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Old 09-29-2013, 02:21 PM   #1
eugeneutopia
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Default Simple question about a spare tire

** Answered **

I did a basic search with by basic searching skills and came up with nothing. I suspect this is because my question is so simple that it's a no brainer for most. I'd rather ask a stupid question than pay to fix what I broke as a result of not asking the question.

My OEM's were 17 x 7, 225/55 17.

I upgraded to 18 x 8, 245/45 18. This was one of the "compatible" options when I used the Tire Rack calculator.

So my question is this: Can I used my OEM spare if I get a flat?

If I understand (and this is a BIG if) the whole +1 sizing concept, shouldn't the circumference of my OEM spare and my new wheel/tire combination be close enough to not worry about screwing up the AWD (when I get a flat and mount the spare for the short trip to the closest tire shop)? Or do I need to get another 18 x 8 + 245/45 18 tire/wheel to use as a spare?
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Last edited by eugeneutopia; 10-27-2013 at 09:00 PM.
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Old 09-29-2013, 02:36 PM   #2
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What size is your spare tire?
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Old 09-29-2013, 02:58 PM   #3
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Originally Posted by SubLGT View Post
What size is your spare tire?
Sounds like a stock 17" doughnut...

From what I have gathered it can affect the awd system depending on which system it is. The tire width and tread pattern have effect of the friction between the tire and the road. That being said... depending if the spare tire was mounted in the front on an open differential, I see not much happening. I.E. stock Wrx front diff. Now move the said tire to the rear of a viscous LSD and there could be damage to the diff. I could guess one would get different answers depending on the type of awd and the settings being used.

I know this because my old GL was a 4x4 and I could buy tires in sets.

I pulled this from smart service subarus website

Q&A- 10. Is it true that I may need 4 new tires if only one goes bad?
"Yes, this is true if you have an All Wheel Drive Subaru. There are a few reasons for this. As a tire wears it’s outside circumference becomes smaller. If a new tire is placed on a car with 3 used tires it will usually have a bigger circumference and therefore roll at a slightly different speed when driving. This speed difference can be enough over time to cause damage to the AWD portion of the transmission. If you have an older Front Wheel Drive Subaru than you can replace your tires in pairs with the new pair going on the front and the 2 best used tires going to the back."

For a while I was going to rotate a 5th spare and matching tire into my rotations, but after much contemplation I decided it was too much of a head ache anyways. Point of my ramble, for a short duration of time, and at low speeds ( 40mph or less) a spare is ok, just expect to buy 4 new tires.
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Old 09-29-2013, 03:52 PM   #4
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Originally Posted by SubLGT View Post
What size is your spare tire?
Quote:
Originally Posted by Board junkie View Post
Sounds like a stock 17" doughnut...
Point of my ramble, for a short duration of time, and at low speeds ( 40mph or less) a spare is ok, just expect to buy 4 new tires.
Board Junkie is right SubLGT, I have the 17" doughnut.

Thanks for the info and the link... went down that rabbit hole and got lots of good info. Never knew a simple fuse removal and replacement was all it took to disable the AWD. Now I'm have visions of all the hooligan things I might be able to do
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Old 09-29-2013, 08:35 PM   #5
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Board Junkie is right SubLGT, I have the 17" doughnut.....................
Do you know for a fact that the donut spare and your OE tires have the same circumference? On some Subaru models, they were different from the factory, believe it or not.

Is your spare a T135/70D17 ?
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Old 09-29-2013, 08:35 PM   #6
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Now I'm have visions of all the hooligan things I might be able to do
I know right?!? So does it convert the power solely to the front, or rear?
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Old 09-29-2013, 08:41 PM   #7
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Originally Posted by SubLGT View Post

Do you know for a fact that the donut spare and your OE tires have the same circumference? On some Subaru models, they were different from the factory, believe it or not.

Is your spare a T135/70D17 ?
I believe it, that's why I don't even carry a spare. I know where you were headed with it though, and it is misleading.
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Old 09-29-2013, 09:01 PM   #8
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Originally Posted by SubLGT View Post
Do you know for a fact that the donut spare and your OE tires have the same circumference? On some Subaru models, they were different from the factory, believe it or not.

Is your spare a T135/70D17 ?
Oh, well crap. I assumed they were. Common sense would dictate that, right?

I'll take a look tonight and get back to you.
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Old 09-30-2013, 12:10 AM   #9
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Originally Posted by eugeneutopia View Post
I did a basic search with by basic searching skills and came up with nothing. I suspect this is because my question is so simple that it's a no brainer for most.
Or that you searched with the wrong words? There are plenty of threads that have broached this question before. Like this one, or this one, or this one.

