A little tweak to the pre-load for better track feel.

In getting the Ninja ready for the track, I've done my level best to tune the suspension on the cheap. Since the Ninja was originally suspended for a much smaller rider than I, it has been a challenge. To get the bike sitting the way it needs to to handle both spirited track riding and my chunky butt I've had to get creative. I've upgraded the front fork springs and replaced the rear shock with a newer generation Ninja shock. These changes have done loads to get me rolling the right way. I have been experiencing lots of fork travel at speed at the tracks. I had some extra time over the week and thought I'd tweak the forks a little. Sit back to see what I did.

First things first, you need to know how much your forks are moving. Dave Moss, a renowned NorCal suspension tuner, has the cheapest answer I can find. A simple zip tie. By wrapping a zip tie around the fork stanchion and setting it against the wiper you can get an indicator of how far your suspension moves after getting it up to speed and temperature around the circuit. Mine is getting somewhere around 68 mm of travel fresh off my track sessions. Doing this and recording the measurement when fresh off the track gives you the best reading as everything is warm and working at optimum and not cold and sticky like in your garage. I can't find solid numbers for dynamic travel recommendations, but my gut feeling is that this is a bit excessive and came be tamed a couple of ways.

To figure out just which direction I need to go to solve the issue, I turn to these two books. I've mentioned them before, but they are worth mentioning again. The Race Tech Motorcycle Suspension Bible is a very good book that explains the inner working of forks and shocks and even has a good troubleshooting guide. The 101 Sportbike Performance Projects is a general book, but has helped me greatly with down to earth, simple, performance upgrades broken down in easy to follow directions. Between the two books I can get solid advice on how to tune the forks for a bit better feel out on the track.

After consulting the Race Tech troubleshooting guide, the two things I may need to try are changing the preload spacers or changing the fork oil height. Changing the fork oil height is a bit of an involved process and requires fork oil which I'm out of. Changing the preload spacers is a bit easier and I have all of the materials and tools on hand. Here is my collection of spacers. I have OEM Ninja 250, OEM Yamaha TX750 and a set of 128 mm homemade spacers that I made when I first changed out the fork springs. I went from 128 to 135 after a kart track day where the front end felt overly soft. This time around I'm going to add a bit more preload and go with some 148 mm spacers.

I bought a 4' section of 3/4" PVC pipe from the local go-fast store (Home Depot) a while ago. The 4' section of pipe can provide plenty of spacers for a grand total of around $5. I also made a special tool to help with removing the fork cap and circlip that holds the fork internals together. I took an old, junk, $1 Store C-Clamp and an extra hose clamp. I cut off the end of the C-Clamp to leave just the smallest of notches so that the tool locks to the upper triple tree and centers the threaded clamp section over the fork cap. The hose clamp helps to keep the tool centered over the fork cap and prevents it from slipping off the fork.

Here is the homemade tool in action. It works well to take the cap off. To put the cap back on, I need to put a jack under the bike and lift the weight off of the front suspension. By doing this I don't have to compress the fork spring as much to get the cap back on. Because I need to lift the front end, I may not be able to do this at the track without some help. I need to figure out a way to do this using my truck's jack for the ultimate in ghetto, paddock thrashing action.

I measured twice, cut once and then sanded the crap to get the PVC nice and square since my cuts always end up veering off the line. My hacksaw sucks for this job as the blades always twist and skew the cut. The pipe cutter is best on copper pipe, but does a good job at making an easy to follow mark on the PVC right where I want my cut to go. I want to cut a few more spacers of different lengths for even more tuning opportunities. I might invest in a miter box and saw to make cleaner, more square cuts.

After adding in the 148 mm spacers and jumping up and down on the bike, my suspension travel reduced from 68 mm to 32 mm. I'm not sure how that will feel out on the circuit, but I can't wait to find out. I will prep a few more spacers in different lengths and tweak my quick change procedure so I can really tune the forks where it counts. After working on getting the preload set, I will look into changing the fork oil height or maybe the oil viscosity for more fine tuning. The only way to go up from here is to add some Cartridge Valve Emulators. I also want to tweak the rear end's suspension. I can do this with a popular GSXR 600 rear shock swap. A quick check on eBay shows that I can pick up a shock for around $30. It would also involve some fabrication and would make the perfect blog post/suspension upgrade. I will detail my tuning sessions if I can get out to the track this month. I'd like to get some data before the 2018 track season starts for me. Swing on back soon for more My Motorbike Obsessions action.

Blue