Front-end Alignment specs and excessive wear inside

[MPTech]

I pulled off my front wheels yesterday to pin the spinner caps and was surprised to find my Mickey Thompson Street Comps 245/45 R17 are showing excessive wear on the inside of both PS & DS (the DS side is completely smooth). The outside on both sides still has plenty of tread, not even close to the wear bar yet. Back tires are wearing normally (still good). I had the front-end aligned when I installed these tires new. Guessing they have about 15k miles.I'll have to do some searching to find the specs I used, but they were the common ones found on the FFR Forum for a Power Steering setup.
Any idea why these may have pre-maturely worn so badly? I don't recall hitting any pot-holes / bumps. I never had this issue with previous tires. They were properly inflated at 24lbs.


These are the latest specs I found, are they still good? Does it matter if I'm running the original SN95 Mustang GT front spindles (‘95)?

Power steering street car:
7 to 8 degrees positive caster (which is better, 7 or 8?)
.5 to .75 degrees negative camber
3/32" total toe in

[Jeff Kleiner]

Wearing the inside is due to excessive negative camber or toe out. If you actually got the .5 to .75 degree negative camber you specified that won’t wear the tires and since you have inside wear on both left and right that points to it being toed out. Toe out will not only wear the tires but can also make the car kind of “darty” at highway speeds.

Jeff

[MPTech]

Thanks Jeff!

Best I can tell (from stored documents), these were the old specs I used last time:
Front:
• 6 degrees caster
• -.5 camber
• 1/16" toe in.
not sure what caused the wear, based on these old specs (I'm going to ask for the specs currently on the car when I take it to be re-aligned).
I know he had trouble setting the caster when I had it aligned last time, due to the UCA adjuster being stock (too long). I cut these down last year, but haven't had a new alignment yet.


This is different than what I found recently, so I'm going with these new specs.
7 to 8 degrees caster
.5 to .75 degrees camber
3/32" toe in
and 24 PSI

Thanks again

[Jeff Kleiner]

Thanks Jeff!

...so I'm going with these new specs.
7 to 8 degrees caster
.5 to .75 degrees camber
3/32" toe in
and 24 PSI

Thanks again

Those are the numbers I always recommend. As mentioned, I suspect that your toe is off.

Jeff

[Mike.Bray]

Give me $50 on toe.

[ProfessorB]

If y'all don't mind me asking... Are these numbers "power steering" or "manual" numbers (or both)? The reason I asked is I bought my first (already built) Cobra a year and a half ago. It was BARELY driveable. The seller, who also owned a Porcsche and a Lambergini, advised me to switch to manual steering as the car was "extremely twitchy". He was right. I soon found this website and started asking questions. I got quite a few "you just need to learn how to drive a Cobra" comments. (These comments were not helpful.) But I DID also get a lot of helpful comments....most of them suggesting an increase in caster. Well, I ended up doing TWO things. I researched the pwer racks and found out the 4-cylinder power rack was a slower ratio than the 8-cylnder power rack so I went with the slower ratio. - I also discovered that in a Mk II that maximum caster with the stock control arms was 4 degrees. Anyway, I changed the upper arms and now run NINE degrees of caster, 1/16 inch toe-in, and neg .5 camber. Couldn't be happier.

[MPTech]

The settings I provided in the original post are specifically for Power Steering.


Power steering street car:
7 to 8 degrees positive caster (which is better, 7 or 8?)
.5 to .75 degrees negative camber
3/32" total toe in

I can't comment on your 4-cylinder PS Rack, here's what I installed: ’93 Mustang PS rack, 3.0 turn. Part# 6406 (Reman from Autozone).
My roadster has never been twitchy, with the exception of a particular piece of highway near me that has bad grooves in it and I do get tramilling on that particular section of road. Otherwise it handles very well. I've run it on a track and a couple auto-x events and was always under control.

[egchewy79]

If y'all don't mind me asking... Are these numbers "power steering" or "manual" numbers (or both)? The reason I asked is I bought my first (already built) Cobra a year and a half ago. It was BARELY driveable. The seller, who also owned a Porcsche and a Lambergini, advised me to switch to manual steering as the car was "extremely twitchy". He was right. I soon found this website and started asking questions. I got quite a few "you just need to learn how to drive a Cobra" comments. (These comments were not helpful.) But I DID also get a lot of helpful comments....most of them suggesting an increase in caster. Well, I ended up doing TWO things. I researched the pwer racks and found out the 4-cylinder power rack was a slower ratio than the 8-cylnder power rack so I went with the slower ratio. - I also discovered that in a Mk II that maximum caster with the stock control arms was 4 degrees. Anyway, I changed the upper arms and now run NINE degrees of caster, 1/16 inch toe-in, and neg .5 camber. Couldn't be happier.

7-8* caster is for power steering. Manual is more like 3-4*. Any more than that the steering effort becomes too great at slow speeds.

[ProfessorB]

The settings I provided in the original post are specifically for Power Steering.


I can't comment on your 4-cylinder PS Rack, here's what I installed: ’93 Mustang PS rack, 3.0 turn. Part# 6406 (Reman from Autozone).
My roadster has never been twitchy, with the exception of a particular piece of highway near me that has bad grooves in it and I do get tramilling on that particular section of road. Otherwise it handles very well. I've run it on a track and a couple auto-x events and was always under control.

MP..... I learned (the hard way) about re-man racks from major autoparts suppliers. The part numbers for racks don't necessarily reflect the EXACT part. For instance, O'Reillys shows two different part numbers for 4-cyl and 8-cyl racks. The only difference is ratio. But the rebuilder/supplier no longer differentiates between the two. They have an "also fits" policy....but they don't tell you that (UNLESS you order a 4-cyl rack twice and get an 8-cyl rack twice and then cal the corporate office in Alabama and complain). They admitted that they still have two different part numbers but they just put "a rack that fits" in the box. And just for everybody's general information, counting the turns from lock-to-lock is not the best way to determine ratio. (Ask me how I kow). The BEST way is to compare "travel"....measure the distance the arm travels for one complete turn and compare it to another rack with a known ratio.
That being said, if it works don't fix it. It sounds like your rack is fine and the ratio works for you. I agree with others, check your toe.