Suspension 101

This Blog post is in support of a series of videos I am producing and sharing via my website www.BretTkacs.com and on YouTube at https://www.youtube.com/c/BretTkacs. As of the posting of this blog only the introduction to suspension springs is online but I am working on a complete series that will eventually complete the this introduction to suspension series.

THE MOST COMMON SUSPENSION ISSUE IS RELATED TO RIDING TECHNIQUE NOT SUSPENSION!

Topics to know:

·  Suspension evolution

·  Function and history of frame and swing arm design

·  Spring function

·  Hydraulic shock absorbers

 

·  Open damper

·  Cartridge system

·  Damping levels

·  Damping speed

·  Optimizing telescopic forks

·  Basic adjustments

·  Suspension geometry

·  Rider/Motorcycle Mass

·  Chain effects

·  Tire Technology

·   Lowering suspension

 
Understanding your suspension components:
Springs: Damping: Weight & Friction:
1.     Spring rate

2.     Multi rate springs

3.     Performance springs

4.     Preload

5.     Spring sag

6.     Damping

7.     Damper rods

8.     Cartridge forks

9.     DeCarbon shocks

10.  Knobs and dials

11.  Suspension fluids

12.  Shim stack

13.  Weight reduction

14.  Sprung vs. un-sprung weight

15.  Stiction

16.  Slick stuff (friction coatings, seals, etc)

17.  Suspension braces

18.  Bearings

19.  Maintenance

Suspension is one of the great mysteries of motorcycling and by many considered a black art. This is because of the blending of the science of suspension with the variables of rider skills, preferences and rapidly changing demands of suspension. Much like a GP race team if the environment is relatively controlled and rapid changes can be made an engineer can work with the human factors to dial in the “perfect” set up. However most of us live in the real world where we constantly change the load the suspension carries, the temperature, surface conditions, traction availability, speeds, riding style (commuting vs playing), and this list goes on and on. This ever changing list of variables are one of the reasons I am an advocate of riders learning about suspension as well as how to fine tune it. Certainly the vast majority rely on the guidance and direction from professionals that can get our suspension in to a working range that is ideal for us and then leaving it up to us to fine tune. This includes spring rates, valving, recommended oil and baseline settings. From this point on it is up to you as the rider to be able to know what to target for change or tweaking.

Suspension is one of the most important items on a bike to have set up correctly. This is a worksheet I created using books such as The RaceTech Suspension Bible, and Wilber’s Motorcycle Suspension Technology in Detail (Optimization – Servicing – Technology – Tuning) along with my many years of teaching suspension courses. The notes and worksheets below are from a 2-day motorcycle suspension care, maintenance and set up workshop I taught for several years. Even though I don’t teach this workshop anymore I hope you are able to make good use of the notes and worksheets included in this document. Please visit www.BretTkacs.com often for new resources.

Suspension has two major jobs; first is to isolate the rider from the road, second is to keep the expand your abilities while exploring new limits, and know how to adjust and improve how it works.  Learning advanced riding techniques will improve your suspensions ability to maintain traction more than any “upgrade” or adjustment.  Often lack of riding technique will cause a bike to lose traction and fall down. When this happens riders frequently blame the tires, the road, or the suspension rather that the true cause… the rider!

If you are an engineer then I am going to disclose to you now that I may choose to use terms deliberately incorrectly so that the average rider can understand what I am trying to convey. This is not a technical article on how to build, design or even rebuild suspension. I am simply trying to demystify something that is a very complex subject with a never ending collection of possibilities, scenarios and exceptions. So feel free to twitch at what you read below and while you watch on my videos…

Common ways to “upgrade” suspension

– rebuild or maintenance existing suspension components

– buy a new bike with better suspension

– match the spring rate to the rider

– match the damping to the spring

– buy higher grade components

– decrease un-sprung weight

improve riding skills

– loose weight (make the bike or rider lighter)

Before you start changing parts dial in the suspension you have. You can often save a lot of money by optimizing what you have already paid for. The more you ask you suspension to do the more likely you may need to change or upgrade suspension. If your suspensions primary job is commuting and an occasional dirt road and you are only 180lbs/81kg then your stock suspension may be perfect for your needs. However if you are doing track-days or taking your big ADV bike on dirt trails or you way 250lbs/113kg then plan to open up your wallet and do some spending.

