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Discussion Starter #1 (Edited)
With the CX-3's AWD system, if I happened to get a flat and the other three tires were about half-way through the tread, would I have to replace all tires to not screw up the system? I know on some AWD systems this is the case (Subaru). Was wondering if it's the same for every AWD vehicle.
 

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If it has gone flat, and the other tires are still new, you don't need to replace them all. The idea behind replacing all is a fail-safe in case you forget to replace the others sometime afterward. You always want to try and keep all tires as close to same condition is possible, especially for AWD's. Of course, this is what I've heard from word of mouth, and what I have practiced myself.
 

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from what i was taught in industry is that all 4 tires should be with in 2/32 of each other as to keep the differentials from burning up the clutches/carrier gears. when going beyond that the diff will start to overheat and eventually fail. I know it may not seem a whole lot but i've seen cx 5, cx 7, and cx 9 burn through their diffs due to owners not maintaining even tread wear on their tires. Also and this is somewhat not fully proven but keeping identical brands of tires is as crucial as tread wear...from my understanding tread patterns can affect the diff as different grips will work the diff hard as well. Patch it if you can otherwise 4 new tires if they are over 2/32 difference from the new one. hope this helps.
 

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What Snoogie says about tire brand and tread was something I didn't mention but should have because it is important. Always make sure to match tire with your others, that includes size, tread, and brand. Like I mentioned before, if wear is minimal, no need to replace all 4, just the one, but make sure the one being replaced is replaced with the same. Not much wiggle room with AWD's
 

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Well that just about writes off every car over three years old in the UK where it is normal for owners getting these things second hand to change one tyre if they have a problem. A tyre is a tyre to most people (sorry, tire to you guys) and once the car gets cascaded to owners with a lower budget, a mixture of tread depths and brands is inevitable. I now am led to believe that if I get a tyre problem once anything more than 2/32 of difference from a new one - that's half a millimetre on a new tyre with 9mm of tread, that I have to change both tyres or it's not clear but the inference here is all four. If that is the case, this car will be gone inside 12 months.

Of course, I've read the disclaimers about tyre radius having a possible adverse effect on systems like the VSC and ABS but they must be able to tolerate some difference in specification. The same applies to road springs, shock absorbers and brake parts but in reality, they often get mixed up with age.

If this is true, would somebody like to explain what is going to happen when a spacesaver wheel is fitted to one of these hyper sensitive Mazdas. I say specifically Mazda because it sure as hell doesn't apply to Toyotas with virtually the same mechanics and systems. And this 2/32 apply to the entire life of the tyre because I'm going to have to buy a pretty accurate gauge when I start measure quarter of a millimetre on a half worn tyres. Maybe Mitutoyo do a three coordinate measuring machine for tyres?
 
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Well that just about writes off every car over three years old in the UK where it is normal for owners getting these things second hand to change one tyre if they have a problem. A tyre is a tyre to most people (sorry, tire to you guys) and once the car gets cascaded to owners with a lower budget, a mixture of tread depths and brands is inevitable. I now am led to believe that if I get a tyre problem once anything more than 2/32 of difference from a new one - that's half a millimetre on a new tyre with 9mm of tread, that I have to change both tyres or it's not clear but the inference here is all four. If that is the case, this car will be gone inside 12 months.

Of course, I've read the disclaimers about tyre radius having a possible adverse effect on systems like the VSC and ABS but they must be able to tolerate some difference in specification. The same applies to road springs, shock absorbers and brake parts but in reality, they often get mixed up with age.

If this is true, would somebody like to explain what is going to happen when a spacesaver wheel is fitted to one of these hyper sensitive Mazdas. I say specifically Mazda because it sure as hell doesn't apply to Toyotas with virtually the same mechanics and systems. And this 2/32 apply to the entire life of the tyre because I'm going to have to buy a pretty accurate gauge when I start measure quarter of a millimetre on a half worn tyres. Maybe Mitutoyo do a three coordinate measuring machine for tyres?

WOW.
I am totally unaware of any of these facts (not doubting, just surprised!).
If AWD systems are this finicky, there must be a lot of toasted AWD systems out there.
 

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using the doughnut to swap out a flat tire will start to ware on the diff but that is why its only a spare. I might of not of said it correctly but its not going to instantly burn up your diff. It will take some time but not long...a spare is just that a spare. I personally would not drive on one longer than the nearest shop.
 

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I always thought that if the tires are new you could just get the same type of tire and you'll be fine. If they are older you might need to replace them all. And if you are changing tires, you need to have them all the same. But I assume you can just ask a mechanic or tires salesperson and they would let you know.
 

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WOW.
I am totally unaware of any of these facts (not doubting, just surprised!).
If AWD systems are this finicky, there must be a lot of toasted AWD systems out there.
I'm pretty sure they are not facts. I'm treating this lot as "fella down the bar says". Sorry but I don't believe a word of it. Isn't 2/32 similar to 1/16?
 

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I couldn't find a max acceptable difference in size in the owner's manual, but it does say that the AWD warning light "illuminates if there is too much difference in tire radius between the front and rear wheels. "
 

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While Im not 100% buying the 2/32 bit, but what is 100% is that having tires with different wear on them causes them to rotate at different paces, small numbers, but still causes a strain. New tires will rotate less often than worn ones over the same difference. I think there is still a sizable bit of room to play with in terms of wear differences, but that is something that will be different from system to system. With 2WD's, you can get away with the 2 in front being different than the 2 in back.

