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...to help you decide what is the best way to go, read this below and make you own choice however one thing that comes out blindingly obvious is that running uneven or odd numbers on your front and rear sprockets will significantly increase your chain life.

Read on!!


14-Tooth vs. 15-Tooth Front Sprocket Wear
For (say) a 96-link chain ...
A 15-tooth front sprocket will contact the same chain link every 32 revolutions. 15 x 32 = 480 links ÷96 = every 5 chain revolutions.
A 14-tooth front sprocket will contact the same chain link every 48 revolutions. 14 x 48 = 672 ÷96 = every 7 chain revolutions.
With the same rear sprocket and at the same road speed, the 14-tooth sprocket and the 15-tooth sprocket both contact the same number of chain links per unit time.
So for example, for every 35 chain revolutions, the 15 tooth sprocket contacts the same link 7 times and the 14-tooth sprocket contacts the same link 5 times.
If we assume that there is a defect on one of the front sprocket teeth (or a particular chain link) that can cause abnormal wear to the same chain link (or sprocket tooth) when contacted over and over again, the 14-tooth sprocket would actually result in (7-5)/7 = 29% LESS defect-related wear than a 15-tooth sprocket.
However, for the same 35 chain revolutions, the 15-tooth sprocket rotates 224 times and the 14-tooth sprocket rotates 240 times so the 14 tooth sprocket (and the chain) would see (240-224)/240 = 7% MORE continuous wear than a 15-tooth sprocket.

Odd vs. Even Sprocket Teeth Wear Pattern
For reduced wear to the sides of the sprocket teeth, it’s better to run odd-numbered tooth sprockets, front and rear. Here’s why.
A chain alternates its links inside-outside such that side-to-side chain positioning is controlled by contact between a sprocket's teeth and the inside links. Because a chain always has an even number of links, each tooth on an even number-tooth sprocket will always contact either an inside link or an outside link. Each tooth on an odd number-tooth sprocket will alternate between inside and outside links that gives a uniform wear pattern to the sides of the sprocket.
Of course, this really isn't a significant problem with steel sprockets, so Ducati uses a 14-tooth front sprocket on some models. Even-tooth rear sprockets are standard on a number of models. However, if you intend to replace your sprockets with aluminum which is a lighter, but softer material, accelerated sprocket wear will be a consideration.
But who cares? A little wear on the sides of a sprocket doesn't significantly affect chain engagement.
==================================================
Wear to the face of the tooth is the reason for using a hunting tooth when meshing two gears. When you have a chain-driven sprocket instead of gear-to-gear contact, the wear issue becomes avoiding the same teeth on the sprockets repeatedly meshing with the same links on the chain.

How often the same tooth meshes with the same link can be calculated by comparing the number of teeth on each sprocket to the number of links in the chain.
The first step is to factor the number of teeth and links into prime numbers. Here’s some common results:
Front Sprockets
14 tooth - factors: 7x2
15 tooth - factors: 5x3
Rear Sprockets
36 tooth - factors: 3x3x2x2
37 tooth - factors: 37
38 tooth - factors: 19x2
39 tooth - factors: 39
40 tooth - factors: 5x2x2x2
41 tooth - factors: 41
42 tooth - factors: 7x3x2
43 tooth - factors: 43
44 tooth - factors: 11x2x2
45 tooth - factors: 5x3x3
Chain Links
94 links - factors: 47x2
96 links - factors: 3x2x2x2x2x2
98 links - factors: 7x7x2
Two numbers are defined as relatively prime if they have no common factors. The front sprocket/chain combinations from above that are relatively prime are:
15 tooth front - 94 link chain, 98 link chain
The sprocket and chain will meet at the same spot every 15 turns of the chain and 94 or 98 turns of the sprocket respectively.
14 Tooth front - none of the combinations are relatively prime. If the two numbers aren't relatively prime, then the number of turns will be divided by the common factors. For example:
14 tooth front - 94 link chain
Here, 14 (7x2) and 94 (47x2) have the common factor of 2. Consequently, the sprocket and chain will meet at the same spot every 7 turns of the chain and 47 turns of the sprocket.
14 tooth front - 96 link chain
Here, 14 (7x2) and 96 (48x2) have the common factor of 2. Consequently, the sprocket and chain will meet at the same spot every 7 turns of the chain and 3 turns of the sprocket.
14 tooth front - 98 link chain
Here, 14 (7x2) and 98 (7x7x2) have the common factors of 2 and 7. Consequently, the sprocket and chain will meet at the same spot every turn of the chain and 7 turns of the sprocket. Not very good for wear.
The rear sprocket/chain combinations are computed separately, the same way as for the front. Here’s the result for combinations that are commonly used:
36 tooth rear (18x2) - 94 link chain (47x2)
Here, the common factor is 2. Consequently, the sprocket and chain will meet at the same spot every 18 turns of the chain and 47 turns of the sprocket.
38 tooth rear (19x2) - 94 link chain (47x2)
Here, the common factor is 2. Consequently, the sprocket and chain will meet at the same spot every 19 turns of the chain and 47 turns of the sprocket.
38 tooth rear (19x2) - 96 link chain (48x2)
Here, the common factor is 2. Consequently, the sprocket and chain will meet at the same spot every 19 turns of the chain and 48 turns of the sprocket.
40 tooth rear (5x2x2x2) - 96 link chain (12x2x2x2)
Here, the common factor is 2x2x2. Consequently, the sprocket and chain will meet at the same spot every 5 turns of the chain and 12 turns of the sprocket.
42 tooth rear (21x2) - 96 link chain (48x2)
Here, the common factor is 2. Consequently, the sprocket and chain will meet at the same spot every 21 turns of the chain and 48 turns of the sprocket.
42 tooth rear (21x2) - 98 link chain (49x2)
Here, the common factor is 2. Consequently, the sprocket and chain will meet at the same spot every 21 turns of the chain and 49 turns of the sprocket.
44 tooth rear (22x2) - 98 link chain (49x2)
Here, the common factor is 2. Consequently, the sprocket and chain will meet at the same spot every 22 turns of the chain and 49 turns of the sprocket.
45 tooth rear (5x3x3) - 98 link chain (49x2)
No common factors. Consequently, the sprocket and chain will meet at the same spot every 98 turns of the chain and 45 turns of the sprocket.
 

