924srr27L Lightweight Doors / Suspension / Bump steer etc..

[924Srr27l]

Are we there yet ?

Almost,

I had a 20 minute call from Holland from one of the INTRAX Engineers who do all the maths.

As you'd expect from an expensive bespoke service & Product, he wanted to know many things about the car's use,

what mods have been done, the wheels & Tyres / brakes being used and also the car's current set up and handling

characteristics...etc

From this the final spec has now gone to build stage and I'm hoping delivery within 2-3 weeks.

We've agreed to use springs on the rear as well as keeping the 27mm Torsion bars, the coil springs will be located

with a low poundage helper spring which can be set uncompressed when the car's static weight is on the axle.

This means the car's spring rate will only use the Torsion spring initially and then under heavier loading / cornering the coil spring

will add to and make the total spring rate higher.

The Springs they make their own from lightweight carbon steel which are an unusual size

2.75" ID (70mm).

The fronts have 40 and the rear 50 positions of adjustment which is at a ratio of 70% Bump & 30% rebound.

The special ARC valve only works in the bump motion, and I'm using standard rubber top mounts.

R

 

[edh]

Are we there yet ?

Almost,

I had a 20 minute call from Holland from one of the INTRAX Engineers who do all the maths.

As you'd expect from an expensive bespoke service & Product, he wanted to know many things about the car's use,

what mods have been done, the wheels & Tyres / brakes being used and also the car's current set up and handling

characteristics...etc

From this the final spec has now gone to build stage and I'm hoping delivery within 2-3 weeks.

We've agreed to use springs on the rear as well as keeping the 27mm Torsion bars, the coil springs will be located

with a low poundage helper spring which can be set uncompressed when the car's static weight is on the axle.

This means the car's spring rate will only use the Torsion spring initially and then under heavier loading / cornering the coil spring

will add to and make the total spring rate higher.

The Springs they make their own from lightweight carbon steel which are an unusual size

2.75" ID (70mm).

The fronts have 40 and the rear 50 positions of adjustment which is at a ratio of 70% Bump & 30% rebound.

The special ARC valve only works in the bump motion, and I'm using standard rubber top mounts.

R

Interesting - so what's the effective spring rates F/R?

FWIW I think you may have got this slightly wrong - the helper spring should be just coil bound at rest, (main spring uncompressed). I'm sure that's what they meant. That is how the KW's are set up.

 

[924Srr27l]

We've agreed to use springs on the rear as well as keeping the 27mm Torsion bars, the coil springs will be located

with a low poundage helper spring which can be set uncompressed when the car's static weight is on the axle.

This means the car's spring rate will only use the Torsion spring initially and then under heavier loading / cornering the coil spring

will add to and make the total spring rate higher.

R

Interesting - so what's the effective spring rates F/R?

FWIW I think you may have got this slightly wrong - the helper spring should be just coil bound at rest, (main spring uncompressed). I'm sure that's what they meant. That is how the KW's are set up.

It is interesting for those that enjoy learning and understanding about things like handling, how it works,

and what it can do for you, rather than a select few that say or ask nothing but give out jibes & pepperoni!

Yes, normally the helper quashes to nothing at rest then any downward movement the main spring will be in force.

This is mostly used for coil springs only (like the front struts) but can also be used on the rear when an additional spring

(Coil) is fitted as a well as the (Torsion) Spring.

I wasn't keen on having any extra springs on the rear as the rear of the car feels very good,

(no wheelspin and no excessive bodyroll) hence I'm reluctant to introduce more stiffness, but the engineer

(Also a Racing driver & winner in Radical sportcars) convinced me that it's just as well that we spec a rear coil if I ever did

decide to attend another track day as it would be beneficial also because the dampers are adjustable with 50 clicks and the ARC

valve was designed / also works very well with hitting circuit kerbs (Btcc style)

So he suggested that I set the spring pan height to still show a relaxed Helper for an inch, then after the spring will

be assisting and adding it's resistance to the 220Lb Torsion bars.

They work in NM and the front springs are to be 34NM (190lbs) and the rear Coils 40NM (230Lbs) but because

of the different front & rear suspension designs and subsequently the MR (motion ratio), the wheel rates will be approx.

