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Yamaha FZ-09 Fork Piston Kit Breakdown

Following up to Tuesday’s fork post…with pictures and some explanations.

As I mentioned, the GP Suspension kit includes the following components:

  • 20 mm rebound piston w/ custom shim stack
  • 20 mm compression valve w/ custom shim stack
  • Rebound needle

Stock needle on the left, GP’s shiny new brass 7.5 degree needle on the right. The larger taper angle allows for more adjustment and better flow characteristics through the rebound bleed circuit.

Here is where the real magic happens in the rebound circuit. The stock piston is on the left, the GP 20 mm piston is on the right. The larger oblong holes you see are the ports used for reverse flow – oil flows through during the compression stroke so that the piston assembly minimally adds compression damping. The 3 large(r) holes in the recessed/dished areas on the stock piston are the high speed rebound feed ports (these are what load the shim stack). As you can see, the GP piston uses double the hole count on a larger hole circle to both flow more oil and obtain more leverage on the shim stack. The ports are nicely machined to improve flow through the port. Now, you’re probably wondering why we’d want to flow more oil through the FZ-09’s rebound circuit. Short answer is, we don’t. The stock setup doesn’t have enough rebound, so we’d actually want to reduce oil flow; the heavier oil used previously with the heavier spring rates was done in the same light. GP, like Penske, RaceTech, Traxxion, K-Tech, etc. make various pistons that are used across multiple bikes. This port design was done to optimize the geometry across a wide variety of applications. So how do we add damping back? Good question…

The stock rebound piston and shim stack is on the left. GP’s setup is on the right. Though the pictures aren’t great, you can see the heavier shim stack. Varying the shim diameter, thickness, and order in the stack controls the mid-high speed damping response. The combined effect of the needle, piston, and new shim stack is a wider adjustment (ranges from less than stock to MUCH more). No more pogo-ing down the road.

Here’s another view of the shim stack, this time assembled. From the left to right, top out spring (takes up unsprung mass when the wheel is in the air), rebound piston holder (needle assembly inside), new check valve (provides ‘unrestricted’ flow during the compression stroke), GP piston, and custom shim stack…all tucked under the factory nut.

These are the compression valves. Similar deal as the rebound piston, but a little different. The larger oblong holes provide the same increased functionality over the stockers. The high speed ports are actually a bit smaller to work in conjunction with the high speed shim stack. Not shown here, but a bleed port has been added to the piston to provide good low speed compression response in light of not having a dedicated/adjustable bleed circuit.

This is the final assembled compression base valve. You can see the shim stack here.

While inside the forks, I did a light polish on the damping rod to reduce sliding friction. I also chamfered the cartridge tube ports to flow a little smoother.



Some FZ-09 trivia, unlike most modern forks, these cartridge tubes are steel, not aluminum.

It’s a good thing I had the bike out when I did. Got a few inches of snow shortly after the ride and the roads are back to shit. Yay…

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Christmas Eve Suspension Tuning

It’s been another couple crazy weeks. Been super swamped with customer orders/projects (thanks, guys!), holiday BS, family-related ‘things’, and of course, general FZ-09 development.

As I mentioned in an earlier post, Barry at GP Suspension sent his fork piston kit. A set of Super Tenere forks just arrived and two more are in transit, so I took the time to get the kit in the FZ-09. Barry worked up a couple nice shim stacks and figured out a good compression bleed size. He also threw in one of their 7.5 degree rebound needles. So all in all, this kit is comprised of GP’s pistons/shims, GP’s needle, some 0.90 kg/mm Sonic Springs, and Silkolene 5wt. Some minor massaging on my part included chamfering the cartridge tube ports and polishing the damping rod.

