below the 78Nm of the original 916, so they are supplied with 14-tooth front sprockets. The 748’s got 520 chains.
The 749’s get 525 chains, probably more for parts standardization than for strength. I remember from the product introduction that that was one of the major design objectives of the new models.
Starting with the higher torque 916-series (and 749R), and continuing with the 996, 998 and 999, the factory moved to a 15-tooth front sprocket and a 525 chain. Why? Because more torque means more chain tension and a 15-tooth front sprocket lowers the tension in the chain by seven percent. A 525 chain has a tensile strength that’s ten percent higher. So you get an overall 17 percent stronger setup.
Still-higher torque SP, SPS, R and Corsa models output over 100Nm so how do they get away with 14-tooth sprckets and light-weight 520 chains? That’s easy. Once you get over a certain torque level (for a given weight bike) the bike will wheelie before the chain tension exceeds it’s strength limits. At least for awhile, chains on these bikes don’t usually see 15,000 miles of service.
So, what does this tell us about changing our final drive components. Three things.
First, as a general rule, it’s better to increase the rear sprocket size to avoid the higher chain tension resulting from a smaller front sprocket.
Second, the heavier the bike, the higher the chain tension needed to make it wheelie and the higher the maximum chain tension it will experience. So, a 680 pound 916-plus-rider will generate a higher chain tension than (say) a lightweight Corsa-plus-jockey or even a Suzuki GS-X. When a chain under tension elongates one percent, it needs replacement. Frequently for a Corsa bike.
Third, combining a change to a smaller front sprocket with a change from a 525 to a 520 chain on a higher-torque model Ducati will significantly weaken the final drive load capacity. Reports of chain failures are common enough, so it may not be wise to ignore this point for the sake of saving 275 grams of chain weight.