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Old 01-20-2011, 09:56 PM   #1
turboedpickup
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Default 2008 Impreza 2.5i 5sp - Flat tire - AWD?

I've been searching and searching - and i'm stilll confused . My sis-in-law's car got a flat... tow truck guy said, as he changed the tire out for the spare, that the tire guys need to take out the fuse after their done.

She drove the car to good-year... they didn't have the Bridgestone RE92A so they sold her 2 "Dunlop Fierce Instinct All Seasons." (wtf are those tires?)

Anyways...she thinks the fuse for the "FWD" is still "in" and not in the spare fuse box... should she take it out? Does it do anything? (other threads say that this only matters for automatic cars)

The car has 25,000 miles on it (with the original 92A's). Do you think she'll need to get the other two tires for the fronts (new tires are on the rear) as well?

Other question (she's just a daily driver kind of person) - are these tires ok...or should she exchange them (if possible) for a better daily driver tire?

Thanks!
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Old 01-20-2011, 10:21 PM   #2
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wait, im confused here, are you trying to say that the front wheels can be turned off so so speak by removing a fuse?

if thats the case youve been grossly miss-informed

if not. as long as the tires are within spec from SOA or SOC then they will not void warranty. i know this one as i have 1 odd tire myself. however you will have to probably fight for this as your dealer will say that it will damage your all wheel drive clutches.

granted its better to have 4 tires of the same name installed on the car all at once to ensure there is no unnecessary wear from tires moving at different speeds for long periods of time. having one or two odd tires will not destroy your car as long as they are close enough in size.

if the car is a dd, just about any tires will do. there are better tires for wear, fuel efficiency and performance, but if you dont care enough to buy purpose built tires, even cheepy tires will do fine, but no more than fine.
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Old 01-20-2011, 10:24 PM   #3
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First of all, this belongs in transmission, but since this is more of a misc. issue, whatever.

#1 AWD cars need the same tire on all 4 wheels. That's the official word on subaru, but as long as there isn't a huge difference in circumference in the wheels, it should be ok. I believe it's a few inches. HOWEVER, in terms of safety, I don't like it one bit. Rolling resistance and other stuff can in fact cause problems with the differentials.

#2 If the FWD is still in the AT transmission, the AWD light will be on in the dash.
To know which fuse to remove, check your owners manual, or the under of the fuse cover on the top drivers side under the hood.

I would DEFINITELY recommend getting the same tires... Whatever it would be. You seem to have just run of the mill passenger tires on. As bad as the RE92s are... I'm pretty sure they're better than THOSE. Really, they aren't bad and they perform great for it's classification... A decent step up would be any Ultra-high performance all-season tire on tirerack for example.

I may be paranoid, but I would not use AWD until you get all tires the same.
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Old 01-20-2011, 11:13 PM   #4
Wrencher86
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If the car's a stick then you can't turn the AWD off. If it's an automatic... I'm not sure they still had that feature in '08. If it does then the AWD light will be on in the dash.

Tires:
Four new tires > two old tires and two new tires no matter what brand

Bridgestone > Dunlop Do what you want but you're not going to get anything for "trade" on the Dunlops.


Slightly off-topic:

Why does everybody bash the Potenza's? I had them on my Civic and loved them. I beat the hell out of that car and those tires still lasted a good 50k miles.
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Old 01-21-2011, 06:28 AM   #5
NH8991
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Quote:
Originally Posted by Wrencher86 View Post
Why does everybody bash the Potenza's? I had them on my Civic and loved them. I beat the hell out of that car and those tires still lasted a good 50k miles.
There are different models of Potenza's, but most people with Impreza'a agree that the RE92s that come with the car are just awful. Yes, they wear ok, but from first hand experience once you start to push it dry grip is average and wet grip is just plain scary . I've had 2 different cars with them on, i took them off the 2nd car as soon as I could.
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Old 01-21-2011, 06:36 AM   #6
The G.O.A.T.
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Thisssss^^^^^^^^^
re92a's are the worst tire i have ever driven with (that includes some 10$ junkyard specials!)
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Old 01-21-2011, 07:32 AM   #7
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Quote:
Originally Posted by formula91 View Post
#1 AWD cars need the same tire on all 4 wheels. That's the official word on subaru, but as long as there isn't a huge difference in circumference in the wheels, it should be ok. I believe it's a few inches. HOWEVER, in terms of safety, I don't like it one bit. Rolling resistance and other stuff can in fact cause problems with the differentials.
This, and as of 98 at least, it was 1/4 inch in circumference (I think, might be diameter).

