MANUFACTURED SINCE 2000 · SONOMA, CA
Griggs Racing Watts Link
Corrected Geometry for 8.8-Inch & 9-Inch Solid Rear Axles
A rear roll center you can tune.
What does a Watts Link do?
A Watts Link (sometimes called a Watts linkage, or a parallel linkage) locates a solid rear axle through two opposed arms and a pivoting bell crank. The axle moves straight up and down, and the rear roll center stays exactly where you set it.
Why trust Griggs on this?
“For the first time in our 17 years of testing Mustangs, rear grip, not front grip, is the limit.”
— Tom Wilson, 5.0 Mustang & Super Fords, May 2005 · Old Blue: 28 SCCA regional wins, 12 track records, AIX champion 2002–03
Watts Link or Panhard bar: what actually changes
The whole argument is one number: where the roll center goes when the car moves.
Bolt the pivot to the axle and the roll center holds still. Bolt it to the body and it moves twice as much as a Panhard bar. Every GR40 Watts Link puts it on the axle.
The roll center sits at the center of the bell crank, so the only question is what that pivot is bolted to. On the axle it moves only as much as the tires compress. On the body it rises and falls with it: a Panhard bar’s failing, with more of it.
The chassis mount is the bracket carrying the outer ends of the arms.
AXLE-MOUNTED WATTS LINK
under ¼"
CHASSIS-MOUNTED WATTS LINK
2"
PANHARD BAR
1"
Roll-center movement through two inches of ride-height change. Less is better; the axle-mounted pivot is the only one of the three that stays where you set it. Under a quarter inch axle-mounted, one inch for a Panhard bar, two inches for a chassis-mounted Watts.
| Where the pivot is mounted | Roll-center movement in 2" of ride height | What that means at the wheel |
|---|---|---|
| Axle (every GR40 Watts Link) | under ¼" | The roll center stays where you set it, so rear roll resistance is the same in the third corner as in the first. Move it on purpose, with the bell-crank pivot, or leave it alone. |
| Panhard bar | 1" (the OE bar on 2005-up Mustangs moves about 1.5" through full wheel travel) | Rear roll resistance changes continuously as the car rises, squats, and rolls, so tire loading changes with it, and the car reads differently loaded left than loaded right. |
| Chassis (a Watts pivot bolted to the body) | 2" | The roll center rises and falls with the body, up to twice the movement of a Panhard bar. Bruce’s conclusion: a properly located Panhard bar beats this, and an axle-mounted Watts beats both. We do not build it. |
Source: Griggs Racing Watts Links Catalog, 1 January 2014, p.7, and Bruce Griggs, Watts Link Mounting — Axle vs Chassis.
Watts Link performance, measured
1.0 s
faster per lap at Sonoma (same car, Watts LINK vs Panhard Bar)
2.0 s+
faster at Buttonwillow, where the esses come in sequence
100k mi
rod ends still in service beyond 100,000 miles of use
In back-to-back testing on the same car, the Watts Link ran 1.0 second faster per lap at Sonoma and more than 2.0 seconds faster at Buttonwillow than the Panhard bar it replaced. Griggs Racing has been building Mustang Watts Linkages in Sonoma since 2000.
Source: Griggs Racing back-to-back Watts-versus-Panhard testing: 2005–2010 Mustang GT, GR40SS system.
Bruce Griggs; Do I Need A Watts Link Or Is The Panhard Bar Enough?
Which Watts Link fits your car?
Solutions for every Solid Rear Axle and Mustang.
Three components make a kit: 1) The center section that carries the bell crank, 2) The arm set, 3) A chassis bracket.
Complete kits and every service part: Watts Link kits · all Watts Link products
Classic · 64–70
On a 64–70 this is not a bolt-on. The car needs a coilover rear conversion, and the brackets weld to the spring pads or axle tube. Call us before you order. GR350-era geometry for vintage Mustang and Cougar; the system locates off existing points.
Fox & SN95 · 79–04
Bolts to the OE 8.8 cover and the existing subframes; the installation cuts one clearance hole in the spare tire well, and the cover panel to close it is a catalog part.
S197 · 05–14
Our most actively revised line: the 2014 redesign simplified the chassis mount to one-piece pillars and a cross-brace that clears 2011-up convertibles. Bolt-on; no welding. Written installation instructions are published for this one.
9-Inch & Banjo
Aluminum center kit for 9-inch and banjo housings. Ships with weld-on brackets (specify your housing brand), plus custom-length arms where the geometry needs them.
Ford 8.8 · Spider
The Spider center kit clamps to any Ford 8.8 housing and carries the bell crank on a machined plate. Pick by the diff cover you run: sheet metal or finned cast aluminum.
Universal & Factory Five
For chassis we have not measured. The pillar kit and custom-length arms let a fabricator set the geometry; the Factory Five bracket is a known fit.
Engineered to Win
Griggs Racing: Champions Made Here
MWL-5400 Spider Center Kit
Fits all OE Ford 8.8 covers, 1979–2014.
MWL-5100-A Chassis Mount
S197 chassis mount · 05–14
MWL-9500 9-Inch Center
Aluminum center, 9-inch housings
IRS-to-solid-axle · SLA + Watts
Will it be noisy on the street?
