Do all 4 tires need to be replaced when just 1 goes bad?

This comes up here or in a coupla other soob forums 2-3 times a year. No one seems to be able to find a benefit to keepimg an otherwise 'normal' soob in FWD mode. You still haul the same weight and have the same frictional losses.

Carl

Carl

No one is saying there's a problem. ALL (as far as I know) AWD systems (and 4WD systems when 'engaged')have the potential to incur damage when 'torque bind' forces develop in the drivetrain while operated on dry (non-slip) pavement-type surfaces. The problem can be more/less severe depending on many different factors.

When you turn - I suppose there could be a slight inclination for the center diff to detect rotational difference front-rear and engage a little. But that issue will go away quickly. BUT, if you have a smaller sized tire on one axle, the CD detects slippage CONSTANTLY - even moving straight down the highway (this is probably the most damaging actually, surface roads with lots of turns and a little gravel, leaves, trash in the gutters MAY present opportunities for 'torque bind' to be relieved with a little tire slippage occasionally) and there is no opportunity for the torque bund to be relased, as could happen on a dirt, gravel, mud or snow covered road.

I have heard of old 4WD vehicles left locked and getting so bound up when someone tried to parallel park they became immovable, a jack had to be employed to release the drivetrain!

Carl

The same as it does UPS.

At least with the 4EAT systems, I don't think there's a "center differential" per se. However - I read a few Endwrench articles that attempt to describe the system. The part I did understand is that the speed of the front and rear driveshafts are constantly monitored and torque distribution adjusted as needed.

You're right, it is an adjustable wet clutch pack I guess - functions like a variable center diff but bears no mechanical resemblance to a 'real' differential.

Carl

Except maybe in FWD mode then I don't have to replace the older rear tires because they are probably less in circumference than the new front tires. I'd like to procrastinate as to when I need to buy the 2 rears until maybe I feel more comfortable buying all four.

I understand - here's a link to a very long, exhaustive thread about the issue;