AWDpower Posted March 26, 2006 Share Posted March 26, 2006 Does anyone know what the acceptable variance between tires are on our cars? One of my "new" BFG KDW's was ruined by a road hazzard today. The tires are only a few months old, with about 10,000 miles on them. They measured 8/32's of tread depth. BFG lists the tire as 10/32's new. I'll measure the new one before it's installed. The tire guy said that it is just inside the acceptable range for an AWD. A temporary road work sign was secured impoperly, and fell into the roadway screw side up. It punctured both driver's side tires, and one is repairable. I shouldn't have any trouble getting the city to pay for one tire. I'll push for all four if I'm forced to replace them all. Jason K. Link to comment Share on other sites More sharing options...
DKB_SATX Posted March 26, 2006 Share Posted March 26, 2006 I think the owner's manual lists the acceptable difference in tread depth. Link to comment Share on other sites More sharing options...
StringFellow Posted March 26, 2006 Share Posted March 26, 2006 Does anyone know what the acceptable variance between tires are on our cars? One of my "new" BFG KDW's was ruined by a road hazzard today. The tires are only a few months old, with about 10,000 miles on them. They measured 8/32's of tread depth. BFG lists the tire as 10/32's new. I'll measure the new one before it's installed. The tire guy said that it is just inside the acceptable range for an AWD. A temporary road work sign was secured impoperly, and fell into the roadway screw side up. It punctured both driver's side tires, and one is repairable. I shouldn't have any trouble getting the city to pay for one tire. I'll push for all four if I'm forced to replace them all. Jason K. I think you are right on the line in regards to if it is acceptable. If I was you, I would keep the repaired tire as a spare in the shed/garage and have 2 new ones installed. I never trust repaired tires.... -S Link to comment Share on other sites More sharing options...
andrew_j Posted March 26, 2006 Share Posted March 26, 2006 I think the owner's manual lists the acceptable difference in tread depth. It is not based on tread depth. It is based on circumference(distance around tire), as long as new tire is within 1/4" circumference of the average of three other tires you are fine. Link to comment Share on other sites More sharing options...
rc0032 Posted March 26, 2006 Share Posted March 26, 2006 Moved to wheels and tires I remember reading 2% is the acceptable variance, but the manual will tell all. Link to comment Share on other sites More sharing options...
edmundu Posted March 27, 2006 Share Posted March 27, 2006 Within 1/4" circumference would rule out almost any used tire! It's 1/4" diameter. So 1/4"=8/32" approx. so divide that by 2 and you have 4/32= 1/8". As long as your exisiting tires have 6/32" tread left(Assuming new tire tread depth of 10/32"), you will be fine. Link to comment Share on other sites More sharing options...
andrew_j Posted March 27, 2006 Share Posted March 27, 2006 Within 1/4" circumference would rule out almost any used tire! It's 1/4" diameter. So 1/4"=8/32" approx. so divide that by 2 and you have 4/32= 1/8". As long as your exisiting tires have 6/32" tread left(Assuming new tire tread depth of 10/32"), you will be fine. Here is the skinny, circumference not diameter On 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. Link to comment Share on other sites More sharing options...
eVoMotion Posted March 27, 2006 Share Posted March 27, 2006 Had a similar issue. Bought a new tire and had it shaved down. Link to comment Share on other sites More sharing options...
Hanger Posted March 28, 2006 Share Posted March 28, 2006 Here's a different question, if happens that my 18" tires blown can i still roll with spare tire for AWD cars? ○ ○ ○ Instagram: itshangertime :spin: ○ ○ ○ Link to comment Share on other sites More sharing options...
MDork Posted March 28, 2006 Share Posted March 28, 2006 i imagine so if youre within the total circumference tolerance Link to comment Share on other sites More sharing options...
Hanger Posted March 28, 2006 Share Posted March 28, 2006 What are the cirumference of the spare tires? right now i'm running on 225/40/18 ○ ○ ○ Instagram: itshangertime :spin: ○ ○ ○ Link to comment Share on other sites More sharing options...
edmundu Posted March 28, 2006 Share Posted March 28, 2006 Here is the skinny, circumference not diameter On 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. I don't know about that. 1/4" circumference works out to only 1/32" of treadwear. So basically, if you have driven on the tire for a few months, it would be unsuitable to just replace it, and you would then need to replace all of them? That just does not make logical sense. As for differences in tire circumference, they are valid, just not at a 1/4" diff. It would need to be something closer to 3/4" to make any appreciable difference, which would put you right at my 6/32 tread left opinion. Link to comment Share on other sites More sharing options...
