One or all four?
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Post Fiend
Joined: Jun 2003
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One or all four?
I ended up having one bad tire on my Navi. It was suggested that I replace all four because of A4WD. What is your opinion? I know I would feel uncomfortable having two (slightly) different tire sizes on my Traction-Loc rear and I certainly would not want the automatic 4WD engaging becuase of a difference in speed between the front and rear.
Anyone perhaps have some detailed specifics regarding the speed differential between front and rear required to engage A4WD?
Anyone perhaps have some detailed specifics regarding the speed differential between front and rear required to engage A4WD?
Sit. Stay.
Joined: Oct 2001
Posts: 18,308
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From: Washington State
Re: One or all four?
Why in the world would you even be considering a different size other than the one that the other 3 are??
If you are just referring to the difference in wear, just replace the two on either axle if it makes you feel more comfortable.
The wheel speed difference would be negligable. Certainly not enough to activate the 4WD.
The speed is measured at the ring gear. If the rear is turning faster (200rpm??) it sends power to the front. (Pretty much...kind a simple explaination.
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If you are just referring to the difference in wear, just replace the two on either axle if it makes you feel more comfortable.
The wheel speed difference would be negligable. Certainly not enough to activate the 4WD.
The speed is measured at the ring gear. If the rear is turning faster (200rpm??) it sends power to the front. (Pretty much...kind a simple explaination.
)
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Post Fiend
Joined: Jun 2003
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Stock (new) tread depth is 13/32, mine were 9/32.
I wasn't considering a different size to replace one tire, I knew the new tire would be slightly taller than the others. This would result is increased rollout and my friends at the dealership mentioned that they has seen a few problems with the transfer case caused my mismatched tire sizes.
I wasn't considering a different size to replace one tire, I knew the new tire would be slightly taller than the others. This would result is increased rollout and my friends at the dealership mentioned that they has seen a few problems with the transfer case caused my mismatched tire sizes.
Senior User
Joined: Sep 2003
Posts: 146
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From: Meridian, Idaho
I don't think there should be a big problem, as long as you replace the tire in kind. Unless the other tire is worn enough so that there is a large difference in tire size. I recently blew both of my rear tires while pulling a horse trailer in BFE. I got a ride to the nearest tire shop about 80 miles away and picked up a couple of "close enough" tires. I got LT265 instead of the stock P265's and it caused quite a problem. My expedition tried to go into 4wd the entire 400 mile trip home. The dealership charged me $100 to tell me to replace the front tires as well. I did that, but my transfer case still seems messed up. Anyway, it's back to the shop for me on Monday. I will let you know what they say.
Senior User
Joined: Nov 2002
Posts: 305
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From: Somewhere West of Laramie
Mount one new tire of the same brand and size and inflate it to the correct pressure,then measure it's circumferance and that of the other 3 tires,if there's more than a little difference replace them all.They just showed this on Motorweek TV a couple of weeks ago.
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Sit. Stay.
Joined: Oct 2001
Posts: 18,308
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From: Washington State
Originally posted by 2003EXPY
...if there's more than a little difference replace them all.
...if there's more than a little difference replace them all.
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Joined: May 2002
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From: Annapolis, Maryland
The big issue is to make sure the tires on the rear axle match up - same size, brand, model & amount of tread left. This will keep the LSD from wigging out and engaging the AWD. If the rear tires don't match up, then the AWD constantly thinks the rear is slipping, and keeps adjusting the transfer case. It can wear it out pretty quickly, and that's not a cheap repair.
However, if your tread is fairly low (say, 5/32"), then you'll have a pull when you put a new tire (about 13/32") on one side - it will pull to the side with lower tread.
As far as the differential speed calculation goes, I think you're probably safe. If Ford has tweaked it to response to such a subtle change, then every joe who didn't rotate his tires would end up buying a new transfer case (~$2,000).
If it were up to me, I'd buy all 4, just because I'd switch to Bridgestone Dueler A/T REVOs and I'd want all of them to match. However, in your case, I think you'd probably be best off with 2 new tires. Make sure the new tires are rotated (or mounted) in the rear to keep you out of the ditches in those turns.
XXL
However, if your tread is fairly low (say, 5/32"), then you'll have a pull when you put a new tire (about 13/32") on one side - it will pull to the side with lower tread.
As far as the differential speed calculation goes, I think you're probably safe. If Ford has tweaked it to response to such a subtle change, then every joe who didn't rotate his tires would end up buying a new transfer case (~$2,000).
If it were up to me, I'd buy all 4, just because I'd switch to Bridgestone Dueler A/T REVOs and I'd want all of them to match. However, in your case, I think you'd probably be best off with 2 new tires. Make sure the new tires are rotated (or mounted) in the rear to keep you out of the ditches in those turns.
XXL