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Hooniverse Asks Bonus: Mismatched tires on AWD cars?

Kamil Kaluski November 30, 2012 Hooniverse Asks

The above picture shows the results of my wife’s adventures in the urban jungle. She does not know how, but she managed to hit a curb. She called me right away and I told her to just drive slowly home as she was only about thousand feet away. I was rather certain that the sidewall was effed and was pretty certain that she won’t damage the wheel in that distance.

I have about forty thousand miles on these tires; I keep them properly inflated and rotate as required. I decided that they were good enough to last through the winter. Given my wife’s misadventure I have decided to order two new tires and keep the best two of the remaining three.

Quick call to our friends at tirerack.com and I am ready to place my order when I was told that, while the name of the tire remains the same, the tire has been redesigned and that the compound and all ratings are different. I was told that having two sets of mismatched tires on an AWD vehicle is not advisable for a lot of reasons; improper wear, damage to AWD system, etc. Still, I ordered just two tires.

Tirerack’s disclaimer makes sense. The AWD system on my 2006 MDX is not an advanced one and, let’s be honest here, 90% of the time it is a front-wheel-drive vehicle. Furthermore, common sense dictates that the same model and same size tire from the same manufacturer cannot be that much different, even after a redesign.

At this point I will wait and see how the car drives with the two new tires. If needed, I’ll order two more tires. What is the Hooniversal consensus on my decision? Wait and see or just order two more now?

EDIT: Damn you all… damn you all to hell!!!! And thank you for the advice. Ordering two more tires. :)

Currently there are "105 comments" on this Article:

  1. Xedicon says:

    Not to be a Debby Downer here, but miss matched tires can be dangerous. Some people would flat out say it's always dangerous, that isn't true, but it can be especially on an AWD car where at times all wheels are driven.

    Look at it this way. 40k miles is a good run, and puts the tires near replacement anyways. You might as well order two more tires and replace em all. That way you know it's safe AND you don't have to mess with replacing the other two in a few months time.

    Just my two cents.

    • I agree.

      I'd go so far as to say replace all 4 but keep the two best worn ones as spares in case this situation comes up again. If you keep the car you may end up using them. If not, include them in the sale and the buyer will know you were extra careful in your maintenance.

  2. Rkw says:

    Sell the car.

  3. Alff says:

    At 40K, I'd probably bite the bullet on 4 new tires. Buying two now simply sets yourself up for another 2 vs. 4 decision some miles down the road. Conceivably, you could end up with mismatched tires for the life of the vehicle as a result of this decision.

    That said, I had a similar experience when I had about 5K on the Subaru's tires. With so few miles, I just replaced one. So far, so good.

  4. OA5599 says:

    If you do decide to have two sets of tires, having the two new ones diagonally opposite (LF and RR, for example) will help eliminate stress on the center differential, assuming that the MDX doesn't have limited slip on the front or rear.

    • Kamil_K says:

      It does not. I don't think it even has a center diff…?

      • buzzboy7 says:

        Well, it has to have some sort of center torque splitter. Possibly some sort of fluid coupling like the old vanagons.

        • Thrashy says:

          The Acura SH-AWD system doesn't even drive the front and rear wheels at the same speed when engaged, *by default.* The basic version overdrives the rear wheels by about 2% versus the fronts, and the fancy one on the RL uses a variable-overdrive box attached in front of the rear diff that goes up to 5% or so. Even then, it only engages the system when the fronts start to slip, via electronically-controlled clutches on each rear axles, instead of just a differential.

          Just based on those facts, I don't think there's any real danger in using mismatched tires with this particular system. Were it an always-on arrangement with tighter mechanical coupling between the front and rear wheels, the story would be different.

          EDIT: Just saw that Kamil's MDX is an older version. Still uses the electronic clutches, though.

    • fixbroke says:

      It might be better to the centre diff, but at the expense of the front and rear diffs. Spider gears in a differential don't ride on bearings – they are on a straight shaft lubricated by the diff oil. For normal differential operation with the wheels running at different speeds (ie. turning) the speed differential is only for a short amount of time. Running different sized tires left and right on a permanent basis will wear down the spider gears and pinion shafts prematurely.

  5. $kaycog says:

    Your wife deserves four matching tires…………..doesn't she?

    • It's so cute when you ladies use a question mark instead of an exclamation point.

    • Kamil_K says:

      I hate when tire sales people say shit like this "think of your wife and children… don't they deserve a safe car? how much is their safety worth?"

      Eff you!!!!

      Not you $kaycog, the tire sales people. Which is why I order from tirerack.

      • $kaycog says:

        Whew! For a second I thought you meant me. Sales people will say almost anything to make a sale. One of the first things I learned about cars was not to have mismatched tires.

      • MVEilenstein says:

        I don't get that from Discount Tire. Most of the guys I deal with are honest and don't try to upsell me much.

        The one thing they all try to sell, though, is tire siping. Biggest scam since chassis undercoating.

