Front springs on the rear (Coupe)

[Rusty]

This follows on from a thread I started in the wanted section linky. The idea is that the front springs were stiffer and so would alter teh handling characteristics of the S2 and dia out a bit more understeer. H&R offer the option of 2 sets of front springs on the coupe to alter the rideheight / stance of the car so I though I'd look into doing it with standard parts to maintain some rideheight. Thanks to S2DriverUK and Jamo for some OE springs. Here's what I found:-

I've done a bit of measuring and have come up with the following numbers:-

Front
D = Outside Diameter = 139mm
d = Wire Diameter = 14.1mm

Rear
D = Outside Diameter = 145mm
d = Wire Diameter = 14.7mm

Now then, here's the science bit as I see it,

Assumptions:-
The OEM springs are not variable rate
The OEM springs are made from the same material
Both front and rear springs have equal numbers of coils (I've counted them and this is true).
The spring rate of a helical spring is proportional to d^4/D^3 using the assumptions above and that they have the same number of the coils. Using this formula, the rear springs have a spring constant approximately 4% stiffer than the fronts! However, the front is 50% heavier (60:40 weight distribution) and so there is 50% more preload on the spring (so it sags more). The increased preload on the front moves the operating region of the spring up the force vs. deflection curve and so the spring requires more force to achieve the same deflection as the rear under static loading conditions. Dynamically the mass means that the increased force is proportional to the increased mass and that's where my knowledge begins to fail me!

Therefore, it looks as though my idea of fitting front springs on the rear really shouldn't make much difference with standard springs!

I think I might just do it anyway as I'm going to rebuild the rear struts at some point ot fit top mounts and bump stops. I'll report on what I find then!

[Flat on my back]

Any chance of getting the spring rate checked? Then we could start a chart of oem springs compared to aftermarket?

[terrybullwon]

Andy i have front H&R's on my rear end, they sit a little higher and like to make you understear

[Rusty]

Cheers for the replies, there might be another option that I'm researching at present. The RS2 spec H&Rs are stiffer than the standard S2 setup (as anyone who's seen Ben's car will testify). so they could go on the back to dial out the understeer a little, I'm trying to find the spring rates. Or, if you can source these separately, then you can go for an ultra stiff coupe! Carful ARB choice could be used to dial the understeer out... 26mm front and rear anyone

Another option is to use the H&Rs fronts on the rear and the standard rears on the front (assuming they are slightly uprated) :O. The rear springs are about 10-15mm shorter than the fronts so should lower the car slightly and if they are indeed stiffer then that should work ok assuming the H&Rs aren't too much stiffer. It's all guess work I'm afraid until we know the spring rates for all the aforementioned springs... and eveen then it's a bit of a gamble I suppose

I've briefly looked into getting the spring rate checked but tno luck, if there's anyone who works somewhere that this could be done then please contact me as I have a few spare springs kicking around now and I think this might be a fairly intersting project for future reference.

[Greg_S]

would have to be RS2 fronts since the rears are different

[Pete Reeve]

Cheers for the replies, there might be another option that I'm researching at present. The RS2 spec H&Rs are stiffer than the standard S2 setup (as anyone who's seen Ben's car will testify). so they could go on the back to dial out the understeer a little, I'm trying to find the spring rates. Or, if you can source these separately, then you can go for an ultra stiff coupe! Carful ARB choice could be used to dial the understeer out... 26mm front and rear anyone

Another option is to use the H&Rs fronts on the rear and the standard rears on the front (assuming they are slightly uprated) :O. The rear springs are about 10-15mm shorter than the fronts so should lower the car slightly and if they are indeed stiffer then that should work ok assuming the H&Rs aren't too much stiffer. It's all guess work I'm afraid until we know the spring rates for all the aforementioned springs... and eveen then it's a bit of a gamble I suppose

I've briefly looked into getting the spring rate checked but tno luck, if there's anyone who works somewhere that this could be done then please contact me as I have a few spare springs kicking around now and I think this might be a fairly intersting project for future reference.

Redditch in worcestershire is the capital of spring manufacture try a company called Spring Masters they should be able to help or point you in the right direction

[Rusty]

Cheers Pete. Are you able to source H&R springs? Can you get them as pairs?

Greg, that was what I meant, front RS2 spec springs front and rear, only downside would be rear rideheight might look a little high but that's unchecked. I'm sure that there must be a piccy of S2_Ant 's car with teh frotn H&Rs all round.

Would be interested to see what Ben's was like on a track, I'm rliably informed it's boneshatterring on the road .

[Flat on my back]

I've briefly looked into getting the spring rate checked but tno luck, if there's anyone who works somewhere that this could be done then please contact me as I have a few spare springs kicking around now and I think this might be a fairly intersting project for future reference.[/QUOTE]

Any decent race prep company should be able to check the springs out, who have you tried down Bris'ol way?

Think there are a few up round this neck of the woods, Merlin Motorsport maybe?

[Pete Reeve]

Yes i can supply H+R springs in pairs

[Greg_S]

I'll see if I can get a side shot of mine for you since mine has front H&R's all round

[Rusty]

How do you find the handling Greg? Does the car understeer any more than you would expect or is it as per standard? I like to look into these things (almost obsessively I have to admit ) because I'm after a bit more aggressive handling from the old girl (hence the 24mm FARB on the rear of a standard car with Konis) and like to think that others might be vaguely interested in the same thing, always nice to suprise people with the handling of an Audi, not to mention the sheer grip of a true quattro car! Love it

[Rusty]

Not tried Merlin at CC but that's a good shout. I'll mail them tomorrow as I'm often at Circuit Motors as Paul there is 'my mechanic' when I need a ramp!

[Greg_S]

There is less understeer from standard, but I fitted the H&R's Konis and RS2 FARB at the same time so its harder to differentiate. would be good to come out in yours to see what it is like with the 24mm rear ARB. have you got p/n & pricing for it?

[Rusty]

Thanks Greg, I'm hoping that any understeer from fitting a pair of fronts can be dialed out using careful ARB selection.

Part number:- Alex at All Audi (24mm/25mm are very common)
Price:- 5/8ths of FA!

Not got EKTA at present but I'm sure Ben can enlighten you, give him a bell.

[Rusty]

Just sourced some RS2 front springs. They're 50% more money than the standard S2 springs but as Ben has proved, they are stiffer and would be very suited to track days but not so much fast road driving so it may be a case of fitting them as and when... Awaiting a few other enquiries to come back but could be interesting! Ultra stiff suspension is't necessarily the best option.

@ S2Avant, what do you think of your suspension on the track or have you not tested it yet?