Yes, I know…where are the pictures??? All in due time! The weather has been craptastic around here recently with over 15″ of snow falling through the past two weeks. So, the roads were covered in salt, cinders, and sand. Fortunately, mother nature sent us a few inches of warm rain the past couple days and all the snow melted. Roads are still spotty, but I made some time to do a test ride earlier today. All I say is ‘wow’. I alluded to this in a previous post, but upgrading a new bike never gets old. Although good results are expected, it’s such a treat taking a ‘good’ bike and making it ‘great’. I’m happy to say we’re there!

Rebound feels great with a proper shim stack (even on the 5wt). Compression is very comfortable over rough roads and transmits just the right level of feel for the street. Brake dive is about the same as the previous setup (springs with 10wt oil), but the high speed compression harshness has been eliminated. Despite the fact we still can’t adjust the compression on this setup, it won’t really matter for the majority of riders. Yes, I have a set of 25 mm cartridges that will go in here, so this bike will be adjustable. But, if cash were an issue, this set up is amazingly good. In the back of my mind, I was expecting to fiddle with the shim stacks a little bit. Maybe add/remove or rearrange a few shims. I should have known better, because Barry took care of it. Take 1 FZ-09, add this fork piston kit, and swap on an 8983…you can keep your Street Triple R any day of the week.

I know a lot of guys are reading this thread who are on the fence about buying an FZ-09, primarily due to the suspension. Don’t fret – take the plunge. As it sits today, the bike is ready for anything you want to throw at it, short of racing. By now you’ve probably figured out that I don’t like to oversell something, so I’ll leave it at that. This kit will be available shortly, with a couple options on shipping/labor – keep an eye on this thread on our sub-forum.

I’ll post some pictures later in the week, but until then…Merry Christmas – Feliz Navidad – Frohe Weihnachten, etc.!!

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FZ-09 on the Dyno

After a full week of short rides here and there, trying to break it in, figured it was time for the dyno. Not only did I want to see how the power output was, but was also curious about the three drive modes and how the power was affected.

Strapped to the dyno, ready to rock.

Strapped down, ready for the first run on the Dyno Jet. Unfortunately, we didn’t have the time to pick up the RPM, so the runs logged road speed and A/F.

All in all, the findings were in line with what a 115 hp bike should put down to the wheel. Like all good triples, the power curve was nearly perfectly linear, though it does favor the midrange.

Dyno plot – A, B, STD modes

As you can see, the STD and A maps are identical in power output. B mode is down ~10-11 hp over ~6,000 RPM. This reflects what you feel in the saddle. Also impressive is the A/F ratio. The peak and dip down low results from rolling in hard off idle and is normal for the dyno. But, importantly, it stays nice a flat throughout and enriches a bit as the revs build. Yet again, this reflects what you feel when you twist the go stick. Nice smooth power, with no inherent lean spots. Well done Yamaha!

The dyno will be revisited once a few more miles are on the bike to look at gear by gear comparisons…

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FZ-09 Project Bike – The Saga Begins


I plan to use this space as a way to communicate not only the direction I personally think the bike should take, but also a way to test the waters on future product development. So without further ado, some catch up over the past two weeks. Some of this has already been shared on the site, though.

5 miles on the clock, freshly uncrated and test ridden post-PDI:

As delivered – brandy new!

There are some definite good elements to the bike’s design, and others, that are less so. I wasn’t sure how I’d like the bike in person, but I think it’s fair to say the overall effect is good. Some of the Triumph owners have reported the overall build quality is ‘cheap’. I think a lot of that banter results from direct Japanese competition. That said, there are some obvious areas of cost cutting. For starters, the LH switchgear and shift lever look a bit unfinished or flat out cheap. Same thing with the horn. But the rest, IMO, looks pretty well sorted.

One of my favorite styling elements (flame if you want) is the tail light. Yes, it floats and kinda looks like an afterthought. However, I personally dig the look. The tail light pattern is also a nice touch:

Factory running lights – loving that pattern.

No need to rehash the ride review here, but I’ll leave it with this…the 847 cc engine is a real gem. Triumph better be paying attention!