DIY Coilovers

[Error404]

I got some KW V1s in the end, 60n front springs, 70n rear springs
The compromise between ride and handling really is excellent.

[jade]

I got some KW V1s in the end, 60n front springs, 70n rear springs
The compromise between ride and handling really is excellent.

What different do you find with the v1 compaired to the coilovers you made, you were obviously not happy if you changed ?

Thanks

[Error404]

I sold them before I finished them because the cost of getting them done right was more than buying a set of KWs. Springs, collars, helpers, getting the Konis dyno'd to match the springs was way more than just buying some KWs, plus they are inox and have corrected steering arm height etc etc

HTH

[jade]

Ok thanks

[jade]

I got some KW V1s in the end, 60n front springs, 70n rear springs
The compromise between ride and handling really is excellent.

Just trying to work out good spring rates for fast road

From what I have read front 350 and rear 400 lbs seem good

May Be I am missing something but 60 nm is 530 lbs and 70 is 619 lbs?


Thanks

[newsh]

I don't understand why the rear springs should be stiffer than the front when there's more weight on the front

[andy10v]

I don't understand why the rear springs should be stiffer than the front when there's more weight on the front

To encourage the rear to loose traction first?

[speeding-g60]

not sure for you guys. but here is my theory for drag racing.

and it seems to be working for me anyways.

i run 900lb/inch springs in the back to prevent squatting on launch.
and i run 650lb/inch in the front, as i do not want too much lift on the same launch.

i want to keep all four tires planted firmly.

my car (without me) weighs ~1600lb front and ~1000lb rear.... and i still squat the **** end and lift the front some. but on the top end at 150+ MPH, it sure is looking kind of funny!

my car tries to lift the front end off the ground still when i launch, but since i have made a best of 1.400 60' time, i dont really think i will spend any time on the suspension yet.

here are a couple pics to show what i mean.

[Error404]

I don't understand why the rear springs should be stiffer than the front when there's more weight on the front

OK! I won't profess to understanding the maths behind it but there is an equation to work out how the various suspension parameters affect weight transfer. As far as my small brain understands it, the theory goes something like this:


When you corner in the car, you get weight transfer from the inside to the outside tyres. Generally, the more weight transfer the less grip because the outside tyres get overloaded until they loose grip. Weight transfer is controlled with the cars roll stiffness but it is not affected by the total roll stiffness but the relative stiffness of the front and rear axles. The roll stiffness is made up from the ARB and the springs.

All other parameters being equal, increasing the front and rear axle roll stiffness by the same amount doesn't affect weight transfer - the total weight transfer remains constant so whilst the body roll is reduced and it feels nicer there is no actual performance change.
It is the relationship between front and rear roll stiffnesses that affects weight transfer. Centre of Gravity is the important factor where weight is concerned, not specific axle weight. It is the track width and centre of gravity that affect the total weight transfer. for example if you could get your CoG to be at ground level you would have zero weight transfer. The amount of body roll is affect by the distance between the roll centre axis and the CoG.

So you would think that more axle roll stiffness would decrease lateral weight transfer but actually it increases it. So for in this instance if you just stiffen the rear axle you increase the weight transfer on that axle, but because the total weight transfer remains constant the net result is reducing the front weight transfer also. So the grip balance shifts forwards and understeer is reduced.

More simply as Aaron has shown above stiffer rear springs also help with traction under acceleration as the front wheels can get more traction with less squat from rear weight transfer - as you want to go WOT as early as possible when exiting the corner less squat helps you with tractive grip.




EDIT: Downsides are more dive under braking and if you take it too far obviously you will get more oversteer.

[Rusty]

Just trying to work out good spring rates for fast road

From what I have read front 350 and rear 400 lbs seem good

May Be I am missing something but 60 nm is 530 lbs and 70 is 619 lbs?


Thanks

No, conversion is 1 N/mm = 5.7 lb/in so 60 N/mm. ~ 340 lb/in.

Alex, weight transfer is caused by the torque reaction to acceleration the mass of the car where the centre of mass is above the ground, if that helps at all.

Newsh, springs are a funny one and depend primarily on suspension design (read leverage). Not able to answer your specific question but I'm sure the answer will be in a book somewhere.

[terrybullwon]

I dunno if I added this but I took 120nm front and rear as was recommended when corner weighting the car

[terrybullwon]

But again my set up is alittle different

[Error404]

your CoG will be much further back than our road cars

[Error404]

This is the equation derived by Bill Milliken to calculated weight shift:



ΔWf = Front weight transfer
ΔWr = Rear weight transfer
Ay = lateral acceleration
W= total vehicle weight
tf= front track
tr= rear track
H= height of CoG above roll axis
Kf = front roll stiffness
Kr= rear roll stiffness
a= longitudinal distance from front axle to CoG
b= longitudinal distance from rear axle to CoG
l= wheelbase
Zrf= front roll center height
Zrr= rear roll center height

[jade]

[QUOTE=Rusty;670290]No, conversion is 1 N/mm = 5.7 lb/in so 60 N/mm. ~ 340 lb/in.

yes, that looks better ! Do you have any recommendations for spring height ? 7" or 8"

Thanks