Fork suspension tuning

[fljab]

My '09A has 115K miles on it and I'm giving it an all around maintenance update including some work on the suspension. I took the fork caps off, drained and flushed fluids and installed some Wilber's progressive rate springs that I had bought along with the rear shock some yrs back here on the forum. I haven't installed the rear shock yet, but it's coming up. I'm still dealing the with the front to include new wheel bearings, tire, and brake pads and fluids flush/replacement. My question is about tuning the forks.

I've read every relevant thread here that I could find, and the TSM on tuning the forks (page 3-36/37). The Wilber's instructions called for 7.5 wt oil and 18mm spring preload. In the book, the preload is set by the bolt which has lines 1 through 6 on it. I've got both of mine set at ~2-1/2 and is exactly equal per my dial calipers measurement from the top of bolt (beneath black knob) to surface of cap bolt. Now that I'm writing this, maybe I should have backed that off until it was just starting to preload spring, then brought it down 18mm? That would make sense, although I had to push down the cap bolt against spring pressure to thread it into the fork tube. So, not sure how to determine correct preload per that 18mm spec.

Rebound damping via the black knob on top. The book says "Minimum 17 clicks out, Standard 12 clicks out, Minimum 1 click out". The problem I'm seeing is that I ran both knobs the entire range and counted 39 clicks on the left fork, but 43 on the right fork. So, going all the way in then backing off - which is how I'm reading the TSM - would or could mean 2 different settings. I set both of mine 12 out.

Compression damping on the bottom of the fork had the same amount of clicks on each side, and I set them in the middle of the range for now.

I'm still working on the front end, but the Wilber's shock for the rear will be installed in the next week or so and I'll need to figure out how to set sag and the adjustments on the shock itself. I'm not worried about it just yet, and there's plenty of youtube, forum threads, etc to look into, so will post here when I get to it.

As much as I'd like a Gen 3, this old bike still has plenty of life left, and with the miles on it, is basically worth less to anyone else than the use of it to me.

TIA all!

 

[Fred W]

Unless you changed the damping valves, IOW if you still have the stock valving, the 7.5W fork oil will be too heavy no matter what spring you have in there. The stock Yamaha fork oil is a very light viscosity oil. Approximately a 3 weight oil compared to most others. I have been using Motul Extra Light as a close approximation of the Yamaha oil, which is harder to find.

Heavier oil will not only increase the baseline low speed damping, which might be beneficial (and is the part that is adjustable with the clickers) it will also increase your high speed damping that is of fixed value set by the shim stacks in the valves. I dont think youre going to be happy with the way it works with that in there.

The damping adjusters are just screws adjusting a needle valve. Fully CW is all the way seated. Thats why you always count clicks out from fully CW. That will open the needle valves the same amount. Where the fully open mechanical stops are may vary, but dont matter.

The only thing the fork preload does is establish the front ride height. It doesnt change how stiff the fork is. That is a function of the fork springs, damping and air space above the oil. If you can achieve the desired ride height then your preload is OK.

Hope that helps

 

[fljab]

Thanks Fred. I did count damping all the way CW, then backed off 12 clicks. I kinda figured what you said, that being all the way in, then backing off an equal amount would be the same or close on both sides. Just the difference in total click counts had me baffled a bit.

I'll look for the lighter oil. It's easy enough to change right now. I have the wheel off as am waiting on brake parts and need to put the new tire on.

On the preload, I'm still worried it's too much, but will look at the ride height after I get both ends finished and the bike loaded back up. Again, that's easy enough to adjust.

 

[Fred W]

If the preload is excessive the front will ride higher, which will make the steering more stable, but slower turning in (think chopper). If you do a lot of straight line highway riding you might like it that way until you get into some twisty turns and have to fight the bike to get it around the corners.

 

[redneckj]

I took the Maxima 5wt out of my GP valved forks and replaced it with Motul 7.5 weight. NIGHT and DAY difference. The 5w did not provide the correct resistance for the valving once the oil got warmed up. The Motul 7.5 weight is very consistent from cold to warm. Cant say enough positive about it.

