What Does Air In Front Forks Do.

[GolfVenture]

I've been told that adding more fork oil will stiffen the ride and removing oil will soften the ride.

 

So what does adding or reducing front fork air do to the ride?

[dingy]

Same thing.

Just easier to adjust as riding conditions change.

Gary

[MikeWa]

More air = stiffer ride

Less air = softer ride

 

Air may also change the riding height slightly.

 

Mike

[Venturous Randy]

The added air acts as additional spring pressure. Adding oil is like increasing the dampening effect and adding thicker oil will do that to some degree also..

RandyA

[bongobobny]

All of the above, but air is compressable whereas oil is not. Therefore air has more of a dampening effect over total suspension travel (the more the travel the more the dampening) whereas the more the oil the stiffer the suspension regardless of travel...

[steamer]

All of the above, but air is compressable whereas oil is not. Therefore air has more of a dampening effect over total suspension travel (the more the travel the more the dampening) whereas the more the oil the stiffer the suspension regardless of travel...

HE'S BACK! Welcome back Bob....and yes, what he said:sign yeah that:

[Marcarl]

Caution: if you put in too much air, you will blow the seals,, not the end of the world, but it will most likely take some oil out with it and make a bit of a mess.

If you put more than the recommended amount of oil in it, the forks may come to an abrupt halt on the way down and cause some damage in the process.

In my opinion, you only need so much oil to do the damping job, any more will cause problems but not have any effect on the ride itself.

[V7Goose]

I do not know who told you about adding or removing fork oil, but that information is just wrong. You need the correct amount of fork oil, period. Too much will prevent the forks from working correctly, and too little will cause foaming and reduce the damping.

 

As others have already said, the air is simply an additional spring. The oil is squeezed through small valves and slows the speed that the fork (or shock) can move. This function is primarily in the rebound, or fork extension, direction. The springs generally control how fast and high the tire comes up on a bump, and the oil controls how fast and far the tire goes back down after the bump. The correct oil weight should allow the tire to quickly return to the original position on the surface of the road without over-shooting (which causes bounce). If the oil is too thick, the forks may not be able to move the tire back down in time to soak up the next bump.

Goose

[MiCarl]

Extra fork oil reduces the size of the air pocket and has the effect of making the spring rate higher. Too much and the forks can hydro lock, damaging seals or other stuff. Best not to do it UNLESS the manufacturer specifies an acceptable range (some Harleys and older, small metrics).

 

I just had a late 70s CB550 in the shop that another place had rebuilt the forks. There was 80ml too much oil in each one. One WAY stiff ride!

[dingy]

I do not know who told you about adding or removing fork oil, but that information is just wrong. You need the correct amount of fork oil, period. Too much will prevent the forks from working correctly, and too little will cause foaming and reduce the damping.

Goose

At the risk of offending Goose, I am going to disagree with his statement that "adding or removing fork oil, but that information is just wrong"

 

Half of it is correct, you should not add more oil than the maximum specified, which on 1st gens is 5.5" with forks collapsed and springs removed. To much oil will severely limit the compression ability of the forks

 

The rest of this is for those who are willing to do some experimenting to tune the bike to what they want, not some cookie cutter approach that one size fits all. If you are the kind of person that thinks, for example, because the tire says 42 PSI on the sidewall, that's all it should ever be, then read no farther. Goose's opinion is the right one for you.

 

Lowering the oil level slightly will help the stiffness of the front end be lessened. And by slightly, I am saying no more than about 7.5" in a Venture. There is little chance of foaming in a touring bike like the Venture. A 250cc motocross bike, ya, it will happen.

 

Lowering the oil level creates a larger air pocket in the top of the fork. Air is a compressible substance. A larger air pocket will allow for a more gradual increase in the stiffness of the springs as the fork collapse due to a impact on front tire or braking, causing a weight shift to front end.

 

Also changes should be done in small increments and a very safe and sane test ride taken after adjustments to see if it is right for you.

 

Since the forks have provisions for either manual or CLASS addition of air, a stiffer ride can be obtained by increasing fork air pressure.

 

I have attached the progressive install manual, which has a chart (Figure 1) that denotes the maximum oil level at 5.5". There is a notation higher than that is 'Oil Level Too High' and a notation below that is 'Safe oil level', and this does show actually more than 7.5"

 

They also say to keep it at shop manual specifications in the text. I contend this is some pencil pusher put this in for legal purposes.

 

Next is a link to one web site saying lowering level is a fork tuning tool.

 

http://www.dirt-bike-secrets.com/oil-level.html

 

http://www.dirt-bike-secrets.com/motorcycle-fork-oil.html

 

Just in case someone asks, What do I do? I keep front and rear end stiff. I ride this bike to its full potential and I like the front end tighter in curves, it is more predictable and responsive. The bike does ride harder on rough surfaces, but it is a trade off for the tighter handling I want.

 

Let the flaming begin !!

 

Gary