Spring hardness in relation to damping

[Anonymous]

So assuming that the damper settings are fixed (on either a non-adjustable shock or an adjustable one left on one particular setting), how would the handling of the car change if you were to change the springs to either harder or softer ones? I'm thinking in particular of the BC ones as you can specify your own rates and whilst this is for the 350Z, the same thought should work on the MR2 hence the question being asked in this section  s:) s:)

Would a harder/softer spring work better with the shock on a particular setting (remembering the BC RS are single adjustable for rebound and compression only), or would there be a benefit/drawback across the entire range? Just trying to get my head around it really and want to make sure I'm on the right idea before I order a set of shocks with too stiff springs!

[markiii]

no doubt Chris will be along with insight soon, but teh way I see it depends on teh weight of teh car and the surfaces your driving on

in an ideal environment with very smooth surfaces you would go for a very hard spring to maintain a flat cornering stance, howeveron teh road that won;t give you any leeway for potholes e.t.c

are you planning on having adjustable damping?

[Wabbitkilla]

I think Mark has it pretty much spot on.

For everyday roads you're probably going to find springs at the softer end more comfortable, but if you want good performance then you're going to have to go harder. But there is a break point where a standard shock will not be able to cope with the power of the spring and things will not be comfortable at all - and handling will be so hard with the return damping almost missing completely that you'll not be having a good time. There must be a balance to be met, but the standard dampers will be setup for standard spring rates within a region of safety. You have room for change, but not much room.

Which I think is why BC's have such a huge range of adjustment on the compression and rebound to cater for a wide range of spring ranges.
Like Mark said, the harder the spring, the flatter you corner ... but also the more control you need of the compression and rebound. Great on a track, but for an everyday driver? Depends what you like, and how good your back is   s:lol: :lol: s:lol:

[markiii]

well we know his back is buggered

[Anonymous]

are you planning on having adjustable damping?

Given how the suspension is set on the 350 Roadster at the rear (i.e. covered in plastics and trim and stuff) I'd be finding myself finding a setting between rock hard and squidgy soft and leaving it there for road and track, as changing it would be a ballache of the nth degree. In that respect, the Teins + EDFC would be a better choice as I can control the damping from inside the car, however do they go stiff enough for track to make it really worth while? I'm not so sure.

On the other hand, with the BC RS shocks I have the ability to pick my own spring rates, which might give a better balance and would allow me to get a better road/track setting than the Teins.


Whilst it's true I've got a dodgy back, given that the VXR was eminently more comfortable for me than the Zed is I'm not convinced that stiffer suspension will really make it any worse. Granted the Exige seats are a billion times more supportive than the stock Zed items, but with the installation of harnesses it might negate some of that. Failing that, it'd be new seats I guess.

[markiii]

are inverted monotubes an option as I beleive you can adjust from the bottom

[FGrob]

the Teins + EDFC would be a better choice as I can control the damping from inside the car, however do they go stiff enough for track to make it really worth while? I'm not so sure.

I think it does, I use it all the time and there is a distinct difference which you can only feel when you drive the car and change the setting as you go along.

I am going to change though to Monoflex but again with EDFC, but with different valving to give a better response.

Rob.

[Anonymous]

Hmm, I forgot about the Monotube Teins, but then you're spending £2000 for something that's almost overkill unless you're on track a lot of the time IMHO, and certainly is if I can get a decent setup out of the BC RS for about £700. Stock spring rates on the BC are 10F 8R, which I was thinking about upping to 12F 10R.

[FGrob]

Hmm, I forgot about the Monotube Teins, but then you're spending £2000 for something that's almost overkill unless you're on track a lot of the time IMHO, and certainly is if I can get a decent setup out of the BC RS for about £700. Stock spring rates on the BC are 10F 8R, which I was thinking about upping to 12F 10R.

Yep maybe, but I'm doing a trade on my old stuff so the costs are limited, but then again if I was buying new I would still consider the Monoflex as it changes the unsprung weight which I'm very interested in.

[custardavenger]

I would fit the stock BC Spring rates, If you feel they are a bit soft then you only have to buy a pair of springs (£150ish) and you have a harder set up.

I assume there isn't an option of loosing the plastics that are in the way or cutting them?

