Suspension Setup

May 2008

I'll be the first to admit that other than tweaking rebound and compression slightly, I'd left my suspension alone due to lack of knowledge and being intimidated by all the settings.  I'm here to tell you that being intimidated by your suspension is a mistake.

Start by setting up your sag, which is the amount the suspension compresses when the rider with their gear is mounted on the machine.  There are two types of sag.....static sag, which is the amount the suspension compresses under the bike's weight, and rider sag, which is the ADDITIONAL amount the bike compresses with the rider aboard.  This will be a basic article on suspension, so I'm only going to focus on rider sag to keep things simple.

You'll need to have a couple of friends around to help take measurements and steady the bike.  Start by picking a point on the tail of the motorcycle that is exactly perpendicular (right above) the rear axle.  Mark it with a small piece of tape and put a dot on the tape with a Sharpie.  Next, rock the bike back on the side stand, or place a jack under the oil pan, and raise the bike until the rear wheel is off the ground.  Once the rear wheel is suspended, measure the distance from the top of the rear axle to the dot on the piece of tape.  Note this measurement, and convert it to millimeters for easier math later.  This is the measurement of the suspension fully extended.

Now do the same with the front.  If you used a jack, simply push down on the rear of the bike until the front wheel comes off the ground.  If using the side stand method, you'll need to have friends help lift the front of the bike until the front wheel is suspended.  Measure from the bottom of the fork wiper (small rubber seal) to the top edge of the lower fork casting.  Note this measurement and convert it to millimeters for easier math later.

Now, get all suited up in your riding gear and mount the bike.  Take the bike off it's side stand and have a friend hold the front of the bike to keep it steady as you assume a tucked riding position.  Now have a friend gently lift up on the rear of the bike and gently let go to let the suspension settle.  Have one of your friends measure from the same spot on the top of the  rear axle to the dot on the piece of tape on the tail and note this measurement.  Now have this same friend push down gently on the rear of the bike and gently let go for the suspension to settle and take this same measurement again and note it. 

Perform this same procedure on the front of the bike, having a friend gently lift up on the front of the bike and gently let go allowing the suspension to settle.  Measure from the fork wiper to the top edge of the lower fork casting the same as you did with the suspension fully extended and note the measurement.  Now have your friend push down gently on the front of the bike and gently release allowing the suspension to settle and take this same measurement from the fork wiper to the top edge of the lower fork casting and note the measurement.

Now convert the rider mounted measurements to millimeters.  Add the first and second measurement you made with the rider mounted together (measurement 1 + measurement 2) and divide this number by 2 to get the average and note this average for front and rear.  Now subtract this from the front and rear fully extended numbers you measured.  This result is your rider sag.  You want the front to be right about 38mm and the rear to be about 25mm.  You adjust sag with the bike's preload.  Tighten preload to get less sag, or loosen to get more.

On my 2005 CBR1000RR with the front preload at FULL HARD I was still only at 46mm of rider sag.  This is 8mm short of my goal of 38mm.  I weigh 172 lbs without gear, 190 lbs with full gear.  This means my front fork springs are too soft and I need to replace them with stiffer units, or better yet, replace the forks with higher performing models.  On the rear, a setting of 6 from full soft on preload got me right about 25mm, and I have a 2006 model rear shock and link installed.

Now rebound and compression damping are completely different from setting sag, and I personally go by feel for what adjustments are needed.  For my first track day, I started with settings that Sport Rider magazine recommended and adjusted as needed.  Here is how my suspension is set today:
 

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