Question: Alignment, vs tire wear? [Archive] (2024)

mx5mia

12th November 2007, 12:47

After installing new tires about 6,000 miles ago, I had a 4 wheel alignment done. Spec's were set as follows:

Front caster: both around +5 degrees
Front Camber: -.8 each side

Rear camber: -1.3 both sides

Front and Rear Toe-In: 1/16" combined

The car has driven and handled very well, and I am happy with the results. When I recently rotated the tires, I measured the tread depth with a dial calipers near each edge, and in the middle. I wanted to see the results of the alignment on tire wear.

Tread depth was greater on all wheels in the middle, so I increased tire pressure 2 psi to 31 psi, and it now responds to input and corners even better. I like this.

But the tread depth measured less along the inside edges of all 4 tires, than the outside edges.

I drive the Miata daily for commuting to work, plus occasional spirited drives with the club. No autocross, or racing.

To get the inside edges wearing more like the outside edges, should I decrease the camber a little, or decrease the Toe In a little?

The car tracks very nicely on the 4 lane, and just a tiny bit of steering wheel movement is all that is needed to zip from one lane to another. Plus the tires feel firmy planted in the corners. More so now with the extra air pressure.

Or,.. might the increase of tire pressure push the center of the tire out more and result in more even wear from this?

Wear difference is not major, but as I am trying to learn more about alignment and how it affects car handling verses tire wear, I thought I would ask this question.

Thanks for your help!

Lanny Chambers

12th November 2007, 14:43

You're probably not driving hard enough, often enough, for the alignment you have. But if you're completely happy with the car's handling, you might want to accept the wear and simply enjoy what you have while it lasts. Rotate the tires front to back at every oil change.

My soft Toyos always get too hard to tolerate before they hit the wear bars, so I don't pay much attention to how they wear. When they no longer stick well in rain, I replace them.

socal pat

12th November 2007, 15:16

mx5mia

12th November 2007, 15:44

Thanks to you both. As I said before, the tire wear was not a major issue, but I was using what I found as a learning tool.

I do not want to degrade performance, as I love the car the way it is! I can't drive too much harder, based on the roads and where I drive.

I drive it over 15,000 miles a year, so rotating every 6,000 miles is enough for me. (Other responsibilities)

Thanks for the feedback! :)

POPSTOY

12th November 2007, 17:14

mx5mia

14th November 2007, 11:46

Another trick is to have the tires swapped side to side, yes that means dismounting and remounting them. I usually do this once during the normal life of the tire. The tire place I go to, gives free repair, lifetime balance, and rotation, whenever I want. Typically if prearranged and written in the service contract, they will swap them once for free. That's why I keep going back to them for anything involving tires. Bob

Thanks for the input,....

Since I use my Miata for commuting, I have on it "High Performance V rated Touring Tires". (not High performance cornering tires) I rotate these in the X pattern, since they are not directional.

I move the rear (driven) tires straight front, and cross the front tires to the back. This has worked for me ever since I have been driving (1965), radial or not tires.

Since this situation is the same on the inside edge for all 4 tires, I doubt if rotation would make any difference.

Again, the amount of wear is not the reason for this post, but I am using this to try to learn more about my Miata and alignment verses handling and tire wear.

Thanks again! :)

wooo

14th November 2007, 12:01

... I rotate these in the X pattern, since they are not directional.... Since this situation is the same on the inside edge for all 4 tires, I doubt if rotation would make any difference...You are correct, the sort of rotation you mention will not effect this type of wear.

However the dismount, remount, and rotate method mentioned by Popstoy will have an effect because it swaps inside edge to outside edge for each tire. I'm not sure what the other (original inside) face of the tire looks like, but appearance shouldn't be a problem with blackwalls, even though you are now presenting the "inside face" to the world.

wooo

14th November 2007, 12:31

After installing new tires about 6,000 miles ago, I had a 4 wheel alignment done. Spec's were set as follows:.....

But the tread depth measured less along the inside edges of all 4 tires, than the outside edges. ...Mine's an NC and I gave it an alignment similar to yours. I've only done about 3,000 miles since so it's hard to tell but I seem to be getting slightly more inside wear on the rear.

I try to imagine what happens as the car leans in a corner. Let's say you get 2 deg. of body roll, so relative to the ground the tires get decreased negative camber for the outside tires, and increased for the inside tires. However at the same time because the outside wheel "bumps" and the inside wheel "droops" then there are camber changes because of the camber curve (available elsewhere). Let's say this is 1 deg more negative for bump, and 1.0 deg less negative for droop.

So now you have the camber (theoretically) of the tire relative to the ground as:
outside = -0.8 + 2.0 - 1.0 = + 0.2 (almost flat to the road),
inside = -0.8 - 2.0 + 1.0 = -1.8 (not flat to the road, but not the high load tire).

