Negative scrub radius - pros/cons
Thread Starter
Drifting
Joined: Dec 2001
Posts: 1,419
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From: Mississauga Ont
Negative scrub radius - pros/cons
In 88 our cars were changed to a zero scrub radius in order to eliminate the car's tendency to steer itself when the brakes are applied.
My question is, why were C4's originally designed with a negative scrub radius, and does it have any advantages over the zero scrub radius of the later cars
My question is, why were C4's originally designed with a negative scrub radius, and does it have any advantages over the zero scrub radius of the later cars
Melting Slicks
Joined: Aug 2003
Posts: 3,394
Likes: 393
From: Lakeville MI
I think the earlier cars were positve scrub. Negative scrub is more typical of front wheel driven cars.
Scrub radius affects road feel/steer feedback of road forces, due to brake slip, cornering slip or road input.
If uneven road force is present with a positive scrub set-up, the road force will act to steer the wheel around its steering axis. This is most noticeable with uneven braking forces at the front axle.
Think of an ABS car on a split mu surface, ice on one side, dry pavement on the other, with a hard brake application. Since the braking forces will be much greater on the dry pavement side, the uneven braking force will cause the dry pavement wheel to be steered further towards the dry pavement side, which is likely to induce a spin and startle the driver with a sharp pull on the wheel.
Zero scrub will not produce the effect, while negative scrub will steer the car toward the ice side of the road, which naturally counters the yaw moment that is developed from the uneven braking.
On the vettes I believe it was changed primarily to reduce the car's tendency to wander over uneven surfaces, but the advent of ABS in 1986 must have also been a factor, that was not originally considered in the 1984 design.
Scrub radius affects road feel/steer feedback of road forces, due to brake slip, cornering slip or road input.
If uneven road force is present with a positive scrub set-up, the road force will act to steer the wheel around its steering axis. This is most noticeable with uneven braking forces at the front axle.
Think of an ABS car on a split mu surface, ice on one side, dry pavement on the other, with a hard brake application. Since the braking forces will be much greater on the dry pavement side, the uneven braking force will cause the dry pavement wheel to be steered further towards the dry pavement side, which is likely to induce a spin and startle the driver with a sharp pull on the wheel.
Zero scrub will not produce the effect, while negative scrub will steer the car toward the ice side of the road, which naturally counters the yaw moment that is developed from the uneven braking.
On the vettes I believe it was changed primarily to reduce the car's tendency to wander over uneven surfaces, but the advent of ABS in 1986 must have also been a factor, that was not originally considered in the 1984 design.
