2.5+ degree camber tire wear?

[Lindenwood]

For all the #noshim folks, can you give me an order of magnitude estimate for tire wear if I run 2.5+ degrees camber daily? I will be running 0 degrees camber and I am very aware that bad toe is what scrubs tires quickly. But, with 0 toe am I looking at 90% of normal tire life?…50% of normal tire life?…25%?

Thanks!

@MasterC17 et Al.

 

[The Other Dan]

Don't run 0 toe. Cause it's not really 0 toe. Run .05 or so. It's a trivial amount, but with all the bushings, and stacking tolerances, .05 ends up being 0 once you start forward movement of the car.
I did that on my fat tired Subaru RSTI and had virtually no inner/excess tire wear running 2.5-3deg of camber.

 

[dsgerbc]

+1 on ^^
Also, your new coilover springs will settle a bit, and give you toe-out.
Keep an eye on it, or it'd kill your tires quick.

You CAN align to zero toe, but make sure it's done with a 200lbs/_insert_driver_weight_here_ worth of weight in the driver's seat.

 

[Lindenwood]

This is partially academic as I research my next set of daily wheels, but it is also driven by my desire to do less of this for (and after) race days .

I have done at least half a dozen full alignments and I regularly keep up with it, but as I get closer to race settings I really like, it would be nice to just lock it in and largely be done with it other than Em for deliberate experimental changes or minor tweaks (I.e. adding 0.5 or 1mm of toe for race day). I only have so much man-cave (garage) time to use before I start causing consternation, and I am using more of it than I’d like cleaning up minor alignment issues after all the race-day adjustments . For example, going from >3 degrees of front camber back to <2 degrees requires a bunch of corresponding turnbuckle movement, which is hard to replicate precisely. I almost always have to go back in and make a minor tweak for a slight steering wheel misalignment, or correct a half-mm of toe one way or another. Rear alignment tweaks after big changes are a bit more tedious since the wheel has to be removed.

 

[Motion122]

Don't run 0 toe. Cause it's not really 0 toe. Run .05 or so. It's a trivial amount, but with all the bushings, and stacking tolerances, .05 ends up being 0 once you start forward movement of the car.
I did that on my fat tired Subaru RSTI and had virtually no inner/excess tire wear running 2.5-3deg of camber.

Yes, I agree. Dynamically you will get some toe out when running zero toe.

What is funny is that I have always done alignments with strings, tape measure and a camber gauge. Put the car on a machine to verify if my method is accurate enough and ended up stating I have zero toe when I have it at 1/16" in. Camber is within .1 to .2 so I am good on that.

Caster at +7 on both sides with no impact on the chassis(tried it at both -3.5 and -1.5 camber). Very even tire wear at -1.5 and even at -2(mostly highway and street). Can't say at -2.5 though. I think you will see some accelerated wear at that setting if you do more commute than canyon runs/autocross/track.

 

[gearchruncher]

Don't run 0 toe. Cause it's not really 0 toe. Run .05 or so. It's a trivial amount, but with all the bushings, and stacking tolerances, .05 ends up being 0 once you start forward movement of the car.
I did that on my fat tired Subaru RSTI and had virtually no inner/excess tire wear running 2.5-3deg of camber.

Are we sure that the car toes out? Seems like a very complicated analysis of the stiffness and location of all of the joints would be needed, and even with that it would not be the same for RWD and AWD, nor under braking, coasting, or acceleration, nor the same for the front and rear axle, nor if you start replacing various parts with aftermarket.

The MacPherson on a STI is really, really different from the double ball joint on the Model 3.

I've had a lot of success at 0 toe and really like the way the car behaves.

 

[Lindenwood]

I don’t necessarily want to turn this into a general alignment thread since there is plenty of discussion on that, if it means we get distracted from the specific experiences about tire wear. (Though, I had the same thought; technically, forces at the wheel would cause both axles to toe in under acceleration and toe out under braking, which is a characteristic of any car with bushings, and is why, for example, the MPP Compression Rod bushings exist).

 

[dsgerbc]

technically, forces at the wheel would cause both axles to toe in under acceleration and toe out under braking, which is a characteristic of any car with bushings,

What you're describing is a positive scrub radius. Some cars are designed that way. Lots of cars are tuned the other way - toe-out on power, toe-in under braking, for safety. I *think* stock scrub radius is slightly negative. Going with +20 effective offset wheels definitely changes that to a positive one.

