Join Date: Sep 2007
Location: Gaseous Cloud around Uranus
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What kind of bike? If your bike has very little rake,it can get twitchy with weight on the front of it.The more weight you add the LESS rake it has.This is why touring bikes have alot of rake to begin with.The turning is sluggish without weight but actually inproves with stuff added to the front.
Without getting technical,as you turn the front wheel,it actually lifts the front of the frame up and down.This is caused from the caster angle(rake on a bike).So,if you add weight behind the axle,the weight from panniers actually help keep the front wheel straight.
If the panniers are in front of the axle,it wants to be in the back.
Thus the trying to get the pannier centered on the axle,hopefully a neutral position.
This is the simpleton version of steering geometry,there's lots more involved.
Now all of this is what happens on paper,it's not written in stone.There are so many variables,no two people will have the same experience.But it should help you understand what is going on.
As a side note,if you ever looked close at a bike that they ride in the circus or do tricks on,many of them will have no rake at all.They will have a straight fork,that's so when they do tricks,the wheel does not want to return to center,their weight being swung around the bike doesn't have an effect on the steering.
Remember the old time Harley choppers with the long forks? Really long forks? They can have massive positive caster,ever when the head tube is raked.When you turn one of those,the frame can lift a couple inches! So the weight of the bike wants to keep the front wheel straight.
Positive caster makes the front end twitchy,because the axle in the FRONT of the fork centerline,but it still wants to roll straight ahead.It still has to lift the weight of you and the bike in order to turn.
Negitive caster makes the front end roll straight,but is NOT twitchy because the axle is trailing BEHIND fork centerline.It still has to lift the weight of you and the bike in order to turn.
The more caster angle,positive or negitive,the more the wheel wants to stay straight.The more positive caster,the more twitchy it gets,the more negitive caster,the more stable it gets.
The closer you get to neutral rake,the less the effect of outside sources,but you sacrifice stability going straight.If you cross the line with positive caster,stability goes out the window.
Basically,it works like a giant front wheel on a shopping cart.
Last edited by Booger1; 05-26-11 at 12:50 PM.