        • dukeisduke says:

          I deal with a couple of different Discount Tire locations (they're called America's Tire on some states), and they've always been fair with me. The ones that impress me as being schlocky is NTB, who runs lots of ads promoting great prices, with disclaimers for "premium installation required".

        • TurboBrick says:

          Big thumbs up for Discount Tire. They sell tires, period. They don't try to sell any extra services. You want an alignment, go to your guy or take a 10% off coupon for Midas down the road. Perfect! The online ordering and scheduling system works great, they give you an accurate quote and they even have VERY competitive prices. Usually they run a $50 or $100 off 4 tires around the typical shopping holidays (and that often will stack with a mfg. rebate even though the counterperson might not admit to that).

          Also, the guys put the lug nuts back on with a torque stick on the gun first and finish off by hand with a torque wrench.

        • gessvt says:

          +1. These guys have earned my repeat business. Never walk out of the store thinking I got taken.

        • salguod says:

          I don't bother with anyone else. Discount will price match anyone, even on special order tires. And when I had a situation like Kamil's (roached one 60K mile tire on my Mazda3 at 40K), they gave me the prorated cash back on all 4 so I could avoid replacing 2 at a time.

          When I tried to save $100 on the first replacement tires for the Mazda and found the touring car tires to be simply awful, they took them back for a full credit toward another set, no hassle.

          I've probably spent north of $6K with them over the years.

        • C³-Cool Cadillac Cat says:

          I had tires siped by them one time. BFG A/T's on a Suzuki Grand Vitara, 'cause it was so pitiful in the snow, anything would help.

          I was wrong.

          My '94 V8 Grand Cherokee Limited with 'rudimentary' Quadra-Trac on those tires, however, unstoppable. I'm not kidding…though part of it is understanding exit speed is proportional to entry speed, in certain situations.

          • MVEilenstein says:

            They claim it helps wet traction, but if I'm buying A-rated tires anyway, they work just fine for me.Sent from my Verizon Wireless BlackBerry

      • Devin says:

        I actually love it when that happens, because I'm single and just say something like "eh, don't care."

      • Dacket84 says:

        I love TireRack as well. Especially since their warehouse is only about 40min away from where I live, I just drive there for all of my tire needs!

  6. Nick says:

    Subaru has a spec in their manuals stating how closely the circumferences (or it may be referred to as "height") of the tires have to be in order to not damage the center differential system. I believe this number was 1.5mm or 1/16".

    I don't know much about the Acura AWD system, but I would believe that this range is probably pretty close for that, too.

    • dukeisduke says:

      Just a 1/16"? That's ridiculous. And if you're talking about "height", that's the radius. But, the circumference makes a difference, too, as a smaller circumference tire will turn more revs for a given linear distance.

      If it were me, I'd sell that thing and get something FWD or RWD, with traction control.

      • Kamil_K says:

        No. I had a RWD 5-series wagon before that. I love the MDX, not seeling it for now.
        Traction control sucks… it does not help a RWD car get traction IMO.

        • Preludacris says:

          Agreed! Traction control, in my limited experience, does not help you get traction. It merely cuts power to prevent wheels from spinning.
          That's how, driving a borrowed Bonneville on balding all-seasons, I once found myself stuck up stuck in a flat parking lot in 2" of snow. Engine just wouldn't rev because it sensed wheelspin. Once I found the button to turn the traction control off, I was free in moments. I imagine a modern AWD torque vectoring system works much better than just cutting power altogether.

          The same car had a terribly invasive ABS system that I wished I could turn off because I felt I was smarter than it.

          • ptschett says:

            I think our '93 Cadillac STS had the same system as that Bonneville. Completely worthless in winter. My dad ended up pulling out the ABS fuse (no override switch!)

          • Mad_Hungarian says:

            My 2005 Town Car is the first and only vehicle I have owned with traction control. The first few times it activated while I was driving it scared the daylights out of me, because it feels very much like certain types of automatic transmission failure. If you have been driving 34 years without TC, your first thought is not "the TC activated." It's "Oh &%#@, something is wrong with my GD transmission, that is going to be EXPENSIVE . . . oh nevermind, I see that little light on the dash." Also, you don't need snow or ice for the TC to be a pain in the arse and a scare of a different sort. Last month I spent a few days in hilly country NW of Baltimore, MD. There was a T intersection at the bottom of a valley, so that any turn was from a downslope onto an upslope, and it was raining. I was turning from the middle onto the crossbar of the T, so to speak, and as soon as I hit the upslope the TC activated and I was hardly moving — and a truck was bearing down on me, coming downhill toward the intersection. I traversed that intersection several times and just about the time I got the hang of it, the rain stopped.

        • ummagumma82 says:

          Plus some of the systems that practically shut off the engine are freaking dangerous. My grandparents have a 2001 Sable that scared me many times. I'd goose it to pull into fast-moving traffic, one wheel would barely slip on a patch of gravel, and it would feel like the engine stalled. Then after what felt like an eternity, the computer would gradually allow the car to start accelerating.

