Raising a Honda That Sags in the Back
What is sag? There are a lot of different kinds of sag but we are concerned in this article about finding "race sag," even if we are not racing. This measurement is how much the rear of your bike should drop into the suspension stroke, from the fully-extended position, with you and your gear and your luggage on your bike. This is important because a bike is designed with a certain amount of balance, front-to-rear and having too much or too little sag will affect handling and suspension performance.
Too little sag (rear end high) can make a bike twitchy and oversteer and let the shock top out too soon when going over bumps and drops in the trail. Too much sag (rear end low) makes steering sluggish and the front more prone to pushing. It also limits the amount of shock travel before it bottoms out.
On most adventure bikes, shock sag is adjustable and you change this by adding or reducing preload (e.g. ride height) on the rear shock spring. Each bike is different so refer to your owner's manual to see how to adjust the preload on your specific machine. Also, there is a measurement for fork sag but since fork preload adjustment is much less common, we are focusing on rear shock sag. For an expert opinion we grabbed Alex Martens, Founder and CEO of Konflict Motorsports to give us his take on how ADV riders should set their sag.
About 30 Percent Give Or Take
The first thing you need to know is how much shock suspension travel your bike has (you can often get suspension travel specs from the manufacturer's website). Then you need to calculate what 30 percent of that is. For example an Africa Twin has 8.7 inches of shock travel and 2.6 inches is 30 percent of that. Therefore, on an Africa Twin, you want the rear of the bike to drop about 2.6 inches from the fully-extended position with you, geared up, with luggage, if that's how you typically ride.
You can make a mark like this or use a feature on the back of the bike to measure to.
The bike is on a stand and the rear tire is off the ground. This measurement is your extended sag.
Start by measuring your extended sag with the suspension completely uncompressed. With your bike on its center stand, dirt bike stand, or floor jack to get the rear wheel off the ground, you first measure from the center of the axle to a fixed point directly above on the rear tail section of the bike. A slightly less accurate, but easier, way of doing this is putting your bike on its side stand and having a friend lift the rear of the bike so that the shock tops out and is fully extended. It doesn't really matter what point you pick (rear handle bolt, rear rack bar, etc.) as long as you use the same spot for each measurement and it is more or less perpendicular to the ground.
If you don't have a stand you can have someone lift the back of the bike to top out the shock. We got the same measurement this way as we did with the bike on a stand.
The extended sag measurement (in inches, cm, or mm, whichever you prefer) is your starting point. Continuing with the Africa Twin, we measured 23.13 inches from the center of the axle to a specific point on the tail section that we marked with a sharpie. Having that measurement allows us to subtract the 2.6 inches (30 percent of 8.7 inches) that we want the bike to drop giving us 20.5 inches.
To make sure the rider's full weight is on the bike, he is using his right arm to balance against the wall.
Take the bike off the stand, jack, or center stand, have the rider sit on the bike all geared up and have him/her use a wall or tree to support themselves as they sit with both feet on the pegs to get the full rider weight on the bike. Now measure the distance from the center of the axle to the same exact spot on the tail section you used before.
You want it to be as close to 30 percent as possible. On the Africa Twin, that is the 20.5 inches we calculated. If the rear of the bike drops past this number, you need to add preload to your shock spring (bring the rear of the bike up). Conversely, if the rear of the bike is too high with the rider on it, you need to decrease the preload on shock spring.
On the AT, and some other ADV bikes, preload adjustment is as simple as turning a knob. On other bikes you might have to turn a ring on top or below the shock spring. Again, check your manual for your bike's preload adjustment method.
Some bikes, and aftermarket shocks, have remote preload adjusters. Turning it to the right increases preload (higher rear end) and turning left decreases preload (lower rear end).
A simpler shock might have this ring with ramped notches. This bike came with a special wrench for this, or you can use a hammer and punch to rotate the ring.
Rider Preference
Thirty percent is a starting point, but depending on your bike, kind of terrain you are on, and rider preference, this can be adjusted.
"If you would like the bike to corner quicker (less input from rider, faster initiation of the corner) you would run the back end slightly higher. If you would like to have better straight line stability through chop, aggressive off-road riding (desert type terrain) setting the rear to be slightly lower will give that handling change.Think of a Trophy Truck vs. MotoGP Bike, Trophy Trucks are front end high, rear end low for straight line stability whereas a MotoGP Bike is front low, rear end high for cornering ability," explained Alex.
Be Mindful Of Changing Loads
Unique to ADV bikes, the amount of weight on a bike changes often. A rider alone without luggage on just a day ride will compress the rear shock much less than a rider, passenger, both with backpacks, loaded panniers, a top case, and extra fuel. Using the same first number you can check how much your bike sags with all the extra stuff, then adjust the spring preload accordingly. If that can't be achieved it might be time for stiffer springs.
"Our philosophy is to spring the bike appropriately for the rider geared up only if the ride with luggage less than 50% of the time. If the client does in fact ride with luggage or a passenger more than 50% of the time we will alter the spring rates drastically."
Set It, But Don't Forget It
Setting sag isn't something you do once when you get a new bike. You need to check your sag every once in a while, or every time you add or remove significant weight from your bike. For a new bike, adjust the sag accordingly, then check it in a month or so because springs do break in.
"Springs do settle or 'set' after break in just like anything else and something we recommend checking every so often or specifically when adding luggage/passenger weight. Another key item to remember is to reset the settings once the associated weights are removed."
The Motool Slacker Digital Scale makes it possible to do this by yourself. There is a remote display that hooks up to your bar.
The Motion Pro Sag Scale II is more commonly used by moto and dirt bike guys/gals. At the top is zero and the numbers increase going down. This takes out the subtraction from the equation once you know how far your specific bike should sag.
A Helping Hand
All of this can get a little complicated, and speaking for ourselves, we thought we were done with math after high school. But there are some tools that can make setting and checking sag easier. The simplest is the Motool Slacker Digital Sag Scale, which also allows you to do this without the assistance of a friend. Once you zero out the measurement with the shock fully extended, you just hop on and read on a digital screen how much the rear of the bike drops. There is also specific sag tools from Motion Pro Sag Scale II and a few other companies that take some of the math out of the procedure.
Author: Sean Klinger
With his sights set on doing what he loved for a living, Sean left college with a BA in Journalism and dirt bike in his truck. After five years at a dirt-only motorcycle magazine shooting, testing, writing, editing, and a little off-road racing, he has switched gears to bigger bikes and longer adventures. He'll probably get lost a few times but he'll always have fun doing it. Two wheels and adventure is all he needs.
Raising a Honda That Sags in the Back
Source: https://www.advpulse.com/adv-prepping/quick-tips-how-to-set-your-rear-sag-on-an-adventure-bike/