Anti Dive Roll Bar Spacers (Revised castor angle)

[FI Spyder]

Since reading this I made a pair of modified (offset) ARB lowering blocks, which pull the ARB forward 20mm giving approx. 4 degrees of caster, this has made a massive improvement to the straight line stability but it still doesn't feel quite right into the corners, insomuch as it tends to "dart" into the corner as you start to turn the wheel rather than a smooth transition.

The Hamilton site said pulling the ARB 14mm forward gives 1.5 degrees increased Castor, different from what you seem to have. ??? Any explanation as to the difference?

[Hasbeen]

"Darting" into corners is more likely to be caused by too much toe, in or out, or play in the tie rod ends or the rack itself. Any slop in suspension bushes will also give something of the effect. I presume you set the toe after playing with the castor, how good were the ends rack & ball joints?

The car tends to grab the steering angle on the outside front wheel, rather than the average of the two as you turn in. Really high toe, particularly with high castor will give you that low frequency high magnitude wheel wobble at around 45 to 50 MPH. This is quite different to our usual 60 MPH wobble.

Hasbeen

[Stag76]

To calculate the caster change:
((Distance from top strut mount to ARB mounting point in lower control arm*2)*pi) Div 360 = mm of adjustment
required for 1 degree of caster change.

[prackers]

It is looking like the difference is down to me not measuring it correctly! The car was on axle stands under the chassis with no weight on the struts and the front end up in the air. Checked it today with the wheels on the ground and it looks like I have 2.5 degrees, so it looks like I could use a little more?

The track rod ends/rack/TCA ball joints are all new, and I set the tracking to 1/2 degree toe in after playing with the caster.

[dursleyman]

How does it drive now?

[sydney.wedgehead]

The ROM states +3.5 degrees +/- 1 degree

I've had my car on a laser alignment and struggled to get +2.5 degrees.

Adjustable front ARB blocks seem like a good solution.

Bean's idea of a compression strut seems even better, but means hanging the ARB behind the front axle line and producing a custom mount to a custom TCA.

[prackers]

Before I put her to bed for the winter the handling was much improved though still could do with improvement. In the spring I will play with the corner weights/ride heights/camber and caster and see if I can improve it some more. I am thinking I probably should add watts linkage or panhard rod to the rear axle also to see if it tames the rear end down any?

[sydney.wedgehead]

It's a lot of work to fit a Panhard rod or Watts linkage.

Richard Hurdwell's comments in the Car and Car Conversions One over the eight article from March 1981 (recently published on Facebook), doesn't talk about either, but does mention removing the rear ARB completely.

[FI Spyder]

Re: all sorts of suspension mods. I have pretty much stock suspension (new regular springs front), KYB gas shocks, hard black poly front, original springs rear with soft poly bushings rear with Koni Shocks (been there since before I bought the car in '06), 13" alloys with Kumho tires ($60 Cdn each, mounted, balanced, new chrome air valves). The car handles like a dream, regardless how hard you take a corner it's tells you it could take it faster up to and including a four wheel controlled and balanced drift with no under or over steer. I set the toe in by string and had no discernible wear, at least until I took it out on the race track for however many laps and brought back to the parking lot with the smell of burning tires. I wouldn't push it now as the tires are 9+ years old and there a little play in the steering which I think is in the untouched rack (time to look into that this spring hopefully. I may have hit a sweet spot.

[Beans]

... I am thinking I probably should add watts linkage or panhard rod to the rear axle also to see if it tames the rear end down any?

Indeed a fair amount of work involved. But if carried out correctly it will reduce body roll. You could always fit (much) stronger springs

[Hasbeen]

If you want to tame the rear end a bit, without upsetting anything else, get a 10% or up to 20% heavier front roll bar made. This will transfer weight from the outside front wheel when cornering, to the inside back, thus increasing rear grip. Unfortunately it will also decrease front grip a little, so don't go too far.

10%is easily handled by the front roll bar bushes, which can be reamed that far without difficulty. Going further requires serious work there.

If you want to get really serious you could get both front & rear bars made. I have 30% stiffer bars front & rear on the 7 & 8, & they now corner very flat. 30% on the back is a bit far, as the 7 now understeers unless provoked, but at a higher speed than stock.

The 8 will understeer if driven slow in fast out, but can of course be provoked into oversteer at will with over 300 BHP. You have to really throw the 7 at a corner to get it's tail out now.

The bars do take away a little of the great "feel" of our cars, much more so with the 8, which has stiff springs & shocks as well. For a road car I would not go above 20% stiffer bars again. Adjustable would be ideal, but too much work for me to bother with.

Hasbeen

[prackers]

Ok now I am now becoming totally confused lol! What do you mean by "10%is easily handled by the front roll bar bushes, which can be reamed that far without difficulty" ? She has an S&S heavier front roll bar (30% iirc) with the medium (orange) polybushes which took a lot of effort to push on/fit and bolted up ok but are (very) tight. Should the pollybushes have been reamed out to allow more give? Currently still on the standard rear ARB. Spring rates are 185lbs/inch on the front and 160lbs/inch rear. Don't get me wrong it handles well and realise it is never going to go round corners like the Westfield or feel as planted as the 4x4 Brera but there is room for improvement (I think), or maybe I just need to get used to it?

Not really intended as a road car, more a toy/learning project/track day car but usable on the road, the SBC 7 convertable will be aimed more at everyday (summertime) use. I have not had her on a rolling road yet but at a guess is around 350bhp ish so ample power.

[Hasbeen]

I was suggesting standard bushes can be reamed out to handle the thicker rollbar.

Did you fit a stiffer rear bar. If not you should have heavy understeer, with a 30% increase in front roll bar stiffness.

If you don't I feel your spring rates are not ideal, are using your power to break the tail lose, or have lucked onto a very good balance of spring rate & roll bar stiffness, hopefully the latter.

We have about 330 BHP from the 4.6L, & in slower corners can chose to push the front off the road, or kick the tail out, depending how the power is applied. It can currently get round high speed curves [above 75 MPH] very nicely, but needs more taming to be good under 50 MPH. More miles in driving experience of the car would also be a great help. We don't drive it hard very often.