Which begs the question, wouldn't you have to rotate tires more often then, since the 4 or doing something different than the others? I'd assume they wear differently, like fronts wearing more than rears? Or am I talking rubbish?
 

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well the 2/32 rule is what i as taught and had experience with many seized diffs from cx 5, cx 7, and cx 9s. in terms of tires 2/32 is quite a big difference. now regarding the rotation frequency as long as you rotate them every time you do an oil change or if you are really diligent check for yourself your tread depth then you should be fine. also the whole fronts wear out faster than the rears that is true in most cases. from my understanding and from what i experienced at bare minimum keep the tire treads close on each axle. for example 6/32 both fronts and 8/32 both rears i find good enough. what is not good is driver front/passenger rear is 6/32 and passenger front/driver rear is 8/32. that will cause both differentials to fail big time and that is a very expensive repair. in general just do your due diligence and keep an eye on your treads. use the penny or quarter or w/e they use now if you dont own a tire tread depth gauge.

Also this is only from my understanding from mazda's differentials and some fords/gm/dodge. this explanation does not answer other makers like subaru or volvo or audi etc. again this is based on my formal automotive education and personal experiences in the industry and i can be proven wrong
 

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I'm pretty sure they are not facts. I'm treating this lot as "fella down the bar says". Sorry but I don't believe a word of it. Isn't 2/32 similar to 1/16?
I agree Anchorman. I am not sure what type of roads they have in North America but in Australia and especially in the suburbs most roads have bends in them. Turning the steering wheel even slightly either way will cause a very slight difference in rotational speed between left and right wheels on the same axle as well as the wheels front to rear. Consequently assuming that the 1/16 inch proclamation is true then Australia should be littered with cars stopped on the road side due to failed differentials. Maybe the 1/16 inch recommendation is just good practice rather than an absolute.

Just as an aside from my university engineering days I always thought one point of a differential was to manage the differences in rotational speeds between wheels on the same axle.

Having owned a range of 4WD and AWD vehicles over the last 35 years, I have never heard of an issue with any make caused by slight rotational variations either front to rear or left to right. Some earlier Nissan's were a little harsh on the rear LSD over time however they fixed that with the R50 Pathfinder in the mid 1990's. Doesn't mean it doesn't happen but the lack of data makes me feel some cynicism towards this "urban myth".

I have also searched the complaints websites to see if there is any historical data of this issue in CX-7s, Tributes, and CX-9s and have yet to find anything attributed to the issue. Turbos on CX-7s are another story though it seems.

In summary to me the evidence is a bit flimsy to convict however I am happy to be proved wrong.

The above is no criticism of any other posters. Instead it is just my feeble two cents worth.
 

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I think the point is you'd be increasing the wear. First, even in a matching set, no tire will be exactly the same circumference just due to variability in tire pressure and wear pattern, so you're always in this situation where there's some strain on the diff. The larger the difference, the more the wear. Too much difference and you'd be significantly increasing diff's temperature, which reduce oil viscosity and effectiveness, and subsequently result in wear on the differential itself. On an AWD, this a size difference between the front left and right wheels, the rear left and right wheels, or the front pair and rear pair wheels can cause excessive wear.

As to bends in roads, yes we have those too. That said, I would venture that 90% of all driving is still more or less "straight."
 

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Don't forget that there is rarely a time when there is a full lock up between front and rear axles on this vehicle so the effects of unequal radius are only going to be side to side, front OR rear. I would not normally introduce any imbalance across an axle but if I had a tyre ruined for some reason, I would probably change one up to half worn and both any more. I have never known any vehicle hardware or its systems to be intolerant of such action.
 
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check carefully

Check the flat tire carefully. If only flat on the bottom (which is most often the case) possible to just fix flat and should eliminate the size differential problem.
 

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also PSA please do not use fix a flat or any of those liquid plugs as they are a pain to clean and fix and in some places (shops or dealerships) may charge you extra if those are found as they are incredibly hard to remove and also damages the tpms sensors in wheels that are equip with them (wheels with metal valve stems).
 

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yea 2/32 is 1/16, its just how we say it in industry as our tread depth gauge just says everything in 1/32 so if u go almost any shop and notice what they write for tread depth its usually */32 and never reduced. it just makes it easier to keep track. and regarding burning out differentials, its hard to do yes but there are a lot of people out there who tend to prove me wrong and break them easily by not being mindful of their tires wearing out among other basic maintenance of their awd system(like changing out diff fluid). the differences in tread depth between tires can be enough to cause clutches in the differential and transfer cases to engage long enough to burn them up. those clutches mostly engages when making significant turns so they dont heat up for long as oppose to if the clutches are engaged in a straight line which is most of our driving then those will heat up and destroy differentials and/or transfer cases. hopefully what im saying makes sense as im not that good in explaining with text, but rather im better showing in person.
 

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I didn't know about using 1/32s to measure tyres - interesting.

Are you saying that burning diffs out only applies to AWD vehicles? The only clutch in a CX3 diff is the AWD drive clutch.
 

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I didn't know about using 1/32s to measure tyres - interesting.

Are you saying that burning diffs out only applies to AWD vehicles? The only clutch in a CX3 diff is the AWD drive clutch.
not to awd vehicles only just in context of current mazdas (at lease in US) are all awd and not 4x4. and i miss "spoke" about clutches rather the carrier in the diff that is splined to each wheel...the pin holding the smaller gears in the carrier i've seen in just sheer away causing failure...i know its an extreme case but its something i would personally see that it would never happen to my first personal awd car
 
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