1999 R6 forks swap what spring rate to choose

[gpspl]

Hello, I want to install 1996 yamaha r6 forks on my FJ1200. What spring rate should I choose? My weight is 118kg

[Pat Conlon]

Stock 1999 R-6 spring rate is .78 kg/mm which is too light for you and the heavy FJ. I recommend 1.0 kg/mm to start, you might need to go to a 1.10kg/mm or heavier spring depending on luggage and passenger.

https://racetech.com/ProductSearch/12/Yamaha/YZF-R6/1999

Remember, the springs control the suspension but the valves control the springs. When you go with heavier springs, you will need to change the valves or you will end up with a Pogo Stick.

Your R-6 forks use 43mm dia. stanchion tubes so you will need to drill out your FJ's triple clamps from 41mm to 43mm.

Cheers.  Pat

[gpspl]

So R6 forks might not be a good option? I was trying to save few bucks using them instead of fz1 or xjr1300 forks

[Pat Conlon]

I thought that the R6 forks were too short for the FJ....are they long enough?

For fork upgrades you have 2 main options
1) Go with a complete front end swap, inc. triple clamps. e.g. Upside Down (USD) forks or,
2) fit new forks in your FJ's existing triple clamps e.g. stay with conventional forks.

For #2, Almost all conventional forks today will have 43mm dia stanchion tubes so then you have open the FJ triples up. Going from the oem FJ 41mm to 43mm you are only removing 1mm of material from the FJ triple clamps, so it's doable, many other folks have done it.

The R6 forks are adjustable cartridge forks, so they are much better than the oem FJ damper rod forks, (assuming proper springs and cartridges)  

If you just plan to use just the forks then you have to think about a few things

1) What are you going to do for the mechanical Speedo drive and front fender?
2) your Front rim...R6 or FJ? What axle size does the R6 forks use? Compatible with rim?
3)  the R6 forks has mounts for the brake calipers, will they fit your rim and rotors?

I think it's just easier to do a complete front end swap.
Everything comes over from the donor bike, including the donor's triple clamps.
Now you have to think about 2 issues:
1) the steering stem, 2 options:
a) stem diameter and length needs to be the same as the FJ so as to fit in the FJ's frame's steering neck, so you may need to press in a new stem (or old FJ stem) into your donor bikes lower triple or..
b) use your donor bike's stem, then you have to weld in a new steering neck on your FJ frame that fits the donor bikes steering stem. uuuugh...

2) Still need to think about your speedometer...retrofit the FJ with a GPS Speedo.

Cheers. Pat

[gpspl]

I got all the parts. I will use xjr1300 triple clamp it works fine with r6 forks. 1999 forks are much longer they are 31.5 inch long. Generally all part for R6 in Poland are much cheaper than parts for fz1 or xjr1300. Like fender for r6 is 20$ and for fz1 is 100$, forks for r6 are 100$ and for fz1 are 500$, rim for r6 is 40$ and for fz1 is 100$.
I was asking mostly about what you said with valves. If I install 1.10 kg springs I need to swap valves and that sound costly and I don't even know how to start looking for different valves.

[joebloggs]

I got all the parts. I will use xjr1300 triple clamp it works fine with r6 forks. 1999 forks are much longer they are 31.5 inch long. Generally all part for R6 in Poland are much cheaper than parts for fz1 or xjr1300. Like fender for r6 is 20$ and for fz1 is 100$, forks for r6 are 100$ and for fz1 are 500$, rim for r6 is 40$ and for fz1 is 100$.
I was asking mostly about what you said with valves. If I install 1.10 kg springs I need to swap valves and that sound costly and I don't even know how to start looking for different valves.

I've fitted 1kg springs in my YZF600 Thundercat forks, they are off the shelf upgrade from Hyperpro for the YZF, there's no mention of needing to change cartridges to suit the heavier spring although of course the bike is a fair bit heavier so may have an effect on the damping. I'm going to leave the forks internals s they are until I've ridden the bike, and go from there.

[Pat Conlon]

The Race Tech web page I listed has the gold compression/rebound valves for the R-6 forks. These valves are adjustable by changing the shim stacks for the springs they will control. They come with full instructions. Follow the links.

Jon Cain did the Honda F3 cartridge conversion on my '92 which used 1.0kg/mm fork springs and the Honda F3 CBR600 Race Tech valves and here's what he used on the Race Tech valves:

Compression bleed #55 drill (.052in.)
Compression stack C38
Rebound stack R20
Rebound needle base setting 1 turn out
Oil 125/150 Golden Spectro cartridge oil

Use these same specs on your 1.0kg/mm springs and Race Tech cartridges, it will get you very close to optimum. Follow the Race Tech spring preload and oil level specs for the R6 forks.

You can try and use the stock R6 valves with 1.0 or 1.10 kg/mm fork springs...see what happens. You can always add the expensive fork valves later, just be careful....you may find those forks to be a tad bit bouncy when you least want them to be....