A few basic coilover suspension questions
A few basic coilover suspension questions
I know these are prob. basic questions, but that's why I'm here 
1) When someone says your coilover suspension needs a bit more stroke (context is the car is hopping around on bumps), is that stroke a function of the shock absorber or the spring, or both? I'm thinking it's either an intrinsic character of the shock absorber itself (if it's made with little allowance for travel ie stroke or requiring too much energy to compress the piston), or extrinsic (if you've lowered the car to the point that it limits the travel/stroke of the shock absorber). Is this correct?
2) Also, my understanding is the looseness or stiffness of the suspension is based on the spring rate (yes there are many other factors, but I'm trying to limit the discussion to the components of a coilover here). In a coilover setup, the shock absorber merely limits what would otherwise be prolonged oscillation of the spring (hence it also being called a dampener). Am I correct thus far?
3) If so, is it correct to say that in a coilover the spring rate affects unsprung weight (affecting road holding/friction w/ the road surface) while shock absorbers affect sprung weight (road isolation and what motion gets transferred to/felt through the cabin)?
4) So given the above, an excessively loose or too stiff of a suspension can be the result of either the shocks OR the springs, or both, correct? Depends on what the primary concern is (comfort or maximal handling).
5) Which leads me to my final question. If it is indeed both, why are we only supplied w/ the spring rates on coilovers? Why aren't the shock absorber units provided as well?
TIA,
~Ramy
1) When someone says your coilover suspension needs a bit more stroke (context is the car is hopping around on bumps), is that stroke a function of the shock absorber or the spring, or both? I'm thinking it's either an intrinsic character of the shock absorber itself (if it's made with little allowance for travel ie stroke or requiring too much energy to compress the piston), or extrinsic (if you've lowered the car to the point that it limits the travel/stroke of the shock absorber). Is this correct?
2) Also, my understanding is the looseness or stiffness of the suspension is based on the spring rate (yes there are many other factors, but I'm trying to limit the discussion to the components of a coilover here). In a coilover setup, the shock absorber merely limits what would otherwise be prolonged oscillation of the spring (hence it also being called a dampener). Am I correct thus far?
3) If so, is it correct to say that in a coilover the spring rate affects unsprung weight (affecting road holding/friction w/ the road surface) while shock absorbers affect sprung weight (road isolation and what motion gets transferred to/felt through the cabin)?
4) So given the above, an excessively loose or too stiff of a suspension can be the result of either the shocks OR the springs, or both, correct? Depends on what the primary concern is (comfort or maximal handling).
5) Which leads me to my final question. If it is indeed both, why are we only supplied w/ the spring rates on coilovers? Why aren't the shock absorber units provided as well?
TIA,
~Ramy
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Joined: Sep 2003
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From: BC, Canada
You're right, it's both the damper and spring that determines the suspension's compliance. A good example of a heavily damped system making the car rough is the R1 FD. Same springs, stiffer shocks leading to a harsh ride. Stiff springs will almost always give a harsh ride. With really good dampers this can be minimised.
A lack of stroke can be the shock bottoming on the bumpstops, or it can be spring bind, or it can be overly stiff springs. All are a little different in how they act. With adjustable shock bodies you shouldn't have bumpstop problems, and with properly sized springs then bind shouldn't be a problem either.
It's not that the spring does one thing and the shock does the other, they work as a team, but a simplification is that the spring controls bump, and the shock controls rebound. In a turn both happen at once.
Shocks can't be given a simple rate. You can look at shock dynos, but it takes some knowledge to know what you're looking at, and then there's different ways to interperate the data. But put simply, the spring determines the damping, so if they're designed properly, there's no need to know the shock rates, as they're set according to the natural frequency of the suspension.
A lack of stroke can be the shock bottoming on the bumpstops, or it can be spring bind, or it can be overly stiff springs. All are a little different in how they act. With adjustable shock bodies you shouldn't have bumpstop problems, and with properly sized springs then bind shouldn't be a problem either.
It's not that the spring does one thing and the shock does the other, they work as a team, but a simplification is that the spring controls bump, and the shock controls rebound. In a turn both happen at once.
Shocks can't be given a simple rate. You can look at shock dynos, but it takes some knowledge to know what you're looking at, and then there's different ways to interperate the data. But put simply, the spring determines the damping, so if they're designed properly, there's no need to know the shock rates, as they're set according to the natural frequency of the suspension.
I wish I could make a longer post, but I'm kinda in a hurry. Dampers can act as additional spring rate if damping is excessive. Because too much of the rebound force is damped by the fluid in the dampers, the spring will not be allowed to return to full extension before the next compression cycle starts.
As the spring is still partially compressed, there is still elastic energy. It still wants to extend. Imagine the motion of the wheel with respect to the chassis in this case. Because the spring is still not in full tension yet, it will continue to push the wheel toward the ground. Therefore overdamping acts like additional compression in the spring.
Shock dynos will tell you the amount of damping force at a given frequency. If you understand a shock dyno, you will be able to choose a suitable spring rate that will ensure neither over or underdamping. Since most people cannot interpret a shock dyno, suspension companies have taken the onus upon themselves to choose an appropriate spring rate for the intended application.
DISCLAIMER: I'm not a suspension engineer.
As the spring is still partially compressed, there is still elastic energy. It still wants to extend. Imagine the motion of the wheel with respect to the chassis in this case. Because the spring is still not in full tension yet, it will continue to push the wheel toward the ground. Therefore overdamping acts like additional compression in the spring.
Shock dynos will tell you the amount of damping force at a given frequency. If you understand a shock dyno, you will be able to choose a suitable spring rate that will ensure neither over or underdamping. Since most people cannot interpret a shock dyno, suspension companies have taken the onus upon themselves to choose an appropriate spring rate for the intended application.
DISCLAIMER: I'm not a suspension engineer.
Senior Member
Joined: Nov 2006
Posts: 731
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From: Dallas TX
Well I'm not a suspension engineer - but I am an engineer. If you are familiar with electrical circuits, a spring/damper is analagous to an L-C (inductor-capacitor) circuit. The spring is the mechanical equivalent of a capacitor. The damper/shock is the mechanical equivalent of an inductor. This is how computer models for suspension design are done. By changing the capacitance (spring rate) and/or inductance (damping factor) you can build a math model to predict the frequency response of your suspension (circuit) design.
link for geeks: http://en.wikipedia.org/wiki/LC_circuit
link for geeks: http://en.wikipedia.org/wiki/LC_circuit
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