Front end floats slightly > 70mph, after changing fork oil

[Darkstar]

Had the original oil in there for ten years but Im light, so it wasn't too soft at first. Slowly though it got spongy and changed it out with weight and amount per spec. Much better, but I have noticed that at high speeds the front has a slight floaty feeling, wiggles a bit easier than before. I thought I had marked the settings on the forks, and put them back to the same place, but perhaps not. Anyone see this?

[herennow]

Could be oil level as that's the one thing that is easy to have different after an oil change, all the rest *should* be the same. Did you measure oil by volume or by height from the top?

[Darkstar]

height

[mr72]

IDK how oil level would affect this at >70mph. More oil will cause it to become stiffer as it gets close to bottoming. But it wouldn't have the effect you are describing.

Did you remove the fork legs from the triples? If so then I think it's more likely you didn't get them in exactly the same spot in the triples resulting in a steeper head angle that will make it have less on-center feel and be sort of darty at high speeds.

It is possible for heavy fork oil to cause packing. Can't imagine how high speeds would affect this. But if you had more rebound damping than compression (IDK if the GS fork does this or not) then successive high speed bumps could cause the fork to come to rest lower in the travel and if you were consistently hitting those bumps at the right rate this could steepen the had angle. Feels very unlikely to me. But maybe you're popping over freeway separations and once you get over 70mph it begins to pack down? What could happen is the fork encounters a bump more quickly than it can finish rebounding from the previous bump, so over and over in rhythm it could result in packing.

Anyway, I think that's unlikely but who knows? What weight oil did you put?

My GS is pretty floaty at speed. To me it's 99% affected by tire pressure. Any chance that's the difference? Coincidental temperature/weather change resulting in lower tire pressure?

[alpo]

I'd say the front end geometry is causing the light feeling at speed. Measure the distance the fork tubes stick out above the upper triple clamp. The shop manual calls for the top of the tubes to be level with the top of the triple clamp:

When installing the front fork assembly, align the upper surface of inner tube with the upper surface of the handlebar holder.

Higher means quicker steering, but less stability at speed.

Mine are up 2.5mm, which makes for a little quicker steering. If I'm going fast I keep more weight on the front end.

[Darkstar]

What weight oil did you put?

as spec'd in SM

To me it's 99% affected by tire pressure. Any chance that's the difference?

I check/adjust before every ride so i dont think this is the cause

Did you remove the fork legs from the triples? [/quote]
Yes, so it looks like it may have moved, and is now time for me to learn how it actually works, thanks!   

[gregjet]

Do youy mean "skatey" like you are on a steel tyre or vague felling in the steering inputs.
Skatey is almost always ( almost) too much tyre pressure. Your tyre choice will have an effect on the pressure you need for need for best feel. If you have gone bigger you will need less pressure if smaller a bit more ( usually). Some brands need lower pressures than others because of their rubber compound and carcass construction. Eg until recently continentals and Metzlers need a little more pressure than Michelins or Bridges ( again usually). Dunlops always feel skatey though they aren't in reality. If you have gone from a Michelin to a Dunlop you will feel like the front is a bit harsh and skatey until you get use to them.

On the fork side way too little or too much preload will give you that feeling for different reasons.
Too much preload and with stock oil the rebound will be too fast and the forks not surface compliant, so the tyre will unload too much. Too little and the forks will wallow in the dead zone and may even "pack down" .
So tyre pressures first then preload/fork spring rate and damping.

One side note. If the rear is too soft, it will sink, and slacken the fork angle too much, and not allow the forks to work at all. This is a common problem in this bikes little brother the DRZ400 ( particularly the SM) . It tends to be less problematic with short travel bikes like the GS500.

[Darkstar]

Do youy mean "skatey" like you are on a steel tyre or vague felling in the steering inputs.

Not vague, lighter. From the sounds of it, I didn't reinstall the forks the same way. I say this because aside from that, Im using the same setup as last year, ie tires, fork oil, tire pressure

[alpo]

Your tyre choice will have an effect on the pressure you need for need for best feel. If you have gone bigger you will need less pressure if smaller a bit more ( usually). Some brands need lower pressures than others because of their rubber compound and carcass construction. Eg until recently continentals and Metzlers need a little more pressure than Michelins or Bridges ( again usually). Dunlops always feel skatey though they aren't in reality. If you have gone from a Michelin to a Dunlop you will feel like the front is a bit harsh and skatey until you get use to them.

I don't know what kind of riding you do, but that is pure bullsh*t. Telling people that kind of thing is going to get someone hurt.

For the street factory tire pressures are the way to go. Once you start going fast and really learning the bike, then you can experiment with tire pressures. Just be warned that too much either way will cause loss of traction, which is usually painful.

FWIW I've run many different brands, Bridgestone, Continental, Dunlop, Michelin and Pirelli, and many models of those brands on the same street bike with the same factory tire pressures. The main differences? How well they stick and how long they last. It's a pretty fast bike, the suspension is right and I don't ride slowly.

Riding on the track is a different story: Tire pressure is different for different brands/models. The manufacturer provides a starting point, but you have to measure between cold and hot to determine what is optimal for you.

[sledge]

So......you have changed your 10 YEAR OLD!! fork oil and now the front end feels different?

Personally.......I am not surprised in the slightest!

[sledge]

"I  don't know what kind of riding you do, but that is pure bullsh*t. Telling people that kind of thing is going to get someone hurt"


You are new to this forum Alpo......stick around, you will soon get used to the BS!

Generally What matters in here is who is doing the talking, not what is being said 

[alpo]

So......you have changed your 10 YEAR OLD!! fork oil and now the front end feels different?

Personally.......I am not surprised in the slightest!

You are new to this forum Alpo......stick around, you will soon get used to the BS!

Generally What matters in here is who is doing the talking, not what is being said 

Tru dat. 

Hey! It's a sunny day! Why am I typing instead of riding?!   

[herennow]

Hey Alpo, I found your comment of the fork offset in the triple trees interesting. I did a back of the envelope calculation which indicates that a 2.5 mm change would make roughly a 0.1 degree change to  steering angle.
I know little about the GS forks but is such a small difference something you could feel, especially considering that there is about 100 mm travel up front as it is?

Sledge has a good point your new oil would be much more viscuous than the 10 year old stuff, (assuming nothing wierd was used by previous owner). Damping would be better now.
Cheers

[alpo]

Hey herennow,

Very slight changes can make a noticeable difference in handling. Definitely something you can feel.

[RichDesmond]

Hey herennow,

Very slight changes can make a noticeable difference in handling. Definitely something you can feel.

For the average rider, on a normal street bike, you're not going to feel 3mm difference in fork height. That much change in fork height makes about a 1mm change in trail. (Trail is what matters, not rake) 1mm is roughly 1%.
On a race bike, which is set up on the ragged edge of stability, an experienced racer may be able to feel that change, but it's going to be barely perceptible.

The OP's problem sound more like too much fork oil.
When you measured the level, did you measure the distance from the top of the fork tube down to the surface of the oil? i.e., what we're really measuring is the air gap. That measurement must be done with the forks fully compressed and the spring and spacer removed.

[HPP8140]

Delete. Wrong post.