Anyone fully understand preload ??

[skint]

I have been doing some reading on suspension tuning and think I understand most of it but I've read conflicting bits of info regarding pre-load.

As I understand it ...

- The amount of spring pre-load does not effect spring stiffness but does effect ride height.

- Increasing or decreasing pre-load does not change the amount by which the spring is compressed (assuming bike is stationary with no-one getting on and off it).

- If you have a great deal of pre-load this will effectively 'extend' the shock meaning that any more sudden extension when riding might cause it to top out.

- If you have hardly any pre-load then there will be plenty of space in the shock to allow it to extend but very litle left for extra compression whoch may cause the suspension to bottom out frequently.

- There are different types of sag but rider sag can be considered to be the amount the suspension compresses when the rider sits on the bike.

Is my understanding correct or am I missing something ??

Where get confused is when I read that changing the preload can alter the amount of sag.

Surely the amount of rider sag as i've defined it above is more or less fixed for a given spring on a given bike with a rider of a given weight.

So, for example, if you increase preload to raise the rear by 5mm then the height without the rider on board will be raised by 5mm and the height with the rider on board will also be raised by 5mm
meaning there has actually been no change in overall rider sag.

What fits in much better with my understanding of things is when I read that preload should be adjusted so that with the rider on board the bike settles at about 1/3 of its total travel.

Any comments/explanations welcome.

Skint

[jonboy]

Preload does not extend your shock, it just increases the amount of time it spends fully topped out.


Erm.. forgot the rest of your questions

[Ichy]

The rear shock is generally of a fixed length irrespective of preload.
Preload is an amount of pressure applied to the spring without any other forces applied, i.e. the rider. Pre load will not usually adjust the ride height of a static bike although ride height can change at various preloads with the same rider.

Basically preload should be set to a specific rider weight. There are a number of measurements that can be taken to give the best possible position, I just can't remember what they are, but for example the bike should only drop by 20mm when the full weight of the rider is applied to a static bike.

There's loads of stuff on the 'net about setting up bike suspension.

[craigs23]

Makes for some interesting reading https://www.sportrider.com/tech/146_9510_tech/

[skint]

I think i nearly understand it now ...

so, if I take the shock off the bike and allow the spring to fully extend and hardly tighten the preload collar at all, i've got very little preload -- right ? if i then put the shock back on the bike, the bike will sit at a certain height. I i then take the shock off and increase preload to the max possible so the spring i realy compressed and then put it back on the bike, will the bike sit at the same height as before ?? (without a rider on). I guess that with max preload when a rider does sit on it, the spring will compress much less than if it didnt have any preload at all ?

Thanks, skint

[skint]

Also, if changing preload changes ride height (which i've read in several places) then this is presumably because when a weight (the rider) is put on the seat of the bike the amount of compression that occurs depends on the preload, morepreload=lesscompression=higherRideHeight. So, surely this must be the case when there is any sort of downward force on the suspension, even if its just the bike without the rider.

Skint

[owdamer]

Heres a way to understand what happens in simple terms.
I put an ohlins shock onto my yzf. I didn't get any setting with it so I guessed. Went out for a test ride, all was going fine so I upped the pace. I went hurtling into a corner, Hit the brakes, Hard on the front, plus a little rear to steady things. Next thing I know the back locked up & the bikes all over the place. After that had happened a couple of times I figured out what was going on. As I hit the front brakes the front was diving, but because the preload was to much on the rear the spring was uncompressing (not sure of the right word!) to quickly and causing the back wheel to jump. Once the wheel is clear of the ground very little rear brake is required to lock it up.

[The Dude]

Following on from what Owdamer has just said. Could that explain why some people find a certain bikes handling to be great while others find the same bike not so great, because maybe the 2 people are different heights and weights, and bikes are usually sold at the manufactorers default settings? And if that is true, would it be a good thing to have a bikes suspension roughly set up for your individual weight and height before you even leave the shop with it? Or would they just laugh at you if you asked a shop to do that? Would they even know how to tailor it to each individual?

[owdamer]

I read somewhere once that the standard suspension on production bikes isn't quite as adjustable as you think. It might have lots of clicks, positions, etc, but the actual difference isn't that great. If you could make a bike unstable simply by adjusting the suspension then the manufacturer would be leaving himself open to massive compensation claims by anyone that crashed.
Of you go out & fit some top notch suspension then you will feel the difference a couple of clicks make.
Another thing is that not everyone like the same feeling. racers especially. some set the bike so it wobbles all over the place where another guy will set his rock hard. now if these 2 racers swap bikes, (lets say they both ride for the same team) they will say that the others bike is unrideable.
If you go to the ohlins website there is a pdf which explains it all in great detail.