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Thread: Replacing just the rear tires 4matic

  1. #1
    Senior Member Ezzzzy1's Avatar
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    Replacing just the rear tires 4matic

    Wondering what anyones tire knowledge says about this. My wifes C300 goes through rear tires about half as fast as the fronts. So I ordered two new rear tires and took them to Costco to have them mounted up.

    I was told that they couldnt do it because the front tires tread were more than 2/32nds worn over the new rears. Basically they are saying that if the new tread is more than 2/32nds than the old tires that it will mess the cars transmission up.

    Ok, I could go either way on this but am wondering what anyones experiences with just replacing rear tires on an all wheel drive car. Are the tire companies just trying to make a buck or does it really matter?

    I suppose my main reason for asking is: even if you put all new tires on the car at the same time. By the time you hit 30k miles, because of the way Mercedes engineered their system, the rear tires are 4/32nds less tread than the front. At this point I am probably 2/32nds different at 15k miles!
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    Gold Member Yearly Supporter Sully's Avatar
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    Re: Replacing just the rear tires 4matic

    Maybe give Damir a ring?
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    Member Vitesse's Avatar
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    Re: Replacing just the rear tires 4matic

    I've replaced only the rear tires on my wife's C300 without any issues. I don't think 2/32 of tire wear will create enough of a difference in rolling diameter for the AWD system to care.
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    Senior Member matt2778's Avatar
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    Re: Replacing just the rear tires 4matic

    The general rule of thumb is 3/32 or less for 4wd/awd vehicles. The 4wd/awd system is designed to rotate the front and rear drive shafts at different speeds when turning. If you have a difference is tread depth front to rear the driveshafts will turn at difference speeds causing increased wear to the transmission/ transfer case. Some vehicles are more sensitive than others. Subaru for example are more sensitive to damage from different tread depths than others.

    Front tires on awd vehicles will always wear faster because they turn
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    Gold Member madvlad's Avatar
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    Re: Replacing just the rear tires 4matic

    Is the C300 the sport model with the staggered wheels?
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    Senior Member Ezzzzy1's Avatar
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    Re: Replacing just the rear tires 4matic

    Thanks for all the info, folks.

    Damir, it is the sport with staggered wheels.
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    Gold Member bulldog's Avatar
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    Re: Replacing just the rear tires 4matic

    I was told when I bought my AWD that if a tire get ruined I cannot buy just one and will have to buy all four new ones; because of same reason…they claim the tread depth is different and will make my ECU spin the tires wrong as it compensates for that difference. Luckily I have not ruined a tire to test this, but I’ve always feared this myself so would be good to know how “true” this is or if it is a ploy to sell more tires.

    Makes more sense, but I was also denied to buy two snow tires on my wife’s Rogue (AWD) as they said they could only install all four because of safety reasons.

    Quote Originally Posted by matt2778 View Post
    The general rule of thumb is 3/32 or less for 4wd/awd vehicles. The 4wd/awd system is designed to rotate the front and rear drive shafts at different speeds when turning. If you have a difference is tread depth front to rear the driveshafts will turn at difference speeds causing increased wear to the transmission/ transfer case. Some vehicles are more sensitive than others. Subaru for example are more sensitive to damage from different tread depths than others.
    Yup, basically what Subaru told me....I have a 2014 WRX.
    Last edited by bulldog; Thu Feb 25th, 2016 at 09:35 AM.
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    Gold Member madvlad's Avatar
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    Re: Replacing just the rear tires 4matic

    Quote Originally Posted by Ezzzzy1 View Post
    Thanks for all the info, folks.

    Damir, it is the sport with staggered wheels.
    So the reason being why is because you can't rotate tires and the rear is kicking down more power and more contact patch with the road so kind of an SOL situation kind of thing on those staggered sets. On AWD you definitely want to keep the thread as close as possible but about 2/32 difference from front to back or viceversa shouldn't cause any issues with the drive train
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    Senior Member Moderator Spooph's Avatar
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    Re: Replacing just the rear tires 4matic

    You should be rotating your tires more often. I'm not familiar with the Merc AWD system and can't explain what really hurts, but I know on the Subaru the viscous difs making up the Symmetrical AWD system burn out with different tire sizes and the only way to combat this is to make sure all tires wear evenly. I rotate my tires every oil change and have never had a problem in the 10 some odd years I've owned Subarus.
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    Gold Member madvlad's Avatar
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    Re: Replacing just the rear tires 4matic

    His tires can't be rotated as wheels are different sizes and bigger ones in the front and smaller rears will cause the car to handle weird, DSC/TCS to go whack too and cause mayhem. The split on these are anywhere from 45/55 or 40/60 causing the rears to always wear faster as they're RWD based cars, just like a FWD based AWD will wear the fronts faster than the rears.
    Last edited by madvlad; Fri Feb 26th, 2016 at 06:57 PM.
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    Senior Member Ezzzzy1's Avatar
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    Re: Replacing just the rear tires 4matic

    I just wonder where this information is coming from.... Either way the tire companies LOVE it. The two front tires that I just pulled had 6/32nds and 7/32nds on them. Basically over half the tires tread was left on the tire.

    I did hear from pretty much everyone that I spoke with about this that Subaru has had issues with tires being more than 3/32nds off.

    I ordered a tire tread gauge, I will probably just watch these tires a little closer and replace only the rears when they to 2/32nds difference.

    Thanks for all the help!
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    Gold Member madvlad's Avatar
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    Re: Replacing just the rear tires 4matic

    It's just information on data they collect over time. In your case I think you're okay as I'm sure MB thought of this given its a staggered set in an AWD and they knew the uneven wear would happen. Most passenger car tires rate anywhere from 9/32 to 11/32 new depending on the type of tire, replacement specs as per the wear bar is 3-2/32... Let's say that the scenario was they saw that your front tires were about 4/32 total and the new measure about 9/32 let's say, well I see why they'd recommend new tires. Now, if the scenario is that your front tires are 7 or even 6/32 and they didn't want to install new tires at 9/32 then that's just plain stupid, you have more than half life still on those. I see more of an issue trying to replace a tire in the same axle with a newer tire being more than 3/32 off. I honestly don't see the issue. Bring me the car and I'll mount the tires, I'll do it and explain this in person
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  13. #13
    Senior Member Ezzzzy1's Avatar
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    Re: Replacing just the rear tires 4matic

    Bummer that its already done, but thanks for the offer homie.
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