Fork upgrade decisions???????

[FJ Flyer]

I believe Henry, with Hippie Cain's help, modified a set of CBR600 cartridge fork internals to fit inside the FJ forks on his '89.  He seemed pretty pleased with the result.

[Thmsdoyle]

Hey Tom, I gotta ask....how much money do you want to spend?

The minimum would be stiffer springs....preferably straight rate springs, not progressive, .90-1.0kg/mm

A good solution: Bypass buying Race Tech cartridge emulators and go straight to RPM valves and springs.
A better solution: Get some RPM valves and '89+ fork lowers so you can run a modern light weight 17" wheel, modern radial tires (wide selection) and the far superior R-1 brake calipers.
A more better solution: Transplant on a USD front end like I have on my '84 from the '91-'93 FZR.
The ultimate itchy bombino set up would be a externally adjustable USD setup from the YZF750 or YZF-R1

How much work do you want to do...and how much do you want to spend?

So I'm assuming 89 and up forks will work on my 84? I'm thinking this the route I'll go along with the blue dots and a 17 inch wheel.
Tom

[Pat Conlon]

Yep, that's what we are saying....

[Thmsdoyle]

Yep, that's what we are saying....

Thanks Pat

[Mike Ramos]

Good morning,

Re: the fork discussion - No doubt relative to strength, the USD's are stronger and perhaps the larger diameter fork tubes are as well. However, as a practical matter SPECIFIC TO FJ's, it is not likely that they perform better than the stock forks with the Fork Valves from RPM when strengthened with the Fork Brace. Although I have not ridden a motorcycle with USD forks, I have ridden with quite a few late model motorcycles that do have them & in comparison the set up provided by RPM has a performed quite well.

In reading the postings it appears that the replacement forks being recommended are from 1990 through 1998, units from 15 to 23 years old. While no doubt an improvement over stock, I question how technology that dated surpasses a more modern concept.

Remember, the Fork Valves are designed using a different concept than adjustable port size & blow off valves. Inherent in their design is the ability to follow the road surface so well that the front wheel 'pushing' is, if not eliminated entirely, minimized to be almost unnoticeable, regardless of speed or road surface.

Based on my experience over many thousands of miles over a WIDE variety of road conditions the Valves adapt to almost every situation [If you review the Colorado video, the forks are working very well; it was an 1100 mile ride to Colorado and the same settings that worked so well while riding IN Colorado without the added weight of luggage were unchanged from the ride TRAVELING there with luggage]. The same with the ECFR - the suspension settings never changed. I travel from far the northern California mountains to the San Francisco Bay Area periodically where the roads are often not in good repair yet I do not change suspension settings.

Another attribute is that while the Valves do minimize front end dive, they also control very well the "spring back" when the brakes are released, eliminating almost all of the chassis upset that would normally occur.

I wish to emphasize I am not denigrating any fork modification(s); as it pertains to my experience & as it relates to FJ's the Fork Valves are not out performed.

I trust the rear shock in development will offer the same attributes; however how will the surface area of one valve small enough to fit within a shock body perform as well as two front valves with their larger combined circumference? No doubt it will be addressed in fine fashion by the gentleman from R.P. M. I certainly hope the wait is not too long.

Ride safe & keep smiling,

Mike Ramos.

[craigo]

I have to agree with Mike on this. Unless you are using your bike for track days or really wringing the hell outta her on the back roads, the USD upgrade is not going to be much benefit.

However, I do not have the RPM valves in my bike, my forks are not stock by any means. One day, I will take them apart and see exactly what is in there, but this being my 3rd FJ and I know that Progressive springs were installed in the 1st 2, the current forks are far superior. And I really doubt that it's just the brace that's giving them that feel.

I will say that if I had the coin and the inclination, I would upgrade to the USD forks because as Pat said, the USD forks get the chicks...

CraigO

[Pat Conlon]

Heh heh, I knew Mike would chime in.....

I do notice the difference with USDs on roads requiring quick side to side transisions...

Now lets talk maintance....

Did you know that the shim stacks on my cartridges breaks down the fork oil quickly?
Do you really want to *have to* take apart your front end, remove your forks, open up the end caps and turn them upside down to drain them, re-fill 'em, and reassemble everything....Every 7,000 to 10,000 miles? 

I use top of the line Golden Spectro synthetic cartridge oil and still the fork oil has the consistency of water when I drain it back out. 
The suspension gurus tell me that "shear" is the main cause of my fork oil degradation, which is common to cartridges using shim stacks.
I can really tell the difference in the performance of the front end when the oil needs changing...

I have to think that the RPM valves have to be easier on fork oil...than my Race Tech cartridges.

Even stretching it out to 10, 000 miles, it's still a PIA to have to change the fork oil....

Something to consider..

[racerrad8]

Heh heh, I knew Mike would chime in.....

I do notice the difference with USDs on roads requiring quick side to side transisions...

