Box Narrow Rear Track - Why?

[kishy]

Is there a particular engineering advantage to the narrower rear track width seen on boxes up to '89?

If the axle housing was newly designed for the Panther right from the get-go and wasn't recycled from another application, I don't see why it was designed to give such a narrow track width. Does it in some way provide smoother ride? Increased weight capacity by moving the end of the axle shaft closer to the spring? Were early years more likely to be equipped with giant balloon tires that might impact the rear wheel well lips?

Just wondering. Seems like an odd design choice when the car was almost 100% brand new everything when it came out. Widening the track has cosmetic and stability benefits as we know.

[jaywish]

I believe it was designed so that the owner would feel good after upgrading to a 90+ rear housing.

[gadget73]

I've been told it tracks more straight, but I don't know that I buy it. I've never been in a car with the wider rear that felt unstable in the back end, other than when there was something actually wrong with a suspension part.

[BigT]

Maybe they were trying to make the mandatory fuel requirements? Less metal = less weight for better mpg.

[gadget73]

can't imagine its a significant enough weight difference to matter.

[His Royal Ghostliness]

Look at a fullsize Ford truck of the same model years, even a 1-tons with the full-float rear axle has a noticeably narrower track width in the rear. Not a Ford-exclusive thing either, it's even more noticeable with GM trucks after their transition to IFS. It's a vehicle dynamics thing, forgot the specifics long ago but there was an actual engineering/design reason for it that has nothing to do with weight savings and such. As to why they kept making the housing wider and wider as time progressed, well with Watts linkage whale Panthers and trucks with outboard rear shocks the reasoning is likely clearance issues with the rest of the suspension, but anything else I'm gonna guess it's for increased stability at higher speeds.

[sly]

I know the outboard shocks are for better handling stability. The rest... no clue. I do know that I curb check a LOT less in the beater than I do the whale.

[kishy]

I could see some (small) possible improvement in tracking straight with a narrower rear track, or more specifically, with the tires being closer to the control arm mounts. Any flex in bushings would have a greater effect the further away from the bushings the tires are. But how much of a real world difference would that make? One tiny steering correction that the driver isn't even aware they made?

The questions about this can come from a couple different angles:
- If the rear track being narrow on the Panthers originally was intentional for some justifiable reason, why was it widened for 90-97 with no other suspension alterations? Maybe the 90 TC would have looked particularly offensive with the 89 axle so it was purely a cosmetic change?
- If the rear track being narrow was a compromise and it needed to be widened to correct some issue, why did it take all the way until 1990 before they did?

Ultimately it's not that important, just one of those things I wonder about.

[turbo2256b]

In general widening the rear track increases under steer narrowing increases over steer compared to the width of the front track.
The closer the spring is to the tire the less spring rate is needed to do the same job.
Also have to look at wheel offsets many of the newer cars with wider housings have inset wheels compared to older stuff. Track width might not be all that different. A wider housing with inset wheels takes some load off the bearings.

[sxcpotatoes]

I was gonna chime in with something similar to what Ivan said about the Ford trucks, mainly that perhaps it had to be narrower for an 8.8 to be an 8.8 to be an 8.8 from F150-Mustang(narrower than panther)-Panther platform vehicles. I mean I think they all interchange, except for maybe the truck leaf spring perches or whatever. I also pointed out to my brother's kids, you can always tell a 4wd ranger/F-150/chevy truck from a 2wd by the way the front tires stick out so much wider than the rears.

[His Royal Ghostliness]

It's as Turbo said, oversteer vs. understeer, it has to do with how the car handles while negotiating a corner, and not so much as how it goes in a straight line (except for when driving in snow).

The wider housing with more offset wheels I think is a follow-up on the front, they needed the deeper front wheels to accommodate the larger front brakes and the redesigned knuckle so in order to run the same wheels on the rear axle they had no choice but make the housing uber-wide. Bearing load, I'm not sure how much it is affected, being a semi-float axle the load plane of the wheel isn't all that important, plus that bearing is IMHO undersized for what it does anyways.