tire wear

[pontiacbird]

on my 68 firebird , I have 1 degre negative camber , 3.5 degre positive caster and 1/8 toe in . My 245-45-17 tires have approximatively 3000 miles and I begin to see light wear on the outside . I thought I would see the wear appear on the inside first ? Is it normal ?

[DusterRT]

That isn't a ton of negative camber..well not for what I am used to seeing at least. Are you doing a lot of hard cornering?

[Norm Peterson]

Are the control arm bushings original or have they been replaced? If so, how long ago?

Crappy bushings can give you one reading when you align it (car at rest) but quite a different value when you're actually cornering it.


Norm

[David Pozzi]

With the extra neg camber you have, you should try some toe out, perhaps zero to 1 1/6" out . The tires leaning inward at the top create a "camber thrust" pushing against each other, this pulls the tires into a toe-in position, they are each pushing inward putting load on the outside edges of the tread.

The chart below shows a 35 lb side thrust (per side) generated by a 1 deg neg camber with 1000 lbs vertical loading.
https://static1.pt-content.com/images/pt/2006/07/fig8-1.gif

[baz67]

With the extra neg camber you have, you should try some toe out, perhaps zero to 1 1/6" out . The tires leaning inward at the top create a "camber thrust" pushing against each other, this pulls the tires into a toe-in position, they are each pushing inward putting load on the outside edges of the tread.

The chart below shows a 35 lb side thrust (per side) generated by a 1 deg neg camber with 1000 lbs vertical loading.
https://static1.pt-content.com/images/pt/2006/07/fig8-1.gif

:hmm: 1 1/6 out David???? Do you mean 1/16 out?

[wendell]

No David was right, 1 1/6 toe out. He's trying to get his camaro to turn in like the Lola.

[derekf]

35 pounds for 1 degree - the chart is for Bias Ply; does that number hold true for radials as well?

[pontiacbird]

tanks very much for your input .
for answer to DusterRT , I dont make competition and except some time , I dont hard cornering . for Norm Peterson , yes my car haved aligned whit polygraphite bushing and sometime after I installed rubber bushing on lower control arm ( I know the guys here like the del-a lum but in quebec the road are often bad and with my experience I prefer my car whit rubber on lca for my applcation ) . this change have possibely accentuate the camber . finaly my car need to return at alignement shop . I have intention to ajust at .5 negative camber and try 0 or 1/16 to in . what do you think ? derekf have a good question , someone have reponse ?

[DusterRT]

I'd try zero toe first. Toe will wear your tires more than a smidge of negative camber alone.

And did you mean that you changed the bushings after the alignment was done? That will throw things off for sure..if that's the case, you'll likely need a full alignment rather than a toe change.

[BonzoHansen]

1 1\6"? Wow, I would think that car would be vary darty (which may be good on the track, I don't know). Does that change with tie rod location (front vs rear aka 1st gen vs 2nd gen)?

[protour_chevelle]

1 1\6"? Wow, I would think that car would be vary darty (which may be good on the track, I don't know). Does that change with tie rod location (front vs rear aka 1st gen vs 2nd gen)?

1 1/6 isn't even a measurement haha.

-Matt

[Grandpa Ronsy]

My thoughts are that the wear on one side of the tire is telling you they are not happy going down the road with the present toe settings. As the vehicle pitches it's weight from side, it probably is a little darty now(may be too small to notice)

If changing the toe out a little evens the wear to both sides of the tyre(Change front to back after the toe change so as you get a fresh canvas so to speak) then the car should be less darty.

The reason for changing the tyres is because even if you change the settings the tyres will continue to wear with the pattern they currently show.

Remember everything is a compromise.

(How'd I go David Pozzi??):drive1:

[David Pozzi]

Oops! 1/16":pat:
A published rule of thumb is .1 deg toe out each side per 1 deg of neg camber, to compensate for camber thrust. That's 3/16" toe out per wheel on a 25" tall tire! So 1/16" total is very conservative.

[Norm Peterson]

And I was perfectly willing to think you meant one and one-sixth millimeters . . .

[DusterRT]

1 1/6 isn't even a measurement haha.

-Matt

Sure it is! Just divide an inch into 6 parts. :rolleyes:

Reminds me of a time I was working on our Formula SAE car attempting to roughly set the toe off the brake rotors with a tape measure. I was measuring and someone else was writing it down, and in the midst of wrestling with the tape, I blurted out, "OK, that's about thirty four and, uhmm..ten and a half sixteenths." Raised a couple eyebrows, lol.