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Thread: Icebreaker II: Those Fairies In Your Suspension

  1. #1
    N00b Mustang's Avatar
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    Default Icebreaker II: Those Fairies In Your Suspension

    So now the thing runs we get to the next challenge: keeping it on the road, as opposed to in the air.

    In that rare moment of honesty some of us will admit Itís hard to be a fantasy racer glamorously heeling it into bends while in reality we hang on for dear life as Japan's finest bounces on and off the deck like a springbok on heat. (Remember all that suspension theory you Googled on the bossí time...?)

    We turn to the subject of suspension. Iíll figure out whatís going on; you come for the ride. It beats work.

    Suspension basics:

    ē Preload determines how much pressure the shock/fork springs need to take your weight without the bike sagging significantly
    ē Compression determines how much of the shock of a bump gets absorbed vs. how much gets transferred to you
    ē Rebound determines how quickly the bikeís shock and fork returns to their normal length after being compressed

    The shock/fork springs compress when you hit a bump. If compression rate is soft, the ride is soft but the suspension bottoms. If itís hard you feel as if you have no suspension at all. Your tender regions get pounded by a jack hammer of Japanís finest.

    Rebound, i.e. the decompressing of the shock/fork springs, must be set in line with compression. If rebound is too slow, after compressing the fork/shock will not return to its normal length quickly enough. The shock/fork spring isnít fully decompressed in time to be ready for the next bump. Effectively the bike has next to no suspension.

    How do we control all this? Read on.

    The fun stuff is compression and rebound. The job nobody wants to bother with is preload. So letís have fun compressing and rebounding.

    Push the nose or tail of your bike down and let go. With a pfft it comes to rest in its original position. Note, comes to rest in its original position. If the suspension consisted of springs only, thereíd be no pfft and it wouldnít come to rest. It would rock up and down like a metronome. We donít want that. We want it to compress the springs, return to its starting position and stay there, ready for the next bump. We want a controlled decompression.

    What causes the pfft and the consequent rock-free stability?

    A rebound control method called damping.

    Suspension 1 Paint.png
    Source: Ikon Suspension


    Inside the spring coils youíll see a rod. That rod disappears into an enclosed cylinder. This cylinder is filled with oil. On the far end of the rod is a piston, with a hole in its crown. As the spring compresses the piston gets pushed into the cylinder of oil. The oil provides resistance, acting as a brake. Oil squirts through the hole in the piston.


    Suspension 2.gif
    Source: Showa Motorcycle Shock_Absorber


    As the spring compresses and de-compresses, the piston slows the compressing and de-compressing of the spring. This stops the shock or fork from bouncing. The spring reaches its normal length and stays put, ready to absorb the next bump.

    Damping control involves adjusting the damping rate so it brakes the spring just enough to prevent rocking, without so severely slowing de-compression the spring hasnít finished de-compressing by the time you hit the next bump.

    Methods of controlling this include varying the size of the hole(s) in the piston, and valves to regulate the oil and, in certain cases, gas flow. There are as many designs are there are shocks but these are the basics.

    Thus your springís de-compression, or rebound, is slowed enough to prevent rocking while still allowing full de-compression of the spring in time to deal with the next bump.

    Damping is controlled by a screw or nut on the shock(s) and, in some cases, on the fork. They all look different but hereís an example.


    Suspension 3.jpg
    (The red nuts are preload adjusters but similar screws, or nuts, if present, will allow adjustment of rebound damping)
    Source: jap4performance


    Too much damping (excessive slowing of the springís de-compression) means the spring isnít ready to absorb the next bump. The feeling is of riding on corrugations.

    Too little damping (allowing the spring to de-compress too quickly) results in a rocking, wallowing ride characterised by a lack of control.

    Who wants to be the guinea pig?

    Iíll be.

    I check the Banditís suspension. The rear shockís damping is set to S. Without a manual I have to decipher that S means. Soft, obviously, but defined as what? Iím guessing it means low rebound damping, erring on the side of comfort. Hmm. The screw turns four times, thatís eight half-turns, between S and H. Letís turn it to halfway; two turns/four half-turns out.

    The only way I can test this is - how convenient! - by going on a ride on the same road I rode previously, to compare.

    Will it be significantly better, only slightly better, or same-old, same-old?

    Watch this space!

  2. #2
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    PING:

    Linus has a few Bandits that cruise the country regularly.

    Check him out on the forum.
    All my posts are my opinion and not those of TB or TB Marshals or any other sane human

  3. #3
    N00b Mustang's Avatar
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    Thanks, I will!

  4. #4
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    Default

    Nice write-up

  5. #5
    N00b Mustang's Avatar
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    Thank you!

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