This is an update to
my other FastAce fork thread of 8/17/15 (I've left out the disassembly info here, as it's all over there). The 18-23 lb/in springs and 3W oil installed at that time were working well, but after the springs bedded in the sag was excessive (32mm static, 67mm 'race') & reduced the effective fork rake & available impact travel, which these forks can ill afford to lose. Zero claims they're 9" travel, but that's including the full length of the bottoming cone - which on these forks never gets used unless you're doing front flips - and some of the top-out spring too. The metal-to-metal limit is 8.45" / 215mm from top-out spring contact to cone bottom, and actual real-world travel is more like 7.5" / 190mm. The plan now is to shorten & reshape the bottoming cones, & add 6mm soft-nylon bottoming washers as insurance.
The new springs (again from
Cannon Racecraft) are 19.0 - 24.0 lb/in (0.34 - .43 kg/mm, 5% stiffer each rate) progressive with the soft/hard 'knee' at 3.0" / 75mm (15mm sooner), and overall length is 16.75" / 425mm (5mm longer, for more preload). A 4mm spacer is also used, for a total of 9mm preload; it's a little much right now, but should be perfect later (we'll see). The other specs were unchanged: O.D. 1.46" / 37mm, I.D. 1.10" / 28mm, wire O.D. .171"/ 4.3mm. Sag is now 24mm static / 44mm race, and if this set is like the first one, this should settle in to about 25S / 50R in a few months. The Cannon P/N for these springs is 37425 .34-.43, but you'll have to specify the 76mm knee point.
Here's a photo of the old and new springs (top spring is the one that came out, new one on the bottom):
The oil situation is very different from last time. I'm now using 420cc per leg (up from 400cc), a blend of 340cc Red Line LikeWater suspension fluid (5.50 cSt @ 40° C, half as thick as the Bel-Ray 3W used last time) and 80cc of Tri-Flow PTFE (Teflon) liquid lubricant. I also coated the springs with Tri Flow, and used Finish Line Stanchion Fluoro Oil on the outside of the sliders. The springs have yet to break in, but the fork still feels slick and will only get better with time. NOTE: like most older-design USD forks, the upper tubes are
not hard-anodized and the springs rub against them pretty good; both the OEM and Bel-Ray oil had a fair amount of fine aluminum dust in it. I was a little surprised that only 370cc of oil came out, when 400cc went in 4 months ago. This is a closed, non-leaking system; where did that 30cc go? It sure didn't spray out the bleeders.
I've got four rides on this setup, and the changes are interesting. Impact absorption & deflection off rocks seems unchanged, though the stiffer springs transmit a bit more shock to the bars (this should change; the first set of springs got noticeably softer after a while). The fork stays more extended on average & the bike feels more stable; before it had good stability under acceleration / OK while coasting / a little squirrely under hard braking, now it feels very good / good / OK under the same conditions. The front end also feels lighter. As expected, with the front stiffer the rear felt too soft, so I increased preload 4mm back there, bringing the rear sag to 32mm static / 88mm race, IMO very good numbers for a 9"-travel rear end w/progressive spring.
The new super-thin fork oil gave me a few clicks of adjustment to play with, but as before, results were not great and I ended up back at 0 clicks rebound damping (although 1 click was also OK if the bumps were spaced farther apart). It seems the rebound clicker affects both rebound and (to a lesser degree) compression over a medium-wide range, while the compression adjuster mainly affects compression over a much narrower range. I think the rebound shim stack in these forks is set up much too stiff, meaning that most of the low-mid velocity rebound damping takes place in the bidirectional clicker circuit, which is
not how it should work. Normally the clickers are adjustable bypasses that kind of 'dilute' the effect of the stacks, as a fine-tuning measure. On these forks the first few CW clicks of rebound damping (starting from full CCW / 'soft') greatly restrict the clicker flow to redirect oil through the stack - which is fine if the stack is set up OK - but since the stack is like a brick wall in these forks, the rebound damping goes through the roof & the fork is still trying to recover when the next bump hits it. The compression stack is a lot better, as the fork is very responsive to bumps at all speeds and resists deflection quite well. I'm still playing with compression settings at this point.
I'm also using the
Outlaw Racing M5x0.8 air bleeders, which work really well and are black/silver instead of electric blue or orange.
It's
critical to use these during sag testing, as you need to know what the springs alone are doing, as well as the spring/air combination.
Ray
Author
Topic: FastAce fork oil change / spring replacement, part 2 (Read 5005 times)