Edited by MG63, 22 May 2012 - 04:35 PM.
Posted 22 May 2012 - 04:33 PM
Posted 22 May 2012 - 04:58 PM
Front Static Sag should be between 5-10% of travel; Front Rider Sag should be between 25-30% of travel.
Rear Static Sag should be between 8-11% of travel; Rear Rider Sag should be between 28-31% of travel. However some, including Dwight Rudder, suggest rear rider sag as high as 33-34%. There are two ways of measuring rider sag which may explain the different recommendations:
1. With the rider seated, and
2. With the rider standing.
The latter places less rider weight on the rear suspension resulting in lower sag values than seated. The bike is most stable in rough terrain when you are standing on the pegs so I suggest that position rather than sitting when measuring rider (race) sag. Another reason for higher rear sag, and an indicator of not enough rear rider sag, is rear brake chatter on downhills.
An issue in measuring sag is friction in the suspension; one element is the resistance to begin moving, or to quickly stop moving called stiction. Stiction causes the suspension to stop moving before reaching equilibrium which creates errors when measuring. Ideally there would be no stiction in suspension but there is and here is how to mitigate suspension stiction when measuring sag.
The important thing on measuring sag is to pick measure points and have a repeatable method of measurements. I use the top of each axle or axle nut and a feature on the frame. So pick a reference point on the front and rear that will be easy for a helper to use when measuring to the axle. My wife is my helper and I use a brake hose guide on the front and a seat mount boss on the rear, plus a tape that is easy for her to use and read. Put the bike on a stand and have your helper measure each axle from its reference point. Drop the bike off the stand.
Push each end down an inch and allow the spring to push the bike back up, have your helper measure and record.
Lift each end of the bike an inch and allow it to settle, measure and record. Average the two measurements from each end and subtract from the fully extended measurements; this is static sag. The reason to do two measurements on each end is because of stiction in the suspension, this averages the two measurements from up stiction and down stiction to yield true sag.
Now the hard part: I do the riding sag in a standing position because I stand when encountering rough terrain. I place the bike next to a wall that I can easily touch to keep the bike vertical. My helper then repeats the process for static sag while I stand in a riding position and keep the bike vertical. Do the arithmetic again and you have riding sag.
Now the hardest part; deciding what to do with the numbers. Any adjustments in spring preload will change both static and rider sag. For fork springs I use 1” PVC tubing that I cut with a trim saw for square ends. The rear shock spring has an adjustment nut but sometimes it is difficult to turn. I spray dry lube with Teflon on the threads and the spring collars. First step is to loosen the jam nut; I use a long drift and a hammer to knock the jam nut loose. One method to turn the adjusting nut is to grip the spring with two hands and turn it; sometimes the nut will turn with the spring. Second is to use a spring nut spanner wrench. Progressive Suspension calls theirs a Spring Preload Wrench. I use a Motion Pro #08-0029 “Honda Shock Spanner Wrench”. But I had to use a grinder to remove metal from the outside of the arch so the spanner would fit between the air box and the shock. The other option is to remove the shock.
If rider sag is less than spec with the correct static sag, your spring is probably too stiff for your riding weight. If rider sag is more than spec with the correct static sag, your spring is probably too soft for your riding weight. I used the word “probably” in the previous two sentences because static and rider sag each have a range of values making determining spring rates somewhat subjective.
Posted 22 May 2012 - 09:21 PM
With proper springs, your rider sag should be 50-60mm up front and in the rear @ 75mm. This should get you in the ball park.
You could try putting spacers in the forks to lower the sag number to 50-60mm, but since you already
have the emulator, the max size spacer should not exceed 3/4" thick. a 3/4" spacer plus the emulator adds up to
1-1/2" total spacer, which when used with the spring inside the fork tube, will bind up all the closely spaced coils of the spring on one end, thus cancelling all the progressiveness of the progressive rate spring and turns it into a straight rate spring.
If you go with too much spacer, then you get dangerously close to binding the coil springs before the forks fully compress, and you
could wind up breaking something.
How much do you weigh?
Posted 23 May 2012 - 07:36 AM
Good stuff here, guys. That's what I was looking for. I weigh right at 180 lbs. with all my gear and tools. Will recheck my measurements using these figures, but it looks like it's new springs for me! THANK YOU, TWO!
Posted 27 May 2012 - 04:24 AM
- Front: 22%-25% race sag (CRF230F = 2.02"-2.38")
- Rear: 30%-33% race sag (CRF230F = 2.70"-3.00")
- Both: 1" of static sag
I'd be willing to bet MX setups use far less race sag but I'm not sure. Be careful with spring spacers. I tried them and they made the front end very harsh. After numerous conversations with John Hlebo and Bruce Triplett they both advised I ditch the spacers and use one BBR spring. They were right - The harshness disappeared with a heavier spring and no spacers. With the RT Emulators I use two stock springs and the race sag is dead on.
If you change a sag setting be sure to change the other accordingly. For instance: My buddy likes his 230 a bit closer to the ground so he uses 3.25" in the back (36%). It just so happened his front sag with two stock springs an RT Emulators was a little over 2-1/2" (27%) so it worked out just right. You need to keep the two numbers in sync to keep the bike's geometry correct.
As far as heavier springs... John Hlebo said he uses the stock shock spring for riders up to 200 pounds. My buddy weighs 190+ and his Hlebo shock is just fine with the stock spring, as is his forks. John advises against a heavier spring unless you are 220 pounds+. Only the static sag will tell you if you need heavier springs. My buddy and I are very good riders and ride very hard. We both use stock fork springs and the forks only bottom in the very worst situations and even then it's usually just a tap.
Edited by VortecCPI, 27 May 2012 - 04:42 AM.
Posted 27 May 2012 - 10:39 AM
Posted 27 May 2012 - 11:28 AM
I drilled the damper rods on my wife's CRF100F after many discussions with my engineering partner and John Hlebo and Bruce Triplett and they are now 100% better. The front tire sticks to the ground and you can plow over roots and rocks without worries, The rebound is still a tad too fast for me but my wife is now safe and satisfied. It is amazing what a difference the right fork oil and a few holes in the right places makes. She used to fight the bike and now she just steers without worries. The stock shock is still a mess but it's the front end that always got her into trouble. I rode the bike over a brick fire pit over and over when I was done and the front end just ate it up. I would have been thrown off the bike or over the bars when it was stock. Simply amazing.
I just rode my buddy's kid's CRF150F around a few times and the forks are terrible. I got beat up badly over every root and rock I hit and the front end wanders around with poor traction. I'm going to give the damper rods in that bike the treatment too in a few days. I'm nowhere near as good as John or Bruce (and never will be) but I can make DR forks a lot better. My wife and I were both amazed at the difference in her CRF100F so I'm going to keep on experimenting. I may also do my buddy's F650GS BMW forks.
Edited by VortecCPI, 27 May 2012 - 11:43 AM.
Posted 28 May 2012 - 05:15 AM
I added the RT emulators about 6 month ago with 1 BBR spring and came out with Vortec's suggested numbers - race sag is 2 1/4 and static sag is 1".
BTW, with the original springs I had 2 7/8" race sag and 1 3/4 static sag. Handling is much improved over logs and sharp edges.