          My Mark VIII had an early traction-control system that just pulsed the rear brakes. It was completely useless, but at least it didn't try to kill me.

      • Devin says:

        Traction control is not a substitute for more driven wheels when you have real winter weather.

        I don't have awd, but this year and its freakish snowfall makes me question that.

    • fixbroke says:

      I always thought it was odd that they make a specification like that, and then include a spare tire that's about 1/2" shorter than the stock tire size.

  7. parkwood60 says:

    Typically people tell you the difference in wear between old tires & new tires cause the worn tires to have to rotate faster, which the ABS/Stability control/AWD computer to think they are slipping. But given that the difference in size between a bald tire and one with full tread is a tiny percentage of the total diameter, being 5psi low would make a bigger difference.

    That being said, if the tires are worn at 40k miles, and you live somewhere with winter weather, why wouldn't you get your wife 4 new tires? I am toughing it out with nearly bald tires on my Chevy Colorado thru the winter, but I live in L.A. and I work from home, so I put about 20 miles on the truck every week, sometimes less.

  8. Irishzombieman says:

    I didn't have a matched set of tires until I was 25. Never crashed until I did.

  9. TurboBrick says:

    It's cheaper to buy tires than to replace broken bevel gears, that's all I'm saying… On a 2wd I'd say screw it, run a donut, 2 retreads and an old snow tire if you want to (and can keep it on the road).

  10. engineerd says:

    Run mismatched tires, and when people criticize you point to all the times the WRC guys run mismatched sets. If it's good enough Jari-Matti Latvala, it's good enough for Mrs. Kaluski!

    • Vairship says:

      Besides, define "matched tires". The front tires will usually have more weight on them (assuming front engine), so the rolling diameter will inherently be less than the rear tires. And of course the tire pressure will never be exactly equal between the 4 tires, so it sounds like baloney to me.

      You want the tires on the right to be about the same as the ones on the left, so that when braking hard all 4 will lose traction (and engage ABS) at about the same time, but even that may be moot with better ABS systems..

      • fixbroke says:

        The manufacturer's specified tire pressure will usually account for the weight difference between front and rear wheels. More pressure on the heavy end.

  11. P161911 says:

    Make sure you keep matching tires on each axle. Otherwise I wouldn't worry too much about it. Unless you can religiously rotate your tires to ensure 100% even wear you will always have a headache trying to find 4 matching tires. I went through this with the first 3 or 4 sets of tires on my 1994 Corvette. The factory tire was an asymmetrical Goodyear GS-C with different sizes front to rear. Also it seemed Goodyear was changing the tire slightly every 6 months or so.

  12. topdeadcentre says:

    I have replaced single tires on my AWD Volvo, and not run into problems, but tread wasn't too worn when I did it. What model tires are you buying?

    Which system exactly does your MDX have? It looks like 2006/2007 was a transition year from one AWD system to the next generation. Some systems (notably the late-1990's Volvo one) were notoriously bad using tires with wear mismatched by more than about 1.5mm and expensive damage transmission parts could be caused by situations like two new tires on the front and two worn tires on the back, and even worse when mismatched side-to-side.

    In your case, I suggest the following: after 40k on the old rubber, the old tires will be badly mismatched with new tires, and after 40k, most tires are ready for replacement anyway. If your winter weather involves snow or ice, for pete's sake, put the new (all season) tires on all four corners BEFORE the storms come.

    My recommendation is to call Tire Rack, and ask if there's any deals on purchasing four of the same tire (there often is) and can you just purchase the other two tires and have them shipped and take advantage of any available deal. When you have the four tires put on, have them check the rim that struck the curb (for out-of-round, and for having the edge bent, aka runout), and get an alignment, too, otherwise your new tires may be mysteriously wearing very unevenly very quickly.

  13. erikgrad says:

    IMHO:If you were planning to replace all of the tires by next spring/summer, replace them all now. If they still have 20,000 miles or more left in them, you could justify buying only two. Alternatively, you could buy 4 of a cheaper but good rated tire, especially given the tendency for the current tires to blow out on curbs.

  14. JayP2112 says:

    It's relive the "autox days" day here!
    I autox'd an old 5000s quattro for a while. It pushed like an anteater in the cones and was killing my street tires. I bought a pair of steelies and some blocky yokohamas. Back tires were Bridgestones.

    Just the difference from brands and MS vs Summer was enough to make it nuts. The steering wheel would go about 15deg to the left when driving straight. I guess the diffs were getting bound up. Drove home and got the other 2 to make a match set.

  15. CptSevere says:

    I used to have a '78 Chevy beater pickup that had a different brand of tire on each wheel. Didn't seem to affect the handling because it didn't handle at all. I sold the truck for eight hundred bucks, which is probably what poor Mr. Kaluski will end up paying for four new tires. There's a lesson there, but I don't know what it is.