PeterJMC Posted March 28, 2006 Share Posted March 28, 2006 Had a similar issue. Bought a new tire and had it shaved down. How was that done, one wheel burnout? Link to comment Share on other sites More sharing options...
edmundu Posted March 28, 2006 Share Posted March 28, 2006 Most tire places have a tire shaving machine... Link to comment Share on other sites More sharing options...
rodan Posted March 28, 2006 Share Posted March 28, 2006 I just replaced all four due to one non-repairable flat. Fortunately I had 27k miles on the old ones. The spare is designed to be 'close' in tolerance to the stock tire, but not perfect. Thus the 50mph restriction. I think you're still ok w/ 18s under those circumstances. I'm running the same size and noted no problems when running the spare (~80 miles total). Link to comment Share on other sites More sharing options...
ilh Posted March 28, 2006 Share Posted March 28, 2006 Here is a Subaru dealer saying 1/4-inch circumference and not diameter. --Lee Link to comment Share on other sites More sharing options...
edmundu Posted March 28, 2006 Share Posted March 28, 2006 Here is a Subaru dealer saying 1/4-inch circumference and not diameter. --Lee Wow:icon_surp Even a dealer has it in writing. But something still tells me it isn't accurate. I just cannot come to terms that a tire with only 1/32" of wear would require that all tires be replaced! Just doesn't add up. Link to comment Share on other sites More sharing options...
NickB34 Posted March 29, 2006 Share Posted March 29, 2006 Sounds like technically it may add up... but not monetarily Link to comment Share on other sites More sharing options...
rodan Posted March 29, 2006 Share Posted March 29, 2006 As speeds increase, that difference in circumference will cause increasing differences in wheel rpm, which puts a lot of stress on the driveline components. It's asking for trouble.... Link to comment Share on other sites More sharing options...
Greg_STL Posted March 30, 2006 Share Posted March 30, 2006 I also had to shave a single tire down to the depth I needed so I could just replace one tire. Tirerack.com will do it for you for $20 (on a new tire you buy from them) if you measure your existing tires and tell them the depth you need. Worked great for me... Link to comment Share on other sites More sharing options...
andrew_j Posted March 30, 2006 Share Posted March 30, 2006 http://www.subaru.com/common/faq/tech_info.jsp#4 Link to comment Share on other sites More sharing options...
red beast Posted March 30, 2006 Share Posted March 30, 2006 try one of these on the new tire http://www.osha.gov/SLTC/etools/woodworking/images/belt_sander.jpg Link to comment Share on other sites More sharing options...
Irrational Exuberance Posted March 30, 2006 Share Posted March 30, 2006 All of the tires on your AWD Subaru must be within 1/4 of an inch of rolling circumference (part that touches the road). This is because of our All Wheel Drive System sounds like it might also be an issue of weight... that extra bit of rubber, when the wheel is spinning at speed, will have more angular momentum than the smaller ones. i guess i could see how in theory this would be a problem one wheel responding differently to power than all the others could make the car tweak, but unless the tire was flly treaded and the others were very low tread, i cant really imagine it beaing a problem as fas as grip on the road. definately not like driving with a donut on. "i like my women the way i like terrorists... ...screaming gods name and ready to explode." http://img255.imageshack.us/img255/5479/troy3nu5.jpg Link to comment Share on other sites More sharing options...
ilh Posted March 30, 2006 Share Posted March 30, 2006 1/4-inch difference at stock size is approximately 1%. At 60mph, this translates to about 8rpm difference. That means your differential is "turning" at 8rpm constantly while cruising down the highway. Is that a problem? Will that kind of speed differential wear out a viscous-coupled LSD? Is this more a problem with clutch-type center "differentials" (aka "active" AWD)? I could see how this could potential result in binding or more wear on the clutches. I'm curious. I would be surprised if this would be as big an issue with say the 5MT. I guess if you have to do it, put the odd-sized tire on the front with the open differential. --Lee Link to comment Share on other sites More sharing options...
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