Thread: 4X4 Driving and inclines.

Go to ABOUT 3:00 MINUTE MARK, AND Watch a Unimog go up a 100% slope (=45 degrees):

[ame="http://www.youtube.com/watch?v=CxdX0au-BNA"]UNIMOG - YouTube[/ame]

Edit : actually - you said Incline, but maybe you mean side-slope....

Side slope: 38 degrees. See around 2:30 secs:

[ame=http://www.youtube.com/watch?v=17PqDnW_dCs]Unimog UHN Extreme Offroader promo video Part 2 of 3 - YouTube[/ame]

Incline.
Perhaps it's because he's trying it in a gutless non turbo landcruiser
I'm thinking CDL, low range 2nd

Supposedly a 40-45% incline with this Rangie and D3.

[ame="http://www.youtube.com/watch?v=4U-yFmnu0sY"]Range Rover Sport + Land Rover Discovery 3 / LR3 extreme steep climbing - YouTube[/ame]

Originally Posted by Disco Muppet

Evening all.
Was hoping some of you clever and knowledgeable types could settle an argument for me that I'm currently having with my wonderful girlfriend (In case she reads this).
What's the greatest incline any reasonable 4WD should be able to get up?
According to her father (mathematician) 18* is the greatest incline possible.
I, however, disagree, having seen some incredibly steep slopes traversed.
So, do I have the smug satisfaction of proving her father wrong (toyota driver ) on a 20* incline, or am I going to be made to look like a right fool?
I have no issue doing the latter, I do it often enough.
Cheers
Muppet

I would like to see his maths to come up with 18 degrees???

In theory, to climb a 45 degree slope you need perfect friction (practically impossible). However that is if the the both surfaces (tyre and hill) are perfectly smooth.

If the force is applied in a different manner then you can climb steeper slopes. e.g. tanks with metal tracks/tines can climb up to 60* slopes if the surface allows them to dig the treads in.

The same can happen with the slight undulations on slopes.

In most cases, somewhere between 30 and 45 degrees is the limit on a smooth continuous slope. Rick's post above showing a 40ish degree slope is close to the limit - noting that the rock would have extremely high friction - the very high roughness "digs in" to the tread.

Some points to note:
Most slopes offroad are not as steep as they seem at the time.
Many vids/pics are shot to make them look steeper.
Don't forget the influence of momentum or wheelbase on short slopes.

EDIT - spudboy - that looks slightly less than 45o - but either way the steps make it easier.

EDIT 2 - this is steeper than 45, but notice it is a short hill, and the driver uses momentum to help him get up.
[ame="http://www.youtube.com/watch?v=wwh6k-NCYfQ"]Dirtbuilt Buggy Climbing Upper Heldorado Waterfall - YouTube[/ame]

Ultimately, it comes down to torque, traction and your centre of gravity!

In practice, you should be able to get 40*-45* and in some cases, going up backwards can help with your CoG too.

M

As the others have said. In theory, which is probably what the father is thinking , the slope you can climb depends solely on the coefficient of friction (although one wonders what coefficient of friction he was using). But the effective coefficient is very difficult to estimate - in fact, in many cases there is effectively a "geared" connection between the lugs on the tyre and the ground surface, so that actual friction is not relevant.

And in practice, no slope is of infinite length, so that in most cases you can use momentum gained before the slope to help.

Of course, in most cases there are other real world factors that work against climbing a steeper slope - for example loss of traction caused by the wheels bouncing on the roughness that aids traction, but when asking "what is the greatest incline", it is reasonable to ask for the most favourable situation.

John

According to Tom Sheppard's "Land Rover Experience" book all Land Rovers (at the time of writing anyway - 1994) have gearing that is sufficiently low to allow a 45° incline to be climbed. The limiting factor is grip.

I have read a forum post by a South African guy who claimed he'd driven a stock Td5 Disco up a 38° hill at a military vehicle testing facility. No idea what kind of surface that is on.