Quote:
Originally Posted by eugeneutopia View Post
So my question is this: Can I used my OEM spare if I get a flat?
Yes.

Quote:
Originally Posted by eugeneutopia View Post
Common sense would dictate that, right?
Common sense would dictate if you use a temporary donut spare as a temporary donut spare is intended to be used - for a limited distance at a limited speed, as spelled out in the Owner's Manual - it's not going to harm anything.
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Old 09-30-2013, 12:40 AM   #10
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Or that you searched with the wrong words? There are plenty of threads that have broached this question before. Like this one, or this one, or this one.


Yes.


Common sense would dictate if you use a temporary donut spare as a temporary donut spare is intended to be used - for a limited distance at a limited speed, as spelled out in the Owner's Manual - it's not going to harm anything.
Topic 1 - I did say basic search skills. Very basic... like one or two words, without a "+" and more importantly, without the word "diameter". I used circumference and spare with no plus sign. So yes, basic, and not any of those which share the word that you used, but I didn't. But hey, good for you. You win the internet.

Topic 2 - "yes". Thanks. 20/20 vision in hindsight. Your breadth of knowledge is inspiring.

Topic 3 - Oh, it will? So, if I have upgraded to 26" wheels, common sense still says that my 17" spare will work, because, well, that's what it's intended for?

You've been a great help. I can't wait until I can return the favor and berate you on a subject you aren't familiar with, so that I can look smarter and make myself feel good about myself by showing that I know more about something than a guy that prefaces his question with "I don't know about this, and I'd rather be safe".

Ever hear of the advice "If you don't have anything nice to say, don't say anything at all"? I'm willing to bet if you tried that, you'd rarely have a chance to speak, right?

Your family must be so proud.

BTW.. reply however you want.. I'm just going to ignore it. Your kind of help (aka criticism) isn't what I was looking for.

Last edited by eugeneutopia; 09-30-2013 at 12:51 AM.
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Old 09-30-2013, 12:46 AM   #11
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Quote:
Originally Posted by SubLGT View Post
Do you know for a fact that the donut spare and your OE tires have the same circumference? On some Subaru models, they were different from the factory, believe it or not.

Is your spare a T135/70D17 ?
Took a look. It's a T155/70D 17 110M. That a good sign?
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Old 09-30-2013, 01:38 PM   #12
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Originally Posted by eugeneutopia View Post
Took a look. It's a T155/70D 17 110M. That a good sign?
Your spare has a diameter of 25.6"

Your OE tire 225/55R17 has a diameter of 26.8"

Large difference

If you visit subaruforester.org you can probably find long discussions about this intentional mismatch

Last edited by SubLGT; 09-30-2013 at 01:43 PM.
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Old 09-30-2013, 03:14 PM   #13
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Originally Posted by SubLGT View Post

Your spare has a diameter of 25.6"

Your OE tire 225/55R17 has a diameter of 26.8"

Large difference

If you visit subaruforester.org you can probably find long discussions about this intentional mismatch
Cool, thanks.
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Old 10-27-2013, 08:59 PM   #14
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Bought a full sized wheel off Tire-Rack on clearance for $49 + $23 shipping and a tire from the local tire yard.

Confirmed that a full sized spare will fit where the oem spare sits, but the foam organizer/cover needs to go away.

Not monitoring this thread anymore. PM anytime
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Old 10-28-2013, 03:55 AM   #15
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Originally Posted by eugeneutopia View Post
Topic 1 - I did say basic search skills. Very basic... like one or two words, without a "+" and more importantly, without the word "diameter". I used circumference and spare with no plus sign. So yes, basic, and not any of those which share the word that you used, but I didn't. But hey, good for you. You win the internet.

Topic 2 - "yes". Thanks. 20/20 vision in hindsight. Your breadth of knowledge is inspiring.

Topic 3 - Oh, it will? So, if I have upgraded to 26" wheels, common sense still says that my 17" spare will work, because, well, that's what it's intended for?

You've been a great help. I can't wait until I can return the favor and berate you on a subject you aren't familiar with, so that I can look smarter and make myself feel good about myself by showing that I know more about something than a guy that prefaces his question with "I don't know about this, and I'd rather be safe".

Ever hear of the advice "If you don't have anything nice to say, don't say anything at all"? I'm willing to bet if you tried that, you'd rarely have a chance to speak, right?

Your family must be so proud.

BTW.. reply however you want.. I'm just going to ignore it. Your kind of help (aka criticism) isn't what I was looking for.


oh...wait
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Old 12-03-2013, 07:24 PM   #16
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oh...wait
Bahaha
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Old 12-04-2013, 10:45 AM   #17
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Awwww, man, I'm bummed that I didn't see this earlier. Of course, eugeneotopia would just have ignored anything I said, anyway, since I'm a big meaniehead who does meaniehead things like link to other discussions about the same topic and answer his question.

