Front Wishbone angle / Adverse Roll Centre changes on lowered cars

[924Srr27l]

My Front wishbones are at an approx 10-15 degree angle and I need to sort this out
as it's adversely affecting the handling


Standard Ride Height (Lower Wishbone level with the road)

Lowered Ride Height (Wishbone angled upwards from the centre pivot point)

The roll-center is determined by the geometry and is the point where the centerline of the car intersects with the line between the strut's pivot axis on the ground (near the tyre's outer edge usually), and the instantaneous center. The distance between the roll-center and the C.O.G. is the lever-arm that pushes the car sideways when there's a lateral weight-transfer due to cornering-G forces.

Note that the minimal amount that you lower the C.O.G. actually results in a much larger lowering of the roll-center. This increases the length of the moment-arm between the roll-center and COG. Meaning that for the same lateral-weight transfer at the same cornering-G, the car will roll MORE than before the lowering.

This has the detrimental effect of causing even MORE positive camber-gain on the outside tyre, causing it to ride on its edge even more and lose grip. The actual amount of reduction in lateral-weight transfer is minimal when lowering the C.O.G.; most of the weight-transfer is due to cornering-G, the body-roll is just in reaction to the weight-transfer.

So the trick is to minimize the negative effects of the positive camber-gain on the outside tyre when the body rolls. To keep the tyre flat on the ground, you can:

- add more static negative camber to account for body-roll, about -4.5 to -5.5 is optimal with stock suspension
- add stiffer springs and/or Anti Roll bars to reduce body-roll for the same amount of lateral weight-transfer
- Extend the BallJoint Pin length with a extension or use different Wishbones with longer Ball pins,
- Bump Steer also needs sorting with a spacer kit to re-position the Tie rod angle


Has anyone else also realised this issue and sorted it and if so How?

R

 

[edh]

What I've done
- add more static negative camber to account for body-roll, about -3 seems to work for a road/track car
- add stiffer springs and/or Anti Roll bars to reduce body-roll for the same amount of lateral weight-transfer
Car isn't super-low, but seems fine. Was getting a bit of roll-oversteer in really fast bends so fitted even stiffer front springs & it's fine.

 

[vitesse]

I thought that adjustable top mounts were to enable correction for this problem.

 

[924Srr27l]

I thought that adjustable top mounts were to enable correction for this problem.

Most adjustable top mounts allow you to adjust the Camber and castor, unless you mean the Ground control USA Top mounted version which
raises the shock absorber about an inch ? this will assist but I'm unsure how much they will change the current angle.

A Longer balljoint pin would do it, either different wishbones, an extension piece or a welded onto the stub axles piece also.

These are for Golf Mk1, designed to fit the 924 Steel Wishbones

R

 

[924Srr27l]

High Strung USA make some nice wishbones with longer adjustable Balljoints, but with the poor dollar rate now they are pricey!
£1000 !

I'm gonna get a quote to make some from my Fabrication man, but probably with bush ends not rod ends
so either rubber poly or weather sealed monoballs from Elephant Racing USA can be used.



And they do a neat Caster block



A UK company make these Motorsport quality balljoints with longer pins




R

 

[edh]

Would be easier and cheaper to raise the ride height of course... unless the "look" is more important

 

[924Srr27l]

Would be easier and cheaper to raise the ride height of course... unless the "look" is more important

Yes it would, and No the looks have no part to play for me.

It's the Lower Centre of Gravity benefits, but with a corrected Suspension Geometry that I'm looking for and
from others people's experience I don't doubt once this is sorted it's a dramatic Improvement.

The reduced from standard ride height doesn't look that extreme, (I've seen much worst)
there's a reasonable amount of daylight underneath.

The Geo and ride height was originally set by a Porsche Race Team
who use specific 5x130 PCD wheel plates to give a more accurate figure than the deflection of a Tyre.

R

 

[blade7]

Would be easier and cheaper to raise the ride height of course... unless the "look" is more important

When I took my car CG to have the geo done I told Chris to set the front arms level, that determined the ride height. When I see cars with the wheels in the arches I think they look nice but I don't fancy the bump steer or maybe breaking the ball joint.

 

[924Srr27l]

It once was a totally stock car at standard ride height.......

In this shot in 2013 there was another 120kg+ to come off, and the ride height was unchanged but had risen.

Even at Full Droop the Wishbones look almost level, this is on Stock Legs and Inserts.

The Droop position needs to be more angled upwards from the outside to the centre X member before it's compressed.

I'll sort it, it's just time and money as usual.

