Spring rate VS arb rate

[jon]

Hi All,

 

I'm at a bit of a junction with my track car and I'm not entirely sure which route to take.

 

Now, I've done a few trackdays this last quarter and I feel i'm getting too much bodyroll resulting in roll-oversteer (I've exhausted geometry etc).

 

My car is running standard ARBs on Tein HA coilovers which have the stock springs on (224lb/in front and 448lb/inch rear)

 

My options are threefold:

 

1) Go for some heavily uprated, adjustable arbs and dial the car in that way

2) Up the spring rates by 300lb/in or so

3) Up the spring rates say 150lb/in and get medium sway bars.

 

Each course his it's own merits. On the one hand, heavy adjustable ARBs will allow me to keep softer spring rates to ride the bumps but go too stiff and i'll lose roadholding. On the other hand and good chassis designer will tell you ARBs should supplement the setup, not be used to brace the car because you've not sprung it enough.

 

Any thoughts / input would be welcome.

 

Many thanks

[Sam@TDi]

An interesting dilemma for sure, and one faced by many people at clubman motorsport level.

 

The accepted "norm" is for close circuit racing track cars to have massively stiff spring-rates and often no anti-roll at all, these are the pros & cons as I see them

 

• + Body roll will be almost totally eliminated, this tends to have a strong positive emotional effect as large roll events can “un-nerve” amateur drivers

• + Vertical load variation from the chassis will be very quickly transmitted to the tire’s contact patch and visa versa, so on a smooth surface the car will feel to respond faster and react more quickly to balancing corrections with for instance the throttle pedal.

• + If the car is using any meaningful aerodynamics it is imperative to keep the aerodynamic devices horizontal to the track surface and often important to keep them at a specific separation from the track, the only practical way to do this is to stiffen the spring system.

 

• - As the total stiffness goes up the systems natural frequency goes up, so the stiffer the chassis as a whole, the more inputs per second may be required to keep it on course, people using an open loop driving process (the playstation generation) generally can’t cope above 2hz …. The BAR F1 car is approx 4.8hz

 

• - If the track surface has many undulations and the spring rate is too stiff to yield the tyre can be forced momentarily past the saturation point. If this happens a net reduction in grip will occur at the saturation limit. This is due to the simple fact that a loaded tyre (one that is producing lateral acceleration) will “un-wind” in one forth of the time it takes it to “wind” back up and start producing lat acc again.

 

• - Having zero body roll means that you lose the chance to take advantage of kinematic geometry changes, such as “toe-in/out on bump” or “camber in on bump”

 

Personally I would strongly recommend option-3. Being able to manipulate roll as a handling modifier is a superb tool to have in the box, you can quite literally decided whether you’d like a push or an oversteer departure, the trick is learning how to drive with the chassis moving and not let the roll events put you off

[jon]

Thanks for the input Sam.

 

My prefered driving style is with a loose end, Tony will be testiment to that by the way I make him setup the car, but i feel due to the roll oversteer i'm having to wait longer than i should be to get on the throttle which is costing me time.

 

While option 3 is the ideal it's also the highest cost option. If it were between 1 and 2 i'm certainly leaning towards 2 at the moment.

 

Another consideration, which to be fair is totally out of my scope, is partnering the suspension setup with the tyre characteristics. Unfortunately that's more resource than i'll ever have

[Tony]

Thanks for the input Sam.

 

My prefered driving style is with a loose end, Tony will be testiment to that by the way I make him setup the car, but i feel due to the roll oversteer i'm having to wait longer than i should be to get on the throttle which is costing me time.

 

While option 3 is the ideal it's also the highest cost option. If it were between 1 and 2 i'm certainly leaning towards 2 at the moment.

 

Another consideration, which to be fair is totally out of my scope, is partnering the suspension setup with the tyre characteristics. Unfortunately that's more resource than i'll ever have

You surprise me jon! I am far from finished with your cars Geometry, the roll over-steer and your current set-up is way beneath what you desire... We need the car weighted and pulled down to measure some real dynamics then conclude the possibilities of the car....

[jon]

I agree Tony, but either way it's too softly sprung! (next time i'm letting you set it up)

 

I've decided to ignore the ARBs for now and up the spring rate, but how do I work out what i want? This is from tein uk...

 

Hi Jon

 

There is a crude way to check if you know how many mm stroke you need.

 

We know the weight of the car, we know the length of the spring; with information of your required stroke value, we can calculate which spring rate you will need.

 

If you want a different length spring and different rate, we can check the stroke values on our springs.

 

Please come back to us if you need our help.

 

Regards

 

Chris Marshall-Dowe

Sales

TEIN UK LIMITED

Unit 7 Avant Business Centre

Denbigh West

Milton Keynes MK1 1DL

United Kingdom

e-mail: sales@tein.co.uk

www.tein.co.uk

Tel: 0870 606 6543

Fax: 0870 600 1161

 

----- Original Message -----

From: jon benson

To: TEIN UK Limited

Sent: Thursday, December 21, 2006 1:24 PM

Subject: Re: Tein Ha

 

Hi Chris,

 

Thanks for all your help.

