Front preload query

I've been watching how much front fork travel I've been using by the zip-tie method (K3 standard forks and springs). To try and learn more about how the pre-load affects the bike, I've increased it a lot in one go (about 5 rings).

The thing is, I can detect very little difference in the handling (probably user error) and almost exactly the same amount of fork travel is used.

According to my understanding, the pre-load has no affect upon the spring rate, but changes the load at which the spring starts to compress. But from there on, the same additional load will move the forks by the same amount.

Therefore; the pre-load adjustment on my bike isn't working, or the effect is minimal across the whole range of adjustment, or I'm suddenly applying more load to the front than I used to.

[Luckypants]

Well your understanding seems sound.... perhaps you were using the full range of fork travel before and are still doing so? how much do you weigh for instance?

Originally Posted by Luckypants

how much do you weigh for instance?

Probably about 13.5 st in gear. Consistently using about 10mm less than full travel - never bottomed them out.

Preload has no effect of travel. It is used to set sag. You need a certain amount of sag so the suspension extends into dips and holes and under heavy braking the rear tyre stays in contact with the ground.

If your forks are bottoming or not getting enough travel you need a different spring rate.

Originally Posted by simesb

Probably about 13.5 st in gear. Consistently using about 10mm less than full travel - never bottomed them out.

That sounds about right.

Originally Posted by Scoobs

Preload has no effect of travel

Well that may answer my question. I know that it controls sag, but I thought (probably incorrectly) that if the spring rate was 1kg/cm, and the forks were 2 cm long, then if the sag was set to 0cm, it would take an additional 2kgs to bottom the fork, but if the sag was set to 1cm, it would only take an additional 1kg.

[Biker Biggles]

The preload only really affects sag,or the amount the bike sttles under its own wieght(static sag)and under the wieght of the rider(rider sag)This is more relevant to when the forks top out than bottoming.What you probably need is stiffer springs and maybe more damping from thicker fork oil?

[Biker Biggles]

Someone beat me to it.

The spring rate remains constant for linear rate springs but will increase slightly (not noticeably) for progressives.

A further thought / point of note. Whacking on loads of preload could make the forks top out as they extend. You'll have too little sag so the forks (and rear shock if the preload is wound up on that) will not have enough negative travel (extension) left to drop into dips etc.

[Sid Squid]

X load and Y bump will compress the suspension Z amount, changes to the preload will not affect that, (unless the preload change were to put the suspension less than Y from the bottom of travel), what preload does is describe where in the suspension's travel you are under any given load and suspension deflection.
Altering the preload doesn't change the suspension at all, (of course it may mean the suspension will run out of travel either extending or compressing before accommodating a given deflection), the purpose of the preload adjustment is allow the suspension to be set such that it will best deal with the majority of deflections it will encounter, which depends entirely upon the specifics of who rides it where and how, which is why there is no 'right' setting. All this must be done whilst accepting there will be foreseeable circumstances outside the capabilities of the suspension, for instance if you have 100mm of suspension travel in total, a bump approaching that size won't be well dealt with by your bike no matter what you do with the preload.