Quote:
Originally Posted by formula91 View Post
#2 If the FWD is still in the AT transmission, the AWD light will be on in the dash.
To know which fuse to remove, check your owners manual, or the under of the fuse cover on the top drivers side under the hood.
This. Again, as of 98. This is a little fuse sitting next to all the relays in the fuse box under the hood.


The problem is the AWD on manuals isn't electronically controlled, so you can't really disable it outside of breaking it.
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Old 01-21-2011, 10:23 PM   #8
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......think what you please... if you dont think im right call loman subaru, rt 46 parsippany nj..

Last edited by Evil XT; 01-22-2011 at 10:00 PM.
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Old 01-21-2011, 11:02 PM   #9
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Quote:
Originally Posted by formula91 View Post
#1 AWD cars need the same tire on all 4 wheels. That's the official word on subaru, but as long as there isn't a huge difference in circumference in the wheels, it should be ok. I believe it's a few inches. HOWEVER, in terms of safety, I don't like it one bit. Rolling resistance and other stuff can in fact cause problems with the differentials.
This is a CYA statement from their legal department, so no one can come back after fcking up their drivetrain and say, "you didn't tell me not to!". The drivetrain has enough tolerance built into it to accommodate any differences you'll encounter between tires of the same size - I ran two different brands front and rear for the better part of the car's first 30k miles, still no trouble at 93k.

The allowable difference in circumference is something like 3%, which roughly works out to bald tire on one side, new tire on the other.

I'm not saying I recommend using different brands at each end, but you won't kill the car.
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Old 01-22-2011, 01:24 AM   #10
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Quote:
Originally Posted by Evil XT View Post
You always change at least two tires at a time. Most imprezas have non limited slips except for the center diff. Too much tread on one side causes tire to spin faster than the other burning up the diffs. But since the diffs are open it shouldnt be that bad.
You're looking at it completely wrong.

The center diff (in the cheap cars) is the only one that's limited slip. It only compares the average speed of the front axles to the average speed of the rear axles. If have different tires front and rear, you WILL ruin the center diff sooner rather than later.


Quote:
See what happens is because the tire are a different size and the STi has 3 LSD's the trans wanted to spin faster than the engine did. So, the tires fed the wrong information back through the trans to the engine giving the cam and crank sensors the wrong readings giving the PCM a heart attack.
This is one of the stupidest things I've ever heard on NASIOC and I've been here a long time... Seriously, I'm not even sure where to start unravelling the stupid.

First of all, the engine or trans doesn't "want to" turn faster than the other. They don't have feelings and desires. However, when there's more torque being developed by the engine than consumed as parasitic losses in the driveline, the engine will make the driveline accelerate. The technical term for this is "I pushed on the gas". Similarly, when the engine is developing less torque than the driveline is burning off as parasitic losses, the driveline will cause the engine to decelerate. This is sometimes called "coasting". Neither of these have anything to do with the mismatched tires. In fact, as COPS has taught us all, you can do those things even once your tires have blown off.

