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2010 Forester Premium X AT
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Discussion Starter · #1 ·
I have a 2010 automatic with a full size spare (OEM size) with an original geolander that is worn down to 6/32.

Say I have a flat on my current set of tires that are at 9/32, and I put the full size spare on, do I still need to insert the fuse? and do I need to keep my speed down while on this full size spare?

I could care less about TPMS lights but I dont want to be damaging the trans/diffs.

I understand that if i were running the donut I would had to insert the fuse and not drive highway speeds, but after reading a lot of posts, I'm still not sure if it need to do these things with the full size.
 

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2019 Crosstrek 2018 XT
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technicqlly, yes, as this works out to just under .6" difference on the circumference. For under say 25 miles or so though I wouldn't worry about it. Now if you are on a trip and have a couple hundred miles to go..yea. Best to put the fuse in once so if you need to do it you won't have any problems.
 

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Discussion Starter · #3 ·
Makes me feel a little better. Do you know what exactly would burn up if I didn't pull it? the electronic clutch system in the trans? Would the diff fluids burn up either way if you had a mismatch on the front or rear axle?
 

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2019 Crosstrek 2018 XT
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The problem I believe would be in the front diff. But again I wouldn't worry about it. You could probably go a long distance 100's of miles and have no problem..but why? I actually put on my full size spare, installed the fuse and drove several hundred miles just for the experience.
 

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Discussion Starter · #5 ·
At least one ~400 mile trip is a weekly occurrence for me, where i sometimes pick up nails and have to slap on the spare and end up driving a long way on the interstate back home on it. Wasnt sure if I was roasting something in the drivetrain by doing this.

FWIW, the geolanders are a LOT louder than michelin MXV's. I can compare it real time!
 

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2008 Forester AE
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We are talking about putting the spare on the rear right?
pulling the fuse won't help is your running mismatched fronts..
 

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2019 Crosstrek 2018 XT
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We are talking about putting the spare on the rear right?
pulling the fuse won't help is your running mismatched fronts..
I don't know what you are saying.....I think its your wording?? Could you clarify??
 

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I don't know what you are saying.....I think its your wording?? Could you clarify??
Right right, right? right! :biggrin: I'll be more clear;

What I am saying is that even if a full size spare is used it needs to go on the rear of the car.

The fuse to disable awd will not prevent damage if two different sized tires are used on the front of the car.
 

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2012 XT Touring 4EAT
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Right right, right? right! :biggrin: I'll be more clear;

What I am saying is that even if a full size spare is used it needs to go on the rear of the car.

The fuse to disable awd will not prevent damage if two different sized tires are used on the front of the car.
Actually, the fuse to disable should not prevent damage if two different sized tires are used on any axle - front or rear.
 

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The fuse to disable awd will not prevent damage if two different sized tires are used on the front of the car.
I am not sure that is correct..although I am not positive. I would have to say if you have a rear differential with "limited slip" would have a problem with different tires on the rear...ie one rear tire different than the other rear tire.

Again..not arguing.
 

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Actually, the fuse to disable should not prevent damage if two different sized tires are used on any axle - front or rear.
I am not sure that is correct..although I am not positive. I would have to say if you have a rear differential with "limited slip" would have a problem with different tires on the rear...ie one rear tire different than the other rear tire.

Again..not arguing.
:Banane35: maybe I've got it wrong.

I know that our 08 4eat manual says the spare must go on the back, and fwd fuse needs to be added. I understood this was because adding the fuse turns the center diff to the front and doesn't drive the rears, leaving it like an open diff in the back so the different tire size wouldn't matter..

If you put different sized tires up front wouldn't it be shearing in the front diff when you drive?
 

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2005 Forester XT 4eat
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I understand what ADC is saying. If you have LSD in the rear, you should not use an undersized spare in the rear. I believe this is why the '04 - '05 XTs came with a full sized spare.

I don't believe any of the '09s were equipped with a rear LSD.
 

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:Banane35: maybe I've got it wrong.

I know that our 08 4eat manual says the spare must go on the back, and fwd fuse needs to be added. I understood this was because adding the fuse turns the center diff to the front and doesn't drive the rears, leaving it like an open diff in the back so the different tire size wouldn't matter..

If you put different sized tires up front wouldn't it be shearing in the front diff when you drive?
The front diff is an open diff. There won't be any shearing. I think the thinking behind putting the full sized spare on the front is for safety, not for protecting the LSD. I would not run a space saving spare for very long.
 

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Don't think on 09+ vehicles the FWD fuse does much. When I had my donut spare on the rear and put the fuse in, I still had power going to the rear wheels because I could spin it very easily in the winter conditions.


The main reason to keep matched tires on the front is so the steering is not affected.
 
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