Ever wonder about fork oil?

[smokinjoe]

Kay!!! Let's see...you have to oil moving, the valving is reactive. pre-load too high, you blow through the stroke...because...you've gone through some of your spring already...and you've shortened the stroke?

Too thick an oil won't let the valving rebound, so you're basically keeping the shock/forks from their full potetial. You, basically have shortened the shock when going over a series of bump(whoops). Right? Because the oil is too thick and can't get back through the valve fast enough, so the spring stays compressed. Is that right?

I understand that oil doesn't effect the ride height, it effects how fast the forks/shock works. Maybe I misspoke with what I was saying, or trying to. The spring holds the front-end up, not the oil.

[markjenn]

FWIIW, I just changed fork oil in my FJR. (I'm always a little amazed at what a chore this is on a new bike compared to the old school bikes where you'd remove the drain plugs at the bottom of the forks, pump the suspension ten or fifteen times to pump out the old oil, pop the fork caps off and add a measured amount of oil back in. What was a 10-min job now easily takes a few hours to remove the wheel/fender, pull the forks, take them apart, measure levels, etc. This is progress?)

Anyway, I did all the req'd reading (well, skimming) and decided to use oil that was close in viscosity to the Yamaha "01" fork oil that presumably the bike shipped with. According to the comprehensive chart at http://www.peterverdonedesigns.com/lowspeed.htm, the Yamaha fork oil is somewhere between a 2.5wt and 5wt Silkolene Pro RSF oil which I happened to have some lying around from doing dirt bikes, so I did a 80-20 mix to match the Yamaha's oil viscosity.

Probably overkill. I was sorely tempted to throw $3/qt ATF in these puppies rather than $15/qt synthetic fork oil.

- Mark

[smokinjoe]

Mark,
Thanks for that linky! Yhere's a lotta crap in there. It makes my head sore! I knew that heavier oils in the forks made the damping "stiffer", but I surely didn't know that it can cause the forks to "pack", which really makes sense. What? Did I just say it made sense? Maybe I'm starting to get it afterall!

[warewolf]

Originally Posted by markjenn

FWIIW, I just changed fork oil in my FJR. (I'm always a little amazed at what a chore this is on a new bike compared to the old school bikes [snip]This is progress?

Bet your FJR doesn't handle like an old school bike, either!

[warewolf]

Originally Posted by smokinjoe

Kay!!! Let's see...

Ya basically got it.

Originally Posted by smokinjoe

The spring holds the front-end up, not the oil.

At rest the spring does all the work. Dynamically, it's a complex system and the fork oil viscosity and damping stacks come in to play.

[bmwktmbill]

Nice thread.
This stuff isn't for the simple minded.
Mark's summary was beautiful.

I try to remember that the idea is to keep the wheel on the the ground even if it is in a hole or up on a bump, and then follow the ground to the second hole or bump and repeat, always keeping the suspension from topping out or hitting bottom.

Like the Wolf said, watch the rebound. I set it full on and then back it off until the stutter bumps are gone and then dial up some compression damping from a neutral setting until the fork or shock feels harsh and then back that off.
You can set things fast with this approach and the rebound is right.
I set the rear/shock first, then the fork.


Put a zip tie on the fork leg to check out the travel.

KEEP NOTES ON EVERYTHING YOU DO.

Don't dis the air spring, add and subtract oil to experiment.
It will exert a significant influence on the fork action.
If you don't believe consider trying sub tanks, You will believe once you turn the tanks on and off and try a handful of brake each way.
They are the easiest way to have both an on and an off road suspension.

You can change the viscosity of your fork oil by adding a teaspoon of gear oil to increase, or maybe kerosene to decrease.

It's all in the name of science.
For the rear shock you can very the N2 pressure. Same theory as the air spring up front but I never tried it.

Go for it yourself, I know nothing.
b.

[smokinjoe]

Originally Posted by bmwktmbill

Go for it yourself, I know nothing.b.

