Happy 2021! This is the first write up for the new year!
I covered the damper oil in my previous write up which would be a good reference, although not specifically related to this theme.
DAMPER OIL / PISTION | Marcus RWD RC Drift Blog (ameblo.jp)
What is PRELOAD?
In simple terms, PRELOAD is how much you crank down the spring adjust nut. Most people use the adjust nut to GAIN or REDUCE ride height. For example, you have a 32mm spring with a certain spring rate. This spring can maintain a 5mm ride height with a 7mm of preload. If you wanted to add 2mm of ride height, you would lower the spring adjust nut, or increase the PRELOAD by 2mm to total of 9mm to get to the desired ride height.
This is what is happening inside the dampers when you adjust PRELOAD.
SO WHAT??
You may be achieving the desired ride height, but what you may not realize is you are also changing the position of the piston within the damper cylinders. This may end up causing the chassis to not have enough droop, or for the dampers to bottom out.
As noted above, focus on PRELOAD for many tuners is the effect to ride height. However, there is much more to it to go to the next level of tuning. In the example above, the 32mm spring is preloaded by 7mm to 25mm. The spring is compressed to 20mm with the chassis sitting still =1G. This means there is 5mm of compression from 25mm to 20mm.
If you lower the adjust nut down by 2mm, the preload increases to 9mm, and the ride height then raises to 7mm. The spring is now preloaded from 32mm to 23mm. The spring is still compressed to 20mm with the chassis sitting still =1G. There is now only 3mm of compression.
The final length of the compressed spring does not change from 20mm if the chassis weight has not changed. The amount of preload does not affect the final length of the compressed springs. Some have a misperception of ‘adding preload’ changes the ‘spring rate’, but preload has nothing to do with the spring rate.
The key here is the position of piston which affects the travel of the suspension. Position of the piston dictates how much compression and rebound travel length there is.
DAMPER LENGTH ADJUSTMENT = THE “HG”
You probably have seen the pricy damper kits on the RC Drift scene...the Overdose HG - High Grade Dampers. There are many advantages to the HG Dampers, but one of the most beneficial features on the HG Dampers is the “length adjustment” with the top cap.
Kazama-Sustex top caps for Tamiya TRF and Yokomo BD are also well known but hard to find as they are out of production. There are some similar knockoffs, but cosmetically not appealing. Wrap Up Next released their version of TRF dampers with rod end screw on caps for length adjustment. TN Racing has a similar design screw on cap for Yokomo BB.
By adjusting the overall length of the dampers, the piston position = suspension travel length can be adjusted.
Taking the same example. By adding more preload, you were able to get the desired ride height, but this also shortened the length of the rebound travel, however there is plenty of travel length on the compression side...changing the damper length can balance the piston position, hence balance the length of the compression and the rebound travel.
With the ability to adjust the damper length, you have the full capability to adjust the piston position. You are also able to adjust the preload without sacrificing the suspension travel length. The same results can be achieved by changing the length of the ball ends on the damper shaft, but not as simple as adjusting the top cap on the fly.
ANY ADVANTEGE/DISADVANTAGE FROM PRELOAD??
YES, but this will be another theme that will require a full write up...and I am still learning the technical effect of more/less preload.
Depending on what selection of springs you have. You can always change the spring rate (hard/soft), but this not only changes preload and ride height. This is a simple method to adjust the position of the piston, but will change the hard/softness of the suspension. Some manufacture offers different spring length with same spring rates.
The preload effects both the compression and rebound of the springs, but more so on the rebound force of the springs.
Different design springs affect the initial compression, and the character can change as more load/pressure is applied.
Linear spring rate vs variable spring rate, more winding vs less, open end vs multiple winding at the end...there is just so many options out there and a challenging subject to write up that can be quantified.
LEVER RATIO
With the evolving tuning techniques in the hobby, damper tuning is a key part of the equation. Higher steering angle requiring the front dampers move inward, and rear suspension has a trend to have more droop for more dynamic suspension movement. Lever ratio tuning is a very effective way to change how the dampers and the springs feel. Lever ratio tuning is closely related to ability to adjust the length of the dampers as well.
IFS (Inboard Front Suspension)
You may wonder why I even brought this up in this write up...IFS is very closely related to this theme.
IFS is a unique mechanism that can adjust the ride height without affecting the damper length or preload. Working with the lever ratio of the linkage and the bell cranks also has effect to the suspension, which takes a bit of getting used to. Overdose GALM was the first dedicated RWD chassis introduced to the market with IFS. The designer has worked with Tamiya TA chassis in the past which is the origin of the GALM chassis.
Happy Drifting!
January 3rd, 2021 / Irvine California
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