Front suspension design

[Jim Craik]

I hope someone with more knowledge can help me here.

I have noticed in my car and photos of original GT40s' that the front suspension is "turned in" meaning the front pick up point is several inches in (closer to the center line) than the rear pick up point. I understand this is for "anti-squat", "anti-dive" reasons.

How does this help? Why does this help and does this really help?

Also, I have noted that most of the kit cars I have seen do not have this feature. Does it make a differance?

It seems to me that it would be fairly easy to replicate if it has a real effect. I do not remember seeing this done to other racing cars.

 

[Jac Mac]

I would suggest it was done like that for footwell room, Anti squat/dive can be achieved with wishbones that are parallel to the vertical longtitudinal centerline by raising/lowering the rear points of the w/bones... at the expense of footroom around those rear mount points.

 

[Francisco]

From what I have read on anti-squat, it is very important on sharp cornering at high speeds as it helps keep the weight of the car on all four wheels as apposed to shifting the weight. Imagen going 25mph and easing on the breaks. You will feel the weight of the car moving to the front of the car.

Higher priced kits have that Anti-squat tendency because they are prepared for track racing. It all depends on what you want to do with your car and were your racing. Thats why some race cars have this feature.

Thats what I got from a quick read on Anti-squat. for better read try Wikipdia.

 

[Rick Muck- Mark IV]

Some of the "offset" may have been due to footwell issues, but look at Costin and Phipps "Modern Sports and Racing Car Chassis Design" published circa 1966 for more info on this type of design.

It is unique to look at the GT40 front suspension in plan view and see how much angle there is on the wishbones!

 

[Trevor Booth]

near enough to 20º

 

[Phil]

Jim:
The tapered footwell is definitely a function of providing enough space to fit pedals and operate them.

The suspension can be engineered to work well as is seen in the original design, and one of the considerations is having enough turning radius before chassis interference is encountered versus straight parallel chassis rails.
Anti-dive, as Jac Mac said is a function of the placement of the front to rear mounts on the upper or lower wishbones, usually done at the upper with the angle being down at the rear mount. This creates a lifting force on the chassis during braking to counteract dive induced by weight transfer to the front.
Anti-squat is usually a feature built in at the rear suspension to counteract the tendency of the rear of the chassis to Squat under acceleration. This is caused by the upright attempting to counter-rotate to wheel direction, essentially trying to walk up over the suspension, and is usually minimized by the placement of the inner radius rod mounts to create the opposite and hopefully nuetralizing effect to limit chassis movement.
All of these features are seen in varying levels on just about all chassis, depending on weight and available component lengths etc., but they are small as a little can go a long way, and in a long component such as a rear radius rod there would need to be quite a change in mounting position at the front to gain more angle so its always a compromise.
Hope some of this helps
Cheers
Phil