Anyone changed fork oil on a Gen III yet?

[sath182]

As the title states, I'm wondering if anyone has done a Fork oil change on a Gen III yet. As an availability concern, I'm particularly curious how the different valving reacts to oils thicker than Yamaha 01 (15.6 cSt @ 40C). I've found a few threads that discuss fork oil weight, but they are all for the Gen II.

 

[Pterodactyl]

" I'm wondering if anyone has done a Fork oil change on a Gen III yet."

Yes.

But I stuck with the stock oil weight.

At 33,000 miles the oil looked, smelled and tasted like new.

 

[sath182]

This bike has over 36k on it now and I'm sure it's never been serviced. It really makes me wish i had money laying around for a new shock more than fresh forks.

 

[Fred W]

Changes in the oil viscosity will affect the 3rd Gen forks in pretty much the same way it does any other hydraulically dampened forks. Thicker oil will increase the damping across the board, both compression and rebound, and at all speed of articulation.

You can lessen the low speed damping to accommodate the thicker oil with the two clickers, but the high speed damping is preset by a series of fixed size orifices and flexible disks at the ends of the valves inside the forks. So, the net effect is that you will have increased the non-adjustable high speed damping, which is not necessarily a desirable thing to do.

I'd stick with either the stock Yamaha fork oil, or something as close to (and as thin as) that.

YMMV

 

[PapaUtah]

Every winter it gets changed. Goes in crystal clear, came out a silver gray the first time...the last two times it came out with just a little haze...easy job. Have stuck with the stock Yamaha recommended fork oil.

 

[sath182]

Changes in the oil viscosity will affect the 3rd Gen forks in pretty much the same way it does any other hydraulically dampened forks. Thicker oil will increase the damping across the board, both compression and rebound, and at all speed of articulation.
You can lessen the low speed damping to accommodate the thicker oil with the two clickers, but the high speed damping is preset by a series of fixed size orifices and flexible disks at the ends of the valves inside the forks. So, the net effect is that you will have increased the non-adjustable high speed damping, which is not necessarily a desirable thing to do.

I'd stick with either the stock Yamaha fork oil, or something as close to (and as thin as) that.

YMMV

Fantastic response Fred, I wasn't clear how the actual damping was accomplished. So I guess that means as stock the harshness of the system will generally be controlled by spring preload and then the adjuster is mainly for gentle ripples in the road and to control nose dive under braking. Thanks again!

 

[Fred W]

I wasn't clear how the actual damping was accomplished. So I guess that means as stock the harshness of the system will generally be controlled by spring preload and then the adjuster is mainly for gentle ripples in the road and to control nose dive under braking. Thanks again!

Well, not quite. All the spring preload adjustment does is alter the ride height. Contrary to common misunderstanding, cranking down on the preload adjuster doesn't stiffen the shock or fork, it just changes what the height (how extended) it will be at rest. When you hit a bump the fork or shock will still move the exact same amount.

When you do hit a bump in the road there are two things that will determine how complaint it is (how far the wheel will deflect) and those are the spring rate in addition to the damping To stiffen the suspension and make it move less for a given bump input you have to either change to a stiffer spring, or to increase the damping.

Damping is resistance to change in the suspension's length over a particular time. As you add damping you will increase it's resistance to compress (compression damping) or extend (rebound damping). So adding compression damping will make the suspension feel stiffer.

In general we say that there are two "speeds" of suspension articulation: fast and slow. "Slow" articulation would be like when you hit a slow roller of a bump in the road, hit the brakes, or add G force to the suspended mass in a corner. "Fast" articulation would be when you hit sharper edged bumps in the road, which is what you really want the suspension to deflect for and absorb. Now realize that changing one will affect the other, and the "speeds" of events are variable and overlapping as well, so it is always a compromise.

The goals in suspension design and tuning are to have the most low speed resistance to suspension length change possible while having the most compliance (least damping) on the higher speed stuff. You want to maintain the chassis geometry, steering angles and ride height on the slow rollers and in corners, with minimum brake diving, but you also want the wheels to be able to move freely and follow the undulations of the road or ground under the bike, and keep the tires' full contact with the road, without upsetting the bike's chassis while riding down the road.

So you see, just putting in thicker suspension oil will be counterproductive.

 

[bigjohnsd]

Hmmmm..............I've run my shock and fork from one extreme to the other with no change in unladen ride height.

All the spring preload adjustment does is alter the ride height. Contrary to common misunderstanding, cranking down on the preload adjuster doesn't stiffen the shock or fork, it just changes what the height (how extended) it will be at rest.

 

[sath182]

Fred I've heard the argument before, and it's taken me a while to wrap my head around it. But mechanically speaking you're right, then only thing that truly changes the assembled spring tension is the spacer.

Now, before the preload/ride height argument has a chance to get out of hand, lets put some ice on it.

In the short term, I'm gonna see how the bike responds at full "preload" and no "preload" as well as full hard and full soft on the comp so I can see what it does... or if I can even tell.

Also I was looking at new bushings and seals, holy nickle and dime Batman! On top the cost of new tires before September. And I still need to figure out a tool to do the job with.

 

[ionbeam]

I'm gonna see how the bike responds at full "preload" and no "preload" as well as full hard and full soft on the comp so I can see what it does... or if I can even tell.

100% chance that you can tell.

 

[sath182]

The springs, probably, but the comp I haven't really noticed much at all. Maybe after new oil (and bushings).

 

[Fred W]

All the spring preload adjustment does is alter the ride height. Contrary to common misunderstanding, cranking down on the preload adjuster doesn't stiffen the shock or fork, it just changes what the height (how extended) it will be at rest.

Hmmmm..............I've run my shock and fork from one extreme to the other with no change in unladen ride height.

How does one ride a bike unladen?

Ride height is the height when the bike is fully loaded. Do not try checking the ride height difference by measuring sag from the totally unweighted position, as the fork top out springs make that measurement confusing.

Instead, measure the distance from some part of the suspended bike to the ground. If you crank the preload adjusters in the bike will sit that much higher (reduced by the angle of the fork legs).

Also, forgot to mention, the rear "hard / soft" lever on the stock rear "A" model shock is not really a preload, or ride height adjustment. It is a soft spring lockout. It actually does change the spring rate.