kyradawg wrote:

Or go here cgi.ebay.com/ebaymotors/Suzuki-GSXR750-S...QQrdZ1QQcmdZViewItem like I did and for $50 + $50 in custom machining get one of these

How did you mount up twin shocks to that beast? Any pics?

wireman wrote:

if you are going roadracing id reccomend going no longer than the stock arm;)

Actually, a longer arm is in the cards.

Other than the normal decrease weight/increase chassis rigidity/improve suspension/etc., my goals with this project are:

1) Increase cornering clearance by lifting the bike up (The old Muzzy-built Kawasaki Superbikes of this era were about 1.5 inches higher at the lower frame rails)

2) Quicken steering by decreasing both rake and trail.

3) Move weight bias forward

4) Decrease the wheelbase if at all possible

#1 can be accomplished a variety of ways. 17" wheels compound the issue. Jacking up the back with longer shocks is easy, but then you run into issues with an improper swingarm angle -- a swingarm with the axle below a line drawn from the countershaft through the swingarm pivot will rise and stiffen during acceleration, which causes problems (ie: loss of traction, potential highsides) at corner exits. Jacking up the rear end past this line decreases the wheelbase, but moves the weight bias even more to the rear. Increasing the front clearance can be done by decreasing the rake and/or by raising the front with longer fork.

#2 (at least the decreasing rake part) can be accomplished by dropping the front or raising the rear. However, simply dropping the front just adds to ground clearance issues, and simply raising the rear causes the issues described in the previous paragraph. The stock '82 GPz 750 has a rake of 27 degrees and a trail of 107mm. The 2007 GSXR 1000 (pretty much the open-class racebike of choice) has a rake of 23.8 degrees and a trail of 98mm. I'd be shooting for 25 degrees and about 100mm. Changing the trail can be done with different offset triple clamps or adjustable triple clamps.

#3 can be accomplished by moving the engine forward within the wheelbase. This can be done by moving the front wheel back (by decreaseing rake)or by increasing the swingarm length.

#4 can be accomplished by decreasing the front rake, shortening the swingarm (with the problems noted above), or shortening the stock frame (difficult at best)or using a custom frame.

So, my planned course of action is to decrease the front rake through either modifying the steering head angle, using custom triple clamps, or both. The resulting loss in wheelbase will then be made up with a longer swingarm. The longer swingarm will also raise the rear of the bike without moving the wheel axle beyond the countershaft/swingarm pivot line.

Those changes will accomplish goals #1-#3, but not #4. The above plan of action will result in the wheelbase staying about the same. That is a good tradeoff to accomplish three first three goals. The only way to accomplish all four would be to use a custom frame, which isn't legal in AHRMA Vintage Superbike.

I'll keep folks posted with details and pics as the project unfolds.

wireman wrote:

if you are going roadracing id reccomend going no longer than the stock arm;)

Actually, a longer arm is in the cards.

Other than the normal decrease weight/increase chassis rigidity/improve suspension/etc., my goals with this project are:

1) Increase cornering clearance by lifting the bike up (The old Muzzy-built Kawasaki Superbikes of this era were about 1.5 inches higher at the lower frame rails)

2) Quicken steering by decreasing both rake and trail.

3) Move weight bias forward

4) Decrease the wheelbase if at all possible

#1 can be accomplished a variety of ways. 17" wheels compound the issue. Jacking up the back with longer shocks is easy, but then you run into issues with an improper swingarm angle -- a swingarm with the axle below a line drawn from the countershaft through the swingarm pivot will rise and stiffen during acceleration, which causes problems (ie: loss of traction, potential highsides) at corner exits. Jacking up the rear end past this line decreases the wheelbase, but moves the weight bias even more to the rear. Increasing the front clearance can be done by decreasing the rake and/or by raising the front with longer fork.

#2 (at least the decreasing rake part) can be accomplished by dropping the front or raising the rear. However, simply dropping the front just adds to ground clearance issues, and simply raising the rear causes the issues described in the previous paragraph. The stock '82 GPz 750 has a rake of 27 degrees and a trail of 107mm. The 2007 GSXR 1000 (pretty much the open-class racebike of choice) has a rake of 23.8 degrees and a trail of 98mm. I'd be shooting for 25 degrees and about 100mm. Changing the trail can be done with different offset triple clamps or adjustable triple clamps.

#3 can be accomplished by moving the engine forward within the wheelbase. This can be done by moving the front wheel back (by decreaseing rake)or by increasing the swingarm length.

