67 Mustang Odd Tire Wear- Advice?

[MSTSFabbed]

Hey guys, long time lurker and occasional commenter but I haven’t posted much.

I’ve got a 1967 Mustang coupe that is a long, slow, lifetime project. I’m slowly realizing I’ve been plagued with the same tire wear issue for a while now and running out of ideas on what to check next.

My front tires are wearing badly on the outside edges. I haven’t run Autocross or really even driven it hard, just occasional commuter duty on these tires over the last couple years.

I’m running modified stock front suspension: 1” Shelby drop, 1” lowering springs, modified but stock geometry LCAs, Unisteer manual steering rack, 1” wheel spacers, 18x9” FR500s up front, with 14” Brembos.

I’ve got a lot of scrub from the spacers and wheel offset, and I don’t know how much the steering rack geometry is effected by being lowered close to 2” up front.

Current alignment is -2* static camber, +4.5-5.5* caster, ~ 1/16” toe in.
I’ve attempted to measure bumpsteer through travel and couldn’t measure anything of major significance, (something on the order of 0.05”) but my set up was pretty sketchy and I don’t trust it a whole lot.
Ackerman measures 11* inside tire with outside turned to 10*, both sides. Long Acre suggests about 13* for a 10* outer setting, but I don’t know how much that applies to street cars versus dirt circle track stuff.

I’ve checked all major components for wear, loose, bent, misaligned etc. I’m not saying it’s all perfect but I haven’t found any glaring issues or big suspicions.

The one thing that has shown up is inconsistent toe measurements. I get a swing of up to 1/2” sometimes with just a drive around the block. So that points me towards the strut rod bushings having way to much play. I’m in the process of modifying those to have rod ends rather than bushings to see if that eliminates the variations I’m seeing.

With as much caster as I have, the front inside still only rolls to about 0* camber at 20* steering movement.
I just can’t quite pictures how I’m scrubbing the outside of the tire as much as I apparently am with as much camber and caster as I have.

Any thoughts or experience is much appreciated!

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Stephen

[dontlifttoshift]

The one thing that has shown up is inconsistent toe measurements. I get a swing of up to 1/2”

Assuming this is isn't a measuring issue, this is your problem. Toe wears tires.

[Josh@Ridetech]

Assuming this is isn't a measuring issue, this is your problem. Toe wears tires.

I was going to say this as well.

[MSTSFabbed]

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I forgot to add pictures of the tires themselves.
I’m guessing that’s with maybe 2-3k miles on them. They are a soft 93TW summer tire.

Man. You think just toe would eat the outside that hard?
I’ve seen my measurements change a bit but haven’t given the variation enough credit. I assumed with -2* of camber, even toe out would wear the inside, not the outside.

I’ve measured with both the string method off the back tire and the two straight edges/tape measures method with everything squared up and leveled out. I built some good square jigs to work off of this last time. It’s no professional laser, but between the two I feel like I’m closing in on accuracy.

Thanks for your input and the sanity check!

[dontlifttoshift]

That's 3000 miles? Something is very wrong. Spend the 150 bucks and have a professional align the car. One of two things will happen.

1. It will confirm your measurements are correct.

2. It will confirm your measurements are incorrect.

Either way you win, you can't make an informed decision about what to do next if you are not sure you have accurate data.

Toe out tends to wear the inside, it sure looks like you are toed in a bunch.

[MSTSFabbed]

Sound advice. Thank you, it’s much appreciated!

Hopefully some mods to eliminate flexing, and better info will start to shine some light on it.

[Cyclone03]

I have to agree with “don’t lift…” something is loose,worn or your measurement technique is flawed.
I’ve autocrossed my 68 Coupe with an FE adding down force to the front with only -1.5 deg of camber and didn’t wear the outsides that bad. -1.5,6deg caster 1/8” toe in.
The light Ackerman would scrub the inside of the inside tire IIRC, the outside would be loaded the most.
It’s been a while for me but maybe at lower loads the OUTSIDE scrubs?

[chpr1972]

I use to align these back when they were almost new. First off, here is stock specs from 1971 Motors Manual in degrees

caster -1/4 to +3/4 desired +1/4
camber left and right +1/2 to+1 3/4 desired left +1 right +1
Toe in inch 3/16
toe out on turns outer wheel 18 3/4 inner wheel 20
With the stock suspension , spring over ball joint, I always thought it was a bad design. The cars had lots of roll. Anytime we got too far outta specs, we had bad tire wear. The one thing we did find out was 3/16 was way too much toe in. 1/32 to 1/16 tops. When radial tire came into being, we went to higher positive caster specs. Unless the car in going to be an autocross only car, I would lighten up on the negative camber, back to -1/4 or zero. Maybe as high as +3 caster. The suspension travel on the Mustang, the setting are not as stable as a spring between ball joints. I would recommend you bite the bullet and have a shop align it to your specs. You ruined a set of $400+ ? tires. Either that, or buy a good alignment set so you can change to autocross settings. I would make sure that you make the mechanic recheck your work also. keep us informed

[Pedigry]

Are your steering tie rods level to the ground when the car is on the ground and loaded? You said you check bump steer but wasn't sure of the measurements. Typically on lowered cars you have to run a bump steer kit which lowers the tie rod to match the drop of the suspension. I agree that a professional alignment needs to be done, but if it comes back good then I would guess it's bump steering. You can typically feel bump steer as it gets sketchy going over bumps. Are you feeling anything like that?

[andrewb70]

That steering rack conversion is probably not doing your bump steer situation any favors.

Andrew

[pitts64]

I never had any luck on cars with the steering linkage under compression (rear steer). I stay with cars like the GM A body that have front steering linkage. I wouldn't go to far (money wise) with this car.

[David Pozzi]

I'm not a Mustang expert, never worked on one. But it appears you have excessive toe in. Either something is flexing or it's bumpsteer. Push up on the inner tie rods, do they move? is there flex at the rack?
I would not change caster or camber, those settings look good.
Do you make a lot of tight left hand turns? How hard are you driving the car?

I'd set 1/4" toe OUT and drive it for a while.