 

I think short term I might as well just up the spring rate and wind the dampers up (i currently run the dampers quite soft, around level 4/6) as i've already pillowball and full camber adjustment, once they pop go for something a little more solid!

 

I'd love to know why tein fitted such a soft spring to the front when the stock weight balance is around 44/56 but at least it gives me something to improve upon Is there any known math in picking the ideal spring rate as i'm shooting in the dark a bit? The car will be around 1050kgs with probably a 42/58 balance in favour of the rear. Used entirely for track work so comfort isn't a problem.

 

thanks

[Tony]

What was the conclusion? Stroke length V rate.

[jon]

To be honest, I don't know.

 

I don't know how much stroke rate i want, I'm out of my depth. All i want is a stiffer car.

[Tony]

To be honest, I don't know.

 

I don't know how much stroke rate i want, I'm out of my depth. All i want is a stiffer car.

Sam's option #3 reads good to me.

[jon]

We're going to do this properly Tony! Will have to create a thread once i've got my head around things, but I need to work out roller centres front and aft, work out where they go with bump and roll etc, work out where i want them then work out the stroke rate from that. Once that is done i can work out the correct spring rate.

 

An MR2 friend of mine has recommended me some 'light' reading about the subject with details of an old, but effective fashion for working this all out (which involves, string, nails and a board)

 

Though your new machine will probably do all this for me when you get it

 

For now i'm not going to touch ARBs.

[Tony]

We're going to do this properly Tony! Will have to create a thread once i've got my head around things, but I need to work out roller centres front and aft, work out where they go with bump and roll etc, work out where i want them then work out the stroke rate from that. Once that is done i can work out the correct spring rate.

 

An MR2 friend of mine has recommended me some 'light' reading about the subject with details of an old, but effective fashion for working this all out (which involves, string, nails and a board)

 

Though your new machine will probably do all this for me when you get it

 

For now i'm not going to touch ARBs.

The new machine does take the master out of the skill but not the skill out of the master..... i think Pull downs/ roll centres and all other related dynamics will explode here...

[Tony]

Topic's bugging me jon.... Personally i would down rate the dampening and the coil platforms (a little).... Up-grade the Roll bars, then progressively re-introduce the suspension dampening and coil rates to suit... You command a different arena now jon where the likes of Sam@tdi and wim cannot satisfy you (on paper at least)

 

All good stuff but proving would be a necessity with this type of development... Experts like tdi and wim would need to work hand in hand collaborating skills... Then driver feed-back would validate or dismiss the set-up. Please note each progressive step totally violates the Geometry dynamics, each chassis change needs complimenting since it's unique, meaning the expectations are more refined and your situation no longer fits a category?

[Tony]

Little bump....

I did forward this topic to an suspension developer who is now part of the clubs collaboration so i am looking forward to some interesting evolutions from this exact type of thread Our interior is growing in strength day by day

[jon]

Wow, that's great news Tony.

 

I'll throw an update in later next month, i'm going to see a guy up north who does a lot of work on mr2s, but he used to race tr6s and basically rebuilt the suspension on that so knows a lot on the subject.

 

I feel the only issue i'm going to have is finding the right damper that fits the sw20. Teins monoflex seem like a good option as a bolt on coilover unit where as the Koni 8611 look even better, just as slot in dampers. I'd just then have to make my own cartridges which is getting a little past me

[The Gazman]

Hi

I haven't had a play with an MR2 yet but my initial thoughts are that uprating springs is a much more controlled way of stiffening up the front end than arbs, your front springs sound a bit soft to me.

Tein do tend to run harder valving and softer springs which do work well on road cars but come unstuck as soon as you really start to push them, Nitron and Ohlins also have the same problem.

I favour a more agressive geo and pumping up tyres to stop the fronts rolling over and I will have a think about this and pass on my ideas to Tony next week.

[Tony]

Hi

I haven't had a play with an MR2 yet but my initial thoughts are that uprating springs is a much more controlled way of stiffening up the front end than arbs, your front springs sound a bit soft to me.

Tein do tend to run harder valving and softer springs which do work well on road cars but come unstuck as soon as you really start to push them, Nitron and Ohlins also have the same problem.

I favour a more agressive geo and pumping up tyres to stop the fronts rolling over and I will have a think about this and pass on my ideas to Tony next week.

Welcome to wim Derek.... Any thoughts on the evolution make then visible here. We are a collaboration of skills and never in competition, our wealth is sharing knowledge.... I think the chassis dynamics considerations and the suspension sections here will keep you busy

[Sam@TDi]

Hi Derek good to have you onboard!

[The Gazman]

Hi again

I put this into the pot at the R&D meeting at the factory today and the general consensus was"too hard on the back and too soft on the front".

We recomend you try 300lb front and 375lb rear.

