All of us like our street rods, but how many of us really like to drive them? I am not asking the question because you are afraid of a rock chip or two, but rather, down deep in the seat of your pants, you aren't particularly fond of the way your ride rides.
There are basics that any rodder should know, and by following proven principles, you can enhance the ride of any street rod. Now, don't expect to get that good-time feeling in the seat of your pants when comparing a solid-axle car to a fully independent car. That isn't going to happen, as modern technology, when applied to a full independent suspension, will be light years ahead of a tube axle followed by a solid rearend. Granted, we street rodders will suffer for vanity's sake, as the look in many cases is deemed to be more important than the ride; but, all of that aside, there is still more you can do.
For some enlightenment on this subject, we have asked many of the industry's experts (Fatman, Kugel Komponents, Heidt's, Air Ride, SO-CAL Speed Shop, Eibach Springs, Aldan shocks, Tokico USA shocks, ECI brakes) to give us some tips.
Compliance ZoneThe suspension is essentially an energy absorption system located between the frame or body and the axles. Without a suspension, there is nothing to prevent the force generated by hitting a bump in the road being transmitted directly from the tire/wheel into the body. As a result, the force from that bump, and the energy produced by that force, will slam into the body of your street rod in a violent fashion. This is not only uncomfortable for the passengers, but it can severely stress the body, leading to squeaks, rattles, and, worse, cracking and bending of the body. Minus a suspension, the upward movement of the tire, as it encounters a bump, will launch the vehicle upward, causing loss of contact between the tire and the road.
The movement of the springs allows for relative motion between the wheels and the body, which can have an adverse effect on handling. Body roll when cornering, as well as the pitch and dive experienced when accelerating and braking, are all the result of suspension movement.
The two critical words that best describe suspension are compliance and compromise. Compliance means "to give or yield," as when the tire/wheel hits a bump. We have no suspension without compliance.
Compromise means finding the best middle ground. Each of the suspension parts has its own job, but they must all work together. A suspension that is too soft will cause poor handling and weak control. A suspension that is too stiff lacks compliance and will not work well on rough or slippery surfaces. If the suspension components and settings at the rear of the vehicle do not match up well with those at the front, the stability of the vehicle will be seriously impaired.
Let's start with some basics, such as toe-in, Ackerman, caster, and camber. Toe-in is usually pretty easy. Either radial or bias-ply tires are happy with 1/16- to 1/8-inch of toe-in. When underway, this actually is reduced to about zero, as any slight slack in the steering system comes from under. Toe-in is used to keep the wheels facing straight forward. Any steering system will have some play, and initial toe-in helps take up that tolerance.
Camber refers to the lean of the tire as viewed from the front; positive camber has the top of the tire leaned out, which leads to better straight-line stability. Positive camber gain geometry increases cornering ability by leaning the tire into the turn like a bicycle, and is achieved by having the upper control arm going downhill toward the center of the car.
Caster is the inclination of the kingpin, or line through the ball joints, as viewed from the side. This is done by setting the upper ball joint slightly behind the lower, not by setting the entire crossmember at an angle. The car actually rises as the wheels turn, using the weight of the car to try to straighten the wheels. Oftentimes, manufactures of frontends in our industry recommend approximately 4 degrees positive caster to decrease power steering sensitivity, since the greater caster increases effort, countering some of the assist. Many '30s to '50s cars, such as '49-51 Fords/Mercurys, '39-48 GMs, and '39-53 Mopars, used negative caster to ease steering effort, but benefit from 1-2 degrees positive for stability.
Bumpsteer occurs when toe-in changes without input from the driver and is most affected by wheel travel. Where you get in trouble is when the toe-in changes without the driver's permission. It's not vibration felt in the steering wheel, which is often caused by loose parts such as U-joints or column bearings.
Steering and suspension geometries must be carefully coordinated. Widened or narrowed suspensions, special tie-rod ends, or changing steering gear from the original design are warning signs. The laws of mathematics and geometry can be ignored, but never changed. For example, '65-66 Mustangs toe-out about 2 inches when put on a lift. This can be tolerated with skinny tires, but switch over to a much wider tire-and especially one with a "soft" compound-and you will learn the hard way what bumpsteer is like in real life. The problem comes when only one wheel hits a bump, causing that tire to steer by itself, making the car dart unexpectedly.
Antidive geometry attempts to prevent forward weight transfer under hard braking. Having the upper control arm hinge axis tilted back does this; it should never be level. At least 3 degrees is required, while excessive antidive will cause some strange camber angles at tight steering angles. Independent rear suspension accomplishes antisquat geometry with a level upper arm and a lower arm axis tilted forward.