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Discussion Starter #4
Actually, I did not write it, this is great work from Shazaam from Speedzilla, I asked a question and this is what he came back with, very good info and I wanted to share it, I summarised it at the top by saying what was optimal, i.e. odd numbers sprockets.

It is always nice to have some insight into what we can do to keep the running cost of our machines down.

hwjar, you should appreciate free information and read my summary first, when you sound unappreciative people may not rush to give you further info, and for your info I clock up considerable miles on my bikes and don't sit there doing math about it.
 

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Monstaman said:
Actually, I did not write it, this is great work from Shazaam from Speedzilla, I asked a question and this is what he came back with, very good info and I wanted to share it, I summarised it at the top by saying what was optimal, i.e. odd numbers sprockets.

It is always nice to have some insight into what we can do to keep the running cost of our machines down.

hwjar, you should appreciate free information and read my summary first, when you sound unappreciative people may not rush to give you further info, and for your info I clock up considerable miles on my bikes and don't sit there doing math about it.
It's always nice to get some educational benefit out of something you love to do. i appreciate you posting this man, and I'm sure others do as well. Don't let the last two throw you off.

[thumbsup] to you.
 

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Pip said:
IDon't let the last two throw you off.
+1

Good post. (If hwajr and robhuber don't want to read technical stuff, there's no end of asinine posts they can read over in nmc ;) )

If I remember, I'll post up a pic of the front sprocket from my "worst case" sprocket choice of 14/42 - even number of teeth both front and rear, and the number of front teeth evenly dividing into the number of rear teeth - about the only other mistake I could have made was running 84 (or 126) links of chain, I think I had 102 links.

big
 

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Monstaman said:
...to help you decide what is the best way to go, read this below and make you own choice however one thing that comes out blindingly obvious is that running uneven or odd numbers on your front and rear sprockets will significantly increase your chain life.

Read on!!


14-Tooth vs. 15-Tooth Front Sprocket Wear
For (say) a 96-link chain ...
.
.
.

That's great, Monstaman! Thanks. [thumbsup]

After changing to 14T on my 2007 695, I trully recommend it with the stock rear sprocket. The best mod one can have almost for free. ;)

Don't know about wear but the change of the pull power is really big.
 

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great post. you confirm what i've been leaning towards, keeping the 15T up front and going to a 41T on the rear of my S4. great info.
 

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Discussion Starter #11
I like the engineering side of our bikes so pay a bit of interest to it, my next front sprocket will be 15 and the rear 41 as well.

What Shazaam does not say is that chain chatter is also significantly reduced having the larger front sprockets.

Check out the GP and WSBK sprockets, they tend to be quite large, not just for gearing either!

For those who wonna bin the article step out of the tech section, or read the top bit only as I did the work for you.

Cheers to thos who appreciate it [thumbsup]
 
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Whooo Big Boy - Someone has got way to much free time!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Is it like Cold where you live?

I think when my chain wears out, I will just replace it and the sprockets at the same time!!!!

Brian F
 

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thank the Monster gods for threads like this. yes this stuff makes my head hurt and he lost me at the first equation, but it's still great info for some of us who want to understand why certain combos work better than others. when i called the closest Ducati shop all the techs were in agreement that 14T was the best way to go on my S4. several S4 owners on this BB disagreed, saying that 15T on the front was better due to chain clearance issues, and that the same thing could be achieved by going bigger in back. the odd tooth count thing is brilliant, since i never would've considered that, but it makes so much sense once explained in such a manner.

for those who just want to trust their techs and pay for whatever they put on, fine, click on the Back arrow. or if some don't care about why things wear out faster, same thing.

i for one think this section of the DML was created exactly for this type of info.

[thumbsup] great thread.
 

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Cool post!

It reminds me of a section from a book I have read Cryptonomicon (Neil Stevenson) The author was talking about if you had a bent tooth on the front sprocket of a bicycle and a corresponding issue with one chain link how and every time they met it would throw the chain.

I'll see if I can find a on-line version of that text, good read.

Great book BTW
 

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Thanks for passing the information on but a bit over my level of understanding. I can figure out your first summary but then its too much. ::)
 

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I ride for fun and truly enjoy mathematics too. This is an awesome post. Interesting and at the same time very informative. We all need to take those variables seriously when considering sprocket changes. Thanks......
 

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Nice Post!!
I have an doubt that with all this Math, I could not figure out.
I have an M600 -2001 Its stock.
I read the manual, and there it says that the diff of the 600, 750 and 900 is only the sprocklet (rear) the spark of 15 theeth are the same.
So, i was thinkng of changing my 46 original sprocklet for an 39 (same as the 900) to raise the top speed of my bike.

What u all think about it?
Will I loose too much "drag"?
Is it a nice change, or do u suggest another change?


Thanks for all the help,

-J.
 

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Discussion Starter #18
Maybe a change like that might steal a bit much power off the bottom, not having a 600 I am unsure of the real world output and rideability of your bike.

Just make sure you do not rob too much from the bottom or your bike will feel like a 400!
 

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What rear sprocket does the 2001 M900 come with? Is 41t the best rear to go with?
Thx!
 
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