Cortina

Have decided to do something about the softness of my rally car (see other posts with in car video if this does not compute).
Having stripped out what I have and measured them (using the bathroom scales / 4 post ramp / steel rule technique) - I reckon the poundage of rears is about 140 / 150 , and the fronts about 180 / 190
Question 1 - does this sound about right ? (I guess springs are standard)
I'm now starting to see the light about comments relating to moving front to back ... still leaves me with a front problem to sort !
Question 2 (and I am guessing I want to start off with something about 15% stiffer) ... rule being to stay as soft as I can on spring rate ....
Are there any off the shelf / out of stock springs anywhere that I can buy ? - Prefer UK base ... as I only have 2 to 3 weeks to sort , it probably rules out USA source ??
I had some custom made here (Ireland) 20 yrs ago for a Lotus Elan , but supplier is out of that market now , so I am trying to track down a new source ... any suggestions ?
(Have seen conversion kits to smaller size (dia) of spring offered , but don't know that I want to go down that route (Homologation ++)) - Looked at 928 International site , but could not see springs on offer ..
suggestions / ideas / answers ???

Cortina

I'm surprised that nobody knows the approx poundage of a standard 928 spring ??

Lizard928

Dont bother with standard size springs. Though, your stock spring rates sound to be slightly weakened due to age, they are fairly correct.

What shocks are you running?
You can get a threaded sleeve to fit over the shock body, and then just use a standard 2.5" ID racing spring. Just use a standard 2.5" racing spring upper perch for the shock.

Start with 800# front and 500# rear.

993turbo

Download the WSM. The OE springrates are listed in there! Also check the color coding on your springs, as they may have been changed.

puyi

Basically, front spring rate is about 38 N/mm (210 Lbs/inch).

For custom made race spring, I suggest using Eibach spring you can find it @ http://www.truechoice.com/
There is certainly an importeur of eibach product in Ireland. You can search Here : http://performance-suspension.eibach...rs_distributor

Best

Puyi

Dave928S

I've run in State and National rally championships here in Australia and I can promise you that if you run high rate springs, as used in circuit/tarmac racing you'll knock the fillings out of you mouth, hammer the crap out of your suspension and stress crack mounting points on your car ... BTDT. The sort of roads you're running on you need a reasonably compliant suspension to handle the pounding, with decent suspension travel, slightly higher rate springs, really good externally adjustable shockers, better adjustable sway bars, less compliance in things like sway bar and other suspension bushes and linkages, and some additional front suspension mounting point bracing. It's all about precise control, and keeping your wheels in contact with the ground as much as possible .. and you won't get that with a bone jarring suspension. Even though your high profile narrow tyres are limiting your performance in a lot of ways, they're probably helping to a degree in absorbing shock loads.

The rates mentioned in the WSM give you a test loading for a set compressed length (about 270 to 280mm) and not a rate of load per unit of compression as per normal spring rating. I've got some front GT springs here which are about the 210/220 lbs. Your springs have probably gone a bit soft, and I wouldn't be at all surprised if your shockers overheat and lose performance when you get well into an event. A heavier rate spring will help, but one of the most important suspension components in rallying is shocks which will handle the hammering without overheating and losing their damping rate, and which have been tuned to work in harmony with the springs. Putting in too heavy a spring will severely limit your suspension travel and therefore the ability to absorb energy over a reasonable length of travel.

A suspension specialist should be able to wind some custom springs for you and revalve some shocks and tune them to suit. The springs shouldn't be doing all the work, and neither should the shocks.

Cortina

I agree with this - plan to go as soft as possible ... have just placed order for 300lb springs , which is as high as I would want to go as a first step. will transfer front to back to give a similar %age increase there (a bit less actually) ....
A racing spring is defn NOT what is required ... interesting that at 300 lbs it is what some suppliers are calling an uprated spring for normal road use ! (They go to 1000 lbs + ...imagine that !!)

Bart-Jan

I've bought 2 pairs of adjustable sleeves that were sold by Rallydesign in the UK. They are meant for Escorts, I believe. The top perches have been slightly modded on a lathe to use the stuck shock upper mount. Now, I can use standard 2.5'' springs, available in many spring rates and many lengths. Cheap and easy to change, without the necessity for dismounting the hole front lot. Of Ebay really cheap and easy...

GlenL

I just put 2.5" springs on my car. Posts and pics here:
http://reutterwerk.com/forums/showthread.php?t=28814

I believe you've got the rates about right. To keep balance the springs should have a 3:2 ratio from from to back. That is 300lb/in front and 200lb/in rear, as an example. Your choice in this matter is good. Vary that for your driving style/preference and if you've lightened the car at one end more. Usually the weight comes off the back more readily.

Ordering springs is tricky as the compressed length decreases with increased spring rate. The front doesn't have a lot of adjustment available, either. What length did you order for the 300lb/in fronts?

dr bob

When using the bathroom scale and the tape measure method of determining existing spring rates, remember to multiply the readings you get by the leverage in the control arms.

mark kibort

just cut the springs by one coil and you will be done!

Cortina

I ordered the 300 lbs fronts with a free length of 13" ..... just worked back from std length , and adjusted for change in spring rate. (std length was 14.40") . Are my sums OK ??

Cortina

Not only the leverage if you want to be precise ... but also need to take angle into account !!

Dave928S

Sounds about right .... and I think you're on the right track in going for that % increase as a starting point.

Variable rate springs are also used in rallying. The good thing about variable rate springs in rally applications is that they not only give you a softer more cushioned landing when suspension is extended, and less jarring at unexpected dips, but also have less tendency to 'launch' you on a crest because the rate drops away with extension. That said .... standard 300lb springs is the place top start .. with good shocks valved to suit. Get that combination right ... then you can make other tweaks ... one at a time.

I'm sure that getting springs and shocks right will give you huge improvements in your times. Look forward to hearing how you go next time. Will you have navigator audio on your next run?

Cortina

Should have audio on next run - In fact we have some footage with that from Manx rally - Camera was mounted on roof for that event rather than inside. Will nag navigator to get it posted !!!