badjer Posted March 31, 2004 Share Posted March 31, 2004 Hi all, I am afraid I know the answer here, but just wanted to be sure. My 96 Outback (5 spd manual) came home tonight with a roofing nail near the sidewall of the passenger rear and the shop said it couldnt be repaired. Since it was closing time, I sprung for 2 new tires on the rear since I knew they needed to be the same size, but figure I would probably be back for 2 more on the front. They said the damaged tire still had 55% of the tread left-- Is this close enough to new that the size difference wont matter between the rear and fronts?? or do I just spring for new tires on the front too?? thanks badjer Quote Link to comment Share on other sites More sharing options...
SevenSisters Posted March 31, 2004 Share Posted March 31, 2004 You can search the archives for the Subaru spec, but I believe it is 1/4" in circumference. My advice to all Subaru owners is to buy an extra wheel and tire and do a five tire rotation. You'll get the same tire cost per mile, but will be out the cost of the wheel. Try a previously used wheel store (junkyard). If you have an unrepairable tire, try to find a used tire of the same brand, size, and tread depth at a tire shop or ask them where you can get a new tire buffed down to the same diameter as the others. Did you pull the AWD fuse? Check your manual, but you want it out of AWD until you get fixed up. Quote Link to comment Share on other sites More sharing options...
kevinsUBARU Posted March 31, 2004 Share Posted March 31, 2004 You can search the archives for the Subaru spec, but I believe it is 1/4" in circumference. My advice to all Subaru owners is to buy an extra wheel and tire and do a five tire rotation. You'll get the same tire cost per mile, but will be out the cost of the wheel. Try a previously used wheel store (junkyard). If you have an unrepairable tire, try to find a used tire of the same brand, size, and tread depth at a tire shop or ask them where you can get a new tire buffed down to the same diameter as the others. Did you pull the AWD fuse? Check your manual, but you want it out of AWD until you get fixed up. Tires need to be within 1/4" circumference of eachother. SevenSisters: 5-speeds manuals don't have the option of putting a fuse in for FWD. On an automatic, if you get a flat, you put the FWD fuse in, and you have to put the spare on the rear regardless of where the flat occured. Quote Link to comment Share on other sites More sharing options...
The Dude Posted March 31, 2004 Share Posted March 31, 2004 That's the first time that I have heard that the spare tire MUST go on the rear axle when the inserted fuse puts the AT into FWD. If I may ask, where did you get that piece of information? It would seem to me it would not matter on which axle the spare was mounted as long as the AT was in the FWD mode. It doesn't matter on the average full-time FWD car. Quote Link to comment Share on other sites More sharing options...
SevenSisters Posted March 31, 2004 Share Posted March 31, 2004 Thanks for making sure badjer had the right facts. I should have read the post better (5 speed) and checked on the fuse being in or out. Too lazy to check my manual. It's got to be a bitch to have to buy all new tires because of one lousy flat. Quote Link to comment Share on other sites More sharing options...
powderhound Posted March 31, 2004 Share Posted March 31, 2004 My question is why doesn't the 5MT require a FWD "limp mode"? I have a tire that is out of the 1/4 inch parameters and wonder how concerned I need to be with a manual. Quote Link to comment Share on other sites More sharing options...
Commuter Posted March 31, 2004 Share Posted March 31, 2004 Technically, the donut spare could go on the front or the back if the center clutch pack is disabled by the fuse. I do recall reading somewhere (SOA site I think) where it is "strongly recommended" that the donut go on the back. The front tires are doing all the work to move the car as well as steer it when the fuse is in. Additionally, the front tires do most of the braking too. Since the donut spare is just a short term use tire with minimal capability, it makes the most sense from a safety perspective to keep two full sized tires on the front when you have a flat. Commuter Quote Link to comment Share on other sites More sharing options...
