For the AWD owners

[darylzero]

I was reading the Trib this morning and thought I would share one of the Q&A's in the Rides section.

Q: I got an oil change recently at a tire shop and the manager told me there was a nail in the sidewall of one of my tires and that it could not be repaired. He then said that I needed to buy four new tires since my Honda is all-wheel-drive. I am not too upset since my original tires are almost due for replacement, but do you think they were trying to scam me?

— T.Q., Bluemont, Va.

A: No, they were not trying to scam you. Replacing just one tire not only affects the things we mentioned in the previous answer, but the difference in diameters continuously activates the viscous coupling for the AWD causing it to overheat and fail. You may end paying more than the cost of a couple sets of tires to replace the coupling.

Link to article

[audtatious]

You would have to have three bald tires and one new one for there to be any chance of the Nissan AWD system having issues or coding. I believe you need 5-10% diameter difference before you may notice anything. The only issues I've seen is when people install different sized tires front/back from a diameter perspective (staggered setup)

[darylzero]

This TireRack article says the same thing as the paper.

http://www.tirerack.com/tires/tiretech/ ... ?techid=18

So if we get a flat tire on our awd rogue we really need to get that donut off asap and get a new tire on there, right? I know you should never leave the donut on long anyway, but it seems much more important for awd cars to get it off asap.

[ImStricken06]

i had 2 tires 15% worn. (almost new)
i put on 2 new tires and guess what = the rear differential would clunk upon pulling off from 0mph.

i put one new tire on each axle, opposite from one another = no problems.

example: (n = new) (u = used)
n---u
u---n

[darylzero]

Was that on your Rogue or another car?

[ImStricken06]

Was that on your Rogue or another car?

it was on my rogue.
the differential would clunk. common person wouldnt pick up on it- but i did and once i did the tire rotation to equalize the wheel speed- it went away instantly.

[audtatious]

Tires are considered bald when one or more of their grooves reaches 2/32 of an inch deep, compared with about 10/32 of an inch for new tires. So, you have 8/32 of usable tread or 1/4". (I found this on the internet concerning tire tread depth and life)

Doing some geometry (circumference = 2 x pi x radius)
Tire X = 225-50-18 with full tread (10/32)...circumference is 84.466" or 26.9" diameter
Tire Y = 225-50-18 with tread at 2/32 (- 1/4" as we are missing 8/32 of tread now)....What is the difference?
Larger tire diameter is 26.9" which is a radius of 13.45". We are subtracting .25" from radius to be 13.20. 13.20 x 2 = 26.4" radius. 26.4" * 3.14 = 82.896" circumference

What is the percentage?

82.896 / 84.466 = .981 x 100 = 98.1%.

So, a 225-50-18 tire new (10/32 tread life) has 1.9% more tread than the one that is worn to replacement (or tread has only 2/32 left)

If the above calculations are correct then how will adding a new tire on one side really throw off the AWD system? It's less than 2%. I'm not trying to say anyone is wrong but I simply can't believe that a car manufacturer would install a system with such strict tolerances from a tire perspective.

This is an interesting topic and why I'm digging up math I have not used since the 70's

[ImStricken06]

subaru is the same way. extremely picky on tires.

[darylzero]

Tires are considered bald when one or more of their grooves reaches 2/32 of an inch deep, compared with about 10/32 of an inch for new tires. So, you have 8/32 of usable tread or 1/4". (I found this on the internet concerning tire tread depth and life)

Doing some geometry (circumference = 2 x pi x radius)
Tire X = 225-50-18 with full tread (10/32)...circumference is 84.466" or 26.9" diameter
Tire Y = 225-50-18 with tread at 2/32 (- 1/4" as we are missing 8/32 of tread now)....What is the difference?
Larger tire diameter is 26.9" which is a radius of 13.45". We are subtracting .25" from radius to be 13.20. 13.20 x 2 = 26.4" radius. 26.4" * 3.14 = 82.896" circumference

What is the percentage?

82.896 / 84.466 = .981 x 100 = 98.1%.

So, a 225-50-18 tire new (10/32 tread life) has 1.9% more tread than the one that is worn to replacement (or tread has only 2/32 left)

If the above calculations are correct then how will adding a new tire on one side really throw off the AWD system? It's less than 2%. I'm not trying to say anyone is wrong but I simply can't believe that a car manufacturer would install a system with such strict tolerances from a tire perspective.

This is an interesting topic and why I'm digging up math I have not used since the 70's

I agree this is an interesting topic. Here is an excerpt from the TireRack link I posted above (it is from a tire dealer so their could of course be some bias here).

As an example of different tire diameters resulting from tires worn to different tread depths, we'll compare two 225/45R17-sized tires, a new tire with its original tread depth of 10/32-inch and a second tire worn to 8/32-inch of remaining tread depth. The new 225/45R17-sized tire has a calculated diameter of 24.97", a circumference of 78.44" and will roll 835 times each mile. The same tire worn to 8/32-inch of remaining tread depth is calculated to be 1/8" shorter with a diameter of 24.84", have a circumference of 78.04" and will roll 839 times per mile. While the difference of 1/8" in overall diameter doesn't seem excessive, the resulting 4 revolutions per mile difference can place a continuous strain on the tires and vehicle's driveline. Obviously, the greater the difference in the tires' circumferences, the greater the resulting strain.

So it seems that even if your tire has 1.9% difference it's the extra revolutions each mile that cause the problem. It sounds like for those 4 extra revolutions each mile your AWD will kick in (if not always on AWD/4WD) when it's not needed. So if you drive 100 miles your AWD kicks in either 100 or 400 times it should not have...??

Or are they saying that the AWD is continuously on because the tires have a 1/8" difference?

[audtatious]

Dunno. IMO it seems overly picky.

[ImStricken06]

how will adding a new tire on one side really throw off the AWD system?

tires wear differently, and not rotating them, will cause uneven wear. this one poster found out the hard way:
converting-my-rogue-from-awd-to-fwd-t563721.html

Update: I took the Rogue to the Nissan dealership as a precautionary measure. As predicted the grinding noise is coming from rear differential. The technician advised that the differential's problem was most likely caused due to continuous use of unevenly worn tires. I do not think I've ever replaced all four of my tires at the same time. Little did I know the importance of doing so for an AWD car. My front tires are good, back are very worn. Is that common knowledge that somehow slipped by me? That an AWD car must have evenly worn tires or eventually it will mess up the differential?

I will call around to mechanic shops for rebuilding differential quotes. As previously stated it doesn't seem removing the drive shaft is an option so now I need to either get rid of the Rogue or give her some serious love.

Thank you all again.

[darylzero]

That is quite the timing of real world experience from lday8610!

[audtatious]

tires wear differently, and not rotating them, will cause uneven wear. this one poster found out the hard way:

I understand that. I just have a hard time with it being THAT sensitive. It is what it is.....

Hell, I'm just surprised I had the above calculations right