Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > Front cog

[DEMON]

Originally posted by B19PSK
Rather than power think pressure, clearly for a given chain size a smaller number of teeth mean a smaller diameter, means a larger pressure on each tooth! IMHO

OK then, i'll ask you some more questions to make you think about this one ...

1.pressure ? I think you should think more of compressive stresses in the sprocket material.

2. The sprocket is still transmitting the same power, but at a slightly different RPM (as you have altered the gearing)...so what about thermal stresses ? think of this... sprockets are transmitting power through friction..friction causes heat.... and the original sprocket was of larger diameter, ie larger surface area, and can therefore dissipate this heat more efficiently. So now you go down one tooth and the diameter is smaller, ie the surface area is also smaller, so the sprocket theoretically is hotter, then the larger one.

Now think of this.... some of that heat is dissipated through windage...ie as the sprocket rotates, air is passed over its surface, and cools it. However some of that heat travels along the drive shaft, and is dissipated through radiation, convection, so surely the smaller sprocket therefore transmits more heat along the shaft...have I got you scratching your head yet.

Next time you come back off a ride, touch the rear and front sprockets, and tell me what you find ?

We have to think of thermal stresses as well as mechanical ones !

From your quote, you are saying that there is agreater stress on the 'tooth' but surely the teeth are of the same form shape and size as the larger sprocket...arent they ?

Of course they are, but we may not have the same number of teeth in contact with the chain as we would with a different size sproket.....

[andyb]

I suspect you will do as you please..............!:P

think of all the extra gear changes.....what about stress on your toe?

[zaker]

Just fitted a new front sprocket on my S4R yesterday, gone from a 15 to a 14 tooth. A lot easier to ride in trafic, and pulls better in top gear from lower speeds aswell. worth it even if you loose a few mph top end !!

p.s. noticed a bit more chain noise since fitting it, more like a whine, chains adjusted perfectly though. Anyone else encountered this ??

[Carbon749]

Originally posted by zaker
Just fitted a new front sprocket on my S4R yesterday, gone from a 15 to a 14 tooth. A lot easier to ride in trafic, and pulls better in top gear from lower speeds aswell. worth it even if you loose a few mph top end !!

p.s. noticed a bit more chain noise since fitting it, more like a whine, chains adjusted perfectly though. Anyone else encountered this ??

Are you sure about the noise .... are you looking for a noise / problem and just became more aware of the noise ?

At the end of the day 748's and 749's have 14t front sprockets as standard with the same size chains as 9** style bikes. OK the 9** puts out more power than the 748 / 749 .... but I would have thought it should be ok. Plenty of people have swapped the 15t for 14t and there are no horror stories. If it was a dangerous modification with problems I would guess that it would be all over the DSC forum.

[Edited on 6-5-2006 by Carbon749]

[Shazaam!]

Originally posted by Carbon749
Plenty of people have swapped the 15t for 14t and there are no horror stories. If it was a dangerous modification with problems I would guess that it would be all over the DSC forum.

I think it would be interesting to try to correlate 14-tooth sprockets and undersized (weaker) 520 chains with the chain failures (and case damage horror stories) that are so often reported here in the DSC forum. Chain tension is higher when you use a smaller front sprocket.

[Edited on 5-6-2006 by Shazaam!]

[zaker]

Originally posted by Carbon749

Are you sure about the noise .... are you looking for a noise / problem and just became more aware of the noise ?

At the end of the day 748's and 749's have 14t front sprockets as standard with the same size chains as 9** style bikes. OK the 9** puts out more power than the 748 / 749 .... but I would have thought it should be ok. Plenty of people have swapped the 15t for 14t and there are no horror stories. If it was a dangerous modification with problems I would guess that it would be all over the DSC forum.


Never noticed it before i have to say, hope to take it on a decent run in next few days, so ille try and get to bottom of it ! watch this space.

Cheers


[Edited on 6-5-2006 by Carbon749]

[Carbon749]

Originally posted by Shazaam!

I think it would be interesting to try to correlate 14-tooth sprockets and undersized (weaker) 520 chains with the chain failures (and case damage horror stories) that are so often reported here in the DSC forum. Chain tension is higher when you use a smaller front sprocket.

[Edited on 5-6-2006 by Shazaam!]

Good point, most of the chain snapping stories seem to blame the DID chain and don't mention the sprocket sizes.

Still have this persistant thought in my mind that 14t fronts are standard fit on 748 / 749. The power output from some of the newer 749 is comparable to the power from older 916's. Ducati must be happy with the power output matched with the 14t sprocket.

[david.hicks]

Test rode a few 996s before buying mine and far preferred those with a 14 front. I discussed the front/back issue with Rich & Dean @ Louigi Moto and they told me they had never seen any problems with running a front 14. Good enuf for me.

[GsxrAge]

Just stuck a new 14 on mine I have a new Afam rear sprocket (£59) that bolts straight on with no need for Carrier but no time to fit it yet.

also fitted new front wheel brgs and new rear pads tonight !

Age

[david.hicks]

So you won't be on the SV for tomorrow's SWB rideout then?