10 common suspension problems and how to cure them | Articles
When it comes to suspension modifications, most people take their cues from fellow enthusiasts—buddies or message board gurus who own a similar car. The plan of attack? Parts sourcing? Those ideas usually come from peers. Of course, you can always count on websites and magazine ads to offer their two cents. Those dazzling pictures of shiny parts coupled with astounding claims of performance increases can be hypnotizing.
Peer acceptance of a parts combination can be quite satisfying, but can these sources really be trusted? Sometimes the hype and online chatter can steer you in the wrong direction, but we’ll set you straight. Here are 10 common suspension ills and how to correct them.
1. Anti-Roll Bar Bind
One of the most satisfying suspension mods typically involves replacing the wimpy factory anti-roll bars with some beefy aftermarket units. The car immediately feels tighter, while body roll is substantially reduced. Dynamic camber is also diminished, yielding more contact patch for better grip in the corners.
Perfect, right? Well, not for long.
Anti-roll bar manufacturers typically use urethane frame mounts to provide a very crisp response. Unfortunately, this creates a “bearing” surface that eventually wears out.
To avoid early complaints of knocking due to wear, the bushings provided 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 or washed out. The bar is then allowed to bind. The result: infinite roll resistance at that end of the car that will absolutely destroy the handling.
Anti-roll bar bushings a bit too tight? Free them up. Grinding down the flat end of the bushing should allow the bar to operate smoothly. Photography credit: Andy Hollis
We have two easy fixes for the common D-shaped bushings supplied with most anti-roll bars: Grind away some material from the flat portion of the bushing, or fit a washer under one or both sides of the saddle bracket. Either step will eliminate bushing bind. We highly recommend periodically greasing the bushings, too.
2. Bottoming Out
Full-on race cars sit nice and low to the ground, so that must be good for all of us, right? Certainly a lower center of gravity pays dividends by reducing weight transfer and the associated body roll. It keeps all four tires working at higher rates of efficiency and does improve handling. Plus, it just looks cool.
But there is a dark side to skimming pavement: The car bottoms out its suspension all the time, unbeknownst to the driver. Riding around on the bumpstops can cause all manner of unusual handling. The car may be wonderful on corner entry but suddenly push like a pig in the middle.
Riding on the bumpstops may also cause even a low-horsepower car to get loose under power. The rear compresses too far and too quickly, transfering too much weight to the outside rear wheel. And we’ve all seen an overly lowered car that drives around town bouncing incessantly on its bumpstop rubber. In this case, the spring rate is near infinite and the damping is practically nonexistent.
A suspension that bottoms out can cause all kinds of handling ills. Keep tabs on suspension movement with zip ties wrapped around the shock absorber shafts or some strategically placed modeling clay. Photography credit: Andy Hollis
The answer is to run the suspension through the entire range of motion without the spring attached. Verify that your bumpstops engage just before a metal-to-metal encounter between the suspension and chassis. Next, reassemble the suspension, secure a zip tie on each shock absorber shaft, and push the zip tie up against the shock body. Then, drive around to see whether the car is bottoming out. The tie will act as a telltale for suspension movement, sliding along the shaft to the point of maximum compression. If it’s bottoming out, adjust the ride height accordingly.
3. Excessive Bumpsteer
In addition to zero suspension travel, there is another, more insidious side effect of lowering a car too much: alignment woes.
Most production automobiles have a wide range of suspension travel, so their suspensions are designed to have benign characteristics within that scope. However, lowering a car can easily shift the suspension into an area where the 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. Just think how bad it would be to drive a car with a rear suspension that toes out as it rolls into a turn.
Figuring out how a suspension will act in its new, lowered state requires about an hour on an alignment rack. Basically, take alignment measurements as the car is raised and lowered. An adjustable suspension is going to help, and we’d recommend taking measurements every half inch. If you’re careful, the process can be done at home with a tape measure or toe plates. Combined with the suspension travel information discussed earlier, these alignment curves can tell you what each end of the car is doing as the suspension moves up and down.
Lowering a car can force the suspension to operate in some unfamiliar territory. Bumpsteer is a common result. Some time on the alignment rack can identify—and hopefully help eliminate—any problems.