Front

Coil 190lbs , MR .90 (171 lbs)

Rear

Torsion bar 220Lbs MR .65 (143 Lbs)

Coil springs 230 lbs MR .65 (150 lbs)

So the rear Wheel Spring rate once the helper is coilbound and both springs are operational will be 293Lbs,

which is why I don't want this amount of stiffness at least not for the first inch or more , but only when really pushed.

It means the rear will have a dual rate, great for ride road quality and then the increase when cornering.

It may for once give the rear some oversteer balance, which if it does and it's too much the springs can be changed

and decreased, but for now I'm going with their spec & expertise.

I've got plenty of wheels and Tyres (Widths & Sizes) to be doing more trials once they are installed, but I'm not planning on

fitting them until the modified wishbones and stub axles are also done and ready to fit...

The idea to test for the first time a revised corrected wishbone Geometry, with less bumpsteer and also

all 4 corners being controlled by the trick valving is far more appealing and effective to judge the change all in one go.

There will also be less unsprung weight (aluminium strut bodies).

R

 

[blade7]

Are we there yet ?

Almost,

I had a 20 minute call from Holland from one of the INTRAX Engineers who do all the maths.

As you'd expect from an expensive bespoke service & Product, he wanted to know many things about the car's use,

what mods have been done, the wheels & Tyres / brakes being used and also the car's current set up and handling

characteristics...etc

From this the final spec has now gone to build stage and I'm hoping delivery within 2-3 weeks.

We've agreed to use springs on the rear as well as keeping the 27mm Torsion bars, the coil springs will be located

with a low poundage helper spring which can be set uncompressed when the car's static weight is on the axle.

This means the car's spring rate will only use the Torsion spring initially and then under heavier loading / cornering the coil spring

will add to and make the total spring rate higher.

The Springs they make their own from lightweight carbon steel which are an unusual size

2.75" ID (70mm).

The fronts have 40 and the rear 50 positions of adjustment which is at a ratio of 70% Bump & 30% rebound.

The special ARC valve only works in the bump motion, and I'm using standard rubber top mounts.

R

Interesting - so what's the effective spring rates F/R?

FWIW I think you may have got this slightly wrong - the helper spring should be just coil bound at rest, (main spring uncompressed). I'm sure that's what they meant. That is how the KW's are set up.

I thought the helper springs were there to keep tension on the main spring if it was unloaded, ie full extension. I set my rears with the main coils just taking the weight of the car.

 

[edh]

I thought the helper springs were there to keep tension on the main spring if it was unloaded, ie full extension. I set my rears with the main coils just taking the weight of the car.

When the helpers are fully compressed....just, then that's almost the situation you're describing.. at rest the torsion bar is carrying the weight. Andy moss set my car up like this and I confirmed it with EMC and Promax

 

[924Srr27l]

blade7

I thought the helper springs were there to keep tension on the main spring if it was unloaded, ie full extension. I set my rears with the main coils just taking the weight of the car.

Oh goody, some content for a change!

Under full droop on a ramp or if you were jumping over a bridge etc.., yes the helper stops the main spring from

dislocating, but it's also used on such small ID springs so that they can be fitted without spring clamps..

Under all loads the helper is fully compressed and coilbound, especially on front struts and on rear coilover

telescopic shock absorbers when the car is using 1 or 2 springs (coils and torsion bars)

Small free length Tender (Higher rate) springs can also be used for Dual rate shock absorbers, and in my rear shock application, I'm planning on setting up the rear collars so that the very small rate tender is still open. Which will only allow the Torsion bar to be offering resistance until a set amount of movement compresses the tender and then the main coil spring will add more resistance in combo with the T bars.

R

 

[blade7]

I thought the helper springs were there to keep tension on the main spring if it was unloaded, ie full extension. I set my rears with the main coils just taking the weight of the car.

When the helpers are fully compressed....just, then that's almost the situation you're describing.. at rest the torsion bar is carrying the weight. Andy moss set my car up like this and I confirmed it with EMC and Promax

I used Chris Franklin at Center Gravity to set up my car [] . I just made sure the main springs were lightly loaded so they were working with the torsion bars.

 

[924Srr27l]

Blade7

I used Chris Franklin at Center Gravity to set up my car . I just made sure the main springs were lightly loaded so they were working with the torsion bars.

