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Old 04-28-2014, 10:54 PM   #1
davidm_sh
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Default spare tire size question

Alright so I have a question. Subies AWD system tends to like all wheels to be the same diameter. So why is it that the factory gave us undersized spare tires?

Example(s)

According to this tire size calculator website - http://tire-size-conversion.com/tire-size-calculator/

I am doing a STi swap and wanted to get a STi spare that would clear the Brembo brakes.

So looking at an 04 STi tire size (that is my swap STi) of 225/45/17 that gives a tire diameter of 25". The 'official spare tire size' from Subaru according to my local dealership is 135/70/17 with a diameter of 24.4".

So my question is simple - why the smaller spare? Why not use a 135/75/17 and get a matching diameter of 25"? I checked the compartant for the spare and in my (Forester which is where the STi swap is) there is more than a 1/2" of extra room in the wheel well for the spare.

Thoughts?
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Old 04-28-2014, 10:58 PM   #2
sc00by4life
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Because it's cheap.

Because it's only meant to be driven on for a very short period of time.
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Old 04-29-2014, 12:18 AM   #3
Uncle Scotty
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i had a brand new 17" sti spare wheel with no tire

i tried for a LONG time to find a spare tire like that


i gave up

i dont give up easily.
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Old 04-29-2014, 04:12 AM   #4
Scoobiesdoobies
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50 miles max distance on spares. Anymore you can damage the diff
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Old 04-29-2014, 06:47 PM   #5
davidm_sh
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Quote:
Originally Posted by sc00by4life View Post
Because it's cheap.

Because it's only meant to be driven on for a very short period of time.
I wouldn't say any donut tire is cheap (been getting prices in the $180 - 190 for just the tire)

I do understand it is meant to be driven on for a short period of time but I would say that is because of the diameter difference more than anything else.
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Old 04-29-2014, 06:48 PM   #6
davidm_sh
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Quote:
Originally Posted by Uncle Scotty View Post
i had a brand new 17" sti spare wheel with no tire

i tried for a LONG time to find a spare tire like that


i gave up

i dont give up easily.
Hey Scotty - long time no see =).

Yah hearing that come from you ... means something [heh] - sigh.

Thanks
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Old 04-29-2014, 06:52 PM   #7
davidm_sh
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what about this idea?

How about a 145/70/17 tire? That comes out to the same diameter as a 225/45/17 and discount tire (in my area) says they might beable to get that.

My only question is would that me to wide of a tire for the spare rim?
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Old 04-29-2014, 08:02 PM   #8
sc00by4life
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Quote:
Originally Posted by davidm_sh View Post
I wouldn't say any donut tire is cheap (been getting prices in the $180 - 190 for just the tire) I do understand it is meant to be driven on for a short period of time but I would say that is because of the diameter difference more than anything else.
It's cheap for the manufacturer.
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Old 04-30-2014, 02:27 AM   #9
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Quote:
Originally Posted by davidm_sh View Post
Hey Scotty - long time no see =).

Yah hearing that come from you ... means something [heh] - sigh.

Thanks
maybe call Luke at TR and see if he can help ya out
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Old 04-30-2014, 09:57 AM   #10
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i ruined the rear diff on my 02 OBS driving 60ish miles on the stupid donut. i stayed at or below 55 and made sure it was properly inflated as well. still essed the bed. i did have a car full of people driving home from a show in denver...

after that, i ran a full size 205/55-16 spare on that car. it fit in the tub perfectly.

i now run that same full size spare in my 08 wrx. the diameter fits in the tub just fine, but the width of the tire holds up the board that covers it in the hatch. not a big deal to me, but still a bit annoying. better than a fried diff though.
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Old 04-30-2014, 08:41 PM   #11
davidm_sh
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Well I ordered the 145/70/17 and will see how it fits on the STi spare wheel in a week or so.
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Old 05-01-2014, 07:39 AM   #12
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Quote:
Originally Posted by davidm_sh View Post
Well I ordered the 145/70/17 and will see how it fits on the STi spare wheel in a week or so.
wellll

was that an xl load rated tire??

load rating is imp0tent heer

that is one reason 'spare' tires arent the same a regular tire of(about) the same size
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Old 05-01-2014, 11:13 AM   #13
davidm_sh
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Quote:
Originally Posted by Uncle Scotty View Post
wellll

was that an xl load rated tire??

load rating is imp0tent heer

that is one reason 'spare' tires arent the same a regular tire of(about) the same size
Good question. It was rated and is a spare tire. I will check with them today to see what the load rating difference (if any) is between this and the stock size.

Thanks
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Old 05-01-2014, 07:32 PM   #14
davidm_sh
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So according to tirerack.com the spare tire (145/70/17 by Bridgestone) does not have an XL load rating. It has a SL (standard load) rating BUT it is spec'd to carry 2094 lbs @ 60psi.

http://www.tirerack.com/tires/tires....omCompare1=yes

So I am thinking it should be ok on my 3350lb (roughly) curb weight Forester XT(STi)?
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Old 05-01-2014, 09:40 PM   #15
Uncle Scotty
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Quote:
Originally Posted by davidm_sh View Post
So according to tirerack.com the spare tire (145/70/17 by Bridgestone) does not have an XL load rating. It has a SL (standard load) rating BUT it is spec'd to carry 2094 lbs @ 60psi.

http://www.tirerack.com/tires/tires....omCompare1=yes

So I am thinking it should be ok on my 3350lb (roughly) curb weight Forester XT(STi)?
oooowwww...it is a real 'spare tire' tire...so it should be fine
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