Spring Rates on Coilovers A discussion
17 January 2020, 04:54 PM
#1
Scooby Regular
Thread Starter
Spring Rates on Coilovers A discussion
Spring rates. The eternal argument and whether we've all been missing something all along.
So. The back ground.
I have had an 06 Spec D ~Wide Trak STI which I've modded a bit, ALK and bigger rear bar and am now on my second set of coil overs, both BC.
My First, a set of ER were very nice but succumbed to the weather and failed. These were ordered +60mm length and came with helper springs.
I then got a set of ZR which I protect from the weather with Neoprene boots and ACF50 successfully. These were +40mm and again came with helpers.
During my time with the ER, I have run 5kg/4kg and 6kg/5kg with helpers.
With the ZR I have run 10kg/8kg, 8kg, 6kg with helpers and 8kg/6kg longer springs and finally 6kg/6kg long springs, no helpers.
Throughout I have been looking for that "something" and until the last change never found it.
How's best to describe it? OK. we all hear complaints about coilovers, every brand. Too Stiff, too bouncy, too low. yada yada yada.
What we need to really think about is this. Damping is required to settle the car after a disturbance., The less you can use the better, both for life of the strut and for comfort. Thus, if you have to wind the damping adjusters right up, as I ended up doing with the ER, you lose out in the end.
So, 2 Pot, a Man used to writing about journeys of a spring nature, and I had a little chat via PM and I finally went for 6kg/6kg, Weird, same front and rear spring rate. How does that work?
The answer was a surprise to me.....
Very, very well.
For research google up the phrase "Flat Ride". I'm not going to go into it here, suffice it to say 2Pot calculated 6kg/6kg should give me Flat Ride at 60mph. And the man was spot on.
Damping is now wound right off. High and low speed comp full off, rebound out to halfway, 15 clicks. The car is soft, supple and controlled, the pitching, harsh, choppy ride I've always had is TOTALLY GONE!
Yes, really. Gone.
It's a revelation.
So, why is this. Why have virtually all the coil over folks bene speccing our coilovers with springs that are too stiff and out of balance?
It's meant to be a discussion so join in.
Finally, I have +40mm travel on my struts, but BC only gave me standard springs. They would become coilbound before the end of the travel if it were not for the helpers. What they do is negate any benefit of the longer travel! I now use Faulkner's 260mm springs. Problem solved, but without any help from BC.
As a final aside. It's quite sad that I've got the feel out of these things I always wanted, just at the point I've finally decided to sell the car. The Coilovers are coming off, getting a clean up and re-grease and will be offered shortly for sale.
Change in circumstances mean I just don't use it anywhere enough to justify the costs of ownership.
So. The back ground.
I have had an 06 Spec D ~Wide Trak STI which I've modded a bit, ALK and bigger rear bar and am now on my second set of coil overs, both BC.
My First, a set of ER were very nice but succumbed to the weather and failed. These were ordered +60mm length and came with helper springs.
I then got a set of ZR which I protect from the weather with Neoprene boots and ACF50 successfully. These were +40mm and again came with helpers.
During my time with the ER, I have run 5kg/4kg and 6kg/5kg with helpers.
With the ZR I have run 10kg/8kg, 8kg, 6kg with helpers and 8kg/6kg longer springs and finally 6kg/6kg long springs, no helpers.
Throughout I have been looking for that "something" and until the last change never found it.
How's best to describe it? OK. we all hear complaints about coilovers, every brand. Too Stiff, too bouncy, too low. yada yada yada.
What we need to really think about is this. Damping is required to settle the car after a disturbance., The less you can use the better, both for life of the strut and for comfort. Thus, if you have to wind the damping adjusters right up, as I ended up doing with the ER, you lose out in the end.
So, 2 Pot, a Man used to writing about journeys of a spring nature, and I had a little chat via PM and I finally went for 6kg/6kg, Weird, same front and rear spring rate. How does that work?
The answer was a surprise to me.....
Very, very well.
For research google up the phrase "Flat Ride". I'm not going to go into it here, suffice it to say 2Pot calculated 6kg/6kg should give me Flat Ride at 60mph. And the man was spot on.
Damping is now wound right off. High and low speed comp full off, rebound out to halfway, 15 clicks. The car is soft, supple and controlled, the pitching, harsh, choppy ride I've always had is TOTALLY GONE!
Yes, really. Gone.
It's a revelation.
So, why is this. Why have virtually all the coil over folks bene speccing our coilovers with springs that are too stiff and out of balance?