Are you using K/W rear shocks & coil springs and the stock 952 T bars ? or different

If at rest the helpers are coilbound the first bit of movement will have the full force of both springs

if there was a way of lightly loading this would be good, but the car's weight is either on or off the coil at rest, unless like my plan the helper is not fully quashed and coilbound? then the first amount of movement

is only using the Tbars resistance. A progressive one piece spring would be an option. Faulkner in the UK can make these to order , like a Snooker Cue they use Tapered Wire which gives the Spring rate an initial rate which increases with more resistance.

R

 

[edh]

...and in my rear shock application, I'm planning on setting up the rear collars so that the very small rate tender is still open. Which will only allow the Torsion bar to be offering resistance until a set amount of movement compresses the tender and then the main coil spring will add more resistance in combo with the T bars.

R

Really? How can it be sensible to introduce a higher spring rate suddenly at some (indeterminate) part of a corner? Surely that has the prospect of making the car unstable?

I can see the benefits of progressive rate springs for road use, but a sudden step?

 

[edh]

I used Chris Franklin at Center Gravity to set up my car [] . I just made sure the main springs were lightly loaded so they were working with the torsion bars.

OK well AFAIK this is incorrect. Depends how "lightly" I guess..

 

[Eldavo]

...and in my rear shock application, I'm planning on setting up the rear collars so that the very small rate tender is still open. Which will only allow the Torsion bar to be offering resistance until a set amount of movement compresses the tender and then the main coil spring will add more resistance in combo with the T bars.

R

Really? How can it be sensible to introduce a higher spring rate suddenly at some (indeterminate) part of a corner? Surely that has the prospect of making the car unstable?

I can see the benefits of progressive rate springs for road use, but a sudden step?

How dare you question "The Roger" - He will have ex-F1 engineers on the case for sure!!!

Don't forget how much lighter his car (and wallet) are than yours, you'll be telling me you don't have a code name for your car next Ed?

It's all academic anyway, as when it turns up he'll only drill holes in it

The smart money would go to Centre Gravity, but I fear that won't happen as Roger doesn't want to hear when he's incorrect.

 

[924Srr27l]

Eldavo

How dare you question "The Roger" - He will have ex-F1 engineers on the case for sure!!! Don't forget how much lighter his car (and wallet) are than yours, you'll be telling me you don't have a code name for your car next Ed? It's all academic anyway, as when it turns up he'll only drill holes in it The smart money would go to Centre Gravity, but I fear that won't happen as Roger doesn't want to hear when he's incorrect.

Intrax engineering has previous F1 experience and Championship success starting with Michael Schumacher in the Benetton.

Centre Gravity don't manufacture & build bespoke Race winning and superior Road Suspension, but unless I'm mistaken their expertise is changing Geometry settings.

The "smart money" has been spent with the experts in Holland that do this for a living and had CG made something similar I'd of spoken to them about it.

The Intrax 1K2 Shock absorbers are lighter than stock units, no need for drilling.

R

 

[blade7]

I used Chris Franklin at Center Gravity to set up my car [] . I just made sure the main springs were lightly loaded so they were working with the torsion bars.

OK well AFAIK this is incorrect. Depends how "lightly" I guess..

I got away with out having to re-index so pretty light. I wonder why some installers used to say you had to ?

 

[924Srr27l]

EDH

Really? How can it be sensible to introduce a higher spring rate suddenly at some (indeterminate) part of a corner? Surely that has the prospect of making the car unstable? I can see the benefits of progressive rate springs for road use, but a sudden step?

Intrax tell me that the Motion ratio of the trailing arms at the end of the shock absorber stroke are closer to .59 so this would equate to an additional 136Lbs of tension / resistance which I think will be corner forces

close to or over 1G which are more than likely to be experienced and achieved only on circuits / track days.

Don't forget the spring rate is based on a deflection of 1" for the rated poundage, So a 200lb spring

will compress 3" with the vehicle weight at rest (600Lbs each corner - inc driver & Fuel)

For a spring to compress another 1" will require a force of 200Lbs which can only be achieved mechanically or aerodynamically.

I don't have that much aero at all apart from the front chin spoiler and the rear Spoiler and Gurney Flap, so this will never experience enough force to compress the car an inch with the power of the air passing over the car.

