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Old 12-17-2010, 10:52 PM   #1
Konrad02ts
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Default Upgrading wheels. Flat tire. Related problems...

I've upgraded my wheels, and thought... huh, what if I get a flat tire, and my spare is the wrong size? I have all wheel drive... If I'm in the middle of nowhere, am I ****ed?!

So, I'm wondering, is the rear differential separated from the front? For example, if I get a flat in the rear, but I swap out both rear wheels with two of equal size, that aren't flat... will I be able to drive without screwing up the differential?
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Old 12-17-2010, 11:08 PM   #2
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The OEM spare tire is smaller than the OEM tires. When you get a flat, you put two good tires on the front and the spare on the rear. Then there is a fuse you pull, which makes the car FWD.

Whether you have aftermarket wheels or not, this will be what you have to do.

All of this should be in your manual. Read it just to be sure.
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Old 12-17-2010, 11:12 PM   #3
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Quote:
Originally Posted by mslstixx View Post
The OEM spare tire is smaller than the OEM tires. When you get a flat, you put two good tires on the front and the spare on the rear. Then there is a fuse you pull, which makes the car FWD.

Whether you have aftermarket wheels or not, this will be what you have to do.

All of this should be in your manual. Read it just to be sure.
The fuse you use to make the car FWD is on auto transmissions only.
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Old 12-18-2010, 01:38 AM   #4
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Originally Posted by MD04WRX View Post
The fuse you use to make the car FWD is on auto transmissions only.
Hmmm... Yeah, I have a manual tranny. So, would I need a spare tire the exact same size as the others?? ...or is there any other option?
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Old 12-18-2010, 02:01 AM   #5
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I solved this by getting a full size spare. I take it with me if i leave town. Around town, AAA will tow me home at no charge. Cheap way to ensure you dont put undue stress on your diff.
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Old 12-18-2010, 02:27 AM   #6
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OK.. Yeah, I figure I'd just get a tow if in town. But... this is probably a dumb question, would most tire shops sell a full size spare? haha
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Old 12-18-2010, 02:30 AM   #7
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Quote:
Originally Posted by Konrad02ts
OK.. Yeah, I figure I'd just get a tow if in town. But... this is probably a dumb question, would most tire shops sell a full size spare? haha
For sure if its a common size.
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Old 12-18-2010, 02:56 AM   #8
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Nice! I'll be sure to visit the tire shop then.... long drive coming up for Christmas... thanks for all the help!
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Old 12-18-2010, 07:56 AM   #9
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The OEM spare's tire is narrower, but the same overall diameter as the OEM tires.

If your aftermarket wheel/tire setup is the same nominal diameter as OEM you're fine. If it's different, you'll need a spare that's the same diameter.

Post your new tire size (and wheel width).
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Old 12-18-2010, 11:35 AM   #10
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This seems way too complex.

When I've gotten a flat, I throw the spare on wherever the flat tire is and drive home or to a local tire shop, whichever was closer.
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Old 12-18-2010, 01:00 PM   #11
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Quote:
Originally Posted by gregr01 View Post
The OEM spare's tire is narrower, but the same overall diameter as the OEM tires.

If your aftermarket wheel/tire setup is the same nominal diameter as OEM you're fine. If it's different, you'll need a spare that's the same diameter.

Post your new tire size (and wheel width).
Yeah, I'm pretty sure my new dire size is different... checked it out on the 1010 tires website.... My new tire size is 215/45/R17 17x7....
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Old 12-18-2010, 01:02 PM   #12
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Old 12-18-2010, 08:02 PM   #13
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Quote:
Originally Posted by gregr01 View Post
The OEM spare's tire is narrower, but the same overall diameter as the OEM tires.
No it's not.
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Old 12-18-2010, 08:50 PM   #14
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Quote:
Originally Posted by Konrad02ts View Post
Yeah, I'm pretty sure my new dire size is different... checked it out on the 1010 tires website.... My new tire size is 215/45/R17 17x7....
Your new tire size is essentially the same diameter as the stock tire size. But, I'm sure you already knew that when you bought the tires, right?

