1968 strut bracket on midyears

[Scott Marzahl]

I read someplace that using a 1968 and later strut bracket on midyears is supposed to help with your handling or suspension setup. Can someone explain how?

Thanks,
Scott

[William C.]

Re: 1968 strut bracket on midyears

It changes the pivot point of the strut rods. The change was made on the '68 up cars to correspond with the change to wider tires in '68 (F-70 vs 7.75)

[Duke W.]

Re: 1968 strut bracket on midyears

The C3 rear strut rod bracket altered the rear suspension geometry by lowering the rear roll center, which yields less camber and track change with jounce and rebound. This was deemed desireable for the wider bias ply tires that were used. Lowering the rear roll stiffness also biased the dynamic response in direction of understeer because it reduced the roll stiffness contribution from the rear spring.

One problem with adding the C3 strut rod bracket to the C2 is exhaust pipe clearance. The C3 pipes had to be flattened more to clear the bracket.

The C2 was designed in the era of skinny bias ply tires, which are more senstive to camber change than high profile radials (but today's wide, low profile ARE quite sensitive to camber change). High roll centers are "good" because they create high inherent roll stiffness contribution from the springs and don't require large anti-roll bars. They also tend to keep the tire more vertical to the road when the body rolls due to cornering reaction force. On the downside, high roll centers create greater track and camber change (camber measured relative to the chassis, not the road) and can give rise to steering twitchness from these affects. This was mitigated in the C2 chassis by designing in toe change to compensate for these effects over most of the suspension movement range.

Modern cars typically have roll centers close to the ground compared to about 5" above for the C2 front and about 7" above the ground for the C2 rear. Low roll centers minimize track and camber changes, but larger anti-roll bars are required to both limit body roll and prevent excess wheel camber relative to the pavement.

EVERYTHING in suspension design is a compromise - change one thing and just about everything else is affected.

I don't think installing a C3 strut rod bracket on a C2 is worthwhile except maybe on a C2 used for vintage racing or a street car with very wide tires, which will require fender surgery. In any event, if you do this you are essentially "redesigning" the suspension, so you better get educated on suspension design before you start messing around with the geometry.

Duke

[Scott Marzahl]

Thanks for the education all.

I appreciate it the education. I don't recall where I read it, but it was an article on making your C2 handle better. Sounds like it's best to just leave it alone.