LAB-244-Setting Motorcycle Suspension Sag & Adjusting Preload

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Setting your motorcycle suspension sag by adjusting preload on your rear shocks is very important. It affects the geometry of your motorcycle and how it handles overall. This doesn't need to be a complicated process as many make it seem in other online videos and articles. We're here to break it down in simple terms for the everyday motorcycle enthusiast. (listen to this podcast episode to get all the details!)

Setting sag just means that you are adjusting how much your bike lowers (sags) and rides in the rear when a rider, passenger, luggage or a combination is on the bike. The bike should only sag down so far and within a pre-determined range. Whether you're riding street, adventure, dual-sport, or dirt, setting motorcycle suspension sag is a universal process.

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Most stock Harley-Davidson rear shocks have a pre-load adjuster knob and the owner's manual gives you load weight ratings and where you should set the preload. The air shock system on the Harley works the same by adding or removing air.  If you install aftermarket shocks of any kind then you'll need to learn how to properly set motorcycle suspension sag.

Finding your sag number:

First, you'll need to know how much overall travel your particular motorcycle shock has. Most OEM or aftermarket Harley rear shocks have 3 in. of overall travel or 76 mm. The rule is that you should take that number and your target sag number should be 1/3 or around 30% of that number. So, 3″ of travel x 30% equals around 1″. So, in this case, you'll want your sag to be 1″ or 25 mm.

On my 2018 Kawasaki KLR 650, the rear shock is rated for 7.3 inches or 185mm of travel. So, 7.3″ x 30% equals 2.19″ or 55 mm. So, my target sag number for my KLR 650 should be 2.19″ or 55 mm.

Tip: I hate math and I'm always in a hurry so I use a Tusk Sliding Sag Scale instead of a standard tape measure. I simply set the sliding sag scale to zero when the weight is off the rear. Then, with the load on the rear of the bike, I can simply look at the sag scale measurement in inches or millimeters. No converting or subtraction! You can get a Tusk Slide Scale right in the Law Abiding Biker Store. 

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How to measure your motorcycle suspension sag:

Note: I'll explain below as if using a standard tape measure on not the easy to use slide sag scale. 

I like to start with no preload added on the rear suspension.

Now, make a mark on your strut or rear fender with a marker or piece of tape. Then, lift the rear wheel off the ground, thus removing all weight from the rear shock. Now, measure from the center of the rear axle to the mark you made and note that measurement.

Next, put the weight back on the rear wheel and shock. Put the rider on the bike and have them bounce a few times to settle the rear shock. Measure again from the center of the rear axle to your mark and document that number.

Now, subtract the second measurement from the first and that is where your sag is.

Adjusting your sag:

 Note: We'll use the above Harley sag number of 1″ for demonstrative purposes here.

If your measurement was over 1″ then you are sagging too much and you need to add preload. By adding preload you are compressing the spring and raising the rear of the motorcycle.

If your measurement fell short of 1″ then you have too much preload on the shock and you need to remove preload, thus lowering the rear of the motorcycle.

Repeat the second measurement as you add and remove preload until you hit your target sag number.

You can't get to your proper target sag number:

Note: We'll use the above Harley sag number of 1″ for demonstrative purposes here.

Let's say you are still at 1-1/4″ even after you've added all the preload adjustment you can by compressing the spring and raising the rear of the bike. You simply can't get it to 1″ because you can't add any more preload. This means your spring/shock is too soft and you should get a stiffer one.

The flip side of that is let's say your measurement is only at 3/4″ and you've added no preload. You can't add anymore sag to get to the 1″ as adding preload would just raise the bike. You simply can't get the motorcycle to sag enough. This means your spring/shock is too stiff and you should get a softer one.

Just understand that if you set your sag for a rider only and you're at the 3/4″ then with a rider or luggage you'll likely be at your 1″ sag. You need to take everything into account.

You should measure motorcycle suspension sag for rider only, rider with passenger and with luggage.  You measure the rear sag with the rider/passenger/luggage on the bike.

Then, simply keep notes of where you should set your suspension preload adjuster for each load. This way you can avoid having to measure again every time you have a passenger or luggage.

Preload adjusters:

Different motorcycle shocks have different styles of preload adjusters. Many aftermarket shocks have a collar you can turn by hand or a system where you use a spanner wrench. My KLR has a 12mm bolt you can turn with a socket.

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