Suspension Tuning – Part 1: Plan ‘A’. Plan ‘B’. Plan ‘C’ It Is!Posted: January 17, 2010
This would have been a heck of a lot harder and not nearly as easy without the help of Mike who is totally awesome and my hero! Kudos, dude! 🙂
I’d (Almost) Rather Watch Paint Peel Off The Walls:
I’m not enjoying this whole suspension thing one iota. Generally, I like technical stuff like this, but for some reason, this isn’t doing it for me. I think I’ve found my own personal Kryptonite. It is so boring, I don’t even want to think about it too much for fear of putting myself to sleep. I’m at work, I can’t afford to take a suspension-induced cat nap. However, I’m also too much of a perfectionist to simply let it fly; to just say screw it and leave it alone in the name of ‘it’s been good enough so far’. On the other hand, I really have to fight the temptation to ‘do my own thing’ and instead force myself to stick to the ‘Rules Of Ideal’ laid out in Trevitt’s book, while I am mentally sorting through how to affect the desired changes before actually touching the adjusters on the bike. I have to keep reminding myself that I do not yet have any ‘applied knowledge’, any idea how the changes I am proposing will actually translate into the real world. In other words, I’m yet too ill-informed (read: ignorant) to make a sound judgment call and to deviate from the guidelines set forth. Maybe that’s why I’m not enjoying this as much as I should, I feel caged in by perimeters and my brain can’t go on a mathematical exploration. Soon, I hope, all in due time. And it takes too freakin’ long. It’s like working out. Painfully slow progress, without immediate gratification (aside from the endorphin high, maybe.) Patience…. Arrgh, there’s that word again!
‘The Conundrum’ or ‘Trying To Keep My Feet On The Ground’
My front sag number is good. It is above 30mm, 42mm to be exact. However, my rear sag number is at 25mm. That may be good for the racetrack (25-30mm), but the range for street riding is 30-35mm. The rear free sag is also out of its ideal range of 5-10mm and stands at 11.5mm at stock settings. I think I have the rear figured out.
The rule is as follows: If you want MORE sag, you need to SUBTRACT preload. If you want LESS sag, you need to ADD preload.
Hence, to bring my rider sag up to 30mm from 25mm, I need to subtract 5mm of preload. Now to get rid of 5mm worth of preload shouldn’t be all that complicated, and it has the added effect of lowering my ride height, which in turn relaxes the front-end geometry. It also should take care of that annoying 1.5mm of rear free sag overage and put it within range.
Adding preload does not compress the spring inside the shock more; well, it would if the shock was either topped or bottomed out. It instead raises the bike on its suspension. Removing preload has the opposite effect: it lowers the bike on its suspension. You can clearly see that playing around with preload settings is one way to adjust your ride height. Just make sure you do it equally in the front and the rear, or you will change your geometry, which will change the way your bike handles. The rule here is as follows: Lowering the rear will relax geometry by increasing rake and trail, which enhances straight-line stability, but steering will be heavier. Raising the rear will make the geometry steeper – more aggressive — by decreasing rake and trail, which leads to quicker steering at the expense of straight-line stability.
Personally, I want one (the lowered ride height), but definitely not the other (relaxing the geometry). The Fat Lady is already a bit on the heavy side when it comes to steering. I don’t want to add to that, so it stands to reason, that I must offset this increase in rake/trail numbers with the addition of a little preload up front. Or conversely, I could raise the fork tubes in the triple clamp to offset the undesired change in front-end geometry. Cranking in preload would raise the front of the bike, which in turn raises my ride height. No-go. This leaves the only viable option: Raise the fork tubes to keep the geometry the same, which also has the added effect of reducing ride height.
As with the rear, adding preload raises the front of the bike; removing preload lowers it. But when you lower the front-end by raising the fork tubes in the triple clamp, the geometry is sharpened (decreasing rake/trail) and when you raise the front of the bike by lowering the fork tubes in the triple clamp, the geometry is relaxed (increasing rake/trail). This is opposite of what happens in the rear. Think of it in terms of a triangle: With A being the front axle, B being the rear axle, and C being the top of the steering head. Connect the three points and you can readily see how slightly moving one point or altering the length of one side has an effect on the others. There’s more to it than that, but for now let it suffice.
The path to be ventured down in the quest for a personalized suspension setup has been made clear. But by how much should I adjust? Generally, raising the fork tubes by 4mm in their clamps will result in a 1mm decrease in trail. How much trail offset could subtracting 5mm of rear preload really do? Can’t be much. Doubtful it’s more than 1mm, probably just a fraction thereof. I guess, I could figure this out with a few calculations of the geometric variety, but I’m way too lazy for that, although I’m entirely anal enough to see myself doing just that… if I wasn’t already half-asleep by the concept to begin with. Obviously, I can’t keep the geometry entirely stock, so decreasing trail by a mil or whatnot doesn’t really phase me. Not right now. As long as it isn’t an increase. Cornering with the handling of a minivan? Sure. Never drove anything smaller anyway. Going around a curve in a bus? Do NOT want. First problem solved.