Did I get that right? :O

Anyway more to the point the tires will present themselves to the road in different ways for each driving condition (straight, easy corner, hard corner, left, right). The resultant wear is a mix of all this. If you want to minimize wear then adjust camber to get even wear ( less negative camber for less inside wear). However as has already been pointed out now you won't have camber optimized for hard corners. So in that case a bit more negative camber, and resultant inside wear might be a good thing.

IMHO. :)

mx5mia

14th November 2007, 13:12

Now that I have several replies, I will mention what one local person told me concerning this inside wear.

He said that too much toe-in will wear the inside edges of the tires more than too much negative camber will.

What do you think of this statement??

I understand that the negative camber is to have the tire tread sitting flat on the road in a hard cornering situation. This makes sense to me. I also understand this has the tire "co*cked" at an angle to the road on straight line driving.

My thinking leads me to think that The negative camber can cause the tire to wear more on the inside, if I do not do enough hard cornering.

I understand toe-in is somewhat to offset the effects of the rubber bushings in the suspension. By setting the toe to the "in" direction, the bushings flex while driving, and the wheels end up more straight ahead (not totally straight, but closer).

Trying to draw a conclusion that makes sense to me.... I think the reason this looked to odd to me is because the middle of the tires had more tread depth. Possibly the tires were underinflated some for my type of driving, and the alignment settings. "I think" the underinflation caused the tires to contact the road more on the edges, less on the center, and now I have the uneven wear exaggerated.

So I increased the tire pressure by 2 psi. I am now running 31 psi. I ran the last set of these at 26 for a while, and the sidewall was mushy and handling was not so great. Increasing the psi to 29 helped. Then trying to avoid a fender bender, I flat spotted all 4 tires so bad I had to replace them. I started this set at 29psi, and above posted the results on the first rotation.

So in 5-6 month's I will have another 6,000 miles on them at 31 PSI, and I will see if this helped.

One last question,.. Do you think the 2 pound change up from 29 to 31 is enough?

Thanks to all for your help! :)

POPSTOY

14th November 2007, 13:39

davidb

14th November 2007, 14:07

Lanny Chambers

14th November 2007, 14:54

He said that too much toe-in will wear the inside edges of the tires more than too much negative camber will.

That is correct--it will tend to scrub the tread sideways, all the time. But your toe isn't even close to excessive, so no one mentioned it. (Assuming your numbers were actual results, not just the target.)

You still haven't told us what size and brand/model of tires and wheels you have. In most cases, 28-29 psi (cold) is plenty, but there are exceptions.

The reason to rotate front-back: most Miatas wear their rear tires about twice as fast as the fronts. There's no advantage to crossing them side to side, unless you enjoy the extra work.

Don

14th November 2007, 19:13

I think that even with excessive toe-in, you would still need some negative camber to wear the inside edges more than the rest of the tire - With zero camber, the scrubbing would be even across the tread and not wear the insides any more than the centers or the outside edges . . . . so I think your friends statement is basically . . . . bunk

Don

davidb

14th November 2007, 23:44

Lanny Chambers

15th November 2007, 00:57

mx5mia

15th November 2007, 10:08

Believe it or not I have followed everyone's comments, and appreciate the input.

I understand the idea of making changes until I am happy. At 26 PSI the sidewalls were mushy, and the car didn't handle well at all. Going to 29 psi made a noticable difference, but not a "great difference". But leaving it at 29psi for a while still gave me more wear on the outside 2 edges, and less wear in the middle. Hard cornering left the tires feel soft when I pushed it.

The recent change up to 31 psi made a great difference in cornering and grip on the road. I can't believe how adding 2 psi made such a difference. The car responds to steering input much quicker, and the grip in a corner so much better. It feels like I installed new tires. This makes me think I am getting close to, or at the potential of the tires.

My question if adding 2 PSI was enough was more of a generic question. When you people make pressure changes to a tire for experimenting, do you change one psi at a time, or "several" psi? I have a dial type pressure gage, not a stick type, so that is a little more acurate for me to read. I was wondering if I should have went 3 psi more, or if 2 psi would be enough to make at a time.

I specifically didn't state what tires I am using, as I am running a Performance "V" rated "Touring" tire, not a performance rated "cornering" tire. The last time I reccommended these to someone using a Miata for commuting I was about laughed off the forum by the high performance cornering and autocross guys. I didn't want to go thru that again, as these tires have proved perfect for "My Use" over the last 25,000 miles, on 2 Miatas.

I drive my Miata over 15,000 miles a year for commuting to work, and on spirited drives with my club. They work super for me. The size is 195-55R-15. The 55 series is 3% more around the circumference, so it gives me a couple percent savings in fuel over a years time. (speedometer closer to accurate too)

The settings I reported inthe first post were from the actual printout of my alignment. I gave him the numbers I wanted, and he nailed it. That tickled me! :)

So I am trying to learn how to get the "best" out of a tire I am already pretty happy with. :) And using the situation I am in as a tool to learn about my Miata! Maybe I will get a digital non-contact thermometer and check the tires after a drive home from work.

Thanks to all for their input so far.

Lanny Chambers

15th November 2007, 14:30

POPSTOY

16th November 2007, 12:04