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Discussion Starter · #1 ·
OK, there seem to be plenty of myths and misunderstandings around suspension sag. I’ll try to explain it as thoroughly as I can while still keeping it simple:

First of all, a few definitions:


Sag = How much the weight of the bike + the weight of the rider compress each suspension, front and rear, from fully extended.

Dynamic sag = The sag of the suspension as the bike is moving. Because it’s virtually impossible to measure dynamic sag — not only the bike is moving but the suspension compression is always changing due to bumps, dips as well as acceleration and deceleration — we need to measure it while the bike is motionless. This brings us to…

Static sag = The sag of the suspension with the bike stopped, measured with the rider on the bike (fully geared), the motorcycle being held upright and the rider in riding position. More on how to measure it a little later.

Free sag = How much the suspension sags without the rider. In most situations, there is no need for measuring the free sag as you will never let your bike go without you on top! However, there are some occasions in which knowing the free sag is helpful, especially when you suspect the spring is simply too stiff... but more on that later.


To understand why you need sag and how much you need, ask yourself this question: What are you more likely to find on the road, bumps or dips?
A: BOTH!

Remember, the main function of your suspension is to keep your tires firmly and uniformly pressed against the ground so you always have good traction. Therefore, in a perfect world, you should aim to always have your suspension right in the middle of its available travel, this way it can be able to compress over bumps and extend over dips, maintaining this ideal traction at all times.

Then why is it that most suspension experts say that an ideal static sag is in the 35% vicinity when what we really want is a dynamic sag of 50%? Well, ask yourself another question: Where in the road do you want to have the best traction available?
A: In the curves!

… and, because in the middle of a curve both you and your bike effectively weight more (due to the centrifugal G force pushing you in the lean) it is expected that your suspension will compress that additional 15%, putting it in that happy middle and providing you with the best traction possible.

BAM! Now you understand sag.



Of course, the 35% recommended static sag is not set in stone as there may be other factors you may want to play with. For example, if you ride very fast in the corners (spirited canyon chaser, track rider, etc.), you will be adding more centrifugal force while cornering than a regular street rider, so maybe you want to set your static sag to 30% or even 25% so you can achieve the 50% —dynamically— in the corners.

Another fun factor to play with is having different sag measurements, front and back. For example, you can have the bike sag a little more in the front to make it dive into turns faster or vice-versa to make it more stable and less twitchy. I recommend playing with this only after you have ridden a while with equal sag front and back, so you understand better the attitude of your bike in the corners.


Anyway, I have father’s day to celebrate so I will write about the right way of measuring sag (and the importance of proper springs) a little later.

Ride safe!
 

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Thanks OfirMX, this clears almost completely the topic.
The only (still) muddy issue is local: here in Italy we usually refer to "Static" SAG to what you call "Free", and to "Rider" SAG to what you call "Static" ... go figure ... 😄

I must remember to switch vocabulary when reading/listening to US sources. o_O
 

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Discussion Starter · #3 ·
Thank you, Skywalker. Many riders here in the US also use the term that way, which only causes confusion. I recommend you get the book The Suspension Bible, by Paul Thede and Lee Parks (also the author of Total Control). It explains these things (and many more) in much greater detail.

 
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Ha! This is great, thanks. I mean I knew this stuff (sort of 🙄) But its awesome you took the time to share. I certainly have a sag problem... lets just say I need to reduce my pandemiclly enhanced backside, like sixty lbs worth, to not need new springs and 20 wt oil. Talk about a performance upgrade! Woohoo, wheelies in third! Little ones... oil and stuff. Ooooh, and my 0-60 will be less not awesome. And I can ditch the XL Joe Rocket for the medium I got in the aughts :sneaky:

But I love tacos 😔
 
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Discussion Starter · #5 ·
Darren... you're on a roll!
 

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Be careful with the tacos, Darren.

Ahh, SVR 2014, the good ole days. :D

Ok, back on topic. This is an important/good thread.
 

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Holy crap that thread is awesome! Hot sauce, yes please... tacos, more please. Amy... frik... baby, you should have gone to rehab 😔
 

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Discussion Starter · #8 ·
Be careful with the tacos, Darren.

Ahh, SVR 2014, the good ole days. :D

Ok, back on topic. This is an important/good thread.
Ah, the good days!
 
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