21/08/2026
Morning everyone, setting sag is a misunderstood often forgotten portion of getting a motorcycle to not only go around corners but also in a straight line.
For the most part, riders read a specification in a magazine (yes Im old) online of from their mates, generally whatever they put into their bike as a setting will be wrong but for different reasons.
The actual mesuring of sag Im not set on, measure it however you want, but make it repeatable otherwise it’s useless.
For the most part that will be standing, in mx and off road, sitting for road, and measure in line with the arc of travel.
Pritty simple so far. Oi.
So for the how why what.
The actual sag number is generated because we need the suspension to extend as well as compress, if we are riding along and there is a hole or depression, we need the suspension (and more so the rear suspension) to extend into the depression otherwise we loose tyre to ground traction and we get wheel spin, loss of control and so on, all of this is also exacerbated by slow rebound damping but that’s another day.
In general ride sag is set as wheel travel devided by 3. So 100/3=33.333mm , 310/3=103.333mm and so on, from there we make an allowance for the use, we wouldn’t run 305mm sag on forks for example, and the bikes geometry which is also for another day, and even the way a bike flexes or a rider uses their riding style to influence the bike.
The biggest deviation for setting sag that Im going to portray is that changing preload is easier to think of if we think in the manner of ride height adjustment rather than turns, so the more preload we apply to a spring (the more stored potential energy) the less sag but also the higher the bike sits in relation to the ground.
We can then use sag in this manner to influence what handling character our bike has, more sag on the rear (without changing the front) will give the bike more stability but more effort is needed to turn and the bike will wheelie more on exit. Less rear sag, less stable, easier to turn but more wheel spin on exit.
So what we are looking for is a balance so that we have some suspension travel for the dips, traction, turning, stability, nimble setting.
Well consider that motorcycle react more like fighter jets so all of the settings work in conjunction and at the same times as one another, if you have a soft fork spring or compression setting the bike will always dive under brakes excessively inducing instability in the braking bumps.
Now ive also introduced the fork sag setting as a concept here, it’s something near all riders and quite a few shops don’t consider, but the concept is the same, fork sag is still needed, it still influences handling and so is still an important measurement to consider.
So the numbers. For my kx250 the sweet spot is forks 52mm shock 112mm measured with me standing in the riding position, forks 5mm plus cap 4.9N fork springs at 6mm preload, but the truth is you’re not going to find the sweet spot in that setting nor a magazine, get out and ride, make a change, ride again.
And that’s what the sat morning setup days are all about at the workshop, and it’s also why I don’t do these setup days at the race track.
Have a great weekend, Im still in France, Aiden and William have a few more days competing in world championships, but on the plane in how many days Robynne?
Enjoy - Craig
