Tire Rotation

[Brisvegas]

I have a question regarding driving on uneven wear tires.

 

From the start, let me be 100% clear, I am not disputing the overall need for the same exact tires and the same exact wear levels on our Subaru AWD vehicles ... all I am trying to do is to ask if there is any tolerance involved in that situation.

 

For example, if I have 4 identical brand new tires fitted, and have an identical new spare tire in the trunk, and If I have only traveled 100 miles on the new tires and I get a flat, I would assume that no forum members would suggest that I couldn't permanently replace the flat with the identical spare? If my assumption is correct that such a tire swap would be perfectly OK, then my next question is ... what about if I had 200 or 500 miles on the original 4 new tires before swapping over to a new spare? Again, without disputing that the basic premise of running the same tires with the same wear is acceptable to all, I'm just a little doubtful that running a new spare with minimally worn 4 tires would cause immediate catastrophic damage. All I am suggesting is that there "might be" a tipping point between what is acceptable in some circumstances, and what is absolutely not acceptable.

 

My questions are based on my upcoming purchase of a set of Michelin tires. I am considering buying 5 tires and rotating them regularly, so as to attempt to keep the overall wear as even as possible. My reason for doing this is to remove the need to buy 4 new tires if one of the tires was ever unrepairable, which is currently what Subaru owners are advised to do.

 

I fully realise that my plan to rotate 5 tires would require reasonably frequent rotations in order to achieve any sort of even wear. I can live with that, but I would just like to canvass the opinions of forum members as to what would be considered to be acceptable mileage rotations (if any).

[silverton]

if you have a set of 5 wheels/tires for your car, there is a 5 wheel rotation pattern. follow it. each tire will get it's own 'off' time and will wear evenly with the rest as they make their 4 corner journey. Just to be safe, do it every 3000 miles. recommended is 6000 but you seem extra concerned, which is fair, tires are quite the investment.

 

thousands of miles wear your tires, not hundreds. well, unless your alignment is buggered you can chew through a set of tires real fast.

[Infosecdad]

I would do this if I had a fifth wheel that matched my others.

 

If you think about it, most tires start around 10/32 of tread and should be replaced around 4/32, that's 6/32 of wear. If you buy 60k mile tires, then even wear would be 1/32 every 10k on avg. If you rotate them every 4-6k miles, then you should be well within the 2/32 difference that Subaru recommends to stay within. Also, to get to 60k miles on all five tires, the car would travel approx 75k miles because of the 5th tire in the rotation. (Assuming my math is correct after a long day).

[tornichoe]

Think the general guidance is not have drastic difference in thread wear between tires; like if you were worn down to 5/32 you wouldn't want to replace one wheel with a new tire or rotate in a tire with 10/32. That large difference in diameter will cause the wheels to spin at differing revolutions per mile.

If the difference is 1/32 or even 2/32, I don't think that will cause too much of an issue long term.

Street cars and tires, IMHO, aren't built to such small tolerances. You'll have errors propagate along the way from tire manufacturer to your air pressure gauge that will all induce minuscule variations in overall diameter anyway...

[ammcinnis]

... most tires start around 10/32 of tread and should be replaced around 4/32, that's 6/32 of wear. If you buy 60k mile tires, then even wear would be 1/32 every 10k on avg. If you rotate them every 4-6k miles, then you should be well within the 2/32 difference that Subaru recommends to stay within.

Excellent analysis. Subaru's published recommendation is no more than 1/4 inch difference in tire circumference, which calculates to 1.3/32 inch (1 mm) max difference in tread depth. A 6,000 mile rotation schedule should be OK, although slightly accelerated wear on the Multi-Plate Transfer Clutch may result, accompanied by slightly higher CVT fluid heating during highway cruising.

 

(Attachment from Subaru Tech Tips newsletter, December 2010.)

Edited March 6, 2022 by ammcinnis

[silverton]

at my dealer we recommended replacement tires when they were 3/32 out from the others. 2 is okay.

[Brisvegas]

if you have a set of 5 wheels/tires for your car, there is a 5 wheel rotation pattern. follow it. each tire will get it's own 'off' time and will wear evenly with the rest as they make their 4 corner journey. Just to be safe, do it every 3000 miles. recommended is 6000 but you seem extra concerned, which is fair, tires are quite the investment. thousands of miles wear your tires, not hundreds. well, unless your alignment is buggered you can chew through a set of tires real fast.

 

Thanks for the input. Rotating every 3000 sounds like a plan that will suit me, so I will be doing that. Below is a video clip on a suggested 5 tire rotation plan, and this is the one I will be doing.

 

[tornichoe]

Rotating every 3000 sounds like a plan that will suit me, so I will be doing that.

