Hey guys! Just got some lighter (.40kg) fork springs for my '06 WR250 and as I installed them and checked the sag in the front, I noticed that my sag numbers actually DECREASED! Per Dwight Rudder's equations I'm supposed to have around 42mm static and 75mm rider sag but I had around 35mm static and 57mm rider sag with my stock .42kg springs. Now, with my 'lighter' .40kg springs my sags are at 27mm static and 45mm rider! What gives?! After a couple hours of head scratching and possibly thinking that the springs need to be broken in to settle, I remembered that my forks have a plastic 'preload sleeve' that's around an inch long. Can I remove this to get my sags right or will the spring length in the fork be compromised and adversely affect the handling? Seems like an easy and obvious route at this point. Maybe I didn't even need softer springs in the first place! I'll experiment tomorrow but any expertise you guys could share would be greatly appreciated! Thanks
Did you notice if the new springs were the same length as the originals? When you screw the cap on the damper rod how much did the spring preload? If the new springs are slightly longer, you may be preloading them more. Due to sticktion front, sag numbers can be misleading and unreliable.
It definitely seemed like it took a little more effort to screw the cap back on but I'll check/compare the lengths this afternoon. Also, to cope with my harsh stock springs I lowered the fork oil level down to about 150mm, now that I put the softer springs in I put it up to 100mm, could this be another cause?
The oil level shouldn't effect the sag. When you screw the cap on the damper rod, the amount of threads left after contacting the spring is the amount of preload. 5-10+mm is pretty normal. If you are unsure of what oil level you want, you can start out at 135mm and add oil later through the bleed screw holes to improve bottoming resistance. On the 45 Zokes, 8cc of oil equals 10mm of oil height.
Wow, you're awesome! Great info! That makes so much more sense now. I've got it figured out now, turns out my forks weren't aligned properly and that helped my sag numbers a bit. I also set the oil level around 130mm. Now, my sags are around 39mm static and 60ish rider (I'd like them to be 42/75), I initially thought I'd have to shave down the plastic 42mm preload spacer but now what your saying is I could just back off the cap from the damper rod a couple turns? I always thought for some reason that the fork cap had to be tight against the damper rod. Thanks again for the info, you're a great help!
The cap does need to be screwed down tight. And you were right, to decrease preload the spacer needs to be cut down. Do you know how much preload you have?
Oh ok gotcha. I'm guessing I'm probably around the 5-10mm range but that's just an estimate. I hardly had to compress the spring to get the cap to thread back on to the damper rod. How much would you guess I should shave off of the spacer?
Leave the cartridge out of the fork tube install spring and cap, turn upside down and measure distance from bottom of spring to mount than add between 10 and 15mm for preload. That is the size of spacer you need to cut.
