GAZ coilover rear spring length question/advice

[SteMarsden]

Can anyone tell me what the standard length spring is for a 318? And can you confirm that its a 275lB rated spring?

When jacking the rear of the car up, the spring becomes 'free'. I know that this is an MOT failure but its annoying to have to hold the spring centrally when the car is lowered.
Im also concerned that if I use the kerbs and the spring becomes dislodges and doesnt seat correctly it will affect the handling for rest of that session/race.

My plan is to buy a pair of springs an inch longer so that the spring stays under compression when fully unloaded.

Is my thinking correct?

Are Faulkners good for these? (its seems you can order a huge range of ratings and lengths in 2.25 ID)
I heard that Eibach 2.25 are very good also....

Help.
TIA.
Ste.

[UweM3]

fitting a longer spring is not the solution. you car will sit too high. What you need is a very soft flat wound helper spring on top of your main spring. (can be bought from Faulkner as well)
Do not forget to buy a "connector ring" which goes between the two springs and locates them on each other

[BadDave]

The unit's Gaz sent me had 9" springs fitted.
I 've preloaded them a little as well.

[SteMarsden]

Sorry, dont think I made myself clear enough.

Uwe, I have enough on the damper body (upto 1 1/2") to drop the seating collars <inch to offset the increase in spring length. Therefore maintaining the ride height and still being able to raise/lower the car 1 1/2" with the new spring.

What are the relative adv/disadv of using a tender spring?

Dave, thanks for that. I may just whizz mine up on the jacks to double-check.

[Bob_S]

ste the tender spring sits on top of the spring in place and simply holds the main coil spring in place unaffecting your ride height

[Brian28]

Tender springs change the spring rate giving a bit of progression, softer until most of the movement is used up from the coils then the harder spring takes over. ie you could have a 600lb main spring with a 200lb tender spring. The initial spring is 200lb so softer for riding kerbs etc, then harder as the 200lb movement is used up and 600lb takes over. There is a formula somewhere for working out what the overall spring rate would be. Kind of part science and part black art, there are a few articles about it if you do a net google search. A helper spring has the coils closed when the car is static on its wheels, so doesn't have an effect on the spring rate, ie a 500lb spring with a helper spring is still 500lb at that corner. When the car is jacked up or when its the inside when cornering, the helper uncoils to keep the main spring and seats in position. The difference really is that tender springs are part of the suspension that effect how the car handles, the helper spring just keeps things in position.

IMO tender springs just make life too complicated unless you really know what you are doing (I don't ) and have easy access to corner weighting kit etc and a shed load of money for testing as there are so many potential variables. If you are going to add another spring stick with a main spring and helper, then if the car is too stiff/soft you only have the main springs to start messing about with. We took a load to an airfield day at Abingdon a few weeks ago and swapped loads of stuff to see what did what, thought we ended up with the cars not too badly balanced. At Brands (when you throw kerbs, gradients and track camber into the equation) they were hopeless and qualifying was a disaster. Changed loads of stuff through the day and got them a bit better. TBH I'd go with what Gaz are recommending at first as it will give you something not a million miles away, you can then start to change stuff as you get to know the car.

Back to the point and your original questions . Whether a 275lb spring is "right" is up to you, as everybody prefers something slightly different in how a car handles and as so much is fixed in PBMW (no rear ARB, standard front ARB etc) you will always end up with the compromise that works best for you between understeer/oversteer/body roll/grip when trail braking/grip coming out of corners etc etc. If you have enough adjustment to wind the spring seat down enough for a longer spring and still have room for adjustment and no issues with clearance anywhere a longer spring should work, or else a helper with your original spring. If budget is an issue (isn't it always) a couple of main springs will be cheaper than helpers + alloy seats to sit the springs on top of one another. Worth a post on Seloc to the other Gaz runners? Funny enough I was at Faulkeners on Friday, they have pretty much everything on the shelf if you need it.

Cheers
Brian

[UweM3]

a longer spring may not work IMHO but I will stand corrected if I see evidence.
If you car is static if will compress a spring at a certain rate. If you fit a longer spring it will only compress the same amount as the shorter spring (just at a higher point on the shock)

So you need to wind the platform down to get the ride height back to the previous height. You may have enough length on the shock body to wind it down but as soon you lift the car the spring will come loose. If you can clear the longer spring with the tyre in the first place.

