Preload?!

FuzzySime

Morning troops,

Had my first ride up to the Cathkin Braes on my spanking new Rockhopper Comp yesterday and im still smiling!

But, iv got a couple of questions....i've worked out the lockout but im confused with what the preload does? Is it to do with rider weight? and what type of riding/terrain is it suited to?

also, (excuse my shoddy terminology :? ) the cables that run underneath the bottom of the main frame that lead to the gear shifter thingys (front and rear derailluers??) twist over each other (don't run parallel) is this normal?

Thanks for any advice, this is my first 'proper' bike and im lovin it!
Cheers Sime,

nicklouse

preload is for setting the Sag. How much the fork is compressed when in the normal riding position.

Set it and leave it.

cables crossing. yes no problem.

FuzzySime

thanks for the quick reply nicklouse!

nwmlarge

to explain it simply

less preload will absorb bigger hits
more preload is better for flatter terrain

supersonic

Not really:

Preload sets the force required to activate the suspension, so therefore sets the sag and ride height of the fork. The spring rate is unchanged - once sagged the fork feels the same under compression.

FuzzySime

supersonic wrote:

Not really:

Preload sets the force required to activate the suspension, so therefore sets the sag and ride height of the fork. The spring rate is unchanged - once sagged the fork feels the same under compression.

So, if i follow correctly, it sets the sensitvity of when the suspension kicks in according to the weight of the rider?

supersonic

Yes, as you load it when you get on the bike. It will still kick in for the same hit once this has happened. More preload = less sag because it is taking more of your weight for that initial compression.

Technically you have shifted the spring curve, but not altered its slope.

nicklouse

FuzzySime wrote:

supersonic wrote:

Not really:

Preload sets the force required to activate the suspension, so therefore sets the sag and ride height of the fork. The spring rate is unchanged - once sagged the fork feels the same under compression.

So, if i follow correctly, it sets the sensitvity of when the suspension kicks in according to the weight of the rider?

well no. the sensitivity of the fork is fixed.

that is the spring rate. It is constant. (except that most have sealed air chambers that add a rising rate Air spring to most forks.

Preload is purely for setting the sag IE how much the riders weight compresses the fork. add preload and you need more force to start the fork moving but the rate stays the same.

The Rookie

To add to the above, preload doens't affect the suspensions stiffness or responce, but it does affect the initial effect, if you have to much preload (extreme would be no compression at all static) then you'd need a bigger hit to get the suspension to deflect at all, also no rebound travel is available so the wheel will lift over potholes rather than follow the terrain, if you ran not enough preload (most units can't let you do it) then you risk bottoming out to often and that's both uncomfortable and can damage components.

Usual advice is to set preload so that static (rider sitting on bike not moving) you use 1/4-1/3 of the available travel, but if the spring weight is mismatched to your weight you may need to run a little more or less.

Simon

nwmlarge

so what i said is right
less means it will absorb the bigger hits ie: react faster to accomodate the bigger bump

Daz555

nwmlarge wrote:

so what i said is right
less means it will absorb the bigger hits ie: react faster to accomodate the bigger bump

Not really. Your comment somehow implies you set the preload for the terrain or that a fork will behave differently across terrain at different pre-load settings. This is not the case - you set preload for your required sag.

Preload lets you set your desired sag. Sag is of course handy in preventing the shock from topping out all the time as the wheel dips.

nwmlarge

so stopping a shock topping out is not changing how it behaves?
yeah ok

supersonic

The sensitivity of the fork is exactly the same once you are at sag point wheter at max or minimum preload. As above if anything, having less preload (more sag) reduces available travel so is not as good for bigger hits.

Daz555

nwmlarge wrote:

so stopping a shock topping out is not changing how it behaves?
yeah ok

You never mentioned top-out in your previous posts. If you had, I'd have been in complete agreement. You mentioned 'bigger hits' , 'flatter terrain', and 'react faster'.

Sonics point about big hits above is spot on.

To the OP - preload is about getting required sag (25% of travel for example). That's all any of us need to worry about.

nwmlarge

fair enough.

Northwind

If this were a motorbike forum, by now everyone would be talking about how it makes the spring stiffer. I love mtb forums, people still get it wrong but at least it's a different wrong