General Suspentions questions/concepts

[the_Journeyman]

I'm a boinger n00b when it comes to anything more than changing springs & oil. 

As I'm working my brick-hard forks to smooth them out a little, I came up with all sorts of questions

I've got old-school non-adjustable USD forks by Marzoochi. I can only change springs, oil & preload shims. This brings my first few questions:

1. Is damping controlled by oil & valving?
2. Is a thicker oil going to have more damping? (makes sense to me)
3. What else does the oil/oil level affect?

Going over rough areas in the road it felt like the front wanted to float or skip and not get pushed back to the pavement after a small bump or a rough spot. The rear also seemed to wallow in the harder corners, like the spring was unsettled. I don't notice the wallow riding solo

4. Was the front behavior caused by excessive damping?
5. Did too little preload on the rear cause the wallow?

After I removed the forks last night, after lowering the preload amount (cut shims down) I compressed them by just pushing down on them with a good amount of force. They would compress about 1/2 way and it was like you hit a stop. After that, the would compress slowly & you could hear the oil being forced through something under pressure (valving?) The oil was different levels in the legs probably because I measured volume going in rather than level. The one with more oil was the one that I really noticed the travel just stop about 1/2 way down. The oil was right at the top of the spring, the other was about 2" lower.

6. Was the hit I was feeling a result of 100 much oil?
7. Would a lighter weight oil reduce this hit feeling?

Matched the oil level to the lower of the two forks, and on reassembly I still feel the hit a little bit, but it is much smoother.

Thanks!

JM

[clubhousemotorsports]

If you have been playing with preload shims be carefull that the hit you are feeling is not the top of the damper cartridge hitting your spacers.

oil does control damping, it also controls bottoming as you are playing with the air spring on top of the oil. as you compress the suspension you compress the air in the fork (you cannot compress the oil) as the air space gets smaller the force goes up exponentially. This adds another variable.

[fasterblkduc]

Ok, are you using the stock springs? I'm unclear about what you've done. It sounds like you've just changed oil, and reduced your preload by cutting down your spacer? What weight oil did you use? Also, what's the level at? It's hard to give you answers without more info.
From the way it sounds, you may have too much oil, too thick oil, and/or what Ducvet said.

If the forks are back on now, bounce the bike by pushing down real hard in the center and make both the front and rear compress. Does the front come back up real slow? Slower than the rear? If so, you could go with a thinner oil. Maybe this little test can't be done because you said it's bottoming.
The bottoming could be caused by the level being way too high but it's hard to tell exactly what's going on from your description.

[the_Journeyman]

I've got aftermarket springs because the originals had a bad case of diving & were way too soft.  My shims are PVC and the damper is not hitting them.  After lowering the level, the bottoming feeling is gone, and the fork about 1/2 travel starts to noticable slow.  I can't bottom the fork just pushing on it.

I'm thinking the oil is 10W, I'll have to check the bottle.  The front seems to return at a normal rate when compressed, I'll give it the above mentioned test once I get home.

I'm not sure of the level, is there a general guideline?  I just made sure it matched in both forks ~

JM
 

[fasterblkduc]

Ahh...now we're getting somewhere. Yes, oil level is critical. It sounds like you went way over and are getting it closer to where it needs to be now.
10W may be too thick too.
Whose springs did you buy, and what rate are they? I'm asking because I can find my set up notes if we are close in weight.
Otherwise, if you have Racetech springs, they have a great tech. support line that you can call to get the correct oil level, weight, preload, etc. for your situation. Just explain what the problem is, and where your settings are currently.

[the_Journeyman]

My springs were picked up off ebay, part of a Hyperpro front & rear springs & oil package.  I weigh in about 170 w/o gear. never stepped on a scale with my gear.  Not even sure what the rate on the springs are.  They were made for a Monster 900 though.  They are stiffer than the stock springs ~

JM

[Slide Panda]

10 w is probably too much.  From what I've gathered most folks use 5-7.5 depending.

The oil in conjunction with the valves does the damping.  Say you're trying to wade though some water (lighter oil) the water will slow your progress some.  But if you swap in mud for the water (heavy oil) your progress is slowed or even halted.

So too heavy an oil can make the forks seem too hard since they won't budge when you hit a bump in the road that requires a high speed damping effect. 

Getting suspension right's an art.  Though I understand the theory of it... I'm going to let someone else mess with it.

[clubhousemotorsports]

I do believe the hyperpro kits are a progressive spring kit .

[ducpainter]

I do believe the hyperpro kits are a progressive spring kit .

I believe you are right.

[the_Journeyman]

I got a rear tire today, I'll let you know how the bike feels tomorrow.  If it still feels like I've got bricks in my forks, I'll drop a weight in oil and try again ~

JM