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Old 04-30-2015, 04:00 AM   #1
ADpete OP
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Location: Canbrerra Australia
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Question swing arm length?

Yet another sportster conversation and I have noticed that some use extended swing arms and some do not. So the question is why, what's the difference between standard length and longer.What are the advantages and disadvantages. I am fitting KTM forks to my 2014 883 iron. Is it necessary to extend the rear swing arm. I not looking for speed just a competent soft roader (l hate that term but it is accurate ) not trials, not CR500 ,nor gs1200 .anyway what about swing arms ?
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Old 04-30-2015, 12:23 PM   #2
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My take on it is, when you increase suspension travel on the front you increase the wheelbase, increase it on the rear you decrease it. Do both and wheel base (for arguments sake) stays about the same, but you have moved the centre of gravity towards the back of the bike, good for traction bad for steering, longer swingarm moves it forwards again. Very general I know but sort of what goes on.
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Old 04-30-2015, 07:46 PM   #3
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Raising the suspention also changes the chain/swingarm relationship. A longer swingarm allows for a higher ride height, and a swingarm angle that is closer to what it was at the original ride height.
Mixing metaphors is like killing two birds with a dog that won't hunt.
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Old 05-01-2015, 08:49 AM   #4
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A longer swing arm yields more wheel travel for the same shock travel.

It also adds leverage at the shock, therefore, a stiffer spring and firmer damping is required to achieve the same handling as original (which is explicitly not the goal here, but is important to understand.)

Yes, the chain has something to do with it, too. The longer the swing arm is, the more wheel travel it will have before the chain fouls the swingarm ---- unless the swingarm pivot is coaxial to the front sprocket. Also, a longer swingarm reduces the amount of chain tension difference throughout the stroke.

The downsides of longer swingarms is that it extends the wheelbase and can make the bike front-heavy (i.e. won't wheelie, which is why drag bikes have extended SA, so they can accelerate harder).

The longer WB can also make turning feel sluggish.

Because the chain has a longer un-supported run, it can flop around and derail more easily unless a MX-style chain guide is fitted -- this assumes a *very* long SA... +2" shouldn't be a problem. And obviously, you need to buy a longer chain every time you replace the chain.
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Old 05-02-2015, 06:42 AM   #5
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Joined: May 2010
Location: vancouver, wa
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23" on my off road bikes

I used my bikes to find some common dimensions for my project. My 400 drz and Transalp have 23" (on center) swing arms. Very different bikes yet they have the same length arms. My old 350 and 250 xr's have 21" arms. I used a cr500 rear suspension on my project bike, which also has a 23" arm. I am guessing off road bike designs have evolved to this dimension.
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