by Gary Jaehne
BASELINE ZRX SUSPENSION SETTINGS (Smoother Ride!)
Having been deeply involved in the suspension game for the last year, since I started teaching free motorcycle suspension seminars here in the San Francisco Bay Area, I've had a lot of experience with helping people optimize their own bikes. Much of my experience on suspension setup has come firsthand, during my road racing efforts that have spanned the last nine years.
The one issue that should always be noted up front, when passing on suspension settings from one person's bike to another, is that the weight of the rider is a big variable in determining the "ideal" settings. In other words, what works for a 160 pound rider will not work verbatim for a 200 pound rider, despite being the same bike. I'll share with you my settings, but take into consideration that my body weight is about 175 pounds, so at least the shock and fork "preload" settings will have to be adjusted up or down, according to your weight, from that baseline. I suspect that the "compression" and "rebound" settings I've mentioned will be pretty close to a perfect starting point, regardless of your weight.
SHOCKS: Compression: "2" setting / Rebound: "IIII" setting/ Preload 2nd softest ramp setting (this Preload was based on achieving 1" of measured "rider sag", with my 175 lbs. aboard. If you weigh more or less, go stiffer or softer accordingly: about 25 lbs. = 1 step position change)
FORKS: Compression: "MINIMUM" (fully counter-clockwise) / Rebound: 1 click out from "Maximum" (fully clockwise till lightly seated, then one click out) / Preload: 4 lines showing (1.5" of measured "rider sag", again with my 175 lbs. Aboard ... adjust up or down from there, based upon your own weight difference: each 25 lbs difference = 1 additional line up or down)
These settings, especially reducing the front fork "compression" to minimum, and nearly maxing out the "rebound", really transformed the bike's handling! The "knock the fillings out of the teeth" feeling that I felt on my first ride with the factory settings has now disappeared.
I hope that this info will be a good starting point for you and others in the group who want to optimize suspension setup.
For comparison, here are the settings the crew at Sport Rider arrived at:
FRONT: Preload: 3 lines showing; Rebound damping: 1 click out from maximum;
Compression damping: 5 clicks out from maximum.
REAR: Preload: position 2; Rebound damping: position 2; Compression damping: position 2.
Suspension lessons from Doug Polen/Dan Kyle
Here's some of the suspension things we learned from Doug Polen, Dan Kyle, and the Ohlins
reps at VIR last weekend.
Dan spent Sunday afternoon in the hotel parking lot suspension tuning any bike that rolled in front of him. He's the #1 Ohlins dealer and makes a ton of parts for several bikes and a well known suspension guru. You rolled your bike up and he took measurements of full droop, bike only sag, bike+rider sag. He'd then set preload to get the #'s he wanted. Get this: 26-30 mm rear rider sag, 36-40 mm (!!) front rider sag. Then he jounced each end and watched/felt the compression/rebound damping and speed. Clicks on the adjusters till he got what he wanted. If the clickers didn't get it, you needed a different spring. Period. Otherwise he got as close as he could. I rolled up with not quite 15mm in front and about 25mm in back. He left the back pretty much alone (Ohlins) and had me take out 3 (!) lines of preload (1.0 RT spring & gold valves). I was aghast and didn't know if I believed him. So he bet me $1 on asking the Ohlins reps when they arrived what they used/recommended. I lost the buck not once, but twice, because I asked Doug as well. He runs 28 rear, 36-38 front.
Suspension performance is entirely about geometry, spring rates, damping characteristics in that order.
The amount of trail the front end has is critical. Optimum for a track is somewhere between 90-100mm. The supersport, superstock guys are constantly trying to alter this # without breaking the rules (can't change the steering stem). You get too little trail and the bike is unstable at speed but will turn like nobody's business. Too much and it's stable but won't turn. Stock ZRX has about 104mm of trail. My trail is about 98. You can reduce trail by raising the rear (flipping eccentrics) or raising the fork tubes (lowering the front), changing the triple trees to a different rake (more rake = less trail).
Spring rates are determined both statically sitting in the paddock and dynamically out on the track. They get close and then ride it. The good riders know the difference between a too soft rear spring and an under damped shock. And after they get it close it's test/test/test to find something better. For the most part, spring rate is a function of overall weight, the geometry that distributes it, and the forces applied to the dynamic package. In the dry you're putting a lot more force into bike so stiffer setup, in the wet the forces are greatly reduced so you need a much softer setup. Sag is a static indicator of correct spring rates and actual performance requirements fine tune it.
Ideally, you want sag to be at the top 1/3 of the available travel so if you have 100 mm of travel, 33 mm of sag is a good starting point.
Damping settings (compression/rebound) are dealing with the speed that the system travels in each direction. Too much compression and the fork is slow on the down stroke, too little and it's too fast. Duh. Rebound is the up stroke, same tuning. Slow forks are stiff. Fast forks are soft. Dial out damping for the wet, dial it in for dry. If you reach the add limit of an adjustment, your spring is too soft. Reach the subtract limit, too stiff.
Doug said there's not a whole lot of changes between tracks to the basic setup. Once the bike is setup right, it's just right and it's not going to get any better. Unless the tire compounds change or the geometry is altered the bike is as good as it's going to be. During the '91 season on the Duc, they found the setup before the season started. Stumbled on it. And then didn't change it more than 2 clicks in either direction for specific tracks the _entire_ season. Mladin at Fontana... stumbled across a setup that was 2 seconds (!!) faster than the field during testing. By the race the rest of them had only found 1 second and Matt ran away and hid. These guys find these setups by trying all kinds of things. Ride height, trail, spring rates, swingarm angle, shock links, damping rates. They try them all and keep track of what works and what doesn't.
Here's another suspension article from http://www.gostar-racing.com/ - How I Setup My Motorbike? (opens in a new window. Need Acrobat PDF reader to view)
Suspension tuning courtesy of Sport Rider - http://www.sportrider.com/tech/suspension/