Quote:
Originally Posted by eugeneutopia View Post
Topic 1 - I did say basic search skills. Very basic... like one or two words, without a "+" and more importantly, without the word "diameter". I used circumference and spare with no plus sign.
I didn't use a + sign either, the search function puts that in there automatically if you search for two words.

Quote:
Originally Posted by eugeneutopia View Post
But hey, good for you. You win the internet.
Hooray for me!

Quote:
Originally Posted by eugeneutopia View Post
Topic 2 - "yes". Thanks. 20/20 vision in hindsight. Your breadth of knowledge is inspiring.
You're welcome. I'm not sure if you're being sincere about the breadth of knowledge bit, but I appreciate it.

Quote:
Originally Posted by eugeneutopia View Post
Quote:
Originally Posted by Patrick Olsen View Post
Quote:
Originally Posted by eugeneutopia View Post
Quote:
Originally Posted by SubLGT View Post
Do you know for a fact that the donut spare and your OE tires have the same circumference? On some Subaru models, they were different from the factory, believe it or not.
Oh, well crap. I assumed they were. Common sense would dictate that, right?
Common sense would dictate if you use a temporary donut spare as a temporary donut spare is intended to be used - for a limited distance at a limited speed, as spelled out in the Owner's Manual - it's not going to harm anything.
Topic 3 - Oh, it will? So, if I have upgraded to 26" wheels, common sense still says that my 17" spare will work, because, well, that's what it's intended for?
Quoting the full discussion so you can follow along. SubLGT asked about your stock spare size relative to your stock wheel/tire combo. You responded that you thought it would be common sense for the stock spare to the be the same size as the stock wheel/tire combo. I responded that common sense would dictate that the stock spare will work just fine with the stock wheel/tire combo if you follow the directions that Subaru put in the Owner's Manual. I was responding to a discussion about using the spare with the stock wheel/tire combo. I don't see where my comment even remote implied that using the spare would be fine with massively oversized wheels. My Owner's Manual doesn't talk about using 26" wheels. Does yours?

Quote:
Originally Posted by eugeneutopia View Post
Ever hear of the advice "If you don't have anything nice to say, don't say anything at all"? I'm willing to bet if you tried that, you'd rarely have a chance to speak, right?
I'd love to know what wasn't nice in my original post. I answered your question, and pointed out that your common sense wasn't being properly applied. I didn't use any mean words or insults.

Quote:
Originally Posted by eugeneutopia View Post
BTW.. reply however you want.. I'm just going to ignore it. Your kind of help (aka criticism) isn't what I was looking for.
Again, I apologize for answering your question and also providing you some links that further discussed the subject.
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Old 12-04-2013, 01:59 PM   #18
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Originally Posted by Patrick Olsen View Post
I don't see where my comment even remote implied that using the spare would be fine with massively oversized wheels. My Owner's Manual doesn't talk about using 26" wheels. Does yours?
Code:
Specification  Sidewall  Radius  Diameter  Circumference  Revs/Mile  Difference
225/55-17         4.9in  13.4in    26.7in         84.0in        754        0.0%
245/45-18         4.3in  13.3in    26.7in         83.8in        756       -0.2%
0.2% difference in revs per mile? Where is the massive oversizing? I'm pretty sure that whatever works with stock size works with his "massively oversized" 0.2% different sized tires/wheels.

Since his stock size is effectively the same diameter, I'd really hope that his Owners Manual talks about using tires of this size.

The issue with the Forester spare is one of the diameter of the well in the trunk. It simply won't fit a larger diameter spare. I'm sure Subaru would use a larger diameter spare if they could.
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Old 12-05-2013, 11:15 AM   #19
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Originally Posted by Concillian View Post
Code:
Specification  Sidewall  Radius  Diameter  Circumference  Revs/Mile  Difference
225/55-17         4.9in  13.4in    26.7in         84.0in        754        0.0%
245/45-18         4.3in  13.3in    26.7in         83.8in        756       -0.2%
0.2% difference in revs per mile? Where is the massive oversizing? I'm pretty sure that whatever works with stock size works with his "massively oversized" 0.2% different sized tires/wheels.

Since his stock size is effectively the same diameter, I'd really hope that his Owners Manual talks about using tires of this size.
What part of 26" wheels do you not understand?

Quote:
Originally Posted by Concillian View Post
The issue with the Forester spare is one of the diameter of the well in the trunk. It simply won't fit a larger diameter spare. I'm sure Subaru would use a larger diameter spare if they could.
The OP updated this thread and said that he put a full-size spare in the car by removing the organizer that sits on top of the spare.
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