Now lets talk maintance....

Did you know that the shim stacks on my cartridges breaks down the fork oil quickly?
Do you really want to *have to* take apart your front end, remove your forks, open up the end caps and turn them upside down to drain them, re-fill 'em, and reassemble everything....Every 7,000 to 10,000 miles? 

I use top of the line Golden Spectro synthetic cartridge oil and still the fork oil has the consistency of water when I drain it back out. 
The suspension gurus tell me that "shear" is the main cause of my fork oil degradation, which is common to cartridges using shim stacks.
I can really tell the difference in the performance of the front end when the oil needs changing...

I have to think that the RPM valves have to be easier on fork oil...than my Race Tech cartridges.

Even stretching it out to 10, 000 miles, it's still a PIA to have to change the fork oil....

Something to consider..

Remember Pat, I do not believe you have ridden a bike with my RPM fork valves, so you really have nothing to compare to. Maybe it is time to convert over your 92 so you have something to compare with. Maybe when you come up for the valve adjust, instead of riding one, put both of them in the trailer and we can do the front end on the 92 at the same time.

Okay, lets talk maintenance.

While your USD shim stack forks require the oil to be passed through the shim stack all the time, it is going to breakdown the oil rather quickly. So, you have to change out your fork oil for maintenance at the intervals you mention above. So, you remove the cap & cartridge, drain the oil and refill I presume.

Now, let look at the RPM valves for maintenance.

Mike has now put over 20,000miles on the fork valves and recommended Motul synthetic fork oil since they were installed. He was concerned about the oil and we dropped it at about 7000 miles before he headed off to the 2012 ECR. The oil came out of the forks the same color it went in, with a slight discoloration. The viscosity was visually the same based on a pour test out of a bottle I poured the oil into.

So, we put that oil back in and it has now covered more that 20,000 miles and there is no difference in performance. The next time Mike is over he should have 25,000+ miles on the fork valves & Motul oil and the plan is to drain it to see how it looks.

The Motul oil is not breaking down because the of the bypass technology in the RPM valve that offers superior ride quality coupled with excellent performance. The oil is not forced through a shim stack all of the time, only when required.

So, when we change out the fork oil, the process is the same as your USD forks. No need or *have to* to disassemble anything from the bike to turn the forks over to drain them.

Remove the caps, pull the springs and use a parts grabber/claw to lift the RPM fork valve and let the fluid run past the valve. Pull the drain plug and let them drain. Refill with clean oil, install the valve & spring put the cap on and you are done. Easy peasy

Depending on the color of the oil on Mike's bike this time, the oil might just go back in. Heck if we can get 50,000 miles out of the oil, we have bypassed the service interval of the USD forks by leaps & bounds.

On another note about shim stack suspension components, since the greatest rear shock option on the planet, the Penske is a shim stack shock, does that mean you need to change the oil in it because it is broken down by having to pass through the shim stack as well. That is not a very good service interval.

If not, can anyone explain why the USD shim stack forks break down the oil faster than the Penske shim stack rear shock?

I will post up tonight regarding the original inquiry on what is the better options based on the actual function of the fork. I have read all of the justifications of the reasons the USD fork is superior to everything else, but after I break it down, there really is only a single benefit, but that benefit is of no use with the latest patented technology. The RPM valves have that technology and there is not a USD fork in the world that does, thus they need the added benefit they offer...

More to come

Randy - RPM

[Pat Conlon]

Thanks for the explanation Randy. Good to know about how well your valves treat the fork oil, just as I suspected.
My USDs, by design, have no drain screw, unlike conventional forks, so you got to turn them (or the bike) upside down to drain them.....sigh.....

Alas, no RPM valves in the future for my '92. I have those forks already converted to the Honda F3 cartridges with the special adaptor hats from Jon Cain. Those Race Tech cartridges a just a bit kinder on my fork oil as they only have compression shims. The rebound is valved thru external adjustment via set screw at the cap.
This is what sold me on cartridge forks.....they are a very nice set up. Kudos to Jon Cain.

You've got to remember, this was done (in the dark ages) many, many years before RPM.

Randy, I understand that your valves may be comparable to cartridges, and in some ways superior (fork oil longevity)
However, setting aside for a moment, cartridge vs RPM valve damping characteristics,  you can not convince me that a 550lb motorcycle with a conventional fork using 41mm stanchion tubes is structurally equal to the same motorcycle with a USD front end.  It Ain't gonna happen.
I have both and I know what I know.
By design the USDs are stronger and suffer less flex. It's just fundamental engineering. The heavier the bike, the more apparent the difference....especially on roads needing quick transitions.

The question that I've come to realize, and I mentioned earlier.....At my age and with my abilities...Am I the kind of rider that can push hard enough to *really* need USDs?

Rest assured, so you guys have the first hand data you need....You and Mike are gonna put some miles on my bike at the next Petaluma WCR.
Cheers..

