New Shock for the RZ

[kobra]

Another RZ upgrade to share. This was a super fun one!!!

The stock shock on the RZ is not terrible, but needed replacement:
-The remote preload adjuster is an interesting concept that ended up working pretty well but is now removed (anyone need a brand new preload belt?)
-I wished it had external adjustments for compression and rebound
-My shock would top-out and make a clunk noise which I think is normal but felt cheap
-While riding, it felt a bit uncontrolled and generally loose. It would blow through travel on g-outs and skip across rippled road surface
-The shock felt a little short so it didn't turn as well as I'd like, I ended up running more preload to raise the rear

Solution? Custom shock! Thanks to you guys I got some good ideas for mounting methods and what options are out there. I worked with my friend who works at FOX and we built a custom one-off shock for my RZ. It took some special bushings to fit on the 20mm linkage shaft, but the rest was pretty straightforward.

We dyno tested the Yamaha shock and got its performance curve as a baseline. I knew I wanted to make it stiffer, and a few mm longer to raise the back end. The new shock has adjustable preload, rebound, and Lo/Hi speed compression with pretty good range. It has a sweet swiveling oil hose to get perfect positioning which was really helpful.

Stock vs FOX (I really need a new workbench top)


I next had to design a mounting bracket. I didn't want to clamp to my frame so I used the grab handle mounting points since I don't use that thing anyway.


I had this one made out of 304 SS by Send Cut Send instead of making it myself since milling stainless is kind of a pain. It was also pretty affordable. I have an extra if anyone is interested (unbent, unpolished).


This is how it mounts up. There is some fore-aft and angle adjustment. The oil hose runs under the frame without touching anything.


You can't even see the shock on this bike since it's so tucked in there, so the only way to show off your bling is with the reservoir.




How does it ride? I was able to get a good hour in before the rain and it's incredible! It's stable, sporty and comfortable at the same time. Way better than my other bikes... Totally worth the time and effort. Next up is the fork rework, because now it's very obvious just how bad the fork is - it just collapses instantly under braking.

Hope you enjoyed. I will post up the fork job when I get to that.

[85RZwade]

Fantastic! Even nicer than the old original Fox shocks

[Smoker]

Nice work. Looks good.

[JonW]

lovely! The bracket is superb and makes this install.

So... will Fox be offering these soon?

[Darrell]

Ditto JonW. There surely would be a small market for these things!

[Yellow and Black RZ]

Awesome. Great work.
So will fox make a part # for it so we can order it?

[kpke]

Nice work kobra!!!

[brrrappp]

Hope your guy at FOX doesn't get in any trouble at work when 10 people call looking for "Kobra Shocks" by Fox

Looks awesome, nice mounting job.

[kobra]

Thanks for the positive feedback guys!! I am so happy with how it turned out, and having something "custom" makes it extra special.

There is no intention for this shock to be available. It's one thing to make 1 shock as a fun project, but to offer it as an official product takes lots of investment and testing. Probably a dozen could be sold, but it's probably not worth it in the grand scheme of things.

[silverstrom]

Nice job kobra. Looks terrific.

Wish I had a friend at Fox...and one at Brembo...etc.

[JonW]

There is no intention for this shock to be available. It's one thing to make 1 shock as a fun project, but to offer it as an official product takes lots of investment and testing. Probably a dozen could be sold, but it's probably not worth it in the grand scheme of things.

Hear all that. defo nice shock and install. lovely job.

Happy to help test one if they need a tester :)

[brrrappp]

Hey Kobra, You mentioned that you did a shock dyno test on your old shock to get a baseline. Did you need to replace the oil and recharge it for that test to be accurate or do they have some magic formula that compensates or factors-out the 35 year old shock having wear/oil degradation and probably low pressure?

Did your friend have access to any prior build data from the past that you were able to use for comparison?

I would have thought a company like Fox would have archived data with part specs, testing results, damping curves, spring weight to rider weight options etc.

[Smoker]

Thanks for the positive feedback guys!! I am so happy with how it turned out, and having something "custom" makes it extra special.

There is no intention for this shock to be available. It's one thing to make 1 shock as a fun project, but to offer it as an official product takes lots of investment and testing. Probably a dozen could be sold, but it's probably not worth it in the grand scheme of things.

You had the connection and put in the work to make a nice custom shock.

Doesn't seem right for anyone else to just plop down some cash and have the same custom shock you've created.

Only if you wanted to, the right thing would be for the manufacturer to supply you with shocks, and you sell them for profit.

Just my opinion.

[kobra]

Hey Kobra, You mentioned that you did a shock dyno test on your old shock to get a baseline. Did you need to replace the oil and recharge it for that test to be accurate or do they have some magic formula that compensates or factors-out the 35 year old shock having wear/oil degradation and probably low pressure?

Did your friend have access to any prior build data from the past that you were able to use for comparison?

I would have thought a company like Fox would have archived data with part specs, testing results, damping curves, spring weight to rider weight options etc.

I didn't attempt to disassemble the stock shock. You'd have to drill a hole into the air chamber and then you have the possibility of damaging the seals when taking it apart. Not really worth the effort. The shock performed alright though, with no sign that it has leaked the air pressure out. It was just a bit soft in general, offering very little compression or rebound damping, and would fall apart at higher speeds due to air bubbles forming.

Funny you mention the comparison. I also used another shock of mine that I really like as a reference. It can be hard to compare because every bike is different (weight, linkage etc) so we just got it close and now I can tune it to my liking with the adjusters... at least that's the idea. I should also add we built this in one evening, so not a ton of time for R&D haha. Most of it was me fitting the reservoir and whatnot.