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I am building my brother an 81 gs400 cafe racer. I am going to need some help with the suspension geometry.

I want the bike to handle better so I need to know what options I have with the front and rear suspension without spending a tonne of dough.

Can I cut the front forks?
what kind of angle do I want on the rear suspension in relation to the pivot point of the swing arm to the frame. All sorts of stuff. Any info appreciated

Your better off to buy slightly longer shocks(good performing, adjustable, modern shocks are fairly easy to find) than to try cutting the forks. They have the added bonus of performing much better than the the stockers ever did even before they were worn out years ago. Get ones 1/2 - 1 inch longer, depending on how much sharper you want the steering head to be. Half an inch will probably get it.

You can also lower the forks in the triple clamps to a piont. That piont is when the front tire can bottom against the lower clamp. This is a bad thing and to be avoided at all costs.

Thanks for the reply buzz, just so I am clear on this I should buy longer shocks for the rear? I am going to have to look into the sag settings for this bike anyways

Yes, it's longer shocks you'll be wantin'. Like I said, you can get a little drop on the forks, but it's not much... millimeters before the wheel contacts something hard or the fork tubes slide into the handlebars.

Once you start messing with suspension, any factory sag numbers are going to be useless, you'll have to experiment once you have it done and see what works best for the rider's weight and the new frame geometry. Half an inch longer shocks will raise the rearend, effectively steepening the steering head angle, putting more weight on the front tire and basically changeing everything the factory had done back when they designed it. Sharper handleing will ensue, but so can headshake and wobble if you get too carried away, so experimentation is coming your way.

Ahh. thats right. Thanks buzz

get GSXR suspension up front, either the newer USD forks or older traditional if you want to keep the look, then get shocks in the rear long enough (as said) to give you a good steering angle, look at what bike steer well, the GSXR bikes steer well but might be too quick steering for you, maybe go with an angle like an SV which turns a little slower, or something along those lines. another idea is to make some sort of adjustable rear suspension mount, kinda like the ducati monster 1000.... that way you can adjust it to your liking. maybe that mount could be a slot with a screw adjuster. or change up the angle of the rear shocks, closer mounting points to the swingarm pivot might help or hinder handeling, make that adjustable as well. you could raise the front and the rear suspensions before you get anything set in stone, for more cornering clearance to really dive into corners with modern day sticky rubber....

I'm no suspension expert and none of these ideas are original and are just compiled from thoughts I have read, but some might have merit