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Compression, Rebound and Armpump
Suspension Q&A with Jeremy Wilkey

08-08-2004, 06:19 AM
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Join Date: Sep 2003
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Compression, Rebound and Armpump
Looking for some input, here is the situation.
'98 YZ250 with stock suspension
190 lbs 5'10"
Motocross track riding at Novice level
Last week I added about 10 ml of oil to the forks which were at 135mm(manual spec with compression set at 5 clicks out). At this time my sag in rear was about 105mm and I was experiencing some harsh bottoming in the front. After adding the oil the bottoming was a little better and I noticed that arm pump had increased about 5 %.
This week I set the sag to 95mm (with 17mm of free sag) and arm pump has increased dramatically. The handling of the bike seems pretty good, corners are OK and it doesn't seem squirmish on straights, maybe I'm not being critical enough?
I was going to reduce the shock compression settings from standard by 2 clicks and increase the fork rebound by 1-2 clicks. Am I heading in the right direction with this?
Thanks in advance for the input.
Craig
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08-22-2004, 04:42 PM
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Join Date: Jul 2000
Posts: 1,063
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Generally, the softer the compression damping is, the less the arm pump. Also your lessening the race sag and increasing fork bottoming resistence (by adding oil) can increase arm pump.
But really you should set the suspension correctly and then put the blame on yourself and not the bike. You are riding too tense, have poor circulation (possibly due to eating/drinking lots of dairy products), don't exercise your forearms properly, and aren't utilizing your legs properly while racing. Also your body position is not far enough over the handlebars.
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My last two bikes: '89 Honda CR250R (stock), '89 KDX200SR with PC pipe, Wiseco piston, racing CDI, 3mm longer tie rods (for MX), stiffer front springs. see http://www.geocities.com/a57ngel/moto/
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08-23-2004, 11:41 AM
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I have increased my fork rebound 2 clicks faster and reduced my shock compression 2 clicks since I posted the question and the bike feels a lot better. I may increase the compression on the shock 1 click to tighten the rear end a bit. The bike doesn't seem to turn quite as tight but its not bad, I feel I'm getting closer to a correct setup.
And yes I do blame myself, I'm 37, somewhat overweight, somewhat out of shape and probably eat way too much cheese, pizza and beef jerky. Beer is good for conditioning isn't it. I am paying close attention to riding position and am trying to correct the things I'm doing wrong.
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