Understanding 4WD entry/exit angles
Submitted: Saturday, May 07, 2011 at 10:07
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Egalitarian
When comparing specs for 4WD offroad competence, am I correct in assuming that the departure angle is as important as the entry angle? In that case, in the following example, vehicle B would be the more competent of the two?
Assume two vehicles, identical length, wheelbase, and ground clearance.
Approach/Departure angles:
Vehicle A: 35/24
Vehicle B: 28/31
Vehicle B is the better of the two, because all though a shallower approach, than A, it’s tail will clear the obstacle on exit. Vehicle A, however, would be more likely to get hung up.
Your opinion please!
Reply By: Fab72 - Saturday, May 07, 2011 at 11:40
Saturday, May 07, 2011 at 11:40
All good until you hang a towbar or bull bar off the ends. After market
suspension and taller wheels and tyres will throw all those equations out too.
Towbars in particular.... some vehicles have very snug designed bars which have little impact on the departure angle, whereas others (thinking in particular on tray back utes) have tongues longer than the dreamtime serpent which absolutley kills off any reasonable departure angle.
Fab.
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Follow Up By: Fab72 - Saturday, May 07, 2011 at 11:45
Saturday, May 07, 2011 at 11:45
Sorry...got carried away. Yes, on paper, vehicle B seems like the better option.
Understand that if vehicle B's
suspension sags more than vehicle A's under load, then any advantage will be lost.
Fab.
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Reply By: Member - Phil G (SA) - Saturday, May 07, 2011 at 17:10
Saturday, May 07, 2011 at 17:10
I'd prefer vehicle A.
An inadequate approach angle is worse than an inadequate departure angle, because you can drag the rear end thru a gully (the towbar is usually the bit you scrape). Try forcing the front end through a gully and you'll do more damage. But most aftermarket replacement bullbars improve the approach angle.
Don't forget rampover angle - trashing the sidesteps and getting hung up on the top of a dune will happen with not enough lift or extended wheelbase vehicles.
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Reply By: Member - Captain (WA) - Saturday, May 07, 2011 at 18:04
Saturday, May 07, 2011 at 18:04
While on paper vehicle B may appear better, in the real world you may often find that vehicle A will actually perform better. The reason being is that mostly you are going forward, so as long as you can climb over the obstacle, you can often drag the rear off the obstacle when it hangs up - how often have you heard that THUMP as your towbar hits a
rock!
Its a bit like power/torque curves, while one seems more powerful on paper, the other drives so much better as it has a broader power band compared to a high but peaky one.
Cheers
Captain
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Follow Up By: Egalitarian - Sunday, May 08, 2011 at 10:07
Sunday, May 08, 2011 at 10:07
Thanks for the comments Feb72 PhilG and Capt WA, this is what I suspected.
And also the observation that it's better to talk to drivers rather than take paper specs at face value.
Cheers
Egalitarian
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Reply By: pt_nomad - Saturday, May 07, 2011 at 18:29
Saturday, May 07, 2011 at 18:29
I think you would be much better off talking with people on the whole vehicle performance off road than completing a paper audit inorder to make a purchase decision.
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