  16. buzzboy7 says:

    I think it would be fine temporary, just not something you want to do a lot of miles with.

    Quote from Wiki on how the AWD works. Sounds like missmatched tires would put extra wear on the planetary gear clutchpacks possibly.

    Current SH-AWD configurations are all mated to a transverse engine, either a turbo-charged in-line four-cylinder Honda K-Series engine in the case of the RDX, or naturally aspirated V-6 versions of the Honda J-Series engine. The engines are mated to a front-wheel-drive transaxle. There is no center differential. The transaxle is bolted to torque transfer unit that spins a center drive shaft that powers the rear differential unit. The rear differential is a T-shaped device. Power coming from the engine is transferred via a central hypoid gear that delivers power to each rear axle. Power to the each axle is modulated by identical planetary gear sets and electromagnetic clutch packs which can vary incoming power side to side.[2]

    As described earlier, SH-AWD can vary torque side to side through the rear wheels. This ability to drive one of the rear wheels with more power (remember the row boat analogy) is accomplished through overdriving the rear wheels with respect to the front wheels. The Acura RL is designed with a third planetary gear set and clutch pack that are packaged into a so-called "Acceleration Device", which is bolted in front of the rear differential unit.[2] The Acceleration Device allows torque to be passed to the rear wheels at a near one to one ratio, but in cornering situations, the Acceleration Device variably increases the torque passed to the rear up to 5%, depending on the cornering situation.[25]

    • Kamil_K says:

      You rule!

      I don't have SH-AWD, wasn't on the '06 MDX. It started on '07+ second gen MDX.

      Also, ordered a second set of tires. Good Guy Tirerack didn't charge me additional shipping.

  17. HoondavanDude says:

    Meh, I'll bet you could patch that.

  18. muthalovin says:

    Go down to the ol' used tire store. Those places amaze me. In a bad way.

  19. wisc47 says:

    Funny, while I was home over Thanksgiving break I used my Mom's Subaru and, just like your wife, had a blowout very close to home. The tires had about 35 thousand miles on it so we just went ahead and got a new set.

  20. I_Borgward says:

    Late to the party (as is often the case), but here's another vote for 4 new tires. Glad to hear you're springing for them, KK!

    Anecdotal tale of woe: My Volvo 240 was equipped with a factory LSD. The previous owner cheaped out and put a pair of mismatched tires on the rear before I owned the car, and drove it that way for who knows how many thousands of miles. All of the tires on the car were pretty well worn by the time I bought it. I replaced all four immediately, but the damage had already been done. During a long road trip, the LSD started locking up when I'd go around corners, making the whole car hop like a bunny rabbit… eeek! I barely made it home. The fix? Swapping the entire rear end out in my garage with a used one from a junker, which was every bit as much fun as it sounds.

    I'd be wary of mismatched tires on any car, and doubly so on anything with AWD or 4WD. I don't even want to think about what the repair bill would be for a center diff.

  21. Target29 says:

    I tend to replace tires by 2's or by the axle. I always have the newer ones on the front. However if I was to replace your tires Kamil I would replace all as it sounds like you need them anyways and if you are going to resell in the next while they will all be matching.

    • Russell says:

      New tyres on front <<<<< WRONG !

      New tires should always be mounted on the rear (YES! THE BACK) of any vehicle.

      Here is why: When a vehicle encounters a loss of traction scenario on the front wheels, traction can easily be established by the average driver by…………………………………… slowing down this is easily recoverable it is called Understeer.

      When a vehicle encounters a loss of traction scenario on the rear wheels , the driver cannot compensate, effectively. This is called Oversteer, or "Fishtailing", and is not easily recoverable by the average driver.

      Therefore, the tires with the "best" tread should be mounted on the rear axle, To avoid possible life-threatening vehicle control problems.

      check out this link from tyre manufacture if you don't believe me. http://www.michelinman.com/care/tip6.html#5

      There are also some videos on the web of the testing Michelin and others have done to probe this point. Google and you will find.

  22. Russell says:

    What a bunch of ill informed old women! There it's absolutely no problem having mismatched tyres on an AWD vehicle, as long as the front pair match and the back pair match. That LH-RH matching is to do with handling stability and nothing to do with imagined potential damage to the fancifully imaged delicate drive train.
    The differential(s) as their name implies allows for any difference between RH & LH and in the case of AWD and difference between front and rear torques and rotational speeds. What do you think happens to a car driving continually around a circular track, where the RH and LH will have significantly different rotational speeds and distances traveled.

    The only damage I've seen to an axle/differential/drive-train that could be remotely tied to the tyres (but is actually a locked hub issue and nothing to do with tyres) is when idiots leave the hubs locked (locked differential) on a 4×4 after offroading and then drive on sealed road surface and end up screwing their Axle due to the circumferential difference traveled by RH vs LH when cornering.
    I have driven and raced various 4×4 and AWD platforms over 20yrs and have never had a problem with mismatched tyres front vs rear, infact it is not uncommon to have different profiles/widths/and even overall diameters front vs rear in AWD racing.

