Adjustment Tech
Omemee, Ontario, Canada
1-705-799-5139
URL: http://www3.sympatico.ca/a.jones/RHA.HTM
(Hmm, those pages seem pretty out-of-date.)
Adjustment Tech suspension kits (ride height adjusters) let you raise or lower the rear suspension without modifying or even adjusting the shock. This is good because you don't introduce changes to suspension behaviour that would result for example from reducing the spring preload to soften the shock and let the back end settle a bit lower. (Now, by changing the length of the linkage dog-bones, which is what the kit does, you do change the angle of the swing-arm to the ground, and lever ratios are altered, but to such a small degree that it's not noticeable under most conditions.)
You can dial in the amount of height change you want by turning the threaded adjusters, and you don't have to remove the kit from the bike to do it. The kit offers a wide range of adjustability, so it's possible to lower the shock so much that you would run out of clearance under the rear mudguard, or so much that you would not be able to lower the front end enough to match without having the front fender bang into the horn or underside of the front fairing. So care must be taken not to get too extreme. I'm told that it varies from bike to bike; the YZF-R6 will tolerate a lot of front-end drop but the CBR600 will not accept much.
The $349 (Cdn) kit for the YZF600R consists of two replacement dog-bones. Unlike the flat stock ones, each dog-bone in the kit has two threaded bolts that are joined in a centre shaft. The bolts are threaded oppositely, so by turning one way the dog-bone contracts, and by turning the opposite way the dog-bone expands. Since the heads of the bolts are much wider than the flat stock item, longer mounting bolts are required. The good news is that they're included in the kit. The bad news is that they take an imperial socket instead of metric.
The kit comes preassembled and adjusted to stock length. The instructions advise you to double-check this against your stock dog-bones. I recommend using some red nail polish to carefully mark the threads on the bolts so you know what your starting point is. It's easy to accidentally turn the bolts while assembling, or mix up your directions while adjusting, and then you can't be sure you're adjusting both by the same amount.
Before installing the kit, I suggest you make sure your suspension is already well-adjusted for your riding style. Start by measuring your static sag front and back and make sure they're dialled in to the proper amounts. That's probably the most important thing before altering the ride height. If you've already compromised correct settings in order to lower the bike, set them back. This may or may not be the "standard" preload settings -- it depends on your weight. Then take the time to find a section of road that's good for testing, and adjust your compression and rebound settings as needed. You want the bike behaving its best before you start changing things, and since the kit lets you lower the bike without fiddling with the shock, you want the shock adjusted properly to begin with. It's beyond the scope of this document to tell you how to adjust your static sag, preload, compression, and rebound.
Now that your suspension is properly adjusted, you can begin. It is important to take careful measurements so you can determine how much you lower the bike. If you don't know how much you drop the back with the kit, you won't know how much to drop the front (by raising the forks in the triple clamps) to match. If the front and back are not lowered by a pretty similar amount, you'll throw off the handling characteristics of the bike. A difference of 5 to 10 mm is perceptible; whether it matters to you is another question :-)
I suggest you make your measurements a few different ways so you have some means of double-checking. Start by having an assistant hold the bike vertical without sitting on it. Take measurements of the front and rear chassis height. At the front I had the fairings off so I measured from the tab on the frame where the fairing bolts on. At the rear I measured from one corner of the reflector on side of the mudguard. Keep these initial numbers for final reference later. Now put the bike on a rear wheel stand, and measure again. This is your first set of working numbers. I next used two bottle jacks positioned under the rear corners of the engine to raise the back of the bike up off the wheel stand. Be careful to raise each jack evenly a bit at a time. When the swing-arm is clear of the wheel stand, you can get started.
Remove the bolts that hold the stock dog-bones in place. Install the Adjustment Tech kit, being careful not to throw off the matching lengths by accidentally turning the adjusters. Your nail polish marks will come in handy here. (As the instructions point out, you don't have to orient both dog-bones the same way. I left them the same, but found that once I got the bike lowered the right-hand adjuster got annoyingly close to the clamp that holds the muffler stem onto the header, so you might want to reverse the right-hand one.) Torque to spec as per the shop manual.
Now you can start adjusting. Turn the centre shaft adjusters the same number of turns, in the same direction. I painted one of the flats on each adjuster so I could count the number of turns and ensure I kept them the same, but I managed to confuse myself a couple times on which direction I was turning, so take care. With the swing arm hanging free, rather than resting on the wheel-stand, you won't need a lot of force to turn the adjusters.
