Race car spring rates, advice needed!

Mac944 · Dec 1, 2014

Hi All,

I have a set of Ledas which I'm looking to replace on my race car with either a shiny new set of Ledas or possibly Gaz.

It looks as though the spring rate on the rears currently is 250lbs but the front springs are corroded and the paint along with markings has flaked off.

The shocks came with the car and are now in need of an overhaul/replacement but the characteristics of the car have changed over the past year so I'm a bit unsure what a good base would be to start with. It's around 100kg lighter (@1055kg) and has a little under 100bhp (and 20 ft/lb torque) more than when the previous owner originally installed the shocks.

I was thinking of going for 225 or 250lbs rear and being unsure what I'm running at the front try possibly 350lbs or 400lbs at the front.

Any suggestions or advice is much appreciated.

Masher · Dec 1, 2014

Can't help with your enquiry I'm afraid, but I would be interested in more pics and spec of the car (assuming I am not asking you to divulge your trade secrets!). Sounds and, assuming that is it in your avatar, looks interesting.
Cheers
Mick

edh · Dec 1, 2014

sounds very soft.. FWIW my track car has 500lb front, 400lb rear.
I presume it still has torsion bars at the rear?

Spring manufacturers will test the springs for you.

TBH I'd just go for a known setup - wouldn't it make sense to buy Gaz dampers & springs from EMC?

chrisg · Dec 1, 2014

Once again Ed has beaten me to it......

However to go one step further, IIRC Turbo cup cars had ~ 400lb/" front springs and were marked with a blue stripe on the springs.

If you're not sure of the poundage, take one of and send it to Coil Springs in Sheffield = http://www.coilsprings.co.uk/

A. They know they're doing

B. They're not hugely expensive

C. They can produce anything you need either in single rate or dual rate springs - so you could uprate your current front springs AFTER you've had them tested.

For a true race set up you've got to be looking at 450 lb" plus, as I'm sure you're aware (relative to roads) track surfaces are like billiard tables = try driving a full race car on any road and see how long you're filling last/ before you blow a shock....

Chris (ex Porsche & R5GT racer......)

Mac944 · Dec 1, 2014

ORIGINAL: edh

sounds very soft.. FWIW my track car has 500lb front, 400lb rear.
I presume it still has torsion bars at the rear?

Spring manufacturers will test the springs for you.

TBH I'd just go for a known setup - wouldn't it make sense to buy Gaz dampers & springs from EMC?

Yep still have torsion bar on the rear, which I believe has been reindexed but I can't be sure. I had considered deleting it but that seems a bit of a faff.

Gaz I can get direct or from EMC, I expect the price will be the same but it's a good point going with EMC as Kevin will probably keep them in stock and know exactly which springs to go for.

Thanks for the suggestion, I'll give them a buzz tomorrow.

Mac944 · Dec 1, 2014

ORIGINAL: chrisg

Once again Ed has beaten me to it......

However to go one step further, IIRC Turbo cup cars had ~ 400lb/" front springs and were marked with a blue stripe on the springs.

If you're not sure of the poundage, take one of and send it to Coil Springs in Sheffield = http://www.coilsprings.co.uk/

A. They know they're doing

B. They're not hugely expensive

C. They can produce anything you need either in single rate or dual rate springs - so you could uprate your current front springs AFTER you've had them tested.

For a true race set up you've got to be looking at 450 lb" plus, as I'm sure you're aware (relative to roads) track surfaces are like billiard tables = try driving a full race car on any road and see how long you're filling last/ before you blow a shock....

Chris (ex Porsche & R5GT racer......)

Great, thanks Chris.

Looks like my estimate for the front wasn't far off, just been digging through the car history and was surprised to find an old receipt for the springs which apparently are 375lb so that doesn't seem quite a way off what it should be.

If you're talking 450lb front what would you run on the rear?

edh · Dec 1, 2014

I think the EMC Gaz setup is particular to them & not the same as the stock dampers you can buy from Gaz - I'm sure I've read that on here.

Neil Haughey · Dec 1, 2014

Do you know which torsion bars you have in the back, assume stock 944 N/A perhaps?

