Had an interesting conversation today about gearing


8 replies to this topic
  • wes513v

Posted February 10, 2016 - 07:54 PM

#1

Talking to a local expert with extensive experience in setting up bikes and he mentioned being able to achieve better suspension action by swapping the front sprocket to a 14 from a 13 and making the appropriate change in the rear sprocket to account for the change. Has anyone else heard of this or done it and could you share what it accomplished?

  • Monk

Posted February 10, 2016 - 08:26 PM

#2

Talking to a local expert with extensive experience in setting up bikes and he mentioned being able to achieve better suspension action by swapping the front sprocket to a 14 from a 13 and making the appropriate change in the rear sprocket to account for the change. Has anyone else heard of this or done it and could you share what it accomplished?


I don't think it's that simple. With a larger front sprocket you get more squat (softer) but with a larger rear you get less squat (stiffer). Accounting for the 2.5-3t change in the rear can be difficult for some swingarms to handle too. Going from say, 13/50 to 14/53, many bikes cannot handle a larger sprocket on the rear or it interferes with the chain guide. Axel position and chain tension also play a major part too...

  • Krannie McKranface

Posted February 11, 2016 - 06:11 AM

#3

Talking to a local expert with extensive experience in setting up bikes and he mentioned being able to achieve better suspension action by swapping the front sprocket to a 14 from a 13 and making the appropriate change in the rear sprocket to account for the change. Has anyone else heard of this or done it and could you share what it accomplished?

 

Way to many variables beside sprocket size that will make more of a difference, and be more practical.



  • grayracer513

Posted February 11, 2016 - 07:52 AM

#4

$10 says it makes no measurable difference whatsoever.  Using stock gearing as the base, changing to a 14/53 from a 13/49 raises the chain line 5mm in front and 9mm in back.  



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  • stevethe

Posted February 11, 2016 - 08:10 AM

#5

The bikes might likely take a 53 on the rear as I use one on my 07 WR450. But I agree with Greyracer your wasting your coin.

  • wes513v

Posted February 12, 2016 - 06:19 AM

#6

I was just wondering about the physics of it. Decreased chain angle as it crosses the swing arm pivot? What would make him think the change was noticeable? With Grays numbers would a 4 mm difference really be noticeable? Seems like a placebo effect based on misapplied geometry. Perhaps the perceived change was slightly more aggressive acceleration from a lower final drive being interpreted as improved action based on what the desired outcome should be? I don't know, I was just wondering if anyone had heard something like that before.

Edited by wes513v, February 12, 2016 - 06:22 AM.


  • TN Dirt Rider

Posted February 12, 2016 - 06:57 AM

#7

Seems like I read something once about how Chad Reed, back in his YZ 250 2stroke days preferred a bigger sprocket (can't remember front/rear or both) because it made the bike stay over in the corners better. Maybe this guy is thinking something similar.

  • grayracer513

Posted February 12, 2016 - 07:18 AM

#8

The theory seems to be based on the idea that the drive load on the chain tends to compress the rear suspension slightly under power by in effect, pulling on the rear end of the swing arm from a point above it.  Then, the logic flows, that the larger sprocket provides more "leverage" to the chain, so it must compress the suspension more.  The flaw here is that the larger front sprocket reduces the leverage advantage that the output shaft has on the chain, which means that the force applied to the chain is reduced, which, when you consider the equally increased advantage at the rear, the net force pulling at the axle end of the swing arm is exactly the same as with the smaller sprockets at both ends.  



  • GHILL28

Posted February 12, 2016 - 06:25 PM

#9

I just did this swap back and forth in the last month for the hell of it.  13/49 up to 14/49, then back again.

 

I noticed absolutely no change in the suspension, except for the slight stiffening from the swingarm being shortened since I did not use a longer/shorter chain.  I guarantee you that's a bigger effect than the chain angle.







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