Downside of AWD!

[paris1]

Here's an interesting online editorial from today's Autoline Daily dealing with tire wear/failure/replacement issues for modern AWD systems. I presume this applies to the system Mazda uses too. My guess is not too many owners are aware of this added complication: http://www.autoline.tv/journal/?p=30272. Go to 4:56 minute spot for the beginning of the segment.

 

[CX-SV]

Yes, thanks, old news. AWD/4wd main impact from a operating cost standpoint is the 1-2 mpg fuel economy difference over time.

Mazda's approach and recommendations apply to all CX-5's (both awd and fwd):
"Always use tires that are in good
condition:
Driving with worn tires is dangerous.
Reduced braking, steering, and
traction could result in an accident.
Replace all four tires at the same time:
Replacing just one tire is dangerous.
It could cause poor handling and
poor braking resulting in loss of
vehicle control. Mazda strongly
recommends that you replace all four
tires at the same time."



Specifically Subaru is the main automaker of concern (and one brand of vehicle I have very little interest in owning), or at least it was in past years because they were adamant about replacing all 4 tires at once regardless of age/condition/wear. "Even so, there are some other solutions that can save you money. In some cases its not entirely true that you HAVE TO replace all 4 tires. Of the major AWD manufacturers, Audi recommends that the tires remain within 4/32nds of one another in tread depth, while Subaru recommends 2/32nds".

 

[paris1]

I'm sure there are many who are aware of this requirement/recommendation going into ownership of a vehicle with one of these systems. My concern, and that of the Autoline Daily presenter, is that there are no doubt many first time AWD buyers who blindly purchase a vehicle not being remotely aware of this and the selling dealer would be disinclined (to put it mildly) to make them aware of it. Having never considered AWD myself, I was only marginally aware of it (that's why the A/D spot was a wake up call for me) and I'm a pretty technically savvy buyer. Kind of makes you look twice at automotive technology that, on the surface, appears to be a quantum leap, but can have a dark side too.
PS: Out of curiosity, is there a way to tell if AWD is engaged in the CX-5 (or other AWD vehicles) so that one would know that a recently replaced tire is causing the system to malfunction?

 

[erhayes]

I suspect that the suggestion of keeping all the tires within a certain circumference is most important for a true full-time AWD like Subaru, Audi, Volvo, Mercedes than for part-time AWD like Mazda, Honda, etc. Ed

 

[paris1]

Good point Ed.

 

[Surfsup]

I'm sure there are many who are aware of this requirement/recommendation going into ownership of a vehicle with one of these systems. My concern, and that of the Autoline Daily presenter, is that there are no doubt many first time AWD buyers who blindly purchase a vehicle not being remotely aware of this and the selling dealer would be disinclined (to put it mildly) to make them aware of it. Having never considered AWD myself, I was only marginally aware of it (that's why the A/D spot was a wake up call for me) and I'm a pretty technically savvy buyer. Kind of makes you look twice at automotive technology that, on the surface, appears to be a quantum leap, but can have a dark side too.
PS: Out of curiosity, is there a way to tell if AWD is engaged in the CX-5 (or other AWD vehicles) so that one would know that a recently replaced tire is causing the system to malfunction?

I would think the tread difference would have to be quite severe. I have a 4wd TOD vehicle now (10+ yrs old). Tires are all different and I have an instant MPG meter on the vehicle. The numbers have always been approximately the same since the life of the vehicle. Now, this is not an AWD, it is a 4WD with TOD. So there may be a difference with the computer system software. If this is true, that is ridiculous. I'm sure there is a factor. The slight difference in wheel treadspeed between tires should be ignored by the computer. It should look at large differences of 5% or more.

 

[xtrailman]

with permanent audi 4wd the allowance was 3mm between tyres.

with part 4wd I have always aimed for the same, but I know someone who has a cx-5 and has just replaced his fronts only, the rears had 5mm left.

I have never had any issues with two xtrails, and I don't expect any with the mazda, the car will flag up any problem via the 4wd logo, its all in the manual. I just try to keep them with in 3mm as I did with the audi, so rotation is the answer, again the book says rotate at 5K miles.

