Thread: How to calculate Gradeability?

An honor to have you on the forum Sir I have admired your work for years.

Originally Posted by isuzurover

Bill - the force required to move a given mass up a vertical (90o) slope (i.e lift it) would be twice the force required to move the same mass up a 45 degree slope.

This is all assuming Zero friction and the same rate of motion.

Lets say your landie weighs one tonne. To move (i.e push) it on flat ground, you only have to overcome the rolling resistance of all the moving parts. To move it up a 90 degree slope you have to lift 1 tonne, to push it up a 45 degree slope is halfway in between ~0.5T + rolling resistance.

All of this assumes you have NO suspension, but the only thing that suspension changes is (anti)-squat and weight distribution between the axles.

I just discovered the "thanks" douver. Ben as simple as it sounds now, that is exactly the information I've been looking for. Other discussions i've read on the subject were unclear on whether the force required for different gradients was linear as you've just explained.
Wagoo.

Edit. and thanks for all the flattering comments gentlemen. I wish I deserved them, but I just copy other peoples ideas and claim them as my own. There's nothing much new in the world of automotive engineering.

One Iota, I'm happy that someone saved those old videos,I thought they were lost forever when Outerlimits had problems
and lost everyones images.Thanks.

Originally Posted by wagoo

Thanks Brian I'll have a search from the Road train angle.

While I have your attention on the anti squat subject, and you are the resident heavy vehicle Guru, would you know why so many air suspended trucks were able to pass engineering approval with such poorly designed rear suspension geometry ? They have short steeply angled radius arms, which are little more than a thick leaf spring cut in half. The panhard rods are also very short by light vehicle standards.I feel sorry for the propshaft universal joints every time I watch one of these trucks moving off.The rear end jacking and axle wrap is really interesting to observe as well.
Wagoo.

I have never had anything to do with air suspended trucks. All I know of them is that they are reputed to do less damage to road surfaces. The industry rushed into air suspension because govt. regulations encouraged the change.

Originally Posted by uninformed

Wagoo,

while much has been said about AS it really comes down to wheelbase and COG. With the COG and the contact patch-convergance point angle constantly changing in real world, what is good and what is bad????

I like to think the flow of power to the ground and the flow of traction to the vehicle (chassis) being important...and while it is possible to make links too long, most OEM links on mainstream 4x4's could benefit from being longer. As you know you can change AS without changing link length and you can change link length without changing AS...

so you have 404's, do you attach the one link to the centerline of upper axleshaft?

what tyre size will you run?
what wheelbase?
any idea of COG height?
what front link set-up will you run?

cheers,
Serg

Thanks Serg,i don't have them yet but have been offered them, and/ or the loan of them to nut out what to do with them. Ideas centre around the 100 inch wheelbase range on moderate 38'' tyres on as low slung chassis as possible.Not many production chassis have a high kickup over the axle. I was thinking welding two rear halfs of Jeep Wrangler chassis together.my current 3 link front has very similar characteristics to a one link, with more complication, so i thought i'd go one link front/rear, with a twist. that is i would like to interconnect the front and rear wishbone chassis pivots via a differential carrier for forced articulation.
From a geometric viewpoint it doesn't matter where you attach the ends of the wishbone to the axle assembly.
Whether or not i go ahead with this project will depend on Vic Roads and the ball and chain, not necessarily in that order and whilst i've built up some fairly challenging cross country tracks on my 40 odd acres, I couldn't rationalise devoting the time and effort to build a truck that I couldn't legally use on the road as well.
Wagoo.

Bill,
Did I put you onto the two 404's?
If they are the one's I am thinking about, how are you collecting them?

Originally Posted by wagoo

Thanks Serg,i don't have them yet but have been offered them, and/ or the loan of them to nut out what to do with them. Ideas centre around the 100 inch wheelbase range on moderate 38'' tyres on as low slung chassis as possible.Not many production chassis have a high kickup over the axle. I was thinking welding two rear halfs of Jeep Wrangler chassis together.my current 3 link front has very similar characteristics to a one link, with more complication, so i thought i'd go one link front/rear, with a twist. that is i would like to interconnect the front and rear wishbone chassis pivots via a differential carrier for forced articulation.
From a geometric viewpoint it doesn't matter where you attach the ends of the wishbone to the axle assembly.
Whether or not i go ahead with this project will depend on Vic Roads and the ball and chain, not necessarily in that order and whilst i've built up some fairly challenging cross country tracks on my 40 odd acres, I couldn't rationalise devoting the time and effort to build a truck that I couldn't legally use on the road as well.
Wagoo.

Sounds interesting Bill. Have you thought about using air springs to do the forced articulation though? It would save a lot of weight...

Originally Posted by Mick_Marsh

Bill,
Did I put you onto the two 404's?
If they are the one's I am thinking about, how are you collecting them?

No mick, My mate's had them for a couple of years. We dismntled one front corner to nut out a possible disc brake conversion, because the drum brakes were too big to fit 16'' wheels without excessive offset beyond the 1'' permissable by Vic roads. We then discovered that the portal box gears were no bigger or wider than the volvo C303 Portals that were subsequently used to build his hybrid, and the complete Volvo assemblies, having the correct right hand differential offset and 61''trackwidth were much easier to fit to LandRovers. The Unimog diffs being huge, much wider and having the wrong front offset, together with the brake issue may kill the project for me too, unless I decide to just use the portal boxes and steering swivels adapted to RangeRover diff assemblies.

Ben, I had thought of airbags in the past, but experience with my old 6x6 showed that the control valves for crosslinking, diagonal linking, height adjustability. plus expansion chambers to maintain a respectable ride at high ride height, excess pressure bleed off valves,adjustable pressure regulator etc made for quite a complex system.Even with all that I had to remember to shut off the regulated air supply to the front suspension before climbing off road gradients because to weight transfer the airbags would expand, the regulator would sense a pressure drop and keep supplying more and more air so that by the time I'd travelled 50 metres the front end was jacked to maximum height,and the suspension was almost rigid.the electonically controlled systems on air suspended RangeRovers may take care of some(not all) of those issues, but I'm a bit of a Luddite and hate electronics.
Wagoo.

Antisquat vs Antidive....???

Antidive is normaly expressed as a percent with regard to the front end diving under braking on level ground...using wheelbase/COG and front to rear break bias to determine.

so if you are climbing, under acceleration I am guessing the front-rear brake bias is not valid....so how is it looked at? as Wagoo has stated he is looking at how the rear works BUT in relation to the front....low AS in the rear on a loose surface climb can result in the front unloading and loosing traction....to high AS and the rear axle wants to crawl under the vehicle,jacking the rig up in the rear and then this can lead to hopping which will cause traction loss...

so is the antidive simliar to AS when accelerating...yes there is the whole COG change and the AD would change as soon as the axle moves away from the body or vise versa...

Bill, are you looking at making the front 1 link exactly the same length and mounting height as the rear???

do you need a panhard?

where is Roll center height on a 1 link?

would you run hydro steering?

Cheers