Ninja Race Bike suspension Set-up.
Now that the front end of the Ninja Race Bike is set up with new forks, seals and fluid it was time to balance it out and do something about the rear. I also wanted to get some measurements for future tuning. The standard thought process for improving motorcycle performance is to spend your money on suspension, then brakes, then the motor if needed after that. Since I want a reliable motor and to eventually race in a production race class, no work on the motor will happen other than regular maintenance. Getting the front and rear suspension dialed in is the key to making the Ninja fast.
Scroll on down for how I finished the project.
And here is the main culprit for needing to upgrade the suspension, my big butt! This is me with all of my race gear on as if I just got off the track. My gear adds a good 20 pounds to my body weight. The little Ninja was never meant for someone so 'stout' to be railing her through the corners of Willow Springs. I wanted a cheap way to get the rear of the bike set up more appropriately for my copious amount of mass. To the Ninjette Forum for the answer!
The answer actually turned out to be a simple one. Apparently Kawasaki increased the spring rate for the new generation Ninja 250s (years 2008-2012). Many owners indicated better feel and handling by doing a simple inter-generational shock swap. Cruising through the eBays lead me to what you see in this picture straight out of the box from the seller. It is a 2008 Ninja 250 rear shock complete with dog bones and linkage for the tidy sum of only $37.60. With the new shock I get a stronger spring and also get preload adjustment that I don't have with the original. One great thing about these little bikes is that the cost of ownership is so low. Most stock parts can be found in good condition and very reasonably priced either new or used without much effort.
To do the swap I un-necessarily disassembled a good bit of the rear end of the bike. You can see the original shock buried between the swing arm and the battery box that is attached to the air box. I removed the seat, both side panels, the inner fender panel and the battery. I didn't really need to remove any of that as you can remove the shock by just supporting the bike from under the engine. It did give me a chance to plan out adjusting the preload with the shock on the bike. I removed the upper bolt after supporting the bike on a bike jack under the sump. I then undid the lower shock mount and nut which let the swing arm drop free. I reversed the process and got the upper bolt torqued down as per the manual's specs.
After all was said and done I pulled out my Racetech Motorcycle Suspension Bible and set about measuring the sag. Based on the type of riding I plan on doing with the bike (track), Racetech recommends 25 - 35mm of sag. Here I am measuring sag using a zip tie. I measured the bottom of the triple tree to the bottom of the fork. I then geared up and sat on the bike while it was balanced in my wheel chock. After I got off I measured how much the zip tie had moved. I was very careful not to bounce when getting on the bike to avoid getting an erroneous measurement. I got a measurement of 17mm of sag for the forks. My goal was 25-35mm so I'm a bit stiff. I will have to adjust my preload spacers by removing them and installing some shorter ones.
In the rear it was the opposite. I had my wife help me measure the change with me on the seat after I measured the bike without rider. My sag measured at 42mm so I'm a bit soft. I can adjust the preload on the new rear shock one more increment before running out of preload adjustability. After that I'll need to get a new spring with a higher rate. When I get to the track this weekend, I'll see if they have a suspension guy that can double check my measurements though I am looking forward to seeing how the upgraded suspension feels. If I really wanted to get some good data, I would head to the kart track and compare my before and after lap times. I might still do that if I can squeeze a Monday session into my life schedule.
That is all for today folks. I have to finish getting the bike checked out before my track day. I also have to get started packing. I have this semi-irrational fear that I'm going to forget something vital and ruin my track day. Kind of like that dream where you go to school not wearing pants. Not going to happen on my watch.
See you next time,
Blue
Scroll on down for how I finished the project.
And here is the main culprit for needing to upgrade the suspension, my big butt! This is me with all of my race gear on as if I just got off the track. My gear adds a good 20 pounds to my body weight. The little Ninja was never meant for someone so 'stout' to be railing her through the corners of Willow Springs. I wanted a cheap way to get the rear of the bike set up more appropriately for my copious amount of mass. To the Ninjette Forum for the answer!
The answer actually turned out to be a simple one. Apparently Kawasaki increased the spring rate for the new generation Ninja 250s (years 2008-2012). Many owners indicated better feel and handling by doing a simple inter-generational shock swap. Cruising through the eBays lead me to what you see in this picture straight out of the box from the seller. It is a 2008 Ninja 250 rear shock complete with dog bones and linkage for the tidy sum of only $37.60. With the new shock I get a stronger spring and also get preload adjustment that I don't have with the original. One great thing about these little bikes is that the cost of ownership is so low. Most stock parts can be found in good condition and very reasonably priced either new or used without much effort.
To do the swap I un-necessarily disassembled a good bit of the rear end of the bike. You can see the original shock buried between the swing arm and the battery box that is attached to the air box. I removed the seat, both side panels, the inner fender panel and the battery. I didn't really need to remove any of that as you can remove the shock by just supporting the bike from under the engine. It did give me a chance to plan out adjusting the preload with the shock on the bike. I removed the upper bolt after supporting the bike on a bike jack under the sump. I then undid the lower shock mount and nut which let the swing arm drop free. I reversed the process and got the upper bolt torqued down as per the manual's specs.
Here is the new shock in place. In this picture I'm illustrating that the new shock, while identical in measured length, needed extra room for the installation. I had to jimmy the jack around and raise the swing arm to get the bottom hole aligned to complete the install. I could visually tell right away that the rear end of the bike sat more upright. When I sat on the bike for the first time with the new shock I could feel the difference in the new spring rate. I originally installed the shock on the lowest preload setting, but after a quick measurement I removed it one more time to add in three more steps of preload (now at 4 of 5 steps). I have played with my spanner to adjust preload with the shock on the bike, but there are too many things in the way to do it. If I want to change the preload, ill have to pull the shock free.
After all was said and done I pulled out my Racetech Motorcycle Suspension Bible and set about measuring the sag. Based on the type of riding I plan on doing with the bike (track), Racetech recommends 25 - 35mm of sag. Here I am measuring sag using a zip tie. I measured the bottom of the triple tree to the bottom of the fork. I then geared up and sat on the bike while it was balanced in my wheel chock. After I got off I measured how much the zip tie had moved. I was very careful not to bounce when getting on the bike to avoid getting an erroneous measurement. I got a measurement of 17mm of sag for the forks. My goal was 25-35mm so I'm a bit stiff. I will have to adjust my preload spacers by removing them and installing some shorter ones.
In the rear it was the opposite. I had my wife help me measure the change with me on the seat after I measured the bike without rider. My sag measured at 42mm so I'm a bit soft. I can adjust the preload on the new rear shock one more increment before running out of preload adjustability. After that I'll need to get a new spring with a higher rate. When I get to the track this weekend, I'll see if they have a suspension guy that can double check my measurements though I am looking forward to seeing how the upgraded suspension feels. If I really wanted to get some good data, I would head to the kart track and compare my before and after lap times. I might still do that if I can squeeze a Monday session into my life schedule.
That is all for today folks. I have to finish getting the bike checked out before my track day. I also have to get started packing. I have this semi-irrational fear that I'm going to forget something vital and ruin my track day. Kind of like that dream where you go to school not wearing pants. Not going to happen on my watch.
See you next time,
Blue
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