\'04 749S - lowered gearing?
 

Hi all,

Newbiw to the Duke fold, so please bear with me! I have a 749S that I'm running in and I find the gearing is a little tall. Has anyone tried adding a couple of teeth to the rear sprocket or dropping one at the front? Is it worth doing?

Also, will it affect the speedo reading? Or is the speed sensor on the rear wheel like my old RSV?

Cheers for any help :)

Twinfan

[Edited on 28-5-2004 by Twinfan]

Speedo is driven by a sensor on the rear wheel local to the caliper.

1 tooth smaller front is easier and cheaper than going up at the rear :)

pretty much everyone with a duke will change the gearing asap. i've dropped one on the front, other may change the rear instead/as well.

i think it will affect your speedo but the top speed taken from your lap timer will still be 100% accurate. the speedo is out about 8% as standard anyway.

Cheers. Anyone dropped one at the front on an '04 749S? Is it worthwhile?

no it will not , the speedo is driven by a sensor reading the speed of the rear wheel , gearing will make no difference to this :bouncy:

I went down 1 at the front and 1 up at the rear on my 999S , noticably quicker acceleration , reduced top speed by 5-10 mph though.

I intend doing the same on the 749R , I'm just waiting for sprockets

Cheers - will go for one down at the front to start with!

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. The 748 and 749 series (with the exception of the 749R) all have torque outputs below 80Nm so they are supplied with 14-tooth front sprockets and 520 chains.

Starting with the higher torque 916-series (and 749R), and continuing with the 996, 998 and 999, the factory shifts 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. Four 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. Changing from a 14-tooth front to a 13-tooth front, for example, increases chain tension even more (9 percent) than a shift from a shift from a 15 to a 14-tooth.

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 10 percent, it needs replacement. Frequently for a Corsa bike.

Three, 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.

Four, there’s a practical limit on the size of the front sprocket. You end up carrying higher loads with fewer teeth. No manufacturer puts a sprocket smaller than 14-teeth on a bike with a torque output of a Ducati.

I think that the above suggestions to put a 13-tooth sprocket on a 749S (because it’s cheaper) are ill-advised. A better solution is to change to a 41-tooth rear sprocket. This will require a new 96-link chain.

Many thanks for the info - very useful. A new chain huh? Maybe I'll stick with what I have...

Question for Mr Cholesterol
 

I have a 999s, with 1 tooth less on the fr sprocket, how much more difference does going up one on the rear make? Any problems with chain length?