Alignment and AWD tire questions

[burn_your_money]

Hi guys,

No where near VWs but my friend has a 03 Subaru Outback and she needs tires.

Q1) How much tread depth difference is permissible on tires? 2 of hers are decent, maybe in the 40-50% range of tread depth and 2 are gone so she was hoping to get away with only 2 new tires. Remember that AWD is the factor here.

Q2) She brought it in to get an alignment and they did one but told her that when she gets new tires she will need another alignment. They mentioned that if she bought tires through them they would do the alignment for free. Sound like a pile to anyone else?

[8v-of-fury]

I have swapped tires ridiculous amounts of times.. New tires, balanced correctly shouldn't affect anything.. New wheels?? Maybe?

[rallydiesel]

What does getting new tires have to do with the alignment specs? As long as the same sizes are used, they won't change anything. Even changing the sizes won't alter the angles enough to warrant an alignment.

[745 turbogreasel]

1 it's a weak point, and trannys are an expensive PITA, I'd avoid it, or keep the baldies well overinflated.

2 Unless much time/rallying has happened in the meantime, sonuds like a pantload.  How is the tire wear?

[burn_your_money]

Thanks for confirming my thoughts guys.

The tires were run under-inflated for an extended period of time, probably almost a whole season. The edges are gone on 3 of the tires. I don't understand why the shop would even only recommended 2 tires. Chrysler dealerships.... I guess they figured a 69 year old great-grandma wouldn't know any better...

She will get 4 new tires and no alignment.

BTW the last alignment was done a week ago and they said with the new tires she is getting (this week) she should would need another one.
 
Thanks again

[RabbitJockey]

yeah theres no reason that tires would change the alignment at all unless the tires are cone shaped haha

[rabbitman]

Bunch of crooks, maybe a different rim offset would warrant an alignment but not just new rubber.

[RabbitJockey]

i would think not even different wheels would make a difference, the angles never change

[Vangruver]

The major need is for evenly worn tires on symmetrical AWD systems IE audi and subbies

This is a quote taken from this page

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=18

As an example of different tire diameters resulting from tires worn to different tread depths, we'll compare two 225/45R17-sized tires, a new tire with its original tread depth of 10/32-inch and a second tire worn to 8/32-inch of remaining tread depth. The new 225/45R17-sized tire has a calculated diameter of 24.97", a circumference of 78.44" and will roll 835 times each mile. The same tire worn to 8/32-inch of remaining tread depth is calculated to be 1/8" shorter with a diameter of 24.84", have a circumference of 78.04" and will roll 839 times per mile. While the difference of 1/8" in overall diameter doesn't seem excessive, the resulting 4 revolutions per mile difference can place a continuous strain on the tires and vehicle's driveline. Obviously, the greater the difference in the tires' circumferences, the greater the resulting strain.

in regards to the alignment? It is common practice in the past to have an alignment performed on a car every time the tires get replaced. Just to ensure even and proper wear. However if the car isn't driven much, or hard in any way, and it tracks "semi" straight people generally don't get alignments on the car.

When ever a car gets suspension worked on, replacement of bushings, tie rod adjustments, an alignment is necessary.

When a car get lowered or raised, an alignement is necessary as well.

When I put on my winters from the summer, i get an alignment.

Proper alignment can mean the cost savings of a tank of fuel over the course of a season. It's worth it in its odd way.