Quote:
Originally Posted by Byzantium View Post
Quote:
Originally Posted by gregr01 View Post
The OEM spare's tire is narrower, but the same overall diameter as the OEM tires.
No it's not.
Bingo!

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Old 12-19-2010, 11:05 AM   #15
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Quote:
Originally Posted by MD04WRX View Post
The fuse you use to make the car FWD is on auto transmissions only.
Gotcha, that's why I recommended re-reading the manual. The only time I have had a flat was when I got TWO at a time, so the spare did me no good anyway.
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Old 12-19-2010, 11:07 AM   #16
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Quote:
Originally Posted by parabellum9x19 View Post
I solved this by getting a full size spare. I take it with me if i leave town. Around town, AAA will tow me home at no charge. Cheap way to ensure you dont put undue stress on your diff.
Can you fit a full size spare in your 08? I couldn't fit one in my 06.
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Old 12-19-2010, 03:27 PM   #17
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Quote:
Originally Posted by mslstixx

Can you fit a full size spare in your 08? I couldn't fit one in my 06.
Not in the well, it rides in the hatch, i keep it clean enough to eat off of.
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Old 12-21-2010, 12:05 AM   #18
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Quote:
Originally Posted by Patrick Olsen View Post
Your new tire size is essentially the same diameter as the stock tire size. But, I'm sure you already knew that when you bought the tires, right?


Bingo!

Pat Olsen
Quote:
Originally Posted by mslstixx View Post
Gotcha, that's why I recommended re-reading the manual. The only time I have had a flat was when I got TWO at a time, so the spare did me no good anyway.
Quote:
Originally Posted by parabellum9x19 View Post
Not in the well, it rides in the hatch, i keep it clean enough to eat off of.
That's good. Never know when you'll be out camping and need a spare plate... or on a zombie mission.

TWO flats at a time?!! That would SUCK! ...yeah.

"new tire size is the same as stock... you already knew that, right?"

Well, surprisingly, I managed to graduate from college. But, I did NOT know that. I assumed it was slightly bigger... then I actually measured it up next to the wrx tire, and it (well the spare) was quite a bit smaller. So, now I'm just confused.... But, I ended up buying a wrx size spare from a guy. So, hopefully, worst case... I won't be ****ed. ....right?
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Old 12-25-2010, 02:52 PM   #19
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Spare's size is 135/70/17, at least for an '04 STi. OA diameter of approximately 24.5".

Last edited by gregr01; 12-26-2010 at 02:37 PM. Reason: d'oh
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Old 12-25-2010, 09:38 PM   #20
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Years ago i actually got two seperate flats in three blocks.

It was winter, snowing like crazy. I ran over a manhole with no cover that was obscured by snow and ice. Popped my tire and bent my wheel.

I changed it in the slush, while city busses ran by and threw freezing sleet on me. Put the donut on. It held 30 psi.

I went two blocks, and hit a pothole that shredded my donut. :-/

Waited two hours for a tow, wet and miserable.

It was the last time i ever used a donut spare.

Never again.
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Old 12-26-2010, 12:56 PM   #21
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Quote:
Originally Posted by Konrad02ts View Post
Well, surprisingly, I managed to graduate from college. But, I did NOT know that. I assumed it was slightly bigger... then I actually measured it up next to the wrx tire, and it (well the spare) was quite a bit smaller. So, now I'm just confused.... But, I ended up buying a wrx size spare from a guy. So, hopefully, worst case... I won't be ****ed. ....right?
Now you have me confused: I'm guessing you accomplished absolutely nothing by buying a WRX spare, since it's probably the same size as your original spare.

As for tire sizing, it should be basic knowledge that when you buy larger wheels you want to maintain the same outer diameter of the tire so that your speedometer and odometer read correctly, you don't compromise fender clearance, etc. http://www.miata.net/garage/tirecalc.html

Quote:
Originally Posted by gregr01 View Post
Spare's size is 135/70/70, at least for an '04 STi. OA diameter of approximately 24.5".
Methinks that should be 17, not 70.
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Old 12-28-2010, 02:47 AM   #22
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Quote:
Originally Posted by parabellum9x19 View Post
Years ago i actually got two seperate flats in three blocks.

