Originally Posted by tanscrazydaisy
4WD/AWD doesn't really help in this instance.... tires are the bigger factor here (I would even use chains going down also).... but the pro-AWD/4WD crowd convenient forgets about this scenario..... as all the care about is just going forward.
Braking & steering are the least of their concerns.
I have driven on the type of FS road featured in that vid in far worse conditions. The Jeep will easily outperform the Mazda downhill because of its gearing and therefore compression braking advantage. I also took this video today to show how superior a traditional 4x4 is downhill to any car in any configuration.
This is a short 14% grade. The Land Cruiser has a 2:48:1 low range transfer case gear and can be selected to stay locked in first gear of the four speed auto transmission. Diff gears have been lowered to 5:29 to compensate for the 37" tires.
When I start driving after putting it in first and low range, it runs up to 2,700 RPM at about 9 mph. Letting off the throttle it drops to idle RPM (900) without any use of the brakes and stays there all the way down the hill, going so slow that I had to pull off the road for safety reasons in order to continue down.
The 2007 Nissan Quest with studded snow tires can be selected to "L" on the 5 speed transmission. It cannot hold speed at all via compression braking and accelerates to 30 mph on this short hill, which would be dangerous in icy conditions. It would continue to run up to 50 mph+ on a longer hill even at much less of a gradient. For example, on a long Colorado pass.
The Quest driver is therefore reliant on constant braking and the associated threat of brake locking whereas the Land Cruiser driver can hold virtually any speed down to idle on any road grade without any use of brakes...and can do this indefinitely.
The belief that any car tire can remotely match this capability is not founded in practical reality. Gearing and engine compression design are critical elements of descent control, and it is people who drive vehicles that are 100% reliant on their tires who have failed to take descent control in any condition seriously.
I need to stop taking phone video in portrait