supra5677
Pro
Posts: 1279
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posted February 27, 2006 11:03 AM
ZX9R swingarm swap
To Board:
Is it possible to put a zx9r swingarm on a zx12r? Without too much headache?
Thanks,
supra
   
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Otis
Needs a job
Captain Kickstand
Posts: 3028
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posted February 27, 2006 11:45 AM
I don't know about the 9R but a few have put the 7R swingarm on the 12.
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supra5677
Pro
Posts: 1279
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posted February 27, 2006 02:25 PM
how long is the wheel base on the zx7r.? The zx9r and the pre production zx12r that Gadson rode have a wheelbase of 55.7 inches. 00-01 ZX12r is 56.5 and the 02-05 ZX12r is 57.1.
I think the shorter wheelbase will allow me to handle a little better in the twisties.
supra
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CrotchRocket
Moderator
Bracket Racing with Betsy
Posts: 8038
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posted February 27, 2006 05:22 PM
I heard that the ZX6 and ZX9 swingarms are very very similar to the ZX12 swingarms...
You have to measure them and let us know!!!
____________
Jason Miller StreetBike Seminars
*****DragRacers do it better, because they dont cut Corners*****
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Otis
Needs a job
Captain Kickstand
Posts: 3028
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posted February 28, 2006 10:02 AM
I know the 7r is shorter which is why it was such a blast to ride a 12 with it on there. Thing handled just awesome.
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redelk
Moderator
Please... speak to the hand.
Posts: 3212
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posted February 28, 2006 06:37 PM
What do you mean "Without too much of a headache."? If you mean something to the effect of just taking the 12R swingarm off, then replacing it with one from a 7R or any other model and that all there is to it... the answer would be... No, it can not be done that easily.
Also, the wheelbase measurements have little to no bearing on what the effects the changing of swingarms will have.
There are dozens of other issues involved. The "simple" ones would be like the actual width of the swingarm at the point where it mounts to the frame. It MUST be the same between the two. Other "simple" aspects include bearings and swingarm bolt length. The more complicated issues are items like dogbone length in the suspension linkage and the swingarm opening at the point where the rear wheel and brake assembly go. It is not a "plug and play" modification.
When using a bike for drag racing purposes, you can usually just stretch it and strap the front end. Frame and suspension geometry are not that big of an issue. If you are wanting to modify the geometry for handling purposes, you have opened up a whole new can of worms.
Factors such as fork location, spring rate, oil weight/level, compression/rebound settings, et. al.... will also play a major role in success or failure of such a project. Notice I have not even mentioned anything about the back end of the bike yet. On the back end, you not only have to deal with simple things like ride height (not necessarily the same as it was with the OEM swingarm), but the shock angle will likely change as well. Issues like swingarm angle and rear tire size will also determine success or failure.
The best route would be to have a custom swingarm made that emulates the OEM swingarm in many of the measurements at the mount point and rear axle. This will allow you to use the majority of 12R OEM parts without having to modify them (i.e. brake bracket and wheel spacers). Otherwise, it will be a lengthy trail and error period as you have to machine down or use other parts from other models to make everything fit properly.
Even when going this route with a custom made swingarm, it does not eliminate the importance of tuning the front suspension to work with these changes in the back. Taking the bike to a suspension specialist (i.e. Computrack) will not insure "perfection" since there is no "baseline" of measurements to work from. Though a place like GMD can get the "numbers" right, there is no universal suspension setting of the compression, rebound and so on that works for all riders, their weight and the conditions of the roads they ride.
You could end up with a bike that snaps into a corner like a GP bike (albeit, one that weighs over 500 lbs wet), but with that "instant response" could come with the price of being excessively "twitchy". This could result in having to do a lot more work to ride the bike at speed and just adding a steering damper will not be the solution. It will wear you out far quicker and you use a lot more force just to keep the bike going in a straight line (corners won't be as much of an issue anymore). Since the great corners are often connected be sections of straight roads, you'll spend more time working harder than you would otherwise. Remember, the bike does weigh over 500 lbs and all the "great handling" in the world will not erase that fact.
I am not saying you should not do it, but it can neither be done "on the cheap" or without a lot of R&D to get everything sorted out. No matter which route you take. The P series 7R swingarm shares several similar measurements to the A1 A2 and B1 model 12Rs. The thing is, there is a slight difference in the location of the mounting point on the frames of those A and B1 models and the results would not be the same. Any model after B1 is a guess at best. Since the rake and trail measurements will likely also change, the load and compression/rebound rates on the forks is now different. Most valving and spring combinations are designed for a 12R's "standard" frame geometry and might not be as effective with a shorter swingarm.
After dealing with the suspension aspects of road racing bikes for just 2+ short years, in hindsight, I doubt I would have switched the swingarm to a 7R version on my A1. Though I had the time to sort it out the best I could (almost a year), I did not have the money to do it right. Using the OEM rear shock (like I did) is a waste of time. You really need one like a Penske 8981 with an adjustable ride height (using shims on the OEM unit does not count).