    You only need 2 new tyres so Cancel the order for the 2nd pair. Btw make sure you put the new pair on the back NOT the front as is the common intuitive mistake.

    • Deartháir says:

      Wow. That information is so bad, ill-informed, out-of-date and misguided as to be dangerous.

      Your information, while still poor, would be distantly correct if we were talking about the 4×4 system in, say, an old Range Rover. Or the original Audi quattro system, or the copy of that system, Subaru. If this were 1986. Since it is not 1986, it's perhaps time to use a little more sense. Modern vehicles use a wide variety of traction-enabling/enhancing technologies, as well as slip-limiters and cornering aids. So could he get by without buying a full set of four? Probably. It would work, in much the same way as Russell's example above of a car going around a circular track.

      Now take that same car around a circular track for 20,000 miles. Just keep it going, and see how long it takes before one or more of the differentials explodes in a sparkly pile of shrapnel. Go ahead, test it with your own car, I await the results. Because that's exactly what you're advising Kamil do with his.

      There are a lot of things you can do when racing a car that you can't do when daily driving a car. You wouldn't put massive camber on your daily-driven car, but you can do it on a track car, because the track car only needs to make it 500 miles or so.

      Like Capt. Severe said above. If your car is a piece of shit, and it's always going to be a piece of shit, and you don't care if it remains a piece of shit for the rest of your days, and aren't worried about wrecking it, or crashing, or killing your spouse, then follow this fellow's advice. Otherwise, swap out all four.

      • Russell says:

        As an Engineer that has worked for Ford, GM, Toyota, Mitsubishi, Subaru and Nissan and designed some of the AWD systems currently in use I can assure you that my information it's not out of date.

        Also i have been personally involved in testing where cars were driven around circular tracks for well over 20k miles and i can assure you that it doesn't destroy the drive train as you claim, or even slightly damage it.

        Just to be clear, my advice is to buy two new tyres, put those on the rear and the matched old pair on the front.

        • Deartháir says:

          Well yes, everyone's an engineer on the internet.

          Why on earth would you put the worn pair on the driving wheels? That makes no sense at all. You're talking about a "can do" situation. As I said, can it do it? Sure. Absolutely. Will it put excessive wear on the vehicle? Yup, sure will. I'll go for a walk, I wouldn't be surprised if I've got a vehicle sitting outside right now that will show what happens if you spend too long on mismatched tires.

          • danleym says:

            As far as putting the tires on the rear- that's all I've ever heard manufacturers recommend, for the reasons outlined in the Michelin link Russel posted. For the average no clue other than point it in a straight line and punch the brakes driver, yes, oversteer is a much more dangerous situation, mostly because the driver is going to freak and do something stupid. Also, if you get sideways on a road, you're a much larger target for oncoming traffic as opposed to if you experience understeer and just kind of drift into oncoming lanes. Either sucks, obviously. On the other hand, for a good driver, who knows how to steer into a slide and is somewhat capable of not panicking and recovering from oversteer, then maybe tires on the front would be a better idea, as long as the car is FWD (or a front biased AWD, like all of the modern stuff).

            As far as the being an engineer who just so happened to have performed the exact random test you specified, yep, I'm tossing out the BS flag on that. You've worked for 6 different car companies? If that's true, how crappy of an engineer are you that you can't catch on in one place?

            • Russell says:

              Dear Dearthair & Danlyn, Yes i am a real engineer, not an "internet engineer". I have an honors degree in mechanical and aerospace engineering from one of the top internationally ranked universities. I'm happy to snap a photo of my degree and email it to you if it really needs to come to that, of course i will expect reciprocation from you on that deal, unless of course your only qualifications are reading auto mags/blogs and kicking tyres and bullshitting at auto shows, in which case a note from your mum will suffice.

              Yes i have worked for atleast 6 automotive companies, not to mention Airbus, McDonald Douglas and Boeing to name a few of the many in the aerospace sector. Why would i want to "catch on" and stay somewhere for more than 12-18 months. As a consultant i would go in solve the problems, collect my large cheque and move on. Honestly the 30+yr career with 1 company is for mugs, maybe you're happy being Dilbert but that's not for me. After less than 20 yrs I'm semi-retired and living the good life in a Pacific tropical paradise.

              • danleym says:

                I'm just happy to know that the best thing to do with your time when living in a tropical paradise is get online and debate engineering with a bunch of people who are professional tire kickers.

                • Russell says:

                  Couldn't sleep due to thunder Storm, came across this thread while flipping through flipboard on my phone while lying in bed watching the lightning flashing on the Pacific.

