10 common suspension problems and how to cure them

Staff
By Staff Writer
Sep 7, 2021 | suspension, Shop Work, Handling | Posted in Shop Work , Suspension & Handling , Features | From the Oct. 2021 issue | Never miss an article

Photography Credit: Chris Tropea, J.G. Pasterjak (inserts)

Looking to make your car faster? Don’t underestimate the power of suspension upgrades. Most people take their suspension cues from fellow enthusiasts–buddies or message board gurus who own a similar car. Peer acceptance of a parts combination can be quite reassuring, but can these formulas really be trusted?

Despite the hype and online chatter, sometimes you need a methodical investigation into the facts. Let’s explore some common suspension problems and how to achieve the best results.

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 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 your wimpy Miata to get loose under power: The rear compresses too far and too quickly, transferring too much weight to the outside-rear wheel. And we’ve all seen the extreme case of a too-low car making like a pogo stick as it rides around town on the undamped, high spring rate offered by the bumpstop rubber.

Photography Credit: J.G. Pasterjak

The Cure:

The answer is to run the suspension through the entire range of motion without the spring attached. Verify that your bumpstops hit just before a metal-to-metal encounter between the suspension and chassis. Next, reassemble the suspension and place a zip tie on each shock absorber shaft. The zip tie will act as a telltale for suspension movement, showing exactly what’s happening.

Push down the zip tie on the shock body. Then, drive around to see whether the car is bottoming out. If it is, adjust the ride height accordingly.

Old Tires

So now we have a tight, stiffened, lowered car with optimal alignment and fresh 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 testing and competition 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–that is, until a fresh set is mounted.

The Cure:

Tread depth is not a good indicator of tire condition, so keep a log for your tires. Track the 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. A durometer coupled with a consistent measuring technique (including temperature) can be handy as well. Don’t test on junk tires, either, as it’s a total waste of time.

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 so-and-so.”

Next, a bunch of people chime in with all kinds of tribal wisdom. Is it good advice? 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 can be closer to optimal.

The Cure:

Those setups from the internet may get you near the ballpark, but how about some real testing using your own car? A stopwatch and skidpad will help determine optimal camber settings, while toe is found using a slalom and an oval.

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 fresh. Oftentimes, weird handling issues arise when an adjuster has some slop in it. It doesn’t take much movement to deliver positive camber or toeout in a turn. Sometimes, this is even accompanied by an audible clunk or snapping sound.

Photography Credit: J.G. Pasterjak

The Cure:

New factory adjusters and bolts are cheap insurance. Install them. You may also wish to invest in some semi-permanent threadlocking compound to keep everything in place. Paint marks can serve as indicators of movement. Finally, do pay attention to correct bolt torques. The all-too-popular PFT setting–short for pretty effing tight–is not a torque spec.

Anti-Roll Bar Bind

One of the most satisfying suspension mods 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, no.

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: an infinite roll resistance at that end of the car that will absolutely destroy the handling.

Photography Credit: J.G. Pasterjak

The Cure:

We have two easy fixes for the common D-shaped bushings supplied with most anti-roll bars. Either grind away some material from the flat portion of the bushing or fit a washer under one or both sides of the saddle bracket. We highly recommend periodically greasing the bushings, too.

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 carryover from a cornerentry 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’ve transferred all the weight off the inside-rear wheel, any additional weight transfer is due to cornering.

The more rear roll stiffness present, the more drastic this changeover can be. What’s worse, the point will differ 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.

The Cure:

Once the inside-rear starts getting light in the turns, your only method of reducing body roll is more front roll stiffness via springs or anti-roll bars. This also helps to reduce the amount of chassis flex you’re inducing with the heavy rear bias on every turn.

This is the key reason why well-balanced cars with 50/50 weight distributions–like BMWs and Miatas–handle so well and are so easy to modify to go even faster. By the way, if you have a rear weight-biased mid-engine car, take everything above and switch those two words.

Once the inside-front starts getting light in the turns, your only method of reducing body roll is

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 strange things 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: disassemble, clean and relube.

Photography Credit: J.G. Pasterjak

The Cure:

Rocking the steering wheel as well as the road wheels will usually uncover worn-out suspension parts. The solution is obvious: Fix what’s broken. Adding zerk grease fittings to brackets can help keep urethane bushings happy.

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 mushy.

We know, stiff shock absorbers do feel good. The vehicle becomes superresponsive to every input, and the driver feels totally connected to the road–that is, until they encounter a washboard and the car chatters right into a ditch. This is an extreme example, but it does show what happens when shock valving is too rigid: loss of grip.

The Cure:

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.

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, autocross, street 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 at other uses. Shock absorbers are the poster child for this concept.

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 abrace between the strut tops. The goal is to support camber angles when 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 situations, but those usually involve reducing noise, vibration and harmonics.

The Cure:

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.

Excessive Bumpsteer and Ridesteer

In addition to zero suspension travel, there is another, more insidious side effect of lowering. 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 horrible it would be to drive a car with a rear suspension that toes out as it rolls into a turn.

Figuring out how a chassis will act in its new, lowered state requires about an hour on an alignment rack as its suspension is moved up and down through its range of motion.

Photography Credit: J.G. Pasterjak

The Cure:

For most production cars, there’s only one way to reduce these effects: 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.

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. Check everything with our plan of attack, and you’ll be well on your way to the best driving experience ever.

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Comments
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Shaun
Shaun GRM+ Memberand Dork
8/6/21 11:39 a.m.

This sort of relates to 'useless chassis bracing' by making a useless brace work:  I've noticed on three cars that had 100k plus on them that tightening the bejezzus out of the fastners that join the steel weldment that serves as the chassis for the dash sub assy to the cars frame firms up the steering feel, makes the car stiffness a few Hz lower, and wipes out some dash rattle & squeek for the price of a skint knuckle or two.    

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