Does the macadem road surface have a great effect on tire wear?

[Arlen G. Holder]

Does the macadam road surface have a great effect on tire wear?

In a previous thread, we discussed tire wear on downhill slow speed (less nominally around 30mph) steering lock to steering lock twisties due to suspension geometries (e.g., camber scrub on the outside edge of the inside tire due to positive caster induced from SAI+IA, with a correspondingly confusing negative force-vector related camber on that same inside wheel).

When I mentioned that to neighbors, they told me that they considered their high tire wear due to the road surface being not all that smooth.

The road surface happens to be not of the best quality, in that it's certainly not "packed" as well as a highway would be, such that, even at times, I've seen mushrooms pop up out of two inches of macadam.

If we assume the road surface isn't well packed, the question is whether tire wear is "appreciably" affected by that road surface?

I didn't see anything in the Gillespie bible on the subject, but I didn't read every page because my head was already spinning just by looking at the diagrams.

Does the macadam road surface have a great effect on tire wear?

[micky]

The one of the right front corner shows that you need a wheel alignment.

[Arlen G. Holder]

It's my fault for showing the tires, where all I wanted to show was the pavement. I'll snap a photo of _just_ the pavement separately, where for te purpose of this thread, we can ignore the vehicle itself in that photo.

I understand that it _looks_ like an alignment problem in that photo, but this happens to _many_ of the cars on this mountain, and, in particular, this vehicle has been professionally aligned by BMW themselves so I can only conclude that the alignment is ok.

Xeno, in another thread, showed this picture, which, I think, is really what's happening in turns, but that's discussed elsewhere:

The only reason for this picture in the OP was to show the road surface.

Please ignore the vehicle.

The thread on that specific "camber scrub" is over here: o Clare - are smaller car tires easier to balance than SUV tires?

And partly here too o How would you run a lateral acceleration test in a vehicle on twisty roads at no more than 40mph?

Where, on turns, a specific "camber scrub" is occurring (we think):

In contrast to that problem set, _this_ thread, is only about how much effect the macadam road surface has on tire wear.

[Thomas]

It is the reason for wear. If you never turned all 4 tires would wear evenly. I never turn the wheels in park. Pure friction. I only start to turn when in motion. I actually think about it.

[Clare Snyder]

Looks like pretty decent ASPHALT to me. Definitely not "Macadam" - or tar and chip.

[dpb]

On 6/25/2019 5:36 PM, Frank wrote: ...

And inflation and driving habits...how aggressive is the dude/dudette?

Then you get into the tire itself....

[Arlen G. Holder]

Thanks Frank, where I never knew there was a difference between Macadam and asphalt.

What would you call this stuff I just showed Clare?

The problem is that these vehicles ALL have the same wear patterns to the OUTSIDE edge, where a tire "rotation" won't help unless we flip the tire on the rim, am I right?

BMW:

Lexus: Toyota:

All are aligned and owned by different people, which averages out the driving habits, wouldn't you think?

The only common factor is the road. o Either the surface (or crown)

o The shape of the road

The main question here is what effect the road SURFACE has on this wear?

[Arlen G. Holder]

Hi Thomas,

Thanks for the advice to "not turn", which, well, which might be a little problematic, given that this is a typical turn where the steering wheel goes from lock to lock at a reasonably steep incline.

[Arlen G. Holder]

Hi Clare, Thanks for suggesting that where I always "assumed" macadam and Asphalt were the "same" thing, but where you make a distinction, which I appreciate, and where this is the overall surface at the moment:

Here's a snapshot of the "layers" that I took this morning for you:

Some people called the lower layers "chip seal", where I'm a bit confused as to how people use the terms "asphalt" and "macadam" but I'm using it interchangeably (our of ignorance).

Nonetheless, the question is whether _this_ road surface is having any major effect on the wear of the tires given the road is windy and steep such that the trucks gouge many of the corners like claws scraping at the surface.

While the road surface is pretty smooth where many of the turns are almost unnoticeable, such as this gradual almost flat curve

Some of the turns you do notice though, such as this basic hairpin:

The end result of either the curves or the road, is this type of one-way unidirectional feathering on the outside edge of the front tires:

It doesn't only happen to my vehicles, as I've inspected quite a few, such as this Lexus SUV today.

Do you think the MAJOR contributor to this Lexus SUV wear has much (if anything) to do with the coarseness of the road surface?

It seems to be the same as this BMW SUV wear, doesn't it?

Both are impeccably maintained by the stealer, and both travel the same road where, the diagnostic goal is to figure out whether the road surface has any appreciable effect on the reputed "camber scrub" we've been discussing.

[Clare Snyder]

"Chip Seal" is Macadam

It would wear less on loose sand - or perhaps gravel or packed limestone dust - but it would wash out during every rain storm. What you have is the best compromize.

