How To Measure Motorcycle Chain Slack

To measure the tightness of the chain, first, put the car on the side support and put it in neutral. Then, find the lower half of the chain, that is, the point in the middle of the front and back discs, our measurements will be made here in a moment.

What you need to measure is how much distance the chain can move in the vertical direction. This distance is what we often call “tightness” or “gap”. Push the chain to the end with one breath with your finger upward, then take another air pressure to the end, and measure the total travel up and down. This value must match the standard value written in the user manual of your car.

Although the standard value of many street cars is about 1 to 1.2 inches (about 2.5-3cm), the difference between different models is really great, so consulting your user manual is an absolutely necessary step. Take a few minutes to measure this value accurately, which can ensure that your car runs smoothly and safely, and save a lot of maintenance costs that may occur in the future.

Correct Chain Slack Is Crucial For Your Ride

Maintaining the chain and keeping the tightness within a reasonable range is definitely the highlight of motorcycle maintenance. It directly affects your performance, safety, and the life of those parts of the transmission system. The wrong adjustment of the chain will lead to a lot of trouble.

What Happens If The Chain Is Too Loose?

It will hit your rear rocker arm up and down when you ride, causing damage, and make you feel the transmission system “clang” when you switch the throttle, with a clear sense of frustration. This situation is often the most easily overlooked by novices. In the worst case, an extremely loose chain may even fall off the crankset, which has a very high probability of instantly locking your rear wheel, with unimaginable consequences.

What If The Chain Is Too Tight?

This will put your front and rear cogs, wheel bearings, and even the output shaft of the gearbox under tremendous and undesirable pressure. This excessive tension will also limit the normal movement of the rear suspension, directly affect the handling of the car, and cause the entire transmission system to wear out prematurely.

Therefore, it is very important to develop the habit of regularly checking the tightness of the chain. Personally, I usually check every 500 miles (about 700 or 800 kilometers) or so, which is a simple preventive measure.

Tools For The Job

To check the tightness of the chain, it is not necessary to the tools of the whole workshop. Basically, these are enough:

A ruler or tape measure: Used to accurately measure vertical travel.
Gloves: Keep your hands clean.
A clean cloth: useful when wiping grease on chains or hands.
If you find that you need to adjust after measuring, then you also need to prepare a wrench that fits your rear axle large nut and chain adjuster bolt.

Measuring Chain Slack Steps

Let me take the whole process apart to ensure that you can get an accurate measurement result every time.

Step 1: Prepare Your Motorcycle

Before starting, make sure the car is parked on level ground. In order to read accurately, it is best to support the car with a side brace, because many manufacturers set the standard value in this state. Put the gear into neutral so that the rear wheels and chain can turn freely, which is necessary for the next steps.

Step 2: Locate The Midpoint Of The Chain

You need to find the center point of the lower half of the chain, that is, in the middle of the front small dental disc and the back large dental disc. This is the standard measuring point in the industry and the most accurate position, because the chain has the largest up and down movement space here.

Step 3: Find The Tightest Spot

The chain wears unevenly during use, which causes it to have different tightness in different positions. In order to find the tightest point, you need to slowly turn the rear wheel while observing the vertical movement of the chain. The point with the least amount of activity is the point where you should be measuring. Because if you measure and adjust in the loosest part of the chain, when the chain turns to the tightest point, it will become too tight, which will damage the parts. Therefore, taking the tightest point as the standard, the risk of over-tightening the chain can be avoided.

Step 4: Measure The Total Vertical Movement

Get your ruler or tape measure ready for formal measurement now. Use finger to gently push the chain up until it touches the rear swing arm or can’t push it, and record this reading on the ruler. Next, press the chain down to the lowest point it can reach and take a second reading. The difference between these two readings is the tightness of your chain. For example, if you speculate 55mm upward and press down to measure 20mm, then your chain tightness is 35mm.

Step 5: Consult Your Owner’s Manual

The range of acceptable chain tightness varies greatly between motorcycles. Although a common reference value for many street cars is between 1.2 and 1.6 inches (about 30-40mm), this is by no means a universal standard. For example, off-road motorcycles require more clearance, which may range from 1.4 to 2.0 inches (35-50mm). Your owner’s manual will provide you with precise recommended ranges for your specific model. Some cars even put a sticker with this message on the rear rocker arm, so you can look down.

Adjusting The Chain Tension (If Necessary)

If your measurement results are beyond the recommended range, you need to adjust them. First, loosen that huge rear axle nut. Then, use a wrench to screw the adjustment bolts (or nuts) at both ends of the rear rocker arm, and move the rear wheel backward (tighten the chain) or forward (loosen the chain).

In this step, there is one of the most critical points: you must ensure that the adjustments on both sides of the rocker arm are exactly the same, so as to maintain the alignment of the rear wheels. Many of the rear rocker arms are engraved with marking lines to help you align them. When the tightness is adjusted to within the standard range, re-tighten the rear axle nuts to the torque value recommended by the manufacturer. After locking, I personally strongly recommend that you check the tightness of the chain for the time to ensure that the value does not change during the process of locking the nut.

Author ：David

As a rider with over a decade of experience turning my own wrenches, I’ve learned that true riding freedom comes from knowing your machine inside and out. Mastering the basics, like getting your chain slack just right, is the key to a safer, smoother ride. I’m passionate about sharing the simple, practical maintenance tips I’ve picked up over thousands of miles to help fellow riders build confidence and keep their bikes in perfect shape.