Fork Springs - What Rate?

[beardo]

I have a 2004 FJR1300A (ABS) and I am considering upgrading the front forks with higher spring rate springs, but I'm confused with the drastic differences in recommendations. My information is as follows:

• Rider InformationI weight 220 lbs.

[*]Passenger Information

• NONE… I do not ride with a passenger

[*]Riding Style

• 70% of the miles are with luggage (stock hard side bags, Givi 46 liter top box, and tank bag) weighing approximately 40~60 lbs60% of these miles are moderately aggressive street riding primarily in curvy terrain
• Remaining 40% of these miles are typical FJR touring miles primarily in curvy terrain

[*]30 % of these miles are without much luggage (primarily only with stock hard side bags either empty or a backpack with may be 4~5 lbs of items)

• 50% of these miles are slightly more aggressive street riding in curvy terrain
• Remaining 50% of these miles are typical interstate driving

I first checked out the Racetech's website and calculator. Using their spring rate calculator I entered "Street" for "Type of Riding" and "220 lbs" for "Rider Weight (without gear)." This resulted in a recommendation of 1.216 kg/mm spring rate for the front and 10.75 kg/mm for the rear.
I then checked out Sonic Spring's website and calculator. Using their spring rate calculator I entered "Standard / Sport Touring" for "Select your bike type", "Aggressive Street" for "Select your riding style", "270 lbs (220 lbs my weight + 50 lbs of luggage)" for "Enter your weight with gear", "610 lbs" for "Enter your bike's weight with a full tank", and selected "Yes" for tank bag. This resulted in a recommendation of 1.2 kg/mm spring rate for the front.

Finally, I emailed GP Suspension with my information shown above and asked for their recommendation as they've been highly recommended by many on this forum. I received an email back with a recommendation of 0.95 kg/mm for the front and 800 lb/in (14.29 kg/mm) for the rear.

Originally, I was thinking about purchasing either 1.1 or 1.2 kg/mm spring rate springs from either Racetech or Sonic Springs and felt that I would not cause an improper balance with the rear stock spring rate set on "Hard" having a spring rate of 11 kg/mm, which corresponded very close to the rate suggested by Racetech's spring calculator. I am now however very confused based on GP Suspensions recommendations. Not only do they recommend a much lighter spring rate for the front, but they recommend a much higher rate for the rear. I don't want to cause an improper imbalance of spring rates between the front and rear springs and had only planned on upgrading the front fork springs now. If the spring rate on the stock rear shock spring is actually that much lower than needed then I may just end up waiting until I start to have problems with the stock rear shock and then upgrade both the front and rear suspension.

I've spent many hours reading threads on this forum as well as searching the internet trying to figure out what would best for me. I don't know if I've just read too much and confused myself even further, but I'd appreciate any feedback you can provide.

Thanks,

BeardO

 

[MCRIDER007]

Finally, I emailed GP Suspension with my information shown above and asked for their recommendation as they've been highly recommended by many on this forum. I received an email back with a recommendation of 0.95 kg/mm for the front and 800 lb/in (14.29 kg/mm) for the rear.

I would go with the GP recommendations but you need to ask them if you can even go as high as .95 Kg/mm in the forks without changing the valving. I have the .95 springs and they are plenty firm.

In regards to GP's rear shock spring recommendations, they use a minimal amount of preload, no more than 10mm, and I think that contributes to the high spring rate but their recommendations are based on actual experience with FJRs. If you don't like the result, its easy to change the spring...and I would wait and do both ends at the same time. When you fix only one end, it magnifies the problems with the other end.

 

[Anthony]

When you fix only one end, it magnifies the problems with the other end.

+1

 

[3dogs]

On the Race Tech website it states that the stock spring for an FJR is .80 kg. Going to a .95 will not be enough spring for your weight. Go with the Race Tech recommendation. Or ask the GP guys if they will refund the money you spent for their spring plus the labor/time you spend when you have to change it because you can't get the sag even close using all the preload adjustment on the forks.

 

[MCRIDER007]

Or ask the GP guys if they will refund the money you spent for their spring plus the labor/time you spend when you have to change it because you can't get the sag even close using all the preload adjustment on the forks.

Actually, you should ask GP Suspension how much you need to reduce the internal preload to get the desired sag with their .95 springs. I think they cut the length of the internal spacers by 5-10 mm.

 

[ahchiu]

There is group buy for HyperPro springs and shocks, you might want to check it out, they said 1 spring will fit riders from 185-260#

 

[Flylooper]

Finally, I emailed GP Suspension with my information shown above and asked for their recommendation as they've been highly recommended by many on this forum. I received an email back with a recommendation of 0.95 kg/mm for the front and 800 lb/in (14.29 kg/mm) for the rear.

I would go with the GP recommendations but you need to ask them if you can even go as high as .95 Kg/mm in the forks without changing the valving. I have the .95 springs and they are plenty firm.

In regards to GP's rear shock spring recommendations, they use a minimal amount of preload, no more than 10mm, and I think that contributes to the high spring rate but their recommendations are based on actual experience with FJRs. If you don't like the result, its easy to change the spring...and I would wait and do both ends at the same time. When you fix only one end, it magnifies the problems with the other end.

I too, am looking to change out my springs and I caught this comment in my "research." I'm wondering what you meant by the comment about changing out both front and rear. I don't believe I'm experiencing any problems in the back, but I am concerned with diving when I break hard. I weigh right around 250 and so I know the inertia of my body is pushing the front end down when I hit the brake. It's more annoying than anything else, to be frank.

In my case, I'm not an aggressive rider. I don't push my bike anywhere close to its limits, although I enjoy twisties as much as anyone, but much more into the touring part of S-T bikes.

So..the question is: If I replace the front only, does it actually cause a problem that didn't exist in back? In other words, is there some kind of relationship between the front and back springs/shock absorber which, if changed something??

 

[JimLor]

I had the 1.1 rate springs for 3 years. Called a couple of weeks ago and talked with Louie about my inability to get even close to recommended sag rates. I went back to the site last week and they have changed the recommended rates. Yours, 220 lbs w/o gear, is .98. Go back and try it yourself. Mine went from a recommendation of 1.167 to .934 a pretty significant change. I talked with Bill a bit later and they're exchanging my 1.1s for .95.