Zako- More than one thing could cause the handling symptoms you are describing, but I can help you with your shock replacement choices.
Tilikum98- Your needs are a bit different, since you are trying to drop the bike significantly in the rear to drag, while keeping it stiff, but I know of options for you, too.
In either case, your best bet for replacement is a quality Ohlins, Penske or Elka. If the price of those shocks is prohibitive, I suggest a newer stock shock be used. Here's the deal:
- Any newer ZX9 or ZX10 model shock is going to be longer than the stock '98-'99 ZX9 shock. Using one of these slightly longer shocks will raise the rear ride height on the '98-'99 models to match the stock height of the '00-'03 ZX9's. For the C models, this added rear ride height generally improves handling greatly!
- All 2000-2003 ZX9 and 2004-2010 ZX10 shocks are made by Kayaba (KYB) and are the same length. It is important to note that the 2006-2007 ZX10 shocks have a different reservoir position than the 2004-2005 and 2008-2010 versions, so you will want to stick with the '04-'05 and '08-'10 versions for your ZX9. The largest differences between the '04-'05 and the '08-up ZX10 shocks are that the '08-up came with a slightly softer spring rate (9.1 kg/mm vs. 10.0 kg/mm on the '04-'05) and features both high and low speed compression adjustment.
- All 2003-04 ZX6 (636 and 6RR) are made by Kayaba (KYB). All 2005-up ZX6 (636 and 6RR) are made by Showa. Regardless of brand, all '03-up ZX6 model shocks are about an inch shorter than the ZX9/ZX10 shocks. The 6RR versions are fully interchangable with the 636 versions, but typically feature stiffer springs than their non-RR brothers.
- To fit any '03-up ZX6 or '04-up ZX10 shock on any '98-'03 ZX9, you will need to use the newer style bottom mounting bushing, which is 2mm narrower (30mm) than your stock bushing (32mm). This bushing simply slides out of your stock ZX9 linkage and the new one slides right back in. While you are making the change, I strongly recommend upgrading to the newer style grease seals, as well, to ensure proper clearance of the shock fork. Again, simply pop out the old seals and the new ones fit right back in on your stock linkage. For the clevis (the forked piece at the top with threads), be sure to reuse your stock ZX9 unit, as different years of ZX6 and ZX10 have different offsets that may cause clearance issues with the ZX9 swingarm.
For the C1...don't just get another ZX9 shock. They wear out and no one wants to rebuild/upgrade them. Even the earliest ZX10 shocks are a better design and more easily rebuilt.
If you are trying to lower the back and keep it stiff at the same time, opt for an '03-up ZX6 shock, which is a bit shorter than the others, and simply place shims (washers that fit are available at both Lowe's and Home Depot) between the clevis and upper shock mount until the desired ride height is achieved.
Hope this helps.
~ C ~
Last edited by Masta' C; 10-26-2010 at 03:24 PM.