You can fit a longer spring and reduce the bump travel of the shock to keep the spring in the platforms when on full drop, but there is a limit to it.

As harder the spring is you use as worse this will get because the hard spring will compress less from cars weight when static and you will loose too much bump travel if you limit the range of the shock too much.

just try out yourself and keep us posted

It seems that in the opinion of GAZ (and I have seen this with LEDA in the past on other E30's) that a helper spring is not required but I wouldn't dare to drive the Nuerburgring without helper springs full stop. (or any other means keeping the spring in the seats at full drop)

[Brian28]

Exactly right uweM3, I was up too early this morning Ste a single spring will only work if you extend the shock fully and stick a spring in that suits, and when you put the car back on its wheels the sag takes it to exactly the right ride height and still have decent suspension travel in both directions. Pretty unlikely in the overall scheme of things, so adding a helper to your existing set up is likely the best bet. Have sent a PM

[handpaper]

I'm running Gaz rear coilovers with 12", 225lb springs on mine and no, it won't go down very far before the springs come loose!
According to my calculations, with these springs the car will have 2" of static sag at the rear. You can wind the spring platform up and reduce this sag (increasing ride height) but you can't drop it further without using helper/tender springs to hold everything in place under rebound.
If anyone has done this I'd be interested to know about it, particularly in the light of Uwe's comment concerning the 'Ring.
My car felt properly planted there last year, but I am considering adding tender springs to the rear this year just to get the back properly low.

(Apologies for thread hijack) Uwe, GAZ and LEDA are probably building suspension for nice, smooth modern circuits, not our bumpy playground
Will we see you out there this year?

[SteMarsden]

Thanks for your input everyone....

After a lot of thought Im going to go for the tender spring option. Faulkner seem to have a number of 2" and 4" options (and collars) so will experiment that way.

Will keep you posted (with my limited testing and (very) limited budget!

Handpaper, were your 225lb springs the standard (non PBMWC) springs supplied by GAZ?

[UweM3]

Thanks for your input everyone....

After a lot of thought Im going to go for the tender spring option. Faulkner seem to have a number of 2" and 4" options (and collars) so will experiment that way.

Will keep you posted (with my limited testing and (very) limited budget!

Handpaper, were your 225lb springs the standard (non PBMWC) springs supplied by GAZ?

Don't want to sound picky, but don't you mean helper springs??
Here a picture of my springs (longer is front I am not running coil over at rear)

[SteMarsden]

Uwe,
Excuse my ignorance.
Whats the difference between a tender spring and a helper spring?
Ste.

[UweM3]

Uwe,
Excuse my ignorance.
Whats the difference between a tender spring and a helper spring?
Ste.

A helper spring is VERY soft and has no other job to do as to hold the spring assembly under tension when on full drop. They are flat wound and go fully coil bound (read collaps) when the car is taken off the jacks.

A tender spring is part of a two spring arrangement where BOTH springs are working. The tender is of a lower rate than the main spring and the twosprings together result in a progressive spring rate. Very complicated if you don't know what you're doing.
I don't know too much about this, so I stay clear and use just helpers and a main spring
Read Brian28's first post, he explained it in detail

I like it KISS = Keep It Simple Stupid

[handpaper]

Handpaper, were your 225lb springs the standard (non PBMWC) springs supplied by GAZ?

No, I specced them to match the rates on H&R's Nurburgring kit. Without lightening they seem a bit too soft; I had to wind up the rear damping further than I would have liked or they would smack the bumpstops coming out of the Karussell.

My front tender springs are 4", 90lb/in, so they run fully compressed most of the time. They do have an effect beyond that of helper springs when coming off kerbs and over crests - their rate is similar to OE (90lb/in vs 108lb/in).

[UweM3]

Handpaper, were your 225lb springs the standard (non PBMWC) springs supplied by GAZ?

