stress from a 12 tooth?

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wornknobby

Member

Feb 5, 2004

625

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• Apr 13, 2006

• #1

I hear that running a 12 tooth front sprocket can add more stress... but more stress to what? just the chain, or is it more stress on the motor as well, i would think that as long as you were shifting when you needed to, the motor would know the difference except for the roation of the rear tire.
just curiou to see if any one knows about this, i did a search but could only find some bits and peices. :coocoo:

I also ask this b/c right now i'm running 12/51 and in the tight woods i ride in i could still use some more bottom, so i bought a 54 tooth, I know at the track i will probally have to go back to my 49 though. :blah:

 

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fatboyslim

Member

Apr 11, 2006

255

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• Apr 13, 2006

• #2

Just go with a 13 or 14 tooth front sprocket, they go well with 50 - 54 tooth rear sprocket.

 

Jaybird

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Mar 16, 2001

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Charlestown, IN

• Apr 13, 2006

• #3

If you have a bike using a 13/52 (4:1 ratio) and another bike using a 12/48 (4:1 ratio) the bike doesn't know any difference at all. They are both exactly the same to the driver shaft, and both require the identical same amount of torque.

But, what is different is the chain pull created. It creates more pull on the chain using the 12/48 set-up. Also, when the chain articulates around the smaller driver (CS) sprocket, the 12 tooth requires the chain to flex a slight bit more than the 13 tooth would.
These two things coupled together creates more stress and wear on the chain, which means that the chain and sprockets will wear out faster with the 12/49 set-up than with the 13/52.

It may be hard to visualize the chain having to work harder with the exact same ratio, but there is a formula that can prove it out. Hopefully you can just trust what I'm saying.

 

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wornknobby

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Feb 5, 2004

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• Apr 14, 2006

• Thread starter
• #4

as long as i only have the stress excerted to the chain, and not the tranny then i'm not worried b/c i can always buy more sprockets and chains if i need to. but i was worring about the stress exzerted to the tranny, if b/c the shaft is now spining faster if that would hurt the tranny at all.....

 

robwbright

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Apr 8, 2005

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• Apr 14, 2006

• #5

I used an 11 tooth for some time last year with no apparent ill effects. . .

 

Jaybird

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• Apr 14, 2006

• #6

Just a heads up...Suzuki used to use 12tCS and went back to the 13T.

See, if you get down to the nitty-gritty of chain engineering, you should never design a drive with the driver having less than 17 tooth on a #50 (520) size chain. Sometimes that simply isn't practical with our bikes, but the smaller the driver, the faster the wear.

 

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wornknobby

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Feb 5, 2004

625

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• Apr 14, 2006

• Thread starter
• #7

ok so not to sound like a broken record or any thing :blah:

but basically i shouldn't have any problems with my tranny from running a 12 tooth...?

b/c i found RK 520 130 link chains from rockey mountain for less than $30...!!!!! :) so buying chains isn't a problem, i just don't want to be splittin cases next season just b/c i ran a 12 tooth. :blah:

 

D

dirt ninja

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Feb 20, 2006

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• Apr 14, 2006

• #8

but.....

You can pick up a front sproket for around 15.00 shipped to your door from ****... You could possibly break a cheap chain if the conditions are right. :coocoo:

 

Jaybird

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• Apr 15, 2006

• #9

4:1 ratio using one gearing set, and 4:1 using another gearing set places the same amount of work on the driver. It has no idea what your sprockets are, other than it takes 4 revolutions of the front to make 1 revolution of the rear.
Your chain and sprocket teeth know the difference.

I have given this explination n the past, and it may help to understand why this happens...

A 12/48 set-up has a total of 60 teeth doing the work. A 13/52 set-up has a total of 65 teeth doing the work, thus the very same results are carried out by less teeth on the 12/48. Which means that each tooth must carry the slack that the missing 5 teeth would have helped with.
The 13/52 has 5 more teeth (or workers) to produce the end results, and have distributed the work better than the lesser gear-set.
Hope that makes sense.

 

rm_racer

Member

Mar 15, 2005

501

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• Apr 15, 2006

• #10

Basically, 12tCS = more wear on the chain. When there is more wear on the chain there is more wear on the sprokets. You can achive the same ratio with a 13tCS, and a differnt rear sproket. You should change them all at once anyway.

Besides, jaybirds the chain expert, right?

 

Papakeith

COTT Champ Emeritus

Damn Yankees

Aug 31, 2000

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RI

• Apr 15, 2006

• #11

No stats from me. For that I'll trust Jay. Just a bit of personal experience. I ran my CR500s with 12: 52. That was on both my 84 and my 98 CR500. Never had any troubles.