2021 T9 Fork oil change?

[Sunde]

Hi gents.
I am rocking a fresh bike with only 5000 kilometres on the clock, so i definitly do not have to change the oil in my forks etc yet.
With that said i feel like maybe bumping up the weight of the oil a bit would help slow the fork down? Rebound on the 2021 Tracer 9 is adjustable and i have dialed it in how i like it. Sadly compression is not adjustable, and regardless of how i tweak preload/rebound the fork dives pretty hard under braking and just does not feel super stable.
  Any of you guys have any experience with just changing the oil on suspension? I'v seen examples of people doing it, and am confident i can easly do it myself. But will it be worth doing? That is my question Any input is very welcome - thank you for your time.

[betoney]

Yes, fork oil viscosity change makes a difference but the biggest difference in can be immediately felt with different springs. 

If you are going to experiment with different fork oils, stick with one brand that you have access to for consistency.  Don't experiment with 5w Bel Ray and then 7.5w Maxima and then 10w Motul as the viscosities can differ by manufacturer for the same weight oil.

http://sonicsprings.com/catalog/calculate_spring_rate.php?osCsid=u9i9jjmlh119c84d8p8seameelqo3skk

http://sonicsprings.com/catalog/index.php?cPath=27_313

[KrustyKush]

Based on doing this same sort of thing myself years ago on other motorcycles, I would say it probably won't help much.  Most likely, you will get a much more dramatic effect by changing out the fork springs for something heavier.  In years past we would buy Progressive springs which feature a variable rate of coil.  They used to do a pretty good job of stiffening up the forks on compression.  The heavier fork oil can contribute, but it also may affect your rebound in unpredictable ways.

In general, I do not do this kind of thing anymore on motorcycles.  Modern bikes, especially the Tracer, have such excellent suspensions, it doesn't seem wise to tinker in that area.  Worst case, you could make things worse, best case you waste hundreds of dollars and time.  And there may not be a lot of technical expertise out there among the mechanics at the shops.  20-some years ago I took my 97 CBR1100XX to the selling dealer shop complaining of a clunk in the front end while going over certain types of bumps.  The tech lied that the Honda front end was "weak" and needed "better internals" and so I allowed him to sell me an expensive "gold valve" thing, and I, thinking he was an expert, paid for his time and parts.  It had no effect whatever on the clunk, and didn't do anything I could detect for the operation of the front end.  Turned out the clunk was caused by a loose steering head nut, which BTW I figured out myself and fixed myself, for free.  This is part of why I avoid the shops and the technical advice obtained there.

[Sunde]

What you are both saying makes sense to be honest
I will not be ripping off the forks to change the oil prematurely if what i am looking at is maybe at the best a 5% positive difference. Assuming i even choose a new oil that actually makes it "better" i guess i could end up making it worse
 i WILL eventually change the oil however, do you guys have any recommendations, even just a ballpark guesstimate as to what weight oil i should be going for? Maybe also what brand? The goal being ever so slightly to stiffen or slow the fork down a bit.
I am relativly light at 75 ish KG's with gear, and often take the bike on weekend trips to local racetracks so i enjoy sporty riding. 

Edited May 19, 2022 by Sunde

[betoney]

30 minutes ago, Sunde said:

I am relativly light at 75 ish KG's with gear, and often take the bike on weekend trips to local racetracks so i enjoy sporty riding. 

75kg is about 165lbs so the springs might be fine for you. 

I'm not familiar with the Tracer 9 forks, do they have separate damping in each leg? rebound in one and compression in another?  If the rebound is fine then you just might be able to adjust the oil in the compression leg?  Maybe start with 10w oil.

[Sunde]

1 hour ago, betoney said:

75kg is about 165lbs so the springs might be fine for you. 

I'm not familiar with the Tracer 9 forks, do they have separate damping in each leg? rebound in one and compression in another?  If the rebound is fine then you just might be able to adjust the oil in the compression leg?  Maybe start with 10w oil.

No compression in either sadly
Rebound is on the right leg, left side can only be adjustet for preload. 
I'll see what i come up with down the line. As you say with my weight its not like the bike is overloaded, its just not as sporty as i'd like, totally capable however, for now its fine. 

[piotrek]

3 hours ago, Sunde said:

No compression in either sadly
Rebound is on the right leg, left side can only be adjustet for preload. 

I suspect that you have a compression valve, but it's non-adjustable (fixed). Both the rebound and compression damping circuits are in the same fork leg on my bike (2015 FJ), but only the rebound damping is adjustable. The only way to alter the compression damping characteristics in this case is switching to a different viscosity oil... but not different enough to render rebound damping adjustment ineffective.

It does sound like the stock springs should work for your weight, although they are likely progressive and may feel more plush than you want. A 3cSt@40C difference in oil viscosity may be noticeable enough to improve things just a bit.

[vancuy]

On 5/20/2022 at 8:32 AM, piotrek said:

I suspect that you have a compression valve, but it's non-adjustable (fixed). Both the rebound and compression damping circuits are in the same fork leg on my bike (2015 FJ), but only the rebound damping is adjustable. The only way to alter the compression damping characteristics in this case is switching to a different viscosity oil... but not different enough to render rebound damping adjustment ineffective.

It does sound like the stock springs should work for your weight, although they are likely progressive and may feel more plush than you want. A 3cSt@40C difference in oil viscosity may be noticeable enough to improve things just a bit.

I agree, Just changing Oil (7.5W)would do for his weight. also the Air Gap to 140-150mm)
I know this by experience. I recently upgraded mine to hyperpro combi kit (Cheaper way to upgrade suspension.). just springs and oil.
Bike corners very well. so planted now. no more break dive. Good enough for someone like me.
I'll never ride FJ-09 on a track. This bike is built for road touring.