No, I specced them to match the rates on H&R's Nurburgring kit. Without lightening they seem a bit too soft; I had to wind up the rear damping further than I would have liked or they would smack the bumpstops coming out of the Karussell.

My front tender springs are 4", 90lb/in, so they run fully compressed most of the time. They do have an effect beyond that of helper springs when coming off kerbs and over crests - their rate is similar to OE (90lb/in vs 108lb/in).

275 is well soft if you want to run Ring spec. I guess you need approx 400 if not more. My rears are 1080lbs in stock position

[SteMarsden]

I also like the KISS philosophy, thats why I need to fully understand this before I do any testing. I'm looking for sound advice from you guys to give me an idea of starting point.

Playing devils advocate, at what kind of poundage would you think a helper spring becomes a tender spring? Would it be around 60lb?

[Black_Potato]

A helper becomes a tender when it isnt coil bound under normal load, when that is would depend on the weight of that corner of the car.

[UweM3]

I also like the KISS philosophy, thats why I need to fully understand this before I do any testing. I'm looking for sound advice from you guys to give me an idea of starting point.

Playing devils advocate, at what kind of poundage would you think a helper spring becomes a tender spring? Would it be around 60lb?

I don't think this can be answered general. Depends what rate the main spring is. If you stick a 60lbs spring on a 800lbs main spring, there will be not much support from the 60 lbs spring and it will get coid bound very soon and may get damaged.

If you're don't know exactly what you're doing I would not start to experiement with tender springs. Each time you get it wrong you need a new set of springs.....

(read Brian28's first post, there is no one size fits all)

Keep in mind I am not a suspension guru, just reporting my own findings

[handpaper]

I also like the KISS philosophy, thats why I need to fully understand this before I do any testing. I'm looking for sound advice from you guys to give me an idea of starting point.

Playing devils advocate, at what kind of poundage would you think a helper spring becomes a tender spring? Would it be around 60lb?

I would say that a tender spring would need to be stiff enough to have an effect on the operation of the suspension, rather than merely retaining the main spring under extreme rebound.

Consider the situation when coming off a kerb or crest.
The suspension is very quickly unloaded and the main spring will reach full extension almost instantly. If your additional spring is of a very low rate (4-10lb/in) the unsprung components (wheel, brakes, strut lower) will effectively be in free fall; only their weight is pushing them downward and this may not be enough to keep the wheel in contact with the ground, especially when running the heavy rebound damping needed to control a stiff main spring.
An additional spring with a rate comparable to the effective unsprung mass (c. 50lb for an e30 rear trailing arm, wheel etc.) will do much more to keep the wheel on the ground - my tender springs initially provide 300lbf when unloaded in this manner, accelerating the wheel downward up to 6 times faster and, hopefully, keeping it on the ground.

Of course, sometimes even this isn't enough.....

[UweM3]

Two stacked springs act as ONE. It's not that the lesser rate tender spring is doing all the work till it get's coil bound, you main spring will compress as well under load. (taking into account the tender spring isn't silly low rate)
And I don't think you can just divide 300lbs by 50 and then conclude that wil be 6 times faster. There is still the damper to over come. Basically I agree with what you are saying but I can get difficult quite quickly when playing with suspension. Obviously you need to find the setup you like and suits your driving style, there is not one size fits all.
You picture has nothing to do with the spring rates, you simply ran out of drop travel
That's a wicked bend and it feels weired with all 4 wheels of the ground

[handpaper]

Two stacked springs act as ONE. It's not that the lesser rate tender spring is doing all the work till it gets coil bound, you main spring will compress as well under load. (taking into account the tender spring isn't silly low rate)
And I don't think you can just divide 300lbs by 50 and then conclude that will be 6 times faster. There is still the damper to over come. Basically I agree with what you are saying but I can get difficult quite quickly when playing with suspension. Obviously you need to find the setup you like and suits your driving style, there is not one size fits all.
You picture has nothing to do with the spring rates, you simply ran out of drop travel
That's a wicked bend and it feels weird with all 4 wheels of the ground

You're right, Uwe, two stacked springs do act as one - but in the cases we're looking at it doesn't make a huge difference.

