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Replace all four?


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2 replies to this topic

#1 OFFLINE   8THFORD

8THFORD

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Posted 14 June 2012 - 02:54 AM

I need a little help. My wife wrecked the drivers side rear tire on her 2010 Flex SEL AWD with 26K. When she went to the dealer to get it replaced she was told she had to replace all four tires because the difference in circumference in the one new tire would wreck the transfer case. Is this true? My first thought was B.S. when driving around any corner the outside tires are traveling at a different rate than the inside tires. In theory this would cause the same damage.

Thanks for the help.
8thford

#2 OFFLINE   Waldo

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Posted 14 June 2012 - 06:04 AM

It is not BS. In fact it's even printed in the owner's manual (page 271 in my 2009 book):


Major dissimilar tire sizes between the front and rear axles could cause the AWD system to stop functioning and default to front wheel drive or damage the AWD system.

It's not the inside to outside difference that's the problem, it's the front to rear. The question is how much is "major". I think you'll probably be ok with as much as a 5% difference, but 2-3% is usually the safe limit. So as long as you're replacing it with the same tire model and the other three have at least 6/32nds of tread left, I'd think you'll be ok.

The Flex doesn't have a transfer case, it has a RDU. Inside the RDU are clutches that control the power split front to rear, but they also account for the slip between the front and rear since there is no true center differential. So if your front and rear tires are different diameters, those clutches have to constantly slip to compensate, that can overheat them and eventually wear them out.

Edited by Waldo, 14 June 2012 - 06:08 AM.


#3 OFFLINE   8THFORD

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Posted 14 June 2012 - 08:19 AM

Waldo,
Thanks, I will check the manual and the remaining tread depth tonight. I'm planning to talk to a mechanic after work as well.






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