Front struts

  • 2009 PONTIAC G5
  • 4 CYL
  • FWD
  • 134,000 MILES
I know the front struts need to be replaced. But are they the sole reason the front tires wear down fast?
Do you
have the same problem?
Tuesday, January 5th, 2016 AT 7:05 PM

1 Reply

That is exactly backward. Struts simply hold the wheel in the position it is aligned to. A badly worn strut can add to tire wear in two ways. The first is if the oil leaks out or the valve wears and lets the oil flow too freely. You'll have excessive bouncing long before bad tire wear shows up.

The second is if the upper seal is so worn that the shaft can wobble back and forth. That is what lets the wheel move in and out on top. That tipping, as viewed from in front of the car, is called "camber", and is the one of the three main alignment angles that has the largest effect on tire wear. A sloppy lower ball joint can cause a change in camber too but the effect on tire wear is much less than from a worn strut.

In an attempt to make light-weight cars ride better, most manufacturers have switched to a softer rubber compound for control arm bushings. That softer rubber wears out faster than the old bushings did. On older cars those bushings typically lasted the life of the car. Today failures are very common. A worn bushing will let camber change too but you'll also notice a knocking or thumping noise, and a constant need to correct the direction of steering.

The second most important alignment angle is "toe". That's the direction the wheels are steering when the steering wheel is straight ahead. The two wheels should basically be perfectly parallel to each other. When either wheel or both are set wrong, both tires will scrub along the road. When incorrect total toe, (both tires measured together), is relatively minor, you'll feel and possibly see a feather-edge pattern on both tires. When it's real bad, direction of steering will be unpredictable and the car will respond to cross-winds and tilted road surfaces.

A sloppy tie rod end is a common cause of incorrect total toe. More importantly, due to the inter-related steering and suspension geometry, a change in camber on most cars will result in a change in toe on that wheel. A change in toe will not cause a change in camber. For that reason, camber is always what is adjusted first on both front wheels, and toe on each wheel is always adjusted last.

You didn't list the mileage, what is wrong with the struts, or why you think they need to be replaced, so I can only suggest that the struts are just one of many parts that affect wheel alignment, and a bad strut is the sole cause for tire wear perhaps two or three percent of the time. By far bad tire wear is caused more by incorrect alignment on one or both wheels due to simple misadjustment or worn ball joints, tie rod ends, and control arm bushings.

When a quick visual inspection fails to reveal worn parts, and the alignment numbers on the alignment computer appear to be correct, the final and most elusive cause of bad tire wear is sagged springs. Altered ride height, whether from a lowered car suspension, raised truck suspension, (both real bad ideas), or weak springs, changes the suspension parts' geometry and interaction. Sagged springs will cause accelerated tire wear even when parts and the alignment are fine. The wheels are designed to tip in and out on top just a little as the car body bounces up and down. That reduces tire wear as they slide left and right across the road surface. Incorrect ride height makes the tires tilt too much or not enough. Not enough tilt make the entire tread surface scrub across the road. Too much tilting causes them to ride on one edge, which then wears real fast.

The people at tire and alignment shops are experts at identifying worn parts and the causes of noises, vibrations, and bad tire wear. A conscientious alignment mechanic will inspect the steering and suspension systems, and he will measure the ride height before taking your money for an alignment. If the springs are sagged from age, the best time to replace them is when the struts need to be replaced because to replace the struts, the springs have to be removed from them and transferred to the new struts. "Quick Struts" are available that have the struts, springs, and upper strut mounts already assembled and ready to install on the car. Parts cost just a little more, but the labor time is reduced a lot. Many mechanics quote these units, even though they are slightly higher in cost, because the entire job gives the owner a higher-quality repair at a lower overall cost.
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Tuesday, January 5th, 2016 AT 8:18 PM

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