Gearing- 14T and 15T gearings, are they comparable?

[hillbillypolack]

I just did the 14T front sprocket swap last weekend, and (finally) the bike is docile in traffic, and doesn't bog at 45 mph.

I will be doing a 520 chain conversion at some point, and have heard positive things about a 15T front (better mechanical leverage, I am told).

IF that is the case, and I am looking for a gearing combo close to my 14F / 41R, then what would be a 15T equivalent?  I assume a 15T / 43T ?

14/41 = .341
15/43 = .348

Would anyone even feel the difference of .007 gearing change?

I am asking since I honestly don't know.

Thoughts?  Or is it just better to stick with the 14 / 41 combo?

[red baron]

It will feel about the same as the 15/43.

It's a good idea and likely the chain will last longer.

[NAKID]

If you want to get REALLY close, 15/44 would be .001 off...

[hillbillypolack]

It will feel about the same as the 15/43.

It's a good idea and likely the chain will last longer.

Why would the chain last longer?  The only thing I can assume is that the front sprocket radius is larger, if that affects any chain wear.

There was a mechanical engineer who posted something about the 15T having a better mechanical advantage over a 14T (larger radius from the countershaft).

Can anyone verify if that is correct, or is it just a hunch?

[mmakay]

Why would the chain last longer?  The only thing I can assume is that the front sprocket radius is larger, if that affects any chain wear.

There was a mechanical engineer who posted something about the 15T having a better mechanical advantage over a 14T (larger radius from the countershaft).

Can anyone verify if that is correct, or is it just a hunch?

There is no mechanical advantage, in fact, the opposite is true.  But, it is indirectly related to sprocket diameter.

Chain drives do not transmit a constant force.  Each time a chain link engages a sprocket tooth, there is a force impulse in the chain.  This is due to tooth profile, centrifugal force, etc.  These pulses wear a chain out faster.  In industrial applications you will rarely see sprockets with less than 20 teeth because that is the "rule of thumb" diameter ratio that more or less eliminates the pulsing effect.  Fewer than 20 and the effect increases pretty dramatically.  If I remember correctly, having only 12 teeth decreases chain life by over 50%.  (I could look up the equation, if you like.)

So that's the semi-detailed explanation ... and yes, I'm a mechanical engineer.

[clubhousemotorsports]

To  make matters even more muddy you also are effecting the squat/antisquat  aspect of the chassis. Playing with different angles as the chain is pulled on by the sprocket (smaller sprocket is pulling from a different angle due to size).

We are splitting hairs here though, ducati has fit 14 tooth sprockets on some of their bikes right of the assembly line (748,916sps) so it is not out of the norm.
If I am putting on a new chain and sprockets I always go for the 15 tooth front. If there are outside reasons where this is not possible it is not that big a deal.

[brad black]

if it's a single sided swingarm bike and the rear sprocket is $300 or more, good motivation to do the front.  if it's a dual sided swingarm and they $100 or less then go up on rear.  a bigger front and rear will also move the chain off the swingarm guard, which might help.

[NorDog]

For the record, gear ratios are calculated by dividing the driven gear tooth number by that of the drive gear.

So instead of...

14/41 = .341
15/43 = .348

...it would be...

41/14 = 2.93:1
43/15 = 2.87:1

[Norm]

To  make matters even more muddy you also are effecting the squat/antisquat  aspect of the chassis. Playing with different angles as the chain is pulled on by the sprocket (smaller sprocket is pulling from a different angle due to size).

This is VERY important if you're setting up your bike for max performance in the twisties. If anyone is interested, I can post a diagram & explanation.

[He Man]

To  make matters even more muddy you also are effecting the squat/antisquat  aspect of the chassis. Playing with different angles as the chain is pulled on by the sprocket (smaller sprocket is pulling from a different angle due to size).

This is VERY important if you're setting up your bike for max performance in the twisties. If anyone is interested, I can post a diagram & explanation.

Please do.

[Norm]

How do I post a pic here?

[He Man]

[xximg]picturelink[/imgxx]

without the xx

also located beneath the ITALICs button.

[Norm]

I still can't get it.

[Norm]

Until I can figure out the picture thing, here's a description:
This is commonly referred to as "pole of the moments". Draw a line along the upper chain line, another line from the rear axle thru the swingarm pivot. Now, draw a line from the tire contact patch to where all 3 lines intersect. The steeper this angle is, the more anti squat characteristics the bike will have. As you can see (figuratively) the sprocket sizes plays a significant role.

[jdubbs32584]

Norm, theres a FAQ that deals with the picture thing. Basically, you need to upload your picture to a place like Flickr or photobucket. Then right click on the picture, select copy image location, and paste it between the img tags.