kevinsUBARU Posted March 31, 2004 Share Posted March 31, 2004 From mysubaru.com: All-Wheel Drive (AWD) vehicles, it is extremely important that the rolling or outer circumferences of the tires be within 1/4 inch of each other. This means that you must physically measure the size of the tire. This is best done with the weight of the vehicle off the tire and at the tread centerline. Also be certain that the tires are properly inflated since this can affect your readings. If you need to replace just one tire, the same holds true. The measured difference in circumference between the replacement tire and the other tires on the vehicle cannot exceed 1/4 inch. Depending on the vehicle mileage, it might be better to replace all four tires. If the vehicle mileage is low and the tires have been rotated and driven at the proper inflation pressures, then you may be within the allowable 1/4-inch difference in circumference. If the difference between the new/replacement tire and the current tires is within this 1/4-nch maximum, then the tire should be compatible. If it is not, then other tires will need to be replaced to conform to the 1/4-inch rule. Exceeding this 1/4-inch difference in tire circumference can place unnecessary wear on drivetrain components, possibly causing them to wear out prematurely. If your vehicle is AWD (All-Wheel Drive) with an automatic transmission and the temporary spare tire has been installed, put a spare fuse (15 amp) inside the FWD (Front-Wheel Drive) fuse holder (refer to your owner's manual for location). Confirm that the Front-Wheel Drive (FWD) warning light comes on before you drive the car. Installation of this fuse deactivates AWD to prevent possible damage to the drivetrain components that can result due to the use of the smaller temporary spare tire. After re-installing the conventional tire, remove the fuse from the FWD fuse holder to restore AWD operation. For more information on tires and temporary spare tire usage, always consult your Subaru owner's manual. I know it doesn't say you have to put the donut on the back, but I didnt pull that out of my rump roast I think it says so in my Impreza manual... Anywhow, take care! Kevin Quote Link to comment Share on other sites More sharing options...
camosuba Posted March 31, 2004 Share Posted March 31, 2004 this 1/4 inch that is being referred to shouldn't that be diameter rather than circumference? Quote Link to comment Share on other sites More sharing options...
Commuter Posted March 31, 2004 Share Posted March 31, 2004 this 1/4 inch that is being referred to shouldn't that be diameter rather than circumference?NO! Circumference. (Repeat over and over and over... ) This equates to 1mm (sorry for mixed units) of tread depth variation. (1/4" divided by (2 x pi) where pi = 3.14). If your tire has an 80" circumference, 1/4" represents 0.3%. Another way to put this - Over a given distance, one tire would rotate 1000 times, the other tire would rotate 1003. It is probably conservative, but it is Subaru's official statement. "The Beauty of AWD." In my travels on message boards over the past few years, it certainly appears that the automatic's clutch pack is more sensitive than the manual's viscous coupling. Commuter Quote Link to comment Share on other sites More sharing options...
duane b Posted March 31, 2004 Share Posted March 31, 2004 Here's something I would like to toss out for thought. If you take two identical tires off the car, one filled to specified psi and the other flat, aren't they the same circumference? Tires don't stretch much when filled up. But if you take those same two tires and put the weight of the car on them, what changes is the the diameter mostly. And from the many past posts on this same subject, most of the concern is about tires properly filled to the correct psi on all fours. So circumfrence wouldn't come into play as much as diameter where all four properly inflated tires are concerned. The reason I bring this up is we had a situation this past summer on a 2500 mile roadtrip. We had a slow leak in one tire. All tires were identical brand, model, size, and approximate wear. After so many hundreds of miles at low psi in one tire (it would leak down to 15 psi and stop) the "AT TEMP" light starts flashing upon start up. When we get back home I took the car (96 AWD Legacy AT) into Subaru for a diagnostics. They tell me the clutch pack has worn abnormally and will need to be replaced soon. They said the cause could be from putting miles at high speeds on the low tire. Not to mention since we bought the car just before our trip, who knows how many hundreds if not thousands of miles this car had been driven with a low tire by the previous owners. I think the dealer we bought from must have kept the tire pressure inflated daily on this car because I didn't notice it when we test drove it. So it would seem logical to me that tire diameter could play into problems associated with clutch pack wear. Anyway just my $0.02:-\ Quote Link to comment Share on other sites More sharing options...