Mechanical (weight transfer) will load the outside suspension whilst cornering, and then amount of force is dependent on the amount of resistance the suspension accepts and then the amount of coefficient of friction from the rubber tyres.

Intrax have a vast amount of experience in what they do, but I also need and like to understand what it is they are doing so for sure I have asked the question about will I have an abrupt rear end but their answer is no, because what their valving and the trick ARC valve is doing is replicating an electronic system which many car's have these days. Which gives a good ride quality but stiffens when cornering hard.

The ARC valve makes the bump stroke much harder than normal sport shocks, because when it encounters a fast piston movement (Bump, pot hole, Curb etc..) it relaxes within mili-seconds and softens.

Of it didn't the compliance would be rock hard and the ride quality and crashy feeling some may of experienced when you've run hard shocks on the road?

When the shock absorber is loaded slowly EG when tipping into a corner with a slower not abrupt amount of force the valving and ARC valve has a lot of strength & support and holds and controls the car's body very well. It's almost like having 2 spring rates in that the shock varies the resistance it offers dependent on how slow or fast the piston rod travels from the road surfaces.

So getting back to these rear coils, which with the intended set up will only come in to play when a very high

amount of cornering load is applied to them which at this point is a good thing as it means the harder I push the more support I will get.

It could offer some oversteer which usually as you know the harder you push a 944 it understeers...

So this could "trim" the rear quite nicely mid to corner exit and reduce the understeer.

Once I'm happy with the set up I might return to Oulton park just to see how they react.

This picture from Elephant Racing (USA) illustrates a helper spring that's not closed and coilbound

but open and it 's like this that I've been recommended to set the rear up like for road use.

R

 

[924Srr27l]

Here's a example from an American Racer... On a 930 with Torsion bars front & Rear but also with additional rear coil springs:

-------------------------------------------------------------------------------------------------------------------------------------

I prepared a 2720 lb track 930 with 23/31 T bars and 250 lb helper coils in the rear (along with a number of other suspension mods as well). The car ran on the track with 520 hp, on 275 and 315 Nitto NT-01 tires. My goal was increase the rear spring rate but I wanted to avoid full coilovers in order to alleviate the need for reinforcement of the rear shock towers. I felt that the relatively minimal coil spring rate of 250 lb/in did not impose enough load to the shock towers to create a problem. I wanted to reduce the squat on acceleration that was causing odd and undesirable handling during corner exits. It also made for a platform that allowed finer, easier adjustment for ride height and corner balancing. The car handled perfectly -- it felt very linear and predictable. There was no tendency for excessive oversteer, and certainly no "snap oversteer" as has been suggested. It felt stable in slower corners (entry speeds of 35 mph) as well as the highest speed sweepers, at over 145 mph. There was no problem with setup, no strange noises coming from the suspension, and no issues with the two different springs "fighting each other." In all, it seemed like an ideal setup that accomplished the goals that I was looking for. BTW, I got the coilovers and some revalved shocks from Rebel racing and was happy with the transaction. There are several seriously fast track 930s around here that are running rear coils and torsion bars with great success. I'm one who's not afraid of an engineering analysis or theoretical discussion, but sometimes, the best way to assess a particular setup is to also consider empirical data -- such as lap times -- from drivers who have demonstrated success. I would certainly think that to run such a setup on the street would be absolutely fine.

-------------------------------------------------------------------------------------------------------------------------------------

R

 

[edh]

Here's a example from an American Racer... On a 930 with Torsion bars front & Rear but also with additional rear coil springs:

R

It's not this that is question - my KW's have a coil spring at the rear. It's quite usual on 944's.

 

[edh]

Intrax tell me that the Motion ratio of the trailing arms at the end of the shock absorber stroke are closer to .59 so this would equate to an additional 136Lbs of tension / resistance which I think will be corner forces

close to or over 1G which are more than likely to be experienced and achieved only on circuits / track days.

Don't forget the spring rate is based on a deflection of 1" for the rated poundage, So a 200lb spring

will compress 3" with the vehicle weight at rest (600Lbs each corner - inc driver & Fuel)

For a spring to compress another 1" will require a force of 200Lbs which can only be achieved mechanically or aerodynamically.

