Little Tire Traction—Part I

June 27th, 2011

Text and Photos by Wayne Scraba

How to Set-Up a Stock Suspension Car

Stock rear suspension drag racing is without question the big buzz today, and we’re not talking NHRA-legal stuff either. Instead, the current fervor is all about quick street cars. This is the sort of car that dominates, in sheer numbers, any of the myriad fastest street car organizations. But in truth, it’s also a wonderful combination for bracket racing, grudge racing or just to have fun.  It’s also perfect for the Pinks All Out format, but that’s another story.

The beauty of a stock suspension car is that anyone can put it together and tune.  For the most part, it’s a pretty basic bolt-in deal. If you can swing a wrench, you can piece one of these suspension systems together. On the other hand, if you have a car with limited wheel well room, there are a few complications.  In our case our project car is an ‘86 Buick Regal. GM G-bodies such as this have tons of aftermarket support, they’re easy enough to find and they’re reasonably affordable. (Have you priced a rust-free ‘69 Camaro lately?)  The only big downside to these cars is the fact the frame needs some massaging in order to fit some decently sized back hoops. For a closer look at the frame fix, see the accompanying sidebar.

Here’s the rearend setup before the gas tank installation and before the brakes and other pieces were completed. We spent a lot of time considering the suspension geometry on the car. As noted, we’re not big on altering the instant center by a huge amount. We’ve seen so-called “lift bars” actually oval the holes in suspension mount points. Chassis experts figure this is because the lift bars are actually attempting to rip the rearend out of the car.

What about the actual suspension arrangement? Big power will usually smoke the tires in an early A-Body (Chevelle, Cutlass, Tempest, etc.) or a late-model G-Body (Malibu, Regal, Cutlass, El Camino, etc.) or a Fox-body Mustang (which, by coincidence, included a very similar rear suspension arrangement).  How do you make it work? When it comes to the back end of any of these cars three major pieces are needed to make them hook: trailing arms, shock absorbers and anti-roll bar.

When it comes to trailing arms, GM, for example, used U-shaped stampings.  As you can imagine, this isn’t the most conducive configuration when it comes to laying down big E.T. numbers, especially with some big grunt under the hood. Boxed replacements are available, but that’s more of a crutch. The real answer is to install tubular components with adjustment capability. Why is adjustment capability important? One major concern is to establish a working pinion angle, however that’s only the beginning. The truth is, the coil suspension found on an A, G or Fox-body is nothing more than a 4-link with angled trailing arms. By incorporting angled bars, the manufacturer saved money. It wasn’t necessary to include a Watts linkage or track locator in order to keep the rearend from falling out of the car. It also meant the car could be a bit lighter, particularly from an unsprung weight perspective.

Instant Centers

The other potential dilemma (at least as far as the GM cars go) is the instant center (IC) location. It’s way out there, and in some cases, ahead of the car or near the engine. Stop right there. What is “instant center”? Instant center or IC is an imaginary point about which the chassis or a suspension member rotates in a given (instant) position. This all sounds complex, but it’s not.  IC is found by projecting lines along suspension members to a point of intersection.  Where those lines intersect is the instant center. IC acts as a pickup point for the rear suspension, even though the points are imaginary.

This shows upper trailing arms from both TRZ and AutoFab, both top quality parts. TRZ pieces (those installed in the car) are at the top. In this case, we decided to stick with one manufacturer for rear suspension hardware instead of mixing and matching.

What about using the old “no hop” bars that were so common in the ‘70s?  The problem is, by altering the angle of the bars, they tend to create a very short instant center. This usually works pretty well in a car with low power, but as you feed more and more torque to it, the car becomes increasingly violent.  And in some cases, the top mount bars (that raise the upper trailing arm location on the rearend housing) have a tendency to hammer the trunk floor when you get on the throttle.

Years ago we spoke to race car builder Jerry Bickel about the subject of IC points, and he noted that many very successful Pro Stock drag cars have instant centers way ahead of the vehicle also, as do any number of cars fitted with torque arm suspension (for example, any of the late-model Firebirds and Camaros). Those cars are known to hook pretty much on grass, and they have decidedly long instant center points. That’s why it’s not necessarily a bad thing to leave the actual suspension mounts in the stock location.

What’s appealing about these pieces is their ease of adjustablity. In the case of a car such as our Buick (stock-style GM triangulated suspension), the upper bars are used to center the rearend housing from side to side (by adjusting one upper). The upper bars are also used to set the pinion angle (by adjusting both uppers in the same direction and same amount). The adjuster for the top trailing arm bars is shown here.

Pinion Angle and Pre-Load

Including adjustable suspension members (upper and lower trailing arms) means you’re provided with the opportunity to fine-tune the suspension and to set the static pinion angle. Why is pinion angle so important?  If the pinion angle isn’t properly set (and controlled), the operating angles of the driveshaft and U-joints can’t be controlled. Pinion angle is measured between the pinion gear flange and the driveshaft. As the suspension in a car wraps up, the pinion is driven upward (not good). In order to insure that the pinion is correctly oriented while under power, it is typically set nose down [i]static[/i].  For most applications with solid rear suspension bushings or spherical bearings (rod ends), the pinion angle should be set between to -1 to -2 degrees (- or minus is negative angle, or pointing down). If the suspension incorporates OEM-style rubber suspension bushings, then a pinion angle of -3 to -4 degrees is preferred. The reason is due to the added deflection in rubber bushings.