 

Be sure to check the thread wear and remaining depth, not just miles. Depending on the thread wear rating of tire you get and your driving style, you could burn through rubber faster than you think.

[Brisvegas]

Be sure to check the thread wear and remaining depth, not just miles. Depending on the thread wear rating of tire you get and your driving style, you could burn through rubber faster than you think.

 

Good points ... I am a very "conservative" driver, but I take on board what you are saying.

[XT-sub]

... I fully realise that my plan to rotate 5 tires would require reasonably frequent rotations in order to achieve any sort of even wear. I can live with that, but I would just like to canvass the opinions of forum members as to what would be considered to be acceptable mileage rotations (if any).

 

Purchasing five tyres is something I have thought about since owning my first Subaru but I’ve always baulked at the idea of replacing a perfectly good as new full size spare with a brand of my choice just to get five tyres – perhaps I should have begun rotating five tyres from new on all our Subarus.

 

My thoughts on tyre rotation.

 

I never rotate any of our Subaru tyres by distance travelled (kms), I rotate by measured tread depth using vernier callipers to measure the thread depth across three parts of the main tread & at each edge (the edges have less tread & if not checked can wear more on the outside due to hard cornering, especially the front left through roundabouts). I keep a spreadsheet for this so I get an idea when to check the tyres & therefore when to rotate.

 

As to recommended allowable tread depth difference, keep in mind the following. We are talking about only one tyre having more tread depth than the rest & the Outback & Liberty both run open diffs. At rest the radius of the front tyres on every Subaru will always be less than the rear tyres due to the engine/transmission weight, especially on the H6. At rest on our 2019 Outback 3.6R I measured from the garage floor 6mm less radius on the front tyres compared to the rear tyres with the recommended front & rear tyre pressures. I don’t know what the difference would be at 80 or 110km/h, but I suspect it could be different & the Liberty could be different again.

 

The following figures may help your decision when to rotate based on my driving style which is probably similar to yours with a bit of spirited driving thrown in now & again, but keep in mind this was on our gen5 Outback 3.6R, not on our previous gen6 Liberty 3.6R (same as yours).

 

Some time ago for my own interest I decided to take some measurements on our 2019 Outback 3.6R comparing the unused full size spare & a tyre on the rear that had travelled 15,000kms (same as the other three). Both tyres tested had 32.5psi tyre pressure. The unused tyre had 7.4mm tread depth at the centre & the tyre that had travelled 15,000kms had 6.2mm at the centre (1.2mm difference).

 

With each tyre in our garage so they would be at the same temperature I measured the tyre circumference at the tread centre using a 30m wind-up fibre tape measure to give a tight fit around the tyre (I removed the moulding tits on the unused tyre to get an accurate measurement). The as new unused tyre measured 230.35cm circumference & the tyre that had travelled 15,000km measured 229.75cm, a difference of 6.0mm. This gives a calculated radius difference of 0.95495mm which includes the difference in thread depth.

 

According to what has been posted, Subaru America’s allowable difference is up to 1/4" (6.4mm) in circumference. How old is that information? What model Subarus is that for & with what transmissions? What diameter tyres? Is it for Subarus with a limited slip rear diff? Note that the Owner’s Handbook for our Australian spec Japanese built cars doesn’t say anything about this measurement but states the following: “You must install four tires that are of the same size, circumference, construction, manufacturer, brand (tread pattern), degree of wear, speed symbol and load index.” - and – “Tire wear varies from wheel to wheel. To maximize the life of each tire and ensure that the tires wear uniformly, it is best to rotate the tires every 10,000 km.” - and - “the amount of wear should be the same for all four tires so that X mode operates correctly.” (X-mode for an Outback only). Ignore the quoted incorrect spelling for tyre.

 

The calculated radius difference between a gen5 Outback’s 230.35cm circumference new tyre & the 229.71cm circumference of that same tyre brand/type with 6.4mm (1/4") less tread depth is 1.0185mm which is the tread depth difference.

 

Please let us know what you think of the Michelins when you get them, I’ve been tossing up between Michelins & Continentals when the time comes.

 

I hope you survived the wild weather & floods up your way ok, so far it looks like we have dodged a bullet down our way. Very sad about the many people who have lost everything.

Edited March 7, 2022 by XT-sub

[ammcinnis]

According to what has been posted, Subaru America’s allowable difference is up to 1/4" (6.4mm) in circumference. How old is that information?

That information has been published, at least twice, in Subaru's Tech Tips dealer newsletter ... first in 2010 and again in 2014. See my earlier post in this thread.

 

 

While the Gen 5 Outback does use open differentials (F/R), the use of a Multi-Plate Transfer Clutch instead of a center differential becomes problematic with mismatched tires.

