As the first Fox Body Mustang reaches its 45th year since its introduction in 1979, it’s uncommon to discover any performance-related aspect unexplored on this classic chassis. Often, companies find themselves revisiting familiar topics with successive owners, dispelling rumors, and presenting facts. One such established company is Maximum Motorsports, celebrated for their expertise in transforming Fox Body Mustangs into precision handling vehicles. We decided to ask a few questions on a hotly debated topic of bumpsteer on lowered Fox Body Mustangs. 

A Little Bump, A Lot Of Action

Before diving into bumpsteer in a lowered chassis, it’s essential to understand what bumpsteer is and how it affects cornering. Bumpsteer refers to the phenomenon where tires steer themselves due to changes in the toe setting as the suspension articulates up and down. Excessive bumpsteer in any vehicle can lead to significant directional changes beyond the driver’s control. If your reaction was a firm “hard pass” after reading that, you’re certainly not alone.

While excessive bumpsteer can lead to adverse conditions mentioned above, Chuck Schwynoch, CEO of Maximum Motorsports, states, “that keeping any toe change to less than 0.020 inch for every 1 inch of suspension travel on race cars. For street-driven cars operated in a civilized manner — something we know nothing about — the recommendation is to maintain around 0.040 inches of toe-out when the front suspension compresses by 1 inch.”

“That spec is essentially the stock Ford design for a Fox. It promotes understeer. It’s an okay number that one would prefer not to exceed. Less toe change is preferable, and less toe-out is preferred over more toe-out,” Schwynoch states. “By adjusting caster to be more positive than stock, the bumpsteer will shift from toe-out in compression to toe-in. By measuring and then adjusting with a bumpsteer kit, the toe change can be made quite small.”

Maximum Motorsports emphasizes that bumpsteer during suspension compression (bump) is more critical than during extension (droop). It’s crucial to minimize toe change close to ride height, prioritizing this over minimizing it at the extremes of bump or droop travel.

The Over Under 

So, what’s the bottom line with all this talk about bumpsteer? Well, toe-out in bump tends to cause the car to understeer when cornering. Understeer, as the name suggests, occurs when the car plows through the corner rather than navigating it smoothly. This is often driver error. On the other hand, oversteer is when the rear end swings out, potentially leading to unintended excursions into someone’s yard or worse, the entourage of amateur filmers lining the cars and coffee parking lot. In our litigious society, it’s preferable to design a car to understeer rather than the alternative.

Although factory settings might seem like the safer choice, and you wouldn’t be wrong, especially in everyday driving scenarios. However, once you hit the track, the dynamics change entirely. The sole focus becomes achieving better lap times. This is why experienced drivers despise understeer. According to Maximum Motorsports, when a car understeers, it’s the vehicle itself that restricts how quickly the driver can navigate a corner. On the other hand, if the car maintains a neutral handling balance or even exhibits a bit of oversteer, the limit to cornering speed becomes more dependent on the driver’s skill. 

Bumpin’ And Grindin’

At this point, you might be asking yourself, “I don’t have any plans to track the car, so should I even bother reading on?” Well, considering how frequently Fox Body Mustangs change hands, it’s important to note that updated front control arms, spindles, or aftermarket products like K-members can all contribute to varying degrees of bumpsteer issues.

Moreover, optimizing the steering and suspension geometry is crucial for achieving the best handling performance and least amount of bumpsteer — a challenging task given the intricate three-dimensional interactions involved. Simply eyeballing it won’t suffice; you’ll need a bumpsteer gauge.

While the track might not be your forte, the option to reduce the 4×4 wheel-to-fender gap seen in your stock Mustang is appealing. As you lower a car, it’s natural to wonder if this will cause bumpsteer. The answer is both yes and no. “When lowering your car, you are not changing the suspension geometry, because the pivot points in the suspension do not change location relative to each other,” Schwynoch states. “Lowering has no significant effect on bumpsteer. The widespread story that lowering causes bumpsteer is false. Moving a suspension or steering pivot point from the stock location will cause bumpsteer.”

Lowering does change camber though, which subsequently affects toe settings. This is why realignment is necessary after lowering a car. For more tech talk on lowering a Fox Body Mustang and the impact on bumpsteer, be sure to check out Maximum Motorsports’ in-depth explanation here.

Maximum Motorsports addresses bumpsteer problems with its bumpsteer kit, available in both bolt-through style and tapered-stud style. The kit includes components that enable a wide range of adjustments. It provides parts to replace the stock outer tie-rod end with a spherical rod-end and includes spacers for precise fine-tuning of bumpsteer.

The Bumpsteer Recap

To recap, if you’re aiming to improve the handling of your 1979-1993 Mustang, the first step is to measure your bumpsteer with a bumpsteer gauge. Regardless of whether it’s assumed to be stock or not, this will establish a baseline of your current situation and help you understand why your car handles the way it does. You’ll always have some bumpsteer, but you can change how much and gear it toward your driving abilities.

Be warned: this might ignite a newfound passion for open-track driving, autocross, or even a High-Performance Driving Experience (HPDE) event, or at least lead you on a deep dive into Maximum Motorsports’ website for technical insights into handling and an assortment of products to optimize cornering for your Fox Body Mustang. In the long run, you’ll appreciate the newfound knowledge and the satisfaction of making a car that’s at least 45 years old out-handle a pack of modern muscle.