[remy_martian]

The rear tires don't steer that much - the four wheel steering (4WS) section starts at 4:38, and he says in the crab mode part that the rears can only steer 10 degrees or so, which is typical of 4WS systems. Crab mode could be handy, but few of many 4WS road vehicles made so far bother to include it. GM themselves did 4WS on a previous truck - the Quadrasteer option for full-size pickups of 2002 to 2005 - and even though the 4WS system was entirely electronically controlled (no mechanical connection to the front steering), they didn't provide any manual tweaking or mode selection and just set rear steer angle based on front steer angle and road speed.

My 02 has 3 modes, selectable on the fly (though the rear and front wheels have to be centered for it to switch):

a) 2 wheel steer
b) 4 wheel steer which is speed dependent
c) 4 wheel trailering mode

The truck crabs during lane changes at highway speed in trailer mode, which is interesting when you intentionally try to "crack the whip", in ice skating parlance. The truck's tail does not fishtail out, the trailer merely follows the hitch ball. Was messing with abrupt lane changes, pulling a 3,000 lb dump trailer, and it was like the trailer wasn't even there. Hopefully. they bring Qsteer back with the eSilverado and its GMC twin.

Low speed crab would be possible on the Quadrasteer with a control module reflash...how to get the source code, lol?

 

[remy_martian]

Now that I think about it, it might crab at low speed in trailering mode. I'll get back to you on that one.

 

[remy_martian]

Gooseneck towing is prohibited on Quadrasteer iirc. It's only a half ton truck, though there are some very very rare 3/4 ton HD ones out there. You also aren't supposed to put oversize rubber on it or lift it.

The steering motor can't handle it. It has a monster spring in the mechanism to recenter on power loss, so it's fighting both the spring and rolling resistance (as well as any friction in the kingpins) when stopped.

It won't switch modes unless the wheels are straight ahead, which can be a real pain at times.

 

[remy_martian]

That model and brand of tires are speed rating Q (99 MPH), so your numbers are pretty darned close.

GM's lawyers have speed limited pickups to 95MPH in the past, so you might even have nailed it.

 

[remy_martian]

I'm still scratching my head on the differing f/b drive ratios. May be a motor efficiency cheat to where there are two drive cycle speeds they are targeting?