RS2 H&R Spring Rates - Tested!

[Lloyd]

I recently bought some H&R RS2 springs via eBay from here:
http://stores.shop.ebay.co.uk/Tom-s-...__W0QQ_armrsZ1

Cost me EU346.50 or about £300. 29969, correct H&R code for RS2.
They turned up in a nice gunmetal finish, a little more subtle than the older lime green versions.

They are 30mm shorter than the OEM RS2 spring. Baring this in mind I imagined they would be stiffer than OEM and/or have a rising spring rate.

Forum members seemed to believe H&R’s are stiffer than OEM RS2 springs. A bit harsh for simple road use but great for track work or pairing with 18” wheels was the general view.

No one seemed to know the actual numbers and H&R were not forthcoming, so I got in touch with my old Mech Eng. Dept to get some real data.

H&R Results:

Fronts seem linear, with a near linear compressive spring rate of 24.5N/mm. Took the fronts to 150mm travel, they were not changing rate much at this point, and looked quite coil bound at the top.

Took the rears to 110mm. They were starting to bend sideways at this point, as the tops and bottoms are not flat. Did not want to bend springs out of line, so stopped test at this point.

Added trend line, linear to rears, you looking at about 40.1N/mm. These are not linear, a second order poly fits quite well, but the rate does not change that much.

The forum suggests OEM RS2 springs are rated as:
Front: Rated at 210lbs/inch (or 37N/mm)
Rear: Rated at 300lb/inch (or 52N/mm)

So, IF the OEM spring rate data is correct above, then H&R springs are softer than OEM RS2 springs! Who would have thought it eh?

[Lloyd]

Graphs...

Attached. . .

[A90TURBO]

Weird?

[Lloyd]

Weird?

Yep, wierd indeed. I would like to validate the OEM data if possible.

[S2central.net]

Intersting... PLEASE test the original RS2 springs on the same rig for thorough comparison

[Flat on my back]

.

The RS2 rear shock is under compression all the time as when fitted with the shock tube, but also moves a very small amount.

Do we need to get the start and finished lenghts to help us here?

[A80Avant]

yes indeed,that would be interesting!

[Rusty]

You need to measure the load at the operating position really and as Paul says, compare to the OE data. 200lbs seems about right for the stock stuff, as with the Avant, the coupe has springs that measure stiffer at the rear.

A reality check would be to measure the size of the metal that constitutes the main body of the spring. I have already measured the coupe AC springs in anoher thread, I'll measure the HnR blues I have in the cupboard sometime soon.

[stiglet]

You need to measure the load at the operating position really and as Paul says

Am I right in thinking that would be around 500kgs per front spring at normal rest position.... ish?

[Rusty]

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
l = free length = ??
c = no. of coils = 6.5

Rear
D = Outside Diameter = 145mm
d = Wire Diameter = 14.7mm
l = free length = 290mm
c = no. of coils = 6.5

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!

Here's the HnR blues that I've just measured:-

Front
D = Outside Diameter = 148mm
d = Wire Diameter = 13.7mm
l = free length = 310mm
c = no. of coils = 7.5

Rear
D = Outside Diameter = 152mm
d = Wire Diameter = 13.7mm
l = free length = 280mm
c = no. of coils = 6.75

The OE springs have 6.5 coils but the top 4 coils on the front HnRs and 3 on the rear HnRs the HnRs will lock very early, thus they will act more as though they have around 4 coils. The top and bottom coils don't do anything really so could call it 4.5 and 2.

Using the d^4/D^3 the relative relative stiffness of the helix (arbitary units, to clear things up I've removed the decimal places, the numbers are not spring rates) is:-

OE Fr 148 (23 for 6.5 coils, 37 for 4 coils)
HR Fr 109 (14.5 for 7.5 coils, 28 for 4 coils, 55 for 2 coils)

OE Rr 153 (23.5 for 6.5 coils, 38 for 4 coils)
HR Rr 100 (14.8 for 6.75 coils, 25 for 4 coils, 50 for 2 coils)

However, this is 6.5 coils vs. approx. 4 so they will be stiffer when the top coils lock. but are softer to that point using simple helix theory.

This would seem to back up your results and that when the top coils compress the springs get a lot stiffer ( your graph is starting to show that).

Also, it's worth noting that the HnR springs looks to be around 10% softer at the rear when compared to the OE setup where the springs are 4% stiffer at the rear! Just what's reaquired on a nice understeery car to begin with . Glad I've got that 26mm RARB to play with

HTH

[Rusty]

Am I right in thinking that would be around 500kgs per front spring at normal rest position.... ish?

Correct, 60:40 weight distribution, 1600kg ish, 960kg front, 640kg rear. I think Raymor has data to confirm this is about right too in one of this threads, I think on tracking setup.

At 320kg the rear springs are at least as stiff as the OE ones taking a tangent to the curve. The fronts are not in the operating zone yet.

Thinking about it, when you jack the car up the front stuts relax a looooooong way.

That's why the tighter coils are there, to stop the spring falling out at full extention.

[stiglet]

I was thinking that could be the reason for wacky values? I don't know. Interesting though.

[Jamo]

Those springs are the wrong colour to be RS2 H&R's they should be green if new or red if the earlier versions

[Lloyd]

Those springs are the wrong colour to be RS2 H&R's they should be green if new or red if the earlier versions

Really, why...? lol.

H&R have already changed colour once from red to green, right?
Green is not very nice. Bet they thought this colour might sell better...

From a previous post - I weighed my car with no passengers, 3/4 tank fuel
and spare wheel - no luggage.

Total: 1640 Kg
Front Axle: 940 Kg
Rear Axle: 700 Kg
57% F
43% R

Ignoring suspension gearing for a moment (Ahem, which is wrong) static pre-load on each front spring is 4610 N, rear 3,433 N.

The test above didn't get to this point with the front springs = shame.
However, the spring rate was linear up to this point and even spacing of the coils
suggests this would hold for the remainder of the travel.

Rears were tested to 4280 N (approx 1.25 G) before stopping.
= Past static pre load point, reasonable for (unladen) dynamic loading on the road?

[S2central.net]

Surely the color is just aesthetic... don't they stamp a number on them ?