From: "Norbert Wank" To: "Vmax Techlist" Subject: Re: suspension sag Message-ID: Dom had it right the first time around - shoot for 33% for street riding and when you prefer a stiffer ride for plenty cornering and racing, decrease to 25%. Always listen to your butt and gut when making subtle changes (prefer to only change one thing at a time: preload, compression and rebound. I have edited an article that was published in "American Roadracing" in June 1997 to match the numbers of Mr Max: DIAL IN YOUR SUSPENSION American Roadracing, June 1997 The current crop of sportbikes have the most sophisticated and adjustable suspension systems ever offered to the generel public. This suspension technology is as well and good if yo uunderstand hiow it works and how it's supposed to be setup, but like the surgeon's scalpel, you can do an aweful lot of damage if you don't know what you're doing when turning the damping dials or changing spring preload. Suspensions etup for any high-performance sportbike begins with setting race-sag. Race sag is the amount the suspension compresses with the rider on board. Before you can set the sag you must calculate what the correct race sag is for your bike. This is done by finding the total suspension travel [Vmax front = 140mm front, 85mm rear] and dividing by three (four for a race bike). [That's between 35mm and 47mm for the Vmax forks, and between 21mm and 28mm on the stock rear suspension.] The suspension travel for any bike can be found in the owners manual [Vmax manual page 8-12]. ... Now get two friends and a metric tape measure. We are going to adjust the sag by varying the preload on the springs. If the bike sags more than the specified amount when you sit on it we will increase the preload by turning the preload collar clockwise; counterclockwise if the bike doesn't sag enough. Put on ALL of your riding gear and seat yourself in the saddle while friend #1 holds the front of the bike so you can get into your riding position. Remember, your feet have to be ON the pegs. Have friend #2 bounce the bike the suspension up and down a couple of times and then measure the distance between the a point on the rear fender and the rear axle [loaded and fully extended index points on the fork stanchions]. Do not hold the brake or turn the front wheel while measuring the sag. Once the first measurement is taken put the bike on its centerstand or on a crate so that threar wheel is off the ground and remeasure the same two points. Subtract the first measurement from the second and the result is your sag. ... Now would be a good time to check and see if the rear shock spring on your bike is the correct one for your weight. You can get the correct sag with almost any spring by adjusting the preload, but measuring the unladen or free sag will tell you if a different spring rate is called for. To do this simply hold the bike upright and remeasure the same two points used for checking the sag, except now, only the bike's weight compresses the suspension. A good free sag number for a street bike is 10mm, but a racebike will work better if the unladen sag is 2mm to 5mm. If you find that your bike has more than 10mm of free sag, your spring is too stiff for your weight and a replacement is called for. The converse is also true. If the bike is topped out, meaning it has no free sag whatsoever, then your spring is too soft. This may sound backwards, but remember if you started with a spring that you knew was too soft you would have to add a lot of preload to get the race sag right, and when you got off the bike and neasured the free sag all that preload would not allow the bike to settle much unde rits own weight. Street bike usually have soft springs and need too much preload. This gives a good free way ride, but if you find that your bike constantly runs wide on the exit of turns you can bet that your spring is too soft. If you are too light for the spring then the bike will have a harsh ride and it will be difficult to control the spring with the rebound damping adjuster. Now that you have the sag right and you have the correct spring for your bike you can begin setting the ride height. The ride height controls the amount of nose-down pitch the bike rides at. Until recently it was difficult to set the ride height independent of the sag. Usually you had to compromise the sag to get the ride height you wanted, but on the GSX-R750 we can shim the top shock mount to make the effective length of the shock longer, thereby raising tthe rear end up and increasing the nose pitch. This has the effect of adding weight to the front wheel. By the same token, if you remove the shims from the shock mount I can lower the rear end and add weight to the rear end, putting the nose of the bike up more." --------------- This article refers to "Superbikes" suspension settings, now you have to consider that superbikes have radical rake and trail angles, and stiffer frames than our Maxes, furthermore, the single rear shock and the radial tires they use, behave very differently than ours. So my point is, that even if you use some guidelines from this article, do not expect the same results they claim. Tires, rider's weight and riding methods, can make a perfectly set bike for a person, a solid brick wagon for another. Mario ------------------- And that brings us back to my original question, which was: does 25 to = 35 percent of total susp travel sound reasonable for rider sag? Sounds = like the consensus so far is "Yes." Mario, what amount of sag works = well for you? Right now, I'm at around 33% in the front, and it sure = works a lot better than 60%. In other words, no bottoming out under = hard braking, and it soaks up small bumps and dips with no harshness. In a suspension clinic I attended recently, the speaker gave very = specific measurements for sportbike sag settings, and said those numbers = aren't necessarily valid for other types of bikes, like cruisers, which = is Mario's point. =20 Dom Ochoa Pleasanton, CA ------------- Dom Ochoa wrote: > I noticed Paul's article indicated 5.5" of front suspension travel, and my service manual confirmed it. But, when I measured it on my bike, I got only 4.5". Will air pressure in the fork prevent it from compressing all the way? > That was Bert's article but the air should only make it firmer, not restrict it at all. Does anyone know if late vs.early have the same amount of travel? -- Paul Sayegh e-mail paul@sayegh.org --------------- Mine is set about 30,%, which is the way I find better results, for the type of riding I do. I like it, a little on the firm side on the curves and under hard braking, gives me more control, and less chance of the front end "tucking in" or the rear "stepping out" because of excessive sag.