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Rear alignment concerns?

Old Jul 26, 2021 | 11:35 PM
  #21  
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Originally Posted by leigh1322
Well personally they did not touch the rear, and it is not inside their own spec of .25 degrees (1/8"), or the book spec.
You are at 3/16" toe in the back and the spec is 1/8" so you have 50% too much.
I would have them fix it.
As someone said it is literally a 15 min job to move a small shim from outside to in.
Someone suggested a 1/32" shim.
But they will not have C3 only shims, and you may not have a 1/32" in there. So...
Buy a shim pack and take it with you.
The only difference really would be less inside edge tire wear on the rear. Do you want to cut it down by 30% or more? It will drive the same. (I had a car that destroyed rear tires do to this issue.)
The front is spot-on.
Thanks Leigh, and everyone else who responded. Planning on just making a small change myself as I can do it in the time it would take to just drive back there, much less have to argue with them to redo the job and then wait again for the car. The pass side will be a quick job to move the 1/32" from outboard to inboard. Have a number of extra shims so with my dig calipers, can get the right adjusted thickness on driver's side as well.

Sounds like no rush, but a quick fix to help the tires wear better. Will also confirm the readings afterward as well, as this is a pretty unscientific approach without a second toe measurement on a rack.

Here is the pass side. Easy to move a shim.



Driver side. A bit more to get the measurement right, but pretty quick job as well.



Thanks.

Last edited by btwick; Jul 26, 2021 at 11:36 PM.
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Old Jul 27, 2021 | 01:05 AM
  #22  
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Half degree neg camber on the rear was what he asked for? Btwick, is your car lowered? If so, how do the half shafts sit, are they level, outer end lower, or inner end lower. If they are near level, or worse inner end lower, then you will want the extra toe in on the rear.
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Old Jul 27, 2021 | 11:41 AM
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Originally Posted by Metalhead140
Half degree neg camber on the rear was what he asked for? Btwick, is your car lowered? If so, how do the half shafts sit, are they level, outer end lower, or inner end lower. If they are near level, or worse inner end lower, then you will want the extra toe in on the rear.
Car is lowered, and shafts are just slightly inner-end lower than wheel side. Sitting on 245/60-15s if that helps. So, the bit of extra toe is beneficial for this car then?
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Old Jul 27, 2021 | 12:26 PM
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Wow your trailing arms look great and new…i wouldnt lose sleep if it drives good..nice ride..
i agree with @leigh1322
Why not adjust as spec’d
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Old Jul 27, 2021 | 01:17 PM
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Yeah I wouldn't lose sleep over it either.
It is not "perfect" but does it really matter?

Here is the rear toe-in or bump curve according to Duntov:

We are most concerned with happens to the toe-in from 2" up or 2" down from normal.
It does look like it loses about 1/8" of toe-in in these conditions.
So a setting of 1/4" toe-in should prevent it from ever making it all the way to zero, or heading over to the dark side of "toe-out"
Toe-out n the rear would make it squirrely, either in a hard turn or under braking, neither of which is good and should be avoided.
So 1/4" is enough. to prevent that. Even 1/8" might be.

Any more just contributes to un-necessary tire wear.
Conversely I definately would not recommend less than 1/8"
But are you even really concerned about massaging 60,000 miles out of a set of tires? Vs 30k or 40k?
There really should be no other effect.
So your alignment is very good, unless like me you just have to have it perfect.

I am pretty sure your right foot will have a much larger impact on rear tire life anyway........
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Old Jul 27, 2021 | 08:38 PM
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Originally Posted by leigh1322
Well personally they did not touch the rear, and it is not inside their own spec of .25 degrees (1/8"), or the book spec.
You are at 3/16" toe in the back and the spec is 1/8" so you have 50% too much.
I would have them fix it.
As someone said it is literally a 15 min job to move a small shim from outside to in.
Someone suggested a 1/32" shim.
But they will not have C3 only shims, and you may not have a 1/32" in there. So...
Buy a shim pack and take it with you.
The only difference really would be less inside edge tire wear on the rear. Do you want to cut it down by 30% or more? It will drive the same. (I had a car that destroyed rear tires do to this issue.)
The front is spot-on.
The rear will vary by 1/16" just with a tire kick,

For me I would just take measurements a few times to see how much it varies, If it measures 1/4" or more vs going in the other direction then I would adjust.

It will never be the same 3-4 times in a row.


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Old Jul 27, 2021 | 09:09 PM
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I would leave it at 3/16" toe in on the rear, I'd even be tempted to add a little more if it still feels a bit squirrely in the rear when accelerating or turning hard. Leigh is on the money as to why - at your current ride height, any travel in bump (such as when accelerating hard, or on the critical outside rear when cornering hard) will result in the wheel and tyre moving towards toe out. You are currently sitting at about the 2" lower point on that graph. You need a decent amount of static toe in to counter this.

Last edited by Metalhead140; Jul 27, 2021 at 09:11 PM.
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Old Jul 27, 2021 | 09:19 PM
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Originally Posted by Metalhead140
I would leave it at 3/16" toe in on the rear, I'd even be tempted to add a little more if it still feels a bit squirrely in the rear when accelerating or turning hard. Leigh is on the money as to why - at your current ride height, any travel in bump (such as when accelerating hard, or on the critical outside rear when cornering hard) will result in the wheel and tyre moving towards toe out. You are currently sitting at about the 2" lower point on that graph. You need a decent amount of static toe in to counter this.
Thanks all for the help. Yes, learned about how my lowered stance means my 3/16 is good to prevent toe out. More of a street car, so won't be hitting too many hard corners with no roll bar and just a lap belt, but from time-to-time.... Also learned from Leigh instead of saying "suspension compression," you can use the word "jounce" and impress your friends.
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Old Jul 27, 2021 | 09:42 PM
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Lol!
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