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Contact & Information
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Ford MustangSuspension
IRS Adjustable Tie Rod Kit, 1999-04 Cobra
Improve the handling of your Cobra IRS by fine-tuning its bumpsteer characteristics. Just as with the Mustang front suspension, the IRS can exhibit undesirable handling behavior due to bumpsteer characteristics. MM's Adjustable Rear Tie-rod End kit allows adjustment of the rear steering geometry in order to minimize the rear bumpsteer effects. As with the front of a vehicle, making changes to enhance the performance of an independent rear suspension system will often require tuning the alignment. Besides the commonly required adjustments to camber and toe, an IRS can greatly benefit from fine-tuning its bumpsteer characteristics. |
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Ford designed the rear suspension to function as a complete system. The static bumpsteer curve was designed to work in conjunction with the compliance of all the rubber bushings in the suspension. When those bushings are changed to a less compliant material, the dynamic bumpsteer curve will change and no longer be what Ford had intended.
While other companies advocate the simple fix of duplicating the 2003 Cobra bumpsteer curve for earlier IRS Cobras, that becomes less and less desirable as the compliance of the OEM suspension is reduced. MM recommends matching the 2003 Cobra static bumpsteer curve only for cars that retain the original factory rubber bushings. Our kit includes instructions to adjust the bumpsteer to match that of the 2003 Cobra. |
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The vertical mounting position of the IRS inner tie-rod end on the 2003 Cobra was altered from its location in the previous years. The new position altered the bumpsteer curve. While this reduced the understeer of stock 2003-04 Cobras, there can still be problems once the vehicle's suspension is modified. We have found significant variations in the bumpsteer curves measured on different IRS equipped Mustangs. Differences in the bumpsteer characteristics exist not just from one vehicle to another, but also on the same car, from one side to the other side. As the level of desired performance is raised, and the number of modifications to the suspension climbs, the importance of adjusting the bumpsteer on each side of your car becomes increasingly important.
With the installation of urethane or Delrin suspension bushings there will be far less compliance in the bushings, and therefore the alignment changes when the car is driven will be smaller in magnitude. The original static bumpsteer curve will no longer allow the same dynamic curve that the car had with the original rubber bushings. This will affect the handling balance of the car, which is why MM recommends measuring and adjusting the rear bumpsteer on your car as an integral part of your performance modifications.
For cars with any performance upgrades, such as springs, IRS subframe bushings, or rear control arm bushings, MM recommends that the rear bumpsteer curve be adjusted to minimize any toe changes with suspension movement. After you test your car with this set-up, you may fine-tune the handling balance of the car by adjusting the rear bumpsteer curve. Only your continued testing will confirm what works best for your car and your driving style.
What is bumpsteer?
Bumpsteer is the term for the situation when the toe angle of a wheel changes as the suspension moves up and down, such as when driving over bumps, or with body roll during cornering. This happens when the arc that the spindle travels during bump and droop is not the same as the arc of the outer tie-rod end. If the toe changes more than a very small amount, the rear wheels begin steering the car. Bumpsteer is commonly measured and then plotted on an X-Y coordinate graph as a curve showing suspension travel vs. toe change. The resulting curve is an illustration of the bumpsteer characteristics. To measure bumpsteer you will need a bumpsteer gauge. MM's Bumpsteer Gauge available in this product section is accurate, yet affordable.
NOTE: You will need to have the rear toe setting professionally adjusted after installing this part. |
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IRS Adjustable Complete Tie Rod Kit, 1999-04 Cobra
The stock rear tie-rod is a weak link in the IRS system. An IRS-equipped Mustang with only moderate performance upgrades can easily attain loads high enough to deform a stock tie-rod. When a rear tie-rod deforms, the rear toe setting changes, causing significant handling and traction problems. A drag race style launch can cause significant deformation, and even complete failure, of the stock IRS tie-rod.
The MM Tie-rod is more robust than the stock unit, making it more capable of withstanding the rigors of drag racing and open track use. We designed it to be considerably stiffer than stock, so it will not deform or fail as easily as the stock tie-rod. |
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Not Just a Stronger Replacement
The MM Tie-rod kit is much more than just a stronger replacement for the stock unit. It has the additional benefit of providing a means to adjust bumpsteer. A Mustang equipped with IRS is more sensitive to rear bumpsteer than it is to front bumpsteer. Even very small changes in the toe setting of the rear suspension can cause instability and asymmetrical handling characteristics. The handling of an IRS-equipped Mustang will benefit greatly from fine-tuning its bumpsteer characteristics.
This kit provides the same bumpsteer adjustment at the outer tie-rod end as our MMIRSTR-1 kit. However, this kit also provides the ability to adjust the height of the inner tie-rod pivot. This gives a much wider range of bumpsteer adjustment possibilities See here for more tech information about bumpsteer specific to the IRS. See here for MM's Bumpsteer Gauge.
The MM IRS Tie-rod Kit includes aluminum tie-rods, spherical rod-ends, an assortment of bumpsteer adjustment spacers, and tapered studs for the IRS uprights. |
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| Application |
Years |
Description |
P/N (Call for Price) |
| Mustang Cobra (IRS) |
99-04 |
IRS Adjustable Complete Tie Rod Conversion Kit |
MMIRSTR-3 |
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