 

On a trackday car we would start at the following geo (just as a point of interest)

Front

Caster=4 degrees

Camber= 1.5 neg

Toe= parallel

 

Rear

Camber=2 degrees neg

Toe= 1.5 per wheel

 

After testing we might run a tad more toe in on the rear and maybe a tad more neg camber on the front, we would be looking to provoke a tiny little bit of understeer.

 

All IOHO

[jon]

Hi Gaz,

 

Funny you put that geo up, that's pretty much what i was moving to next (i currently run just about that toe but -2 camber front and -1.5 rear).

 

I agree the ratios are all wrong on the current setup but would you really recommend spring rates that low? Bearing in mind i run a really soft bar might something like 400front and 525rear make more sense for track only work?

[The Gazman]

Hi Gaz,

 

Funny you put that geo up, that's pretty much what i was moving to next (i currently run just about that toe but -2 camber front and -1.5 rear).

 

I agree the ratios are all wrong on the current setup but would you really recommend spring rates that low? Bearing in mind i run a really soft bar might something like 400front and 525rear make more sense for track only work?

 

When you say soft bar ar you talking standard, if so I would stick with our suggestions.

I also take it that we are taking fully adjustable Tein shocks with standard valving?

I would only run your existing camber on a front engined rear wheel drive car, we think you are right to move the other way.

[jon]

Yes, the standard bar. They're tein HA dampers which tein think will control anything up to 500s before needing revalving. 16 stage adjustable but unfortunately no separate bump and rebound.

 

As I said, i liked a lose rear but more recent temperature analysis shows i've got things a bit wrong, see

 

http://www.wheels-inmotion.co.uk/forum/ind...p?showtopic=633

 

I've some more data from a donnington session if you're interested, that's a little less NSF bias.

 

The car currently understeers but i run big aero on the rear.

 

Anyway, back to my point, why lowish spring rates? I figure if i'm going to buy more springs i might as well throw something in harder than i have, the car currently feels softer than it should.

 

Thanks for your suggestions

[The Gazman]

Hi Gaz,

 

Funny you put that geo up, that's pretty much what i was moving to next (i currently run just about that toe but -2 camber front and -1.5 rear).

 

I agree the ratios are all wrong on the current setup but would you really recommend spring rates that low? Bearing in mind i run a really soft bar might something like 400front and 525rear make more sense for track only work?

 

When you say soft bar ar you talking standard, if so I would stick with our suggestions.

I also take it that we are taking fully adjustable Tein shocks with standard valving?

I would only run your existing camber on a front engined rear wheel drive car, we think you are right to move the other way.

 

I think the front will feel soft, you will be surprised what a difference 75lb on the front will make on such a light car.

We don't think you will have much compliance on the back with those current spring rates, we would run a bit lighter on the springs and turn the dampers up until we felt they were working properly, its possible you could be running on the springs with no control.

[The Gazman]

Hi Gaz,

 

Funny you put that geo up, that's pretty much what i was moving to next (i currently run just about that toe but -2 camber front and -1.5 rear).

 

I agree the ratios are all wrong on the current setup but would you really recommend spring rates that low? Bearing in mind i run a really soft bar might something like 400front and 525rear make more sense for track only work?

 

When you say soft bar ar you talking standard, if so I would stick with our suggestions.

I also take it that we are taking fully adjustable Tein shocks with standard valving?

I would only run your existing camber on a front engined rear wheel drive car, we think you are right to move the other way.

 

I think the front will feel soft, you will be surprised what a difference 75lb on the front will make on such a light car.

We don't think you will have much compliance on the back with those current spring rates, we would run a bit lighter on the springs and turn the dampers up until we felt they were working properly, its possible you could be running on the springs with no control.

[jon]

Righto. I'll go up to around 320 on the front and leave the rear as it is just to save cost and report back. I'll also redo my geometry to something close to the discussed settings with Tonys input.

 

I'll also be throwing on +20 section tyres front and back (eg 245 rear instead of 225), perhaps i'll save that mod so i can judge what's doing what. Nothing worse than bolting on X mods at once and not knowing what's helped.

 

Also, i don't mean to be rude but what's your background Gaz? Tony rates you and you came to some sensible geo settings very quickly so you obviously know your stuff, the next question is how?!

[The Gazman]

Righto. I'll go up to around 320 on the front and leave the rear as it is just to save cost and report back. I'll also redo my geometry to something close to the discussed settings with Tonys input.

 

I'll also be throwing on +20 section tyres front and back (eg 245 rear instead of 225), perhaps i'll save that mod so i can judge what's doing what. Nothing worse than bolting on X mods at once and not knowing what's helped.

 

Also, i don't mean to be rude but what's your background Gaz? Tony rates you and you came to some sensible geo settings very quickly so you obviously know your stuff, the next question is how?!

 

I front a company called Absolutely Shocks and we specialise in developing bespoke fast road and trackday kits and geo for popular sports cars.

Between my R&D and me(mostly him) we have 35 years experiance setting up everything from road rally to grasstrack, formula 3000 cars and saloon car racers. We don't know everything but we have a good all round knowledge of basic set-ups and track geo.

[jon]

Impressive resume there I look forward to more of your posts.