ADVrider

Go Back   ADVrider > Bikes > Some Assembly Required
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 04-30-2015, 04:00 AM   #1
ADpete OP
Gnarly Adventurer
 
ADpete's Avatar
 
Joined: Jul 2006
Location: Canbrerra Australia
Oddometer: 233
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 ?
__________________
PETERD
ADpete is offline   Reply With Quote
Old 04-30-2015, 12:23 PM   #2
XRGRIFF
Adventurer
 
Joined: Mar 2005
Oddometer: 41
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.
XRGRIFF is offline   Reply With Quote
Old 04-30-2015, 07:46 PM   #3
k-moe
Beastly Adventurer
 
Joined: Jun 2012
Oddometer: 2,860
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.
k-moe is online now   Reply With Quote
Old 05-01-2015, 08:49 AM   #4
Roadracer_Al
louder, louder, louder!
 
Roadracer_Al's Avatar
 
Joined: Aug 2007
Location: Oakland, CA
Oddometer: 1,663
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.
__________________
When they say Harleys are for 1%ers, I don't think they mean guys who sell crank and get in bar fights any more.
Roadracer_Al is offline   Reply With Quote
Old 05-02-2015, 06:42 AM   #5
layzrider
Layzrider
 
layzrider's Avatar
 
Joined: May 2010
Location: vancouver, wa
Oddometer: 202
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.
layzrider is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 08:41 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2015