 

[CX-SV]

I've never had any issues or malfunctions with AWD and 4WD systems (both full time and part time) in Toyota, Ford, Jeep, Mercedes products in past years.

Ed brings up a good point regarding full time AWD, especially regarding Subie.

And was there a period in past years where Subaru had it's share of problems related to such systems, (which may have led them to having the most conservative requirements for tire replacement)? Subie experts/owners past and present might know...

 

[tdfiver]

Way back in 2001 I had a Landrover Freelander diesel (commercial). I went onto the old British Steel works (Corus/tata) which had mainly unmade roads and my Freelander did 99,000 miles over 3 1/2 years. It really had some stick but I never ever had any problems with the awd system, which is basically the same as the CX5. The tyres were replaced as a nd when required, not rotated and even mixed makes.

Although I did have plenty of other problems, brakes wore out really fast as the roads were made up from crushed slag from iron production which ground everything away, the window mechanisms collapsed in the front drivers door and rear door, and I went through 3 windscreens and 2 headlights.
Driving on those roads was really hard on vehicles.

 

[dougal]

I suspect that the suggestion of keeping all the tires within a certain circumference is most important for a true full-time AWD like Subaru, Audi, Volvo, Mercedes than for part-time AWD like Mazda, Honda, etc. Ed

Yup, with my old Outback, I had one tire that would always loose a little air. That caused the dreaded torque bind and a $1500 repair.

 

[CX-SV]

PS: Out of curiosity, is there a way to tell if AWD is engaged in the CX-5 (or other AWD vehicles) so that one would know that a recently replaced tire is causing the system to malfunction?

To answer your question, see below.

Per the 2013 owners manual, if the AWD warning light comes on ("4wd"), there's a problem:


This warning light stays on for a few
seconds when the ignition is switched
ON.
The warning light will illuminate or flash
under the following conditions:
l Illuminates when there is an
abnormality with the AWD system.
l Illuminates if there is too much
difference in tire radius between the
front and rear wheels. l Flashes when the differential oil
temperature is abnormally high.
l Flashes when there are continually
large differences between front and rear
wheel rotation, such as when trying to
pull away from an icy surface, or when
trying to extricate the vehicle from
mud, sand or similar conditions.


In short, most auto-savy types are aware of this with awd (it also comes up with awd sport sedans and staggered wheel fitments), it's not that big of a deal and really doesn't make cost of ownership oppressively high. The biggest cost factors with awd are fuel economy penalty plus purchase price premium (less higher resale value), the extra cost of tires with infrequent single/multiple tire replacement is less significant for most awd owners.

 

[SayNoToPistons]

Queue the CX-5 owners with staggered wheels and tires with AWD.

 

[brandini]

You can order shaved tires from TireRack IIRC so you can order a single, new tire that's the proper circumference.

 

[CX-SV]

Queue the CX-5 owners with staggered wheels and tires with AWD.

Feel free to elaborate pls... Yep, that's a pretty rare setup with CX-5 owners.

 

[SayNoToPistons]

The activation of the rear differential is done so electronically with an electromagnetic clutch as well. The system assumes symmetric front and rear tire circumference. The mechanism reacts upon that assumption in association with the AWD engaging from variation in front and rear wheel speed difference. Mix that with owners that choose staggered tires on their AWD that didn't come staggered... Well...

 

[GAXIBM]

Per the service manual, the computer program controlling the tire pressure monitoring counts the difference in the rotational speed of the different tires as a low tire turns faster at the same speed as an inflated one. It has a "learning phase" after you reset it (up to three times) so it will learn the difference in a worn tire and a new tire and not alarm due to different tire sizes. The AWD and lock up clutch system and Traction Control could be using the same program to determine when the difference in wheel speed is outside of the normal difference to the known difference in the wheel speed so it will know when to engage. All I am saying is it may be smart enough to take different tire size into account or it may not be smart enough but the TPMS is smart enough. In any case if I had a AWD I would make sure to monitor the tire pressure and reset the TPMS per the operators manual up to three times to make sure the TPMS had completed its learning cycle and was not in alarm when the tire pressure is correct.