It's meant to be a discussion so join in.
Finally, I have +40mm travel on my struts, but BC only gave me standard springs. They would become coilbound before the end of the travel if it were not for the helpers. What they do is negate any benefit of the longer travel! I now use Faulkner's 260mm springs. Problem solved, but without any help from BC.
As a final aside. It's quite sad that I've got the feel out of these things I always wanted, just at the point I've finally decided to sell the car. The Coilovers are coming off, getting a clean up and re-grease and will be offered shortly for sale.
Change in circumstances mean I just don't use it anywhere enough to justify the costs of ownership.
24 January 2020, 11:13 AM
#2
Glad it improved the issue 
Road cars:
Flat ride is taken into account by car manufacturers.
Why wouldn't you take advantage of settling the chassis, between maneuvers and road imperfections, by initially calculating the flat ride, using weight distribution, suspension motion ratio, the speed around which you want flat ride to occur etc.
As above: 6kg/mm front and rear, is around 60mph - a commonly achieved speed.
The ra-r used 6kg/mm front, 5kg/mm rear, more of a road/track day car - flat ride around 100mph.
When I specified the WA/A2 springs, I selected 4.4kg/mm front 4kg/mm rear = flat ride around 60mph and more positive chassis rake.
The gas fill pressures of inverted struts are, imo, too high. This has a big, negative, impact on ride quality (also changes ride heights), particularly at the lighter rear, as the strut motion ratio is 1:1
Why select spring rates that are too high, for the intended purpose? Then use the damping to mask the problems that creates. Unless all you're bothered about is dropping it on its **** and wrecking its handling?
And, why the obsession with more rebound damping (sprung mass) than compression damping (un-sprung mass)?
"The un-sprung mass when undamped is a greater disturbing factor to the ride and handling of a race or sports car or any moving vehicle for that matter than the sprung mass, a fact that is not yet widely accepted but true" (Jan Zuijdijk, 2013).
Vehicle Dynamics and Damping first revised edition (2013) Jan Zuidijk
£2.69 Amazon download
I'm not re-inventing the wheel; all the info is out there.
Road cars:
Flat ride is taken into account by car manufacturers.
Why wouldn't you take advantage of settling the chassis, between maneuvers and road imperfections, by initially calculating the flat ride, using weight distribution, suspension motion ratio, the speed around which you want flat ride to occur etc.
As above: 6kg/mm front and rear, is around 60mph - a commonly achieved speed.
The ra-r used 6kg/mm front, 5kg/mm rear, more of a road/track day car - flat ride around 100mph.
When I specified the WA/A2 springs, I selected 4.4kg/mm front 4kg/mm rear = flat ride around 60mph and more positive chassis rake.
The gas fill pressures of inverted struts are, imo, too high. This has a big, negative, impact on ride quality (also changes ride heights), particularly at the lighter rear, as the strut motion ratio is 1:1
Why select spring rates that are too high, for the intended purpose? Then use the damping to mask the problems that creates. Unless all you're bothered about is dropping it on its **** and wrecking its handling?
And, why the obsession with more rebound damping (sprung mass) than compression damping (un-sprung mass)?
"The un-sprung mass when undamped is a greater disturbing factor to the ride and handling of a race or sports car or any moving vehicle for that matter than the sprung mass, a fact that is not yet widely accepted but true" (Jan Zuijdijk, 2013).
Vehicle Dynamics and Damping first revised edition (2013) Jan Zuidijk
£2.69 Amazon download
I'm not re-inventing the wheel; all the info is out there.
Last edited by 2pot; 24 January 2020 at 11:14 AM.
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25 January 2020, 07:09 PM
#3
Scooby Regular
Thread Starter
It is truly difficult to state the change in feel the flat ride gave when I went out on my first drive on the 6/6 setup. I'd wound the damping right off from 8 out to 15 out on the front when I changed springs. The rear was at 10 out from before. Within a mile or so I'd got out and wond the rears off to 15 out too.
The feel is like a smooth and well controlled production car. So unlike any other setup I'd had on my car since going to coilovers.
Damping and feel is more like an M3 on bumps. Totally controlled.
Very very impressed.
Thanks again.
The feel is like a smooth and well controlled production car. So unlike any other setup I'd had on my car since going to coilovers.
Damping and feel is more like an M3 on bumps. Totally controlled.
Very very impressed.
Thanks again.
Last edited by Markyscoob; 25 January 2020 at 07:10 PM.
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