swingarm lengths?

b1broc

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what are your guys thoughts on the length of the swingarm? I have been puting together a 1981 cafe,tracker style. I have seen people stretch the stock swingarms 3 or so inches. are they doing this for fuction? or a look? I have an xs 400 swingarm that bolted right up. I know the shock mounts are different. i actually like the 400 mounts better. I question the length... should i stretch it? or is it a waste. or should i say the hell with it all and mod a box swingarm like i really want..:shrug:
 
xs400 has 17mm axle, plus I think there is an offset at the pivot, which may cause sprocket alignment issues. So you need to factor that into the decision making.
 
The XS400 swingarm will be pretty flexy on the heavier and more powerful 650, particularly if stretched--IMO not a real good idea. Let me know if you need a swingarm, I have a few.
 
Was really wanting to upgrade to like a alum box swingarm..I dont really know what would be close to fitting that wouldnt need a ton of work. I know I dont want to make it a mono shock the radian swingarm looks nice. But id really like to stick to aluminum.
 
Well this thread sort of stun off... lol

how about answering the swing arm lengthening bit.... say to 2-3 inches.
Any gains worth the effort???
 
Here is a list of pros and cons I found.... the thing is i doesn't mention any particular length for any particular bikes:

More swing-arm length has the following effects:

» The center of gravity moves forward, loading the front wheel.
» The turning radius is increased and turning is slower.
» Weight transfer forward on braking is reduced, the rear brake does more work.
» Weight transfer backward and traction on acceleration are reduced.
» The swing-arm arm is less rigid due to increased span length.
» Clearance to the inside of the rear fender and support loop is reduced.
» The brake torque link and chain guard must be extended, and links added to the chain. In
extreme cases a tensioner should be added to the lower chain row.
The shock absorber & spring presents its own problems:
If the extra swing-arm length is added rearward of the lower shock mount (usually the easist method, since it avoids re-locating the shock mounts):
» The spring and hydraulic valve rate becomes effectively weaker, because leverage against the
shock is increased.
» The shock’s travel (and therefore the maximum suspension travel) is slightly reduced.
» The rear wheel’s positions (droop, loaded, and full compression) are all slightly higher, the
chassis and seat are slightly lower, and a small amount of rake & trail are added to the steering.
» Due to the forward inclination the suspension becomes slightly “rising rate”, where the rate per
inch of travel increases as the compression limit is approached.
 
I think MMM (650central.com) has lengthed his swingarm about 1 1/2" for his race bike. You would need to contact him to get details. A bit of length might add stability when the front is dropped and the rear raised to get the fork angle less for quicker steering. Two SA's I know of are the SR500, which is maybe an inch shorter, and the TX750, which is an inch longer. There are guys who have dealt with both these SA's so you need to did around to get accurate particulars.

I've decided to keep my SA at the stock length. I have longer shocks on the back and the forks dropped about 1/4" in the triples. I like the sharper turn in and a longer wheel base would make my XS less fun to ride around town.

Tom
 
Tom, the TX750 and the 74 up XS650 swingarms are the same length. The TX750 was just made of larger diameter tubing. There are pics on here somewhere with both side by side. The earlier, 70-73 650 swingarms are shorter than the later, about 1.5 inches if I recall right.
Leo
 
I received the XS650 list for several years. It's a forum via email. There were a couple of older guys there who built custom frames, custom swingarms, street trackers and so forth. It was suggested repeatedly that the XS 650 does benefit from a little stretch, resulting in a better balanced better handling bike. I corresponded with one of the guys who built custom chromolly box section swingarms - any length you wanted... he felt that 2" stretch was the sweet spot. Sadly he died.

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has anyone ever used a dirtbike box alum swingarm? like from the early 80's? i know they were pretty simple then. I understand that some mods would need to be done.. maybe lots, but i have alot of time.... and am in no hurry.:D
 
has anyone ever used a dirtbike box alum swingarm? like from the early 80's? i know they were pretty simple then. I understand that some mods would need to be done.. maybe lots, but i have alot of time.... and am in no hurry.:D
Check out This Project I stumbled across. He's converted the KX swingarm to a single pivot dual shock setup. I actually have a newer KX125 frame complete with swingarm and inverted forks, thinking seriously about using both.
 
I received the XS650 list for several years. It's a forum via email. There were a couple of older guys there who built custom frames, custom swingarms, street trackers and so forth. It was suggested repeatedly that the XS 650 does benefit from a little stretch, resulting in a better balanced better handling bike. I corresponded with one of the guys who built custom chromolly box section swingarms - any length you wanted... he felt that 2" stretch was the sweet spot. Sadly he died.

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By any chance was the guy who built those swing arms the "crazy russian"? I have one of his swing arms on "madness" FKA "rods hotrod" but haven't checked the length.

View attachment 48858
 
56UIS4G.jpg
if anyone is interested, it's a pretty good fit. Haven't decide whether to add shock tabs or try to get the single shock working.
 
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