Rear end wander on icy roads

[markwb]

Originally Posted by amc49

You need at least some semblance of good tire on front OR back, not having it (running bald) is a driver competence issue. But only the unlearned put the new tires on the back on FWD, if I need back ones, the new go on front and old go to back.

Roger that! That's how we were taught and it's common sense old school. I don't understand where this rationale comes from when it comes to placing two new tires on the rear wheels of a front wheel drive car and leaving the older worn tires up front.

[amc49]

That method can be perfect enough to never need to pay for alignments as I do. I line up my own using that and other ideas. Once you are close enough to start splitting sixteenths you are there, no car on the planet cares about amounts of error smaller than that, the deflection from actually driving the car will be more. It's funny to hear all these people talk about digital numbers that bye and large mean very little in many cases.

The rear may be SUPPOSED to be narrower than the front but careful measurement can show whether that too is the case real world. Every car can vary slightly from that, you just gotta shoot the lines and see where they end up, then adjust to fit the need.

[sailor]

markwb - AFAIK, the "rationale" came from chain store lawyers who felt that it would be hard to defend a suit claiming that the worn tires on the rear let the vehicle "skid out of control" causing an accident. From there it spread, like a (leave bleep to imagination).

This is not "logical" says Spock...

Unfortunately "logic" and "legally defensible position" have little in common...

[markwb]

Thank You, sailor.. :)

[amc49]

The thinking is still stuck in the past of RWD cars which did it easier. The logic doesn't have to make sense to a lawyer, it just has to work.

[thenorm]

Originally Posted by amc49

You realize of course if you set rear at dead zero static then it will be slightly toe out when car moving from rubber bushing and other part deflection right? A slight toe out like that could easily make the car do what OP complained of. I'd be looking for ever so slight toe in that would neutral out to zero while moving. Even a bit of toe in there acceptable, it makes the rear stay better on a set line.

true, but put even a bag of groceries in the trunk and the compression of the springs will cause toe in. also many people keep stuff in there trunk permanently. i know i've got some boots, a shovel, windsheild fluid and some oil.

i dont believe that a very slight toe out will cause the wobble. I also want to avoid much static toe in, as putting alot in your trunk (or compressing hte springs coing around a corner) will cause a lot of toe in which IMO is worse.

anyways i think we can all agree that minimal toe in in the rear is called for (between 0 and v.slight)

[sailor]

thenorm - honestly, the "wiggle" in my experience came from toe-in - so minimizing that should help. (Winter driving specific info., summer or performance driving preferences could vary)

[berndt]

Here's the finished deal. A shim was added to the rear left, apparently..

[sailor]

Hmmm...

I'm seeing a MAJOR adjustment (needed) to front toe, as well as a change in L.R. camber.

The ODD thing, is that there isn't a "shim" to adjust camber on the Focus (it COULD be done, but it would be quite difficult) The normal way to make such an adjustment would be with a "camber bolt", which replaces an upper control arm bolt and can be twisted for some adjustment, then tightened in place.

[berndt]

He called it a shim. I suppose I could look and see what that part looks 'new'. He charged me, like $70 for the part. Sound about right for a shop cost + markup? I plan on keeping that sheet he gave me, and going back in a few months, maybe when winter is over, and getting it checked again, and make sure its not going out of spec over time...