Because the STi has 3 LSDs and they're somewhat strong, the LSDs are actively trying to equalize the rotational velocities of the 4 wheels. When you have mis-matched tires, the different sized tires will have different rotational velocities for the same linear velocity across the ground. This pisses off the LSDs because they're trying to force everybody to turn at the same speed. So one of two things happens. Either the LSDs cause one or more tires to skid across the pavement in order to equalize rotational velocity or the LSD itself will bind and release as it's unable to force the wheels to match speeds. Either of these will feel like a binding and popping sensation. Both the tires and the diffs will be destroyed over time.

Finally, the tires, nay, even the driveline, cannot cause the crank and cam position sensors to report false readings and confuse the ECU. While they is a physical connection between the tires and the cams (via the driveline, clutch, crank, crank sprocket, timing belt, and finally the cam sprocket), the cam and crank are where ever they are and the sensors will report that. They don't become in the "wrong" place or report bad data just because the tires are mis-matched.


Quote:
Since the manual subarus have a locking center diff
Manual Subarus do not have a locking center diff. They have an extremely weak (4kgf/100RPM) viscous-coupled LSD in the case of the 5MT or a electronically-controlled clutch-pack LSD in the case of the 6MT.

Quote:
one front tire and one rear tire HAVE TO spin.
No, not really. It's a limited-slip, not a locker. If you were to put both front wheels into the cradle and drag both rear wheels along the ground on a tow truck, the center diff would exert 4kgf of force per hundred RPM of shaft speed mismatch onto the front driveshaft. Obviously, this would not be enough to force the chained-down front wheels to turn so the center diff would quickly overheat and the LS unit would fail. At this point, the center diff would become and open diff and the car would merrily roll down the road without any concern.


Quote:
So usually when the wrecker comes the dude usually disconnects the driveshaft at the rear end or takes it off all together.
I assure you, this is not the case. The driveshafts on a Subaru are not trivial to disconnect. This is why it is required to move a Subaru on a roll-back/flatbed and why they cannot be towed by a typical tow truck.

Quote:
On an automatic its slightly different. Auto AWD cars are usually FWD until they need it. The center diff on an automatic has clutch packs (MPT as it called) that detect slipage. This is where your fuse comes into play. Plug the fuse in and it makes it FWD and anything from the center diff back is rendered usless.
You are almost, but not quite, on this one. The automatics have an electronically controlled clutch-pack slip limiting unit inside an open diff. Under 4-wheels-gripping conditions, the TCU does not command the clutchpack to tighten. When the TCU detects slip on one or more wheels, the clutchpack is commanded to tighten, acting to limit the speed differences between wheels. When you remove the AWD/FWD fuse, the system defaults to a fully open center differential, which is why it can be towed.

Finally, where ever you work, quit. It's terrifying that you're allowed to touch the public's cars with the amount you don't know.

Quote:
Originally Posted by Tim25RS View Post
This is a CYA statement from their legal department, so no one can come back after fcking up their drivetrain and say, "you didn't tell me not to!". The drivetrain has enough tolerance built into it to accommodate any differences you'll encounter between tires of the same size - I ran two different brands front and rear for the better part of the car's first 30k miles, still no trouble at 93k.
I would posit that you have killed your center differential's VC LSD unit and just haven't noticed. Again, when the VC unit fails, it fails open in most cases. This means the car will drive completely normally except when you try to get yourself unstuck from the snow/mud/etc.

As a point of reference, I have managed to ruin my stock VC unit simply by running a tire pressure front vs rear that worked well for handling but resulted in a speed difference between the two ends that fried the VC unit. That's a pretty small difference over a 4psi argument.
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Old 01-22-2011, 10:37 AM   #11
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^^^ What he said.
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Old 01-22-2011, 04:16 PM   #12
Tim25RS
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Originally Posted by williaty View Post
I would posit that you have killed your center differential's VC LSD unit and just haven't noticed. Again, when the VC unit fails, it fails open in most cases. This means the car will drive completely normally except when you try to get yourself unstuck from the snow/mud/etc.
You posit incorrectly, everything works fine. I would posit that something other than a 4psi difference in tire pressure killed your VC unit, since the factory-specified pressures are different front to rear by 3psi.

