18/9kg springs for a track car ?

[GodISmE]

Hey, I'm wondering whether I should go with a rather safe 14/6 or with 18/9? Swift springs on Supersport Stance true coilovers.

The car weighs about 1400 right now. No aero yet but I will be adding it in future. Maybe also removing some more weight to get down to 1350 kg.

Edited July 20, 2017 by GodISmE

[Ekona]

If you're going lighter, you won't want the stiffer springs as you'll have less mass to move around. 14/6 will be fine.

[GodISmE]

But aero will "add some weight", won't it?

[Ekona]

Not unless you're adding bags and bags of it and you're intending on wind tunnel tuning it, not really. Might add another 20kg at 100mph, but that won't be much use in the low speed corners at all. Aero on road cars (assuming you're keeping it road legal) is more about reducing lift than adding downforce.

[MrLizard]

would also add that if you get the suspension correct and have some sticky tyres on the mechanical grip of the car will far outweigh any aero affect you get at fairly normal/track speed If you are unsure on the springs get both and see which you prefer?

[350Butcher]

I've been talking with Motion Control Suspension in the States this week and their upper recommendation for spring rates for fast road with track use is 14/9.

 

When I your post before I thought 18 fronts would be too hard and it seems 6 on the rear would be on the soft side from what MCS have said. With the 'Ring in mind, which I know you're looking at, too hard a setup is gonna hurt your time as with the surface there and riding the curbs etc is could knock the car off line and be a handful!

 

I'm no expert but this is just my opinion. Every driver is different with different styles and preferences so its always going to be quite a personal decision but I think it would be a good setup.................its what I'll be ordering anyway!

[MeisterR]

Assuming we are talking about true coilovers rear, those rate is a little scary.

 

18kg/mm in the front is hard, but bearable... around the right figure for Semi-Slick.

14kg/mm in the front is on the harder end of a fast road car (slightly over).

The front rate are fine, as the 350Z suspension design mean the front isn't very sensitive to springs rate change.

 

The rear in true coilovers design on the other hand is VERY sensitive to springs rate change.

9kg/mm:  Very hard... I wouldn't use that on a road car at all.

6kg/mm:  Still very hard, should work with Semi slick but I would advice to be very careful on the road.

 

If I were to make a setup, it would be 18/6 and this will be for a very track focused car that I wouldn't really want to see on the road.

14/6 will also work, but it will be a little more tail happy.

 

I am going to highly advice AGAINST using a 9kg/mm rear springs in a "true coilovers" design.

To make a 9kg/mm rear springs rate, you would need something around a 27kg/mm front springs.

And this type of springs rate (wheel frequency) are getting up to profession race driver / touring cars running on slicks.

 

On a road car, I always prefer the OEM rear design.

A true rear on a race car allows better utilisation of the springs rate, and so you can provide more precise control when designing the suspension.

But that really isn't needed on a road car, and the OEM suspension is actually not a bad design for what you need to with the car.

 

My 2p to help out.

 

Jerrick

 

[GodISmE]

On 7/11/2017 at 22:03, 350Butcher said:

I've been talking with Motion Control Suspension in the States this week and their upper recommendation for spring rates for fast road with track use is 14/9.

 

When I your post before I thought 18 fronts would be too hard and it seems 6 on the rear would be on the soft side from what MCS have said. With the 'Ring in mind, which I know you're looking at, too hard a setup is gonna hurt your time as with the surface there and riding the curbs etc is could knock the car off line and be a handful!

 

I'm no expert but this is just my opinion. Every driver is different with different styles and preferences so its always going to be quite a personal decision but I think it would be a good setup.................its what I'll be ordering anyway!

Be careful with that Martin. Stance also recommended 14/9 to me (Swift springs on their Supersport coilovers). It was ok until I started to really push the car on tracks and drive at the limit.  I found the car extremely loose, especially at corner entry which resulted in a few near spins at a high speed. If it wasn't for my sim experience and knowing how to save it at the last minute, I would probably end up in a wall.

Only now with shocks set up to full hard (front) and almost full soft (rear), wider tires at the back (275/35/18 vs 255 at the front) and a removed rear sway bar have I found a relatively good balance. But this is addressing the symptom instead of the root cause. That's why I want to get the balance right with the springs now and put the rear sway bar back on to get some balance setting options. I've already ordered 6kg srpings and I'll start with 14/6. Michael Gardner uses this combo and he seems to be doing quite well

 

 

Edited July 20, 2017 by GodISmE

[MeisterR]

1 hour ago, GodISmE said:

Be careful with that Martin. Stance also recommended 14/9 to me (Swift springs on their Supersport coilovers). It was ok until I started to really push the car on tracks and drive at the limit.  I found the car extremely loose, especially at corner entry which resulted in a few near spins at a high speed. If it wasn't for my sim experience and knowing how to save it at the last minute, I would probably end up in a wall.

