MM News

Busting the Myth of the Watts Link

Real-world testing puts theory into perspective.

Advocates of the Watts Link base their arguments of superiority on theory rather than testing. What happens in the real world reveals the true story about the Panhard Bar vs. Watts Link debate for the late-model Mustang.

Why do people claim a Watts Link is better than a Panhard Bar?
The bell-crank and link system of a Watts Link keeps a car's chassis centered over the axle as the suspension moves the chassis up and down, whereas the arc of the Panhard Bar's movement shifts the chassis sideways during that process. While those are the facts, they're not the whole story.

What's wrong with sideways movement of the chassis?
When the rear of the chassis moves sideways relative to the tire footprint, it causes the car to point in a different direction than where the driver is steering. To get the car pointed back in the direction the driver intends, he or she must correct course by steering the front tires. The "rear steer effect" can make the car feel unstable and unpredictable. While that is an undesirable situation, the Watts Link folks ignore key factors that make this slight sideways movement unimportant when considering the big picture for late-model Mustang handling. Read on for details!

How much sideways movement does the Panhard Bar cause?
The arc of the MM Panhard Bar causes a maximum lateral movement of 0.17" on a Fox/SN95 Mustang. This maximum occurs only when the body rolls all the way to full bump or full droop. This much suspension travel very rarely occurs during hard cornering. More typically, suspension travel is less than 2". The arc of the MM Panhard Bar at 2" of travel causes only 0.050" of lateral movement of the chassis relative to the axle. Even when more extreme cornering loads cause 2.5" of travel, there is still just 0.079" of lateral movement. During normal street driving, when it's more typical for suspension travel to be 1", the resulting lateral movement is a minuscule 0.010". These dimensions are small enough to be irrelevant.

Why is the sideways movement caused by the Panhard Bar irrelevant?
We know it's a little confusing, but here's a more complete explanation: It's not that the arc itself is irrelevant, or that the lateral movement it causes is irrelevant. The takeaway here is that the amount of movement is absurdly small. That's what makes it irrelevant.

I'm a perfectionist; why not eliminate even 0.050" of movement?
Out in the real world, tire sidewall deflection has a much greater impact on your Mustang's handling during hard cornering. The sidewall flexes far more than you might think, and that affects handling much, much more than 0.050" does.

Here's what happens: while you're driving straight the tire tread is planted on the ground. As you steer into a corner the tread remains on the ground, but sideways loading forces the chassis, the axle assembly (because the Panhard Bar firmly connects the two), and the wheel toward the outside of the corner. The tire sidewall flexes uncontrollably when the wheel gets heavily loaded at that point, allowing significant sideways movement of the wheel/axle/chassis. That movement is enough to make meaningless the effect of the tiny 0.050" shift. A Mustang with a Watts Link suffers from the exact same sidewall deflection.

How much does the sidewall flex and distort the tire?
During hard cornering, the tire sidewall deflection will cause the wheel/axle/chassis to move as much as 2" sideways relative to the tire footprint (and also depending on what equipment you have installed on your Mustang). That 2" is huge when compared to the 0.050" movement caused by the MM Panhard Bar arc.

How do you know the tire flexes that much?
Because we've seen it happen! Now you can see it, too, in this undercar video.

Since the tiny amount of lateral movement is irrelevant, and now that I understand the impact of sidewall flex, are there other reasons to choose a Panhard Bar instead of a Watts Link for my Mustang?
Yes! In the specific case of the late model Mustang, there are several reasons why we recommend a Panhard Bar instead of a Watts Link.

Roll Center Height
Late-model Mustangs handle better when the rear roll center is lowered from the stock location, near the top of the differential cover. Why? Here's the really short explanation of a very technical subject: compared to a lower roll center, a higher roll center causes more jacking forces, which raises the center of gravity height, which increases lateral weight transfer, which transfers weight from the inside tire to the outside tire, which reduces overall cornering grip.

With a Panhard Bar the roll center is located at the height of the rod. The MM Panhard Bar for Fox/SN95 Mustangs lowers the rear roll center about 9" from the stock height to just below the rear differential cover. The roll center of a Mustang Watts Link isn't nearly that low because it's at the pivot of the bell-crank. The bell-crank pivot can never be placed as low as the MM Panhard rod because the lower part of a Watts Link assembly hangs far below the bell-crank pivot. To maintain adequate ground clearance for the Watts Link assembly the bell-crank pivot must be placed far above the MM Panhard Bar height, resulting in a much higher roll center--and less cornering grip.

Watts Link advocates often point to the many purpose-built tube frame race cars (IMSA and Trans Am, for example) that were equipped with a Watts Link. However, they ignore that since the 1980s those racecars have used Watts Links in what's called a "lay-down" design. The bell-crank pivot is mounted vertically to the bottom of the differential, with the bell-crank swiveling in the horizontal plane underneath it, placing the roll center very low. Those racers know that having a lower roll center is critical for best handling. However, this design is difficult to build for the Mustang 8.8" cast-iron center section, and extremely problematic for a street-driven Mustang because it would significantly reduce ground clearance.

The MM Panhard Bar offers much better clearance for tailpipe routing than a Watts Link. That affects most of our customers, as few Mustang owners will put up with dumps or the expense of custom-built tailpipes. The MM Panhard Bar is designed around the factory tailpipe routing, making it much easier and more practical to install.

Some Watts Links for Fox/SN95 Mustangs also require extensive (and expensive) modifications to the spare tire well in the floorpan, which is far beyond what most people with street-driven Mustangs would consider doing.

The MM Panhard Bar is much less expensive than any Watts Link on the market for the Fox/SN95 Mustang.

Winning racers agree!
Maximum Motorsports is not the only proponent of a Panhard Bar over a Watts Link. SCCA autocross C/Prepared National Champion Mike Maier recently dominated the class and won by over one second in his Fox Mustang. What's his secret? Maier discovered that the handling problem he had been fighting for years, which he thought was caused by never getting the shock adjustment quite right, actually came from the high roll center of his Watts Link. He switched to a Panhard Bar and instantly solved his Mustang's handling problem, leading straight to his dominating win of the C/P National Championship.

Myth Busted!
We hope it's clear to you now that the MM Panhard Bar provides obvious advantages over a Watts Link for your late-model Mustang. Here at MM, we're all about using engineering and real-world testing to inform our customers about the smartest choices they can make for their Mustangs.

Let's recap the two big lessons we've learned here today dispelling the notion that a Watt's Link is superior for the Mustang:
  • The lateral movement from the Panhard rod's arc is so small it's irrelevant.
  • Tire sidewall flex far overshadows the effect of even that tiny movement.
And here are the biggest reasons an MM Panhard Bar is a better choice for your Mustang than a Watts Link:
  • More rear cornering grip due to a lower roll center
  • Better fitment with tailpipes
  • Lower cost

Thanks for reading. If you have any further questions on this topic, let us know. If not, pick up an MM Panhard Bar today!

For more information see our MM Mustang Panhard Bar Tech page.