                  Yeap I've got plenty of time to waste on such threads, i don't have a boss or a mortgage to answer

                  Cheers

                  • Kamil_K says:

                    I actually agree with you… which is why I ordered only two tires originally… and yes, they were going to go on the back of the vehicle.

                    I can still return two of them, it will only cost $25…. But I think I'll just put t them on at this point…

                    • Russell says:

                      Yeap, if the order is already in motion then no point to go back on your word and spoil your rep with your dealer. Fit 4 new tryes but keep the best two old ones as back ups next time you need a matching pair.

          • You are not an engineer? I thought all of us were.
            As for new tires (or the ones with better thread) always recomend to put them on the rear. especially in aquaplanning conditions it can safe you.

            • Deartháir says:

              Again, doesn't make sense. If you gave a shit about safety, you'd be replacing all four. So you're putting the worn tires on the drive (or, technically, drive-biased) wheels, which also do the steering, and will see more wear.New tires on the rear used to apply to rear-wheel-drive vehicles. I've never seen anything anywhere that says its a better idea to put the worn tires on the drive wheels. I'll happily be corrected on that, but again, since on an AWD car you should be replacing all four, it seems like a self-defeating cycle.

              • Dear Mr. Deartháir, maybe it does not make sence in Canada, but in Brazil where you can loose 2 almost new tires in one pothole, you definitly aren't going to throw the other 2 away. In this situation it does not matter if FWD or RWD or AWD, the better option is always the tires with the better thread on the rear wheels. It's in Portuguees but it explaines it well. [youtube W8ieA0DZmN8 http://www.youtube.com/watch?v=W8ieA0DZmN8 youtube]
                BTW I also do have some kind of automotive engineering degree, but have acted the last 25 years more as mechanical engineer.

                • Deartháir says:

                  I suppose that could be part of it. You don't have our temperature extremes.A common problem to run into here is tires that have been driven extensively outside of their recommended temperature boundaries. Most all-season tires sold up here, for instance, are not recommended above 30C or below -5C. You can get both ends of that range in a month or so. 35C in August, -10C in October. When that happens, you start seeing tires that either have really rapid wear, or no wear at all (usually on winter-biased tires).Again, a quick skim through manuals and tech books that are available to me all say the same thing I'm saying: new tires on the front for FWD or FWD-biased AWD, and ONLY if you don't have the ability to replace all four.Now, maybe that's a different recommendation for the Canadian climate. I have only that to go on, not having lived in your beautiful tropical climates.

          • Russell says:

            Why would i put the more worn tires on the front? Because it is safer! Do i need a better reason than that

            • Deartháir says:

              If safety is your priority, why wouldn't you replace all four?

            • Deartháir says:

              Let's see. Volvo says, replace all four, replacing two voids warranty, in the event of an emergency, replace two, put them on the front axle.

              Toyota (Rav4) says, replace all four, replacing two voids warranty, in the event of an emergency, replace two, put them on the front axle.

              Ford says, replace all four, replacing two voids warranty, in the event of an emergency, replace two, put them on the front axle.

              Volkswagen says, replace all four, replacing two voids warranty, in the event of an emergency, replace two, put them on the front axle.

              I can keep going?

              • Van_Sarockin says:

                Sounds like the tire supplier's wet dream. That and the liability lawyers getting some night sweats. Frankly, it also suggests a lack of confidence in their product by the manufacturer. Your concern and indignation might be better directed to the car companies who seem unwilling to invest in, or stand by, their product – and who seem to think that requiring the expenditure of hundreds of additional dollars for a damaged tire is acceptable..

                As for safety, there's really no issue, unless the remaining tires are overly worn. If mismatched tires put such stress on the AWD system that it produces failure, pull off the road. You will have sustained a failure of propulsion, no more, no less.

                • Russell says:

                  Yeap companies love to tell you you HAVE to (unnecessarily) replace stuff just so they can sell you more.
                  I have seen car manuals when they were being written for particular global models and counties that didn't have strong consumer protection laws or active motoring organizations got the "suckers version". Ie ridiculously short service intervals, and sneeze or blink and your warranty is void.

                  • Russell says:

                    A classic example, in some countries the current Honda Stream wagon (tyre size is around R15"x8"x60%] had normal tyres and a spare. In other markets it has run-flat tyres and no spare but a aerosol can of inflation-repair-glue. A normal tyre here costs about usd$60 while a run-flat tyre is around usd$700 each! . A Honda dealer tried to con my female friend into parting with usd$2800 for 4 new run flats. Luckily she called me and i told her, go to Any tyre shop get 4 normal tyres for usd$240 and if you ever get a flat call a cab or a tow-truck neither one of those is going to cost the remaining usd$2200 even if you had to call them 10 times.