The formula for the rate of two stacked springs is :
1/combined = (1/A + 1/B), so for my setup (1/650 + 1/90) = 1/79; the combined rate is 79lb/in against 90lb/in for the tender alone.

"I can get difficult quite quickly when playing with suspension"

I'm hoping you mean "It can get difficult[..]" Uwe, I'd like to stay friends

[UweM3]

"I can get difficult quite quickly when playing with suspension"

I'm hoping you mean "It can get difficult[..]" Uwe, I'd like to stay friends

there was no deeper meaning behind. Just a statement of my own experience (or better experiements!!!)
Sorry if that came across as personal attact, wasn't meant like that.

[handpaper]

Wasn't taken as such, Uwe, no problem

[SteMarsden]

Brian, Uwe, Handpaper,

Thanks for all your input.
I had a look at this last night and there seems to be about 30mm of 'free play' when the rear of the car is jacked up and the spring is unloaded.

I have about 60mm (upper) and 35mm (lower) of threaded body on the damper to play with adjustment wise.

So. The plan is to keep the existing 275lb main spring, and fit a 4" 125lb tender spring.
I then hope to test back to back with the existing set-up to see which I prefer.

Last questions (I promise!)
In your opinions is a 125lb spring too aggressive?
And should I also buy 90lb springs? (to test with or for the wet?)

TIA.
Ste.

[handpaper]

Here's Pooky's advice to me:

Hmm, hard to explain.

The rate of the helper spring is not important, just its length and block load (load at which it goes solid). The block load determines at what point it starts to open in rebound. Then the length and the rate of the helper and main spring combined determine at what point they both unload completely, i.e. how much extra travel you get.

Its pretty complicated and I won't be able to explain it on a post as it takes some trick excel spreadsheet tools to calculate. Best go to Eibach's website as they have a calculator and all the ERS springs to choose from.

My suggestion is you'll need a helper spring with a block load of about 800 to 1200 N on the front.

Using the block load figure above as 1000N (102Kg or 225lb), we can try to translate it to suit your setup.
The front end of an e30 weighs roughly 650Kg (stripping doesn't change this much), so the block load of the tender spring is roughly 1/3 of the static load on it.
Assuming a stripped car weighing 1100Kg, with 450Kg on the rear axle, the 'correct' tender spring would have a block load of 75Kg or 165lb. A 4" tender in that range will compress by about 3", so its rate would be 55lb. Faulkner do a 50lb, 4" spring; this is about as close as you need to get.

Alternatively, if you're happy with the car's handling apart from the spring coming loose, get a 4lb, 4" helper spring. This will retain your main spring without affecting your overall spring rate (much).

[UweM3]

handpaper, withoug getting into an argument but I am a little bit puzzled about your math. Not the calculations, they are correct. Just the application. You quote pooky who really has an understanding of the stuff due his work envolvement and he clearly states that it's tricky and needs a complicated spreadsheet to calculate the right spring rates and you just work it backwards with the values given for YOUR springs to determine a spring rate for Ste's tender spring. He is running completly different springs and maybe different shocks.

I do not want to sound negative and I will be the first to admit that I don't have an indepth knowledge of suspension dynamics but I just can't follow you thought process.
If it would all be that easy (with two lines and a pocket calulator) why do all the race teams employ an army of datalogging technicans and suspension experts?

Sure some basic math can/need to be done to have a starting point but for my liking there is too much to go wrong and for the level I am driving (track days NO racing) I just stay away from unpredictable results. I may have a go if I can see a possible benefit (or if I have a first hand example to copy) but I am very reluctant to waste time and money.

People do study this stuff for years and still get it wrong and a lot is down to personal preference and driving style. Not everything suits every driver. I have a lot more experince with bikes and I have encountered setups in one team differing like night and day and the two drives achieved almost identical laptimes. If they would have swapped bikes the result would have been a disaster for both.

