Bump Steer Explained and How To Fix
There’s nothing quite like hitting the open road in your classic ride. You feel the rumble of the engine, the cool wind blowing, and hear those sweet exhaust notes. Then you remember that these old cars just don’t handle like a modern car. They wander all over the road, especially when you hit a bump. Why is that? Bump steer.
What Is Bump Steer?
Bump steer is when the toe angle is changing. To break it down more, when the suspension cycles through it’s range of motion, the front wheels are both moving either towards the center of the car or away from it. This can cause the car to move around when hitting bumps in the road in an unpredictable fashion.
Why Do Classic Cars Suffer from Bump Steer?
There are two main reasons that classic cars are prone to bump steer.
Design Standards of the Past:
Back in the 1960s and 70s, cars weren’t built for the high speeds we expect today. Driving at 55 MPH was normal, rather than 80 MPH with the air conditioning blasting. As a result, the engineering tolerances and design dimensions were not as precise as modern vehicles, but was acceptable for the time.
Tire Technology:
Original tires on these classic cars were typically bias ply tires, which work best with negative caster (where the upper ball joint is positioned ahead of the lower ball joint). Today’s superior radial tires are designed for positive caster (with the upper ball joint behind the lower one).
When you add aftermarket suspension upgrades such as tubular control arms that correct the caster on these older cars, the spindle rotates. For example, on a Chevelle, this rotation lifts the steering arm away from the ground by even a small amount—sometimes only half an inch to an inch. This slight change can throw off the length of the steering arms, leading to bump steer.
There’s a lot of math and science to steering – but the general rule of thumb is that your steering arms need to be the same length and at the same angle as the lower control arm to not experience bump steer.
How To Fix Bump Steer
Luckily, fixing bump steer isn’t a hard or expensive job. The easiest way is to buy a kit which replaces the outer tie rod that mounts to the spindle. Typically these kits will utilize a rod end on them, which is a more precise part than a ball joint. Then they have multiple sleeves that allow you to space the rod end down away from the steering arm on the spindle.
Why Do You Want To Fix Bump Steer?
Simply put, your car will drive much nicer down the road. With the front end not moving around it will feel more solid and connected to the ground. The steering will feel more precise and confidence inspiring. Fixing your bump steer is a cost effective upgrade that pays huge dividends.
If you have any other questions regarding bump steer, or want to fix the bump steer on your car, hop on over to SS396.com or give our friendly techs a call at (203) 235-1200!