Before you spend a penny on suspension do the following procedures:

  • Confirm correct spring rates with fork and shock sag set around 1/3 of its total travel
  • Properly align the chain. If this is not correct the bike will corner improperly and sprocket wear will be increased.
  • Ensure the tires/wheels are balanced, if the wheels are out of balance, you may experience a vertical vibration and head-shake.
  • Set tire pressure (Use the tire manufactures recommendations not the Max sidewall pressure)
  • Check steering head bearings and torque specifications (if too loose, there will be head shake at high speeds.)
  • Inspect suspension components and suspension linkage for wear and condition

Initial suspension set-up

  1. Set Static sag 33% of total travel (average 25-35 mm) and check for free sag, front 5%-10% (average 5mm-10mm) and rear 1%-5% (average 1mm-5mm)
  2. Check for excess stiction (Front <10 mm good, >20mm bad, rear should be near 0)
  3. Set rebound and compression settings on forks and shock to manufacture recommendations or to the middle of their adjustment range
  4. Tune fork rebound
    • Front end should rebound and settle only a few mm, less for heavy rider, more for light riders (up to 15 mm)
    • For sport riding set as describe and then slowly tune out settling to 0mm
  5. Tune fork compression (this is difficult to do static and is best done during test rides)
    • Softer = comfort
    • Harder = sport (Too much compression = head-shake and reduced traction on bad roads or high speeds)
  6. Tune shock rebound
    • Press down hard, bike should return to full ride height in less that 1 second with a visible delay at the end of its travel (too much rebound = BAD)
  1. Tune shock compression (difficult to tune static… take it for a test ride)
    • Add more for sport riding or heavy loads
    • Less for Touring comfort, rough roads, or light weight riders.

Setting static sag:

  1. Look up your total suspension travel on line for the front and rear (in mm).
  2. L1= Next take a base measure by measuring a point above and below the point of movement (example; axle to triple clamp) on the rear measure from the axle to a point 10 degrees forward on the body or frame (straight up is ok too). This measure as to be take while the suspension is fully extended (lifted off the ground)
  3. L2= have the rider sit on the motorcycle with their feet on the foot pegs in the riding position in full gear with an average load (panniers on or loaded, with passenger or empty). Then compress the suspension (do front and rear separate) and very slowly release the suspension and then remeasure the same points used to get your L1 (the same person MUST read the measurements)
  4. L3= have the rider sit on the motorcycle with their feet on the foot pegs in the riding position in full gear with an average load (panniers on or loaded, with passenger or empty). Then uncompressing the suspension (do front and rear separate) and very slowly lower the bike/riders weight loading the suspension and then remeasure the same points used to get your L1 (the same person MUST read the measurements)
  5. Next add L2 &L3 togethers and then average them by dividing by 2. Subtract the averaged number from L1 (total available travel) this will give you the static sag number.
  6. The final step is to calculate what percentage of sag you have. Depending on the use the ideal sag ranges between 25%-33%. Of course there are variables that need to be considered in deciding where you want your suspension to sit and there may be exceptions where you may want/need more or less then the normal range of 25%-33%

 

If your spring is perfect for you then you may end up with zero shock preload. Keep in mind that fork spacers may require a “preload” spacer to fill space. A properly matched spring should allow about 5%-10% (for most street bikes this is about 10mm-15mm) of free sag (the sag under the bikes own weight). A spring that is too light (low spring rate) for the rider will require significant preload which will cause the bike to have no free sag. A heavier spring (high spring rate) will still allow free sag but will not require as much preload to set the proper static sag.

Even though you may be able to achieve the proper static sag with a light spring the spring is still too light to do the job and will end up providing a harsh ride and still bottom out. A properly match spring will provide both a comfortable ride and resist bottoming out.

Think of riding in a 1 ton truck with no load. It rides very harsh but when you add a load it handles and rides smoother. In comparison a ½ ton may drive smooth empty but if you put a heavy load in it will sag more, ride harsh, have loose steering (due to attitude change) and bottom out.

Static Sag = L1 – [ (L2 + L3) / 2 ]  (also known as Race sag or Rider sag)
L1= suspension free length

L2= rider, gear & bike, suspension raised and settled gently

L3= rider, gear & bike, suspension compressed and released gently

The answer is the static sag – you want around 1/3rd of the total travel (25-35 mm for most street bikes) , if your preload adjustments are near max or minimum then you need a different spring rate

Fork Damping Adjustments (common locations)

Rebound adjustments are located near the top of the forks.

Compression adjustments are located near the bottom of the forks.

Spring preload adjustments are located at the top of the forks.

Note: It is becoming more common (mostly on European brands) to have both the rebound and compression adjustments on the top of the forks. When this is done normally each fork only offers one adjustment.

 

Shock Damping Adjustment (common locations)

Rebound adjustment is commonly located at the bottom of the shock

Compression adjustment is located near the top or on a remote reservoir

Spring preload is located on a ramp adjuster or double collar and thread at the top or bottom of the shock spring

This Tuning Guide Assumes Correct Spring Rates and Sag

Front Suspension Tuning (Forks)

Lack of Rebound

  • Forks are plush, but increasing speed causes loss of control and traction
  • The motorcycle wallows and tends to run wide exiting the turn causing fading traction and loss of control.
  • When taking a corner at speed, you experience front-end chatter, loss of traction and control.
  • Aggressive input at speed lesson control and chassis attitude suffers.
  • Front end fails to recover after aggressive input over bumpy surfaces.