 

[bigjohnsd]

On the advice of Dave Moss, a somewhat renowned Northern California Suspension Guru, I ran Maxima Green 10 WT in my '13. It helped me quite a bit, a little harsh on really sharp bumps at speed but overall was a great improvement over stock.

Had I not sold the bike I would have gone to a 7.5 wt equivalent.

Somewhere on here is a link to a Fork Oil Weight Table that ranks the oils by their actual viscosity as one MNF 10 wt is not the same as another.

Good luck, keep track of your baseline and what you do so you can go back if it isn't working out.

 

[MCRIDER007]

I took the Maxima 5wt out of my GP valved forks and replaced it with Motul 7.5 weight. NIGHT and DAY difference. The 5w did not provide the correct resistance for the valving once the oil got warmed up. The Motul 7.5 weight is very consistent from cold to warm. Cant say enough positive about it.

This is a little like comparing apples to oranges in that the GP damping valves were engineered using a 7w oil whereas the OEM damping valves were engineered using a much lighter oil. Which oil works for one fork may not be the best for another, I would follow Freds advice and use a light 5w for OEM damping valves.

 

[hppants]

Kind of following this. I've ordered an aftermarket rear shock for my '14 with 53K on it. A little voice in the back of my head is telling me that as soon as I test ride the new shock, I'm going to need to re-do the front fork.

 

[draco_1967]

Kind of following this. I've ordered an aftermarket rear shock for my '14 with 53K on it. A little voice in the back of my head is telling me that as soon as I test ride the new shock, I'm going to need to re-do the front fork.

This will happen, guaranteed!

 

[MCRIDER007]

Kind of following this. I've ordered an aftermarket rear shock for my '14 with 53K on it. A little voice in the back of my head is telling me that as soon as I test ride the new shock, I'm going to need to re-do the front fork.

You will not not have to re-do much. The GEN3 forks are much different from earlier FJRs in that they come with much heavier springs and far superior damping (with ALL the damping in the right leg). If your sag is excessive or you have too much fork dive under heavy braking it might be time to replace the fork springs. Save time and dollars by buying OEM springs, that way you will not have to adjust the spacer lengths.

When you replace the fork oil it really doesn’t matter what oil you put in the left leg since it doesn’t have any damping, just get the oil height as recommended.

 

[Fred W]

On the advice of Dave Moss, a somewhat renowned Northern California Suspension Guru, I ran Maxima Green 10 WT in my '13. It helped me quite a bit, a little harsh on really sharp bumps at speed but overall was a great improvement over stock.
Had I not sold the bike I would have gone to a 7.5 wt equivalent.

Somewhere on here is a link to a Fork Oil Weight Table that ranks the oils by their actual viscosity as one MNF 10 wt is not the same as another.

The harshness over sharp bumps is because the heavier oil is not right for the shim stack in the stock valves and is providing excess high speed compression damping. Low speed damping can be adjusted via the clickers. The high speed not so much. That’s why I don’t recommend just going with heavier fork fluid unless you also change the valves out.

As John mentions, one brand of 5 weight may be similar to a much higher or lower weight rating from another manufacturer. When you switch fork oil brands, and even when switching the oil type within a brand, it’s best to have an idea what the actual viscosity of that oil is so you can adjust it to what you want.

Google Peter Verdone suspension fluids to find the chart mentioned.

 

[BanjoBoy]

On the advice of Dave Moss, a somewhat renowned Northern California Suspension Guru, I ran Maxima Green 10 WT in my '13. It helped me quite a bit, a little harsh on really sharp bumps at speed but overall was a great improvement over stock.
Had I not sold the bike I would have gone to a 7.5 wt equivalent.

Somewhere on here is a link to a Fork Oil Weight Table that ranks the oils by their actual viscosity as one MNF 10 wt is not the same as another.

Good luck, keep track of your baseline and what you do so you can go back if it isn't working out.

I thought it was FredW who posted this suspension chart in 'nother thread? Thanks Fred.

https://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid

After studying it for weeks, I finally went with the RedLine yellow, (Think it's 5w?) and have been happy.

 

[Fred W]

Yeah, it probably was me. I have CRS these days. But the links to Peter’s viscosity charts have moved over the years so a google search on his name will get you the goods. So, there you go.

Anyone else have PMS?