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lollersk8s
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Replacing all 4 tires on awd?

It's a subaru with full time awd, chick says tire shop insisted she get all four new tires after she came in for a puncture on one. She went for it. Tires weren't bald or anything, had a bit of tread left.

I get that tire diameter changes a tiny bit with wear and it has awd, but diameter doesn't change THAT much on passenger cars/SUVs, unless you wear some 44" Super Swampers down to nothing... So is that a must? I'm thinking maybe two new ones on the same axle is as much as you need, as long as the other axle has some tread left.

But I never really dealt with full time awd.
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Old 10-16-2014, 01:55 PM lollersk8s is offline  
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Typhoon43
 
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She got taken. It's not like she drove 3,000 miles with a 13" doughnut spare and a 24" Donk wheel on the other side
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Old 10-16-2014, 01:57 PM Typhoon43 is offline  
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lollersk8s
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I was thinking she got had yea. It's not a solid coupling like a t-case right? I'm not even sure it matters on the same axle with an open diff.
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Old 10-16-2014, 01:58 PM lollersk8s is offline  
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pyramid
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why didn't they just patch the puncture?

second best option is a new tire shaved to match the tread depth of the other 3, if the shop can do that.

but yeah, you are not supposed to run a mix of fresh tires and worn tires on permanent AWD.

diffs are more expensive than tires and running tires of significantly different diameter/tread depth tires on an AWD can void the warranty on your diffs.

http://www.tirerack.com/tires/tirete....jsp?techid=18
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Old 10-16-2014, 02:14 PM pyramid is offline  
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Typhoon43
 
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Quote:
Originally Posted by pyramid View Post

Great article from a company that wants to ....wait for it.... SELL YOU TIRES.

Seriously, if your tire is 3 pounds underinflated on one side you'll have circumference differences
That's not enough to fry a limited slip diff. No way. Not believing it.
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Old 10-16-2014, 02:44 PM Typhoon43 is offline  
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pyramid
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Tire rack will shave your one new tire to size instead of selling you a complete set of four.

I refuse to run different size tires on all our AWD cars but the cost of a set of tires is fairly trivial to us.

Honestly, I'd put a matched set of takeoff tires on one of our cars before mismatching.
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Old 10-16-2014, 02:54 PM pyramid is offline  
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GhEttOrAiD
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Quote:
Originally Posted by pyramid View Post
Tire rack will shave your one new tire to size instead of selling you a complete set of four.

What.... wow I did not know that
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Old 10-16-2014, 07:00 PM GhEttOrAiD is offline  
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pyramid
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Quote:
Originally Posted by GhEttOrAiD View Post
What.... wow I did not know that

Yeah...

Quote:
Matching Tires By Shaving Them to Maintain Equivalent Tire Tread Depths

What does a driver do if one tire has to be removed from service when it and the other three tires have already worn to two-thirds to one-half of their original tread depth? Simply installing one new tire runs the risk of drivability problems or expensive driveline damage. Replacing the other three partially worn tires along with the damaged tire significantly increases the cost.

Tire Rack can provide a solution by matching the tread depth of the replacement tire to the tread depth of the partially worn tires that will remain on the vehicle by removing tread rubber from a new tire on a specialized machine that operates as a tire lathe. While this may seem counterintuitive, the value of the mileage sacrificed by the one replacement tire is considerably less than the cost of rebuilding worn driveline components.

Tire Rack has offered a tire shaving service that has been primarily used for preparing competition tires for racetrack use. This same service can also be used to remove tread rubber from new pairs or individual street tires used on four-wheel drive and all-wheel drive vehicles to allow them to match the remaining tread depth of the other partially worn tires that will remain on the vehicle. In addition to providing equivalent tread depth to eliminate driveline stress, shaved tires will also better match the traction and handling qualities of the remaining worn tires.

While the cost of our street tire shaving service will range from $25 to $35 for each tire, it is significantly less than the cost of unnecessarily replacing the remaining two or three good tires with lots of mileage still available from them.
http://blog.tirerack.com/blog/motors...e-at-tire-rack
and
http://blog.tirerack.com/blog/docs-a...-shave-as-well
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Old 10-16-2014, 07:16 PM pyramid is offline  
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lollersk8s
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Quote:
Originally Posted by pyramid View Post
why didn't they just patch the puncture?

second best option is a new tire shaved to match the tread depth of the other 3, if the shop can do that.

but yeah, you are not supposed to run a mix of fresh tires and worn tires on permanent AWD.

diffs are more expensive than tires and running tires of significantly different diameter/tread depth tires on an AWD can void the warranty on your diffs.

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

Not buying it, they have tires to sell. Their calculations prove nothing - so the difference is 3 turns per mile. They JUST explained how a differential works by allowing slip in turns, so unless you always drive straight (unlikely) you are already making the wheels turn a different amount of times per mile... DUH

Their 1/8th of an inch is also bogus compared to how much a tire changes due to air pressure, caused by under-inflation, or even over-inflation because that side was in the sun. I think such differences are well within the system's design. On the other hand Tire Rack has legal obligations, so they will shave your tires for a "small fee" just to be safe and also add another $120 to the total.

