Replace tires in pairs?

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It seems most auto manufacturers recommend replacing tires in pairs for 2wd vehicles and all 4 for those with AWD. I understand the AWD recommendation, but the 2wd puzzles me.

Is the 2wd a theoretical safety issue or is it based on a concern that different diameters of tires on the driven wheels will create additional wear on mechanical parts?

I just had an unrepairable flat on my 2012 Focus. The OEM tires have about 7/32nds of tread remaining (compared to 10/32 new) and the dealer is suggesting getting 2 new tires. Given this small difference, my instincts are to get a single replacement and bias the tire rotation pattern to leave It on the front until overall tread wear is evened-out. Thoughts? Thanks!
 
Sounds like a bottom line issue to me. Will he refuse to sell you just one. For a brief period I had a Conti on one front and a Yoki on the other side, both close to new. Didn't notice any difference, although Camry steering is a bit, well, isolated. No braking pull issues and we do some pretty hard braking hereabouts just to get to work.
 
More for handling differences than for mechanical wear.

Different tread patterns, even the same tread patterns with different wear/depth, will handle grip differently. It's impossible to predict how that will affect handling...but it won't be a positive effect...

Now, in your case, I would simply replace the damaged tire with new since you've got the same tire make/model, and it's still relatively new...so any adverse effects will be minor...
 
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What's not to understand? It'll heat up the differential just like it would in an AWD car if you have tires of different diameters.
 
Originally Posted By: horse123
What's not to understand? It'll heat up the differential just like it would in an AWD car if you have tires of different diameters.


Maybe, but as most fwd cars don't have a limited-slip differential is this really the case?
 
I try to keep my tires matched up well, especially on 4x4's, but the reality is that unless you are extremely picky, anal retentive or are running obvious mismatched sizes (or capability) of tires then the differences really aren't as big as the tire shops want you to think. I had a F250 with brand new BFG AT KOs on the rear and almost worn out KO's on the front. Ran 4x4 in inclement weather and moderate offroad conditions all the time with no obvious problems. Our Oldsmobile has tires matched per axle but different front and rear. A slight lateral traction issue was noticed this past winter so I moved the less grippy tires to the front, NO BIG DEAL.

But for your average lay-person, I guess the tire shops do have some decent advise.
 
Originally Posted By: Danh
Originally Posted By: horse123
What's not to understand? It'll heat up the differential just like it would in an AWD car if you have tires of different diameters.


Maybe, but as most fwd cars don't have a limited-slip differential is this really the case?


There would be increased wear on the differential in the trasaxle for sure. Would it damage anything? Slim chance of it. I know a few people who replace tires as they pop. No transaxle issues yet.
 
Originally Posted By: Danh
Originally Posted By: horse123
What's not to understand? It'll heat up the differential just like it would in an AWD car if you have tires of different diameters.


Maybe, but as most fwd cars don't have a limited-slip differential is this really the case?


It will heat up differentials more, no matter the type.
 
Thing is, what if you have to cock the wheel slightly to fight a crown in the road, or to fight your own weight in the drivers seat? That will change the suspension geometry, and one tire will suddenly be the "inside" tire turning a different speed.

I say throw it up front and try to wear it down fastly.

FWD transaxle differentials don't like one-legged spinning and catching, like doing burnouts on ice then grabbing traction. Throws their pins. The world's most gentle turn, evidenced by 3/32 of rubber, shouldn't hurt them.
 
If traction is different enough between the tires it will pronouce itself in difficult conditions like ice, heavy wet or snow braking during cornering or emergent move. Thankfully stability control compensates for bad tire placement mostly.
 
The recommendation is for stability reasons in low traction conditions (eg rain) or in performance driving (tire traction at the limit).

Part two of the recommendation is always have the tires with the best tread depth or overall traction on the rear wheels, including on Front Wheel Drive (FWD) vehicles.

Essentially it's about elimination of the rear of the vehicle breaking traction before the fronts because it can cause a dangerous rear end tail-out condition (oversteer). Consequences include an increased risk of rollover when the rears have less traction than the fronts.

