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Do you need to replace all of your tires?? Read first before making a thread.


blackfang
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Mods, if you want to make this a sticky, feel free. If not, that is ok.

 

There seems to be quite a few threads dealing with damaged or blown tires to where they need to be replaced and how many do they need. I am going to expand on this.

 

My experience on this issue is being in the Automotive industry for 6 years and as a Subaru Service advisor. I have also worked in the tire markets as a certified Michelin/BFG Salesman.

Also, the info I am giving you is my view and facts on this subject from first hand knowledge and the failures of the AWD system due to this. If you disagree with it, then so be it, it is your car and your money. I have seen plenty of failures and people end up forking over to me their money because they made the mistake.

 

Whenever you have to replace any tire on a Subaru, you must measure the circumference of the new tire when it is mounted. Then you measure the old tires. If there is more than a 1/4 inch of difference in the measurements, you should replace the other tires.

 

Folks, do NOT let the 1/32nds or 3/32nds rule fool you. That is not the correct method and it will cost you transfer clutches. Normally the 1/4inch threshold is around 15,000 miles, but I have seen a forester make it to 19,000 and still be within 1/4 inch.

 

If you do not do this, you are increasing the chances of damaging the transfer clutches/center diff or prematurely wearing them out on your awd. Automatics tend to be more prone to this than manuals. It isn't really a matter of if it happens, but more of a when.

 

 

Hope this clears up any confusion on whether you need all new tires or not.

 

Also proper tire rotation's and frequent alignments(I recommend once a year) help prevent irregular wear on the tires. Lack of rotations can also cause awd problems as well.

Edited by blackfang
[SIZE=1][URL="http://public.fotki.com/blackfang/"]Pics[/URL] [B]08 KawasakiZZR 600- exhaust and other mods 98 Camaro Z/28 HT- some mods......street/strip car 07 Legacy 2.5i- SPT exhaust...daily driver[/B][/SIZE]
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Hopefully this will help some out.
[SIZE=1][URL="http://public.fotki.com/blackfang/"]Pics[/URL] [B]08 KawasakiZZR 600- exhaust and other mods 98 Camaro Z/28 HT- some mods......street/strip car 07 Legacy 2.5i- SPT exhaust...daily driver[/B][/SIZE]
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Possibly so, but until now there wasn't a thread addressing that, so it might reduce some of them. Definitely worth a shot.
[SIZE=1][URL="http://public.fotki.com/blackfang/"]Pics[/URL] [B]08 KawasakiZZR 600- exhaust and other mods 98 Camaro Z/28 HT- some mods......street/strip car 07 Legacy 2.5i- SPT exhaust...daily driver[/B][/SIZE]
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  • 1 month later...
hmmm... if I replace my 17" to 18" rims, can I still use the spare tire on my LGT? I just want to make sure. I thinks its a NO?

 

Heh. I see you've done a search and found this thread. Post the tire size selections that you made and maybe blackfang will chime in.

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I would be interested to know how much a couple of psi difference between tyres makes on the circumference.

 

I had the exact same question. On long trips I'll be carrying a full size spare with no wear on the tread. This will make the tire slightly larger than the stockers. I figured if I run it with 5 psi less air it will make up for the difference in circumference. But I have no idea how much air pressure difference to use.

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hmmm... if I replace my 17" to 18" rims, can I still use the spare tire on my LGT? I just want to make sure. I thinks its a NO?

The spare is just used to get you to a place to fix the tire/replace. If that is all you are going to use it for you will be ok. Now if it is going to be on there for more than a few days, that is a no no anyways.

 

When you measure the circumference, do you have the car in the air ?

 

I would be interested to know how much a couple of psi difference between tyres makes on the circumference.

 

You need it off the ground enough to get a tape measure around them for an accurate reading. Once the new tires are mounted on the wheel and inflated, you measure the circumference of it. Then measure all the rest.

Edited by blackfang
[SIZE=1][URL="http://public.fotki.com/blackfang/"]Pics[/URL] [B]08 KawasakiZZR 600- exhaust and other mods 98 Camaro Z/28 HT- some mods......street/strip car 07 Legacy 2.5i- SPT exhaust...daily driver[/B][/SIZE]
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  • 4 weeks later...

I am going to bump this, rather than making a new thread for a related question-

 

I am at ~25K on my 08 and am still on the stock tires, which I rotate every 6-8K. For summer, I want to run some 3-season tires, so I am considering different options.

 

I had an E36 with M3 rims, which are staggered. I sold the rims with the car (stock rims were on it, with A/S tires), and trashed the rears, which were useless. I now have 2 good (formerly front) tires with about 3/4 tread. A guy an hour or so from me has a pair of the same tires (brand, sizes, model, etc.) will approximately the same mileage. What is my margin for error as far as differences between the pair that he has and the pair that I have?

 

08 2.5i, if it mattters...

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:munch:

 

"wearing out" tires is not something that has happened to me in 60k miles. I keep damaging mine somehow. :spin:

 

great thread btw. I've wondered this but I replace all 4 tires every time.

"The penalty good men pay for indifference to public affairs is to be ruled by evil men." - Plato
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Whenever you have to replace any tire on a Subaru, you must measure the circumference of the new tire when it is mounted. Then you measure the old tires. If there is more than a 1/4 inch of difference in the measurements, you should replace the other tires.