Ackerman is named after an Austrian carriage designer who realized the inner wheel has to turn tighter, or toe out, in order to track properly in a turn. The outer tie-rod pivot must lie on a line passing through the center of the rearend and the lower ball joint. That means a front steer requires the tie-rod pivot to be outboard of the lower ball joint, and inboard for rear steer. Some designs violate this concept, compromising the tire contact patch by toeing in, causing loss of traction. Since the effect is greatest at extreme turn angles, skinny tires mask the effect while fat tires magnify the problem. Hot rodders get in trouble when they decide to swap steering arms to relocate the steering, such as Corvairs with Pinto racks, rear-steered Mustangs, and T-buckets with early Ford spindles with a front tie rod.
Vega Cross SteeringCross steering is not a recent innovation, in fact, Ford cars used cross steering from '09 through '27 (Model T) and again from '35-48. However, in the world of street rodding, the Vega cross steering (Flaming River, Borgeson, Remy, Unisteer, etc.) came into popularity in the mid-'70s and has taken root ever since, especially on '28-34 Fords.
The steering box mounts far forward on the driver side of the frame in a street rod, generally on the inside of the framerail. The draglink runs laterally across the chassis where it connects to the steering arm of the right spindle. The Pitman arm pivots side to side, moving the draglink left and right laterally to steer the car. (In some lakes modified-style street rods, the Vega box is mounted on its side and is pressed into service similar to a Corvair or Ford pickup box might have been used.) Cross steering is ideal where space is an issue since the box is compact in size and is durable.
An advantage of cross steering is that steering geometry is not affected by the type of radius rods used to hold the axle. Frontend movement, as controlled by the radius rods that locate the axle front to rear, is not relative to the steering movement because the draglink is mounted laterally (side to side). It's a widely held misconception that ill-handling characteristics such as bumpsteer and oversteer do not exist with a cross steering setup-wrong.
Lateral movement of the draglink controls the steering or directional change of the car. In other words, when the steering wheel is turned, the draglink will move laterally in relation to the axle/spindle assembly, causing the spindles to turn and the car to change direction. But what if for some reason the draglink moved in relation to the axle assembly without the steering wheel being turned? The spindles would still turn and the car would change direction. How can this happen? Remember that an early Ford transverse spring is free to move side to side on the shackles even though it is anchored to the frame via its crossmember. This lateral movement of the frame in relation to the axle also means movement in relation to the steering gear and the attached draglink, resulting in unwanted, unpredictable steering movement.
The answer is to eliminate or control the lateral movement between the frame and the axle. This is done by installing a Panhard rod, or sway bar, which is a lateral link connecting the frame and axle. But since this link controls movement relative to the steering draglink, the mounting position and angle are important to correct steering geometry.
Mustang SteeringAlthough Mustang steering has fallen out of favor with rodders over the past two decades, there can be no denying that it was very popular beginning in the early '70s. A removable column on later Mustang boxes ('69-73) also allows the adaptation of tilt columns from other cars. The common mounting position sets it back out of the way of most factory or custom exhaust systems. Another not too well-known feature fact is that the Mustang (also Cougar) steering gears are available in two ratios: four turns lock to lock (most common), or five turns (slower steering)
When it comes to steering installations, however, there is more to it than just mounting the box and hooking up the draglink. What appears proper and should work correctly when the chassis is sitting on stands in the garage may in fact be all wrong. The arbitrary placement of steering components can mean incorrect steering geometry and serious handling problems once the car is on the road.
Street rods built decades ago didn't seem to have major steering problems aside from being hard to steer. This is because the frontend design and steering setup was left basically stock. Even if the car had a dropped axle and a later ('49-56) Ford pickup steering gear, the steering geometry had not changed enough to cause trouble. In the meantime, rodders started installing the smooth-operating Mustang steering. What seemed to be a great improvement only made the car handle dangerously strange, an example being the car turning to the left or right when going through a dip or over a bump. At the same time, the steering wheel would rotate a small amount to either direction. This strange action became known as bumpsteer.
Bumpsteer results from incorrect steering geometry that causes the car's steering to change direction during vertical suspension travel. With the design of the Mustang box, the Pitman arm is opposite that of the early Ford steering box in that it rotates above the sector shaft instead of below the sector shaft. This drastically changes the draglink angle and steering geometry in relation to a basically stock-style frontend design. By stock we mean a frontend using either stock or split wishbones or hairpin-type (single-pivot) radius rods.
