Suspension Setup 101 Part I: Setting Sag

Pity the motorcycling newcomer. On top of acquiring an acceptable machine, learning to ride it and dividing one's attention between actually operating the bike and keeping errant cars and trucks from dealing death blows out on the mean streets, newbies must also eventually deal with the arcane and often-confusing subject of suspension tuning.

Ooooh. The words alone strike terror in even the most seasoned riders.

Forget such involved concepts as spring rates, preload, compression and rebound damping. Newcomers are likely to take one look at the bewildering array of knobs, clickers, nuts and screws on today's sportier motorcycles and simply ignore the whole thing. Which would be a mistake, of course, because the simple truth is that proper adjustment of your motorcycle's suspension can make a huge difference in the way your bike handles--and how well you're able to ride it.

Race Tech's ( Paul Thede has dealt with dirt- and streetbike suspension modifications for nearly two decades, and his take is this: "Proper suspension setup is key to riding fast and safely. [Your bike's suspension] requires proper adjustment to work to its maximum potential. The cool thing is, suspension tuning isn't rocket science."

He's right. Basic suspension setup isn't overly difficult, especially if you take things one stage at a time. And stage one in the quest for a well set-up streetbike suspension is to dial in spring sag--that is, the distance the fork and shock compress with a rider aboard (laden) compared with the fork and shock fully extended (or unladen).

Step one is to determine your fork and shock's fully extended (unladen) measurements. To do this you'll need to get both wheels off the ground, though not at the same time. On bikes with sidestands, the front wheel can be raised relatively easily by rocking the bike over on its stand and raising the front end; this is much harder to do with the rear wheel, but it can be done if the person doing the raising is both strong and coordinated. Centerstands make raising the rear wheel simple, though an underengine stand (or a sidestand) will be necessary for bikes lacking them.

For the back wheel number, measure the distance from the axle vertically to some point on the chassis using a tape measure; metric figures are easiest and more precise. A graphic point on the sidepanel or the bottom edge of the panel itself work well as reference points. Be sure to mark the exact points you used because you'll need to refer to them again. Record this measurement on a notepad next to the notation marked "R, unladen." Up front, extend the fork completely with the wheel in the air and measure from the wiper (the dust seal between the shiny slider and textured stanchion) to a point on the bottom triple clamp (or the lower fork casting on an inverted fork). Record this measurement next to the notation "F, unladen."

Now you're ready to record the same two measurements with the fully outfitted rider on the bike (these would be the "laden" numbers). Ask a buddy to hold the front or back of the bike while you get settled, and have a third person (preferably the one who took the unladen measurements) record the laden numbers front and rear. Mark these as "R, laden" and "F, laden." Subtract the laden front and rear numbers from the unladen front and rear numbers and bingo!--you've got your two sag numbers.

Thede likes to work with 30-35mm of sag on streetbikes, 25-30mm for racebikes. Your numbers will likely be higher than these (a softer ride), in which case you'll want to increase spring preload on the shock and/or fork. If your numbers are less than these (a firmer ride), try reducing preload a bit. Adjust things until the measurements fall within acceptable parameters. You'll have to remeasure after making the preload changes, of course.

Remember, there is no magic number. If you like the feel of the bike with slightly less or more sag than these guidelines, no worries. Your personal sag and front-to-rear sag bias will depend on various factors, including chassis geometry, track or road conditions, tire selection, rider weight and/or riding style.

Next month we'll turn our attention to rebound and compression damping.

Doing a decent job of measuring and setting spring sag means drafting a few friends to help. Be sure you're wearing all your gear when taking measurements; measuring spring sag without a stand will be easier as well.