 

Folks, do NOT let the 1/32nds or 3/32nds rule fool you. That is not the correct method and it will cost you transfer clutches.

Check your math. A 1/32" (0.03125") difference in tread depth is equivalent to a 1/16" (0.0625") difference in diameter and a 0.20" difference in circumference, well within the 1/4" (0.25") threshold you cite.

 

On the other hand, 3/32" (0.09375") difference in tread depth is equivalent to a 3/16" (0.1875") difference in diameter and a 0.6" difference in circumference, well beyond the 1/4" threshold.

Edited by sactojesse
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  • 1 month later...

My issue is that I am right at the 1/4 (also at 2/32) inch give or take small errors on my half either way. I have put about 20,000 fun, sporty kilometers on my tires, so I must be under measuring...

My options are to replace all 4, replace 2 or order 1 shaved from tirerack

Tirerack sounds good until you pay $80 to ship to canada plus the currency conversion and installation adds up to roughly $250 cdn for one tire

Will replacing one pair of wheels still do damage?

 

Any suggestions?

 

Thanks for your time

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Check your math. A 1/32" (0.03125") difference in tread depth is equivalent to a 1/16" (0.0625") difference in diameter and a 0.20" difference in circumference, well within the 1/4" (0.25") threshold you cite.

 

On the other hand, 3/32" (0.09375") difference in tread depth is equivalent to a 3/16" (0.1875") difference in diameter and a 0.6" difference in circumference, well beyond the 1/4" threshold.

 

When going by tread depth difference one makes assumption that tires have the same circumference to start with.

It may or may not be the truth.

 

It is safer to take a tape and measure circumference.

 

Krzys

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A more cost effective way to deal with this situation, i.e., blown tire, need a new one, now it is bigger than the other three, is to reduce the circumference of the new tire to match the others. This is known as tread shaving and has been around for a very long time (perhaps Xenonk should chime in on this).

 

The minimal cost of tread shaving is much less than buying three other brand new tires.

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  • 2 weeks later...
  • 2 weeks later...

so I replaced one tire w/ new (on rear)....other tire on the rear (the older one) is about 1/8" less in circumference from my measurement so I'm replacing it also to be safe.....

 

Should the new tires go on the front or rear now?

 

I was going to keep the fronts as is but move them to the rear, putting the new tires on the front.....

thoughts??

 

2003 Subaru Legacy automatic

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You need to check the measurements of all the tires. If the others as in your case the other 3 are more than 1/4" difference, you should replace the other 3 as well.
[SIZE=1][URL="http://public.fotki.com/blackfang/"]Pics[/URL] [B]08 KawasakiZZR 600- exhaust and other mods 98 Camaro Z/28 HT- some mods......street/strip car 07 Legacy 2.5i- SPT exhaust...daily driver[/B][/SIZE]
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Check your math. A 1/32" (0.03125") difference in tread depth is equivalent to a 1/16" (0.0625") difference in diameter and a 0.20" difference in circumference, well within the 1/4" (0.25") threshold you cite.

 

On the other hand, 3/32" (0.09375") difference in tread depth is equivalent to a 3/16" (0.1875") difference in diameter and a 0.6" difference in circumference, well beyond the 1/4" threshold.

 

My math has nothing to do with it. Granted you might be safe with just 1/32nds, however, that is not the most accurate way of measuring. How do we know the tire is exactly 1/32nds all the way around in tread on all the tires and that all the tires circumference is the same. You can't, so it is safer to measure with the tape measure to get an accurate measurement among all the tires. I can assure you, if you just measure the tread depth, you will be damaging the AWD at some point.

 

When going by tread depth difference one makes assumption that tires have the same circumference to start with.

It may or may not be the truth.

 

It is safer to take a tape and measure circumference.

 

Krzys

 

Exactly.

Edited by blackfang
[SIZE=1][URL="http://public.fotki.com/blackfang/"]Pics[/URL] [B]08 KawasakiZZR 600- exhaust and other mods 98 Camaro Z/28 HT- some mods......street/strip car 07 Legacy 2.5i- SPT exhaust...daily driver[/B][/SIZE]
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This was something I really didn't know about when buying the LGT (my first AWD car). I think I've been ok so far (had to replace 4 tires instead of 2 once) in 60K miles because I stumbled upon the info in time when I needed it.

 

But, it's definitely something I'll think about twice before doing again (buying AWD). Rarely need AWD in NorCal, unless we head up to Tahoe in the winter.. We do that maybe 2x a year..

 

Too many unexpected restrictions: 1/4 rule for tires, don't pull parking brake for skids, etc, etc.. I survived plenty of Canadian winters with FWD, and even the occasional RWD adventure ('79 Dodge)..

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I'm a little confused.. reason being my 05 lgt.. it is a 5eat and the split ratio front/rear is different..

 

So my question is.. lets say the back two tires are the same diameter.. and the front two are the same diameter.. but compared from front to back they are different.

 

So how would running lets say a new set on the front and a used set on the back affect anything? I could see if you ran 1 new and 1 used on each side of the rear and wear the rear diff over time..

512whp/465ftlb 2005 5EAT Legacy (Build Log)

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