marv_springer said:
Sorry to "but-in".... but I was discussing this w/
colbystephens on another thread....
Just so I understand, are you saying that a more narrow track rear axle allows a tighter turning radius?
I can't agree w/ this.... Please educate me.
Here's a diagram showing a theoretical turning radius.
I can't see how the width of the rear axle would affect it.
Marv
Your picture makes sense, but it does not account for friction and drive motion vectors (not sure if that is the correct term though)
I think it has to do with rear tire scrub and leverage. The rear axle is a fixed unit (i.e. the rear wheels track one direction...front to back). If they were mounted on casters and the front wheels were driving the vehicle, it wouldn't matter how wide the rear axle was because the front wheels would travel in there natural path and the rear would follow. Because the rear axles drive the vehicle forward and have to travel a wider arch with a wider axle there is more resistance and leverage of forward motion. I didn't believe it at first, but have seen it demonstrated with r/c vehicles. (same chassis, front end, etc., but swapped in different rear ends with the same gearing and tires size, just different widths). One thing I saw is that it took a noticeable difference in width to change the amount of turning radius, so a few inches on a real life vehicle wouldn't seem to make much sense, but someone hypothesized that it had to do with the difference in weight (the vehicle was scale size, but not scale weight) allowing the tires to slip more.
This is by NO means a scientific test, but I did see it with my own eyes. It does oddly make sense that as the wheels move toward the center of the vehicle that they would push the vehicle in the intended arch of the front wheels, but the furthur out they became they would leverage against the turning motion of the front wheels.
I would ASSume it's much like pushing a shopping cart. If you push it forward then turn slightly the cart will turn. If you push in the middle it will continue to turn a short while until it straightens out. If you push on the outside of one of the handles the cart will tend to turn to the opposite side. The furthur out to one side of the handle you push the quicker it will turn the other way. I'm assuming a wider rear tire acts the same way. When taking a left turn, the left rear tire is trying to keep the cart straight (more pronounced with a locker/limited slip). The furthur out the wheel is, the more it fights the turning effort of the front wheel.
Ideally (for turning), the rear wheel(s) would be dead center, but then you would lose stability (plus it would be an engineering nightmare for a rear wheel (4WD) vehicle). I'm ASSuming the engineers figured a slightly narrower rear (even if marginably smaller) would yeild a slightly better turning radius without giving up much stability.
In a vehicle that is going to be seeing heavy loads (i.e. dually pickup or cargo van), they were more concerned with safety/stability than parking lot turning radius therefore a wider rear end.
Maybe somebody who know a heck of alot more than I, can chime in and prove/disprove this theory.
AGAIN, I AM NO EXPERT ON THE SUBJECT, SO TAKE WHAT I SAY AND HAVE SEEN WITH A GRAIN OF SALT...
Ok I am stupid but please explaine how it makes the turning radius smaller. I just do not get it?