Bumpsteer can be eliminated from a Mustang steering installation if a four-bar setup is used. The parallelogram design features of the four-bar keep vertical suspension movement of the axle and spindles relative to the movement of the draglink. It's simply a matter of making sure the draglink is parallel to the four-bar.
Four-Bar SuspensionThere may be no more popular suspension component in street rodding than the four-bar. It should be noted that "four-bar" is a registered trademark name for the parallel link radius rod kits originally manufactured and sold by Pete & Jake's back in the '70s until today. This design was seen on IndyCars and other race cars as far back as the '30s. Today, any number of companies offer the parallel link setup, and this system can be seen on literally thousands of street rods and is used on both the front and rear suspension.
The four-bar design uses the principle of the parallelogram. That is, when one end of the figure moves in relation to the other, all sides remain parallel. Using this parallelogram for a hookup on each side of the axle allows the axle to move vertically without easier change. Each end of the axle can move independently from the other with no bind. The axle is not trying to twist because caster is constant at each end of the axle, regardless of axle movement. The axle can move freely, being dampened only by the spring and shocks the way it should. Ride is improved much like independent because axle movement is not being transferred into the frame trying to rock the car with each bump.
Split WishbonesWhen an axle held by split wishbones moves up and down, it experiences caster change. This is due to the axle pivoting from a centerline. This would be fine if every time the right wheel went over a bump the left wheel did the same, or you entered every driveway straight on, or the car did not want to lean to one side when taking a corner. Unfortunately, this is not the way it is. Bouncing up and down on the front of your frame in the garage is totally different than the kind of action it is going to see as soon as you get to the end of the driveway.
Because each end of the axle is pivoting from a separate point (not a single point like un-split stock wishbones) when the right wheel goes over a bump or moves vertically, the caster on the right side is going to change, but the left side is going to remain the same. What happens between the two sides changing caster is an axle that is twisting or attempting to twist. An I-beam axle can twist and will probably never break. A tube axle will not twist, so when you hit a bump, something has to give, something is forced to twist, and eventually break. This is far from an ideal situation. Yet, all of us have seen tube axles with split wishbones and the owners will tell you they have driven them for years with no problems. Well, no problems of which they are aware, but realize time isn't the culprit-it's miles driven. The more miles you drive, the sooner the problem will arise.
Bending Spindle ArmsBending spindle arms is less of a common practice today, but it was more so back in the '60s and into the late '70s. Nowadays, manufacturers offer bent spindle arms (today, spindle and steering arm assemblies can come as two items that bolt together, and you can purchase steering arms that are already "bent").
The moment you install a dropped-type axle, the spindles and the tie rod connecting the spindles move up vertically in relation to the axle, radius rods, frame, etc. This usually causes the tie rod to interfere with the radius rods, front crossmember, and even the crankshaft pulley on the engine. The solution is to heat the spindle arms with a large acetylene torch and carefully bend the arms to reposition the tie rod so the spindles can turn lock to lock without interference. The tie rod will most likely need to go above the wishbone (depending on the amount of axle drop) if you are using a stock or split wishbone. Here you will want to try and position the tie rod as low or as close to the wishbone as possible since frame clearance will be the main problem. If you are using a four-bar setup, you can take advantage of additional tie-rod-to-frame clearance, as the tie rod can be positioned lower directly behind the axle. You will maintain maximum turning radius and have sufficient frame clearance by bending the arms to center the tie rod in the lower cradle of the axle bracket.
Some good rules to follow when bending spindle arms are:1. Keep the centerline of the kingpin and the rod end hole parallel. This is done by bending the spindle arm in two places. If these bends are too close to each other, the length of the arm will be shortened, critically affecting the steering geometry. Try to make the bends as far apart as possible.
2. Proper steering geometry when the spindles are turned left or right is regulated by the angle of the arms. A simple guide to correct turning geometry is to project a line from the center of the kingpin to the center of the rearend. Then make sure the center of the tie-rod end hole in the spindle arm is also on this line.
3. Bending spindle arms made of forged steel (like original Ford spindles) or cut from steel plate is no problem. Heat the metal only enough so you can bend the arms using a large Crescent-type wrench. If the metal gets too hot, it may crack or crumble during the bending process. Do not heat or try to bend any item that is "cast" material.
While many of the principles mentioned above apply to street rods, no matter if they are equipped with full independent or solid-axle suspensions, there is plenty more we can learn about independent front and rear suspensions. Next up is some real-world experience from Don Prieto as to what happens when you tinker with an independent suspension system.