They why not buy the Tein controller and mod it to fit the BCs. I'm sure it could be done though it may not give the correct readings.

Anyone got a spare one and I'll have a look at it.   s:D s:D

[Anonymous]

I assume there isn't an option of loosing the plastics that are in the way or cutting them?

There is, but it's not something I really want to do unless I absolutely have to. I can't remember off hand if the adjustment point would sit in the boot or the space for the roof: The boot wouldn't be so bad I guess, but I'm very loathe to touch anything in the roof space.

[ChrisGB]

Sorry it took a while to get onto this, supposed to be working...

The damper adjustment is there to control the body movement relative to the road (the road is the fixed datum and the body moves relative to it).

Damping is split into two duties, compression and rebound.

Compression damping is the damping force exerted when the spring is compressed ( when the car goes over a bump, up a slope, rolls in a corner etc). The job of compression damping is to prevent the upward movement of the wheel continuing after it initially deflects (which would allow the wheel to lift off the ground, propelled by the momentum it built up as it was compressed) and to prevent overshoot of downward movement of the body. It is a relatively weak damping force and on single adjustable dampers, it does not change by a huge amount when adjustment is made.

Rebound damping is the damping force exerted when the spring is extending (when the car's body responds to the bump, slope change, roll etc because it is being forced upward by the spring). The job of rebound damping is primarily to prevent the upward movement of the car from continuing after it initially deflects in response to a bump (which would pull the wheel away from the ground).

The damping force interacts with the spring to control the speed of movement in the system. Take a weak spring with a given weight on it and allow it to bounce, that bounce will be at a set frequency if the spring and weight are constant. A stronger spring with the same weight on it will bounce at a faster frequency. Now the damping needs to be matched to the spring strength to soak up the bounce.

For a soft spring, less damping force is required in rebound as the spring will not push the body upward quickly or with much force. For a harder spring, the damping needs to exert more force as the body will be pushed upward more quickly. The amount of extra force required may be significantly more than the spring rate would imply because, the stronger spring will also limit the compression travel, so the force of damping will need to be applied over less distance in many driving situations.

On the car, if you start with say 6Kg front springs and the suspension is tuned for everyday comfort, the spring / car system is going to be designed to bounce at around 1Hz. The damping force that works to control this in rebound will have to work at this speed to prevent the car from just bouncing along. Now say we change the springs to 12Kg instead. The body will now bounce at 2Hz. To the driver, this means a car where the suspension will only travel about half as far in roll, so will load its outside wheel in half the time of the 6Kg sprung car. The driver feels a big increase in the reaction speed of the car, particularly on transitions. The downside is that the increased stiffness will also mean less isolation from bumps. Now if the damping was set to the 6Kg springs, so that when the car cornered or braked, the damping contained the bounce upward at the 1Hz speed, when you run the 12Kg springs, the car will bounce instead of settling. The driver may experience this as a car that will not settle into the corner properly. You turn in and the springs on the outside of the turn compress, then half a second later, they rebound pitching the car flat and unloading the outside wheels before re compressing and reloading.

Now my pet peeve is the idea of using damping to prop up the springs or make them drag in order to change the handling balance. IMO there is one optimal setting for any given system. In the ideal system, the springs control the body movement and the dampers prevent momentum of body movement from having an effect. As close as you can get to this is optimum and once that balance is found, I cannot see any reason to adjust away from that.

In terms of handling, a car with the compression damping turned up far enough to "help" the springs is going to feel a little odd in its responses. Transient loading will lag behind the natural periodicity of the system making the car feel hard to find a rhythm with. Too soft in the damping and the body control suffers making the car feel like it needs two bites to load into a corner.

In terms of ride comfort, too hard in the damping has the car thumping in compression, not flowing over the road, and lagging in rebound, so bumps cause the wheel to stay off the ground for a long time. Too soft and the wheel travel suffers and soft rebound leads to patter, both leading to a fussy and rattly feel to the ride.

With the BCs on the MR2, now they are run in, they have been left set where they are for over a year. Comfort and handling are both worse if I go either side of the settings I have, so sweet spot has been found. It did take a little while to find it though, so some time adjusting will be needed.

Out of curiosity, what are the standard spring rates on the Zed? And have you seen the BC ER series, they look like a really nice next step up.

