Rodding has come a long way since the days of long-distance driving that brought on the lump in your throat, butterflies in your stomach, and the puckered feeling in the seat of your pants. Nowadays we take it for granted when we jump onto the interstate that our rod will perform flawlessly. The days of reoccurring breakdowns are over--well, for the most part.
So what's next? Making your street rod handle the way a new car does is neither impossible nor is it "wimping out." There's absolutely nothing wrong with having your street rod handle and ride like its garage mate. Street rods should and can handle well, and that should be the goal of every rodder--a safe and well-handling street rod.
If you remember back to the STREET RODDER February '04 issue, we performed a track test on two Deuce highboy roadsters--one was the McMullen clone with a solid axle fore and aft and the M-2000 with full independent front and rear. The McMullen clone pulled a 7.55 seconds at 37.93 mph on the slalom course, while the M-2000 came in at a quicker 7.48 seconds at 38.28 mph. The McMullen clone sports an I-beam axle in front and a Halibrand quickie in back, while the M-2000 is fully independent courtesy of Heidt's Hot Rod Shop. After the story came out, we had the opportunity to speak with Gary Heidt and asked him if he had plans for making an antiroll bar or bars for his open-wheel SUPERRIDE IFS kits. He was quick to point out that he was in the process and it would be just a matter of time and his independent kits would have the antiroll bar as an option. (Let's say it right here and now: when ordering an independent system from Heidt's, make sure to order antiroll bars.)
Before we get deep into the retrofit results, let's understand some suspension basics. Several years ago SRM Tech Editor Ron Ceridono wrote a series of articles, titled "Basic Training," with the intent to provide grassroots understanding on a number of rodding subjects. Since no one explains it better than Ron, we have revisited antiroll bars, understeer/oversteer, and shock absorbers from one of his articles to help each of us understand the basics.
Often called sway bars or stabilizer bars, it reduces the body roll, or lean, of a car in turns. These bars are mounted in such a manner that when the car leans in a corner, the bars help keep them "flat." The stiffer the bar, the more resistance it has, and the flatter the car will corner. In this way, weight is more evenly applied to all four wheels; the bar is really trying to lift the inner wheels in a turn, which tends to keep the inside of the car on the pavement to help the vehicle stay more level with the road. That is why the front-to-rear balance, or selection of the size of the bar, is so important. Additionally, there are no adverse effects when the antiroll bar is properly designed and installed on your street rod.
All but the lightest cars can benefit from antiroll bars, and although many factory cars have them only on the front, using them on both ends is desirable. Of course, when using antiroll bars fore and aft, they must be coordinated. Too stiff of a bar in the front leads to understeer; too stiff in the rear causes oversteer (that's why they're never used on the rear only).
We initially equipped the M-2000 with Heidt's 3/4-inch front and 5/8-inch rear antiroll bars. In our tests, we then went from a front 3/4-inch antiroll bar to a 7/8-inch. In back, we went from a 5/8-inch to a 3/4-inch. Many factors determine the roll stiffness of a particular antiroll bar installation. The bar diameter, the length of the bar, the length of the arms, and the attachment points onto the suspension components all affect roll stiffness. For example, just analyzing bars and arms only, a 3/4-inch bar with 6-inch long arms is really stiffer that a 1-inch bar with 15-inch arms. The 15-inch arms have more leverage on the 1-inch bar and have to twist it less for a given amount of suspension deflection than the 6-inch arms would have to twist the 3/4-inch bar. Then you factor in the attachment points to the suspension, which are the location on the control arms and rear axle housing. The narrower on the housing the attachment points are, again, the less the bar is deflected for a given amount of suspension travel. There is really much more that meets the eye as far as roll stiffness is concerned. That is why in many installations, a 3/4-inch bar can actually have a stiffer effect on a car than a 1-inch bar in another car. You cannot look at only the bar and tell if it's a stiff or soft installation.
Understeer and Oversteer
Two of the most frequently used terms to describe a car's handling characteristics are oversteer and understeer. Understeer means that the car is not turning as sharp as the wheels are turned. In other words, the tires slip and the frontend slides toward the outside of the turn. In racing terms, the car is said to have a push. Oversteer means the rearend wants to slide to the outside of the turn--racers describe that as being loose. A perfect example of oversteer is the way a sprint car gets crossed up in a corner and hangs the rear out. A neutral-handling car goes around a corner without either end sliding (or sliding the same amount). A neutral-handling car goes around a corner without either end sliding (or sliding the same amount) but may feel as though there is not much load on the steering wheel. Understeer scrubs off speed in a corner, and because some drivers panic when the rearend comes around, understeer is the handling quirk of choice for most suspension engineers. The reason a car will feel loose, especially in the rear, is because the antiroll bar is actually trying to lift the inner wheel off the ground in hard cornering. So when you go into a corner hard, you are really driving on three-and-a-half tires instead of four. If you do not have full tire-patch contact, you are certainly going to break that end of the car loose.
