Can anyone tell me what we did wrong?
Posted December 13, 2011 - 10:01 AM
Posted December 13, 2011 - 10:09 AM
Posted December 13, 2011 - 11:29 AM
Has he ridden the bike ? Did the rebound feel too fast then, or like gray said was this a test in the garage ? With heavier springs, the forks will rebound faster and you'll more than likely need to run with more rebound (fewer clicks counter-clockwise from being bottomed out).
Where are you with your 6 clicks ? Do you mean you've turned it 6 clicks counter-clockwise after you've turned the adjuster clockwise as far as it will go ? Or are you starting with the adjuster backed out all the way (maxed out counter-clockwise) and turning it in 6 clicks ? Or do you mean that you put it back to the old setting, turned it clockwise 6 more clicks and it's still too fast ?
We need a little more info...
Posted December 13, 2011 - 01:14 PM
Posted December 13, 2011 - 02:16 PM
The standard setting for my '09 is 12 out (12 clicks counter-clockwise), I run my bike at 9 out. What I've done before (although I'm not proud to admit it) is before I've started taking my forks apart I'll record all of my comp/reb. settings, then when I'm done servicing I'll set the clickers back to where I'd initially had them... most of the time.
I have on one occasion, forgot to set the clickers after I've finished working on the forks/shock. It'd be a good idea to go over all of the settings on the forks and on the shock.
Here are MXA's fork/shock settings :
Spring rate: 0.47 kg/mm
Oil height: 350cc
Compression: 12 clicks out
Rebound: 12 clicks out
Fork leg height: 5mm up
Notes: The stock oil height is 350cc, but if you feel that the forks are too soft in the second half of the stroke, add 5cc of oil to each leg. Kayaba’s SSS forks are very sensitive to oil height changes and 5cc makes a big difference.
Spring rate: 5.5 kg/mm
Race sag: 100mm
High-compression: 1-1/2 turns out
Low-compression: 11 clicks out
Rebound: Ten clicks out (12 clicks stock)
Notes: Riders who weigh over 200 pounds should consider stepping up to a 5.7 shock spring. On the high-speed compression, make small (about 1/8th turn) adjustments to the dial to adjust the attitude of the chassis at speed. Yamaha’s high-speed compression clicker is very sensitive.
Posted December 13, 2011 - 02:34 PM
Posted December 14, 2011 - 10:28 AM
Thanks a lot for the help!!
Let us know if any of this made a difference...
Posted December 14, 2011 - 02:54 PM
Posted December 14, 2011 - 03:01 PM
With heavier springs, the forks will rebound faster and you'll more than likely need to run with more rebound (fewer clicks counter-clockwise from being bottomed out).
If you add stiffer springs, you make the stock Rebound less effective. You have to go more clockwise. Usually, changing springs requires changing shim stacks.
I run heavier springs in my '09 but have left the shim stack alone, I'm sure it would help but like you've said running with slower rebound should compensate for the new springs. I'd change the shim stack(s) myself if I wanted to spend the time testing/tuning... don't really have that desire though.
Posted December 14, 2011 - 04:37 PM
Posted December 14, 2011 - 09:32 PM
So, a reasonable change but I was no where from maxing out my rebound with the aftermarket springs. I may have gone in 2 clicks max from where I had the rebound set (both ends) with the stock springs in the bike.
I had 7 Honda's before my first '09 yz450f, I just sold that one and bought another new '09 - was starting to get a few hours on the old one and thought I'd freshen up with a new bike. Anyway, I guess it's pretty obvious that I'm happy with the yz's !
Posted December 14, 2011 - 10:43 PM
It's also important to remember two more things:
First, the mid valve is a part of the total compression damping, so tightening the rebound adjuster reduces only a part of the total compression bleed.
The other thing is that the resistance to oil flow of the rebound valve is far greater than that of the mid valve, so changes to the bleeds affect the rebound more than the mid.
The statement regarding heavier springs vs. rebound is only true if the rider weight remains constant. A bike set for the right rebound rate with light springs would need more rebound damping if the springs were changed to stiffer ones, but a bike that ran, say, 10 out on rebound with a 180 pound rider would set up at about that same point when resprung for a 220 pound rider once that rider was aboard. Rebound damping works against the uncoiling spring, but also against the weight of the rider, so as long as the springs match the heavier rider's weight at the same proportion that the old springs matched the lighter one, not much will change.
Posted December 15, 2011 - 07:45 AM
On a YZ450 fork, the rebound adjuster has some effect on compression because the same bleed circuit is used on the mid valve, which is a part of the compression damping in that fork. The compression adjuster, however, has no direct effect at all on rebound, as it bleeds the base valve, which has no rebound functionality.
So...If you increase the compression dampening with the clickers on your forks....does it also INCREASE the rebound, or DECREASE the rebound? This may be obvious to those that understand the physics behind what's going on inside, but to a schmuck, it seems to be an obvious question...Same question on the rear shock: Increasing the rebound is also said to "affect" the compression....how does it affect the compression, and does it affect BOTH high speed and low speed compression..?
Posted December 15, 2011 - 02:07 PM
With any of the adjusters, what they actually do is to control the size of an oil circuit that allows oil to bypass the valve they are connected with. The effect is that as this circuit is opened up by backing out the adjuster needles, the valve assembly can move at a faster speed before there is enough pressure to lift the shim stack and open the ports in the piston. Once that point has been reached, the bypass controlled by the adjuster very quickly becomes almost or completely ineffective. In fact, as the speed of the shaft is increased, the oil velocity through the bypass will eventually reach a maximum, and if the oil pressure is significantly increased beyond that point, the circuit will "lock up" hydraulically, somewhat like a traffic jam, and the flow will be reduced dramatically, handing off the excess to the valving.
In the KYB fork, there is one rebound and one compression adjuster. To the extent that they control any particular valve, these influence both the high and low speed elements of the stack. It's probably true that the clickers on the fork have more effect on the low speed operation than on the high speed because of the locking phenomena just mentioned, and because the major effect of the clickers is to delay the operation of the valve stack. The higher speed elements of the stack will be less affected.
The rebound in the KYB shock will effect both low and high speed elements of the rebound and main compression stack. The shock low speed compression adjuster has a very minor influence on high speed compression, while the high speed adjuster has virtually no influence on low speed.
Also remember that "speed" in reference to damping units refers to the speed at which the unit is being compressed or extended.
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