I don't have that much aero at all apart from the front chin spoiler and the rear Spoiler and Gurney Flap, so this will never experience enough force to compress the car an inch with the power of the air passing over the car.

Mechanical (weight transfer) will load the outside suspension whilst cornering, and then amount of force is dependent on the amount of resistance the suspension accepts and then the amount of coefficient of friction from the rubber tyres.

Intrax have a vast amount of experience in what they do, but I also need and like to understand what it is they are doing so for sure I have asked the question about will I have an abrupt rear end but their answer is no, because what their valving and the trick ARC valve is doing is replicating an electronic system which many car's have these days. Which gives a good ride quality but stiffens when cornering hard.

The ARC valve makes the bump stroke much harder than normal sport shocks, because when it encounters a fast piston movement (Bump, pot hole, Curb etc..) it relaxes within mili-seconds and softens.

Of it didn't the compliance would be rock hard and the ride quality and crashy feeling some may of experienced when you've run hard shocks on the road?

When the shock absorber is loaded slowly EG when tipping into a corner with a slower not abrupt amount of force the valving and ARC valve has a lot of strength & support and holds and controls the car's body very well. It's almost like having 2 spring rates in that the shock varies the resistance it offers dependent on how slow or fast the piston rod travels from the road surfaces.

So getting back to these rear coils, which with the intended set up will only come in to play when a very high

amount of cornering load is applied to them which at this point is a good thing as it means the harder I push the more support I will get.

It could offer some oversteer which usually as you know the harder you push a 944 it understeers...

So this could "trim" the rear quite nicely mid to corner exit and reduce the understeer.

Once I'm happy with the set up I might return to Oulton park just to see how they react.

This picture from Elephant Racing (USA) illustrates a helper spring that's not closed and coilbound

but open and it 's like this that I've been recommended to set the rear up like for road use.

R

Still not convinced - you're saying that they won't ever come into play on the road, but you don't know.. You're almost doubling your effective spring rate when it happens. A bit like hitting bump stops?

I think the pics are red herrings btw..

 

[924Srr27l]

Here's a example from an American Racer... On a 930 with Torsion bars front & Rear but also with additional rear coil springs:

R

It's not this that is question - my KW's have a coil spring at the rear. It's quite usual on 944's.

There's no Fish in the Photos, they are to illustrate what an uncoilbound helper looks like.

The 930 Racer's experience is a good indication on what adding extra springs (Only on the rear) can provide,

which may be considered as an excessive oversteer situation but his finding were reported as working great.

He added another set of Springs (250Lbs) to his torsion Springs already so he also doubled the rear spring rate.

Your Standard 24mm torsion bar springs are rated at 137Lbs, and would think the KW rear coils are rated at higher

rate so you've also doubled the total rear spring rates as they work together.

This is why you hear the Need to reindex from manufactures because the rear coil springs in many kits (GAZ, Avo, Spax, KW)

use a spring which is a higher rate than the stock Torsion springs, hence they would override the T bars and it's best

that the car rests on the T bars first then the coils for road use, or they effectively do nothing like Gerry's (Cater-racer) racecar.

Intrax are one of the highest spec manufactures in the world up there with Penske and Ohlins, these guys have proven their

knowledge and expertise on many circuits, if you're not convinced it's ok.

If i'm not convinced the £4000 was well spent after fitting and testing, I'll not have an issue telling all either,

but I'm up for trying.

R

 

[blade7]

Blade7

I used Chris Franklin at Center Gravity to set up my car . I just made sure the main springs were lightly loaded so they were working with the torsion bars.

Are you using K/W rear shocks & coil springs and the stock 952 T bars ? or different

If at rest the helpers are coilbound the first bit of movement will have the full force of both springs

R

KW's with standard 91 turbo torsion bars. 7 or 8 years ago when I fitted them most suppliers said re-indexing was required. This suggested to me they were either touting for business and/or they thought the rear coilover springs should be supporting the weight of the car. The 968 MO30 rear shock has a coil spring, so it would be interesting to know when they come into effect. Other than that I think all your suspension hypothesis is a load of techno babble, and your 924 would be blown away by something like a Cayman S.

 

[edh]

I think the reindexing was a bit of an urban myth. It all depends on the individual car & also how low you want to run. You might have enough on the spring plates, you might not.