As you can see by my posts, me either

[Bobmws]

I read through alot of the Verdone website article on oils, and followed the links to suspension tuning via spring rates, spring sag, damping and oil height. Very informative stuff, thanks for finding that link.

[Ratman]

I used to race off road cars, and developed much of my Shock oil theory there.

Lately, last 15 years I've been riding bikes. I've concluded that the cheapest oil that will do what you want is the best one.
A shock oil should be slippery, have a viscosity, and resist aireation.
Slippery isn't so important because you want to slow the slide down with the dampening action so adding a bit of friction (With cheap oil) is just fine.
Viscosity is just a matter of finding out what weight suits your riding style.
Most oils have additives to reduce aireation.
......oh, and it shouldn't cost 40 dollars a gallon. Whos's idea was that?

So I use 30 weight motor oil and thin it 4 to 1 with mineral spirits. I make a gallon of the mixture at a time and add it to my forks as needed. I might decide to change the mixture if I want more or less dampening.

A very important thing is to know your mixture so you can repeat. I like fine tuning by adding a little more thinner or motor honey as mentioned, but the trouble is you can't reproduce that. But anyway, you can develope your own Viscosities if you keep track of what you are doing.

Of course, if you have more money than time, go for the store bought stuff..........nothin really wrong with that.

And then I like changing springs for the riders weight and what he is doing with the bike. And I like fine tuning with fork air.

Packing the shocks down with too much rebound damping is a real bad thing. I once did three endows in an at Southbay raceway, San diego by increasing the rear dampening (a lot) in an off road car.......then I hit two bumps in a short space (before the shock could reset)..........what a ride that was.

[nomiles]

Thanks Meat Popsicle, for posting this info, it's just in time for my Progressive spring install.

[bmwktmbill]

Rat,
Man, I love you brother.
For racing applications please recommend full synthetic purchased at Wally World.
b.

[sailah]

When I pressed the tuners I was buying valving and springs from as to the best fluid to use, they pretty much all recommended Silkolene RFS Pro synthetic oil in 5 wt for my 525 WP 48s. That's what I used, it works great and apparantly lasts quite a bit longer (5x). It's not cheap but since I figure it will be changed every year or so, not a big deal.

[meat popsicle]

Originally Posted by nomiles

Thanks Meat Popsicle, for posting this info, it's just in time for my Progressive spring install.

Your welcome. I too am about to upgrade my front end, with 0.50 springs and some subtanks from Infinity Machine and Design. The Red Line LightWeight fluid shouldn't hurt either - even at $10/leg because its something that I change about 1x per year. That ain't enough to get me in a mood to reinvent the wheel...

P.S. hey warewolf! where ya been, riding?

[warewolf]

Originally Posted by meat popsicle

P.S. hey warewolf! where ya been, riding?

G'day Meat, yes riding quite a bit. Plus busy working and trying to cut down on the computer time - the local advriders use a local forum so advrider.com hasn't seen much action lately. The 640A is getting along sweet, specially since the front rim was straightened, had a few big trips written up elsewhere. Been racing the 2T in cross-countries and that is chewing up a lot of shed time at about 3x race time.

Recently replaced the fork oil seals and dust wipers on the little beastie. It's an '03, so it has the same 3-bush WP 48mm forks as the Adventure. I used docs/info from here to do the work, there are some differences to the docs and the earlier 2-bush 43mm forks... it will end up in the mighty index over the summer break.

Interesting that riding the bike with leaking fork seals has allowed dirt & water to enter the forks. The fork oil was a mess, probably a lot of that due to the 6-hour race in the rain and hence mud. You know that oil leaks out past the seals, but I hadn't considered that crap could be forced in through the seals. Next time I won't leave it so long, but I didn't think it was that bad... mea culpa.

[meat popsicle]

Originally Posted by warewolf

... mea culpa.

mea tu

I am not prepared to swap the seals out. I just have the heavier springs, subtanks, and oil. Unfortunately I haven't been riding as much as you...