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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!
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!
