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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / November 2006Dissimilar tires
We've got a '96 Subaru outback wagon with 187,000 miles on it. About a year ago, my wife had a flat. The local repair shop replaced the tire, claiming it could not be plugged. Since then, she has driven perhaps 10,000 miles on it. The other three tires still have some life in them. Our Subaru dealer claims that this tire is 1 inch larger in circumference from the rest, and that this will cause problems in the drive train. Since we now drive this car once or twice a week, at most 5000 miles per year now, is this a problem? Or is the dealer just trying to sell us a new set of tires? Thanks, John > We've got a '96 Subaru outback wagon with 187,000 miles on it. About > a year ago, my wife had a flat. The local repair shop replaced the [quoted text clipped - 5 lines] > circumference from the rest, and that this will cause problems > in the drive train. What are the measurements of each tire. You will find numbers like 235 45 17 on the sidewall of each tire. > Since we now drive this car once or twice a week, at most 5000 miles > per year now, is this a problem? Or is the dealer just trying to > sell us a new set of tires? Yes, but probably with good reason. > Thanks, > John You can go to a truck tire shop or a retread shop and have the tire shaved down so it matches the others. Kinda a waste of rubber, but that will mean you don't need 3 new ones right away. The dealer is likely right on the potential for problems, some 4x4 systems are really picky about matching rotations when under power. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > We've got a '96 Subaru outback wagon with 187,000 miles on it. About > a year ago, my wife had a flat. The local repair shop replaced the [quoted text clipped - 12 lines] > Thanks, > John > You can go to a truck tire shop or a retread shop and have the tire > shaved down so it matches the others. Kinda a waste of rubber, but > that will mean you don't need 3 new ones right away. My mechanic tells me you can't shave tires that have been used. Once they've been used, little pieces of grit get stuck in the tread, which tears up the machine's cutting blades.  SignatureTeGGeR® >We've got a '96 Subaru outback wagon with 187,000 miles on it. About >a year ago, my wife had a flat. The local repair shop replaced the >tire, claiming it could not be plugged. Since then, she has driven >perhaps 10,000 miles on it. The other three tires still have some >life in them. Okay, probably a bad idea. >Our Subaru dealer claims that this tire is 1 inch larger in >circumference from the rest, and that this will cause problems >in the drive train. Is it? What are the numbers? If it is indeed the wrong size, you have trouble. >Since we now drive this car once or twice a week, at most 5000 miles >per year now, is this a problem? Or is the dealer just trying to >sell us a new set of tires? At LEAST replace tires in pairs for God's sake. And use the right size. --scott Signature"C'est un Nagra. C'est suisse, et tres, tres precis." John D'Errico wrote: (96 Subaru outback wagon 187k Miles) A repair shop replaced a flat tire 10,000 miles ago. Our Subaru dealer claims that this tire is 1 inch larger in circumference than the rest, and that this will cause problems in the drive train. Is this a problem or is he just trying to sell us a new set of tires? ______________________________________________________ A 1-inch circumference error is a 0.159-inch radius error. In a 2WD vehicle, non-matching tire diameters on the drive axle will cause the differential gears to work continuously instead of just when turning, and there could be some steering pull from the different tire torques applied. Both effects are minor, and cars have operated reliably for years with mismatched tires. In 4WD vehicles one mismatched tire could put unwanted strain on interconnecting gearboxes. Call the Subaru dealer back and ask the manager exactly why the mismatched tires cause drive train problems in your car, then make an informed decision. Good luck. Rodan. > At LEAST replace tires in pairs for God's sake. And use the right size. > --scott When going down this thread, I was hoping that someone would point out the wisdom of replacing tires in axle pairs. In bad weather, it can be darn near suicide, in some cases, not to do it. Running one tire on an differential driven axle set that is significantly different in circumference than the other, is heap bad medicine. > > At LEAST replace tires in pairs for God's sake. And use the right size. > > --scott [quoted text clipped - 8 lines] > different in circumference > than the other, is heap bad medicine. Sounds like a new set of tires this year instead of next spring. Thanks, John > Sounds like a new set of tires this year > instead of next spring. > > Thanks, > John You likely have a viscous coupling in your AWD transaxle. (assuming Subaru=AWD in most cases) If this coupling fails from being run with dissimilar tire diameters, you will pay a whopping price for a new unit. I would be more upset at the incompetent sack that put a wrong size or wrongly-marked-from-factory tire on your car. That is, unless he only had that size and told you the dangers first but you OKed the replacement anyway. Toyota MDT in MO > Our Subaru dealer claims that this tire is 1 inch larger in > circumference from the rest, and that this will cause problems > in the drive train. Well, your dealer is right. Especially if your wagon is an AWD vehicle. On a GM vehicle with auto 4x4 or AWD, the factory spec is that all the tires should be within 3mm tread depth of each other. Otherwise, you will experience problems with the drivetrain eventually. Ian shiden_kai <V-L-M@hotma1l.com> wrote in article <8Jq3h.264765$R63.72660@pd7urf1no>... > > Our Subaru dealer claims that this tire is 1 inch larger in > > circumference from the rest, and that this will cause problems [quoted text clipped - 9 lines] > > Ian One-inch in circumference would be equal to .318" in diameter - OR approximately 8mm in diameter - or 4mm in tread depth (radius). You gonna' quibble over a silly millimeter? Rubber deflection alone - or a pound or two in air pressure difference - could account for that much difference. > One-inch in circumference would be equal to .318" in diameter - OR > approximately 8mm in diameter - or 4mm in tread depth (radius). [quoted text clipped - 3 lines] > Rubber deflection alone - or a pound or two in air pressure > difference - could account for that much difference. Hey, I guess you are the expert then!...Feel free to run your AWD vehicle with a worn tire....I could care less! The more of you that do this type of thing, the more work there is for me. Ian > > One-inch in circumference would be equal to .318" in diameter - OR > > approximately 8mm in diameter - or 4mm in tread depth (radius). [quoted text clipped - 10 lines] > > Ian Technically, you would have to quibble over 4 silly millimeters. Anyhoo, the fact is that the wheel/tire assembly was rotating one extra inch per revolution verses the other tires. Hmm, where does all of that friction go? cough!::viscous coupling:::cough! Toyota MDT in MO shiden_kai <V-L-M@hotma1l.com> wrote in article <DcT3h.265910$1T2.189299@pd7urf2no>... > > One-inch in circumference would be equal to .318" in diameter - OR > > approximately 8mm in diameter - or 4mm in tread depth (radius). [quoted text clipped - 8 lines] > care less! The more of you that do this type of thing, > the more work there is for me. Just pointing out that a "whole inch !!!! " difference in circumference is not that far off from the manufacturer's specs. that YOU quoted..... > shiden_kai <V-L-M@hotma1l.com> wrote in article > <8Jq3h.264765$R63.72660@pd7urf1no>... [quoted text clipped - 17 lines] > > You gonna' quibble over a silly millimeter? well, four, actually. > Rubber deflection alone - or a pound or two in air pressure difference - > could account for that much difference. Which is a good argument for paying attention to tire pressure on any vehicle, but especially an AWD one or one equipped with a LSD. "rubber deflection" can safely be ignored because if all tires are equal they should be deflecting a similar amount in steady state, straight-ahead driving. You're free to have your own opinions, but on any AWD vehicle I would definitely follow the manufacturer's recommendations WRT tire replacements, and on any LSD vehicle I would at least replace the tires in pairs. nate |
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