Ok, you asked for it ... grab a crate, some sausages and a pillow
This is from an engineer and NOT me, I am not that cleva to work this shit out, the ultimate info from this is you are better to run uneven numbered sprockets front and rear and a larger front sprocket places a lot less anger on your chain.
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.
Reply With Quote
Originally Posted by 98tls
Bookmarks