Purpose of Pre-load

[ddemair]

This has probably been discussed before so a link to the relevant thread would be appreciated.

Now, please correct me if I'm wrong, but it seems to me the purpose of pre-load is maintain proper sag depending on rider/passenger/luggage weight. After all, spring rate is not affected, rebound is not affected, but spring travel IS affected. In fact, it's reduced. I think that means less chance of bottoming out since the spring is starting out somewhat more compressed before the bike hits a bump.

BUT, other than reducing the chance of bottoming out (it doesn't happen often anyway) is maintaining proper sag the only real-world reason to set an appropriate pre-load?

 

[Larry Fine]

A given weight , or weight increase, will compress a given spring a given distance.

The "preload" adjustment only changes the starting height, and the added weight sets the end height.

Thus, what you're really adjusting is the ride height after all loading is applied to the bike.

 

[ddemair]

Thus, what you're really adjusting is the ride height after all loading is applied to the bike.

Thanks, this is my exactly interpretation of pre-load.

 

[dduelin]

Ideally adjusting rider sag sets the suspension's dynamic travel to the middle 1/3rd of available travel. As such it allows the suspension more travel under compression. It adds travel for most riders as the stock springs are too soft for most American riders and all two up couples.

I'd disagree about the ST's fork not bottoming out under the average weight rider on bumpy roads or when riding and cornering aggressively. You can place two zip ties around a fork leg with the upper one set at maximum travel and the lower one pushed against the dust seal of the slider. After a spirited ride including a full-on threshold braking stop there will likely be zero to less than 5 mm separation of the ties.

Secondarily, preload can change or fine tune steering and handling characteristics by raising or lowering either end of the bike which changes steering geometry. A rider that likes to sharpen steering inputs could raise the rear or lower the front to add rake and reduce trail or do the reverse to slow steering inputs and help the bike track naturally to the outside of corner exits under power.

 

[bdalameda]

The biggest mistake people people make is thinking that spring preload will adjust the spring stiffness. The pre-load is there to adjust the ride height it cannot change the spring rate. A too soft spring cannot be helped by adjusting the preload.