Tire replacement on 2001 Sport with 4x4

[Velvis]

Is it ok just to replace just the front tires or should all four be replaced? It's not AWD and I very rarely actually put it in 4x4 and when I do it's just to get out of my parking spot when it has snowed significantly.

 

[XLTrunner]

If your dash switch gives you true "2WD" option, you're fine with just replacing the fronts. I did this very thing for many years with both my '93 & '95 Explorers. However, this all changed when Ford eliminated that 2WD option and replaced it with AUTO/4HI/4LO. In the case of the latter, it's imperative you have a matched set on all four corners to avoid possible damage to your transfer case.

 

[J_C]

I'd get 4 matching tires, though if you lack the 2WD mode selection, you can DIY disable the 4WD, clutch power with the "brown wire mod".

How to: - The Comprehensive Brown Wire Mod Thread

Per Rick's request, this will be come the comprehensive brown wire mod thread. It will (hopefully) save a lot of reading through the twenty-some page original thread. (Rick, please note I will upload my images directly to my EF gallery as soon as I can find a program that will allow me to...

www.explorerforum.com

If you truly only want 4WD to get out of a snowy spot, non-matching tires would work in 4WD because they're substantially slipping, but it is still some wear on the drivetrain on dry pavement in 2WD-only mode, because there's a viscous coupling on the clutch pack that always applies a little torque to the front.

 

[C420sailor]

Only the AWD has a viscous coupling. The 4WD is far, far less sensitive to individual tire wear.

 

[J_C]

^ That's not the info I've seen. Example:

Rick's Free Auto Repair Advice

Rick's Free Auto Repair Advice has over 1,500 auto repair and information articles for DIYers and car owners.

ricksfreeautorepairadvice.com

Borg Warner 4405 transfer case in Automatic Mode
The transfer case includes a viscous clutch that is normally applied at a minimum duty cycle which transfer most of the torque to the rear wheels. The viscous clutch is filled with a high viscosity fluid, which flows through slots in the plates. The resistance to shear causes the plates to transmit torque at the needed ratio.

... Tire pressure and size can have a substantial effect on the inputs from the drive shaft speed sensors to the GEM. Even a few psi difference in tire pressure or tread wear between the tires can set a trouble code.

Note how it states "transfer most of the torque to the rear wheels". It's still providing some to the front. It may be less sensitive to differing tire sizes but less is not none.

 

[C420sailor]

I just looked at an exploded diagram. The BW4405 doesn’t use a viscous coupling—the 4404 does. The 4405 uses a traditional clutch pack, which is engaged via duty cycle application of a solenoid. This is how the brown wire mod is possible—it would not work with a viscous clutch.

I could be wrong, but based on my research, the viscous coupling of the 4404 is less tolerant of tire circumference due to heating of the fluid in the coupling. The clutch pack isn’t as susceptible.

What say you, transfer case experts?

 

[J_C]

^ My understanding of it is that while there is a clutch, there is the property of viscous coupling occurring, not the entirety of the drive, present even when the electromechanical clutch isn't engaged, which results in a small % of torque always going to the front wheels. This would be easy enough to check, putting it on a lift, or jack stands on all 4 corners, then put in drive and see if the front wheels spin.

 

[JonathanZ]

Is it ok just to replace just the front tires or should all four be replaced? It's not AWD and I very rarely actually put it in 4x4 and when I do it's just to get out of my parking spot when it has snowed significantly.

It's always best to replace all four tires when you can. I had unrepairable road damage to one of my rear tires on my 1994 4WD and Michelin no longer made a replacement tire, so I replaced both rears with the nearest Michelin equivalent. I suggested placing the new tires on the front, not the rear, and was told it was better to have the newer rubber on the rear, as losing control of the rear end in a skid was more likely than losing control of the front -- hopefully you can steer the front end out of a skid.

 

[J_C]

^ But that wears out your already worn, front tires faster if you're not going to eventually rotate them (which in theory also voids the warranty on the new ones), so eventually they'd be on the rear anyway.

I know that many places make this statement to put new tires on the rear but their reasoning is terrible. If the replaced tires had not worn more than the ones staying on the car, you'd have no new tires yet, and have to drive below a certain speed to stay safe, whatever the conditions dictate. Putting new tires on either the front or rear, you stay just as safe staying below that same speed in the same conditions.

If the old tires staying on the vehicle are really that much of a risk, they should be replaced, not gambling on which axle to put them on, not assuming any kind of loss of control is acceptable. It's kind of strange that people don't consider that.