The car needs the alignment "customized" for the road. The ONLY thing that will stop the problem is more negative camber on the outer wheel through the turn. The easiest way to do that is to add negative camber to the alignment. Changing caster can change the camber on turns too, but adds a layer of possibly unforseen side-effects. -1 to -1.5 degrees caster added to both front wheels will reduce the wear SIGNIFICANTLY without causing any noticeable change in handling (at least negative changes)

[Xeno]

Not if you remain within specs, as I suggested. Caster *aggravates* the camber roll on turns. Running it down to minimum spec keeps the handling as specified by the manufacturer.

On the other hand, if the car already has a spec of +1 to +1.5 camber, and you reduce it by that amount, that means you have effectively no

*static* camber so steering will be guaranteed to be vague in the straight ahead position. What's more, steering will be heavier in turns and more liable to be affected by steering shimmy.

That is precisely what I have been saying, drop the caster.

[Arlen G. Holder]

Hi Xeno & Clare,

One thing that I shouldn't be confused about, but that I am, is that most people I asked said they had NEGATIVE front and rear camber.

NOBODY said their static camber was positive.

Does that make sense?

Also, if you look at the road, it has a high'ish crown, given that it's never flat even once since it's a long five miles of twisty mountain grade.

It's so steep in mosts places that trucks literally run off the road or dig INTO the road, surprisingly:

Two thought questions about the CROWN of the steep twisty road:

1. How does the crown affect the customization of alignment for tire wear? 2. Is the crown part of the wear problem (we haven't mentioned it yet)?

[Xeno]

On 27/6/19 3:46 pm, Arlen G. Holder wrote:

Yes. It depends on how the manufacturers set up their cars ex factory and what they have in the specs. It has to be said too that a lot of people wouldn't know the difference between positive and negative. Have you looked up the actual specs for these cars? FWIW, FWD cars tend to be a little different because they *drive* the front wheels. Also, a car with struts is going to get less camber roll under weight transfer/suspension jounce. Because of this, they may start at less camber, even 0, and then have a limited movement into negative territory. Different suspension types have different sets of compromises and you need to look at the specs of each car in terms of suspension type and drive arrangement. Look at this one for example.

Focus on the Camry 4 cyl spec - it's -0.72, not a range, just a preferred setting. They just give a tolerance on top of that. The tolerance is +/- 0.75 so you could have the camber set to anywhere between 0 and -1.5 degrees of camber, noting that the higher your static camber goes, the more likely you are to have camber wear issues in straight running, made worse with wider tyres. If you look at the SAI, it is close to 12 degrees - at the top end of SAI specs. That means this car will be less reliant on caster for self centering of the steering. The caster settings at what appears to be 0 +/- 0.75 seems to point to that. Certainly, at a zero setting, caster won't be doing much to influence steering self centering and, it has to be said, won't be worsening the effects of camber roll.

Your road is more than cambered, it's superelevated, that is, the road has a cross slope on its full width. This not only assists drainage but helps vehicles round the curve, the cant assisting the turning vehicle even at slow speeds. We have a severely off cambered roundabout here that regularly catches trucks out. Saw a tanker over on its side recently when the driver misjudged the curve.

You can vary the caster slightly to compensate for the crown, at least a

*normal crown*. A little more on the nearside perhaps. Roads, in this country at least, aren't crowned like they used to be. Your pics show a huge cant in the road to the inside of the curve which would put pressure, at slow speeds where cornering inertia has less effect, on the outside edge of the inside wheel which is already positively cambered to the extreme.

[Arlen G. Holder]

Hi Xeno,

I don't know the specs, but they're all high end vehicles such as this Lexus SUV

or this BMW SUV

Very few seem to be FWD - most seem to be RWD or AWD like the X5.

A few have reported high negative static camber, but, as you noted, a lot don't know offhand what the camber is - but none who have reported have said it was ever positive.

Notice though, that those Avalons are _all_ negative camber setups. It doesn't seem that any cars (yet) have the Bugatti style positive camber.

Notice though, that it's always negative (so far) camber, which seems to be what I need to assume, since I'm asking for help solving a systemic problem in hundreds of cars now that you've helped me identify the primary issue: o Low speed camber scrub of the outside edge of the inside wheel

Ah! Nobody talked about the width of the tires yet!

Are you saying that the low speed camber scrub of the outside edge of the inside front wheel is worse with width? If so, that's one possible amelioration, albeit there isn't much of a range that one can choose in tires that's practicable.

I get your point that positive caster is likely the most important to lower, where, within range, it's the most bang for the buck.

In general, the bigger trucks have to back up a couple of times to make most of the curves, where in some of the curves, the trucks dig into the roadway, as you could see in that photo.

Unfortunately, I didn't snap any photos of the width of the road, just the corners.

It's nighttime here, so tomorrow I'll look for this "cant" in the road that you speak of, as I'm not sure I understand what you're trying to tell me as for its effect on the camber scrub of the tires.

CANT:

SUPERELEVATION:

[Thomas]

I only meant to say do not turn while parked. I bet you can wear out a new fron set in a day if you tried. Sometimes there is no choice such as when boxed in, but when not boxed in start to roll b4 turning. Further reading allowed me to see your question better.