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Frame Geometry
- chetriply
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I also understand that different things work for different people and someone may have discovered something that we're all missing. My concern is that someone may end up getting hurt trying these "new" methods. The information is out there so don't be afraid to read everything you can get your hands on (and there's a ton of it).
I'm doing the same swap on my KZ100 except I used a GSXR front end. I mocked the frame and swinger up with struts to determine the proper shock height. Then I checked different manufacturers, Progressive, Work, Ohlins, to find the shocks I needed, then fabbed the upper mount. Lot's of work but worth it.
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- Hatman
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What about this swingarm droop? As you raise the back the swingarm droop becomes grater.How much weight do we put into each peice?Gets confusing.:side:
BTW, upon re-reading this thread I realized I wasn't clear on one point -- the rear axle should be at or near the countershaft/swingarm line with the rider aboard. Since you'd normally shoot for 25mm to 30mm laden sag (sag with the rider aboard), be sure to factor that into your calculations.
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- mark1122
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Post edited by: mark1122, at: 2006/12/29 15:46
76 KZ, frame gusset work,1200CC.Ported by Larry Cavanaugh, 1.5mm.over intakes, Carron Pipe, ZRX12 rear end, and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg, Ont. Can.
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- loudhvx
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the swing arm axle should be in line with a line drew through the drive and the swing arm pivet. Mine is going to be way off(4 1/8"). My old set up was 1 11/16" below.Now what?
That is called anti-squat geometry. If all three points were in line, the back end would squat too much and the rear tire would spin at launch. You want the swingarm pivot to be above the line created by the two sprocket centers. In other words it should form a triangle when unladen. Typically, the three points should line up when the rear shock has used about 40 to 50% of it's travel.
Too much anti-squat will jack-up the back end at launch, too little will cause it to squat. If it squats too much, you'll just spin the rear tire. If it jacks up, you'll be more prone to wheelies.
The final amount you want is determined by the tire (much like everything else on the bike).
The problem is that you need to juggle all of the factors for the suspension before you build and it's easy to neglect one or another.
If you want to do it right, you want to start with this John Bradley book volume 1. This book gives good advice for starting points on spring rate, laden sag, unladen sag, anti-squat, etc. etc. When you alter one, you have re-check all of the others, but the book gives a good place to start and will tell you what factors to consider when altering things.
I followed his advice on the minor changes I did on my bike and the bike never handled better.
Volume 2 is out now also, but I haven't picked it up yet.
The book is not cheap, but will probably pay for itself, and definitely follow Hatman's advice and really consider the source of information on the net.
Also, if you don't mind spending a little money, Works will custom-make a shock for your needs based on the geometry you send them on paper. When I did that, the shocks they sent me matched what the book said I needed (I didn't mention the book when I ordered them). I was lucky enough to talk with one of their techs instead of sales staff, though.
Oh, and on the leaning shock question, theoretically, leaning it will make the rate more progressive, but will reduce the initial rate (and preload). Mounting it closer to the rear axle, you will regain what is lost by the angle, but then there may be an issue of the length of the shock being too short.
Post edited by: loudhvx, at: 2006/12/29 17:04
1981 KZ550 D1 gpz.
Kz550 valve train warning.
Other links.
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- Hatman
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I have Foale's book, but not Bradley's. Amazon has Bradley's book for $65, but the wait is 4-6 weeks. Foale's book is available for immediate shipment from his website.
Thanks for the input, loudhvx.
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- mark1122
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Post edited by: mark1122, at: 2006/12/30 11:32
76 KZ, frame gusset work,1200CC.Ported by Larry Cavanaugh, 1.5mm.over intakes, Carron Pipe, ZRX12 rear end, and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg, Ont. Can.
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- mark1122
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Fork extensions on eBay
Post edited by: steell, at: 2006/12/30 11:54
76 KZ, frame gusset work,1200CC.Ported by Larry Cavanaugh, 1.5mm.over intakes, Carron Pipe, ZRX12 rear end, and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg, Ont. Can.
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~ (k) / (z)
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- Hatman
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I haven't really seen them around since the old chopper days. It was a cheap way to get extended forks. The problem is you've now created a new weak point and a source for flex in your forks. I think there's a reason why they really haven't been around since the old chopper days decades ago.