              • Russell says:

                LOL, do they mention having incorrect tyre pressure in any one or more tyres voids warranty, since as many have pointed out that's the same or more effect than mismatched tyres.
                Technically going over your service interval by even 1 mile voids your warranty, as does not using genuine parts which for some like Honda includes Honda spark plus and Honda oil. It's all BS by the auto companies to screw more money out of you and also give then an OUT if they decide they'd rather not honor a particular warranty claim.
                So the spare tyre or mini-spare tyre they supply as OE with the car will void the warranty if i use it after the other Tyres have done more than say 10k miles?

                • Deartháir says:

                  Again, how, as an automotive engineer, are you not aware that they don't put mini-spares in an AWD vehicle for that exact reason? How, as an automotive engineer, are you not realising that the manufacturers say these things for a reason? And why, as an automotive engineer, do you seem to be agreeing that what they say is good advice, and then saying not to follow it?

                  • Russell says:

                    Really they don't put mini-spares in AWD cars for that reason?
                    Funny that The country I'm currently living in has mini-spares for audi R8, Q7 and Q5, Volvo v70 and V90, Honda crv, subaru wrx, hyundai santafe and tucsun, kia sorento, kia sortage, bmw x3, x5 and x6.

                    Yes they day these things for a reason, just not the reason you think it is, but rather covert their arse reason and screw the consumer reason.

                    When did i say that their advice is "good" and that i agree with it?

                    • Russell says:

                      Whoops just checked my neighbors r8, using run flats & no spare.

                      But my Q7 definitely got mini spare.

                    • Deartháir says:

                      Maybe they do things differently where you are, then. Around here, they usually use a full-size spare, or at worst, the speed-limited skinny tires that are the same diameter as the stock tires, and limit your speed to 60 km/h, and your distance to 60km, so as not to put stress on the AWD system. I haven't even seen a donut spare in years, other than on an older car.In the interest of fairness, as with Brazil Reporter, let's say this: it does look like, after forcing Google to look in countries outside of Canada and the US, that they have different recommendations in other countries. Around here, we see a lot of damage that comes from, for instance, putting only two new winter tires on an AWD vehicle. When two wheels can spin more easily than the other two, the limited slip system is kicking in a LOT, and those systems fail prematurely. Overheating, burning out, what have you. Now, that would probably be less of a factor in a country where you don't get snow as much as we do. If you have a front-drive biased AWD system, and the front wheels are slipping a lot, and it's always trying to force power to the back, that's going to eventually cause wear; if you live somewhere where that slippage isn't normal, that's not a concern. But I also notice that for a lot of vehicles — including some of the ones you listed — Canadian vehicles get a bunch of extra traction control equipment that is a pricey upgrade elsewhere. The CR-V, for instance, gets five more traction control nannies than elsewhere.Mr. Reporter made a good point, and got me thinking about it. In a country where perpetual losses of traction are not a major consideration, the rules would probably be different. If you're in Texas, for instance, all of this would probably not be a concern. Your average soccer mom will not be regularly spinning the tires. Up here, they're doing it a dozen times a day.That would also explain why I NEVER see the tiny donut spares anymore. Maybe Canadian vehicles are built differently because of the climate. That I don't know, but I'm going to have to assume that's the case. I've got a dozen automotive techs reading your posts, saying, “Doing that will blow your diff!”, but when we talked about it, we realised that the rules would be different if the weather was consistent. We don't see these problems as often in the summer, so a climate that stays the same year round would have different rules.This would almost be worth exploring further. I'm now really curious what other items are in the “Dear god, NEVER do that!” category for one country, but in the “Yeah, go ahead” category for another.

                    • Van_Sarockin says:

                      It sounds like you're saying that those differentials can't differentiate. To which, I would say that manufacturers should spec durable equipment. This is rather confusing, especially if there is a fluid clutch between the front and rear wheels. The other point here, is that is you are driving on snow, slush, ice and loose dirt a great deal, the differential and the nannies are already managing to cope with different rates of wheel rotation. The additional difference of a marginally taller or shorter tire should not increase the difficulty of the task appreciably.

                    • Deartháir says:

                      Again, it has less to do with the tire size, and more to do with the grip level. If you've got two tires that will spin because they can't grab the ground, and two that can grip fine, you're putting wear on the clutches, on the brakes — since most cars use the brakes for some sort of slip arrest system — and even on the transmission. We've all used shitty old tires to do burnouts. Why? Because they slip better.

                      Is that where this whole argument came from? The tire size? Did I miss that? Shit no, tire size only matters if you're dealing with a huge difference — like the donut spare mentioned above. What matters is wear level, and traction. Having a tire that's a fraction of an inch smaller won't make any appreciable difference at all. Having two tires that can't grip, and two that can, that's what will make your difference.

                      And you're right, a viscous coupling system really won't care about the difference between the two of them, but… does anyone use those anymore? Seriously, I'm asking, I have no idea, I thought everybody had gotten rid of them years ago, since they can only put like 10% of the power to the rear wheels.