I don't I have uprated rear torsion bars from Weltmeister USA and it makes a big difference when choosing springs. NineX recommend Eibach springs and fitted a set on my rear coil overs, I have previously bought springs from Faulkaner. We went from 325 down to 250 on the back after a couple of long discussions where we both concluded on the change needed (my torsions are about 225 lb/inch effective way stiffer than stock). I run 600 lb/inch up front but some will say its a bit stiff and go for 550 lb/inch. Paul Follett posted in an article from from several years ago in PP that he went up to 800 lb/inch up front in his 968 so quite a range to choose from.

I think with Gaz/Leda and probably a fair few other setups you will be looking at a front effective rate between 20% and 35% stiffer than the back. I very greatly prefer the rear to be much softer than the back and to some extent feel like I wasted 4 years before finding a handling nirvana setup for me.

Its easy to play with the numbers: front effective will be roughly spring rate * 0.8 (600 lb/inch spring gives roughly 480 lb/inch effective rate)
rear effective depends on the torsion bars but stock 944 is about 140, turbo about 175 you then add on the coil over rate * 0.54.

Thus my setup is 600 * 0.8 = 480 front
225 + (250 * 0.54) = 360 rear
Which means my front effective (wheel rate) is about a 1/3 stiffer than the back.

To do the same with standard rear torsions I would need 360 - 140 = 220 / 0.54 = roughly 400 lb/inch rear springs.

Something which can complicate matters is something Andy Duncan warned me about which is torsion bars sagging over time and loosing rate which is why he prefers to fit new aftermarket bars, I already had mine changed years ago when the car was just a track day thing. I am not convinced personally this effect is going to make a huge difference.

Cheers Neil now paying for a house rather than racing.

Mac944 · Dec 1, 2014

ORIGINAL: edh

I think the EMC Gaz setup is particular to them & not the same as the stock dampers you can buy from Gaz - I'm sure I've read that on here.

Ah, OK well I'll give Kevin a call and check what their spec is.

Neil Haughey · Dec 1, 2014

Mac I reckon your fronts are either 400 or 450 if they came in a Leda/Gaz set and the car handles nice.

Mac944 · Dec 1, 2014

Thanks for the info Neil that's very informative.

The Leda receipt mentions 375lb although it's possible they were changed later as I found another receipt for the rears which stated 150lbs which I know is incorrect as I've taken down the markings directly from the springs which is 250lbs.

I believe the torsion bar is N/A stock but I may just get a new just to be sure.

Thanks for everybody's input, I wasn't expecting quite so much useful info but I have plenty to mull over now.

Mac944 · Dec 1, 2014

ORIGINAL: Masher

Can't help with your enquiry I'm afraid, but I would be interested in more pics and spec of the car (assuming I am not asking you to divulge your trade secrets!). Sounds and, assuming that is it in your avatar, looks interesting.
Cheers
Mick

I think there are some pics floating around on the forum somewhere of the engine rebuild earlier in the year. There's lots of external pics on the Classic Sports Car Club photographers website and quite a bit of in car race footage on Youtube.

I've been fairly open with the guys in the paddock with the spec, I've not disclosed the finer details of course ;-)

267bhp
1055kg with fuel
Steel lined block
Forged pistons and conrods
Larger throttle body
Larger injectors
Reprofiled cams
Aftermarket ECU
Race wiring loom
Fibreglass front end
Polycarb windscreen and side windows

Masher · Dec 2, 2014

Thanks. I ought to get along to a Future Classics meet next year. If you're not too busy maybe we'll get a chat.
Your FG front end looks way nearer than the job done on mine. Mine looks like the garage threw the bumper at the car and screwed it on where it landed! I plan to take it off this winter (when I get the car back) and see if my non-existent DIY skills can improve it.

I have the EMC Gaz Gold suspension fitted to my car (track car) along with the beefiest anti roll bars EMC could get (can't recall if they are M030 944 or 968 - must have a look). Has always felt a bit soft to me. Car currently with Augment who have sent video of the suspension to Chris at CG. Both agreed the car used the rear torsion bars too much, in fact the rear springs were loose with any sort of body rise - rattled like hell. AA are currently re-indexing the car which should drop the car solidly onto the springs and I'll take a view from there. My point - I am an amateur doing trackdays running EMC Gaz Gold suspension and it feels a bit soft to me. I can imagine a race car needs stiffer springs. That said, I think EMC have met with some success racing 944s so maybe I am talking rubbish [8|]

Cheers
Mick

Cater_Racer · Dec 2, 2014

ORIGINAL: Mac944

ORIGINAL: Masher

Can't help with your enquiry I'm afraid, but I would be interested in more pics and spec of the car (assuming I am not asking you to divulge your trade secrets!). Sounds and, assuming that is it in your avatar, looks interesting.
Cheers
Mick

Click to expand...

