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2005 OTB/Forester Hybrid Automatic
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Discussion Starter · #1 ·
The Subaru Outback and Forester are all-wheel-drive (AWD) vehicles which means that at any time all four wheels can be providing forward thrust. The wheels are interconnected by transmissions that are fluid-driven and can absorb intermittent minor differences in the rotation of the wheels such as occurs during cornering or slight differences in road traction. However, a large difference in tire circumference constantly applied generates heat that is ultimately destructive to the transmissions. Therefore, the circumference on the tires must be as close to equal as is practical. Subaru expects that all four tires are the same make and model and states that the tires must be similarly sized with no greater difference in tread depth than 2/32” which is more easily measured than the circumference.

This requirement creates a dilemma when there is a non-repairable failure in a tire if the set of four tires has been used for more than a short period of time. Tires are repairable only if there is a small hole in the center 50% of the tread and not if there is any kind of damage in the outer area or sidewall. The introduction of a new tire that is not as worn as the remaining original tires creates a circumference mismatch that reportedly can lead to transmission damage. As a result, an owner can be faced with replacing all four tires and ending up with three partially worn tires that have much, perhaps ¾, of their useful life remaining. Only if the car is at the end of its useful life or is going to be otherwise soon disposed of might the owner buy a non-matching fourth tire and chance the possibility of eventual transmission failure.

If the owner intends to keep the car for an extended period of time, drive more than the average amount of miles, properly maintain the car, and buy quality tires that are more costly, then there is a strategy to eliminate the risk of an unscheduled large expense to buy another set of tires:



Buy two extra rims for the car. They can be purchased used for $50-$75 from a salvage yard. Although it's possible to rotate six tires across four rims, mounting/demounting can result in damaging the bead and is not worth the risk.
Buy six new tires from a dealer that is part of a national chain and that provides lifetime free rotation. The mileage warranty should be approximately equal to the number of miles one would drive in 4-6 years. Rotating tires is essential to achieve the full lifetime of a set and can be a significant expense if not included in the original purchase price.
It is not necessary to purchase supplemental road hazard insurance because the extra tires provide that coverage and receiving a new replacement tire creates the original problem being addressed by this strategy. This saving offsets some of the cost of buying the extra rims.
Have the tires rotated every 5,000 miles at the same time as the oil is being changed. At any one time, two tires are in storage until they are rotated onto the car

The only additional cost is for the two rims. Although each tire should still be useful for the full mileage warranty period, the set of tires will actually last 33% longer in elapsed time/vehicle mileage. In the event there is non-repairable damage to a tire, it is just disposed of and the rotation continues with five tires. Only if more than two tires are irreparably damaged is it necessary to buy a new set of tires.

The tire rotation strategy is as follows:
Remove front tires for storage
Move rear tires to front and cross-over
Mount tires previously in storage on rear and cross-over from prior position

To implement this strategy, it is recommended to keep a record of the usage of each tire to ensure that all the tires are used approximately the same mileage and are rotated properly from the rear of the car to the front and from side to side.
As this whole procedure is initially confusing for tire mechanics, before I take the car in for a rotation, I use playground chalk to write in big letters where that tire should end up:
LF = Left Front
RF = Right Front
LR = Left Rear
RR = Right Rear
The chalk washes off in the next rain or can easily be sponged off.

If taking a long trip beyond the range that is safe for driving on the emergency spare tire provided with the car, it is advisable to carry one of the mounted full-sized spares so a new set of tires does not have to be purchased on a moment’s notice in a distant city.
 

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2016 Forester
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The tire rotation strategy is as follows:
Remove front tires for storage
Move rear tires to front and cross-over
Mount tires previously in storage on rear and cross-over from prior position
If I’m understanding this correctly, I believe this results in a significant difference from the recommended 4 tire rotation pattern for the Forester. In the following examples I’m adding LS = Left Storage and RS = Right Storage to your designations.

With the recommended 4 tire rotation, a specific tire ends up in all 4 possible wheel locations on the vehicle. For example, the tire starting at the Left Front gets moved to LR, RF, RR, LF and then continues to repeat. 

(Recommended rotation being back tires to front with cross-over and front tires to back without cross-over, with the assumption of non-unidirectional tires.)

With your 6 tire rotation (as I’m understanding the above), a specific tire ends up in only 2 of the possible wheel locations on the vehicle. For example, the tire starting at the Left Front gets moved to LS, RR, LF, LS, RR, LF and continues to repeat. The tire never ends up in the RF or LR positions.

