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swingarm angles

  • Thread starter Thread starter KoolKat
  • Start date Start date
K

KoolKat

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Hi there,I have some questions for people that have converted there GS's to single shock rear ends,or tried longer twin shocks.
I have modified my Katana to suit '88 gsxr750 single shock suspension,and before I completely weld up the frame,I was looking for advice on swingarm and steering head angles.
I was able to measure the linkage angles while they were in the gsxr frame,and have tacked my frame mods in place replicating them,but would like other peoples thoughts here.This places the steering head alot steeper than stock too,even a little steeper than the gsxr.
Thanks!
 
IMHO steering head angle is king - it determines rake, trail, your ride height and your swingarm angle too. Too steep and your bike will be super twitchy and unstable at speed, and prone to tank slappers. Too flat and it'll handle like a Winnebago. Sooo, for my project, I picked a steering head angle of 23.5 degrees as 23 degrees is the head angle of the GSXR 1000 that the suspension came from which I think is a bit aggressive (steering dampeners are stock on those bikes). It's a good compromise between stability and quick steering IMHO.

Make SURE you get your rear shock linkage and angles right, replicating EXACTLY the angles that the shock and linkage were designed to be used at. I fubared mine the first go-around and had to tear them out (they were tack welded in) and redo them since the shock didn't have all the travel it's supposed to. Find a close-up photo of the shock and linkage from the bike you're getting the suspension from and replicate that on your bike.

IMHO you may want to do a bit of frame bracing around the new shock mount areas, especially the top to distribute the new significant load into the frame. Notice how much bracing/gusseting they used on the stock shock mounts to dissipate the forces - you have to remember that the frame wasn't designed to take that much force in the area that we're putting monoshock mounts, so it should be braced IMO.

Good luck on the project and post lots of pics - it looks great. :)
 
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Thanks for the reply!
I agree 100% with you on all counts here.I am looking at 24 deg head angle and 13 deg swingarm angle.The 'arm angle was measured using the floor as the horizontal...not the countershaft to swingarm pivot,which is possibly how the factory bike specs are measured and given?
The only angle I forgot to measure from the donor bike was the lower link that the shock attatches to,but I think that by getting the others in the right places this link will have to be very close to correct.I removed the spring and cycled the suspension,and the linkages seem to be keeping a rising rate design,so I think I'll weld up the frame and try it...before paint!

I have welded in braces around the steering head and at the back of the tank area,and have built a stiff section for the shock to mount to.I'll be adding a cross brace above this area too.
I have to make some pieces for the gsxr footpeg brackets to bolt to,but that will be easy done,and I have kept the left side originals for the moment so I have a reference for peg position etc.

This picture is with the suspension half way through it's travel.I found that the shock adjuster nuts/spring would just hit the 'arm......but I couldn't position the lower linkage pivot point any closer to the bottom frame tube with out ovalizing it.I ground a little from the 'arm and it clears no roblem now.
 
This is a piece I made for the steering stops,it's now welded to the frame.
 
I used 3/4 diam tubing to brace pieces of the frame,and will use this stuff around the shock mount area too.I like the look of tubular pieces rather than flat steel,and I believe it will be stiff enough for the job.
 
Nice work all around, really like the look of the steering stop you made. The shock looks a bit tilted too far forward, was it like that on the donor bike?

A few pics that may help for ideas etc.

Frame bracing pics from OSS, I wound up using round tubing for everything except the top shock mount, which is rectangular tubing:

http://www.thegsresources.com/_forum/showpost.php?p=601969&postcount=364

This is the way I did my rearset mounts:

DSC01393-small.jpg


DSC01429.jpg
 
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Yes,the shock was at the same angle when in the gsxr frame.I see that yours is alot more vertical (nice work by the way:-D ),but I guess there have been a few years of development between my parts and yours which maybe the reason mine looks a bit odd.Before I tacked the pieces onto the frame,I tried to make them as 'universal' as possible incase I wanted to try other shocks etc later,and was actually happy that the top shock mount position was close to flush with the frame tubes.I was keen to use the bolt-on aluminum gsxr top mount too,that way I could make a different piece to adapt to either a mistake or a later model more adjustable shock.I have to try the exhaust on the bike,and no springs in the forks or rear shock,to make sure there is some ground clearance here.It will be close I'm sure,but it sits on the side stand properly so it has some chance!
A couple questions for you if I can,
What angle is your swingarm when at ride height?
Do you happen to know the dimenssions of your shock,eg: length,width,stroke etc?
When the bike is upright (off the stand),what is the height of your swingarm pivot?

Thanks alot!
 
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