[Twisty50]

I just finished replacing the fork seals. Not fun but not too bad. The dealer recommended I use 20w fork oil. Could this be right? What will using a higher weight oil do to the bike. Handling ect.

[sheepofblue]

Originally Posted by Twisty50

I just finished replacing the fork seals. Not fun but not too bad. The dealer recommended I use 20w fork oil. Could this be right? What will using a higher weight oil do to the bike. Handling ect.

20W sounds more like proper weight for sliders rather than cartridge shocks

[Twisty50]

That's what I thought. He asked if I was going to be 'ridding hard' wheelies ect. I told him yes and he recommended 20w. I want the bike to handle though. Does anyone know what going to this weight will do to the handling?

[zerogara]

Originally Posted by Twisty50

That's what I thought. He asked if I was going to be 'ridding hard' wheelies ect. I told him yes and he recommended 20w. I want the bike to handle though. Does anyone know what going to this weight will do to the handling?

For the past 15 years finding fork oil of that viscocity is hard, more common are 5w, 7.5w, 10w.
In the old days people used 30w engine oil on forks. That is not necessaraly a less viscous oil than fork oil, or shock oil, the measurements are not comparable. Same goes for 80w90 gear oil, and 30w engine oil debates.

If you use a less viscous oil you may either experience hydraulic lock, or blow a seal or something else, but something will have to give and liquids always win the battle between pressure, metal, and seals. Hydraulic lock translates to immidiate loss of control and possible serious damage to the bike suspension and frame. It is almost as bad as bottoming.

Dumping despite of how "stiff" it is will never prevent bottoming, it just slows the rate it happens. 0 damping means a plain spring pogo stick. Preload does not make a sprinh stiffer, it just makes it not work till an equal to its preload force is exerted.

For every given spring and motion/travel rate/speed there is a "perfect" dumping rate. The problem is that shocks and forks can not adequately vary their dumping to meet all conditions. Have you seen high speed and slow speed dumping adjustments on modern MX bikes. Imagine if you had infinite adjustments for every single speed of travel. Perfect suspension!

On the rear they have achieved "some" variable geometry with links, while in the front it is less variable (caster changes from max braking to max acceleration). This variation also affects spring and dumping rates. The effective vertical rate of the spring and dumping rate changes when geometry changes.

So what is there for a man to do? Pick up a good starting point, then go one click up and down for each adjustment and keep playing and keep record of what your combinations are till you find what makes you feel better. Once you change one thing only and it feels better, the ideal for the rest of the adjustments changes. It takes a lot of fiddling. And then tires will change, pavement will change, temperature will change, and there you go again!

If you are not racing it doesn't matter as much, try to enjoy your rides and spend less time fiddling with stuff.
I have more fun riding an hour more, than wasting 4 hours making an adjustment that would give me 7hp more!

Says the man that has fiddled countless hours for years trying to get these dumb flat slide Mikunis to work properly on an RG500! The RC51 is short of like mom's station wagon compared to that neurotic little rocket!