Design drawing for Sierra Seven Tiebar to replace anti roll bar
One big problem with the RH7 is roll stiffness at the front, the standard anti-roll bar has to control the roll for a much heavier car where the centre of gravity is far higher and the polar moment of inertia is higher. In a car with low weight and low centre of gravity the roll bar is way too stiff.
Another problem that also affects the front geometry results from the fact that the anti-roll bar is mounted under the engine bay panels. In its original Sierra home, the anti-roll bar is inclined up at about 15 degrees, in the seven it is inclined down at about 8 degrees, this imparts a twist on the bottom track control arm, putting undue strain on the compliance bushes. On most cars this offers mechanical resistance to roll, and in turn places strain on the inner TCA bushes and the nylon bushes in the top arm.
If you are going to retain the anti-roll bar then ensure that the standard outer TCA bushes are replaced with heavy-duty equivalents, these are produced by Quinton Hazell and are available at most good motor factors. Using the standard bushes under the stresses imparted by the misplaced roll bar allows the hub to move fore and aft up to half an inch without control, this gives woolly steering at best and at worst is dangerous.
My own experience with a standard roll bar was of heavy initial understeer as the front suspension seemed to work as a single unit, this made the transition to oversteer under power much more dramatic which stopped the car being steered easily on the throttle. I had the roll bar on my seven machined to half thickness at the point where there is a natural bend down under the sump. This maintained the section front to rear where the location shock loads are taken, but thinned the section from top to bottom thereby lessening the roll stiffness. This lessened the understeer considerably and in view of this I removed the front anti-roll bar altogether and fitted tie bars (beautifully made by Richard Halfacre from Rugby - thanks Rich!). After driving his immaculate seven fitted with these the handling felt very neutral and convinced me it was the right thing to do.
My advice to everyone is, DO IT, the cars handling is absolutely transformed; turn in is crisp, and the car can now be placed easily, steering now only needs one hand, and the understeer is vastly reduced, roundabouts now only need a quick flick!
Original design from Hood Owner Richard Halfacre 01788 810288