Written by Andy Hollis
From the Dec. 2015 issue
Suspension mods are one of the first things we enthusiasts delve into when looking to improve the performance of our cars. And we don’t do it alone: We decide on parts and a plan of attack with help from dozens of influences. Other owners of similar vehicles advise us, whether in person or on Internet forums. The websites and magazine ads of parts retailers, with their dazzling pictures of shiny wares and astounding claims of performance increases, also get our credit cards itching.
But does all this information add up to a suspension setup that meets our goals? Some problems are obvious, but others hide themselves well. Here are six common suspension pitfalls that may be holding you back.
1. ANTI-ROLL BAR BIND
One of the least expensive and most satisfying suspension mods involves replacing the wimpy factory anti-roll bars with some beefy aftermarket units. It immediately makes the car feel tighter and cuts body roll substantially. Dynamic camber is also reduced, adding more contact patch in the corners for more grip.
Perfect, right? Well, not for long.
Anti-roll bar manufacturers typically use urethane frame mounts to provide a very crisp response, but this creates a bearing surface that eventually wears out. To avoid early complaints of knocking due to wear, the provided bushings are almost always too tight when first installed.
Sure, you can lube them up to reduce some of the offending stiction, but the grease quickly gets pressed out, allowing the bar to bind. This, in turn, provides an infinite roll resistance at that end of the car that will absolutely destroy the handling.
SOLUTION: Easily fix those common D-shaped antiroll bar bushings by grinding some material off the flat portion of the bushing or by placing a washer under one or both sides of the saddle bracket. For sure, grease them periodically.
2. BOTTOMING OUT
Race cars sit nice and low to the ground, so a slammed suspension must be good for your car, too, right? Certainly a lower center of gravity pays dividends in reducing weight transfer and the associated body roll. This keeps all four tires working at higher rates of efficiency and does improve handling. Plus, it just looks right.
But there is a dark side to slamming, one that emerges when the car constantly bottoms out its suspension– usually unbeknownst to the driver. Riding around on the bumpstops under cornering loads can cause all manner of unusual handling.
Your low-powered Miata may be wonderful on corner entry but suddenly push like a pig in the middle. Or perhaps it gets all loose at corner exit as the rear compresses too far, allowing all the weight to transfer to the outside-rear wheel. That’s not too much power causing the wheelspin–it’s too little bump travel.
Likewise, we’ve all seen the extreme case of a slammed car making like a pogo stick as it rides around town on the undamped, high spring rate of its bumpstop rubber.
SOLUTION: The answer is to jack up the car, remove the springs, and run the suspension through the entire range of motion without them. Verify that your bumpstops hit just prior to a metal-on-metal encounter between suspension pieces. Trim or stack bumpstops as necessary.
Next, reassemble the suspension, but place a zip-tie or O-ring on each shock shaft so you can easily monitor suspension movement. Drive around to see whether your suspension bottoms out, and adjust the ride height up or down accordingly.
3. EXCESSIVE BUMPSTEER
There is another, more insidious side effect of lowering. Most production automobiles are designed to operate with a wide range of suspension travel, and to have benign characteristics within that range. Lowering a car takes it out of that range and many times puts it into a zone where the suspension geometry does all kinds of wacky things.
Massive toe changes can occur with the slightest up or down movement. Even worse, body roll can cause the car to toe in or out. Think about a car whose rear wheels toe out as it rolls into a turn.
SOLUTION: Figuring this out with an adjustable coil-over suspension usually only requires about an hour on an alignment rack. Simply take alignment measurements as you raise and lower the suspension in half-inch increments. If you’re careful, you can also do this at home with a tape measure or toe plates.
With these curves in hand, you can figure out what’s going on at each end of the car regarding ride (both sides up and down) and roll (up one side, down the other).
How do you fix things that are out of whack? For most production cars, the only thing you can do is reduce the effect by limiting the suspension movement through stiffer springs–and with matching shock valving, too. Alternatively, you can pre-compensate for factors like instability from excessive dynamic rear toe-out by using a large static toe-in alignment setting.
4. NON-OPTIMAL ALIGNMENT
Speaking of alignments, what’s yours? You’ve seen the thread a million times on message boards: “Need the best alignment specs for so-and-so car.” Sometimes the original poster will also include a list of the car’s mods.
Next, a bunch of people chime in with all kinds of tribal wisdom. Is it good advice? Well, maybe. It depends on how close your car’s complete setup is to the ones those guys used to come up with their alignment recommendations. It also depends on your desired purpose for the car. If you’re competing, the grip level and turn configuration of the courses or tracks will also have a huge influence on optimal settings.
SOLUTION: We’ve detailed the testing process before in our “Dialing In” article, which ran in our November 2009 issue.
The short of it is that you figure out optimal camber with a skidpad and a watch. Toe is determined using a slalom and an oval. Those setups from the boards may be good ballparks, but you must test to find the right settings for your car and your situation–especially when you consider the lowering geometry and bumpsteer pitfalls we discussed earlier.
5. WORN/BROKEN PARTS
All of that setup work goes right out the window if the adjusters slip under load or the attachment points are oblonged or cracked. Many of us are flogging older cars, and some of their parts may be far from new. As a result, it doesn’t take much movement to deliver toe-out or positive camber during high-g corners. Sometimes this slip is even accompanied by an audible clunk or snapping sound.
SOLUTION: New factory adjusters installed with threadlocking compound are cheap insurance. Paint marks can serve as indicators of movement.
Plenty of other worn suspension parts cause handling headaches, too. We’ve wasted a whole day of skidpad testing because of a loose upper ball joint. Rock the wheel aggressively to check for this issue.
Bad tie-rod ends can cause dynamic toe, as can worn internal steering rack parts. Easily check these by rocking the steering wheel with the vehicle at rest. And bad wheel bearings will do weird stuff to camber, toe and even your brakes. Again, rock the wheel to check.
Finally, check those suspension bushings, especially if you’ve replaced them with aftermarket urethane or Delrin. Delrin units typically require yearly maintenance: Disassemble, clean and re-lube. If they aren’t maintained, rust can creep in, causing bushing bind and a host of unusual handling behaviors. Consider using grease fittings.
6. TOO MUCH SHOCK VALVING
Damping your new lowering springs properly will likely require more valving from your shock absorbers. That said, one size does not fit all, and “too stiff” is just as bad as “too soft.”
Certainly, stiffer feels better. Your vehicle becomes super responsive to every input and totally connected to the road–that is, right up until it encounters a washboard surface and chatters right off the road. This is an extreme example of what’s going on constantly when the valving is too stiff: loss of grip. There is a compromise between proper control of the spring rate and suppleness over the road or track surface.
SOLUTION: Optimal valving can offer both control and comfort, but it may require a custom re-valve to achieve. Off-the-shelf shocks can deliver the desired performance, but only if they’re used in the situation they were designed for. This includes the type of activity (track, autocross, street use) and the aggressiveness of the rest of the car setup. The more you optimize a component for one type of use, the worse it is at other uses. Shocks are the poster child for this concept.
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