So far so good, but what about preload?  Preload is a major tuning tool in traditional drag race 4-link cars, but when it comes to a triangulated 4-link, it’s not quite the same. Here’s why: In a high horsepower combination, engine torque tends to roll-rotate the chassis. This means the car bites better in the right rear. That extra bite tends to move the car toward the left. In a low powered combination, the forces that rotate the rearend (torque rotation) tend to provide more bite to the left rear tire. In either situation it’s possible to counteract the forces with preload. In a conventional, non-triangulated 4-link (like you’d find in a conventional drag race car setup), you can shorten the upper right bar to increase the preload on the right rear tire. If you can lengthen the same bar, then more load is placed on the left rear tire. Sounds easy enough, but it doesn’t work that way with a triangulated 4-link.

On cars equipped with triangulated upper control arms setting preload isn’t possible with the upper bars. When one upper control arm is adjusted then you’re actually shifting the rearend housing left or right (depending upon which of the bars you adjust). The folks from TRZ Race Cars point out that the upper bars on a triangulated 4-link are used to center the rearend housing from side to side (by adjusting one upper). The upper bars are also used to set the pinion angle (by adjusting both uppers the same direction and same amount). Adjustable lower bars are used to center the tires front to back in the wheel well and to make minute wheel base dimensional changes. Then how can you tune or preload the rear suspension in one of these cars? Simple. You use an anti-roll bar (ARB or simply a sway bar) to do the job. Then adjustable shock absorbers (front and rear), front suspension limiters, and to a lesser degree, specific spring rates are used to get the car to hook.

What follows are a series of photos detailing a (near) bolt-in suspension arrangement we installed in a G-Body Buick. Check it out.

How to Set-Up a Stock Suspension Car

Text and Photos by Wayne Scraba

Stock rear suspension drag racing is without question the big buzz today, and we’re not talking NHRA-legal stuff either. Instead, the current fervor is all about quick street cars. This is the sort of car that dominates, in sheer numbers, any of the myriad fastest street car organizations. But in truth, it’s also a wonderful combination for bracket racing, grudge racing or just to have fun.  It’s also perfect for the Pinks All Out format, but that’s another story.

The beauty of a stock suspension car is that anyone can put it together and tune.  For the most part, it’s a pretty basic bolt-in deal. If you can swing a wrench, you can piece one of these suspension systems together. On the other hand, if you have a car with limited wheel well room, there are a few complications.  In our case our project car is an ‘86 Buick Regal. GM G-bodies such as this have tons of aftermarket support, they’re easy enough to find and they’re reasonably affordable. (Have you priced a rust-free ‘69 Camaro lately?)  The only big downside to these cars is the fact the frame needs some massaging in order to fit some decently sized back hoops. For a closer look at the frame fix, see the accompanying sidebar.

What about the actual suspension arrangement? Big power will usually smoke the tires in an early A-Body (Chevelle, Cutlass, Tempest, etc.) or a late-model G-Body (Malibu, Regal, Cutlass, El Camino, etc.) or a Fox-body Mustang (which, by coincidence, included a very similar rear suspension arrangement).  How do you make it work? When it comes to the back end of any of these cars three major pieces are needed to make them hook: trailing arms, shock absorbers and anti-roll bar.

When it comes to trailing arms, GM, for example, used U-shaped stampings.  As you can imagine, this isn’t the most conducive configuration when it comes to laying down big E.T. numbers, especially with some big grunt under the hood. Boxed replacements are available, but that’s more of a crutch. The real answer is to install tubular components with adjustment capability. Why is adjustment capability important? One major concern is to establish a working pinion angle, however that’s only the beginning. The truth is, the coil suspension found on an A, G or Fox-body is nothing more than a 4-link with angled trailing arms. By incorporting angled bars, the manufacturer saved money. It wasn’t necessary to include a Watts linkage or track locator in order to keep the rearend from falling out of the car. It also meant the car could be a bit lighter, particularly from an unsprung weight perspective.

Instant Centers

The other potential dilemma (at least as far as the GM cars go) is the instant center (IC) location. It’s way out there, and in some cases, ahead of the car or near the engine. Stop right there. What is “instant center”? Instant center or IC is an imaginary point about which the chassis or a suspension member rotates in a given (instant) position. This all sounds complex, but it’s not.  IC is found by projecting lines along suspension members to a point of intersection.  Where those lines intersect is the instant center. IC acts as a pickup point for the rear suspension, even though the points are imaginary.

What about using the old “no hop” bars that were so common in the ‘70s?  The problem is, by altering the angle of the bars, they tend to create a very short instant center. This usually works pretty well in a car with low power, but as you feed more and more torque to it, the car becomes increasingly violent.  And in some cases, the top mount bars (that raise the upper trailing arm location on the rearend housing) have a tendency to hammer the trunk floor when you get on the throttle.