For most production cars, there’s only one way to reduce the effects of bumpsteer: Limit the suspension movement through stiffer springs. Don’t forget to match the shock valving, too. Alternatively, you can pre-compensate for things like instability caused by 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 threads a million times on message boards: Need the best alignment for this particular make, model and modifications. A bunch of people will then chime in offering all kinds of tribal wisdom, including “blessed settings” that usually have someone’s name attached to them. On Miata.net, for example, two popular alignments offered are the Lanny Alignment and the Icehawk Alignment.
Are these doled-out alignments any good? Maybe, maybe not. It depends on how closely your car’s complete setup matches the one used to determine the alignment. The two cars also need to share a similar purpose: If they both compete at the same site or track, the settings will be much more helpful.
There is no recipe for optimal alignment. Finding the right camber angles—ones that keep the tires flat during cornering—requires individual testing.
The blow-by-blow procedure for uncovering the optimal suspension alignment for a particular car can be found in the November 2009 issue of Grassroots Motorsports. Here’s the quick version: A stopwatch and skidpad will help determine optimal camber settings, while toe is found using a slalom and an oval.
Those setups from the internet may be a good ballpark, but you must test to find the right numbers for your car, in your situation. This is especially true when you consider our earlier discussion about lowering geometry and bumpsteer.
5. Loose or Slipping Bolts and Adjusters
Once you have that optimal alignment figured out, you’re good to go, right? Wrong. If a suspension component slips under load, you’ll end up right back where you started.
Many of us are flogging older cars, and some of their parts may be far from new. Often, weird handling issues arise when an adjuster has some slop in it. It doesn’t take much movement to deliver positive camber or toe-out in a turn. Sometimes, this is even accompanied by an audible clunk or snapping sound.
The early Miata suspensions originally featured D-shaped eccentric bolts that are known to slip. The new, superseded replacement parts secure themselves with a pair of notches. This is an inexpensive solution to an insidious problem. Photography credit: Andy Hollis
New factory adjusters and bolts are cheap insurance. Install them. You may also wish to invest in some semipermanent threadlocking compound to keep everything in place. Paint marks can serve as indicators of movement. Finally, pay attention to correct bolt torques. The all-too-popular PFT setting—short for pretty effing tight—is not a torque spec.
6. Worn-Out Parts
Although alignment parts can be among the first to go bad, plenty of other worn-out suspension components can still ruin your fun. We’ve wasted a whole day of skidpad testing thanks to a loose upper ball joint, while bad tie-rod ends and worn-out steering racks can cause dynamic toe changes. Bad wheel bearings will do weird stuff to camber, toe and even your brakes.
Finally, check those suspension bushings—especially when they’ve been replaced with aftermarket urethane pieces. Those urethane components typically require yearly maintenance, which should include disassembly, cleaning and relubing. If left untouched, rust can creep in and cause bushing bind, leading to a host of unusual handling issues.
Lurking just beneath that shiny rubber boot is the devil. This ball joint had about a quarter inch of play. The result: dynamic camber changes of nearly three-quarters of a degree. Photography credit: Andy Hollis
Rocking the steering wheel as well as the road wheels will usually uncover worn-out suspension parts. The solution is fairly obvious: Fix what’s broken. Adding zerk grease fittings to brackets can help keep urethane bushings happy.
7. Old Tires
Now we have a tight, roll-resistant, lowered car with optimal alignment and fresh OE parts to keep everything in line. But we’ve still got to make sure the tires are up to snuff. This is especially true when using tires that quickly go through heat cycles, like most R-compound rubber.
Worn-out tires have caused plenty of frustration through the years. What’s worse is that it comes on slowly. In fact, the driver may not even notice how bad things are getting until a fresh set is mounted and the car suddenly handles perfectly again.
Obviously these tires are no longer suitable for service, but how many of us have run tires that were past their prime? Use a simple logbook to keep track of tire life. Photography credit: David S. Wallens
Tread depth is not a good indicator of tire condition, so keep a log for your tires. Track time of use, heat cycles and so on, and you’ll quickly develop a sense for when the performance drops off and by how much. Consistent measurements taken with a durometer and thermometer can be handy as well. Don’t test on junk tires, either, as it’s a total waste of time.