Removing the cross-over when mounting the storage tires on the rear would change the movement of the tire starting at LF to LS, LR, RF, RS, RR, LF and then repeat, covering all 4 possible wheel locations like the recommended 4 tire rotation does.
 

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2005 OTB/Forester Hybrid Automatic
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Discussion Starter · #3 ·
I see your point and agree that your analysis is correct. I was not aware of the specific Subaru recommendation but was focused on ensuring even mileage on all six tires and changing the direction of rotation of the tires every 5K miles. Your proposal will result in an individual tire being on the same side of the car and rotating in the same direction for 10K miles, in storage for 5K miles, and then on the other side of the car for 10K miles. I can't guess what the difference in tire wear might be between the two schemes but I'm guessing that if the alignment of the car is properly maintained it would be minimal. I'll appreciate the contribution of anyone who might know. The main objective of tire rotation plans in general is to reduce the impact of misalignment. I purchased a lifetime alignment package and am certainly getting my money's worth from it. However, I will periodically skip a crossover to address your point. Thanks!
 

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2016 Forester
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5 is common for people with full size spares, but I've never heard anybody doing 6 tire rotation.

The proper sequence for 5 tire rotation is Spare>LR>LF>RR>RF>Spare, I suppose you can adapt it for 6 tires by doing Spare 1>Spare 2>LR>LF>RR>RF>Spare 1.
 

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2012 Forester X Auto
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@lxrsub -
Interesting take, but then there are some other issues to be addressed.
TPMS sensors for one, since the car is limited to 4 captured sensors, and while you could ignore the light, you could also have a catastrophic tire failure due to pressure loss, or you could add in the cost of a programmer to keep TPMS relevant. You would need to reprogram the sensors at every rotation.

Uni directional tires wouldn't work in the six rotation scheme either.

There is also considerable expense (+50%) with buying, mounting and balancing 6 vs 4 tires, and that's an upfront cost.

I've found that with the non-repairable lightly worn tire scenario, I can trade in the 3 used tires for a substantial cost reduction in the new tire purchase.
If you live in an area with a lot of road hazards, the six tire rotation might be worth it, but for myself, I've only had 2 required 4 tire changes in 20 years.
I don't think I would be ahead financially had I gone with your scenario, but that's me.
 

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2005 OTB/Forester Hybrid Automatic
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Discussion Starter · #6 ·
I generally agree with your points but with the following comments:

My 2005 car does not have TPMS so that has not been an issue for me. I did not know that there is a limit of four captured sensors. What is entailed in programming the system and can it be DIY?

I made the mistake of buying unidirectional tires once in my life. In order to properly rotate them through all four wheel positions (as specified by Subaru), they have to be remounted on the rims. When I was switching tires from all-season to snow tires twice yearly in New England, I saw this damage the bead of a tire, which is why I buy an extra pair of rims.

There certainly is an initial 50% extra cost to buying two extra tires. However, the lifespan of the tires in terms of mileage on each tire is the same, but over a longer period of time. So in terms of tire miles per dollar spent, it's a wash. Regarding the cost of rotation and balancing, in recent years I have bought tires at Sams Club where $15 per tire buys installation, road hazard protection, and lifetime free rotation and balancing, a great buy.

Someone else commented that this six tire rotation strategy could extend the usage of tires beyond their age limitation but that person drove very few miles per year. I average 30K miles per year.

My one time attempt trading in three moderately (50%) worn tires did not result in a significant discount on the new set, which is why I decided to implement the six tire rotation strategy. Since then over 160K miles, I have twice experienced irreparable road damage that would have required the purchase of four tires if I had not been carrying a full sized spare with matching wear. I live in NC and one event was on an expressway in Chicago and one was in downtown Portland, OR. I guess I've not been lucky. After these events, I was able to quickly continue merrily on my way without being compelled to purchase four new tires on the spot. Instead I could wait to buy a new set when the five remaining tires from that set were close to being worn out and a sale was occurring.

I guess I will have to rethink this when I get a car with TPMS.

Thanks!
 

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2015 Forester CVT
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Speaking of 6 tire rotation - to prevent from having to buy 4 new tires when 1 gets damaged beyond repair...

BTW, would be even easier with a 10 tire rotation if you have 2 Foresters... :)
 
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