I have a 2006 XC90 AWD. Just got a flat on the rear driver side. it's non-repairable because the puncture is on the side wall. The tires are fairly new with about 85% tread left.Called Volvo dealership and was told that I need to replace all 4 wheels regardless how much tread was left. Ask why all 4 wheels and was told that tires with different tread depth will cause the AWD transmisson to stop working. This certainly does not make sense to me. do you think it's another wayof dealer gouging? Need your wisdom on this ASAP.

 

Welcome to the forum.

I started looking into replacement tires recently as a maintenance itemand was told I would need to replace all four. The explanation I was given was that it had to do with the circumference of the tires.

When making turns,tires with different circumferencesaffect the differential(s), because the rear tires track inside of the front tires, AND the tires on the outer side of the turning direction have to turn faster than then the tires on the inner side. All of this affects the operation of the AWD systems. I did considerablecheckingand all this held up everywhere I searched (online and industry contacts) and with nothing to refute it, so am inclined to believe it's true.

That said, not sure I would buy tires at a dealership... their mark-up is way expensive. You should be able to get correct tires for your Volvo at any local and reputable tire shop at a much better price. Check their website first, you might even score a $25 or $50 coupon towards your purchase.

Another alternative (and this from a mechanic) is to check with a localwrecking yard to see if you can find a correct tire from a vehicle with similar mileage that's thesame size and make and in good shape and etc. That would be theonly way to replace just the one tire, as the circumference issue comes into play in a difference of as little as 3000-4000 miles .

I think the only gouging you're asking about is paying the dealer markup on tires, unless they give you a very very good deal. I've never seen good tire prices at the dealer, however.

 

thanks for the quick reply. Do you think I can just replace the rear two tires intead of all 4?

 

You should replace at least two of them on the same axle. Put the new ones upfront and you should be just fine. the older ones you had to do all four.

 

B5254t, thanks. I was thinking two of the same tread level on the same axle should be fine also. Why putting the new ones on the front and old ones on the back? The owner's manual says the other way around - tires with more tread should go to the rear axle.

 

hi again pluto168,

I did some more reading on your situation last night, and also read that the new tires should go on the back, but not one source explained why this was the case.

I did find an interesting but very technical writeup on why it's recommended to replace all four. Seems it started with racing applications and found its way to passenger vehicles due to the way the axle and gearsets are manufactured. I'll post it if you want.

More importantly though, I found out that TireRack has the capability to "shave" a new tire down to match the tread depth of your existing three tires. They do this in situations like yours, where there is 50% or more tread life left on the other three tires. Give your local Tire Rack outlet a shout. Their website says they charge $25 or so for the service and takes a day or so. They comment thatit's much more reasonable to do this than to buy additional tires. I thought that was pretty good, coming from a place that makes their money from selling tires.

Good luck and let us know what you decide to do.

 

Thanks, bluemagicbus!

yes, please post the tech writeup.

I'll go with the TireRack shaving approach then.

One thing that still puzzles me is that:the owner's manual says tires with more treads should go to the rear axel - this implies that it is OK to have tires with different tread level. Am I reading it wrong?

 

You're welcome pluto168.

The owners manual thing puzzles me too, because, forAWD applicationsits recommended to replace allfour tires at the same time (or keep them the same size, anyway).

Being a maintenance-consciencious owner,at the proper service interval you'll have the tires rotated, right?(and we know that rotation these days is only front to back and never crossed left to right anymore, right?) At that point the rear tires with more tread depth will now end up on the front.

Does that mean that there will be a problem 50% of the time when the newertires are on the front? I can't get my mind around this one
[sm=dontgetit.gif]


Then again if you just get that one new tire shaved and all four willmatch again this will become a moot point.


Here is the write-up I found, I cut and pasted it to my desktop the other evening thinking you may want it. It was on a engineering forum and I found it by yahoo-searching for mismatched tire diameter or something like that. It made sense to me after I read it 2-3 times. I didn't save the url, sorry:

The issue arises because of the bearings within a typical diff gear set...there aren't any.

Stated more accurately, there aren't any rolling element bearings in a diff gear set, because there isn't space for them, and because even properly sized rolling element bearings would fail from false brinelling because of limited motion.

What has been shown to work well enough, in axle diffs, is hardened gears with hardened backs running on iron housings and hardened bores running on hardened pins, with all bearing surfaces intentionally relieved (with tool scars, etc) to allow lubricant to occasionally find its way to the sliding surfaces.

What happens when you run such a gearset at a higher than normal duty cycle is that it gets hot, and eventually the lubricant fails, and things progress badly from there.That's why 'stock' cars on short tracks have pumps and big coolers for the axle lube.