Because it's important to preserve suspension travel, you don't want to lower the bike any more than is necessary to let you get enough of your feet down to feel secure. If you are 5'0" and expect to get flat-footed, I don't think you're going to have any suspension travel left. So start off with just a few turns on each side. Then carefully lower your bottle jacks so that the bike sits back down on the wheel-stand. Repeat your measurements at the rear and compare to your first set of working numbers to see how much you've lowered the back so far. If you know you want more, jack the bike back up and turn the adjusters some more. When you think you're close enough to try it out, take the bike right off the stand and sit on it to see. Keep in mind that you haven't lowered the front yet, and when you do, you'll get a wee bit more overall lowering effect.
Once you're satisfied with the seat height, put the bike back up on the wheel-stand, and repeat the rear measurement. Subtract from your first working number to see how much you've lowered the back. That's how much you have to lower the front next.
To lower the front, you have to raise the fork tubes in their clamps. A few things must be taken out of the way first. Loosen the pinch bolts on the handlebar bosses so the tubes can slide through the bosses. The bosses must stay with the triple clamp -- your handlebars will not rise when you raise the fork tubes.
Loosen the lower and upper triple clamp pinch bolts. This will be easier if you remove the windscreen so you can reach through with a wrench, but it was still a tight fit for me. The fork tubes did not immediately shoot up through the clamps on me; I had to persuade them to move, so don't worry about the front end collapsing on you. Using a precision 6" steel rule, measure the amount by which you raise the fork tubes above the top triple clamp, and be sure it's exactly the same on both sides. Since the forks aren't vertical, the amount you need on the front is not exactly the amount you measured at the rear, but it is pretty close, so start with that. When you think you've got it set right, tighten up the triple clamp bolts (follow the service manual instructions for order and torque). Now measure your new front height and subtract from your first working number for the front to see how much the front has been lowered. You want this to be the same as the back. Repeat if necessary.
Once it looks like you've got it right, take the bike off the stands and have your assistant hold it vertically again without sitting on it. Remeasure front and rear height and compare to your initial reference numbers. If things went well, the change in height, front and back, measured this way, corresponds to the change in height, front and back, measured with the bike on the stand. I introduced these multiple measuring methods to save some hassle of constantly putting the bike on the stand and jacking it up and then taking it all down again, so I hope it saves some work.
Make sure your triple clamps and handlebar bosses are properly torqued. Now you're ready to take the bike for a test-ride.
But first some cautionary notes. You must realize that you are giving up suspension travel, or more precisely, clearance for suspension travel, by lowering the bike. The fork and shock will have the same amount of travel as they originally had, but they will have less clearance before the rear hugger hits the underside of the tail, or before the front fender hits the horn or underside of the nose fairing or the radiator. Normally the suspension reaches the limit of its travel before running out of clearance. But if you get carried away lowering the bike a lot, these parts may start banging into one another, particularly if you ride rough roads, or do wheelies, or if you are heavy.
We lowered the bike about 1.5" for a rider who is 5'3" and not very heavy. So far there has been no interference. But if you look up the total fork travel, and subtract your static sag, and subtract the amount by which you've lowered the bike, you'll find that there's not a whole lot of travel left. I suggest you put a zip-tie snugly on the fork tube and slide it down against the dust scraper, then go for a ride and see how far up the tube the zip-tie gets pushed due to suspension action. This will give an indication of how much fork travel you're using and whether you might be on the verge of having parts collide. Relocation of the horn might give more clearance; I haven't studied the front end carefully enough to determine what would hit first.
If you find that you are using enough suspension travel to warrant interference (or clearance) concerns, consider increasing preload a little. Stay within normally acceptable sag numbers to preserve good suspension behaviour, but move towards the firmer end of the range. The typical rules of thumb suggest 33% sag for normal street use, and 25% for more sporty or aggressive riding. Try 25%.
Note that if you lower the bike more than just a little, you will likely find that the kickstand is too long to let the bike lean over far enough. I definitely had to shorten the kickstand after lowering the bike 1.5". It was standing almost vertical, very precariously. A local shop cut out the inch or so of metal between the kickstand's foot and the tang you use to push the kickstand down into position. The foot is now immediately below this tang. This gives enough lean angle to be comfortable; maybe not quite as much as stock, but almost.
I intend to update this report with the actual measurements I used on this bike, but until then, I hope you find it useful and not too confusing.
Back to my YZF600R page.