R

 

[944Turbo]

You can get longer wishbone balljoint kits
http://www.paragon-products.com/Ball-Joint-Rebuild-Kit-p/rb-944bk19gck.htm
Tony

 

[924Srr27l]

You can get longer wishbone balljoint kits
http://www.paragon-products.com/Ball-Joint-Rebuild-Kit-p/rb-944bk19gck.htm
Tony

Yeah thanks these are 19mm pins, mine stub axles are the 17mm 924S / early 944 type.

R

 

[944Turbo]

Yes you have to have the hub machined (reamed) to accept the 19mm early or late.
Tony

 

[924Srr27l]

Yes you have to have the hub machined (reamed) to accept the 19mm early or late.
Tony

Hub ? You mean drill the Stub axle ball joint hole bigger from 17 to 19mm ?

I'm not sure if the early and late wishbones are the same? EG will a later balljoint kit fit the early arm?

R

 

[924Srr27l]

1. - add more static negative camber to account for body-roll, about -4.5 to -5.5 is optimal with stock suspension
2. - add stiffer springs and/or Anti Roll bars to reduce body-roll for the same amount of lateral weight-transfer
3. - Extend the BallJoint Pin length with a extension or use different Wishbones with longer Ball pins,
4. - Bump Steer also needs sorting with a spacer kit to re-position the Tie rod angle


Update:

One - Cambers increased on the front from 1.25 to 2 degrees neg

Two - I'm not going stiffer than 190lbs front coils and 27mm hollow 220lbs T bars, (Higher would not be tolerable on the road)
but I have just fitted stiffer Bilstein Mono B8 Inserts and stiffer Nankang Ns2-R Tyre all of which are a lot harder and harsher than
the Spax GAS inserts and Pilot Sport3 Tyres.

Three - I'm still looking into the best cost effective way of installing a longer Ball pin and /or a different Wishbone

Four - When three is sorted I'll also fit a tie rod bump steer kit

R

 

[944Turbo]

Yes you have to have the hub machined (reamed) to accept the 19mm early or late.
Tony

Hub ? You mean drill the Stub axle ball joint hole bigger from 17 to 19mm ?

I'm not sure if the early and late wishbones are the same? EG will a later balljoint kit fit the early arm?

R

the wishbones are different between early and late - steel and alloy and I believe various dimensions for pre and post ABS offset ( later cars had ABS offset even if they dont have ABS)
I haven't done the mod - though I think Peter Empson may have after he had an original ball-joint fail at Brands hatch.

from the link (second para refers to the mod) -
"The pin length is approximately 1.125" longer than the standard length pins. This allows for a corrected control arm geometry on cars lowered from 1.5" - 3" from the factory ride height. Factory ride height is measured with the control arm plane parallel to the ground (stock ball joints) at static suspension weight. To eliminate binding on cars on the lower end of the range a heavy enough spring rate should be used to keep the suspension travel from reaching the end of the ball joint pivot range.

The spindles must be machined at their clamping distance to be a true 19mm. This is done by first installing a standard 17mm ball pin to the spindle. With the pinch bolt torqued down you will need to measure the distance between the pinch gap. Remove the pin and shim the inside of the pinch to this measurement using a clamp to hold it in place. The 17mm bore must be aligned in a vertical mill, drilled undersized and reamed to 19mm.

Though the material we use is extremely tough it can be susceptible to fatigue fractures depending on track conditions and driving style. Though the pins will probably last much longer than a single season during the harshest conditions we strongly recommend they be replaced as part of an annual maintenance procedure. Reduced price pin replacement only kits are available to all previous customers."

 

[944Turbo]

Meant to add are you still running the original arms or the alloy ones - is the pic above with the red ARB from your car?

 

[944Turbo]

Actually did the 924 swap to alloy arms in 85/86 with the 44?

 

[924Srr27l]

Meant to add are you still running the original arms or the alloy ones - is the pic above with the red ARB from your car?

Yes that's before the 2.7 Install, it's running the 944 early shorter length aluminium wishbones with 17mm ball joints.
The 924 and early 944 bones are the same dims, just different material. the later longer to jack the strut angle outwards further
then the offset was reduced from et23 to et55, the later stub axles are thicker and the wishbone pin thicker.

I'm looking to modify (Cut & Weld) a set of Late aluminium bones and fit a longer or adjustable ball joint / coupling to get the angles right. I'm hoping to not have to change the stub axles, hubs or anything else.

R

 

[924Srr27l]

Actually did the 924 swap to alloy arms in 85/86 with the 44?

Don;t think so? Mine 's a 1987 and had Steel front arms but Aluminium rear trailing arms.
R

 

[Mike_Pollock]

There are 3 basic wishbones 924/944 steel for 23mm offset., alloy for 23mm offset and alloy for 52mm .