So, Here’s How It’s Gonna Go Down:
- Lessen the rear preload by 5mm.
- Raise the fork tubes in the triple clamp by 4mm to affect a 1mm trail decrease to offset the slight increase from step 1.
- Go for a test ride.
But… The Fat Lady Is A Little Weak In The Knees
Technically, that would be her elbows, if she were to be properly antropomorphosized. However, that would be messing up my play on words, so the knees it is.
The front is a different story, though. Even though the sag number, being 42mm, is above its suggested minimum of 30mm, I would like it to be less. The front is already in danger of bottoming out, and I wasn’t even riding it all that hard when I went for my zip-tied test ride to check used suspension travel. Have I ever bottomed it? I don’t think so. I don’t even know what that would feel like. The result is loss of traction, but there are a multitude of reasons for losing traction, only one of which is bottoming the suspension. I would think I would notice the upset, but I can’t be sure of that. I could go out and try and do it on purpose, but I’m too chicken for that. Plastics are expensive, and I still haven’t repaired all the kisses from the last time I bounced the suspension. ;P
In order to move the travel up towards the middle I’d have to dial in more preload. Well, crap! Here we go again with the ride height increase. Can’t do that, unless I wanna start riding in hooker boots. Even though Icon makes a really cool pair that would do just fine. =D Those would go great with that Hayabusa vest I got for Christmas, too. Hmmmm…. Where was I? Oh yeah, I ‘member now… suspension travel. The Fat Lady’s at rest at 42mm (apparently I weigh ten mil, I like that way better than pounds, especially if you don’t tell anybody your spring rate =D), with the free sag being at 32mm. The halfway point of total travel, which is 116mm, is at 58mm. Looks to me like we need to crank in 16mm of preload, to raise the Fat Lady up on her fork tubes from 42mm to 58mm. Yeah. Not happening. I could offset the16mm ride height increase by raising the fork tubes by an equal amount and we’d arrive at a nice 20mm adjustment: 16mm to offset the added preload and the 4mm previously dialed in from the rear adjustment. That would effectively decrease trail by less than 1mm total. The Hayabusa’s trail is listed as 3.9 inches at stock settings, converted to metric that’s 99.06mm. I don’t even know if I have enough room between the actual top triple clamp and the top cover. And why in the hell didn’t Suzuki make the holes big enough for the fork tubes to fit through? Their band of merry lawyers decide that we needed a way to lower the front end about as much as we needed a top-speed unrestricted bike? I’d get rid of the blasted thing, if it weren’t for the small inconvenience of the clip-ons being attached to it. What brainiac came up with that idea??? Probably the same asshole who thought black plastics would be awesome under white paint.
Here’s How We’re Gonna Rise To The Occasion:
- Take the cover off and measure the clearance between it and the fork tube caps. If it’s 20.5mm or more, proceed to the next step. If it’s less, proceed to Step 7.
- Raise the fork tubes by 16mm to offset the added preload to prevent the inevitable ride height increase.
- Crank in 16mm of preload.
- Measure rider sag and free sag to ensure that the numbers are still within their respective ranges.
- Go for a zip-tied test ride. If all checks out, proceed to the next step.
- Get a New York style cheesecake and celebrate the completion of the first part of this odyssey. Stop. You’re done for now. Next up: Damping.
- Go for a ride to Greenville, SC.
- Buy a 2010 BMW S1000RR in Acid Green. 8)
- Go for a spirited ride!
- Damn, this thing comes with a suspension, too. Take it from the top…
My Work Here Isn’t Done (Just Yet):
I ran this ‘proposal’ by a very dear Twitter friend of mine, @mikegreenwald, who kindly offered to help me sort out my suspension woes and be my technical advisor. J He checked this thing for me, to make sure I had my facts straight and my train of thought was in the right direction. Then he gave me an alternative course of action, mostly to keep me firmly grounded. Here’s what he suggested I’d do, considering that I can go from tip-toeing to flat-footing the beast depending on the footwear I’m wearing any given day. Then there’s the matter of that awesomely sweet, but too tall, Suzuki OEM gel seat I got for Christmas. I had to take it back off, because I could only barely back the bike out of my own driveway in my Sidi boots. Here’s what he suggested I’d do first: Mechanically lower The Fat Lady.
- Get dog bones (lowering links) for the rear and drop her ass by 2 inches.
- Get 1-inch bushings for the front, to stick under that dreadful top triple clamp cover to make room for raising the fork tubes in their clamps to drop her 1 inch in the front.
- Get an adjustable kickstand, so the newly lowered Fat Lady won’t be tempted to take an asphalt nap while I’m not around.