Again, I'm not saying I recommend running 2 different brands, but it shouldn't damage anything.
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Old 01-22-2011, 05:18 PM   #13
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Quote:
Originally Posted by Tim25RS View Post
You posit incorrectly, everything works fine.
How do you know? Drives fine? It'd drive fine if the center LS unit failed.


Easiest test for the end user is to set the car on jack stands, lock the parking brake TIGHT, put it in 1st gear, and let the clutch out. Then tell us what happens.


Quote:
Originally Posted by Tim25RS View Post
I would posit that something other than a 4psi difference in tire pressure killed your VC unit, since the factory-specified pressures are different front to rear by 3psi.
I didn't say there was a 4psi difference between front and rear, I said that there was a 4psi difference between the f/r split Subaru calls for and what I'm actually running.
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Old 01-22-2011, 05:29 PM   #14
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Originally Posted by williaty View Post
How do you know? Drives fine? It'd drive fine if the center LS unit failed.
I know because I've driven it in low grip conditions and it behaves exactly as you'd expect it to. I'm not going to risk actually damaging it in some idiotic test just to prove something to some guy on the internet. sorry.


Quote:
I didn't say there was a 4psi difference between front and rear, I said that there was a 4psi difference between the f/r split Subaru calls for and what I'm actually running.
You said there was a 4psi difference. I took that to mean 4psi front to back. If the difference was actually 7psi or more, it's no wonder you damaged your driveline. That's quite different from running different tire brands within factory spec, though.
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Old 01-22-2011, 05:32 PM   #15
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Originally Posted by Tim25RS View Post
I know because I've driven it in low grip conditions and it behaves exactly as you'd expect it to. sorry to burst your bubble.
"Exactly as I'd expect it to", frankly, is almost no different than with it completely open. The stock 4kgf/100RPM VC unit is unbelievably weak. Frankly, it's so weak I honestly don't see the point of going to the expense of having it. You wouldn't be able to tell in normal driving, you wouldn't be able to tell driving with all 4 wheels in snow. You might be able to tell if you had one end of the car on glare ice and the other on dry pavement but I wouldn't hold my breath. That's why you'd have to test it carefully to know.
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Old 01-22-2011, 06:14 PM   #16
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sorry you're not satisfied. feel free to continue thinking my car is broken.
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Old 01-22-2011, 07:25 PM   #17
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She might have to purhase 4 brand new tires.
There cant be more then 5K miles difference on any of the times(thats a example)
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Old 01-22-2011, 09:14 PM   #18
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Originally Posted by Pks17 View Post
She might have to purhase 4 brand new tires.
There cant be more then 5K miles difference on any of the times(thats a example)
That's not a good rule of thumb. I can take econo-tires and drive them in such a way that I won't exceed the 1/4" circumference difference for 20,000 miles. I can also take a set of summer tires and wear them more than that in 500 miles.
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Old 01-22-2011, 09:29 PM   #19
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Wow. Thank you all for the responses. Since she already went and got the other two tires - I let her know to get the other two (I never even heard of the brands). I told her to talk to me next time her tires blow out... I have a tire place and tires to recommend. She's not an aggressive/fun driver in any way - so totally all about decent performing all seasons for her.

Anyone have any further recommendations - I was thinking Falken 912's, S Drives, G-Force Sports, but... those aren't necessarily all seasons. But whatever - she'll be good until her next tire needs.

And thanks again for the fuse clarifications. Finally clear.
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Old 01-22-2011, 09:57 PM   #20
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HAHAHA...I knoew I should have kept my mouth shut around you jerk offs...
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Old 01-22-2011, 10:14 PM   #21
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HAHAHA...I knoew I should have kept my mouth shut around you jerk offs...
Yes, being stupid in public never really works out the way you'd hoped...
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