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Prof's Patch: suspension basics

Modern bike suspension features amazingly complex and expensive components and it’s where the majority of the cost goes in building a bike. For example, a $12,000 TM has over $6000-worth of Ohlins suspension! But no matter what suspension your ride has, you can transform your ride by simply setting up the suspension properly. Were not suggesting that stock suspension is safe for hitting ramps – it’s not. If you come up short or flat-land with stock suspension, it’s gonna hurt. In this issue we’re going to get comfortable with the basics of suspension adjustments.

THE PROF’S SUSPENSION DICTIONARY
Clickers – Common term for all the adjusters on suspension. Their position is always measured out from fully clockwise.
Compression – The direction the suspension travels when the wheels move up towards the bike.
Rebound – The direction of suspension travel when the wheels move down and away from the bike.
Free Sag – Also known as “static sag”. This is the amount the bike settles as it comes off a stand under its own weight.
High Speed/Low Speed – The rate at which the suspension moves – not related to actual speed the bike is travelling.
Preload – The amount a spring is forced in from its natural free length.
Race Sag – The amount the bike settles as it comes off a stand and you then sit on it.


FRONT FREE SAG
With the bike on the ground, put a cable tie around one fork next to the dust cap, then gently pull up on the bars until the fork is fully extended. The distance between the cable tie and the dust cap is called “free sag”. This figure should be between 35mm and 50mm. Front free sag is adjusted by changing springs or pre-loading them with spacers. Remove the cable tie before riding or it will destroy your dust caps!

REAR SAG
Free sag
Put the bike on a box stand and measure from the rear axle vertically up to a point on the side cover and mark this point at a convenient height (say 600mm). Now, drop the bike off the stand and let it settle, then measure how far ithas settled. This is called free sag and should be around 25-30mm (except for KTMs, which must be exactly 35mm because of their Positional Damping System and the shock needs to know exactly where the wheel is).
The rear free sag can easily be adjusted to within 25-30mm by tapping the preload collar nuts on top of the spring with either a collar spanner, or a hammer and drift. Clean the threads first and spray them with WD40 or similar before you start. KTMs have a split collar, so don’t forget to back off the locking screw.
Race sag
Once the rear free sag is set correctly between 25-30mm, sit on the bike in a neutral position and get a mate to measure how much it sags from your first measurement. This is called “race sag” and if it’s greater than 105mm or a third of the rear-wheel travel, you’ll need a heavier spring in your shock.

REAR REBOUND
This is almost always found at the bottom of the shock and controls the low-speed rebound (how fast the rear end rises after being compressed).
If it’s too tight (say, three clicks out from fully clockwise), the bike will ride low in the rear through whoops. If it’s too loose (say, 20 clicks out), the bike will pogo you over the hangers after landing from jumps. A normal setting is 7-12 clicks out.

REAR LOW-SPEED COMPRESSION
This is the screw in the middle of the adjuster bolt, and controls how fast the rear-end drops through the curve of an up-ramp or when pre-jumping. If this is set too loose, the bike will fishtail under acceleration. If it’s too tight, the bike won’t wheelie easily, but will get great traction. A typical setting is 9-5 clicks out.

REAR HIGH-SPEED COMPRESSION
This is the big nut on the outside of the adjuster bolt. If it’s too tight, the bike won’t cope with little square-edged bumps like corrugations on dirt roads, but if it’s too loose, the suspension bottoms easily. Most tuners prefer to run these as loose as possible. A starting setting is half a turn in from fully wound out.


FRONT LOW-SPEED REBOUND
These are generally on the top of  White Power, Marzocchi, Ohlins and Kayaba forks and on the bottom of Showas (Honda, Kawasaki and Suzuki) and control how fast the front end raises itself after braking or landing from jumps. They also control ride height when riding over uneven ground. For FMX, it’s best to run them pretty tight, but if your bike jumps out of rutted turns, it means the adjustment is too loose. Test that both the front and rear ends rise together by locking the front brake and pushing down hard on the pegs. A bike’s front-to-rear balance essential. A typical setting is 9-5 clicks out.

FRONT LOW-SPEED COMPRESSION
These are generally found on the bottom of White Power, Marzocchi, Ohlins and Kayaba forks and on the top of Showas (Honda, Kawasaki and Suzuki) and determine the rate at which the front end dives under brakes and through the transition of ramps. If it’s too soft, the front end will ride low, but too hard and it’ll be difficult to set into a turn. A common setting is 10-5 clicks out.


WRAPPING IT ALL UP
What about front high-speed compression, you ask? Only Ohlins and Marzocchi-equipped bikes have this adjustment and that’s why race teams fit them. These brands aren’t necessarily better, but they’re a lot easier to tune.
Front and rear high-speed rebound isn’t super-critical except if you’re Backflipping and you need a balanced, tight, high-speed rebound. This severely limits your pop off the ramp, but top-level FMX is now all about flipping.
For some good, simple notes and ideas on setting your suspension, try and get hold of an older CR owners’ manual. Honda’s detail in these was awesome and goes fully into what fixes what. Last, if you have to run your clickers tighter than the numbers in this story, your suspension needs re-valving. Closing clickers right up is dangerous … and so is riding FMX on stock suspension!