[MoleMan]

@Silverton,

 

3/32 of mismatched tread is tolerable but it’s pushing what personally I would say replace. I really do not like more then 2/32 of treadwear difference regardless of what car I am driving. I think most dealers say this not to upset about three quarters of customers that would argue why the Need to buy all four. This is a common argument I see quite often at local tire shops.

 

To the OP as others have said a fifth wheel rotation schedule is published and available. With the OP being from Australia I can very much understand the need for a extra full size wheel/Tire combo. In fact on my daily driver since I am so remote areas and stretches of I-80 I did place a full size tire/wheel combo in the trunk. However it’s more for safety then anything else.

[Ovcoursitsilver]

Do your tires have a directional tread pattern? If so, you would need to be rotating 6 tires.

 

Unless you live in an area where tire punctures are common, all this may be overkill. In 53 years of car ownership I’ve only had one tire fail to the point that it’s irreparable and that was because it was worn almost to the point of replacement. I will continue to rotate my tires but I’ll take the chance on having to replace all 4 prematurely because of a road incident.

[Brisvegas]

Do your tires have a directional tread pattern? If so, you would need to be rotating 6 tires.

 

Unless you live in an area where tire punctures are common, all this may be overkill. In 53 years of car ownership I’ve only had one tire fail to the point that it’s irreparable and that was because it was worn almost to the point of replacement. I will continue to rotate my tires but I’ll take the chance on having to replace all 4 prematurely because of a road incident.

 

They are non directional. I fully understand what you are saying. In 50 years of driving I have had 2 punctures that I recall. (somewhere in those early 50 years I probably had others seeing as how during those early years "good" tyres on the beaters were I luxury very few kids could afford Those two punctures that I mentioned have happened in the last 6 months. I can change a tyre and have "plugged" both of the punctures successfully ( and I guess now there will be a discussion on the safety of plugs ) .... but as MoleMan referenced in his post ... traveling very long distances brings with it possible challenges. I have just returned from a 3000 km trip (which I do annually) and whilst changing/repairing a tyre is not a challenge for me ... on some of my trips, being "in between civilisation" might create a challenge that I could do without. As I am ready for a tyre change, I think for me, it's a no brainer to buy 5 tyres and rotate them accordingly.

[XT-sub]

That information has been published, at least twice, in Subaru's Tech Tips dealer newsletter ... first in 2010 and again in 2014. See my earlier post in this thread.

 

 

While the Gen 5 Outback does use open differentials (F/R), the use of a Multi-Plate Transfer Clutch instead of a center differential becomes problematic with mismatched tires.

 

Thanks. So as far as we know that could be fairly old information referring to older model Subarus or one particular model or models that are still being serviced? Or are there more detailed figures somewhere?

 

No disagreement from me in regards to what you are saying about the use of a Multi-Plate Transfer Clutch instead of a centre diff. But I can’t see how Subaru America can just give a blanket ‘all 4 tyres should be within approximately ¼” of each other in circumference when measured at the centre of the tread’ statement in the Tech Tips newsletter when there are so many different transmission types & tyre diameter/circumferences over the years. Perhaps that ¼” is for the worst case vehicle, gearbox, front/centre/rear diffs, tyre combination scenario, or perhaps it is for the best case scenario.

 

Some of my thoughts:

 

What is the front to rear mismatch if only one tyre on one axle had ¼” more circumference than the other three compared to both tyres on the same axle (both on the rear for example) having ¼” more circumference than the other two?

 

There are already mismatches front to rear with correct tyre pressures due to the lower radius measured from the ground at rest (what happens at different speeds, tyre pressures & with different loads)?

 

The TR690 CVT coupled to the turbo petrol & H6 engines varies the front to rear drive depending on what the vehicle is doing at any particular time, not sure about the TR580. From memory I’ve seen this go over a range of 90% front to 55% rear. Compared to this the manual transmission models are usually default split at 50/50, although I think this can be varied on some models.

 

The load in the rear will cause a front to rear mismatch if the tyre pressures aren’t adjusted to suit, & correct if I’m wrong, the US cars don’t have recommended tyre pressures on the B pillar to cater for varying loads whereas the Japan built Australian spec cars do.

 

The older model Subarus & smaller models that run smaller diameter wheel/tyre combinations will have a different circumference to say a Gen6 Legacy/Liberty or gen5 Outback with 18” rims.

 

I’ve made a note to myself to see what the CVT temperature is on our Outback with one mismatched tyre compared to other records I have with matched tyres.

[Painless]

I have always rotated at 10k mile intervals.

Every other oil change for me (easy to remember).

Start looking for deals @ 5/32" then replace all four.

Unless its wintertime, then replace all four immediately.

No issues for either Legacy relating to tires.

Currently:

2016 237,000 miles

2019 124,000 miles