Some. We would rather tell you than have you find out.
The priority is handling accuracy, which costs some noise and harshness. A rod-end linkage transmits. On a stripped track car nobody notices; on a street car with carpet and a quiet exhaust some drivers hear the rear end working over expansion joints.
The current design already answers most of it. The rod ends are PTFE-lined and made here to our specification with a pre-load on the ball, which is what stops them rattling. New ones carry about five foot-pounds of breakaway torque and feel slightly stiff until they break in. The bell crank pivots on Delrin, which passes less sound than steel. (We used to offer a Quiet Watts Link with a urethane bushing on the chassis end; subjective testing across many cars showed little if any difference, and it is discontinued.)
The arms carry spherical rod ends at both ends. The loads they feed into the body land on a bolt-on chassis bracket we can replace, not on thin chassis sheet metal.
A noise-sensitive customer with a 2014 GT500 put it best after his install: the car “makes a faint sound back there, but it is not intrusive, and actually it is just different than before.”
When a rod end finally needs replacing, no special tools are needed and no realignment either, if the installer counts the threads coming off and puts the new one on the same number of turns.
What yields in a hard hit, and what doesn't
We designed where it should break.
Something in the rear has to be the fuse. We chose which part, in advance: the links at the ends of the bell crank.
The bell crank runs in double shear behind a stabilizing plate. The links at its ends are left in single shear, and they are the parts meant to yield: the crank twists or fails before the chassis brackets, the frame, or the axle housing does. In the hits we have seen, the rod ends yield a considerable distance before they let go, and they have not disconnected.
An intermediate plate carries the crank instead of the cast diff cover, so a crash does not empty three quarts of gear oil onto the track. Many cars go back out the same day on a center-link service kit.
— Griggs Racing engineering
Questions we get asked
Does the Watts Link's lateral arc matter, or is it lost in tire flex?
The arc was never the point. Any well-built lateral locator keeps lateral movement small. What separates designs is where the roll center sits and what it does under load: a Panhard bar’s effective roll center differs loaded left versus loaded right, while a Watts Link pins it at the pivot, symmetric in both directions and adjustable in height. You tune the rear of the car with the roll center, not the last hundredth of an inch of arc. — Bruce Griggs
Which mounting is right: axle pivot or chassis pivot?
Is a Panhard bar the same as a track bar?
Does Panhard bar length matter?
How do you adjust a Watts Link?
Will it survive street miles?
Who invented the Watts link?
How do you tune it?
This is the order I run it in. Work one change at a time, and write down where you started. I have watched too many good afternoons get lost because nobody recorded the baseline.
If you drive on the street or run HPDE days, you do not need any of this.
It assumes corner-weight scales, a tire pyrometer, front tire temps within a 20-degree spread, and a long unbanked sweeper.
GRIGGS RACING · REAR SETUP SEQUENCE · SONOMA, CA
1
Set the baseline
Put the bell-crank pivot in the second hole from the top and set cross weight to 49% ±0.1%. Every later change is measured from here, which is why it gets written down before the car turns a lap.
WHAT MOVES: bell-crank pivot → 2nd hole from top
cross weight → 49% ±0.1%
2
Read the corner with throttle
Mid-corner, under steady power and near the limit of adhesion, add a little more throttle to widen the radius and watch what the car does. Straightens and needs more steering input: understeer. Needs less input to hold the line: oversteer. Moves off line evenly front and rear with no change in input: neutral.
WHAT MOVES: nothing on the car: this is the measurement
3
Dial neutral with rear spring rate
Baseline balance is a spring job, not a Watts job. If the car understeers, increase rear spring rate relative to front; if it oversteers, reduce it. Repeat step 2 until the car reads neutral.
WHAT MOVES: rear spring rate, relative to front
↺ REPEAT STEP 2 UNTIL NEUTRAL
4
Move the Watts one hole
Now the roll center does the work. To reduce understeer in both directions, raise the Watts; to reduce oversteer in both directions, lower it. One hole at a time. Each hole is a significant change, and if a hole does nothing you can feel, the baseline is still off or aero loads are overriding the chassis.
WHAT MOVES: bell-crank pivot ±1 hole → rear roll center up or down
5
Bias the car, then read the tires
On a track with tight corners one way and sweepers the other, cross weight handles the asymmetry: raise cross % to reduce oversteer turning left, lower it to reduce oversteer turning right. Confirm with tire temps: the primarily loaded side should average equal front to rear.
Worked example, R-compound tires on a cool day, right-hand-dominant track: LF 205 avg / LR 205 avg on the loaded side; RF 167 / RR 163 on the unloaded side.
WHAT MOVES: cross weight %
verified against front/rear average tire temps
You cannot tune for bias until baseline and balance are right. And if you race the car, this is the procedure. If you drive it on the street, you do not need any of it; I would rather you spent the money on tires. — Bruce Griggs
Do you actually need one?
“If you need to win, or impress at the car show, install the Watts. If not, don’t.”
— Bruce Griggs, on choosing between a Watts Link and a Panhard bar
Plan the rear around geometry that stays put.
Watts Link systems for every solid-axle Mustang since 2000: machined, welded, and track-proven in Sonoma, California.