Sorry if this sounds sarcastic, but this pertains as much to component wear as whether your shoes wear as much if you walk in circles vs. Standing in one spot and turning around. While doing an alignment, it is necessary to turn the wheels left and right by hand. It takes very little effort to do that compared to if you were to try to hold the wheels straight by hand while driving. Road forces from hitting bumps in the road and from normal braking put a real lot more stress on the parts than simply turning the steering wheel while standing still. If a tie rod end were sweating from trying to turn a wheel while standing still, it would be dying from exhaustion each time the brakes were applied.
The reason you think there's excessive stress on the parts is that's what you feel when you're trying to turn the steering wheel. The steering system parts are just doing what they're designed to do. You may be influenced too from previous negative experience, especially if you owned a front-wheel-drive Ford product. Some of their models from the '80s were well known to have worn tie rod ends in as little as 15,000 miles, and the original equipment replacement parts didn't last any longer. Your car doesn't have that problem in its history.
To add another dimension to this sad story, you have to look at "caster". That's one of the three main alignment angles although it's usually not adjustable on front-wheel-drive cars. If you look at the strut from the side of the car, you'd see the top is more to the rear than the bottom. If you had upper and lower ball joints, the upper one would be more to the rear than the lower one. That's "positive caster". Many years ago we had negative caster. That made for real easy steering on heavy trucks with no power steering. In the mid '60s when we started driving faster, we went to positive caster because it makes for a more stable car at higher speeds. Less steering correction was needed to keep the car going straight. The problem is that makes for harder steering, so we added power assist.
To explain what caster does, imagine if your steering pivots were that upper and lower ball joints. If they were straight up and down, that would be 0.00 degrees. A common alignment spec is around 3.00 degrees meaning the upper ball joint is more to the rear than the lower one. (This can be seen in the fork of a motorcycle too by the way it tilts to the rear on top. That would typically be about 15 degrees). Now, to exaggerate for clarity, suppose you kept tilting the upper ball joint and spindle more and more to the rear until the upper ball joint was straight back from the lower one. That would be 90.00 degrees, and of course that is not practical, but look what would happen now if you turned the left wheel to the left. It would try to pivot down into the road, or in this case push that corner of the car up. You're raising the car with the steering wheel.
For that part of my story we're using 90.00 degrees, but even with the common 3.00 degrees, you're doing the same thing. When you turn to the left, the left wheel causes that corner of the car to go up, and on the right side, that corner goes down. When you let go of the steering wheel, those two ride heights want to equalize, just like with two people on a teeter totter. That equalizing is what causes the steering wheel to return to center by itself.
My reason for mentioning all this is if you only had one wheel to work with, as in when parts in the steering system are disconnected while the car is on a drive-on hoist, when you set the car down so its weight is on the tires, that 3.00 degrees of caster will cause that wheel to turn toward the center of the car so hard that you will need both hands and a lot of grunt to tug it back straight. That's just with 1,000 pounds of car weight on that wheel. You can have four or five that much weight momentarily when you hit a bump or pot hole. There is no way you could hold that wheel straight by hand, but when the other wheel is doing the same thing in the opposite direction, and you connect them with a steering linkage, they offset each other and you don't feel that stress on the parts. In fact, that constant hammering is WAY more important as far as wear than the microscopic wear from turning the steering system while standing still. If turning while standing still caused excessive wear, the parking lots would be full of cars with worn parts.
To say this a different way, if we used a scale of 0 to 100 where "0" means no wear at all, and "100" means the force was sufficient to break a part, I'd estimate the force from hitting a pot hole is 20, from normal braking is 15, from turning while standing still is 3, and turning while moving slowly is 2. It really never comes up in discussions in suspension and alignment classes because is not a contributing factor in the life of parts.
Monday, April 27th, 2015 AT 9:29 PM