Only now with shocks set up to full hard (front) and almost full soft (rear), wider tires at the back (275/35/18 vs 255 at the front) and a removed rear sway bar have I found a relatively good balance. But this is addressing the symptom instead of the root cause. That's why I want to get the balance right with the springs now and put the rear sway bar back on to get some balance setting options. I've already ordered 6kg srpings and I'll start with 14/6. Michael Gardner uses this combo and he seems to be doing quite well

 

 

 

That 14/9 setup is doing exactly like what my dynamic model say it would then.

 

A 14/9 setup with the OEM rear in board springs actually would work very nicely.

But to offer a 14/9 on a true coilovers setup honestly will require the engineer to go back to school.

 

Like I said, 14/6 will work but a little tail happy.

If I was to suggest, a 14/4.5 actually will make a good front biased setup that would be a good fast road & track setup.

 

That is of course assuming the damping deal with this springs rate well and will not over critical dampen the springs.

 

Jerrick

 

[MrLizard]

7 hours ago, MeisterR said:

Assuming we are talking about true coilovers rear, those rate is a little scary.

 

18kg/mm in the front is hard, but bearable... around the right figure for Semi-Slick.

14kg/mm in the front is on the harder end of a fast road car (slightly over).

The front rate are fine, as the 350Z suspension design mean the front isn't very sensitive to springs rate change.

 

 

My 2p to help out.

 

Jerrick

 

 

Must admit I have found the front to be very sensitive at 10/10ths to front spring rate change, quite a few factors at play really with front camber/weight/damping/tyres etc... 

[GodISmE]

I think that 18/9 could be ok for more experienced drivers - on a flat and fast track and with proper aero. Definitely not the right time for me as this is still my first year with 350z and actually with a track car  

I will try 18/9 one day as I already have 9's for the rear  

 

@MeisterR care to share the math behind that model? I was always wondering what that whole wheel frequency is about but I never had time to learn it. Is there a formula to calculate the right spring rates for a given car weight/tire combo?

Edited July 20, 2017 by GodISmE

[350Butcher]

So a bit of an update from my end!!

 

I have indeed posted some bum info with the 14/9 setup........this was I think for 2 reasons......firstly I don't think we (me and sales guy) were sure what we were talking about when it comes to spring rates neither were we sure whether I was going down the divorced spring or true coilover setup on the rear so there was some confusion and a result bum info!! Sorry about that.

 

I have been in direct talks with MCS now as distributor in UK guy was out of his depth and quite rightly said I should get advice from the guys themselves. (I needed advice too as I am no suspension guru I just know how I want me car to handle) I did a far bit of homework before pulling the trigger on ordering the MCS's and if you've not heard of them or Jerome Van Gool have a little look in to them.

 

With their advice I have gone with 600lbs fronts 300lbs rears (true coilover rears) think that equates to 11/5.5. with their 2WNR dampers. This was for a fast road / track setup given all the details for my car specifically, weight, geo, tyres used etc. I can't wait to get them on and see how they transform the car

 

Hope that helps a bit and can I say its great to have input from Jerrick a suspension guy and Lizard a racer on this topic too!

Edited July 20, 2017 by 350Butcher

[MrLizard]

sounds like a sensible decision butcher. Make sure you record your thoughts on track and assuming they are adjustable have a play and see what helps/hinders  

[350Butcher]

Cheers

 

Yeah I think it should be pretty serious with these on. I'm looking forward to dialing them in and as you say keeping records on what settings have what effect.

 

They have 18 clicks of rebound and 14 clicks of compression and have a blow off valve superior to Ohlins DFV system, my expectations are sky high!!.........and so they should be!!

[GodISmE]

Are you getting sway bars too? 

[MeisterR]

To calculate the bounce frequency (wheel frequency) is calculated using  sprung corner weight, springs rate, motion ratio.

It gives you a level playing round to evaluate what the wheel is seeing.

 

Because a 10kg/mm front springs on a 350Z is "lighter" than a 7kg/mm springs on the front of an EVO.

But what the wheels see is the important part.

 

The 11/5.5 seems to be a lot more sensible.

Jerrick

[350Butcher]

2 hours ago, GodISmE said:

Are you getting sway bars too? 

