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Old 08-06-2013, 10:42 AM
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Ron Sutton Ron Sutton is offline
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Let’s talk rear suspensions …

Other than singular purpose built race cars … like Formula, Indy, GTP, Midgets & Sprint Cars … production type bodied cars’ typical limiting factor … is front tire traction during cornering. In PT cars we can’t go any faster through the corners than the front end has grip.

As we optimize front end grip & maximize cornering speed … tuning the rear suspension is the key to achieving a balanced, neutral handling track car. This is assuming you have a tunable rear suspension. The key areas of tunability are roll center, anti-squat, lift/push ratio, rear steer, spring & sway bar rates, shock valving & track width.

If you haven’t gone off the range with track width split or tire size split … it is relatively easy to balance the rear grip to the front for a neutral handling track car. But you need to have a tunable rear suspension … and the knowledge to do so.


There are four common types of rear suspensions utilized in Pro-Touring cars today ... 3-link, Parallel 4-link, Triangulated 4-link & Torque Arm. Ladder bars should not be seriously considered for any corner carving car, as they go into instant bind with body roll & offer practically no articulation.

The typical Torque Arm suspension is similar to a 3-link, using two lower trailing arms (or "control arms") ... but instead of the third link being on top (centered or offset) & pivoting ... it mounts solidly to the housing & extends quite far forward (closer to the center of the wheelbase) with its 3rd pivot point.

Assuming each type of rear suspension is set-up correctly, rod ends spaced away from brackets properly with high misalignment bushings & clocked correctly ... the 3-link & Torque Arm suspensions allow the rear axle to articulate more (roll angle in relation to frame) than the 4-links.

They all will bind at some point of articulation. The Parallel 4-link allows the least articulation before bind ... the Triangulated 4-link allows a little more articulation before bind ... and the 3-link & Torque Arm offer quite a bit more articulation before bind ... all things being equal.

A triangulated 4-link is simple, and fairly common as a factory style rear suspension in many cars. It could be argued it will handle more torque under hard launches than 3-links, but if you were going to drag race it with slicks, you would want a Parallel 4-link, not a triangulated 4-link. You want the push & pull forces going through the links to be parallel with the chassis … not angled within the chassis.

Torque Arm suspensions are also common as a factory style rear suspension in some cars. They are the simplest of the designs, allow a high degree of rear end articulation & can take high shock loads from hard launches. They can be made "a little" adjustable, but typically offer less adjustability than the other designs, as far as controlling the front Instant Center, rise leverage & anti-squat. If designed well & installed as instructed, these make a great all around suspension for the person that doesn't want to tune much.

3-links are very common in road racing, especially in full body cars like GT1 & the Trans Am series, because they allow for the most articulation & can be highly adjustable & tunable for track conditions. You also see them a lot on top AutoX racers.

3-links, Parallel 4-links & Triangulated 4-links can be made very adjustable if designed & installed with multiple or variable mounting points. But most "street kits" are sold with little or no adjustment to protect non-tuning novices from themselves. If you know set-ups or plan to learn, you may want to pick a system designed for adjustability. If not, pick a system designed for your application, install as directed & run it.

3-links can handle drag racing up to a point, but it wouldn't be my choice if the car was planned for super high hp, high rpm, clutch dropping, slick running, wheelie pulling launches ... as there are only 2 rod ends "pulling" through the top link to lift the whole car. 4-links can handle more launch load (like drag racing), because the force going through the rear end & rear suspension that "pulls" the top links(s) is spread over 4 rod ends.

Parallel 4-links, 3-links & Torque Arm suspensions require a device to keep the rear end centered in the chassis, like a panhard bar or watts link. A triangulated 4-link does not require this, as the 2 or 4 links running at an angle keep the rear end in the location you put it. There are pros & cons both ways.

A suspension with a panhard bar or watts linkage ... "can" allow for easy roll center changes, if the mounting brackets allow for adjustment. (Many ProTouring focused kits offered do not have adjustment capabilities) Again, decide if you want to "set it & forget it" (sorry Ron Popiel) or if you want a suspension that is tunable for optimum performance & varying track conditions.

For a track car, I can’t fathom not having an adjustable rear suspension. But if your PT car doesn’t have a rear suspension, that doesn’t mean you shouldn’t do track days. Rock on & have fun. Just know if the rear needs to be loosened or tightened up, to balance out the car for neutral handling, you have less tuning options.

For the best adjustable rear suspension for road racing, track car, or AutoX car, is the adjustable 3-link, as it has the best articulation. The adjustable parallel 4-link will work well as long as the car doesn’t require a high degree of roll angle for the suspension to work, but it's not my weapon of choice.

For the best non-adjustable rear suspension for road racing, track car, or AutoX car, is the Torque Arm suspension, as it offers good articulation. The non-adjustable 3-link & parallel 4-link “can work well” … providing the instant center location provides a decent anti-squat percentage for your application. Triangulated 4-links are rarely adjustable, but still ranks at the bottom as the push pull forces aren’t parallel with the car (which is desired) and the roll center is not separately adjustable, as it does not use a panhard bar or Watt’s link.

For drag racing, the advantage goes to the Parallel 4-link, with the Torque Arm suspension 2nd (for handling launches BUT not very adjustable), Triangulated 4-link 3rd & the 3-link 4th (only due to strength concerns).

For a "cruiser/driver" that will only occasionally see the track, with little or no tuning ... any of them will work fine ... but the Torque Arm suspension is best here & the triangulated 4-link 2nd ... which is why you commonly see these two suspensions in factory production cars. They both work fine in many hot rod & street performance applications. They are not better than the others, just simpler & effective. Plus these two allow you to keep the rear seat if that is important to you.


Offset 3-links

The rear end housing wants to rotate the same direction the driveshaft is … counter clockwise from the rear view, clockwise from a front view. So as torque is applied the left rear tire is loaded more & the right rear tire is loaded less. This makes the car want to “drive” to the right, a small amount, under hard acceleration. As you make left hand turns the car has more “forward bite” during corner exit … than right hand turns, which have less “forward bite” during corner exit.

The difference isn’t huge, but it exists. If it isn’t counteracted … the effect amplifies with increased power output.

For 3-links, the upper link can be offset to the passenger side to help counteract this torque on acceleration. Very few people can tell you accurately how far to offset it, because it changes with gear ratio & friction within your rear end. I have my own proprietary formulas I use, based on my knowledge of where the force comes from & high tech testing of dynamic loads. This allows me to calculate the amount of force difference from the left rear to right rear tire & offset the top link precisely to zero out any torque steer. I don't share this formula publicly, but I do offer this service as one of my 70+ tech services you can see HERE.

The formulas I’ve seen other people use involve rear steer, which makes no sense for handling cars. A rule of thumb is 8-12% of track width. In many race applications, it makes sense to make the top link mounts wide, so you can adjust the top link side to side to dial this in. Sometimes in the real world, packaging challenges play a role.

Ron Sutton Race Technology

Last edited by Ron Sutton; 12-06-2014 at 07:09 PM.
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