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My latest thoughts on damping

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Posted by: marcusgunby---------------------

Now some of the older members may have followed my ramblings from a few years back and will know when i came here i knew little of suspension other than how to change the oil.Nowdays i feel i have a understanding of suspension but no more-the compliments i get are gratefully recieved but i am only giving eductated guesses alot of the time.

So heres my thinking today.

Most(or nearly all) forks i revalve i end up with softer, or alot softer valving-now this is also using low to medium midvalve lift so its not a straight comparison.However as alot of riders complain of bottoming on std forks i struggle to see how when i lighten the valving it doesnt compromise bottoming(they dont generally complain of bottoming)so im thinking although std damping/valving  will make a fork/shock bottom less it isnt as big a difference as i would expect.So does the springs and airgap play a much bigger role as long as we have a resonable amount of damping.

 

Also do we get to a stage where more shims eg on a base valve makes little or no difference?i get the impression some std stacks must hardly open at all-and this is proved by the debris caught in the piston-its very small sometimes and yet doesnt get flushed away.I know gold valves have some incredibly stiff stacks but they have a wide piston hole so this offsets it.

The CR125 base valve(2000) is unreal stiff considering it has 3.5mm piston ports.

here it is(this is what zenith found today)

24.1(13)

22.1(2)

20.1(2)

18.1(2)

16.1

14.1

11.25

now i assume this has the typical zero lift midvalve,so what im thinking is, what would anyone do if a rider wanted it stiffer(dont assume im after tuning advice as no one has ever asked me this)

any ones thoughts??

 


Posted by: russ17---------------------

Marcus! I do feel that springs and the air spring do play a big part in bottoming. I too always lighten up the compression 99% of the time. But I also feel the mid comes into play as far as bottoming is concerned. I run woods set ups in my bikes and there plush but not mushy and when we ride moto's we very rarely bottom. but I am by far not a pro. Why would you want anything siffer!


Posted by: mxneagle---------------------

My first preference would be to switch to a 2 stage stack to keep the low speed about where it is while increasing the midspeed without blowing the high speed off the map. I'm not much of a fan of single stage stack for outdoor stuff. I think its feels like the forks blow through the low speed stuff and deflect on the square edges.

However, with all the discussion about the mid-valve I'm becomming more and more concerned about "diminishing returns" by simply upping the base valve stack and questioning just how much stress I'm putting on the mid-valve shims.

I'm also not abig fan of the bumper bottoming system over the bottoming cone system. I'm not really sure exactly what they are trying to achieve?


Posted by: marcusgunby---------------------

I using midvalve stacks with very little damping but low lifts and then i think it allows me to run a soft base valve.Ive tried 2 stage stacks and single stage and as long as the single stage is light and low lift i dont feel any downsides.It just confuses me more people dont hate the std setups-maybe they dont know any better?

My 03 fork is the 1st one ive had with the bumper-i havent rode it enough to form a opinion.I liked my modified Cr forks with the bottoming cones-didnt use the bladder however.Ive spoke to a few people who prefer the cones to bumpers-i will get to know how i feel on this by this seasons end.

 

Going back to the original 2000 cr fork i guess what im saying is, if we added more shims to the base and midvalve would it really increase damping much as maybe we have reached a stage where we get little increase in damping from big increases in stack strength??


Posted by: shed---------------------

I had a long and reasonably eloquent post all written out in reply to this thread. Then the connection poo'ed itself and I lost it. Damn!

Anyway the main gist of it was that I kind of agree with you about you current way of thinking regarding fork tuning. In essence I think that I want a really plush initial stroke - acheived with soft damping - but quite a high rising rate - acheived by using a small air gap. This would allow me to run much softer for more of the stroke ie over 95% of a track. The rising rate then takes care of bottoming resistance over jumps.

Why do we give up 3" of initial fork travel due to sag? Why dont we preload the springs until the suspension noticeably "tops-out" along the straights, then back the pre-load off a bit? I could then 2" more suspension travel to stop my arms gatting battered.


Posted by: bclapham---------------------

3 inches of fork sag sounds a lot to me, i thought forks should only sag between 30-50mm? i know its hard to get reproducable and precise measurements, but what would be a good approx value of fork sag?