frag Posted March 31, 2004 Share Posted March 31, 2004 An easy and exact way of knowing if your tires are whitin specs (1/4 inch in circumference) in real world conditions is to do as I did: put a piece of duct tape on the tires walls right next to the foot patch of the tires and draw a pencil line where the tires touch the ground. Have someone counting the tire revolutions or measure the proper distance in an empty parking lot and give the front left wheel 40 revolutions. Very easy to see what lines are > or < ten inches (radial measurement) from the others. Quote Link to comment Share on other sites More sharing options...
cookie Posted March 31, 2004 Share Posted March 31, 2004 when I first got my car with about 80,000 miles on it I noticed no one had ever taken the original spare and put it in rotation. So now I have four well worn tires and a new spare made in 1998. Quote Link to comment Share on other sites More sharing options...
Commuter Posted April 1, 2004 Share Posted April 1, 2004 Diameter and circumference are directly related (via pi). What matters with a tire is the effective diameter (or circumference). Also called rolling diameter (or circumference). The earlier post of info from mysubaru.com mentions "rolling or outer circumference". A tire is flexible, so this dimension changes with tire pressure and load. Yes, it's entirely possible that a low tire for many miles could have damaged the clutch pack. The AWD system thinks that one wheel is slipping and engages it. In fact, you know this was happening since the AT fluid heated up. I've picked up nails and have also had a slow leak happen a couple of times. Knock wood, it seems that it didn't do any permanent damage. I don't think I ran for too long in that state, so I got away with it. Commuter Quote Link to comment Share on other sites More sharing options...
rideabmx Posted April 1, 2004 Share Posted April 1, 2004 These things are good to know; glad I found this post. Originally I thought I read somewhere that it was a 1/2" difference in DIAMETER. A 1/4" difference in circumference makes much more sense. It's also pertinent to me at the moment. I got a new set of tires in December right before a huge road trip. After we made it down to Death Valley (from Corvallis, Oregon), my girlfriend hit a huge rock on the Racetrack road and put a big bulge in. Got the tire replaced, and didn't worry about size differences because the other tires only had a few thousand miles on them. We went back to Death Valley again for Spring Break (beats the Oregon rain!) and of course ended up with a irreparable tire issue (this time a huge hole) and of course in almost the exact same spot on the Racetrack road. Now that tire has to be replaced (of course), and now I'm a little worried about this circumference thing. I didn't think ahead to buy an extra tire and put it in rotation--that would have been a great idea. Is cutting down tread to match the other tires something that's easily done? What do you all think about having 3 separate tire circumferences on there (2 tires at the original wear depth, 1 tire at the first replacement depth, and 1 tire at the new depth)? Would it be possible to alter the effective "rolling" circumference via air pressure? Thanks, Josh Quote Link to comment Share on other sites More sharing options...
Tiny Clark Posted April 1, 2004 Share Posted April 1, 2004 I don't know why they couldn't put an inside vulcanized patch on that hole in the first place. Oh wait, they sell new tires... Quote Link to comment Share on other sites More sharing options...
rideabmx Posted April 1, 2004 Share Posted April 1, 2004 Apparently that was their original intent. I used Fix-A-Flat to seal it, and the guy said that Fix-A-Flat doesn't work on anything over the size of a small nail hole (on the inside surface of the tire). When I came back to get the car, he said that it was the size of a nickel and that I needed a new tire (with absolutely no explanation of how Fix-A-Flat held up). Since the tires are under warranty, they're giving me the tire for free, so I'm sure they're not lying. ~Josh Quote Link to comment Share on other sites More sharing options...
cookie Posted April 1, 2004 Share Posted April 1, 2004 industry at the big flee markets.I have had good luck finding a match there for a FWD. Next I will be looking for three vintage 1998 brand new Michellins I think. I hope they still make that model. Quote Link to comment Share on other sites More sharing options...
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