Spring Strength & Damping

[Rob H]

Some help needed from the more knowlegable.
I have some sets of springs from Tamiya, they all seem to be made from the same guage wire. Which ones would be the softest, the ones with less or more turns / coils.
Also, last week, I ran the car Tamiya DF-03 with the current damper set up which worked well on bumpy ground. This week ran with a different chassis and battery configuration which made the car much lighter (about 150 - 175 rams) but the front was bouncing at high speed.

Can you tell me what I need to look at, front damper oil or springs to hard?, which to change first to try to prevent the bouncing?
regs
rob

[Northy]

More turns / coils = softer

G

[sosidge]

And your lighter car should be able to run on a softer spring. Heavier car is putting more downward force on the suspension that the effect of the bumps needs to overcome, take away weight from the car and the bumps create a greater net compression force on the suspension. Inertia also comes in to play, a heavier car feels smoother and more settled anyway (but is slower around the track in theory).

[SlowOne]

In theory...

As the guys say, less coils will mean a higher spring rate given the same wire and length of spring, and a lighter car will use a softer spring. However...

There is only one way yo know the spring rate, and that is to test it. If you're after a definitive number, then there are charts available if you ask around. However, if you're after a comparison, then it's easier.

Get a round dowel with diameter about the same as the inside diameter of the spring - it must be a nice easy fit inside, with good clearance. Now, place it upright on a flat surface, and pop on a spring you know works. Over the top of that, place your new spring. Push on the top spring so you are compressing both at the same time. The springs will collapse as you push down, and one will collapse faster than the other - that's the softer spring. By carefully observing the rate at which they collapse when you push down, you can see what rate they go at, as some are not linear.

With damping, the oil is absorbing the energy taken up in the spring, and dissipating it at a controlled rate. For a heavier spring, you need more damping as the heavier spring will return its energy faster, so you'll need a thicker oil to maintain control. In reality, the changes of springs we make are quite subtle, so the change in oil is less critical. However, if you remove 10% of the weight of the car (150g) then some change in oil is worth trying.

The bouncing you get with the lighter car is a hard spring with not enough damping if the chassis bounces up and down and won't settle, or too much if the front wheels bounce on and off the ground. Whichever it is, change the system accordingly.

If you're expecting an answer to what to do, I'm going to disappoint you! It's too many years since I ran Off-Road. Having run a B4 RS RTR under the expert gudance of Tom Yardy, I just did as I was told and it all worked fine! Hope the theory helps you. :)