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littleted

Original Poster:

4 posts

100 months

[news] 
Friday 27th May 2011 quote quote all
Hi, Does anyone have a starting point for the suspension spring rates for a blade engined westy. Its a live axle car and at the moment it is so hard that it wants to fly off the road on any bump.I want a compromise so that it is not too soft for track days.

Sam_68

9,939 posts

133 months

[news] 
Friday 27th May 2011 quote quote all
Do a search on the WSCC technical forum, it's been discussed many times, but before you start messing around with spring rates, make sure your dampers aren't set too stiff.

The range of ajustment on Spax dampers, for example, is really too stiff overall for a light 'Seven' type car, so try full soft at the rear and one or two clicks up from full soft at the front as a starting point, and work from there.

Tyre pressures should be pretty low, too - 16 to 18 psi is typical.

littleted

Original Poster:

4 posts

100 months

[news] 
Friday 27th May 2011 quote quote all
thanks sam, I have it fully soft on the dampers at the moment, but they are only one way damping so in effect the rebound is not damped. which makes things worse. the car weighs in around 500kgs and about 55% rear to45% front weighting. I ran it at silverstone with 22psi in the tyres (toyo r888 semi softs) It still felt too hard.I tried to measure the rear springs i reckon they are about 175lbs/in. I will try the wscc forum again I am a member so maybe I missed something Cheers

Sam_68

9,939 posts

133 months

[news] 
Saturday 28th May 2011 quote quote all
If the 175lb springs are on the rear, then it does sound a bit on the stiff side (though some people run that firm for track use). Personally, I'd be looking at about 120-130lb on the rear for a dual-purpose track/road car(though I will admit that I like a bit more compliance than some).

The fronts will be much stiffer (getting on for twice as stiff, though it depends on engine weight). Main principle I stick to when changing spring rates is to stick to a similar ratio of front:rear stiffness unless you want to change the basic handling balance (in which case the general rule of thumb is increasing relative stiffness at front = more understeer, decreasing relative stifness at front = more oversteer). So you need to get your existing spring rates accurately measured, by someone with a spring tester (doesn't cost much if you take them off the dampers first).

For example, if you find you have 300lb. fronts and 175lb rears, ratio = 1.71:1, so changing to 120 rears you'd want as close as you can get to 1.71x120 = 205lb fronts. Obviously, this is a rough principle, subject to final tuning.

22psi in the tyres definitely sounds too much for a BEC, so I'd start by dropping those to 18psi (but keep an eye on temperatures and feathering).

It's also well worth getting your dampers dyno'd and re-valved to suit the spring rates (if they're capable being re-valved, that is). One-way dampers are damped on rebound, incidentally - rebound damping is just linked to the bump damping (so if you increase bump stiffness, you increase rebound stiffness at the same time). Typically, rebound damping on one-way adjustables is around 1/3rd of the stiffness of the bump damping, though.

littleted

Original Poster:

4 posts

100 months

[news] 
Saturday 28th May 2011 quote quote all
I reckon you're on the same wavelength as me. I like some compliance so I can feel the car shifting its weight in the corners. A guy I spoke to on my last trackday said he used 120lb springs on a caterham for the road so I will try something nearer that rate. I'm going to invest in some new dampers as well probably pro techs as I hear good things about them. Thanks again for your advice.
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procomp

71 posts

106 months

[news] 
Saturday 28th May 2011 quote quote all
Hi

Spring wise you want 250Lb -275Lb front depending on preference/use. At the rear a pure track car can run 120Lb - 140Lb. But for road use with the chance of passengers at some point your looking at 150Lb.

As mentioned the Spax dampers simply will not work with those springs as they are valve far to stiff on compression meaning whilst you may have them set soft for compliance the rebound will not have control of the spring. Protechs are the way to go and try some research for companies who supply them with the corect valving to suit the individual application.

Cheers matt

Mr Sparkle

1,875 posts

58 months

[news] 
Sunday 29th May 2011 quote quote all
Sam_68 said:
Stuff
Very interesting, I was wondering about this myself.

Sam_68

9,939 posts

133 months

[news] 
Sunday 29th May 2011 quote quote all
Mr Sparkle said:
Very interesting, I was wondering about this myself.
I must stress that the principle of maintaining the same ratio of front:rear spring rates is a general rule of thumb only, mind you, and I suppose I ought to add that you need to take into account ARB stiffness as well: it's maintaining the same ratio of front:rear roll stiffness that's the ultimate objective, as this governs how much the car 'leans' diagonally onto one corner in a bend (and hence understeer/oversteer balance).

There are lots of 'ifs' and 'buts', though, and lots of other tuning factors that can be applied to bring things back into balance, so it's certainly not a cast-iron rule.

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