 

[Lindenwood]

What you're describing is a positive scrub radius. Some cars are designed that way. Lots of cars are tuned the other way - toe-out on power, toe-in under braking, for safety. I *think* stock scrub radius is slightly negative. Going with +20 effective offset wheels definitely changes that to a positive one.

Totally fair!

 

[gearchruncher]

What you're describing is a positive scrub radius. Some cars are designed that way. Lots of cars are tuned the other way - toe-out on power, toe-in under braking, for safety. I *think* stock scrub radius is slightly negative. Going with +20 effective offset wheels definitely changes that to a positive one.

No, this has nothing to do with scrub radius. Scrub radius is the arc the wheel takes as you turn the wheel.
However, bushings moving all over the suspension joints can change toe, and the forces on these bushings change depending on braking, accelerating and turning.
Zero scrub radius does not mean no forces on the bushings. Look at your suspension- it's full of long cantilevers and compression/tension rods that have to transmit fore/aft forces to the rest of the car. They will deflect even with no scrub radius and in a straight line, and that deflection will cause toe changes, and that toe change is highly dependent on suspension and steering geometry and pretty independent of scrub radius.

 

[dsgerbc]

No, this has nothing to do with scrub radius. Scrub radius is the arc the wheel takes as you turn the wheel.
However, bushings moving all over the suspension joints can change toe, and the forces on these bushings change depending on braking, accelerating and turning.
Zero scrub radius does not mean no forces on the bushings. Look at your suspension- it's full of long cantilevers and compression/tension rods that have to transmit fore/aft forces to the rest of the car. They will deflect even with no scrub radius and in a straight line, and that deflection will cause toe changes, and that toe change is highly dependent on suspension and steering geometry and pretty independent of scrub radius.

thread derail complete.

 

[dsgerbc]

it's full of long cantilevers and compression/tension rods that have to transmit fore/aft forces to the rest of the car.

While finding the exact numerical values of deflections is complicated, figuring out what will happen qualitatively in particular situations to the first order of approximation is not.
We can safely ignore the top arm, it's far away from action, it's not gonna move much, and there's a U-joint in there.
There are three linkages below - two suspension arms with bushings and a steering linkage. Normally, there are also steering rack bushings to consider, but the Tesla rack appears to be quite rigidly mounted.

Depending on the scrub radius, and ignoring the edge case of zero or near zero radius (where it can swing slightly positive/negative depending on bushing deflection), which bushings are gonna compress is pretty clear. Under braking, if the center of the contact patch is further away from the center of the car than the projection of the suspension's rotational axis on the ground (positive scrub radius), the braking force will push to move the wheel to the rear and while its rotational moment will push to toe-out the wheel. The laterally rigid steering joint will move a bit to the rear, the lateral link will move inward a bit and to the rear, and the compliance link will comply the most inward/rear.

Now, if you slap MPP's compliance link bearings on w/o changing the lateral arm bushing for their bearing as well - things become weird. You lateral arm is not the main compliance point, but you'd still get toe-out.

In regular driving, with most of propulsion done by rear wheels, the rolling resistance is pushing on the front wheels just like braking does, leading to a hair of toe-out with positive scrub radius. And a hair of toe-in with negative scrub radius. This is all in comparison to the static zero-toe alignment.

So, I do think that the scrub radius does matter quite a bit. So, running those 15mm spacers or +20 effective offset wheels will affect wear.

Now, this is all basic physics. And there may be effects that I'm ignoring which I shouldn't. I'd love to hear those.

 

[Lindenwood]

Bottom line: I’m not going to get the actual answer to my question and I should just go for it .

 

[TacoSteve]

Bottom line: I’m not going to get the actual answer to my question and I should just go for it .

After 5,000 miles at -3.5ish camber & 0 toe my 265 ps4s's had noticeable camber wear. My best guess is that I would have been in the cords with another 7500 miles. Hope that helps.

 

[tm1v2]

Bottom line: I’m not going to get the actual answer to my question and I should just go for it .

Yes please, come back in a while with the answer. If I take up autocross in this car I'd also like to find one alignment that balances autox with the street miles. Minimal per-event maintenance/adjustments will be my car setup goal.