Springs or oil height

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#1
What would be the difference in feel between heavier springs or a higher oil height? I know oil height affects the last 1/3 or so of travel, but a spring also gets stiffer as it moves through the travel. I put some heavier springs (.44 to .46)in my 04 YZ250 and it does not dive enough in corners to make the front end bite like I like it. I use an o-ring around the tube and I'm getting full travel. I have mixed rates before (.44+.46 makes .45) and have not had any problems, but I wonder if a lower oil height with the .46's or higher with the .45's might do the trick. Any suggestions?
 

marcusgunby

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#2
A spring actually doesnt get stiffer as it compresses-if it takes 0.44 kg to compress it 1mm-it only takes 0.44kg to compress it another 1mm.its a straight rate.Thats the difference.The fork springs set the ride height really.The airspring,fork spring and damping all control bottoming.I would go back to 0.44s unless you are heavy and then fine tune airgap for bottoming.
 
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#3
You said the same thing I said in a different way. Use for example a 25lb per inch spring. It takes 25lbs for the 1st inch 50lbs for the second inch and so on. So even a straight rate spring is somewhat progressive in nature. The rate does not change, just the force to move it a further distance in the travel. (250lbs to move it 10 inches) I know this is not near as progressive as the air space though. I am heavy (225 lbs) and the spring rate calculators call for .46 or .47, but I ride a little farther back on the seat than I should at times and did not get the dive in the corners to make the front wheel bite. Do you still think I should do the .44s with my weight or try something different? Thanks, Mike
 

marcusgunby

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#4
I understand you completely.Not to split hairs but you are describing a straight rate-a progressive would be 0.44kg for the 1st mm, 0.45kg for the 2nd mm etc.Important to get our terms correct of we get lost easily:)
for your weight i think the 0.46 is right-the problem you are having is classic YZ-front feels stiff initially and doesnt bite, then as you jump it blows through the stroke and bottoms-worst of both worlds im afraid.

 

did i say revalve?????suspension shops must love the yzs???
 
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#5
Thanks, I was thinking I might have to do that, but wanted to try a few things first. This 04 is much better than my 03, but still leaves a lot to be desired. Mike
 

marcusgunby

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#6
Yes ive heard the 04 is much more rideable.They went to a 2 stage base valve and that helped.I dont understand yamaha-they have a larger cartridge size than the others-but due to that the shims distort easily-so they make the midvalve with a thick plate to stop overstressing of the shims-then they add lots of lift to really make sure the shims dont bend-so you have a checkplate(read RT type mid)mid design that has lots of shims that dont bend much-can anyone else see why they do this????its almost like admitting the big cartridge was a bad idea but they stick with it??
 

bclapham

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#7
Marcus: whats your opinion on the 01 and earlier yz forks? they didnt have that kind of check plate on the piston like the newer ones. I am hoping to get back onto the yz again in a few weeks and i have a feeling that its going to be a shocker after riding the rm, i dont think the low lift really worked on my yz forks, just like when i got too many shims on the mid on the rm forks.
 

marcusgunby

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#8
The main thing i hate is heating the cartridge(or whacking it with a hammer) to get them apart-i dont mind shims warping after a time as forks need to be serviced like a engine,if they neglect this then they get a bad handling bike.