Posted by: marcusgunby---------------------

I assume we have so much sag to keep traction in negative g situations.If we top out at all, the wheels will try lift off the ground and give up grip.Bruce cant honestly remember the ideal front sag.I think jer has it on his site.


Posted by: Onore GT---------------------

I have tried hydraulic stops vs the bumper system back to back in a KYB fork, the bumpers definately have an improved feel in your wrists, particularly under braking or other places where the fork is deep in the stoke and then suddenly the rest of the travel is used up.

A hydraulic stop can be tuned only for a certain speed the fork is compressed. If the fork is compressed faster or slower than the effective speed range, the fork will hydrolock at the top of the stop or fall through the bottoming stop, either giving you a jolt in the wrists. It is scary to hear that clack from the bumper forks when you truly do bottom hard but the feeling is no different than the fork hydrolocking with 20mm of travel left.

A combination hydralic bumper system would probably be the ticket...


Posted by: Onore GT---------------------

Shed, Along with Marcus' comment, think about the reason for suspension, is it solely to insulate the rider from bumps and maintain a comfortable ride? Not entirely, suspsension absorbs irregularities in the riding surface to maintain proper frame geometry. Every suspension tuner balances the task of maintaining frame geometry so that the bike will steer and accelerate well but still has some comfort so the bike can be ridden for a decent length of time at a good pace.

There are some old threads about contractive suspension, check them out you might find them interesting...


Posted by: JTT---------------------

Quote:
Originally posted by shed
In essence I think that I want a really plush initial stroke - acheived with soft damping - but quite a high rising rate - acheived by using a small air gap.


My only concern with this approach is you could quickly end up "mushy"...you loose that precise feel at the front end in particular. If you ever rode an XR (stock) you can understand what I am trying to get at. Feels good at low speeds, but looses control and feel at higher speeds.


Posted by: Rcannon---------------------

I hate to bug you guys about this because you are talking abotu a higher level than I understand, but here goes.

Can you feel the difference in a set of forks that are setup with stiff springs vs stiff valving?

I am asking this, I suppose. What is the best way to make forks stiffer. With valving or springs?

How might forks feel set stiff with both of these options?


Posted by: flynbryan---------------------

I'm agreeing w/JTT here on his comment. I ride HS right now and really a fan of softer valved MX settings as aposed to true offroad damping(ie: KTMexc's, Kawaski KDX's, Honda XR650r's. I just like MX based suspension in that it seems to stay up in the stroke a little better. It seems like all the offroad specific bikes I've ridden dive through the intial stroke too easily. Maybe its because I raced MX for several yrs., but I feel more confident on this type of setup.


Posted by: bclapham---------------------

Quote:
Originally posted by Rcannon
I hate to bug you guys about this because you are talking abotu a higher level than I understand, but here goes.

Can you feel the difference in a set of forks that are setup with stiff springs vs stiff valving?

I am asking this, I suppose. What is the best way to make forks stiffer. With valving or springs?

How might forks feel set stiff with both of these options?


Roland, from my limited knowledge, i think the valving will be more important than the springs when looking for stiffness. a few old threads ago, i was told the spring rate is just to keep the bike at the right level and a begginer that likes a plush ride and a pro that wants a stiff ride that weigh the same will probably use a similar spring rate.(think sag numbers, they dont differentiate for rider skill)

if you are looking for a stiffer fork, you can easilly do a "california revalve" (i came up with this term last night after taking apart some forks that has been done by a local suspension shop). It looks like all they had done was put in new spring, turned the forks upsidedown, whipped out the base valve with the impact wrench and added a few more shims! not bad for $150, i am sure with a simple computor program its easy to revalve any stock bike in this manner for a given rider weight........one would think for that much, they would have looked at the midvlave also, maybe its good enough stock?


Posted by: shed---------------------

I have an XR650r and previously 2 XR600s. None of these have been ridden at particularly high speeds, but for the average UK trail ride or enduro I like the plushness of the stroke. I understand what you are saying regarding maintaining frame geometry and keeping the bike stable at higher speeds ie reducing the forks just blowing through the stroke. I think that I would improve this with increased spring rate (theoretically this will also require an increase in damping). This will tend to reduce changes in frame geometry - increased damping will only reduce the rate of change of geometry.



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