8. Too Much Shock Absorber Valving
Properly damping your new lowering springs will likely require more from your shock absorbers. That said, one size does not fit all, and too stiff is just as bad as too soft.
We know, stiff shock absorbers do feel good. The vehicle becomes super-responsive to every input, and the driver feels totally connected to the road—that is, right up until a washboard surface is encountered and the car chatters off the road. This is an extreme example, but it does show what happens when shock valving is too stiff: loss of grip.
Shock absorber valving and spring rates go together. Dampers that are too soft won’t adequately control the springs, while running an overly stiff shock absorber can lead to traction issues.
There is a compromise between proper control of the spring rate and suppleness over the road or track surface. Optimal valving can provide both, but that may require a custom revalve to achieve.
Off-the-shelf shock absorbers can deliver the desired performance, but only if they’re used in the situations they were designed to encounter. This includes the type of activity—track days, autocrosses, work commutes or whatever—and the aggressiveness of the rest of the setup.
The more you optimize a component for one type of use, the worse it is in other situations. Shock absorbers are the poster child of this concept.
9. Useless Chassis Bracing
While this one isn’t typically a problem per se, it is a common waste of money that slows down the car. Why? Added weight.
Ever since the earliest strut cars came out, enthusiasts have been adding a brace between the strut tops. The goal is to support camber angles when the suspension is loaded in a turn.
That thought process makes sense, but why do you see these braces on double A-arm cars? True, they can be beneficial in some areas, but those usually involve reducing noise, vibration and harmonics.
Unnecessary chassis reinforcements just add weight. Before installing a brace, ask yourself if it’s providing form or function. Photography credit: David S. Wallens
The car may feel better with the part installed, but does it actually perform any better? Without testing, you can’t tell. And the answer is often no.
To test a bar’s effectiveness, tightly bolt down one end while leaving the other only semi-tight. At the looser end, apply some paint between the bar and the strut top.
Now, drive around in a circle at the limit of adhesion and see if any of the paint is broken. If so, how much did the bar deflect? That’s the amount of flex, if any, you are trying to reduce.
10. Too Much Rear Roll Stiffness in a Nose-Heavy Car
This one is the source of endless debate on message boards, especially when it comes to front- and all-wheel-drive cars. The fact of the matter is that, past a certain point, no amount of additional rear roll stiffness will affect the basic steady-state handling of the car. Period.
It may feel like it’s happening, but most of that is carry-over from a corner-entry oversteer condition that’s lasting through the middle of the turn. This is especially true with short corners, like those that are only 90 degrees.
Here’s a breakdown of the physics involved: Once you have transferred all the weight off of the inside-rear wheel, any additional weight transfer due to cornering forces has to come from the front. The ratio of front to rear roll stiffness controls how that weight transfer occurs, but only up to a point. After that, the car will suddenly move toward understeer.
The more rear roll stiffness, the more drastic this changeover can be. What’s worse, the point will be different depending on the grip level of the surface and tires. What may be great on concrete will be too snappy on asphalt—and totally undriveable in the wet.
Additionally, more rear stiffness will not affect body roll once past the point of total rear-weight transfer. Body roll is the result of weight transfer, and at any given lateral acceleration only so much of that can happen at the rear. The rest will happen at the front, and the car will roll more.
Once a car is lifting its inside-rear wheel under hard cornering, only the front suspension is adding cornering forces. Increasing rear-roll stiffness can just lead to drastic handling swings. Photography credit: David S. Wallens
Once the inside rear starts getting light in the turns, your only method of reducing body roll is to add more front roll stiffness through either springs or anti-roll bars. This will reduce the amount of chassis flex induced by the heavy rear bias. It’s also the key reason why well-balanced cars with 50/50 weight distributions—BMWs, Miatas and the like—handle so well and are so easy to make even faster.
Some Parting Advice
Anything discussed here sound familiar? If so, heed our advice and you’ll save yourself a lot of frustration.
When things just don’t seem right with your car’s handling, investigate. Some problems are obvious, but others hide themselves well. Many times the fixes are inexpensive or even free. Check everything with our plan of attack and you’ll be well on your way to the best driving experience ever.