2000 CR250 suspension tuning questions


James

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First, I have read all of the threads here about shims, check valves, mid valves, gold valves, etc. etc. (so please don't tell me to do a search) I have bought the Race Tech kits, watched the videos, and studied the shim charts, so I have a general idea of how to adjust a stack and what each part does.

I weigh 240 lbs, ride motocross at the beginner/intermediate level, and plan to jump some big stuff (if I'm not already). I have .46 fork springs and a 5.4 shock. Forks and Shock have recently been serviced and have stock valving. Fork oil level is at maximum for the spring (400cc I believe). All is in good condition, properly installed, not binding, linkage is lubed. The clickers are in the stock position and I prefer not to change them unless that is the BEST solution to my situation. Race sag is set at 3.75 inches.

My goal is to get a smoother ride on the choppy stuff so my hands don't go numb and my arms and shoulders don't hurt from the pounding. I also feel like the bike bottoms too easily over larger jumps. I would like to adjust this myself so I can do it quickly and know what is going on. The reason I am asking this question is that I would like to eliminate AS MUCH trial and error as possible. I am also quite interested in this for educational purposes and I am going to do it myself either way...so I'm not just trying to get a handout, just some guidance.

For the shock: I assume I should install the Race Tech kit as instructed since there isn't a mid-valve variable.

What is the best solution for the forks:

1. Install Race Tech kit and eliminate mid-valve (what I read would suggest no and I think I would like to keep it)
2. Stiffen the mid-valve and/or adjust the float?
3. Install the Race-Tech kit at a lesser stiffness and leave midvalve stock (I don't have a clue about compensating for leaving the mid-valve in on Race Techs chart - they wouldn't tell me)
4. Adjust portions of the stock base valve (less low speed, more high speed)
5. Can the oil level go higher?
6. Some combination of above or your suggestions?
 
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marcusgunby

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If i was you i would do excatly what the instructions say-the reason being a fork with a checkplate and well set up will be worlds better than a midvalve fork thats badly valved.Race tech can then guide you to get better settings if need be.

I have looked at gold valve stuff and cannot compare it to any of my settings, as the valve has the ports at different spacing to std.
If you leave the midvalve in very few people will be able to help with such a combination.

Are you sure those springs are stiff enough?
 

James

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They are the closest without going over to the recommended spring on the race-tech site. I read where Jeremy said that they are finding you get a better over-all ride with slightly softer springs and the appropriate damping as opposed to stiffer springs than needed.

I intend on working on it til I get it right...as I said..learning experience. Also, I don't want to be guilty of "castrating" my forks as John C puts it...so I am hoping to keep the mid-valve.

Based on all of the previous threads I read, I am making these assumptions:

1. the stock valve flows pretty much the same as the race tech valve
2. Need to increase mid-valve damping to reduce bottoming since about 75%0f the fluid flows through it.
3. Increase the low speed damping to also aid in bottoming resistance
4. Maybe reduce high speed damping to help with harshness.

Just trying to see if I'm on the right track
 

marcusgunby

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When you say increase or decrease damping the problem is how to compare a 21mm shim?(i think the gold valve uses these) strength to a std shim.The flow of the ports is proportional to the strength of the stack needed to control the flow-so a high flow piston will need more shims to control the damping.
 

James

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Well, let's get rid of the GoldValve variable for a second and say on the STOCK Piston and Valving that is set up for whatever weight rider it was, to get the result I am after (much improved bottoming resistance and less harsh on the low stuff), are these assumptions correct:


1. Need to increase mid-valve damping to reduce bottoming since about 75% of the fluid flows through it.
2. Increase the low speed damping to also aid in bottoming resistance
3. Maybe reduce high speed damping to help with harshness.
4. Assume oil level is at maximum (because I think it is)
 

marcusgunby

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Now James i like the way you are thinking-eliminate as many variables as possible.

I would reduce midvalve lift as a 1st step so it comes onto play earlier-then it has more chance to do its job.Remember suspension is meant to bottom once every lap on the hardest landing.