Instead of trying to sort all of this out on your own (there are no "professional guidelines" available for such swaps), a more practical route would be to do the following.
1. Try a different brand of tires and experiment at different tire pressures. You'd be surprised at the difference it could make if your sag is set properly and your fork oil is fresh.
2.Have the forks revalved and run a different spring rate that is best suited for your weight and riding level. When it comes to front suspension parts, I personally prefer Traxxion over RaceTech. But each to their own. Also, how much you spend is directly proportional to how much of a change you will experience. Getting a complete set of Ohlins Superbike forks is also a very expensive waste.
3. Replace the rear shock with one from Penske, Elka or Ohlins. You do not need one with all the "bells and whistles" (like 3-way or 4-way adjustable damper), since for most mere mortals, we will more likely make it handle worse with all those additional adjustments.
4. Go to a local or nearby club level road racing event (CCS, WERA, CMRA, etc.) and find one of the companies that do suspension tuning. Not only can they sell and install the previous mentioned items, but have a far better understanding on how to adjust them all to work together, rather than against each other.
5. To get the "best possible" handling with your new suspension, get a set of aftermarket wheels that are not only lighter, but have a better MoI (Moment of Inertia). Of course, your "wallet thickness" will have a major influence here.
A good review of aftermarket wheels can be found here in this article in Sport Rider magazine...
http://sportrider.com/features/146_0402_bg/index.html
Two places to look for information on suspension tuning are....
http://www.sportrider.com/tech/146_0006_susp/
http://www.roadracinghelp.com/technical_articles_menu.htm
The second website is that of Marcus McBain at Racing Performance Services. He does suspension tuning for many CMRA and AMA riders. The link will take you to a menu of several articles that both explain how a bike suspension works, as well as basic tuning information.
If you haven't changed your fork oil or checked the nitrogen in the rear shock in a while (or ever), doing any kind of suspension modification is a total waste of time and money. When getting your nitrogen level checked, make sure that your dealer or mechanic has a "nitrogen needle", because the 12R shock does not have a Schrader valve like most shocks. Motion Pro sells one for less then $25 (PN 06-8075). To access the refill "nipple", just drill a hole in the protective rear cap on the nitrogen reservoir and pry it off. If your real careful, you might be able to reuse the cover (after plugging the hole you drilled with a rubber plug), but odds are it will be toast. There is no replacement part for it, but even when being exposed to debris from the rear tire, it will have no adverse effect. Just clean that area when your cleaning the rest of your bike and you'll be fine.
Bottom line is that suspension tuning does not have to be a "Black Art". Simple things like replacing your fork oil and recharging the nitrogen in your rear shock (at least every year), can make a world of difference. On our endurance race bikes, we at least change the fork oil after every race (which can be from 4 to 8 hours long). A rear shock could easily lose half of its nitrogen pressure in less then two year's time. As well as properly setting your sag after each set of new tires you put on the bike will give you a good baseline to start from when setting your compression, rebound and other settings.
Do the "simple stuff" first. Talk to suspension tuning experts at the track. Don't call GMD or RaceTech and expect them to have all your answers. They will just try to sell you something and give you "baselines". The same applies to what the magazines or what your riding buddies suggest is the "perfect" set-up. It don't work that way. Again, it might be a good start, but every... I mean EVERY rider is different. Be it weight, riding style or road surface conditions.
If you still want to change your handling after talking to the tuners, ask them what they can do for you in the way of "package" deals. I understand that such folks might not be in your town. The nearest one to our team isn't even in our STATE and it is a 260 mile one way drive to the nearest track. Still, unless you know suspension tuning, your a professional road racer, have a degree in mechanical engineering AND a unlimited amount of money and time on your hands... your better off just changing your fork oil, setting your sag and checking your tire pressure.
____________
There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely games.
-Ernest Hemingway
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supra5677
Pro
Posts: 1279
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posted March 03, 2006 02:19 PM
thanks redelk. Thats WAY more than I ever wanted to do! I just wanted the bike to get into the turns a little bit easier...
supra
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12r1
Expert Class
Posts: 390
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posted March 03, 2006 06:11 PM
When I tried 17/48 gearing, it moved the axle all the way forward in the swingarm slot. This made quite a difference in the twisties. How 'bout taking a couple links out of your chain, to move it forward??
jeff
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Marcos Peguero
Zone Head
Posts: 568
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posted March 04, 2006 04:22 AM
I have a zx7r model P swingarm in stock, but after the R D of all the things involved to make it work I decided not to do it.
I changed the fork springs with hyperpro, fork oil, a 190 on the rear (powers and road on each rim), 8mm less on the front, and the lowering link MUZZY on the short one, a hyperpro stering damper.
The bike is nimble and can turn very easy.
Remember to use the correct tire presure, for me is 34 psi on both.
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