Changing gearing -- front vs rear

Kabara, Richard M. richard.kabara at pw.utc.com
Wed Jun 25 07:35:54 PDT 2008


Uuuh, Randy, you're absolutely right, industrial chain drives have to run
for millions of hours. However, factors that affect chain wear in those
lightly loaded situations may also apply to the our compromise bike
situation.
I apologize that the context of that quote was lost. The author was talking
about the 'polygon effect', which I poorly tried to describe as chain 'hop'.
The difference between the radius to the chain line on the sprocket when the
tooth is at TDC versus when the chain pin is at TDC. As sprockets get
smaller (i.e. going from 15T to 14T) that radius difference progressively
increases. For a constant counter/shaft speed, the chain speed has to
accelerate and decelerate each time it passes over the peak of the polygon.
That's true weather or not it's a motorcycle or industrial machine chain.
The polygon effect adds a pulsing and dynamic loading on top of the chain
tension load applied to the sprocket teeth, which will accelerate wear.
That's all I was trying to say...

The other fact that remains true is one of my bikes, 2006 GSX-R750, which I
consider highly refined and optimized 'production' sport motorcycle (you may
disagree, I realize it's no Bimota or MotoGP bike) does run a 17T c/s stock.
For many years, Suzuki has been compromising the component weights,
handling, chain line affect on rear suspension, co$t, etc, etc and they
still chose to use a 17T. Why didn't they chose a 14T to reduce sprocket
rotating mass/chain mass and get the chain line closer to the swingarm
pivot? I'm not sure, that would be an interesting discussion with an
engineer at Suzuki....

Rich

-----Original Message-----
From: Randy Grein [mailto:randygrein at comcast.net] 
Sent: Wednesday, June 25, 2008 12:16 AM
To: Suzuki SV650 Mailing List
Subject: Re: Changing gearing -- front vs rear

Um, yeah. Industrial designs also underload chain & sprocket rigs  
compared to bikes by a factor of 10 or more IIRC. Bikes are a serious  
mechanical compromise, this is just one area.

Another issue, or used to be is the chain angle. The ideal is to get  
the countershaft as close to the swingarm pivot as possible, and  
equalize the sprocket sizes to eliminate chain pull on the swingarm. A  
mid-80's Bimota design had an extra wide swingarm that used  
freestanding outboard pivot points concentric with the countershaft.  
Chain slop was minimal and didn't vary throughout wheel travel.  
Complex and heavy though.


Randy Grein, WMRRA #41

On Jun 24, 2008, at 7:26 AM, Kabara, Richard M. wrote:

> I looked up some stuff last night...
> The book I was referring to "The Racing Motorcycle, A technical  
> guide for
> constructors" John Bradley. He claims "Industrial designers try to  
> avoid
> anything less than 17 teeth"
>
> Two data points on OEM stock c/s sprockets that I have in my garage...
> 2003 R6 - 16 tooth
> 2006 GSX-R750 - 17 tooth
>
> These are 'cutting edge' sportbikes where weight and compact design  
> are
> critical, still they use 'big' c/s sprockets. Of course they set the
> internal ratios to work with those sprockets, would not work on  
> SV...or rear
> sprocket would have to be unreasonably large.
>
> Moral of the story is: for long term sprocket wear, bigger is  
> better. So if
> you want to shorten your gearing, run 15/48, not 14/45. As Jim already
> proved with his 15 tooth c/s sprocket going for four years.
>
>
> -----Original Message-----
> From: Kabara, Richard M. [mailto:richard.kabara at pw.utc.com]
> Sent: Monday, June 23, 2008 5:41 PM
> To: Suzuki SV650 Mailing List
> Subject: RE: Changing gearing -- front vs rear
>
> Thanks Zoran, it's 520
>
>> From the RK chain website, comparing their "standard O-ring" chains
> http://www.rk-excel.co.jp/global/chain/chain_application.pdf
>
> 520 is 3.36  lbs / 100 links
>
> 525 is 4.30  lbs / 100 links
>
>
> So the 525 is 28% heavier.....I'd call that significantly heavier!
>
>
>
> -----Original Message-----
> From: zoran [mailto:zv30 at sbcglobal.net]
> Sent: Monday, June 23, 2008 5:24 PM
> To: Suzuki SV650 Mailing List
> Subject: Re: Changing gearing -- front vs rear
>
> 520.
>
>
> Zoran Vujasinovic
> Twin Works Factory
> 775-786-4881
> www.twfracing.com
> ----- Original Message -----
> From: "Kabara, Richard M." <richard.kabara at pw.utc.com>
> To: "Suzuki SV650 Mailing List" <sv650 at micapeak.com>
> Sent: Monday, June 23, 2008 2:26 PM
> Subject: RE: Changing gearing -- front vs rear
>
>
>> I'd bet the SV400 uses a lightweight chain, like a 418? (not sure  
>> of the
>> spec) not the heavier 525 chain the SV650 uses, so the SV400 may be  
>> more
>> tolerant of the 14 tooth c/s sprocket.
>>
>> Rich
>>
>> -----Original Message-----
>> From: Jim Stewart [mailto:js at strappe.com]
>>
>> Well, Zoran tells us that the SV 400 has a 14 tooth sprocket stock.


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