#4 can be accomplished by decreasing the front rake, shortening the swingarm (with the problems noted above), or shortening the stock frame (difficult at best)or using a custom frame.

So, my planned course of action is to decrease the front rake through either modifying the steering head angle, using custom triple clamps, or both. The resulting loss in wheelbase will then be made up with a longer swingarm. The longer swingarm will also raise the rear of the bike without moving the wheel axle beyond the countershaft/swingarm pivot line.

Those changes will accomplish goals #1-#3, but not #4. The above plan of action will result in the wheelbase staying about the same. That is a good tradeoff to accomplish three first three goals. The only way to accomplish all four would be to use a custom frame, which isn't legal in AHRMA Vintage Superbike.

I'll keep folks posted with details and pics as the project unfolds.

Mine's all done on the cheap, and is even period correct: I just changed from my stock LTD offset fork to one from a GPz750 (thanks RRRR!) I made my own rearsets, but they're more like midsets, nothing too extreme. Superbike bar. Tapered steering head bearings. Fork brace. I'd like to switch to an 18" rear wheel and a stronger swingarm if I could find them for cheap.




Post edited by: guitargeek, at: 2006/12/11 03:36

mine has a 2001 gixxer inverted forks with stock rim and race tires. rear is a 2004 gixxer 600 swing arm with race 180 tire. both tires are sticky as heck. gixxer pegs mounted high on the frame, might move them up further. hit beg to soon, i have ore rear tire, so they need to go higher!!!! i was able to hang with the newer bikes in the corners on my '78 650. gotta love that.

now going to up it to a '80 750 engine for a little more umf. love the corners. dragging pegs and getting low. but i like to go fast on the straights also. i guess i love both worlds!!!!!!!!

Or go here cgi.ebay.com/ebaymotors/Suzuki-GSXR750-S...QQrdZ1QQcmdZViewItem like I did and for $50 + $50 in custom machining get one of these



Peace&Love:blink: , Darren

i see a honda 750 dragster in my home town for sale!
iv seen it and heard it to, very nice sound...and fast!
i want to know if i can adapt the swing arm to my bike and maybe the ignition and air shifter..
its a 1970 cb750 built as drag bike
ill go look and ask more info and ect... i want to know ( got a list) things i should ask him, does anyone have any suggestions what to ask?

or is it a wast of time ???


thanks steveo

The longer the wheelbase the slower the bike will turn, alterntively with a longer arm comes greater high speed stability and less step out exiting turns. The modern trend is to use as short of wheelbase and the longest of swingarm possible. For our bikes if maximun handeling is the concern use a set of offset triple trees to pull out about two degrees of rake which will shorten the wheelbase, then you can take advantage of a swingarm that is a couple millimeters longer therby increasing turn in and stability. The best arm that I could find for my Z1 project is the 2001-2003 GSX-R 750/1000 piece it is the same length as the stock piece within a few millimeters and has world superbike winning stiffness. It really is an awesome piece the 750 arm is bare aluminum and the 1000 piece comes powder coated black.

Peace&Love;) Darren

Post edited by: kyradawg, at: 2006/12/10 12:17

Post edited by: kyradawg, at: 2006/12/10 12:23

the extensons for gsxr swingarm not quite done

wireman: Exactly. Why put all the effort and money into the motor and not be able to effectively utilize the motorcycle in a safe and fun way? Been there done that myself, unfortunately. That's one of the reasons I'm here telling folks to do 'the package' if at all possible. Notice in my signature: Stage I, Stage II, and Stage III Z1/KZs ...

The Stage I has a slightly warmed over motor: 987 cc Yosh piston kit, stock cams, Mikuni 29s, GEREX CDI, Kerker 4-1 pipe, top three horizontal frame tubes braced, aftermarket engine mounts/bolts, braced stock swingarm, etc. This is my 'cruiser' KZ so to speak.

Stage II's frame is braced considerably more, with 17" radial tires, GS1100 swingarm, hotter cams, Yosh 987 cc pistons, GEREX CDI, rear disc brake, Works Performance shocks, etc. Upgrades coming include 998 Yosh piston kit, ported head with 37.5/31 mm SS valves, etc.

Stage III will have an even more braced frame to go with an even hotter motor, ZRX1100/1200 forks/wheels/brakes, 1075 cc or 1197 cc piston kit, Web 110 cams, ported head with 37.5/31 SS valves, Mikuni RS 34 mm carbs, etc.