Chris

[FGrob]

No need to apologise Chris, it must have take at least two days the right that lot up  s:lol: :lol: s:lol:    s:lol: :lol: s:lol:    s:lol: :lol: s:lol:  

OK I can see where you are coming from, but no single road is the same and certanly if you do a little tracking, what is good for a road set-up is not going to be as good for a track set-up, as you say you have to compromise, but by having the ability to adjust the setting while driving the car to me has been a big benefit, I know what the best settings are for my car I've used it enough to find them.

The biggest factor which you fail to address is the "wife" factor, the one where she say's WTF have you done to the car, which is why I have that special button which is for when the wife is in the car, not matter how well the car handles at speed I know I will get the "how fast are you going" comment which normally comes after I've heard her teeth rattling together because I've forgot to change the shocks setting from when I was on my own.  s:flame: :flame: s:flame:    s:flame: :flame: s:flame:  

A good example of the benefits of adjusting shocks for everyday driving is going down the motorway on a very windy day at speed, on normal settings the car starts to move around a little, adjust the setting up to track setting - generally motorways are smooth enough to do this, and the wondering feeling goes away the car tends not to lift as much and feels a whole lot more stable in these conditions, as said it's all about compromising to suit the conditions that are around you at that point in time.

OK Chris - rip it apart.  s:lol: :lol: s:lol:    s:lol: :lol: s:lol:    s:lol: :lol: s:lol:

[Wabbitkilla]

I think out of all this Dan, it's possible to see that it's preferable to be able to adjust the damping on the coilovers.
This isn't exactly easy with your plastics in place, so there is the option of going with the Teins and EDFC, expensive though.
However I remember seeing when I was in BC Racing / Apex Racing that BC do some extenders for the adjustment knobs. I wonder if there would be a way to route these through your plastics somehow so you get the best of both worlds?

 m http://www.bcec.com.tw/products/OTHER/knob.htm m

[custardavenger]

You could probably rig a flexible shaft up without too much trouble.

[Wabbitkilla]

Sorry, forgot to mention the BC extenders are flexible ... I think they'd be worth a punt, and it's a cheap solution.

[Anonymous]

Out of curiosity, what are the standard spring rates on the Zed?

According to the Z wiki, spring rates are 314lbs F and 427lbs R. What that actually equates to in proper money I have no idea  s:oops: :oops: s:oops:

The ERs do look nice, but I've yet to find anyone using them on the Zed: For that kind of money, most end up with the KWs of some kind.

[loadswine]

Dan,those rates, are not in whole KG, looking at the Tein site anyway. I reckon about 5.5 and 7.5 as far as I can see.

Chris, what rate do you think the BCs should be on the rear with a V6, in your view?

[ChrisGB]

No need to apologise Chris, it must have take at least two days the right that lot up  s:lol: :lol: s:lol:    s:lol: :lol: s:lol:    s:lol: :lol: s:lol:  

Took about 20 mins, but am supposed to be writing a QMS for a company at the moment. Keep getting distracted  s:lol: :lol: s:lol:  

OK I can see where you are coming from, but no single road is the same and certanly if you do a little tracking, what is good for a road set-up is not going to be as good for a track set-up, as you say you have to compromise, but by having the ability to adjust the setting while driving the car to me has been a big benefit, I know what the best settings are for my car I've used it enough to find them.

It is a nice idea to have the ability to adjust dampers to suit the road type you are on, but if the spring rates are matched to the car and the damping matched to the spring rates, adjustment should not really be necessary. If the springs are a little soft / hard or the balance front to rear is not suitable for say track work, then the ability to stiffen it up with damper adjustment is useful. However, having the right spring rates for the job would be my preferred course of action.

The biggest factor which you fail to address is the "wife" factor, the one where she say's WTF have you done to the car, which is why I have that special button which is for when the wife is in the car, not matter how well the car handles at speed I know I will get the "how fast are you going" comment which normally comes after I've heard her teeth rattling together because I've forgot to change the shocks setting from when I was on my own.  s:flame: :flame: s:flame:    s:flame: :flame: s:flame:  

But you are missing the point here, surely by having the wife not like the car, you get a really good weight saving 'cos she stays at home. Not to mention the reduction in whining noises.  s:wink: :wink: s:wink:   Seriously though, if the springing and damping are well matched the ride comfort should be fine. If the dampers are helping the springs, it gets harsh and then the missus complains. I must admit that with the 4/6Kg springs, my other half moans a bit and they are noticeably stiffer than the Tein SS. I reckon she would be happier with the Tein SS, but I have to drive it. If the damping is softer than ideal, ride quality does suffer though and if I go stiffer than optimum, the ride gets really harsh. More to the point though, once I have gone too firm in the damping, the car wont flow on uneven surfaces.