I think there are some pics floating around on the forum somewhere of the engine rebuild earlier in the year. There's lots of external pics on the Classic Sports Car Club photographers website and quite a bit of in car race footage on Youtube.

I've been fairly open with the guys in the paddock with the spec, I've not disclosed the finer details of course ;-)

267bhp
1055kg with fuel
Steel lined block
Forged pistons and conrods
Larger throttle body
Larger injectors
Reprofiled cams
Aftermarket ECU
Race wiring loom
Fibreglass front end
Polycarb windscreen and side windows

mmmmm, interesting.......

edh · Dec 2, 2014

ORIGINAL: Neil Haughey

Its easy to play with the numbers: front effective will be roughly spring rate * 0.8 (600 lb/inch spring gives roughly 480 lb/inch effective rate)
rear effective depends on the torsion bars but stock 944 is about 140, turbo about 175 you then add on the coil over rate * 0.54.

Thus my setup is 600 * 0.8 = 480 front
225 + (250 * 0.54) = 360 rear
Which means my front effective (wheel rate) is about a 1/3 stiffer than the back.

To do the same with standard rear torsions I would need 360 - 140 = 220 / 0.54 = roughly 400 lb/inch rear springs.

Neil

I found different numbers for effective spring rate : My calcs used 0.94 F / 0.42 R = 482F / 316 R

Using your numbers my setup would be 410F, 365R. Mike Wilds commented that my car was a bit loose, but I like the way it works now. I guess a race car can achieve sharper turn in through aggressive geo, which I can't really do as mine is a road car as well. I've got -3 deg camber and a smidge of toe in

Masher

I'm surprised you think the EMC setup is soft - I remember talking to them about setups when I bought my car (fitted with KW's). They were firmly of the opinion that KW's were way too soft - and they were right....which is why I have now got stiffer springs. I was getting some disconcerting roll oversteer when really pushing through fast corners like Craner curves [

] I think Gerry (cater racer) has gone firmer on his KW's.

As for helper springs / reindexing. The orthodox position (via EMC and Promax) as I understand it is that at rest, the rear helper spring should be just fully coil bound. Maybe you don't have rear helpers? I have read reports that Gaz are noisy

Cater_Racer · Dec 2, 2014

Mines way too soft on the front, I need to go up to something similar to Neil. It's a winter project for Tom who's got the car at his place.

The backs I have the standard KW's but re-indexed the torsions to fully bound helpers at rest. It feels about right.

I'm only putting out 180BHp and 1200kgs, so it's no wonder Anthony goes past me like I'm standing still, when it's still going that is [

]

Mac944 · Dec 2, 2014

ORIGINAL: Cater_Racer
I'm only putting out 180BHp and 1200kgs, so it's no wonder Anthony goes past me like I'm standing still, when it's still going that is []

Don't worry Gerry, you have a bit of time to play catch up. I have no intention of doing anything quite as drastic for next season [

]

Mac944 · Dec 2, 2014

ORIGINAL: Masher

Thanks. I ought to get along to a Future Classics meet next year. If you're not too busy maybe we'll get a chat.
Your FG front end looks way nearer than the job done on mine. Mine looks like the garage threw the bumper at the car and screwed it on where it landed! I plan to take it off this winter (when I get the car back) and see if my non-existent DIY skills can improve it.

Sure, pop along for a chat.

The shut lines in the pic look OK but up close they are a bit of a mess, in fact not a lot lines up but putting a big sticker over the car seems to help [

]

Mac944 · Dec 2, 2014

Just spoke with Kevin at EMC and it does indeed appear they have their own setup and recommended spring rates based on the car and the tyres I'll be running. There should be enough adjustment in the external reservoirs to tweak if necessary, so should be a good base to start with.