In most cases, street rods aren't driven hard enough to exhibit severe under- or oversteer, but the tendencies are there nonetheless. There are some standard design features on most rods that impact the overall under-/oversteer scenario. It's certainly understandable that a Hemi-powered T-bucket with cycle tires up front, or a blown big-block Pro-Street Willys with 16-inch wide slicks on the back, will have some peculiarities when thrown into a corner, but less obvious factors play a role as well. Big and little rubber certainly plays a part, as well as a heavy engine hanging over the front wheels--both of these factors promote understeer. However, on the other side of the handling coin is the prodigious horsepower many rods pack that make it easy to break the rear wheels loose in a corner--a classic way to induce oversteer. Although most street rodders don't normally push their cars to the limit in terms of handling, you should know what your car is capable of, for evasive maneuvers if nothing else.
Really a misnomer, shock absorbers should be called dampers because that's what they do. Shocks dampen, or slow the action of the springs. Most shocks use a piston, forcing oil from one chamber to another through an orifice. The size of the orifice may be larger or smaller in one direction or the other to tailor the shocks' action for the application. Some shocks also have a gas chamber with nitrogen under pressure to aid in damping.
QA1 Double-Adjustable Shocks
Available in April 2005, the entire double-adjustable line features 24 positions of compression adjustment and 24 positions of rebound adjustment, providing 576 possible combinations to maximize the performance of your street rod. These shocks are revalveable and rebuildable by QA1-authorized service centers and are available with a combination Teflon/Kevlar, replaceable, self-lubricating, low-noise spherical bearings or with one-piece bushings. The shocks used throughout our testing were the one-piece bushing style.
To help us understand how "tuning" a car's suspension through the use of antiroll bars and adjustable shocks is a good thing, QA1 sent two of their people to help us out. Technical Support Specialist Nate Thiesse and Design Engineer Karl Hacken were on hand for all of the testing, and with their guidance (and Gary Heidt's), we were able to make the M-2000 turn in some very impressive slalom results, but more on that later.
Follow along with the chart that gives the results of changes in antiroll bars, shock adjustment (as well as single to double adjustable), and a change in spring rates. It was apparent that by stiffening the car with the larger bars, increasing the compression and rebound, and softening the springs, the car reached the optimal handling. However, we also found out that by taking this combination and driving it on surface streets, the car was harsh-riding and undesirable to drive. It may have been a great combination for autocrossing or some other form of competitive event but not what you would want to drive cross town or cross country.
What we did find out was the M-2000 without antiroll bars and conventional coilover shocks turned in a best of 7.48 seconds at 38.28 mph in our standard 420-foot slalom course. However, by adding a front 3/4-inch antiroll bar and a rear 5/8-inch bar, we immediately achieved times in the 6.5-second bracket, making the car a second quicker! That's a dramatic change in performance; all the while the excellent characteristics associated with an independent suspension weren't compromised.
By changing over to the QA1 single-adjustable (Ultra Ride) shocks and "tuning," the individual shocks adjustment we managed an impressive 6.38 seconds at 45.16 mph. Maintaining the 3/4- and 5/8-inch antiroll bars the four shocks were set at 8 with 350lb springs in front and 450lb springs in the rear. This would be compatible with an all-around street setting that would yield a desirable ride as well as ideal handling characteristics. By keeping the same antiroll bars and spring rates but going to QA1 double-adjustable shocks set at front compression 14 and rebound 20 with the rear compression 10 and rebound 6, we achieved a best of 6.25 seconds at 45.81 mph. The shock change alone gave us a 0.13-second improvement and a little over 0.6 mph gain--impressive! We finally managed a best time of 6.14 seconds at 46.63 mph over the two days of testing. We did this by increasing the anti-roll bars to a 7/8 front and 3/4 rear. The double-adjustable shocks were set at a front compression 8 and rebound 18 and rear compression 8 and rebound 8 while we lowered the spring rates to 300 pounds in the front and 400 pounds in the rear. As we mentioned earlier, while this yielded the best performance, it did make for a harsh-riding roadster.
Having a front antiroll bar is better than none at all. But two is better than one as long as they are matched to the vehicle size and intended performance. To further enhance ride and handling performance, the ability to "tune" each individual shock is good, but the ability to tune compression and rebound of each shock is ideal. The times are changing all right, but are you keeping up with the times? The question you want to ask yourself is, "Have I done everything I can do to make my street rod ride and handle the best it can?" If the answer is no, then what are you waiting for? The summer is getting close and it will soon be time to have fun with your car. And that means driving it.
We ran the M-2000 through the 420' slalom course 85 times running the combination of 3/4"
No, there aren't two M-2000 roadsters. Through the magic of modern digital technology, we
As part of the slalom testing, 39 runs were made with the QA1 single-adjustable shocks in
It took a lot of man hours (two full days at California Speedway) to change antiroll bars
Gary Heidt jumped right in the midst of the fray and was twisting wrenches along with the
It's amazing the positive impact an antiroll bar can have on the handling of a street rod.