[RichBaker]

Randy, I understand that your valves may be comparable to cartridges, and in some ways superior (fork oil longevity)
However, setting aside for a moment, cartridge vs RPM valve damping characteristics,  you can not convince me that a 550lb motorcycle with a conventional fork using 41mm stanchion tubes is structurally equal to the same motorcycle with a USD front end.  It Ain't gonna happen.
I have both and I know what I know.
By design the USDs are stronger and suffer less flex. It's just fundamental engineering. The heavier the bike, the more apparent the difference....especially on roads needing quick transitions.

The reason USD forks were introduced was because they eliminate whole boatloads of flex from the front end. It is the ONLY reason they were introduced. Conventional cartridge forks are otherwise equal....

[Mike Ramos]

Take two...

Well Pat, I would have responded sooner but I misplaced my wallet which contains my user name. But alas I found it...

Okay, I agree with you that the smaller stanchion tubes are not structurally equal to the USD forks.  But as it pertains to the FJ's, that is not the issue. Any benefit of the strengthened USD forks will be minimized by the limitations of the frame itself.

It is the performance/reaction of the forks to the various road surfaces.  As experienced first hand while competing against late model motorcycles with USD forks, the Fork Valves leave nothing to be desired and are on par with any of the latest offerings. There is a posting from the Cherohola that shows how the FJ was overpowered by the late model motorcycles, however once the turns were entered, the old FJ with the skinny stanchion tubes and skinny axle axle performed very well, and well beyond all expectations.

Concerning the fork oil issue which has been recently discussed: prior to installing the Fork valves I would normally change the fork oil when I cleaned the air filters. However, when I voiced my reservations to Randy, he drained the fork oil and sure enough it was like new.

I do thank you for the opportunity to ride your motorcycle at the West Coast Rally. However I must respectfully decline - just as with drinking & smoking, my parents suggest that I do not date the chicks before I turn twenty one. They fear that I may be corrupted by undue influences.

Respectfully,

Mike Ramos.

[Flynt]

More to come

Randy - RPM

I like the sound of that...  could I have the stiffer forks (to go with the stiffer '92 frame) and the superior valving technology?  I hate or!

Frank

[racerrad8]

I like the sound of that...  could I have the stiffer forks (to go with the stiffer '92 frame) and the superior valving technology?  I hate or!

Frank

Nope, you are stuck with OR for now. The cartridge technology has not been broached by the manufacture. USD forks have dual pistons and they have not established a way to incorporate the IAT bypass into the valve(s) and they tell me they do not have enough time to venture that way as they cannot keep up with the demand for the products they manufacture now.

On another note, I am going to be testing forks tubes, 41 & 43mm for flex. I have already gotten the specs on the FJ 41mm fork tubes and have plenty on hand, and I have a call into a couple of places to obtain a 43mm fork tube for testing the flex.

Once I get the 43mm tube in hand I will do the testing and we can have solid numbers to compare the two for flex.

I can tell you, that since the RPM fork valve has come onto the market and they use a much softer spring than the old school design products which has significantly reduced the flex of the FJ forks as well. If there is not a big, stiff spring controlling the travel, the tube is able to travel more freely and there is not as much induced flex due to spring resistance.

Randy - RPM

[axiom-r]

Wow Pat and Mark- thanks for the props on my FJ!  I have to agree your bike holds a slot on that list and it is only a matter of taste on which one it might be...  we should all be proud and happy to bring these FJ's up to "awesome".

I will say that one of the benefits I enjoy with the USD front is the way the fork sliders are stashed away behind the fender- I do long miles on my bike and I flog it in the turns too (albeit not quite as hard as some of our own here) when the bike had OEM forks on it they got ruined twice just by touring.  The sliders got badly pitted from rock impacts and I could not keep seals in them - even after careful de-burring.  I replaced them and it happened again....  I even used those plastic guards- to no avail.  I was envious of the newer bikes that had that problem eliminated with the USD design.  I won't even bring up the 6 piston calipers and huge floating discs which was by far the most dramatic difference with the conversion. It took the longest adjustment period as well - the brakes are freaking amazing compared to stock.

About the mechanical drive for the speedo- I think you could chose to use any USD fork set from a modern bike and then use the most modern front wheel that still has the mech drive (can't recall the YZF750 wheel I think) and make spacers to align it.  

For me the simplicity of keeping the entire front end together from the 07 R1 was more important and when (see, now I say "when" instead of "if") I launch into the next set of mods (*****1350*****) I will also endeavor to add a Cable X Box to get my speedo working.....

I have been reading and rereading the threads from both the 1350 builds - Thanks Franks & Randy too!! - for blazing a trail to follow!  

Cheers to all!


PS - Monkey! Glad to hear about your front end work !!

[Thmsdoyle]

Ok, starting my search for 89 or newer forks for my 84 upgrade. If anyone comes accross a set let me know.