Cycle News test rider Jason Abbott got intimate with the KX450F’s trick new Showa SFF-Air TAC fork. Photography by Kit Palmer
For the last three years the Kawasaki KX450F has ruled the big-bore class with its superb power delivery, excellent chassis and loads of adjustability, allowing each individual rider to tune the bike to their specific liking. A few years ago, Kawasaki was one of the first manufactures of the modern era to introduce lighter and more adjustable air forks on a production motocrosser. The KYB units worked well and we were impressed with the KX’s springless boingers, but inconsistency left us chasing that perfect setup day in and day out. But that is about to change.
For 2015, the big news with the Kawasaki KX450F is its new fork. Kawasaki ditched its first generation, KYB single-chamber air fork for Showa’s latest SFF-Air Triple Air Chamber (TAC) fork. Here’s the straight talk—this fork is t-r-i-c-k. It’s a very high-tech and complex piece of equipment and it’s nearly identical to the works forks that the factory boys—Ryan Villopoto and Jake Weimer—have been running on their works KX450Fs. The only real difference is theirs are built with a little more durability in mind (after all, they do ride a bit harder and hit things a little harder than we do), otherwise, these are the same units as found on RV’s and JW’s bikes.
Kawasaki focused most of attention on the 450’s suspension and chassis for 2015.
The important difference between the old air fork and the new air fork is the additional two chambers in the TAC fork. In a nutshell, this means more adjustability—a lot more. And, not to mention, improved fork performance and reliability.
We recently got the chance to spin a few laps on the 2015 KX450F for a quick, first-ride impression, and we focused most of our attention on the 450’s suspension and chassis because that’s exactly what Kawasaki did with the 2015 KX. Besides the new fork, the Showa shock took on some revisions to compliment the new TAC fork. It also has a new subframe that is 50 grams lighter, now that that the frame’s thickness has been reduced from 2.0mm to 1.8mm. Don’t worry, Kawasaki claims that a new process has enable them to maintain the subframe’s overall strength and integrity. Another benefit of the smaller walls is that the subframe is slightly narrower towards the midsection.
Both the front and rear axles are slightly lighter, too. And to improve braking power, the KX450F now has an “oversize” front-brake rotor. It’s gone from 250mm to 270mm in diameter and is made by Braking, the highly regarded aftermarket brake company.
But it’s the fork we were excited about. As mentioned, it’s extremely adjustable now, which, depending on how you look at it, could be a good thing or “bad” thing. These forks certainly require more attention and some bike owners just aren’t into that. They just want to get on the bike and ride, and they rarely worry about things, even simple things like tire pressure, let alone complex air forks. And these forks certainly to require a lot of know-how and understanding how they work (and we’re still learning), but for those who are willing to accept these new responsibilities and is a little suspension savvy, these new Showa SFF-Air TAC forks can be a game changer.
The new KX450F feels a lot like last year’s, only better.
We spent most of the day with the Kawasaki staff and Showa technicians to get a better understanding of these new forks and how they work. When you first lay eyes on them, you can’t help but get a little intimidated by the two shrader valves at the top of the right fork leg, which are accompanied by an external chamber with another valve on the lower leg. Left leg is the old-school compression-on-the-top and rebound-on-the bottom adjustment system, but it’s the right leg that has all of the good stuff, mainly the inner chamber, outer chamber and balance chamber. After staring at the schematic sheet for a while and talking to the Showa technicians about the new triple air chamber features and overall design we started to wrap heads around it all, but it’s not until you put some time on the bike and start to make a bunch adjustments that you really start to understand how this new air fork really works.
Just like any fork, there’s a process and certain steps you must follow in order to tune this new-generation Showa fork. The inner chamber is where the majority of the adjustments take place, and this is the area you go to first when tuning. Kawasaki claims that over 60 percent of the “total force” is in the inner chamber and this is where you feel the most difference when adding or subtracting air pressure. When you add air to the inner chamber you get a more firm feel from the fork but you also notice a change in fork ride height, as it raises up a bit, at this time you now go to the lower fork leg where the balance chamber is located to reset the ride height in order to improve cornering capabilities and initial plushness you might have lost when adding more air to the inner chamber. These two areas of adjustment are extremely noticeable and are easy to adjust. Once we got the ride height back to where we wanted, the mid-stroke got a little softer and, at this point, we went to the outer chamber’s shrader valve located on the top of the fork to “fine tune” and get a better feel in the middle of the stroke.
The Showa techs claim that only six percent of the “total force” is located in the outer chamber where the fork seal is located, as a result, damage (like a fork ding caused by a rock or contact with another bike) and possible resulting total air-pressure loss from the outer chamber will have zero effect on the inner (or balance) chamber pressure and, most importantly, minimal effect on overall fork performance. What this means to you and me is that if you blow a seal on the air side during a moto, it won’t result in a DNF. In fact, you probably won’t even know it happened.
Cycle News test rider Derek Kelley was impressed with the KX’s powerful yet smooth power delivery.
On the left leg, where the compression and rebound is located, we went with the recommended Kawasaki settings at first. It wasn’t until we adjusted the air pressure in the right leg did we adjust the left. We tried adding some more compression in the left just for the heck of it but preferred the feeling we got out of adding air in the right leg. In the end, we slowed the rebound down on the left leg in order to give the forks a more controlled feel and also to aid in holding the front end down in corners.
By the end of the day, we had our bike’s fork completely dialed in and were very impressed with its performance. We’re anxious to spend more time on the bike on different tracks. Once you find that magic setting, Kawasaki assured us that most adjustments from there on out, from track to track, won’t be so involved and will instead be minor and relatively simple, and that the fork will still feel the same as it did after a week sitting in the garage. Yes, this all might sound a bit confusing but it’s not too hard to figure out. But we have to admit, we certainly had the advantage by having Showa techs right there at our side. Oh yeah, with every KX450F purchase, you get a very cool digital air-pressure gauge.
A larger front rotor improves braking power, and you can see the “Balance” Chamber at the bottom of the right fork tube.
Out back, we felt that the new Showa shock worked well and seemed to match the new fork like it’s supposed to. We did add some compression to bring up the rear and slowed the rebound to achieve a feel that we liked. The all-important number on sag was 105mm which is the same as before.
At the end of the day, we ended up with a well-balanced suspension that was plush on initial stroke, firm on the middle, had excellent bottoming resistance, was more predictable and had much better feel overall than previous KX450F. So what’s great about the new Showa SFF-Air TAC fork is that from braking bumps to corners to high speeds to hard landings, you’re able to address each individual area of performance with the TAC fork thanks to its massive amount of adjustability.
Elsewhere, the next biggest difference between the 2014 KX450F and the 2015 KX is braking. The larger front-brake rotor is very much noticeable. It has a better bite while still maintaining a well-controlled feel at the lever. It is definitely a welcomed change.
Despite getting a new piston that bumps up compression a bit and is supposed to improve combustion, the KX’s motor, which was already trench digger, felt very similar to last year’s but with a hint more pull from mid to top.
Overall, though, the KX450F does feel to be an improved machine because of its new suspension. Like we said, we’re anxious to visit other tracks and play around more with the new Showa SFF-Air TAC forks, which just could be the best darn forks ever fitted to a production motocross bike. If not the best, most definitely the trickest.
2015 Kawasaki KX450F