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#1 2016-09-26 15:55:08

Bryan
why don't you remember my name?
Supporter
From: Western WI
Registered: 2007-01-14
User Number: 1768
Posts: 10184

Feathering tires

Hey, I'm back.

So I have this problem with the rear tires feathering (or cupping, whatev) on the inside rears.  My alignment is solid, tires aren't even that old, and the prevailing thoughts from my regular mechanic is that the added weight in my situation is what's causing the feathering.

Weight?  Yeah, for the new folks - I usually have a couple hundred pounds of samples and gear in the back - I usually try to distribute it well, heavier stuff towards the front, but there's a decent amount of extra weight in the back most of the time.  I don't drive like anyone's grandmother, unless their grandma has a disregard for speed limits and a generally hostile attitude towards other drivers.  Almost all highway miles.

Current setup is some 90k mile old KYB GR2 struts, Eibach pro-kit springs the same age, and 3/8" Paranoid saggy butt spacers in the rear.  Conti Extreme Contact DW with 2 summers' wear on all 4 corners, and winter I think they're Dunlop WinterMaxx, will be going into 3rd winter.

New tires will likely just do the same, and I'm not keen on annual replacements (I drive ~25k miles a year or more).

Am I due for new struts/springs?  I did pick up replacement Pro Kit on a killer deal.   Will the tires still feather no matter what, due to the driving I do (as my mechanic says)?  Is there a setup I can go with for the next 100k miles that I need out of this vehicle, that won't fuck up my handling?  I love me some exit ramps.  Or should I get 2 new tires and have them do the alignment with my car loaded?

2006 2.5i with 217k on the clock.


I'm cold, and there are wolves after me.

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#2 2016-09-26 17:32:04

Skorpion25i
Just a dumb 20-somethin' year old
From: Epping, NH
Registered: 2013-10-12
User Number: 11520
Posts: 2021

Re: Feathering tires

Have you actually seen the alignment report? Rear alignments on Subarus are screw-y especially lowered even a little bit.


2006 Turboless Unicorn. Red. CWP. UEL. HBE.
2016 Subaru WRX. Crystal White Pearl 13.8 @ 100.5

Sellin' Subarus since '13 cool

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#3 2016-09-26 17:53:13

sohlman
21O2OLOR
From: Sacramento, CA
Registered: 2013-10-29
User Number: 11977
Posts: 1454

Re: Feathering tires

Skorpion25i wrote:

Have you actually seen the alignment report? Rear alignments on Subarus are screw-y especially lowered even a little bit.

This. Camber bolts may be what you need.


06' Silver Aero 5MT - Cobb Turboback, Stage II  93 octane tune, ST coilovers (KW Variant1s), Cobb short shifter, 22mm front and 24mm rear whiteline sways and endlinks, engine rebuild (Manley forged rods and pistons)
White 2015 WRX - Whiteline rear swaybar, Perrin brass shifter bushing, Cobb J pipe, Cobb Accessport, custom buzzard damage

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#4 2016-09-26 22:52:09

snowphun
Member
From: Central CT
Registered: 2005-11-09
User Number: 890
Posts: 267

Re: Feathering tires

Camber doesn't cup tires, toe does. Zero toe front and rear. ZERO.

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#5 2016-09-29 10:54:38

krazykarguy
Worst ninja editor, ever.
Supporter
From: South Carolina
Registered: 2007-04-06
User Number: 1944
Posts: 8208

Re: Feathering tires

arrow-up This. I demanded zero toe on my last alignment prior to my 1,000 mile trip from VT to SC, and the shop complied. The problem with most alignment shops is that they will do the least amount of adjustment to get the readings "into the green". So if the maximum toe setting is 0.5, you can be damned sure that the car is going to have 0.4999 unless you request otherwise.

I also suggested to Bryan on FB that the possibility that his rear bushings are worn right to the limit of serviceability. I have inspected cars where on the ground, the bushings appear worn, but in the air with the wheels at full droop, the bushings have zero deflection. Alignments are done on the ground.

Typically, the most worn spots on a bushing are in the directions of movement, and the points in a fully loaded state - not necessarily the least-possible load state (i.e. on a lift during an inspection). Just a few mm of oscillation caused by a worn bushing can cause a feathered tire.

I would not point to the lowering springs immediately, as this lowering does not have an effect on the toe so much as it does the camber. In addition, the car also has strut spacers installed - reducing the effect of the lowering spring by the thickness of the spacer. IIRC, the Eibach Pro-Kit is a 1" rear drop, and the spacer is 3/8" - meaning that the effective drop in the rear is 5/8" - a negligible amount. Camber bolts will not solve a feathered tire wear issue.

IMHO, get an alignment where you specify the toe settings, and if that does not solve the issue, start checking into replacement arms... Or do both! big_smile


2005 Aero 5MT
2014 Ford Mustang GT Premium 6MT - Sterling Gray Metallic

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#6 2016-09-29 12:31:02

ikbrown
long live R0LO!
From: Fair Oaks, CA
Registered: 2011-10-06
User Number: 6094
Posts: 4966

Re: Feathering tires

Sounds like Krazy has the right idea in that w/ the extra weight regularly being carried around there may be bushings holding your suspension in place that are now worn out to cause some irregularity in your alignment when driving (trailing/control arms, lateral links, etc.) - replacing those, and probably the struts as well would probably solve the issue.

I like the idea of starting with a precise alignment though to see if that alone helps before spending more.


2005 Saab 92x Aero 5MT | The basic mods, Stage 2.04
1968 Dodge Charger 383 | WIP, restored almost everything but body work
2014 Subaru Forester | Wife's car

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#7 2016-09-29 16:12:51

Bryan
why don't you remember my name?
Supporter
From: Western WI
Registered: 2007-01-14
User Number: 1768
Posts: 10184

Re: Feathering tires

That's a good idea, and one that's easily actionable.  I'm about 10 days away from a month abroad, so this might all just wait until I'm putting winter rubber on in Nov.


I'm cold, and there are wolves after me.

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#8 2016-10-03 20:31:48

eurocoffee
under attack *
From: Boston MA
Registered: 2012-04-30
User Number: 7218
Posts: 830

Re: Feathering tires

krazykarguy wrote:

arrow-up This. I demanded zero toe on my last alignment prior to my 1,000 mile trip from VT to SC, and the shop complied. The problem with most alignment shops is that they will do the least amount of adjustment to get the readings "into the green". So if the maximum toe setting is 0.5, you can be damned sure that the car is going to have 0.4999 unless you request otherwise.

This. In the 6 months I've been working with our alignment machine, I'm amazed at the amount of customers who come in to have us correct previous alignments from other shops. "In the green" is literally as close as some shops try to make it, doesn't matter if one wheel is pointing +.08 and the other -0.5, if it's in spec and they are rushed, they ship it. Nevermind that you can cheat the machine to get the correct numbers and then hit print... Chasing the adjustments to spot on is time consuming, and can be impossible if the bushings are too soft (old) or if hardware seizes (rear eccentric bolts).

You may want to have the alignment done with the car at least partially loaded, since that is probably how you're using it most.


This is my Saabaru. There are many like it, but this one is Mine!

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