Decisions...Change front or rear sproket???

Re: Decisions...Change front or rear sproket??? (galaxy)

I would recomend replacing the rear one anyways. There has been some debate over the additional abuse that a 14 tooth sprocket puts on a chain. The radius is too small and it prematurely wears the chain, not to mention that you then only have 7 teeth at a time in contact with the chain as opposed to 7.5 (I don't think that this is an issue at all). Look at ALL of the japanese bike (which run the same chains as yours) and they have 16, 17, and even 18 teeth on some of them. I would recomend going up 2 teeth on the rear sprocket and don't take the chain out of the box unless you really need it (depending on how many miles you have on it, the chain may have stretched enough to allow it to fit). The machining option for your front seems like an awful lot of work (to potentially end up not even working).

But that's just my

Re: Decisions...Change front or rear sproket??? (galaxy)

I've run it both ways on my 900SS. It was 15/40 stock. I ran a 14/40 combo until just a few weeks ago. I was very happy with that combo and it was inexpensive. When it was time for a new chain, I reused the original 15T front, and picked up a 43T rear and new chain. I have to say, even though I was a hard advocate of the 14T front being just fine and I didn't really believe all the stuff you read about increased chain wear and lost power due to the tighter radius of the front sprocket, the up three in the rear is WAY better. One down in the front and up three in the rear is NOT exactly the same ratio. You get a shorter gearing with the up three and therefore a little more of the reason we do this to start with. With the 14T I could easily power wheelie in first but I had to work at it to get a rise out of second. Now second gear power wheelies are much more common without even really trying. Not that I am some wheelie freak, but you certainly notice the difference when you're on a spirited ride! It also pulls better when rolling on the gas at highway speeds. A real noticeable improvement.

By going back to the 15T front, and up to a 43T rear I used 98 links vs. the 96 that were on the stock chain. That puts the adjusters at a little better than the 1/4 way mark on the swing arm.

OK, sorry this turned into a long reply! My opinion after living with both... Go with the new rear.

Hey guys, just what I was looking for...Thanks for the input. Just to answer some of your questions... I was not replacing the chain anyways. It was an assumption on my part that if I go up three in the rear I would need one. The machining of the front sproket while yes, it is alot of hasstle, it would work, and come out a bit cheaper than doing the rear. I also know that the ratio is slightly different 15/42=2.8 and 14/39=2.785 Very close. I doubt I would notice the differene in ratio. I am also not set on changing one over the other, just getting some input/research.

JeffKoch, I have a 2004 800SS, and yes I am correct, no one makes a 14t front sproket for my bike. My sproket does not have the shoulder on one side and flat on the other like say a Afam15604 (which is what's listed) Ducati lists a sproket in their catalog, but they are all wrong and don't work on the bike.

Oh yea, is there a way to tell for sure if I would need a new chain?? My adjustment right now is about dead center of the range. I guess it's not good to go to the foward or aft extremes?? Looks like you could change your wheelbase by up to an inch or better with just chain arrangement. Probably better off with a new one to keep the axle about mid way anyways...no???

One more, is the Afam 50602 the correct rear sproket???


Modified by galaxy at 3:10 PM 2/16/2005

Re: (Shazaam!)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Shazaam! »</TD></TR><TR><TD CLASS="quote">If you have two setups having the same gear ratio, one with a 15 tooth front, the other with a 14 tooth front, the chain tension will be greater in the 14 tooth setup.</TD></TR></TABLE>

Um, Shazaam, you've said this at least three times now on at least two different boards - twice I've pointed out that you are incorrect, and twice you've neglected to reply... This is incorrect based on high-school physics. Changing front sprockets *cannot* increase the chain tension by itself, the only thing it can potentially do is allow you to apply more engine torque to the chain by running lower RPMs, which will result not only in more chain tension by more acceleration. This is obvious if you consider what force is responsible for rear-wheel torque - it can only be chain tension acting on the moment arm of the rear sprocket radius. Constant acceleration = constant rear wheel torque = constant chain tension, regardless of what front sprocket you are running.

The practical effect is that if you use your new small front sprocket to help pull wheelies, then yes, you'll be putting more tension on the chain - but no more than you would if you'd added some go-fast mods to the motor to allow you to pull the same wheelies with the original taller gearing.

Normally I'd suggest going down a tooth in the front rather than up 3 in the back, because it's simpler and usually cheaper (and people run 14T sprockets on 748s for years and many thousands of miles, so the practical effect on wear is minimal), but since you'll have to do some custom machining to get a smaller front sprocket to work, you might as well go the rear route. You will wind up changing the wheelbase more, of course, unless you also add a chain link.

Re: (CuStOm)

I can't really say for sure concerning accelerated wear with a 14T, but I ran the the stock chain for 16K miles. 99% of that time was spent with a 14T counter shaft sprocket. I took pretty decent care of the chain with cleaning and lubing, but I do tend to run my chain a little looser than I should. I will say the chain was pretty much dead, and possibly should have been replaced sooner.

