Replacing Four Tires: Do I Need an Alignment?

Factual Questions
21

If I was not considering getting an alignment before I got new tires. . .I would ask them why they think I need one. If they impressed me with their explanation, then maybe I would. I would ask a lot of questions. Then let them know. I don’t think you should feel pressured into it. That’s not the kind of place I want to do business with.

I go to a place that insist upon replacing the rotors along with the brake pads. . . I think that’s BS, but I’ve done it. I like the place and generally trust their judgement, and the money is not a major problem.

Come to think of it, probably most auto maintenance is not really needed. Really. But, I want my car to last a long time.

22

If you are replacing rotors every time you replace brake pads, then that is definitely BS. Either that or you are braking WAY too hard.

One reason to replace the rotors is that you have worn them down too far. Back in the old days, rotors were a lot thicker and it was difficult to wear them out. These days, rotors are made to be very thin to save weight and eke out that last tiny fraction of a mile per gallon in the car’s performance. But still, you should go through several sets of brake pads before needing new rotors.

The second reason is if you do a lot of hard braking. The excessive heat from such braking can warp the rotors. Again, in the old days, rotors were a lot thicker, so all you needed to do was machine the rotors down flat to get rid of the warp and you’d be good to go. Todays thin rotors often can’t be machined since machining them even once will put them below their minimum thickness spec.

It’s the same thing if you let your brakes go too long and grind them down to metal-on-metal (probably not an issue for you, but could be an issue for those who ignore that horrible squeak when the pads get too thin). In the old days you could machine out the grooves you made in the rotors, but these days the rotors are too thin to do that and they must be replaced.

If you feel a pulsing when you press on the brake pedal, that could be a warped rotor. So if you feel that and the mechanic wants to replace the rotors, that’s probably not BS. If you feel a grinding when you press the brake pedal, then that’s also probably not BS.

I personally replace both rotors at the same time, so if a mechanic says one is bad but wants to replace both, that’s not BS either. You can end up with uneven braking (the brakes pulling to one side) if you only replace one of the rotors.

The next time your mechanic says the rotors need to be replaced, ask them why. If they say the rotors are too worn, ask them what the micrometer measurement was and what the minimum spec is. If their reason is more along the lines of “better safe than sorry” then that’s BS.

23

The GMC dealer I do business with has a lazer machine that checks alignment when you use the quick oil change service. When I had the tires on my 2018 Acadia replaced in the fall of ‘22 they checked it at no cost (which they do routinely on any quick lube service au gratis) and alignment wasn’t needed. However as other posters have said, I would agree that checking alignment at minimum should be done with new tires.

24

In the old days the saying was “set the toe and let ‘er go”, there isn’t necessarily all that much that is easily adjustable, or maybe more correctly unless someone is banging into curbs there isn’t much to get out of alignment.

Lots of DIYers used to adjust or check the toe-in with little more than a set of jack stands and carpenter’s string. “Toe” is just the slight adjustment made to the front tires, they are slightly splayed in or pigeon toed to counteract the tendency for the front tires to splay out when the car is rolling forward. I think the net effect is the tires run straight and true rolling down the highway. If this adjustment is defective the tire or tires will “scrub” the road surface excessively and wear rapidly or unevenly. Camber and Caster are less likely to be a problem and settings are probably built in to the axle.

I don’t believe many cars have a “toe out” do they? Anything is possible I suppose.

25

Race cars.

Slightly toe-in gives you more stability, which is good for normal driving. When you are racing and you want performance in turns, stability makes the turns a bit sluggish. If you set the front wheels slightly toe-out, then the tire on the inside of the turn pulls the car into the turn more quickly. The weight of the car then shifts to the outer tire for the remainder of the turn which keeps it stable.

The cost of more responsive turning by making the car slightly toe-out (aside from additional wear on the tires) is that you reduce your straight-line stability.

For basically the same reasons, if you like drifting, you don’t want stability in the turns, so setting the car toe-out is going to make it drift more easily.

Most cars are slightly toe-in because that gives you the best stability. There might be some performance cars that have either no toe or are slightly toe-out, but outside of racing or performance cars and drifting I’m not aware of any cars that are designed to be toe-out.

26

That depends on a number of factors:

  1. How old is your car, and when is the last time (if ever) you had an alignment?
  2. How much do you drive, and what is the condition of the roads?

I deal with Chicagoland roads and high speed interstate driving. After 2 1/2 years, my tires are very worn. When I go to “Just Tires” on Columbus Day for 4 new ones, I’m going to emerge new, balanced and aligned before the winter weather begins.

On the other hand, if your mileage is minimal, not high speed interstate, and you drive like “Miss Daisy’s” chauffeur, you may very well not need an alignment.

27

Hm - is that maybe why go-karts are kinda squirrely and “touchy” in the handling? They sure do handle responsively.

28

Some of that is due to how far the wheels turn vs. how much you turn the steering wheel, but yes go-karts do tend to be adjusted to be slightly toe-out. Castor seems to affect how squirrely and touchy go-karts are as well. You can adjust them with a bit more castor and the steering will become less twitchy, but then they will be less responsive in the turns. Most people seem to prefer them twitchy.

29

“Castor” is a plant whose beans can produce a nasty oil.

“Caster” is the attribute of wheels and axles.

Caster has little to no impact on tire wear. Excess caster produces heavy(er) steering and a strong(er) tendency for the steering wheel to return to neutral when released. The effect is subtle within normal ranges of running gear design.

When reversing, if you crank the steering wheel & let go it’ll try to wind all the way to hard left or hard right rather than returning towards neutral. That’s a direct consequence of caster being negative in the reversing direction. While moving backwards, caster is a positive feedback loop not a negative one.


Switching to camber:
Old fashioned cars with rigid axles tended to have limited camber adjustment. More modern cars with modern suspension have camber adjustments as well. Which if mis-set will wear the inner or outer edges differently.

Here’s some limit cases of badly set camber: Extreme camber - Google Search. These of course rely on custom suspension components to get that weird, but ordinary car suspensions can achieve much smaller values of the same effect, with the obvious consequences for tire wear and tire adhesion.

30

I spel gud.

I’m an engineer, what do you expect? :stuck_out_tongue:

Thanks for the correction.

31

My computer has learned to substitute all sorts of words for similar words. I swear they’re crowd-sourcing their spell checking these days with some of the silly stuff it comes up with.

32

I did the deed today. Told the guy that I didn’t think it needed an alignment but if he disagreed to call me. He didn’t, I didn’t get one, I feel empowered now.