Too Much Rebound

  • Front end feels harsh.
  • Suspension packs causing the bike to skip over subsequent bumps and wants to tuck the front.
  • Under hard acceleration, the front end may tank slap or shake violently due to lack of front wheel tire contact.

Lack of Compression

  • Front-end dives severely, sometimes bottoming out over heavy bumps or during aggressive breaking.
  • Front feels soft or vague similar to lack of rebound.
  • When suspension is compressed a clunk is heard due to bottoming the fork travel.

Too Much Compression

  • Front end rides high through the corners, causing the bike to steer wide. It should maintain the pre-determined sag, which will allow the steering geometry to remain constant.
  • Front end chatters or shakes entering turns. This is due to incorrect oil height and/or too much low speed compression damping.
  • Bumps and ripples are felt directly in the triple clamps and through the chassis. This causes the front wheel to bounce over bumps.
  • Ride is generally hard, and gets even harder when braking or entering turns.

Rear Suspension Tuning

Lack of Rebound

  • The ride will feel soft or vague and as speed increases, the rear end will want to wallow and/or weave over bumpy surfaces and traction suffers.
  • Loss of traction will cause rear end to pogo or chatter due to shock returning too fast on exiting a corner.

Too Much Rebound

  • Ride is harsh, suspension control is limited and traction is lost.
  • Rear end will pack, forcing the bike to run wide in corners due to rear squat. It will slow steer because front end is riding high.
  • When chopping throttle, rear end will tend to skip or hop on entries.

 Lack of Compression

  • The bike will not want to turn in or feels heavy.
  • Suspension may bottom causing a loss of control and traction.
  • Excessive rear end squat, when accelerating out of corners, the bike will tend to steer wide.

Too Much Compression

  • Ride is harsh, but not as bad as too much rebound. As speed increases, so does harshness.
  • There is very little rear end squat. This will cause loss of traction/sliding.
  • Rear end will want to kick out when going over medium to large bumps.

Common Tuning Terms:

Damping –  Damping is how suspension energy is controlled through the process of converting excess energy to heat. This is done by controlling the speed of oil through the suspension by using a series of holes or valves.  Damping is speed sensitive not position sensitive.

PreloadThis is the amount of load (compression) being applied to the spring in relation to its free-length (non-compressed state). A common misconception is that preload changes spring force… it does not.

Rake – Angle of neck at normal chassis attitude

Sag / Static Sag-  is how far the bike compresses between fully extended and how far it compresses with the rider onboard.

Free Sag This is the amount the bike settles under its own weight with no rider on board.

Stiction – Amount of friction resistance there is to start suspension parts moving.  Static + Friction = Stiction

Suspension Travel – Total movement from top to bottom of forks / rear shock(s)

Trail/ Caster – Length made by a line from rake angle to vertical line measured from center of axle spacing in normal motorcycle attitude, this allows the self-righting effect of the front wheel.

 

Here is a worksheet you can use if you want to work on dialing your bike in on your own. Keeping notes is critical for making accurate changes or to reset the suspension if you make things worse and just need to go back to what you know before trying again.

When tuning suspension don’t choose your favorite (smooth) road. Choose roads or trails that will challenge. Take your bike to the places where you need suspension. As an example on my heavy ADV bikes I look for whoops and sharp hill crest where the back of the bike is likely to hop in the air or bottom out at he bottom of the ruts.

You also must be able to accurately repeat each run through a section at the same exact speed, path and tension. If you cannot be consistent then your settings will be subjective. I recommend attending a class with me or another trainer that can help you accomplish this.

 

Suspension Tuning Tracker

Full range of adjustments Front Rear
Total suspension travel    
Rebound adjustment range    
Low speed Compression adjustment range    
High speed compression adjustment range    
Ride Height adjustment range    

 

Initial settings Front Rear
Static sag    
Rebound adjustment    
Low speed Compression adjustment    
High speed compression adjustment    
Ride Height adjustment    

 

First adjusted settings Front Rear
Static sag    
Rebound adjustment    
Low speed Compression adjustment    
High speed compression adjustment    
Ride Height adjustment    

 

Final adjusted settings Front Rear
Static sag    
Rebound adjustment    
Low speed Compression adjustment    
High speed compression adjustment    
Ride Height adjustment    

Always make small adjustments, more is not always better.
Keep notes. Suspension tuning is an art, be patient.

 

Tuning NOTES:

Road Riding – Predictive Cornering

Predictive cornering is a strategy where I utilize primary and secondary indicators to compile all the available information to predict where the road is going, identify potential hazards, and reduce the compression of information. Eliminating one or more of the above strategies is often the cause or primary factor in riders crashing in curves. Predictive cornering is used to determine the following:

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