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Help: Front suspension setup the old way?

Discussion in 'Racing, Motorsports, and Track Days' at netrider.net.au started by RedNinja, Sep 8, 2008.

  1. Hey all,

    I have been playing with the setup of my race bike (CBR250R), which has bugger all adjustments for front suspension (ie. none) and have been told a few things that I can do to improve things. I am unsure if ihey are crap or not, so I just wanted to see if anyone understands these ideas (below), who could maybe reply to help me to understand.

    They were:

    1. If I drop the height of forks through the triple clamp more the bike will turn-in faster?

    2. If I add more oil to the front forks, there will be less air to compress, so the forks will respond more slowly at speed. Hence less likely to vapour lock?

    3. Using spacers in the tops of the forks (20 cent pieces) will simulate pre-load? So I can have a crack at setting static sag correctly...

    Any experience with these ideas here folks? I just don't understand, except for maybe the 3rd point.

    Thanks for reading,

    Cheers RN.


     
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  2. 1. If I drop the height of forks through the triple clamp more the bike will turn-in faster?

    Yes, will also hold a tighter line

    2. If I add more oil to the front forks, there will be less air to compress, so the forks will respond more slowly at speed. Hence less likely to vapour lock?

    Only affects the bottom 3rd of travel

    3. Using spacers in the tops of the forks (20 cent pieces) will simulate pre-load? So I can have a crack at setting static sag correctly...

    yes.
     
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  3. Yes. It will also be less stable at speed, and you will have less ground clearance. A similar effect which actually gives MORE ground clearance can be had by raising the rear through a ride height adjuster or similar.
     
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  4. Thanks Ian,

    Just with your response to point 2, I am not sure I quite understand. Does that mean the first third of travel will slow down? So initially it will be slower to respond to smaller bumps?

    Becasue I got told to drop 15mm extra oil in each fork to slow it down a bit, to be more stable on corner entry. So would this be correct then?

    Many thanks on the fast response too :grin:
     
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  5. Bottom 1/3 of travel = final 1/3 of travel = last bit of travel before you bottom out. Not first 1/3 like you are thinking.

    I would run a heavier weight oil to slow it down rather than reducing the air gap.
     
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  6. Ah got it now, thanks :)
     
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  7. putting spacers above the spring doesn't simulate pre-load it is preload and there is no point in doing that and lowering your forks as you are counter acting each other.

    If the bike is too slow and you have run out of rear pre-load (or you are too short) then you need to lower the front end.

    If you do this, but are running out of travel then you need stiffer springs. More pre-load will push you back towards where you were.

    the air gap determines the rising rate effect of the forks. The less the initial gap the faster the rate rises. so you can use this to counteract bottoming. But it may make the forks to stiff too quickly.

    Swings and roundabouts.

    I say get your fork oil right, then you rear ride height, then look at the front ride height.
     
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  8. All preload does is set the sag, determining where the forks sit within their stroke with the rider on them. Typically a road bike will have the sag set so that with rider aboard, about 1/3 of the travel is used. In a road situation you do not want too much preload as the forks will top out, ie, they will have nowhere to go downwards if you hit a dip or a hole. You normally operate within the middle 1/3 of the stroke and the last 3rd is what is available for extreme braking, large bumps.

    In a race bike, the tracks are usually smooth and have an absence of large dips and holes (unless you go to Winton). You can therefore run more preload, which will in turn give you more available suspension travel.

    Dropping the forks on a bike with RWU forks decreases the available suspension travel. The intent of dropping the forks is to speed the steering and enhance flickability, at the expense of stability. Drop them too much and the steering is extremely fast, but the bars wag around a lot (and this can be quite disconcerting if you do not run a damper).

    If you drop the forks but then pump up the preload, you will move the suspension higher up the stroke, regaining some of your travel but also raising the front of the bike as well. However, if you drop the forks but still maintain the same preload, you will likely bottom the forks out under heavy braking.

    The intent behind changing the level of oil is to increase of reduce the air gap. Air is compressible, therefore the more air you have, the more there is too compress. Reduce the air and replace it with non compressible hydraulic fluid, then there will be less air.

    Damping rod forks such as yours (and mine) have limited adjustments and even the addition of emulators results in little discernible difference.

    Your main adjustments are the weight (thickness) of the oil, changing the spring weight and changing the volume of air.

    Ideally you raise the rear, but your bike (and mine IIRC) are not permitted to do this.
     
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  9. Don't put washers on top of your fork spring. Fit the correct spring.
    Think about a set of "Gold Valves" too.
     
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