VeteranXX Contributor
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Imagine you have a fairly new Subaru Forrester with about 17000 miles. Someone slashed one of your tires. You get the tire replaced.
Mechanic claims that, because you have AWD, you need to replace all 4 tires to avoid damage to the transmission. The treads on the three remaining tires are ok.
Is it necessary to replace all 4 or is the mechanic just trying to screw the owner out of money?
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VeteranXX Contributor
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Buy one new (of the same tire), shave to same diameter as the other 3.
Having mismatched sizes can indeed damage driveline parts.
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VeteranXV
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If you stop posting ****, people won't slash your tires.
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VeteranXX Contributor
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AWD tires need the same wear..I am not sure if a couple thousandth of an inch will tear up the drive train, but I know you cannot mix sizes(ie..195/75/24 and 205/70/14 are si ilary sized, not exact, but you do not put on size on front and the other on the back, or you tear up the drve train)...Be on the safe side and get a new set...
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VeteranXX
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He's full of ****. The difference in tire diameter won't damage the transmission, but it may make the car pull to one side.
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VeteranXX Contributor
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Quote:
Originally Posted by Phydeaux
He's full of ****. The difference in tire diameter won't damage the transmission, but it may make the car pull to one side.
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I'm guessing the mechanic didn't say transmission.
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VeteranXV
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i think you have made enough threads tonight
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VeteranXX Contributor
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Quote:
Originally Posted by PessimiStick
I'm guessing the mechanic didn't say transmission.
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No. The claim was that the transmission would be damaged. Didn't quite make sense to me but I'm not big on how vehicles work.
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VeteranX
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increased friction on the newer tire will cause your driveshaft to explode
a good mechanic would recommend buying an entire new car, not just new tires
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BP's Pimpx Contributor
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get some spinners to avoid any possible damage to your alternator too
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VeteranXX Contributor
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I was also thinking about replacing my muffler bearings and blinker fluid. Seriously though, does having 1 new tire cause damage to a vehicle?
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VeteranX
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i dont know what your blinker fluid has to do with your tire being slashed usually a good idea to keep that stuff topped though so your nighttime visibility doesnt go down and you dont get a ticket
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VeteranXV
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Quote:
Originally Posted by Wyrm
No. The claim was that the transmission would be damaged. Didn't quite make sense to me but I'm not big on how vehicles work.
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and can't think logically for a second.
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VeteranXV
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You want them to be reasonably similar in wear, but they don't have to be exact. How much tread (% out of 100) would you say remains on the 3 existing tires?
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VeteranXX Contributor
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Quote:
Originally Posted by Snipes
You want them to be reasonably similar in wear, but they don't have to be exact. How much tread (% out of 100) would you say remains on the 3 existing tires?
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I'm really not sure...it's not my vehicle. I may be able to look into it soon. I just got a call from someone this morning about this mechanic's claim and was asked for advice about whether or not to replace all the tires. The one tire was replaced in a hurry and as the result of an emergency. I simply advised the vehicle owner to leave the shop where the emergency replacement was conducted and return to their usual mechanic for better advice.
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Last edited by Wyrm; 06-15-2009 at 01:48..
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Computer Monkey
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anyone here that doesn't own a subaru should have no say in this thread. i have one.
subaru center diffs are very sensitive to differences in tire circumference. the maximum allowed difference between all tires for the circumference is 0.25 inches. the only way to accurately check is to properly inflate the tires, lift the wheel you're measuring off the ground, and measure at the centerline around the tire.
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VeteranXX
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Small differences in the tire diameter equate to minor changes to the number of revolutions per mile a tire makes. These minor differences add up over the long haul of "miles" driven when a noticeable discrepancy appears between the number of revolutions one tire has made, versus another. In other words, 1 tire has physically traveled farther then the rest of the tires.
The newer tire being larger will have a rotational speed that is lower then the remaining tires. In 2WD vehicles this isn't a concern. Even in certain older 4x4 drive trains this can be excused, but in many AWD designs this can be a problem. AWD drivelines often utilize viscous coupling in their design to mitigate rotational differences in each wheel that naturally occur while driving. For example, when the vehicle makes a sharp turn, the wheels on one side of the vehicle will travel farther (faster) then the other pair of wheels. The AWD differentials allow the couplings for each axle to slip to compensate for these momentary differences.
However, in the case of a mismatched tire, the differentials are forced to continually compensate for the difference which overloads them and they suffer premature wear and mechanical breakdown as a consequence.
Considering the cost of repairing the AWD components, the Industry always recommends keeping the tires as close to identical as possible. Obviously, there are common-sense exceptions to the rule, such as near-new or zero wear scenarios, but no shop or dealership is going to risk an expensive warranty claim over something as simple as tire wear.
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Last edited by Hellsfury; 06-15-2009 at 01:46..
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VeteranXX Contributor
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These last two posts are quite good. Good work, TW!
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VeteranXV
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Quote:
Originally Posted by Hellsfury
Small differences in the tire diameter equate to minor changes to the number of revolutions per mile a tire makes. These minor differences add up over the long haul of "miles" driven when a noticeable discrepancy appears between the number of revolutions one tire has made, versus another. In other words, 1 tire has physically traveled farther then the rest of the tires.
The newer tire being larger will have a rotational speed that is lower then the remaining tires. In 2WD vehicles this isn't a concern. Even in certain older 4x4 drive trains this can be excused, but in many AWD designs this can be a problem. AWD drivelines often utilize viscous coupling in their design to mitigate rotational differences in each wheel that naturally occur while driving. For example, when the vehicle makes a sharp turn, the wheels on one side of the vehicle will travel farther (faster) then the other pair of wheels. The AWD differentials allow the couplings for each axle to slip to compensate for these momentary differences.
However, in the case of a mismatched tire, the differentials are forced to continually compensate for the difference which overloads them and they suffer premature wear and mechanical breakdown as a consequence.
Considering the cost of repairing the AWD components, the Industry always recommends keeping the tires as close to identical as possible. Obviously, there are common-sense exceptions to the rule, such as near-new or zero wear scenarios, but no shop or dealership is going to risk an expensive warranty claim over something as simple as tire wear.
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That's a pretty informational post right there.
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VeteranXX Contributor
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On a side note, this person's tire was slashed at 1 in the morning at a rest stop. The person is also an attractive young female. Pretty ****ing creepy.
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