Phizinza Posted February 16, 2011 Share Posted February 16, 2011 Ok here is the situation. I managed to get a flat, so I am running a spare. The spare is a steel wheel so I was thinking of putting the tyre off it on to the mag which has a flat. The mags have 215/60R16 Yokahama Geolander G900B's. The Spare has a 215/60R16 Yokahama Geolander G035. The G035 has a diameter of about 5mm less then the G900B's. That is about 1/5th of an inch. And I mean diameter, not circumference. Is it ok to run the G035 in place of one of the G900B's? Link to comment Share on other sites More sharing options...
johnceggleston Posted February 16, 2011 Share Posted February 16, 2011 Ok here is the situation. I managed to get a flat, so I am running a spare. The spare is a steel wheel so I was thinking of putting the tyre off it on to the mag which has a flat. The mags have 215/60R16 Yokahama Geolander G900B's. The Spare has a 215/60R16 Yokahama Geolander G035. The G035 has a diameter of about 5mm less then the G900B's. That is about 1/5th of an inch. And I mean diameter, not circumference. Is it ok to run the G035 in place of one of the G900B's? short term maybe, but not long term. if it is an auto trans you can put a fuse, any fuse, in the FWD holder under the hood and it will not matter. but this is a short term fix. is the flat tire beyond repair?? the circumference of all 4 tires need to be with in 1/4'' of each other . a 10' or 8' steel tape measure, 1/4'' wide, is good for checking the circumference. Link to comment Share on other sites More sharing options...
Mike104 Posted February 16, 2011 Share Posted February 16, 2011 What John said! Here is what Subaru says: http://www.subaruoutback.org/forums/66-problems-maintenance/30110-tire-circumference-spec-confirmed-subaru-techtips.html#post294007 Short answer, not recommended. Link to comment Share on other sites More sharing options...
Setright Posted February 16, 2011 Share Posted February 16, 2011 Well, if you run the odd-size tyres on the front axle, you shouldn't worry. The diff in the front is open, allowing different wheel rotational speeds without frying anyything. Sure, the open diff will be working constantly, and might just heat the diff oil up a little, but not enough to kill anything anytime soon. The rear axle has a limited slip, which well get hot and bothered pretty quickly. (The center diff won't notice anything. That's only if you fit two larger tyres on one axle alone.) Link to comment Share on other sites More sharing options...
MilesFox Posted February 16, 2011 Share Posted February 16, 2011 one odd size tire will not hurt, ans any difference in rotation will be absorbed by the front or rear open diff. This would cause no more wear on the driveline than driving in a wide circle. if you have a rear LSD, put the odd tire on the front. You do not want 2 of the same size tires on one axle if they are different size then the other axle. If you are forced to 2 odd size tires, mount them diagonally from eachother. Link to comment Share on other sites More sharing options...
johnceggleston Posted February 16, 2011 Share Posted February 16, 2011 i had a tire with a nail in ti and as the tire got low i would feel slight torque bind in my 97 obw. as the tire got lower the binding got worse. i finally got out and look ed to see what was causing the problem. found it. the nail was on the corner of the tread and the side wall and so i cannot patch, plug or repair it. at least that;'s what both tire shops told me. so i swapped on my winter tires a little early last fall. with spring just around the corner, i now have to decide if i can replace just the one tire. i thought it was a no-no to have one mismatched tire. Link to comment Share on other sites More sharing options...
Phizinza Posted February 17, 2011 Author Share Posted February 17, 2011 I have open front and rear diffs. Also it is a 5MT. So its half half here. Hmmm. I know it has to do with the difference between front and rear speed on the centre VLSD diff. And if it is too different the friction of slipping burns out the centre diff. I onlt need to run the tyre for 6 months or so, then I need to replace all 4 (will be getting 1 or 2 spares as well and rotate them all every so often. The hole is in the side wall. These yoka G900's are freaking stupidly thin. Link to comment Share on other sites More sharing options...