Low speed i would think needs to be increased.
As for decreasing High speed-i would leave for now as 3 changes to a fork is alot.
 

tankslapper

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Decreasing the float on the midvalve will bring midvalve stack into play earlier and may increase bottoming resistance but if you also stiffen midvalve stack up it may also increase mid-stroke harshness, also making midvalve stack work at lower shaft speeds may also make small choppy bumps feel even worse and increase arm fatigue, do you agree? also goldvalves I think are even higher flow than stock valves and need even heavier valving than stock possibly making the forks feel even harsher!
 

marcusgunby

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Tankslapper the gold valves do have large ports but installing a stiffer stack to compensate will not necessirly make them worse.If you install gold valves with a stifffer stack you will end up with a similar set up to std.I have found generally valving the type of piston you have is more important than if its low of high flow.Both can work really well if valved correctly.

When we are talking midvalve float it all depends on how much float we are talking about-decreasing to 0.5mm of lift on a softish stack shouldnt produce arm pump.
I think midvalve lift should be used more to tailor for rider speed and keep the base valve the same-any thoughts?
 

JTT

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Not sure about that Marcus, I had played some with float, but needed changes to the basevalve to get things close. My limited experience with midvalve lift is that the changes are more subtle and limited in range, compared to the basevalve, which will allow you room for large changes (if necessary). This, is in referance to Twin Chambers of the vintage we are speaking anyways.
 

tankslapper

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JTT, I would agree about the basevalve having considerable effect as I mainly alter the midvalve if the forks feel harsh after modifying the basevalve stack first
 

marcusgunby

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Yes i like the way this is going,now assuming we have a good base valve stack that works for a average weight rider in mx.We now have a faster rider weighing the same and riding mx-do we
make the LSC damping stiffer on Base valve
make midvalve stiffer
make midvalve stiffer and lower lift
do all of the above.
Alter HSC as well?
Set air gap smaller and do none of the above.
please discuss:)
 

James

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Actually, I was hoping to keep it on the topic of the heavier than average rider described above, with the specific goals mentioned, and keeping in mind that he might not be so fast :D.

So tankslapper, back to an earlier question of mine.....If I want to leave the midvalve in with the RaceTech piston and valve assembly, based on your comments, it would be best to try and get close to desired performance on the basevalve and then address harshness with the midvalve. In a simplistic situation.....if the basevalve was satisfactory and the forks were performing as desired EXCEPT for the harshness, how would you address this in the midvalve???
 
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tankslapper

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marcus, in reply to your comments, for a faster rider I would make adjustments first to the basevalve stack probably stiffening up the HS part of the stack first and perhaps setting a smaller air gap and/or fitting stiffer springs hoping to retain the LS pickup and plushness on the smaller choppier bumps. I would then let the rider try the bike without modifying the midvalve and see his reaction. If he felt it was blowing through the stroke too quickly or felt harsh I would thn alter midvalve float or stack depending on what he was experiencing, but may also make small alterations to his airgap or springrates too. It is a difficult to say exactly what the order would be as it would it depend on the rider's comments or watching the bike turn, jump etc.

James, in reply to your comments I have had little experience with Race Tech gold valves but as they recommend disabling the midvalve when using their basevalve this must be for a reason. I would have thought when using their gold valves and a heavy stack and leaving the midvalve stack in, the forks may feel very harsh but I have never really experimented with them.
 

JTT

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Marcus, my initial reaction would be to slightly increase the midvalve and lower lift, assuming the riders are very much alike in their stype and preferances...all this is dependant on the rider personal preferance though, as I personally find that this is the single biggest obstacle in many cases. If he/she was experiencing mild bottoming, I might increase oil level as well.

James, as for your situation, if you are really intent on trying the midvalve with the Gold Valves, I would suggest you start with the stock settings, as you will be entering "unknown waters", then experiment from there. Remember that the "check valve" is only a extremely stiff (ie: rigid) stack with a ton of lift (making if virtually freeflowing). Harshness is one of the few things that RT people seem to never complain about, but there may be a penalty in overall performance and precision. You may need to go slightly softer on your base stack in order to use the midvalve as well, as James eluded to.
 

marcusgunby

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Sorry james for hijacking your thread.Just trying to set up a lively discussion.I would like to add to the other posters in the thread i dont have a answer to my comments -just more questions.

To try to assist James, remember the fork will just feedback a certain amount of damping to you.You cant feel if its from the base valve or the mid.You feel the total damping of the 2 combined.With that in mind you can adjust a base valve to compensate for a stiff midvalve(upto a point) and vice versa,So if you start with a std midvalve and a gold valve and build it to there specs.Ride it and then adjust the base valve to get the desired ride quality.If you have exhuasted base valve settings and its still bad then go onto the midvalve.This will eventually get you a great fork but it will take alot of work.
 


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