A general answer to your question on when do you know a chain needs to be replaced... I am sure there is a more scientific/specific answer, but I've always been told if you can pull the chain off the rear sprocket and expose more than half of the tooth, time to change! I could definitely do that with my old chain, so just for a reference, I tried it with the new chain, and I could barely pull it off the sprocket at all.

Re: (JeffKoch)

Jeff, I’m sorry for not responding earlier and not giving a complete explanation. No disrespect intended, I have the highest regard for your posts.

So here goes ...

Let:

T = torque output of the engine at any given RPM
R14 = radius of a 14-tooth front sprocket
R15 = radius of a 15-tooth front sprocket
F14 = chain tension using a 14-tooth speocket
F15 = chain tension using a 15-tooth sprocket

Sprocket circumference is proportional to the number of teeth, so from the geometry,

R15/R14 = 15/14 (Eq. 1)

From a free body diagram of the front sprockets,

T = R14 X F14

and

T = R15 X F15

or

R14 X F14 = R15 X F15

Solving for F15, and substituting using Eq. 1 we get,

F14 = (R15/R14) x F15 = (15/14) F15 (Eq. 2)

Therefore, the chain tension using a 14-tooth sprocket is 7% higher than the chain tension using a 15-tooth sprocket for any given applied torque.


This result can also be shown by considering the rear sprocket:

Consider the following near-identical final drive set-ups:

Case 1: 14-tooth front, 38-tooth rear sprocket. Ratio; 38/14 = 2.71
Case 2: 15-tooth front, 41-tooth rear sprocket. Ratio; 41/15 = 2.73

For simplicity, assume that they’re equal such that:

38/14 = 41/15

or,

41/38 = 15/14 (Eq. 3)

T1 = torque applied to the rear wheel for Case 1
T2 = torque applied to the rear wheel for Case 2
R38 = radius of a 38-tooth rear sprocket
R41 = radius of a 41-tooth rear sprocket
F14 = chain tension for Case 1
F15 = chain tension for Case 2


Again from the geometry,

R41/R38 = 41/38 (Eq. 4)

From a free body diagram of the rear sprockets,

T1 = R38 X F14 (Eq. 5)

and

T2 = R41 X F15 (Eq. 6)

The final drive gear ratios for Case 1 and Case 2 are the same - which means that the torque multiplication is the same, so the torque applied to the rear wheel is the same at any given engine torque output level and RPM.

Therefore,

T1 = T2

substituting from (Eq. 5) and (Eq. 6),

R38 X F14 = R41 X F15

or,

F14 = (R41/R38) X F15

from (Eq. 3) and (Eq. 4)

R41/R38 = 41/38 = 15/14

Substituting,

F14 = (15/14) X F15

Which is the same result as (Eq.2)

So here is an example where you have two setups having the same gear ratio, one with a 15 tooth front, the other with a 14 tooth front. As I said, the chain tension will be greater in the 14 tooth setup.

Re: (Shazaam!)

Shazaam, I understand and absolutely agree with what you're saying , but I'm saying something different. The chain tension is the only force on the rear sprocket (rear wheel torque = chain tension*rear sprocket radius), so for a fixed rear sprocket radius and chain tension, the rear wheel torque (that accelerates the bike) is the same. Also, rear wheel torque = engine torque * rear sprocket radius/front sprocket radius, so to obtain the same rear wheel torque (and therefore the same acceleration) with a smaller front sprocket you don't need to apply as much engine torque.

If you use the same amount of engine torque, then yes the chain tension will go up, as you point out (chain tension = engine torque/front sprocket radius), but you'll be accelerating more quickly because you'll be applying more rear wheel torque ( = chain tension * rear sprocket radius).

The factor that determines your chain tension is really how quickly you are accelerating, which is why I pointed out that hopping up your engine will also increase chain tension. If you accelerate at the same rate, your chain tension will be the same no matter what sprocket you are using. This is why I think it's misleading to say the chain tension increases if you drop a front tooth - it will if you use the lower gearing to pull harder (the wheelie example), but only if you do so. And in some cases it might even go the other way, if your revs increase to the point that the engine torque curve falls off.

Isn't this more fun than oil threads, BST wheel threads, and Ducati/RC51 pissing-match threads?

Re: (JeffKoch)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JeffKoch »</TD></TR><TR><TD CLASS="quote">
Isn't this more fun than oil threads, BST wheel threads, and Ducati/RC51 pissing-match threads? </TD></TR></TABLE>


YES!!!!!

This is the stuff boards should be made of...

But, I still think he should sell his 800SS, since he can't get a front sprocket for it and get a ZX-6RR, so it will be more dependable. Damn Ducati.