                    • Van_Sarockin says:

                      Again, it's about different rotational rates. Precisely what differentials are created to contend with. If the tires were mismatched on the same axle, you'd have a big problem before too long. I suppose if your fronts were bald and the rears had perfect friction you'd also be setting yourself up for some problems. The tires on the van seem to have about 10-20,000 miles left on them. Not new, but not played. So the old ones won't be in a permanent state of slippage by any means at all.

                      If it makes you happy, then by all means spend twice the money so your tires can all be equally shiny. But it's not going to increase safety attributable to an AWD system. Obviously a new snow tire has more capability that a partly worn one, but I don't think that's your point either. I have FWD and I put snows on all the wheels, and I've certainly seen deeper tread perform better than shallow tread. But this concern for unrealistic levels of safety delta will also lead you to strap on a helmet before leaving the house when it's cloudy.

                    • Russell says:

                      Nice back pedal Dearthair, but your earlier statement " Now take that same car around a circular track for 20,000 miles. Just keep it going, and see how long it takes before one or more of the differentials explodes in a sparkly pile of shrapnel." Clearly implies you were claiming drive trains can't handle differences in tyre diameter and not differences in grip between miss matched tyres.

                    • Deartháir says:

                      Yes, because cars don't have centre differentials… which would be impacted by the differing traction presented by different pairs of tires as you described. I used YOUR example to prove the point.You know what, I tried to be civil because other people made good points for you. Enjoy your repair bills. It's easy to see why you worked for a dozen different companies, if you're that dedicated to a “good enough… barely” approach. Glad I'm not relying on your advice for anything expensive.

  23. Russell says:

    Btw 40k miles is not great mileage, i have never got less than 50k miles from tyres on various AWD road vehicles such as Audi, Subaru, Honda, Mitsubishi, Kia and i am pretty harsh on the break and the gas pedals. But i regularly (approx 10k miles) get an alignment and switch front-to-back and left-to-right.

    • danleym says:

      Normally I'm not nitpicky on spelling and such, but I would like to point out our automotive engineer above who does not know the difference between "break" and "brake".

      • Russell says:

        I'm typing these lengthy posts from a smartphone, it uses swype text system that often wrongly auto-corrects. I though i had corrected that wrongly auto correction, it seems the auto correct thinks it knows better and re auto corrected when i posted.

  24. luisthebeast says:

    QUESTION

    Is this AWD system the one that kicks in only when it senses slip? If so, run the new tires on the front old tires in the back.

    BUT, just like everyone else said, you should just spring for the four new tires.

    • Russell says:

      New tyres on front old tyres in back <<<< WRONG ! ! ! please see above for explanation why.

      • luisthebeast says:

        Why?

        The car is a FWD car so you would need newer tires for better traction and turning, avoid understeer. Less grip in the rear would mean the car would have a tendency to oversteer but given the bias on most cars towards understeer, it would handle more neutrally.

        • skitter says:

          My example was with an understeering econobox with new tires on the front and bald tires on the back. Did a full 360 in the wet at 60mph, hit second, went straight, bought more tires.

          Some of us have to do everything the hard way.

          • luisthebeast says:

            That's an extreme example though. Bald tires won't push away the water and hydroplane. As soon as there's no grip in the rear and massive grip in the front, you'll spin in a snap oversteer fashion.

            If Kamil's old tires still have some tread left, they should still have decent wet weather ability, perhaps even some snow ability.

  25. Russell says:

    Btw from Kamil's explanation " the tire has been redesigned and that the compound and all ratings are different." I think you will find that the new tyre design involves only a change of compound, and ply layup and possibly tread pattern but is sill available in the same rim size and wall height profile and width as the old tyres.

    So as long as he used matching treads on front and matching treads on rear (for stability/handling reasons) then there would be no problems, even if the fanciful claims of drivetrain damage were plausible since all four tyres would be the same size (except for the Minor difference of about 3/8" between diameter of new and old tyres).

  26. Van_Sarockin says:

    Just buy the replacement pair. I'd be surprised if you didn't have more variation between the remaining older tires than between them and the new ones. Between temperature, pressure, wear characteristics and suspension behavior, it's more than likely that every tire on the car is a few percent different in size and behavior from the others. This is why god invented differentials. We're also talking about daily driving a minivan, not winning the Targa Florio on bias plies.

  27. Justin Rajewski says:

    Bullshit. If it was so dangerous, you'd go flying off the road anytime you had one tire low on pressure because the rolling radius would be different. As long as you don't have clutched or viscous couplings in the system, go with it. DO NOT put same size tires cross corner from each other. It creates the same thing as stagger on a circle track car and will make it loose in one direction and tight in the other. Same axle or same side depending on your diffs.

  28. MJMcG says:

    The mileage quotes here is weird.

    How does anyone get 40,000 from a set of tires? Seriously, Presume you replace when they still have thread?

    Unless you just do highway mileage, this seems a bit high. I can kill a front set in 20,000 without any bother. and I drive gently, just nearly all in bad traffic.

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