I do like the discussion with like minded people like you (who clearly think about the stuff) and do not want to get this down the wrong way but for my part I do not want to recommend things to other people I am not 100%sure about. (or at least not without letting them know I am not sure)

[handpaper]

Uwe, the math is basic - it's still beyond some people though, which is where all the 'black art' bullshit comes from.
Pooky stated above that the block load of the tender spring was the important bit, and gave a figure for my application. My only assumption was that the block load/static load ratio, 1/3 in my case, could be valid in other cases, too. This seems to make sense - the tender spring won't start opening until the main spring is unloaded by 2/3 and thus doesn't affect the overall spring rate for most of the time.
The spreadsheet Pooky mentions almost certainly does little more than automate the calculations I did above, perhaps also creating a graph of spring rate vs load or extension.

I'm not sure what relevance datalogging has to this discussion, race teams use it to find out what the suspension is actually doing; the changes they make to the suspension as a result will be governed by calculations similar to those above. Suspension experts are people whose job it is to do these calculations and to make useful guesses when data is limited. They're probably more concerned with damping anyway, since that can get much more complicated.

The setup I described in my post above is quite predictable; it will provide extended rebound travel and prevent the main springs coming loose. Ste may not even notice any difference - if he's been running as described in the first post it's possible the suspension has never been in that position.
For Ste, a light helper/tender spring might help, can't hurt and has to be better than the MoT failure he's got now

Uwe, I look forward to threads like this one where I can discuss interesting things with informed and curious people. I respect your experience and honesty and appreciate the maturity that lets us discuss our differences without resorting to insults and profanity.
In light of that, I'll add a disclaimer :-

While I believe the options I described in my previous post will enhance the performance of your suspension, I must make it clear that I hold no qualifications in this field (GCSE Physics and Maths excepted) and recommend you seek the advice of a professional

Happy now?

[UweM3]

Happy now?

Of course

Good to see that we can keep this at this high level. At the end I am keen to learn as well (even if I am a little bit stubborn at time). You're absolutely right about the "black art", sometimes things are simple.

what I meant with data recording was that is used to verify calculations in the field.

I hope we can meet up sometime, guess that will be a whole evening bashing our heads together (with a few beers....)

[SteMarsden]

Thanks for all your Technical input.

I'm going to go away and fit some springs (not decided on poundage yet) and do some testing after corner-weighting the car.

I have decided on back to back testing and hope I do notice a difference!

If you ARE going to get together for a head-banging session, is there any chance of an invite so I could maybe learn something too? I thought karting was difficult enough with no suspension!

[UweM3]

If you ARE going to get together for a head-banging session, is there any chance of an invite so I could maybe learn something too? I thought karting was difficult enough with no suspension!

come to the Nuerburgring

[Brian28]

Driver preferences, track differences in both surface type and layout, bumpy bits and smooth bits, fast corners and hairpins, front toe in/out, rear toe in/out, front camber, rear camber, front ride height, rear ride height, castor, ARB thickness and adjustability front and rear, tyre pressures front and rear and left to right, bump damping front to rear and left to right, rebound damping front to rear and left to right, all this before spring rates even come into the equation, I still think setting up a car is as much black art as science

[handpaper]

Thanks for all your Technical input.

I'm going to go away and fit some springs (not decided on poundage yet) and do some testing after corner-weighting the car.

I have decided on back to back testing and hope I do notice a difference!

If you ARE going to get together for a head-banging session, is there any chance of an invite so I could maybe learn something too? I thought karting was difficult enough with no suspension!

OK, head-banging session @ the Lindenhof, Nuerburg, 13/09/09, 21:00 - 02:00

To make things even more interesting I'd also invite Pooky for technical know-how and Ed for experience and colour. Davenotouring, Karan and Theo325 also deserve places at the table.

Karting? "Ok, so you turn the wheel, the outside front wheel goes up, the inside front goes down and the inside rear lifts off the ground and lets the kart turn. But it only works properly if you're on the brakes when you do it."
Sometimes having more bits (suspension and a diff) make things simpler

[cragles]

SteMarsden - our car has the exact rear gaz coilovers as your car, and yes they come "loose" when the car is jacked up, but it passed an MOT like that no problem on Thursday, once I had the certificate I queried it with the tester, who said he saw this, but made the intelligent decision that since the spring cannot come completely "free" from the strut, it passed. He says the reason that check is in place is for drastically lowered cars with the rear springs in the standard seperate position, which can come "loose" completely when the car is jacked up.