Thread: How to calculate Gradeability?

Geez Wagoo.... sorry to offend, but usually a bit of light hearted banter is welcomed on this site

Originally Posted by wardy1

Geez Wagoo.... sorry to offend, but usually a bit of light hearted banter is welcomed on this site

No Wardy, I'm sorry for being uncharacteristically snappy last night.Wife was on my case, bashing my ears about something or other when I just wanted to wind down a little.
Wagoo.

Originally Posted by Dougal

Wouldn't 45 deg be a 100% slope?
So your gradability answer of 92% would be pretty close.

It's good to finally make the agrover connection.

Thanks Dougal, Yes 92 and 100%(45 degrees) are reasonably close, but what about my theoretical 90 degree climb based on tractive effort and vehicle mass being equal?
Seem to me if one replaced the road wheels with toothed gears of the same diameter (pinions), and these meshed with a vertical toothed rack, then the vehicles tractive effort should be capable of climbing the vertical plane. But 90 degrees is something like 1000% not 100.That's what confuses me about the formula. Does it require just as much torque to climb 45 degrees or 100% as110% 120% !50% and so on? I wouldn't have thought so.
Wagoo.

Alan,
I've been trawling through Wagoo's posts. He is a very serious guy.
I was going to suggest he might not be the sort of person who would not be seen at pre dinner sherry's or post dinner port's at Firth Camp but, after that last post (#23), you're welcome to join us at the next one Bill.

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

Originally Posted by wagoo

Thanks Dougal, Yes 92 and 100%(45 degrees) are reasonably close, but what about my theoretical 90 degree climb based on tractive effort and vehicle mass being equal?
Seem to me if one replaced the road wheels with toothed gears of the same diameter (pinions), and these meshed with a vertical toothed rack, then the vehicles tractive effort should be capable of climbing the vertical plane. But 90 degrees is something like 1000% not 100.That's what confuses me about the formula. Does it require just as much torque to climb 45 degrees or 100% as110% 120% !50% and so on? I wouldn't have thought so.
Wagoo.

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.

for those that dont know or know of Wagoo, his knowledge and experience are a HUGE asset to any forum he cares to contribute to.

Originally Posted by Brian Hjelm

There used to be gradability and startability formulae in the road train regulations of the state registration authorities. Try an on-line search.

For vehicle dynamics formulae, get a copy of the Chevrolet Power Catalog from a GM Goodwrench Performance Parts dealer or mail order direct from GM goodwrench in Detroit. Chapter 9 is all about suspension and steering characteristics and calculations.

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.

Edit. Uninformed, (Serg),Off Topic but, I didn't have my tape measure with me today, but later model Holden jackaroos seem to have quite long rear lower control arms. Have you looked at those?