A good example of the benefits of adjusting shocks for everyday driving is going down the motorway on a very windy day at speed, on normal settings the car starts to move around a little, adjust the setting up to track setting - generally motorways are smooth enough to do this, and the wondering feeling goes away the car tends not to lift as much and feels a whole lot more stable in these conditions, as said it's all about compromising to suit the conditions that are around you at that point in time.

Hmm.. I am reckoning you may want to increase the ratio of front to rear spring stiffness, it is often the case that a car that is stiffer than it should be at the rear can be more sensitive to crosswinds.

OK Chris - rip it apart.  s:lol: :lol: s:lol:    s:lol: :lol: s:lol:    s:lol: :lol: s:lol:

You asked for it  s:lol: :lol: s:lol:  

The more I look at the suspension setting for the MR2, the more I think that the spring ratios on the Tein SS is too close front rear. The stock suspension is close to 2/3 Kg/mm F/R. The Tein SS is 3/4, so the front is relatively hard compared to the rear. I have been in a Tein SS equipped car being driven "enthusiastically" and it felt good. I run 4/6 and the front feels subjectively more direct and the rear more mobile. Perhaps the idea is to reduce the risk of oversteer / improve high speed stability? The USA get 3/6Kg on the Tein SS which I would imagine would make for a very responsive car, but one that needs a smooth driving style to exploit at speed. I suppose that is the joy of modifying, you can make the car just how you like it.

Chris

[ChrisGB]

Out of curiosity, what are the standard spring rates on the Zed?

According to the Z wiki, spring rates are 314lbs F and 427lbs R. What that actually equates to in proper money I have no idea  s:oops: :oops: s:oops:

The ERs do look nice, but I've yet to find anyone using them on the Zed: For that kind of money, most end up with the KWs of some kind.

You get 2.204 lbs to the Kg and 25.4mm to the inch, so:

314 lb/in / (2.204 x 25.4) = 5.6 Kg/mm

427 lb/in / (2.204 x 25.4) = 7.6 Kg/mm

An increase to 8/10 is going up a fair bit and is also changing the ratio to a relatively slightly stiffer rear end.

With the choice of which coilover kit to go for, you have the option of fixed spring rates and adjust damping to vary the setup, or have a range of spring rates and adjust them to get the sweet spot, then damping can be set and left alone. For me, getting the spring rates just as I want them would be my preferred option.

I reckon the other element with matching damping to springs is that the car will be more adept at changes in surface conditions. If the damping is helping hold up the body, when you run onto rough surfaces, you will need to soften it. When we were out on the island, even running into big speeds on roads that were shall we say "less than perfect" the spring damper combo of the BCs never needed adjusting and never let the car lose contact with the road. Sure it got a bit rough at times, but never harsh.

if you wanted to try the BC equipped MR2, you are more than welcome. Not the same as the Zed, but will give you an idea of the amount of change that doubling spring rates will give you.

Chris

[ChrisGB]

Chris, what rate do you think the BCs should be on the rear with a V6, in your view?

I have been pondering this one for a while  s:wink: :wink: s:wink:  

With a 1mz and S54 box, it could be that a change to 7Kg at the rear would just give the same periodicity (bounce frequency) as I have now with 4/6. However, it may be the case that I will need to go stiffer and lose the rear ARB. If I do this, I may end up at 5/8 or even stiffer at the rear. Get the engine in and see how it feels seems the best option at the moment. For the 3vz, keeping the 3Kg fronts, perhaps go to 5Kg in the rear and see which way it takes things? I think the rears on the BCs work from 6-10Kg/mm at the rear 4-8Kg/mm at the front, so would use 4/6 as a starting point with the 3vz. That will make for a harder ride than you have now for sure though.

Chris