Heidt's supplied us with two different antiroll bar setups: one was a front 3/4" with a re
Heidt's antiroll bars come with the required bushings and brackets to attach them to the c
QA1 has introduced double-adjustable shocks featuring 24 positions of compression adjustme
The double-adjustable shock provides 576 possible combinations for ride tuning. Pictured h
QA1 Technical Support Specialist Nate Thiesse (right) and Design Engineer Karl Hacken (lef
The double-adjustable shock provides 576 possible combinations for ride tuning. Pictured h
The trick aspect of the QA1 double-adjustable shock are the two knobs; one controls the 24
Since it is a gas adjustable shock in virtually any directio, the knobs can be at the top
We used the QA1 double-adjustable shock at all four corners, which gave us numerous combin
Our test facility is California Speedway in Fontana, CA. After testing, there was the obli
By the end of testing, Gary was adept at changing out an antiroll bar in a matter of minut
Aside from using two different diameter (3/4" and 5/8") rear antiroll bars, we also explor
The rear lower shock bracket also serves as the mounting point for the roll-bar link to at
We found, as could be anticipated, that the larger antiroll bars allowed the car to perfor
Since the M-2000 was retrofitted with the antiroll bar, Heidt's made and installed bracket
The front antiroll bar mounts in a similar fashion to the rear bar by attaching to the fra
The lower shock mount serves as the point of anchor for the antiroll bar link on the botto
Here's a close view of the rear antiroll bar mount that captures the urethane bushing that
This is the front antiroll bar bracket with the same style of urethane bushing that "captu
|Single-adjustable shocks with 3/4" and 5/8" antiroll bars|
|Run #|| Time|| MPH|| ARB (front)|| ARB (rear) || SAS (front)||SAS (front)||SR (front)||SR (rear)|
|4||6.83 || 41.92|| 3/4"|| 5/8" ||4 clicks||4 clicks ||350 || 450|
|8 ||6.91|| 41.44|| 3/4" ||5/8" ||6|| 6|| 350 || 450|
|*14 ||6.38 ||45.16||3/4" ||5/8"||8|| 8||350 ||450|
|16||6.60||43.38|| 3/4"||5/8"|| 10||10|| 350 ||450|
|Single-adjustable shocks with 7/8" and 3/4" antiroll bars|
|Run # || Time ||MPH|| ARB (front) ||ARB (rear) || SAS (front) ||SAS (front)|| SR (front)||SR (rear)|
|*28 ||6.53 || 43.85|| 7/8"|| 3/4"|| 6|| 8||350||450|
|34||6.56||43.65||7/8"||3/4"||4|| 4|| 350||450|
|Double-adjustable shocks with 3/4" and 5/8" antiroll bars|
|Run # ||Time||MPH|| ARB (front)||ARB (rear)||DAS (front)||DAS (front)||SR (front)||SR (rear)|
|41||6.49||44.12||3/4" ||5/8" ||8c/8r||0c/8r ||350||450|
|44 ||6.46|| 44.32||3/4"|| 5/8"|| 8c/8r||0c/12r||350||450|
|49||6.47||44.26||3/4"|| 5/8"|| 8c/8r||0c/16r||350||450|
|55||6.33||45.23||3/4"||5/8"||14c/20r||0c/16r|| 350 ||450|
|57||6.29 ||45.52||3/4" ||5/8"||14c/20r||0c/6r||350||450|
|*59||6.25||45.81||3/4"|| 5/8"||14c/20r||10c/6r||350 ||450|
|Double-adjustable shocks with 7/8" and 3/4" antiroll bars and "lighter"-rated coilsprings|
|Run # ||Time ||MPH||ARB (front)||ARB (rear)||DAS (front)||DAS (front)||SR (front)||SR (rear)|
|74||6.29 ||45.52|| 7/8"||3/4"|| 8c/16r||8c/8r||300 ||400|
|*79||6.14||46.63||7/8"||3/4"|| 8c/18r||8c/8r||300 ||400|
|Run #: ||Sequence of run|
|Time: || E.T. in seconds to travel the 420' between the cones|
|MPH:|| Miles per hour achieved at end of 420' between the cones|
|ARB (front): || Antiroll bar (front)|
|ARB (rear):|| Antiroll bar (rear)|
|SAS (front):|| Single-adjustable shock (front), turning knob clockwise increases setting|
|SAS (rear):||Single-adjustable shock (rear), turning knob clockwise increases setting|
|DAS (front): ||Dual-adjustable shock (front), compression and rebound settings|
|DAS (rear):|| Dual-adjustable shock (front), compression and rebound settings|
|SR (front):||Spring rate (front): Weight required to deflect (compress) spring 1". Lower the rate (numerical number), the softer the spring|