[Luddite]

I'm in no way (and certainly wouldn't profess to be) a suspension expert. I rely on proven experts like the two I've quoted above if I want to know anything. So a few words on their qualifications...

Niall Mackenzie is a successful former racer with 7 500GP podiums and 3 BSB championships. He has a wealth of experience on a wide range of machines under a wide range of conditions.

Tony Foale is a professional engineer, Bachelor of Technology and Master of Engineering Science. Sometimes, when a person is an acknowledged expert on something, people say "Oh, he wrote the book on that". Well, when it comes to motorcycle suspension and chassis design, Tony Foale actually DID write the book on that! (Check out his website https://motochassis.com/ there's a lot of useful information and interesting articles there.)

When people with that experience and those qualifications say the same thing, I tend to believe them.

Originally Posted by Uncle Bob

Yeah but that's the STATIC i.e. without rider position! It's the suspension's position WITH a rider that's way more important! Unless the bike is going around on its own it's a bit irrelevant.

Not actually irrelevant because, although the suspension may be compressed with the rider on board, that is not a constant state. There are times when the rider's weight is effectively removed from the equation. For example

• (on the rear shock), under heavy braking when all weight is transferred to the front
• (at both ends), going over a rise in the road like a hump-back bridge
• (at both ends), dropping into a hollow or pothole

Originally Posted by Uncle Bob

As for the second point, it's kind of true, but that's what rebound damping is supposed to control.

Up to a point, but if you're increasing rebound damping to control the results of insufficient static sag, you'll just be creating other problems elsewhere. For example, on a washboard surface, the suspension may tend to "pump down" over a series of bumps as the spring fails to return to it's static position before hitting the next bump, perhaps eventually even bottoming out.

Better to minimize the topping-out by setting the correct sag than masking the problem with excessive damping.

Originally Posted by Uncle Bob

Static sag alone will not stop the suspension topping out. The suspension can still top out regardless of what your preload is set to, it's not a 'top out prevention device'.

Correct, any suspension set-up can top- or bottom-out given the right extreme conditions. But, by having the correct static sag, you will minimize the times that happens. That's what Tony Foale wrote:

"• The static loaded position of the suspension is closer to the rebound stops, and so there is less suspension movement available before topping-out. So that occurs more often."

Originally Posted by Uncle Bob

If preload, and therefore (rider) sag, is set correctly, there will be enough travel in the fork\shock for the suspension to move up and down...

Also correct. But how do you know when it's set correctly? With my DU737, the "correct" setting was between 25-40mm so my original 26mm was "correct" according to the book. It wasn't until I also checked the static sag that I was able to arrive at the correct setting for my weight. Correct rider sag will, by definition, also include the correct static sag.

While suspension experts like the one Mossleymonster visited will no doubt be able to set the correct dynamic sag without also checking the static sag, the fact that they haven't checked it doesn't mean there isn't any or that it's not important to the overall set-up. I would still recommend that the home twiddler, without the experts' training and experience, still checks both figures to ensure that the final set-up is correct.