Max's extensions are a different animal. Basically they're a new, taller fork cap that let's you slide the forks down into the top clamp up to 20mm. The connection between the new fork cap and the original fork leg is still contained within the top triple clamp, so flex/distortion won't be an issue. Also, you'll notice they're built around the rebound adjuster, so that doesn't have to be modified.
At $200 for a pair, it seems to be a pretty expensive way to gain such a small amount in fork length. Ideal for the roadrace bike for which they're designed, but not much use for your purpose.
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- Bad Kaw
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First: your bike looks fantastic.
Second: There sure is a lot of theory discussing and conjecture on this topic and a lot of it sure sounds logical. However, I have a ZX9R inverted front end on my KZ and I run 17s on it and I installed a set of Ohlins shocks that were not made for the bike and it raised the ride height in the rear. All of this contributed to steepen the rake angle.
I'm in the middle of adding a mono-shock rear and even wider PMs and I've posted it in the projects under 'Project J' or something like that if you want to 'peep' on it (it's in progress):whistle: .
My point is this: there is no comparison between before and after. It's so much better the way it is now, and I think it's going to be better when I'm done. Admittedly, I'll be payinga LOT more attention to detail when I set-up the rear end; but, my point is this: the stock stuff is 19/18 with skinny (ie flexy) parts, and now it has sticky tires, light wheels, impressive brakes, and handles waaaaay better. It's still a flexy-flier, but I haven't addressed the frame, yet...but comparing where it came from to what it is, there is no comparison; it's that much better.
78 Kawasaki Z1R
81 Kawasaki KZ1000J (mods)
82 Kawasaki ELR Clone (1000 J)
82 Kawasaki KZ750R1/GPz750 ELR-ed
70 Kawasaki KV75
83 Honda CB1100F (few mods)
79 Suzuki GS1000 (rolling frame / project / junk)
84 Suzuki GS1150ES (modified project)
83 Yamaha XJ900R (project / junk)
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- Fossil
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Mark 1112,
First: your bike looks fantastic.
Second: There sure is a lot of theory discussing and conjecture on this topic and a lot of it sure sounds logical. However, I have a ZX9R inverted front end on my KZ and I run 17s on it and I installed a set of Ohlins shocks that were not made for the bike and it raised the ride height in the rear. All of this contributed to steepen the rake angle.
I'm in the middle of adding a mono-shock rear and even wider PMs and I've posted it in the projects under 'Project J' or something like that if you want to 'peep' on it (it's in progress):whistle: .
My point is this: there is no comparison between before and after. It's so much better the way it is now, and I think it's going to be better when I'm done. Admittedly, I'll be payinga LOT more attention to detail when I set-up the rear end; but, my point is this: the stock stuff is 19/18 with skinny (ie flexy) parts, and now it has sticky tires, light wheels, impressive brakes, and handles waaaaay better. It's still a flexy-flier, but I haven't addressed the frame, yet...but comparing where it came from to what it is, there is no comparison; it's that much better.
I agree, 1112's bike does looks great.
Bad Kaw, how much shorter are your forks than stock, and how much did the Ohlins shocks raise the rear? Did you find you needed a steering damper? Thanks
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- Hatman
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loudhvx wrote:
If you want to do it right, you want to start with this John Bradley book volume 1.
BTW, if you're interested in Bradley's book, Michael Moore at Eurospares ( www.eurospares.com ) is the U.S. distributor. $80 plus $8.10 Priority Mail delivery, and they have them in stock. Michael also has some interesting chassis design & building info on his page, and hosts a couple of e-mail lists related to the topic.
Bradley's book is one that's been on my wish list for some time now. This discussion spurred that memory, so I ordered it Friday!
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- mark1122
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Mark 1112,
However, I have a ZX9R inverted front end on my KZ and I run 17s on it and I installed a set of Ohlins shocks that were not made for the bike and it raised the ride height in the rear. All of this contributed to steepen the rake angle.
Thanks I'll check out your new project j.
How long are your zx9 forks from axle center to top ?What is your new rake and trail?
76 KZ, frame gusset work,1200CC.Ported by Larry Cavanaugh, 1.5mm.over intakes, Carron Pipe, ZRX12 rear end, and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg, Ont. Can.
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~ (k) / (z)
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