MilesFox Posted February 17, 2011 Share Posted February 17, 2011 if you spare is undersized on one axle, the center diff will still rotate with one front and one rear tire of the same size. the front or rear diff spiders and carrier(if in front or back) will rotate more because of the size difference, but the center will feel no effect. this would have the same action as driving in a very wide circle on the diffs, as they are designed to do. Link to comment Share on other sites More sharing options...
Fairtax4me Posted February 17, 2011 Share Posted February 17, 2011 i had a tire with a nail in ti and as the tire got low i would feel slight torque bind in my 97 obw. as the tire got lower the binding got worse. i finally got out and look ed to see what was causing the problem. found it. the nail was on the corner of the tread and the side wall and so i cannot patch, plug or repair it. at least that;'s what both tire shops told me. so i swapped on my winter tires a little early last fall. with spring just around the corner, i now have to decide if i can replace just the one tire. i thought it was a no-no to have one mismatched tire. I patched a hole in the corner of one of the tires on my old truck several years ago. Put about 15k miles on it like that. Still holds air just fine. Link to comment Share on other sites More sharing options...
Setright Posted February 17, 2011 Share Posted February 17, 2011 1999 Outback...are you SURE the rear diff is open? Link to comment Share on other sites More sharing options...
Phizinza Posted February 17, 2011 Author Share Posted February 17, 2011 But if 3 are identical and one is different (smaller) the end the tyre is on will have less rotations then the other thus having to slip the centre diff. And it being a VLSD the slippage will cause heat. The question is, how much difference would it take to be harder on the VLSD then a tight windy road? Hrmm if you spare is undersized on one axle, the center diff will still rotate with one front and one rear tire of the same size. the front or rear diff spiders and carrier(if in front or back) will rotate more because of the size difference, but the center will feel no effect. this would have the same action as driving in a very wide circle on the diffs, as they are designed to do. Link to comment Share on other sites More sharing options...
Phizinza Posted February 17, 2011 Author Share Posted February 17, 2011 1999 Outback...are you SURE the rear diff is open? Yes, I am from Australia, we got the Gen3 in 99 looks like this. It is a dual range 5sp manual with open rear diff, 4.11 ratio. Link to comment Share on other sites More sharing options...
987687 Posted February 17, 2011 Share Posted February 17, 2011 You're not supposed to have more than 1/4" circumference difference between any two tires. Link to comment Share on other sites More sharing options...
Gloyale Posted February 17, 2011 Share Posted February 17, 2011 one odd size tire will not hurt, ans any difference in rotation will be absorbed by the front or rear open diff. This would cause no more wear on the driveline than driving in a wide circle. I disagree with this reasoning. The total pinion shaft speed of a diff is a function of the average between the wheels each side. Throwing off the average of one diff (one odd size wheel) creates a small differance between the front and back diffs' repsective pinion speeds. Now this is a small difference, and it's absorbed by the center diff. This does however create a "slip" in the viscous center, which on a long drive will eventually be heated and try to lock. It won't be able to, you'll just cook it in the end. The viscous unit isn't designed for extended, constant slipping of the plates. Link to comment Share on other sites More sharing options...
Setright Posted February 18, 2011 Share Posted February 18, 2011 We have progressed into a theory/practice conflict, like so many internet discussions I wouldn't panic about fitting my space-saver spare wheel, with stock diameter, along with my too-large winter tyres. Sure, I would't run this setup for years, but honestly, real-world driving is nothing like the theoretical operation of the AWD system. Motorways here in Denmark are never perfectly straight. Someone (a smart person, in my opinion) decided that by having the motorways curve slightly, drivers tend to stay awake because the have to steer the car. Obviously, very large radius bends, where 80mph(130km/h) doesn't push the limits of cornering grip. Why do I share this information? Because driving on these sweeping motorways doesn't cook the center diff, just like MilesFox says it won't Link to comment Share on other sites More sharing options...
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