OK - riddle me this..... (lol): everything you always read and see about suspension and spring rates has one basic premise - the right spring rate (front and rear). The theory seems to make sense - the right spring with the correct amount of pre-load will allow the bike to sag a little under its own weight (so that the bike is not topped out), and sag under the rider so that there is range of motion in both directions for the suspension to work. And while sometimes those "exact" numbers vary, there is a general premise and range (be it 5 to 10 mm under the bike's weight, and 30mm under the rider - that sort of thing). And if the numbers can't be somewhat achieved, then the spring rate is wrong. you see this in videos and stuff from Dave Moss, Suspension for Mortals from Traxxion, etc. It's everywhere. And I have never heard of whif of, "well that's only a baseline." or "well, that's true for amateurs." It's like gospel. But you see the pros actually changing spring rates, and I know someone who recently got advice on changing the spring rate. And even different rates for different tracks. Well, how then does the sag theory hold water? Shouldn't it be as simple as one spring rate gets the bike and rider into the correct range of the spring to allow range of motion in both directions? So who has anything real on this one? Chip? RM Racing? Other people who have really dealt with this?
As Dave Moss himself has said in many of those OTT videos......pre-load numbers like that are in fact only used by mere mortals such as ourselves. Pros don't deal with that because they use preload to manipulate how the bike is handling on the track. For Joe Schmoe who is not only not going anywhere near those speeds but probably couldn't tell the difference in subtle changes like that, ballpark preload #'s work just fine. Same thing with spring-rate numbers as well. Mortals use pretty standard rates for the the weight of their body and the motorcycle. Pros manipulate different rates to achieve better grip and handling characteristics for the speeds they are riding at.
The pro pros don't measure sag.....they do math. The trick is you have to be fast enough to know the difference. You have to start somewhere to know where to start. Most mortals aren't that fast, so they fall under the safe sag 'umbrella'. Most of those rules go out the window when you can actually override these settings and know it.
Interesting thread. I was in the ESP pits last weekend in Vegas. After Chris Peris won the HW Solo race he and Phil had a talk about the rear spring. I must say Chris's download on what he felt was fascinating. Phil listened and then changed the spring. I think a rider above a certain level can obviously feel much more than mortals. The guys at ESP can interpret the riders info and translate it into what the rider is looking for. For most people getting suspension close is enough....but I think the Pro's are like a tuning fork and they know when they can get more. So deviating from what is the norm...might be the norm at some tracks, and the compromise they arrive at may hurt performance in a particular spot, but might give gains in others. or...maybe it just feels good. or...I could be wrong.
Pretty much a reason I laugh my ass off when I see a street bike with a name brand forks on. But thats a whole new topic
AGREED, but the pro's also mess with the internal Compression and rebound stacks, top out springs, piston size etc etc
ok - well this makes me feel a little better. It really stems from the fact that I got a new-to-bike, and the front fork springs are too stiff according to the sag approach. But I REALLY like the feel, and am using 90% of the travel (from the zip tie). Still have compression two clicks more than halfway damped (AK-20's) - so it's not like I am not using any damping - actually added the two clicks after setting it in the middle but getting more waggle than I wanted under hard braking - the two-clicks helped it. I don't consider myself "slow", but I know I'm not "FAST". Anyway - given how I like the front end, but the sag says I'm way off on the spring rate, I was questioning all of this.
For most riders, yes. At least, that's what they settle for. What you have to consider when deviating from the "baseline" setup is what forces are at work on the motorcycle when it is in motion. Then things like mixed spring rate front ends, changing the air gap by adding or removing fork oil and things like that come into play. Two scenarios: one rider is a track day rider who weighs 225 lbs. The other rider is a front-running club racer who weighs 150 lbs. Both riders may need .95 or 1.0 springs, but for entirely different reasons. Even on the same bike, the front ends will need to be set up differently to work well for both riders, and use very different sag numbers. The most important thing is to have a reliable trackside suspension tuner you can trust who can pick the right setup for you, not just set your bike up with "by the book" numbers. The trouble with guides meant for mass consumption are that they need to be very vague and very general to appeal to the majority of riders. It's not a bad place to start, but it's also not as good as it could be because of all the variables that need to be taken into consideration. By the way, in my shop, the words "Sport Rider recommended settings" is punishable by death.
By the way, if you ever want to have an interesting conversation, talk to Greg White about what it was like to ride Ben Spies' bike at Laguna Seca (in 07, I think?). For anyone who has seen Greg, you know he's not a small dude. However, during that conversation, he used the word "stiff" a lot. You wouldn't think a bike "sprung" for Ben Spies would be too stiff for someone Greg's size, but it has to be. The difference is the pace and the forces being exerted on the suspension, not the weight.
Yup When they had that press day last year at Fontana and all the mag guys got to ride Mladin's bike they said it had 1.1 springs in the forks, and they swapped them out for 1.0 for all the testers.
I've forgotton who told me this, but I've heard that Mladin actually made Ohlins go and custom-make a spring, because they didn't have one in their lineup stiff enough for him.
As others have eluded to, in almost any motor sport the faster you go the stiffer the suspension because of the physics involved: force = mass x acceleration. Heavy and slow can exactly equal light and fast. I guess I'm glad I don't have the acceleration part figured out yet because I'm maxing out the mass part ;-)
Mladin's setup might surprise you - it wasn't like that. I change springs a lot. Tracks are different, lateral forces are different, riders want different feel. I remember Billy Eisenacher winning a gazillion races on softer than stock setups, and Jamie Hacking winning races on truck springs. There is no magic setup - except the one that sets the lap record. Use what works for you and what makes you feel comfortable. The key is having an open mind to try things.
On top of everything above, on bikes with adjustable chassis, the top level guys may be changing front end geometry with adjustable triples, swingarm pivot location, and the rear end suspension parts (dog-bones etc.), all which change the forces from the spring.
