I, like many of you, am very interested in getting the most out of our somewhat featureless suspensions without changing hardware. We have rear preload and front fork height. Thats it. I spent the last few days reading and watching as much as I could to dial in a base setting that I could use as a launch point for myself. Dave Moss Tuning had excellent resources. The first stop for me was setting an appropriate sag front and rear. From DMT and others I gleaned that 35-45mm front and rear is a good setting for average use, 25-35 for track use, and anything under 25 or over 45 is borderline dangerous. At 190lbs I determined that setting 5 on the rear preload got me to 40mm sag. We're limited by having set preload levels on the castle nut, so thats as close as I could get to my 35mm sag goal. The front forks sat at 33mm without adjustment. I wanted to even the rear and front as much as possible and this is when I realized how much the fork height geometry really helps us budget suspension owners. The stock forks come set at 6mm from tree to cap. By increasing that gap to 10mm, I was able to effectively shift the weight forward and even my sag out to 35mm/35mm front and rear with 2-3mm given or taken with a tape measure. Next I'll be measuring out the gap between my average "bottom" on the front forks while riding with the actual mechanical bottom-out of the forks. DMT recommends a 20-30mm gap. This measurement will inform me of whether or not I need to move to a heavier fork oil from our stock 10wt. I'll post my results and pictures at a later time if anyone is interested.
Setting Sag Research
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Update: Big difference. Turn-in is smoother. The bike now seems to "anticipate" turns as I shift my eyes and weight, and feels comparatively like its turning itself. U-turns at full lockout are easier. The front end diving during engine-breaking is less in 1st gear and all but gone in the rest. This gives the effect of making the slow down with engine breaking feel more controlled. I'm no longer sliding my crotch into the tank which seems counter intuitive because i lowered the front end. My guess is that my hips are in a more natural position, and so I'm sliding forward less when i shift positions on the bike or hit a bump.
Bad news: My bottom out test left me at 22mm from bottom out under "normal" riding conditions. Thats just above DMT's danger range. I did an emergency breaking test and was easily able to bottom out doing a hard brake from 15 mph. Dave Moss recommended the geometry and preload changes Ive already done, plus a change to 20wt fork oil for the Z650 specifically in the comments of one of his videos. Thats going to be my next step when I have the time and patience and it should correct the bottom out issue.
Bad news: My bottom out test left me at 22mm from bottom out under "normal" riding conditions. Thats just above DMT's danger range. I did an emergency breaking test and was easily able to bottom out doing a hard brake from 15 mph. Dave Moss recommended the geometry and preload changes Ive already done, plus a change to 20wt fork oil for the Z650 specifically in the comments of one of his videos. Thats going to be my next step when I have the time and patience and it should correct the bottom out issue.
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Any update on new fork oil being better? Intrigued by the geometry change, but I wonder if thicker oil without the geometry change up front would be just as effective. I have andreani cartridges on order, and am interested to see how much of a difference those make and if end up needing to adjust fork height.
I just ordered 20w fork oil to change it out. I'm a big dude, and I even sent Dave Moss an email and he suggested that I replace the fork oil with 20W. Guy is pretty cool, he took the time to write back to me. Suggested the most pressing issue, after changing out the fork oil, is the rear shock. At my 235lbs, he said that will quickly become an issue as I get better and better.
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