The above is totally incorrect. Preload only adjusts the ride height. It is used to set static sag.The dampening rate is in the case of the M109 built into the shock which as you know is not adjustable externally. OK!No difference.
The adjustment is firmness not height.
Now, you might expect firmness to impact height, but that is not really the case.
Firmness in this case is dampening rate. The softer the setting, the faster the shock will respond and the farther it will travel in response to a given impact event.
Under a static load, you are more on the spring and will end up at the same height.
Completely disagree.The above is totally incorrect. Preload only adjusts the ride height. It is used to set static sag.The dampening rate is in the case of the M109 built into the shock which as you know is not adjustable externally. OK!
:agree:but when you put rider and passenger weight on the bike when set at 1 the bike does sit lower from less spring tension.It occurred to me that I may be using some term-of-art incorrectly, so let me boil it down to my actual point without potentially misusing some pre-defined term;
Crank that collar all you like and measure your height and there will be no change.
:agree: And sag must be measured with the riders weight on the suspension.The above is totally incorrect. Preload only adjusts the ride height. It is used to set static sag.The dampening rate is in the case of the M109 built into the shock which as you know is not adjustable externally. OK!
Agreed. That is why we call it preload. You are adjusting where a given amount of weight will fall in the possible range of motion of the nitrogen filled portion of the shock.:agree:but when you put rider and passenger weight on the bike when set at 1 the bike does sit lower from less spring tension.
While that may be why you want to take the measurement, the idea of preload would be to make the adjustment so that load changes end up at the same height and therefore at the same starting point in the range of motion and therefore in the same range of dampening rate.:agree: And sag must be measured with the riders weight on the suspension.
Good on yer! maybe the laws of physics & mechanics are different over there?Completely disagree.
Go adjust your setting and let us know what it does to ride height.
I have measured and it does nothing.
And you are an expert how? Because you changed out your shock and ride a trike?Good on yer! maybe the laws of physics & mechanics are different over there?
Certainly wouldn't let you get too close to to any race bikes suspension front or rear.
I have learned far more here than I have contributed.Square rounder you don't have to explain to this barsim. I am sure he doesn't have a clue on how a simple shock like the one on the works. We all know your knowledge of the 9 and you are a great contribution to this forum.:bigthumbsup:
:agree: I keep mine at 1 and it does drop. People ask me also what bones i have in it. I set it up to 4 this weekend to ride some two up riding and it did seem to be sitting higher. .I've never measured, but before I gained some weight, when I rode solo I set it on #1. People would commonly ask me how far I lowered it. There is a noticeable height difference with the pre-load adjustments.
Motorcycle suspensions are designed so that the springs are always under compression, even when fully extended. Pre-load is used to adjust the initial position of the suspension with the weight of the motorcycle and rider acting on it. Both the front forks and the rear shock or shocks can be adjusted for pre-load on most modern motorcycles.
The difference between the fully extended length of the suspension and the length compressed by the weight of the motorcycle and rider is called "total sag". Total sag is set to optimize the initial position of the suspension to avoid "bottoming out" or "topping out" under normal riding conditions. "Bottoming out" occurs when the suspension is compressed to the point where it mechanically cannot compress any more. "Topping out" occurs when the suspension extends fully and cannot mechanically extend any more. Increasing pre-load increases the initial force on the spring thereby reducing total sag. Decreasing pre-load decreases the initial force in the spring thereby increasing total sag.
Since the weight of the motorcycle and rider are the only forces compressing the suspension from the fully extended position, preload doesn't change the forces on the springs under riding conditions. Changing the pre-load does not change the way the suspension reacts to bumps or dips in the road surface either. Two simple examples using the motorcycle's forks shows why:
Since the forces are the same in both examples the reaction of the suspension to bumps and dips in the road will be the same. The difference is that there is less chance of topping out in example 1, less chance of bottoming out in example 2. Motorcycle manufacturers generally provide optimal total sag settings.
- Suppose that the bike and rider put a total weight on the front suspension of 300 lb. Suppose the spring rate of each fork spring is 50 lb per inch. Installing a 1 inch long spacer in each fork leg gives a pre-load of 50 lb per spring, a total of 100 lb. When the weight of the rider and motorcycle are loaded onto the suspension it will compress 2 inch from full extension (2 inches total sag). Now the force exerted on (and by) each fork spring is 150 lb (1 inch pre-load + 2 inch total sag = 3 inch total spring compression) for a total of 300 lb, balancing the weight of the bike and rider.
- Suppose we now install a 2 inch long spacer in each fork leg. The pre-load is now 100 lb per spring, a total of 200 lb. The total sag will change since we still have the same 300 lb loading the forks. The total sag will now be 1 inch. The total force on each spring is the same as before, 150 lb on each fork spring for a total of 300 lb force. The front suspension's initial position is 1 inch longer than in the preceding example (1 inch less total sag).
This is also why too-soft springs cannot be "fixed" by adding pre-load, too-stiff springs cannot be "fixed" by reducing pre-load. Changing to springs of the correct spring constant for the total weight of the bike and rider is the only solution.
Some motorcycles have externally accessible pre-load adjustments. Typically, this is a screw-type adjustment that moves a backing plate inside the fork against the top of the fork spring. The farther down the adjuster is screwed, the higher the preload.
A few motorcycles allow adjustment of pre-load by changing the air pressure inside the forks. Valves at the top of the forks allow air to be added or released from the fork. More air pressure gives more preload, and vice versa.
Pre-load on bikes without adjusters can be changed by disassembling the fork and changing the length of the spacer between the top of the fork spring and the fork cap. Spacers can be installed under the rear shock springs similarly. A longer spacer gives higher preload, and vice-versa.
The pre-load on both forks should always be the same. Dangerous handling behavior and possible mechanical damage can result otherwise.