This will ensure that I can have both feet firmly on the ground, even with the gel seat, no matter what boot I’m wearing. It will also lower her CoG (center of gravity), which is a good thing, but this, obviously, comes at the expense of reduced ground clearance. This will set me back by about $285, if I get all three parts at the site Mike hooked me up with. I was encouraged to go cruise the web for myself and he also told me to sleep on it. So I did (both).
Sometime The Next Morning (At Work):
Hmmm… I’m at work. I’m getting paid to… well, currently I’m getting paid for suspension tuning research. Ha! That makes me a professional by definition. Cool. 8P So, I’ve looked around online to see what’s available in the way of lowering my bike mechanically, then I’ve slept on it. Now, I’m sitting at work, tweaking this 2nd draft of my blog post and mulling it over.
Any solution that I come up with has to adhere to ‘The Fat Lady Prime Directive’. Which is a self-imposed rule that states that anything put on the bike has to
- improve performance, ergos, or riding quality;
- cannot hinder performance, ergos, or riding quality;
- has to be of equal or higher quality than the OEM part it replaces;
- can’t weigh more than the OEM part it replaces;
- be a Farkle (functional sparkle) rather than just a Pretty (non-functional, cosmetic only).
I think I’m going to break Mike’s idea down into two parts with a little tweak thrown in and merge it with my ‘proposal’. We’ll call this the MiMo Hybrid ;P:
‘I See That 165 And Raise You… 165’ or ‘The MiMo Hybrid’
I’ve decided against the lowering bushings. That will definitely get my front-end lowered by that inch Mike was suggesting to me, but it doesn’t leave room for more adjustability or fine tuning later. I will still not be able to raise the fork tubes any higher, since the OEM top triple clamp is retained. I want this fixed. I hate limitations that are there for no reason other than being there. It’s a matter of principle, like that X-TRE to derestrict the bike. But now that I have land speed aspirations, this actually has moved from principle to the realm of necessity. Anyway, that top triple clamp has either got to go or I need to have the holes drilled out in the OEM part to accommodate the 50mm fork tubes. Which one I’ll do depends on several factors, primary of which is cost. Secondary is time. Obviously I can’t wait around for a few days for them to mod the thing, I’m a commuter. I gotta have my bike. Besides, three days without riding and I’m in danger of nutting up and risking being stuffed into a straight jacket by the good folks in white lab coats of Milledgeville. 😉 The custom top triple clamps that meet my standards can be had anywhere from $165-$349, and I’m currently leaning toward the $165 model, since it’s skeleton and thus weighs a lot less than the OEM. Looks sharp, too. But I haven’t seen a pic of it on a Gen 2 Hayabusa and don’t know if — when all put back together – it would clear the fairing or the Double Bubble windscreen. More research is needed before I settle on which I’m going to end up ordering.
I will then go ahead with my proposed suspension adjustments. I’m too curious to see my work in action. I can’t help myself. I put in all this brainpower, and I need to see my narcoleptic time spent in action and see for myself how it translates into ‘real world’ application. This is my maiden voyage, after all, I need to finish it.
Once I’ve played around with the new settings, and had time to delve into damping forces a little, I’ll order the lowering links. However, I don’t think I’ll be going with dog bones. I want more control over my adjustments to satisfy my inner control freak and the touch of OCD I’m blessed with. Again, I would like to leave my options open, because I don’t know what I may want to do in the future. I may want to slam it all the way down, then I’m stuck buying different links. Or I may decide I don’t like a 2-inch drop in the rear and want it adjusted to 1 ¾” instead, then what? I want full adjustability. And it has to be somewhat simple to do. Like the link Ducati puts on some of their bikes. Brock’s makes a set of ‘Window Links’ that seem to fit the bill. (I just hope I’ll be able to check out without adding that Alien Head full exhaust system to my cart, too.) The links also run about $165. I see a pattern forming here. Along with the lowering links of choice, I will also get that adjustable kickstand, which also costs… wait for it… wait for it… $165. What’s up with THAT? Again, more research is needed before I finalize my decision on which parts I’ll actually end up with.
Now, I’m going to employ Mike’s suggestion of the 1-2-inch drop in the rear, and the 1-inch drop in the front, and feel that out. Then I can put that awesomely trick gel seat back on and roll it in functional style (until my ass gets too hot in the summer!). =D
[Pics will be added later, too awkward on the BlackBerry]
Linkage to the entire series:
- Suspension Tuning – Part 1: Rider Sag, Free Sag, and Preload
- Suspension Tuning – Part 1: Plan ‘A’. Plan ‘B’. Plan ‘C’ It Is.
- Suspension Tuning – Part 1: Exploratory Surgery
- Suspension Tuning – Part 1: Let’s Go Shopping!
- The (preliminary) results: OMG! OMG! OMG! The Fat Lady Can Dance?
- Suspension Tuning – Part 1: The Fat Lady’s Got Slammed
- Suspension Tuning – Part 1 (Results): There’s a first time for everything…