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2007 GT Avalanche fork tuning

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2007 GT Avalanche fork tuning

Old 03-19-16, 02:06 PM
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johntamrhein
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2007 GT Avalanche fork tuning

I recently acquired a 2007 GT Avalanche used, of which I installed a bike motor kit.
It's a $950 Heat-treated aluminum XC "triple triangle" frame with disc brakes and 4" travel front adjustable shocks.
The forks sag a bit much, especially with the added weight of the motor kit, with myself, on it.
The forks have a Preload adjustment on only one of the fork tubes, the left side, with a "+" and "-" to indicate, which way to turn, I suppose, the adjuster, to either increase or decrease the Preload adjustment, as I'd imagine.
I tried turning the what appears to be the adjuster, by hand, although it was too difficult to turn by hand, and I didn't want to break it.
How do I adjust the Preload on this bike?
Which way do I turn it?
How do I know when I've reached the end of the adjustment travel?
Will this preload adjustment prevent fork spring sag?
I was also told, Cross-country (XC) bikes should run stiffer suspension, with less sag, than mountain bikes, of which have front and rear shocks, as opposed to XC bikes, which only have front suspension.
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Old 03-19-16, 08:46 PM
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gsa103
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The preload on those is pretty worthless. The most realistic option is to replace the coil spring, if there's a stiffer spring available. You just need to look up the fork model. Rockshox usually has 3 different spring options.
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Old 03-19-16, 10:50 PM
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I haven't heard anything nice about the stock suspension RockShox forks on this bike, and how they should be swapped out.
Remember this is now a motorbike, and I just want the shocks to soak up some road bumps, nothing off-road.
I don't know how expensive new fork springs are, but maybe there are helper springs available-very short coil springs used in conjunction with the original fork coil springs, to add some stiffness, for short money.
I'm more of a motor-biker, a mountain bike with a motor on it, than a mountain biker. And thus I'm not all tech savvy with the elite accessories of mountain biking, as well as some of its terms.
Just what exactly is the Preload?
I understand compression, damping, and rebound, but I'm not familiar with the Preload.
Does this have to do with adjusting the fork spring sag, which may also be referred to as preload?
Even though the adjuster on the top of the left fork is practically useless, to familiarize myself with it, before making another decision, how would I generally make an adjustment with the top left fork adjuster?
Why is there only one adjuster on only one fork tube? Aren't these independent front forks, and hence, would require an adjuster on each fork?
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Old 03-20-16, 02:50 AM
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What fork is it?
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Old 03-20-16, 10:52 AM
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Most bike forks have the compression (spring/air) in one leg and the damping in the other leg. That's why the preload is only on one side (the side with the spring). A lock-out would be on the other side (damping).

Preload compresses the spring, so that you have to apply more force before the fork starts to move initially. More preload = more force (and less sag). Unfortunately, the preload doesn't change the spring rate, so once the fork starts to move, it's going to behave in a very similar fashion.

There's a good chance the preload knob is jammed at one end or the other. Taking the fork apart might allow the knob move easier (without the spring pressure on it). My experience is that the preload never did make much difference, so if the fork is too soft, its likely still going to be too soft (I had a 2009 Avalanche)

There aren't any helper springs, but you can frequently just buy a stiffer replacement spring for ~$40. Rockshox is very good about having 3-5 different springs for most of their fork models, Suntour usually only has one model. If you have a Rockshox fork, you best bet is look up the model and see if you can get a stiffer spring. If you have a Suntour fork, your best option is their customer loyalty program, and buying a better fork from them.
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Old 03-24-16, 05:20 AM
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Thanks for the info.
I was thinking in terms of dirt bike forks, of which have a fork spring in each tube.
Anyways, I got the Preload adjuster to turn with channelocks, and there was a lot of adjustment there.
Seemed like I turned it forever.
Since it turned so many times, I didn't bother trying to reach the end of the adjustment, that is the stiffest Preload setting, but stopped when I got rid of much of the sag, leaving close to the recommended 1/4 of total fork travel for sag left while sitting on the bike.
And this bike, practically bottomed out, or reached the end of its travel, before I completed the adjustment.
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