Not trying to invade asia here but I'd like to see a third party breakdown of this.
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Old 10-16-2014, 08:45 PM lollersk8s is offline  
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lollersk8s
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Quote:
Originally Posted by Typhoon43 View Post
Great article from a company that wants to ....wait for it.... SELL YOU TIRES.

Seriously, if your tire is 3 pounds underinflated on one side you'll have circumference differences
That's not enough to fry a limited slip diff. No way. Not believing it.

Mismatched sizes is one thing, but a small difference in wear has to be within design specs of the diffs...

They are talking about 835 vs 839 rotations I'm supposed to believe that

(1) the OEM system can't handle that and
(2) you don't normally create more difference than 3 turns over 1 mile.

No proof of either claim, nice try TireRack
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Old 10-16-2014, 08:49 PM lollersk8s is offline  
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pyramid
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Quote:
Originally Posted by lollersk8s View Post
Not buying it, they have tires to sell. Their calculations prove nothing - so the difference is 3 turns per mile. They JUST explained how a differential works by allowing slip in turns, so unless you always drive straight (unlikely) you are already making the wheels turn a different amount of times per mile... DUH

Their 1/8th of an inch is also bogus compared to how much a tire changes due to air pressure, caused by under-inflation, or even over-inflation because that side was in the sun. I think such differences are well within the system's design. On the other hand Tire Rack has legal obligations, so they will shave your tires for a "small fee" just to be safe and also add another $120 to the total.

Not trying to invade asia here but I'd like to see a third party breakdown of this.

changes in tire pressure for whatever reason would be temporary, not for the entire life of the tire.

it's one thing to have an underinflated tire for a week or two. it's entirely another thing to have an imbalance fucking with your diff(s) for 10k or 20k or 30k miles.

Also, tire rack isn't trying to sell you 4 new tires for your AWD car, they recommend shaving one new tire to the same tread depth as the remaining tires.
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Old 10-16-2014, 08:56 PM pyramid is offline  
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lollersk8s
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Quote:
Originally Posted by pyramid View Post

I refuse to run different size tires on all our AWD cars

That's good and I certainly hope so

What is in question is what constitues a differnt size? Apparently Subaru allows 1/4 inch in circumference . From a quick mental guesstimate that falls within 1/8th inch diameter difference on something like a 21-22+ inch tire.

http://forums.nasioc.com/forums/show....php?t=1005313

21" dia. circumference = 65.973
21.125.circumference = 66.366

Since tires are flexible, i think any height difference on one corner will be negated by the suspension and pressure/passenger weight. Then there are posts like this:

Quote:
Originally Posted by Dumbass at NASIOC
OMG seriously? 1/4" is a very small difference.

I searched NASIOC for exactly this info when I needed new tires, and couldn't find jack (My car didn't come with an owner's manual). Now 2 months later I see this.

I have a set of 235/40/17 on rear and 225/45/17 on front.

Is the damage serious? How much of a concern is this?


lol

two months of that and he's asking if anything is wrong, so I think mild/non-extreme wear difference is ok
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Old 10-16-2014, 09:03 PM lollersk8s is offline  
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Well, the thing is, if you have slightly mismatched sizes on the highway with anything fancier than open diffs, you are going to heat it up more than usual, making fluid less effective, and causing accelerated wear. It's not like you are going to go out and immediately cook the diff, but you will severely shorten it's service life.
Old 10-16-2014, 09:09 PM gribly is offline  
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lollersk8s
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Quote:
Originally Posted by pyramid View Post

Also, tire rack isn't trying to sell you 4 new tires for your AWD car, they recommend shaving one new tire to the same tread depth as the remaining tires.

Shaving is still $35x4 or something, but most other shops like Discount Tire don't and simply bully you into getting a set of four, even if you have newer tires.

They have to cover their ass legally, and push rubber so they'll tell you there's no other way out.

This is another reason I'm glad i don't need AWD in southern cali
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Old 10-16-2014, 09:11 PM lollersk8s is offline  
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lollersk8s
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Quote:
Originally Posted by gribly View Post
Well, the thing is, if you have slightly mismatched sizes on the highway with anything fancier than open diffs, you are going to heat it up more than usual, making fluid less effective, and causing accelerated wear. It's not like you are going to go out and immediately cook the diff, but you will severely shorten it's service life.

Except this seems to be hard to prove. The TireRack math shows there's a difference of 3 turns per mile if we pretend there were no other turns and the wheel is solid steel. I just don't think it matters at all in reality, given the same brand and size of tire.

If they offer shaving and youre a perfectionist, thats fine, i just feel bad for the soccer moms who get bullied/tricked into a whole set of four
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