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Old 11-23-2014, 05:01 PM
 
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I have a areostar van with electronic 4wd. All for tires are 215\70\14. Can I change rear two tires to 215\75\14?
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Old 11-23-2014, 05:17 PM
 
Location: Chicago
38,691 posts, read 86,783,990 times
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Absolutely not. It's crucial for AWD vehicles that the tire diameter be the same on all 4 wheels. Assuming the 215/70/14 is the OEM size, you may be able to go up to 215/75/14 at all four corners, though it's important to make sure that there won't be any clearance issues in the wheel wells. Also be aware that going from a 70 aspect ratio 75 will cause your odometer and speedometer to under-report by roughly 3%.
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Old 11-23-2014, 07:34 PM
 
Location: Prosper
6,268 posts, read 12,101,075 times
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Quote:
Originally Posted by steele.baker View Post
I have a areostar van with electronic 4wd. All for tires are 215\70\14. Can I change rear two tires to 215\75\14?
Yes, you can.

Quote:
Originally Posted by Drover View Post
Absolutely not. It's crucial for AWD vehicles that the tire diameter be the same on all 4 wheels. Assuming the 215/70/14 is the OEM size, you may be able to go up to 215/75/14 at all four corners, though it's important to make sure that there won't be any clearance issues in the wheel wells. Also be aware that going from a 70 aspect ratio 75 will cause your odometer and speedometer to under-report by roughly 3%.
Normally what you say is correct for AWD vehicles, but not in this case. The Aerostar employed an electronically controlled magnetic clutch for the front wheels, so there is no mechanical limitation by having front/rear wheels rotate at different speeds.

The newer 911 turbos use a similar type electronic system, so staggered tires can now be run whereas they could not on previous generations (993, 996.)
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Old 11-23-2014, 07:37 PM
 
Location: North Pole Alaska
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Do not listen to the guy above me!!! The way the system works is it detects difference in wheel speeds and automatically engages the awd. So with that being said if you put different size tires on one axle it will think that its slipping all the time. Constantly engaging and dis-engaging the magnetic clutch destroying it!!!!
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Old 11-23-2014, 07:44 PM
 
Location: Prosper
6,268 posts, read 12,101,075 times
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Quote:
Originally Posted by usafracer View Post
Do not listen to the guy above me!!! The way the system works is it detects difference in wheel speeds and automatically engages the awd. So with that being said if you put different size tires on one axle it will think that its slipping all the time. Constantly engaging and dis-engaging the magnetic clutch destroying it!!!!
No, it won't. In fact, the standard tire size was 215/75/14 to begin with.

The system does not work the way you describe at all. The van is primarily a RWD drivetrain, with the front wheels only being engaged when the rears lose traction. At that point, the clutch for the front diff is activated.

Now, the clutch WILL engage more frequently, you're right there. But that isn't going to harm anything. It's part of normal operation, under the same conditions you'd get while towing or something similar and the front wheels need to have more power sent to them, nothing more.

EDIT: Not to mention, even if it were a completely mechanically linked system, you could still run the larger size, because the diameter difference is only 3%. That is within spec for every single AWD system I have ever seen, and ones that are much more precise than what was put out by Ford.
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Old 11-23-2014, 10:05 PM
 
Location: Chicago
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Straight from the Aerostar owner's manual: "WARNING: The tire size on the E-4WD must be maintained." And no it doesn't only send power to the front wheels when it detects slip; the default torque split 33/67 F/R. And depending on what model year it is, the OEM tire size may be 70 or 75 aspect ratio.

OP, if you want to prematurely wear out your transfer case, go ahead and put different-diameter tires on your car. Otherwise, keep them the same size.
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Old 11-24-2014, 01:43 AM
 
Location: Vermont
959 posts, read 1,327,884 times
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Not taking sides, but shouldn't you just call the dealer and ask?
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Old 11-24-2014, 06:23 AM
PDD
 
Location: The Sand Hills of NC
8,776 posts, read 14,134,753 times
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Quote:
Originally Posted by harpoonalt View Post
Not taking sides, but shouldn't you just call the dealer and ask?
Why would anybody call a dealer who actually services the auto in question when you can get on the internet and get free "expert" advice from anomous persons with no liablity for damages caused by bad advice?
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Old 11-24-2014, 06:34 AM
 
Location: Billings, MT
8,989 posts, read 7,076,226 times
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Generally speaking, AWD and 4WD vehicles will specify in the Owners Manual that all four tires MUST be the same size and Load Range, and SHOULD be the same tread pattern.
OP, what does the Owners Manual for YOUR vehicle say?
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Old 11-24-2014, 06:34 AM
 
13,563 posts, read 16,060,181 times
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Quote:
Originally Posted by PDD View Post
Why would anybody call a dealer who actually services the auto in question when you can get on the internet and get free "expert" advice from anomous persons with no liablity for damages caused by bad advice?

Absolutely!

In a similar vein, whenever a person has problems involving the law, it is much better to get legal advice from non-credentialed, anonymous people--with unknown agendas--via the internet, rather than consulting an attorney.


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