It was winter, snowing like crazy. I ran over a manhole with no cover that was obscured by snow and ice. Popped my tire and bent my wheel.

I changed it in the slush, while city busses ran by and threw freezing sleet on me. Put the donut on. It held 30 psi.

I went two blocks, and hit a pothole that shredded my donut. :-/

Waited two hours for a tow, wet and miserable.

It was the last time i ever used a donut spare.

Never again.
.....that would REALLY suck! ....I think I might just do some research on runflats.

Quote:
Originally Posted by Patrick Olsen View Post
Now you have me confused: I'm guessing you accomplished absolutely nothing by buying a WRX spare, since it's probably the same size as your original spare.

As for tire sizing, it should be basic knowledge that when you buy larger wheels you want to maintain the same outer diameter of the tire so that your speedometer and odometer read correctly, you don't compromise fender clearance, etc. http://www.miata.net/garage/tirecalc.html


Methinks that should be 17, not 70.
Yeah... the wrx spare didn't end up working out... so no loss I guess. I think I'll just buy an extra 17 inch wheel. slap a 215/45/17 on it and hope for the best. altho... I think I might just research runflats
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Old 12-28-2010, 09:27 PM   #23
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Quote:
Originally Posted by Konrad02ts View Post
Yeah... the wrx spare didn't end up working out... so no loss I guess. I think I'll just buy an extra 17 inch wheel. slap a 215/45/17 on it and hope for the best. altho... I think I might just research runflats
The WRX spare didn't end up working out how? I think you still aren't getting the message here - your stock spare (or the WRX spare, which is probably the same size as your TS spare) will work just fine!

Spare - 135/70-16 = nominal 595.4mm diameter
TS stock tire - 195/60-15 = nominal 615mm diameter
WRX stock tire - 205/55-16 = nominal 631.9mm diameter
New tire - 215/45-17 = nominal 625.3mm diameter

So, your new tires fall in between the stock WRX and stock TS tire sizes. As long as you use the donut spare in accordance with the instructions in the Owner's Manual you will do no harm to your drivetrain.

Run-flats are a horrible idea. They're heavier, they cost significantly more, they ride poorly due to the stiffened run-flat structure inside, and there's a grand total of 1 run-flat option in the tire size you're running.

A full-size spare is unnecessary. If you want to spend your money to give yourself the peace of mind that you're protected from a problem that never existed, knock yourself out!
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Old 12-29-2010, 08:58 PM   #24
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Originally Posted by Patrick Olsen View Post
The WRX spare didn't end up working out how? I think you still aren't getting the message here - your stock spare (or the WRX spare, which is probably the same size as your TS spare) will work just fine!

Spare - 135/70-16 = nominal 595.4mm diameter
TS stock tire - 195/60-15 = nominal 615mm diameter
WRX stock tire - 205/55-16 = nominal 631.9mm diameter
New tire - 215/45-17 = nominal 625.3mm diameter

So, your new tires fall in between the stock WRX and stock TS tire sizes. As long as you use the donut spare in accordance with the instructions in the Owner's Manual you will do no harm to your drivetrain.

Run-flats are a horrible idea. They're heavier, they cost significantly more, they ride poorly due to the stiffened run-flat structure inside, and there's a grand total of 1 run-flat option in the tire size you're running.

A full-size spare is unnecessary. If you want to spend your money to give yourself the peace of mind that you're protected from a problem that never existed, knock yourself out!

Thank you for all the info first and foremost. I've been doing some research on differentials, and ran across something saying "no more than a 1/2" circumference difference between the tires to avoid any damage to the differentials..." Not that i think my car is warrantied anymore anyway, so if I total my diff... I guess I'd pay for it anyway.

According to your calculations, there is a 30mm difference in diameter between wrx 215... and TS spare. That's more than 1/2"

I think I'll use my best judgement... Thanks again.

Oh, and the wrx spare didn't work out because the guy I was buying it from told me it was an STi spare. Just my luck...
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