When A Change Is MadeOK, we now know suspension is important, but what happens when changes are introduced to shocks, tires, sway bars, and other items in the compliance zone?
Questions like: "What do you think it'd do if we had antiroll bars?" "Should we have had more tire?" and the like were kicked around. We called around to those who should know, and one thing led to another. Enter one Jerry Kugel of Kugel Komponents, our suspension mentor.
"If you guys want, I'll put a new setup on the roadster and we can share the results," he said. "I'll learn something too."
We jumped at the chance, and the little black '32 spent several days at his shop in Yorba Linda, California, receiving new front and rear antiroll bars, new stiffer front springs, and new Aldan adjustable shocks on all four corners.
In anticipation of the test, we acquired a set of American five-spoke wheels and a set of Toyo TI-S tires. We chose the tire and wheel package as much for the look as we did for the performance. There is nothing special about either, and they can be purchased at any reputable tire and wheel dealer anywhere. We did not want to have to answer lots of questions about using unobtainium components, so it was off the shelf for us.
Understand that this car had a very nice boulevard ride with the original suspension package, and we didn't want to sacrifice our comfort for some "go-cart" handling, teeth-jarring, stiff suspension just to get better numbers. No siree, Bob!
The change in the overall ride was indiscernible with the addition of stiffer springs and the adjustable shocks set in the center of the scale. We did notice that the addition of the front and rear antiroll bars did their job, as body roll on the street was noticeably less and therefore better and more comfortable to drive in a hurry.
We went back to the same location where we did the initial testing at California Speedway in Fontana and we were even able to use the exact patch of macadam so the results would not be skewed by a change in surface. The slalom course is best described as a test to determine the ability for a vehicle to change lanes back and forth at a maximum speed without losing traction.
We opened the test on the slalom course with the seven cones set at 70 ft apart and the timers set to measure the time it takes to traverse the entire length. The resultant time is converted to mph average over the full course. Driver Jason Scudellari made our first few passes after warm-up, and we were right on top of the earlier tests. A 6.56-second best time from the first test was bested by a 6.45 on the second run. We knew we were headed in the right direction. Jason reported that the car was loose (under steering) on entry, then neutral, then loose on exit of each direction change compared with a completely neutral handling setup from the initial test. He did admit to entering the course at a higher rate of speed, and that could explain the difference.
We softened the compression on the rear shock-three runs offered no improvement. We then returned the compression to neutral and tightened the rebound-three more runs and no improvement. Driver reported loose condition with both adjustments.
We then tested with the same full-loosen-change to the front shocks and again no improvement. With the retightened fronts, we then tightened the rebound and loosened the compression on the rear and we noticed our first improvement with a low of 6.35. To what does that translate, you ask? While it may sound small, the average speed through the course increased from 43.4 to 45.5 mph. The driver said it was much easier to control at this setting.
The next disconnected the rear bar in an attempt to tighten up the handling even more. With the shock settings the same, we saw a best of 6.17 seconds-better still.
The next step was a big one. We changed tires and wheels and returned all the settings and bars to their original position. We turned a best of 6.25-not better-but the driver reported a much better feel with the tires giving more confidence.
We then disconnected the rear antiroll bar, the change that brought about the best increase in speed with the smaller tires. Voila! We registered an "off the chart" 5.97 seconds (48.2 mph), the fastest of any hot rod ever tested by this group.
Satisfied with the slalom speed, we moved to the skip pad. In this test, as in the previous tests, we used a 200ft circle with the time measured from a rolling start measuring the elapsed time around the course then consulted the chart to convert to g-force. We reconnected the rear antiroll bar and gave it the gas.
With the tires howling in protest, Jason pulled a best time of 11.48 seconds, which converts to a measurement of .94 g's. This, compared to a best of 12.35 (.80 g's) turned in the original test, is a substantial improvement and just what we were looking for. The driver even pulled in at one point and had the shoulder harness tightened.
"It's trying to throw me out of the car," he exclaimed.
That brought a big smile of satisfaction to the faces of all participants.
Driver observation: With the new tires, the car generated much more grip, but compared to the original set, they stuck very good up to their limit and then let go. They did not give the kind of on-the-edge feeling the 65 series tires did.
Well, there is a real-world example of what happens to an independent-equipped street rod when changes are made. Moral of this story: All components of a street rod's suspension are related and you cannot change one without affecting the other. Oh yes, and plan out any changes you want to make and be sure all components will work well together.