Years ago we spoke to race car builder Jerry Bickel about the subject of IC points, and he noted that many very successful Pro Stock drag cars have instant centers way ahead of the vehicle also, as do any number of cars fitted with torque arm suspension (for example, any of the late-model Firebirds and Camaros). Those cars are known to hook pretty much on grass, and they have decidedly long instant center points. That’s why it’s not necessarily a bad thing to leave the actual suspension mounts in the stock location.

Pinion Angle and Pre-Load

Including adjustable suspension members (upper and lower trailing arms) means you’re provided with the opportunity to fine-tune the suspension and to set the static pinion angle. Why is pinion angle so important?  If the pinion angle isn’t properly set (and controlled), the operating angles of the driveshaft and U-joints can’t be controlled. Pinion angle is measured between the pinion gear flange and the driveshaft. As the suspension in a car wraps up, the pinion is driven upward (not good). In order to insure that the pinion is correctly oriented while under power, it is typically set nose down [i]static[/i].  For most applications with solid rear suspension bushings or spherical bearings (rod ends), the pinion angle should be set between to -1 to -2 degrees (- or minus is negative angle, or pointing down). If the suspension incorporates OEM-style rubber suspension bushings, then a pinion angle of -3 to -4 degrees is preferred. The reason is due to the added deflection in rubber bushings.

So far so good, but what about preload?  Preload is a major tuning tool in traditional drag race 4-link cars, but when it comes to a triangulated 4-link, it’s not quite the same. Here’s why: In a high horsepower combination, engine torque tends to roll-rotate the chassis. This means the car bites better in the right rear. That extra bite tends to move the car toward the left. In a low powered combination, the forces that rotate the rearend (torque rotation) tend to provide more bite to the left rear tire. In either situation it’s possible to counteract the forces with preload. In a conventional, non-triangulated 4-link (like you’d find in a conventional drag race car setup), you can shorten the upper right bar to increase the preload on the right rear tire. If you can lengthen the same bar, then more load is placed on the left rear tire. Sounds easy enough, but it doesn’t work that way with a triangulated 4-link.

On cars equipped with triangulated upper control arms setting preload isn’t possible with the upper bars. When one upper control arm is adjusted then you’re actually shifting the rearend housing left or right (depending upon which of the bars you adjust). The folks from TRZ Race Cars point out that the upper bars on a triangulated 4-link are used to center the rearend housing from side to side (by adjusting one upper). The upper bars are also used to set the pinion angle (by adjusting both uppers the same direction and same amount). Adjustable lower bars are used to center the tires front to back in the wheel well and to make minute wheel base dimensional changes. Then how can you tune or preload the rear suspension in one of these cars? Simple. You use an anti-roll bar (ARB or simply a sway bar) to do the job. Then adjustable shock absorbers (front and rear), front suspension limiters, and to a lesser degree, specific spring rates are used to get the car to hook.

What follows are a series of photos detailing a (near) bolt-in suspension arrangement we installed in a G-Body Buick. Check it out.

Sources

TRZ Motorsports

Division of Southside Motorsport Technology, Inc

2450 Smith St

Kissimmee, FL 34744

407.933.7385

www.trzmotorsports.com (http://www NULL.trzmotorsports NULL.com)

Autofab Race Cars

7443 Washington Blvd.

Elkridge, MD 2107

410.796.8777

www.autofabracecars.com (http://www NULL.autofabracecars NULL.com/)

Strange Engineering

8300 North Austin Ave.

Morton Grove IL. 60053

847.663.1701

www.strangeengineering.net/ (http://www NULL.strangeengineering NULL.net/)

Aurora Bearing

901 Aucutt Rd.

Montgomery, IL 60538

630.859.2030

www.aurorabearing.com (http://www NULL.aurorabearing NULL.com)

The frame was modified by cutting away the outer frame rail with a simple 4.5-inch angle grinder and a cut-off wheel. The frame rail was cut back to just past the factory seam, and the cuts were cleaned up with an angle grinder.

Tire Tuck

Notching a Frame to Accept Big Rolling Stock

GM’s G-bodies are perfect race candidates, at least on the surface. When initially planned, the inspiration was weight reduction and everything, including the glass, got thinner. The bodies arrived fully framed, with relatively spacious engine compartments that could accommodate anything from a V-6 to a rat motor. Unfortunately, there’s a fly in the ointment, lack of rear tire room.

In stock form, a P275-60R15 drag radial is as big as it gets. You’ll struggle to fit a 9 x 28-inch slick. The problem spots within the wheel well are the leading and trailing edges of the frame rail. Here, the factory frame moves outward toward the exterior quarter panel and that’s where big tires encounter interference.

The fix is to notch the frame. Once the frame is properly notched though, a G-body can accept tires ranging from P325-50R15 radials to 11.5 x 28.00-inch slicks, and that’s with the stock inner wheel well untouched. Here’s a short thumbnail sketch of how it’s accomplished.

Source – Tire Tuck

Lejeune Performance & Fabrication

201-1492 Admirals Rd.

Victoria, B.C., V9A 2R1

250.381.4513

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