Changing fork springies

[Paul Myrus]

Hey folks, for those of you who switched out their fork springs, did anyone get a .95kg weight? and how does it feel?


I'm 100 kg, 6ft2. The reason I ask the question is the Dublin suspension specialists suggested I go for a .90kg spring to compensate for Irish and UK roads compared to the states or Europe. If those who swapped out to a .95k spring set up, did it feel to harsh? or just right for their weight.


Any help greatly appreciated.

 

[Gary in NJ]

A few items of note here...

First, the fork springs support the weight of the bike and rider. It's simple math. At 100kg, you're a fairly large guy - if you have used a suspension calculator like the one at Race Tech (racetech.com) and it suggests a 0.95kg/mm spring rate, then that's what I would use. If the calculator suggests a rate that is between available rate springs, go lighter (round down) for street use.

Second, "harshness" (a subjective term) is a result of the compression damping and has little to do with the springs. As mentioned above, the springs support the sprung weight of the bike and rider and damping controls the rate at which suspension compresses and rebounds. This is what we perceive as ride quality.

Third, we have damping rod forks - they will ALWAYS feel harsh over fast or sharp bumps; they will always be soft (shoot through their travel) during braking and they will always wallow when introduced to a road surface with a "rocking" motion. It's the inherent limitation of the design. As long as you are updating the springs, now would be a very good time to install Race Tech Gold Valve Emulators. The GVE's will have a transformative effect on the ride quality by providing rate-based control of the fork motion.

I have used GVE's on every bike I've owned with conventional forks for the last 25 years (probably 12 bikes) - everything from dirtbikes to custom street bikes - and I have never been disappointed.

Going back to your original question, I'm using 0.85kg/mm fork springs, but I'm only 170 pounds. Using your weight (220 pounds) the racetech calculator suggests a rate of 0.93kg/mm - right in the middle of available rates. Personally I'd use the 0.90kg springs. Not because they will ride better, but because you may not be able to obtain the correct sag settings with the 0.95kg springs.

 

[zixaq]

Check the RaceTech calculator, but I suspect if you ride bumpy roads and don't ride track you'll want to go a little lower at 100 kg. .90 seems about right. I'm about 110 kg and .95 was my suggested spring rate.

That said, the damping rods will still suck. Going with a slightly higher viscosity fork oil can help; gold valve emulators or R6 fork swap would be the next major improvement over new springs.

 

[major tom]

I just looked at Race Tech web site and the recommendation is for .90kg springs.Same weight as you {170ilbs stripped) 450 lbs semi wet, street riding. I'm going to install emulators this winter and already have the .9kg springs which I bought years ago. You had me worried I made a mistake We'll see. You might be right, the streets here in the city are rife with ridiculous expansion joints. Drives me nuts.

 

[Gary in NJ]

Major Tom, as a rule of thumb I'd rather go a step lower on the spring rate and adjust ride quality with damping. At 170 pounds we're between 0.85 and 0.90 kg/mm, so I went to the lower value.

Zixaq, going to a higher viscosity oil with damping rods helps with low speed compression damping, but high speed events will hydrolock sooner with a higher viscosity oil. Force increases exponentially with rate, so forcing a heavier oil through the same size oraface at a higher rate will cause the suspension to go harsh sooner and faster.

 

[major tom]

Useful new slant on this, namely being able to dial in correct sag. I have after market fork spring preload adjusters. I reckon if can only obtain correct sag with them screwed mostly out .90kg springs are too stiff. What weight oil do you use? We seem to have the same goals. Thanks.

 

[Gary in NJ]

Tom,

I too have adjustable fork caps (Slingshot). Here is my set-up:

GVE 3 turns out
15wt Silkolene Fork Oil
Air Gap at 130mm
Spacer cut for 10mm of preload (adjuster all the way out)
Three rings showing on adjuster.
Race Sag ~ 35mm
Resulting Free Sag ~10mm

My resulting free sag tells me that I have the correct spring rate. Ideally you want to be in the 10-15mm range. For Race Sag I always shoot for 25-30%.

 

[FinalImpact]

Although on R6 forks, they'd have me at .9kg/mm but the .85 produces 32/11mm sag and bike is perfect.

If you have rough roads I'd be hesitant to go above actual 10wt. And I use yamalube year after year so there is no trickery via oil wt from different manufacturers.

As mentioned above, setup with proper sag is huge. Control of damping forces is night and day difference.
It doesn't matter how you get there forks vs emulators but setting the bike for you, your environment, and your style makes everything better! Do it!

FWIW: I am glad I went for external adjustments as it's allowed for fine tuning I know I would not have done if it meant opening the fork up.

Also, if you're under your suggested spring rate, don't hesitate to overfill when it comes to oil. Its like fine tuning the spring rate as it effectively reduces the air volume in the fork increasing the spring rate during hard braking/max compression. 20 to 40mm is not unreasonable.

 

[Gary in NJ]

When using and setting up a GVE, it's important to know that the first 1/3 of fork travel will be used for sag, the second 1/3 is controlled via the GVE, and the final 1/3 of travel is controlled via the oil height. With the GVE, the air gap (oil height) controls the amount of usable travel. Ideally we want to use about 85-90% of travel during extreme compression events. If under heavy brake testing you are using less then this goal range (it can be measured by putting a zip-tie on the fork stanchion) you should remove oil in 10mm increments. If you are using more then this range or bottoming, you would add oil in 10mm increments. Bottoming is bad. Never allow the forks to bottom as it can result in a loss of control.

With a GVE, rebound motion is changed/selected via the oil weight. The baseline is generally 15wt. Going lighter allows for faster rebound and going heavier slows the rebound. As FinalImpact noted; there is little commonality between manufacturers of fork oil. So if you are going to go from 15wt oil to 10wt, choose the same manufacturer otherwise you may go from 15wt to 15wt…or 5wt – there’s no way to know.

 

[Paul Myrus]

Thanks very much for your input guys, ill go for the .90kg as opposed to the .95, and let my mechanic set up the sag, he does most of the high end track bikes here, so it will be in good hands.




2006 Fz6.