The 4WD's center diff gets stressed in the same way when you run different tires f/r, and is not typically equipped with a pump and a cooler.

If the FWD has a planetary diff (as opposed to a bevel gear diff), the torque split is typically not 50/50, and there may or may not be rolling element bearings or clutch packs present, but they all are designed to deal with only so much heat, and if you operate them too far off design condition, bad things happen.

 

OK.

TireRack does not carry the brand that I have on the vehicle. I called a few tire shops locallyand none of them does the shaving work.

I then called Volvo USA customer care and was told that if the tire wear is within 1/16th inch of a new tire, it is accpectable to replace just two on the same axel. So this is what I will do - replace the 2 rear ones.

What you pointed out on the tire rotation is still a mystery though...

 

Talked to my Goodyear dealer about this and they said the "rule" is toreplace both tires on same axle if the difference is more than 3/32". Any difference in tire wear between front and back is not really a concern since thetraction control orAWD slip diff. willcompensate for the difference in front vs. back rolling distance anyway.

 

For all cars except rear-mount engine (e.g., Porsche) and mid-mount engine (Ferrari, Lambo, Honda NSX, etc...) or RWD, the fronts generally wear out faster. This is generally true on FWD & AWD. The fronts are under more stress with driving the wheels & steering, and under braking the weight of the car shifts to the front. And yes the tyres on AWDs should still be rotated (many modern tyres are direction-oriented and if reversed, the original performance is lost. Look for the directional arrow on the sidewall).

Some XC90s seem to have been sent to the market with incorrect alignment setting. After replacing the tyres, I would have it aligned at a reputable shop or dealer as suggested by many. Expect this service to be between approx $70 and $120; quality laser alignment isn't cheap. And make sure that your XC90's ball joint recall has been taken care of:

http://www.autobuyguide.com/2006/12-...lls/index.html

Best of luck to you,


JPN

 

After I have read these posts, I have my 2 tires replaced for $566. I have purchased this car used. The original tires has one brand new, one almost new. Two older. Now I have driven for around 5,000 miles. I took the car to American Tire, they measured one tire has 9 (brand new is 10) left, one has 8 left. Two has 4.5 left. They say I should replace the tire when they have 4 left. I replaced 2 older tires.I will start to rotate them every 5,000 miles so they should be wear out around the same time. Next time I could replace all 4. I do feel the difference when driving now. I am not sure if it will help my transaxle / driveshaft problem. I sure hope so.

 

Old topic but I have same issue with my 2005 XC90 2.5T with 85K miles.

- Goodyear Assurance tires with about 8K miles on them.
- Currently tread depth is 8/32 inches (vs new = 11/32 inches)

- LF tire has sidewall damage (hitting curb) and bulges slightly. This has to be replaced for safety reasons.

- Local Discount Tire shop told me that for 4x4 vehicles as long as the difference in tread depth is less than 4/32 inches, the drive train is unlikely to be damaged.

- They recommend: the brand-new tire to the rear axle (so the REAR axle will have 11/32" and 8/32" tires), and move the "old" tires (with 8/32-inch depth) to the FRONT axles. Does this sound right?

 

The concern is with the older AWD systems that use a viscous coupling. Too great of a tread difference will wreck it. The newer AOC systems are different and can handle a difference

 

Thanks ES6T...

I am wondering my options (I have Haldex AOC system in my 2005 XC90):

a. Replace only 1 tire:
- FRONT axle: 8/32" and 8/32"
- REAR axle: 8/32" and 11/32" (one new tire)

b. Replace only 2 tires:
- FRONT axle: 11/32" and 11/32" (two new tires)
- REAR axle: 8/32" and 8/32"

Any suggestions?

 

Volvo has an old bulletin about replacement tires on the old system. It did not give a specific max difference, but did say put two new on the front as a minimum. There is no spec I can find for the AOC systems, but I can say I have seen cars come in with different tires and no AWD problems.

 

Per tire shop recommendation, I bought 1 brand-new tire (same brand and everything: Goodyear Assurance Fuelmax type):

---> FRONT axle: two "old" tires with 8/32" depth
---> REAR axle: 1 new tire 10/32" and 1 old tire 8/32".

Car drives fine.

The difference is 2/32" = 1.6mm, which I think is negligible for the REAR axle.

However, when I bought this vehicle (2005 XC90 2.5T AWD), I kind of had a plan B from reading forums: if and whenever the AWD takes a dump (bad transfer case, driveshaft, Haldex, AOC etc.) I was prepared to convert the vehicle to a FWD car.

So, having slightly mismatched tires in the REAR axle should be fine. In the worst-case scenario (which I think is very unlikely) of rear diff going banana, the car will be a FWD machine...lol.

 

Yeah I think you'll be fine. I just don't have an exact spec to back it up.