So, change in pairs, and rotate if necessary so that the new pair go on the rear axle.

If you know how to drive, and are familiar with a vehicle in oversteer conditions, well, that's one thing. But average to novice drivers or drivers who have never driven a safety instruction where vehicle dynamics are explored in a controlled environment where accident avoidance, skid control, etc are taught, will naturally respond to understeer better than oversteer.

Modern vehicles are built with inherent tendencies to understeer unless the car is a performance model. Even then only Rear Wheel Drive models have much of an oversteer tendency. If the front tires have the greater grip, the vehicle dynamics can surprise the less experienced driver.

Now, what you are "supposed" to do vs what you can get away with, differ. As long as you know the risk and the why, do what you feel is best.
 
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Are you getting the exact same model tire?

On a car I had they had one of the asym tires rotated the wrong way where the front had 1 tire spinning the wrong way. Even the difference in tread caused the car to drift and pull to that side.

So having a completely different tire can also cause pulling and alignment issues.

If you're getting the exact same tire I think its less of an issue for 3/32 difference
 
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Always replace tires in pairs, and put the best ones on the rear axle if you're only doing 2 at a time.

The best course of action is 4 new tires and then rotate until they're all worn out, but I understand not everyone has the means to do so...
 
The problem is that vehicles tend to pivot around odd tires in emergency maneuvers. The more odd the tire, the more the tendency. This tendency isn't noticeable until you try to preform an emergency maneuver (quick turns, or heavy braking) and by then it is too late.

If tires are replaced in pairs, this tendency is much much less - although, if there is a significant difference front to rear, the rears could try to become the fronts - very bad!
 
Well look, if you end up replacing both tires, make sure to bring home the one with 7/32" tread and put it on Craigslist. Someone who is less particular than any of us would be more than happy to buy it from you. I just sold a set of 3 tires from our Corolla when 1 was not repairable. The rest had about 30% tread. I wanted matching tires and Costco had the $70 off set of 4 Bridgestone. Got the turanza serenity plus.
 
Thanks for all the replies. As there seems to be no hard and fast answer I checked Tirerack's technical section. Tirerack generally suggests replacing tires in pairs or fours and even offers a "tread-shaving" service to bring a replacement tire to the depth of the others on AWD vehicles.

On the other hand, it seems some tread variation is allowable even on AWD vehicles. Tirerack cites 3 manufacturer recommendations for their AWD vehicles:

Audi allows up to 4/32 inch variation in tread depth among the four tires

Porsche (Cayenne) says all tires must be within 30% of remaining treadwear (so I guess 1 new tire at 10/32 would require the more worn tire to be at least 7.5/32)

Subaru says all tires must be within 2/32 of one another

While these recommendations are primarily for preserving the mechanical bits of AWD systems, they presumably also consider driveabilitydriveability aspects.

So, if these variances are acceptable on AWD vehicles one would expect their 2wd brethren to be even more forgiving. So the official answer to my questions remains "it depends"...
 
Also remember on what is the main factor why the question is brought up?

The answer to that is always "to save money".

If you take the cost out of the equation, then there is clearly no technical downside to replace in pairs.
 
Originally Posted By: raytseng

Also remember on what is the main factor why the question is brought up?

The answer to that is always "to save money".

If you take the cost out of the equation, then there is clearly no technical downside to replace in pairs.


Of course not. You can make the same argument about replacing all four. But I think a better characterization is "to not waste money" by unnecessarily disposing of tires with lots of life left in them.

And, ironically enough, this is a forum where posters move heaven and earth to save a couple bucks on a jug of oil and chastise those who don't run full 10,000 mile OCIs on synthetic.
 
I'd probably get one and do a modified rotation that leaves it on the front an extra couple times

or buy 2 and keep one as a spare incase of another flat. Depends on the deal I could get.

Or if you hate the tires go for the triple rebate july 4th deal and replace all of them and sell the OEM on craigslist
 
I would get a new matching pair and put them in the front of the car. Take the one odd tire and store it until you need it or the wear matches the other 4 tires, then use it in a 5 tire rotation or just keep it as a spare.
 
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