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\'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? |
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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: |
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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 Quote:
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? |
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One down at the front and 1 up at the back is the equivalent of 3 (and a bit) up at the back , the advantage being you do not need a new chain to do it where you probably would have to replace the chain too if you just altered the rear sprocket. In reply to Shazzams post , I will check the front sprocket on Mrs eggs 749S when I get home for number of teeth , I thought it was a 15 front standard so going down to a 14 is not an issue , I do know without checking though that ALL 749's and 999's come fitted with 525 chain and sprockets as standard. [Edited on 31-5-2004 by yellowisfriedegg] |
You're right, I had forgotten that the 749’s get 525 chains. Probably more for parts standardization than for strength requirements. I remember from the product introduction that that was one of the major design objectives of the new models. |
According to the info I have here all the 749's have a 14T front. 13T are like hens teeth and run the chain too tight. Only real world alternative is to up the rear. 3T is a good start, and you may get away with the standard chain? Both Renthal and STM do alloy real sprockets for them now. Rentha are about £25, the STM £58 but are real works of art :biaggi: |
Looking at ducati.com (not sure if this is accurate) 749S has 14F 39R with primary drive 1,84 (is this 1.84:1 ? ) 749R has 15F 35R with primary drive 2,11 I not sure which way the maths goes, so which has taller gearing ? Rob :puzzled: |
If it's any help, I went up 3 teeth on the back, the gearing is spot on now and still using the standard chain. :roll: |
When you say still using the std chain to get an extra 3 teeth in. How much did you move the rear wheel forward then? which mark are you on on the swingarm? Any piccies? |
749R, going from a 15/35 to a 15/38 using the same chain will shorten your wheelbase 12mm. In general, it's better to go to a longer wheelbase than a shorter wheelbase because it improves high speed handling. Superbike corsa swingarms, for example, are 15mm - 25mm longer than street versions for this reason. Shortening the wheelbase beyond the stock setting is really not a good idea. A good approach gearing is to set the wheelbase at maximum (still allowing the adjuster an additional 10mm for chain stretch) and then use a combination of sprockets and chain length to shorten the gearing. The length of each link from pin-to-pin for a 5XX chain is 5/8-inch (16mm.) So in your case of using a 15/38, if you use the next longer length (adding two links at a time) you’ll get a wheelbase 4mm longer than stock instead of 12mm shorter. I’d do it. |
We knew that........:smug: |
I'll get me coat ... :sniff: |
er... not really...:frog: |
how do you work out that two links are worth 4mm? |
Hi Shazaam, I presume that adding 2 link increases the chain length by 32mm, but because the rear sproket is larger thats why the rear axle only moves 4mm Is this right Rob |
Shazamm, thanks for the advice. What combination would you recommend ? I will post a photo to show how far the back wheel has been pulled forward. Regards |
Pics as promised of swinging arm. Regards ![]() [Edited on 5-6-2004 by 749R] ![]() [Edited on 5-6-2004 by 749R] |
Hi 749R, where did you get those swinging arm protectors Rob |
My mate made them up. Have a look at the Phots section and you will see the full bike. :biaggi: |
i've just gone the alternative gearing route taking the rear up to a 41T and moving to a Tsubaki Sigma X Ring chain at 100 links. noticed the swing arm protectors too - i've just bought some from a company in Australia via e-bay! cost me £21 including p&p - will post pics when they arrive. |
Does anyone know a good reliable online store for getting sprockets and chain, since i've got my rear wheel off now (damned punctures) and would be the ideal time to fit a larger rear sprocket for the quicker acceleration. I'd go to the local shop but i'm working nights and tend to miss most of the day :rolleye: |
B + C express mate..... tsubaki chains, did erv2 chains, renthal sprockets etc etc.... |
749r, Looking at your piccies, and you say up 3 teeth and std chain, i cant help but note how short your wheel base is!! have you measured it? Measure from the swing arm pivot to the centre of the wheel spindle, what you got? then ask JHP etc what would be good, i recon 500mm is the desired length.. |
Will do Andyb. |
back to those swing arm protectors - got mine from Australia for about £21. Had to buy an m6 threaded rod from Focus DIY and a couple of nylon locking m6 nuts. Whole job done in 5 minutes. Costs saved at my Cadwell spill - PRICELESS!! :sing: Protector was a little scuffed and full of earth but the swing arm, rear brake etc. is unmarked |
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