 

Already have Eibach bars fitted...........although I think I'd go for the H&R bars now

 

52 minutes ago, MeisterR said:

Because a 10kg/mm front springs on a 350Z is "lighter" than a 7kg/mm springs on the front of an EVO.

But what the wheels see is the important part.

 

The 11/5.5 seems to be a lot more sensible.

Jerrick

 

That's what makes it all so difficult to decide spring rates, every cars different, suspension pivot points and spring location change it all and every driver likes a different handling car!

 

I'm assuming what the wheel sees at 11/5.5 is fairly equal to slightly front biased?  

[MeisterR]

1 hour ago, 350Butcher said:

That's what makes it all so difficult to decide spring rates, every cars different, suspension pivot points and spring location change it all and every driver likes a different handling car!

 

I'm assuming what the wheel sees at 11/5.5 is fairly equal to slightly front biased?  

 

It isn't too bad, you just got to look at the wheel frequency... which is why it is important.

As that already include the suspension motion ratio (the leverage between the suspension and the wheel)

 

So one car might use 6kg/mm, the other car may use 14kg/mm.

However, if both car provide 1.8Hz wheel frequency, then you know both are going to roughly do the same thing, even though one car is using more than double the springs rate.

 

Actually, according to my calculation it is rear biased.

So that mean on throttle, the rear will want to come around more.

Not a huge problem, and the wheel frequency don't look out of this world (it is a little stiff in the rear).

 

But I won't look at it and go that it is a death trap in the making.

 

Jerrick

[350Butcher]

That's what I mean about it being difficult though, I wouldn't know where to start working out a cars wheels frequency and suspension motion ratio with only a socket set and a calculator in my garage at home.................we need suspension people like you with fancy maths and computer engines to tell us Jerrick!

 

With my car I meant in terms of spring energy to the ground it must be slightly more at the front, as its got to deal with the engines weight and braking forces etc?  Handling wise they've delivered exactly what I asked for then which is good to know, want the front as sharp to remove as much understeer with on throttle oversteer so I can steer a little with my foot.

 

Have you had any experience yourself with the MCS stuff?

[MeisterR]

Nope, it isn't about how much energy transfer to the wheel, but what the wheel see in terms of force and how much weight is acting on top of it.

Think of it this way, with a true coilovers setup, the front ratio is about 0.6:1 and the rear is about 1:1 (rough number).

So with a 11/5.5 setup, the wheel will see 6.6 front and 5.5 rear.

 

As you say, because the front is holding up more weight, that is why the 5.5 rear is actually stiffer than the front.

Calculating the numbers are easy, interpreting it and then using them to build suspension is the more difficult part.
I have seen plenty of people calculating numbers, then come up with something that can only be classified as "vehicle dynamically worthless".

 

I haven't had any experience with MCS, so I cannot comment.

 

Jerrick

[350Butcher]

Thanks for taking time out to answer this so well, some really good info there.  You answered what I meant even though I used the wrong terms to describe it and I understand the rear being stiffer as a result of the weight distribution.

 

I think that's the same with everything, I have definitely worked out a far bit of "vehicle dynamically worthless" info myself over the years..........but that's what we learn from!

 

[GodISmE]

I still don't know what you two are talking about lol  Yeah, the front vs. rear ratio I get but how do we calculate the wheel frequency and what is the motion rate about? I'd like to understand the physics and the math behind it!

Edited July 25, 2017 by GodISmE

[350Butcher]

This is a good link I found to it all

 

http://eibach.com/america/en/motorsport/products/suspension-worksheet

[msitpro]

Just found this thread via google search. All good info which backs up what I've been saying for the past year.

 

When I bought my BC BR 'true' rear coils after only 3 months of Z ownership, I did not know about motion ratio.

 

I soon learnt what it was when my back broke on every speed bump. (Car is used 95% fair weather road driving but also occasional hard track driving.)

 

BC spec these with 12k rear spring out the box!!!

 

I switched to a 6kg/mm Swift rear spring (and from 14 front to 8 - probably should be 12-14 front still for balanced wheel ratio really)

 

 

Anyway ... I have a new dilemma where I have reduced rear tyre/wing clearance (fat arse semi slicks) and can't 'tuck' my tyres under compression. I have static ride height currently with about 35mm compression available before fouling arch.

 

Been looking at adding a tender spring in addition to the original 12k spring on the back, so it goes from an effective 5k spring then into the 12k .... but this may induce some undesirable handling when compressed beyond the tender spring binding point.

 

Been delving into tender spring rate, free length/travel length before binding, calculating corner weight to work out the static ride height compression of the tender spring.... hmmm.

 

 

 

Anybody know the typical forces a wheel would see under hard compression over a bump???