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-   -   Do I need a New "Donut" Spare Tire?? (http://legacygt.com/forums/showthread.php?t=200114)

Almatti 01-21-2013 05:00 AM

Do I need a New "Donut" Spare Tire??
 
I upgraded to Legacy Limited 17" Wheels on our 2010 legacy Premium (OEM 16" Wheels) [thanks to Steve]. It just occurred to me (my older son just had a flat on his Elentra): Do I need to buy a new Donut Spare tire & wheel?? Is the Donut Spare for cars with 17" wheels also 17" - i would think so ??

Ellesedil 01-21-2013 05:26 AM

For an AWD vehicle, all of the tires must be the same overall diameter so that the differentials in the car are not overworked.

In case you were wondering, my parents just bought an Impreza and we were talking about tire sizes for it just before winter started, so we went outside and snagged the tire size off the spare. It's overall diameter was nearly the same as the original tires on the car itself. Your Legacy should be no different.

If you're still unsure, it's a simple matter of taking the size of the original tires and the size of the spare and calculating their overall diameters.

minuccims 01-21-2013 06:40 AM

The outer tire diameter for the 5th gen Legacy family is about the same; They all come with the same donut spare.

I will say this outer diameter is LESS than stock diameter. The recommendation is to not drive fast, and don't drive far. Last time I needed the donut spare, I lowered the air pressure in the tires to better match the spare's OD. Drove slow and less than two miles to a tire shop.

I have an 07 OB; that OD is greater than our spares. Go figure since our gen stepped up a size for sidewall aspect ratio. Do not know if the current OB use the same donut as the Legacy.

Almatti 01-21-2013 06:54 AM

my question here is: for 2010-2012, do the Legacy Limiteds which come with 17" wheels (stock) have the same size Donut Spare in the trunk as the Legacy Premiums which come with 16" wheels. Since I upgraded my wheels to 17" Limited versions, I have the OEM Donut Spare for a Premium in my trunk. Do I need to replace that with a Limited Donut Spare ??

minuccims 01-21-2013 07:31 AM

Just checked; spare is T135/70/R17. LGT OEM rims are 18". Yours should be identical.

bucko3the7man 01-21-2013 07:56 AM

Miata.net tire size calculator. Google it, use it

Rutchard 01-21-2013 09:23 AM

It's all about the tire size, not the wheel size. What size tires are you running on your 17" wheels?

ehsnils 01-21-2013 10:18 AM

Since I have two set of wheels, one winter one summer I have one from the other set as spare.

awalegacy 01-21-2013 05:52 PM

If you bought the right size tires with your new 17" wheels, the diameter of the tire should not have changed at all. Even if you went to 18" wheels, with the proper tire size, the overall diameter should remain the same.

All of this means that you should not need to change your spare.

On another note, I'm pretty sure the donut that comes with these cars IS undersized.

ssbtech 01-21-2013 06:16 PM

Didn't the 2010+ do away with the rear limited slip differential?

You won't be overworking the diff with one tire smaller than the other.

TwoTone 01-21-2013 07:35 PM

Quote:

Originally Posted by ssbtech (Post 4256189)
Didn't the 2010+ do away with the rear limited slip differential?

You won't be overworking the diff with one tire smaller than the other.


You willing to pay for someone's repair on that incorrect assumption?

apexi 01-21-2013 08:20 PM

1 Attachment(s)
Put this together quick for what its worth.. my oem subaru tire size versus my oem spare tire size. And based off other threads, it looks like Almatti went with a 215/50/17 tire, so theres a comparison between that tire size and the size of a 16" spare tire found in a 2010 legacy. I used discount tire's calculator, found here http://www.discounttire.com/dtcs/infoTireMath.dos

*Decided to add a 3rd image on the end comparing the size of stock 16" tire for a 2010 legacy, versus the size of a 16" oem spare tire

ssbtech 01-22-2013 12:15 AM

Quote:

Originally Posted by TwoTone (Post 4256279)
You willing to pay for someone's repair on that incorrect assumption?

What part of my "assumption" was incorrect?

ehsnils 01-22-2013 02:53 AM

Quote:

Originally Posted by ssbtech (Post 4256189)
Didn't the 2010+ do away with the rear limited slip differential?

You won't be overworking the diff with one tire smaller than the other.

You still have the center diff to worry about.

Almatti 01-22-2013 07:46 AM

apexi, You guessed right. have 215/50/17s on the new wheels. The OEM were 205/60/16s !!!. I have not been able to check my OEM donut spare yet. (just had knee surgery). But judging from the chart you posted, it seems the overall circumference is about .2 inches LESS with the OEM wheels andd tires vs. the new 215/50/17s on the upgraded Subaru 17" wheels. That should be alright for using the Donut spare for emergencies.

To ssbtech: I don't think that Subaru would put a Donut Spare for use in a flat tire emergency (granted for limited use and limited speeds 50mph MAX), where it would damage the AWD drive train in any way. Donuts Spares are for very limited usage on all cars. They were created for weight reduction, more trunk space available, and for emergency usage only until you can get to a real tire change and repair or buy a new tire if that's required. I wouldn't drive for any great distances.

From apexi's chart it appears that the slight variance won't matter for emergency usage and doesn't require upgrading to different Donut Spare. for those of you have 17" wheels on 2010-2012 Subaru Legacy (the 2013 Legacy premiums have upped the standard wheel size to 17"), I'm curious if the Donut Spare is the same one used for 16" OEM wheels...


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