Thread: combined trailing arm mount/body outrigger

Originally Posted by uninformed

does this make any sense

Yes.
Consider AS at ride height level as well as ride height climbing (rear compressed more) and descending (rear extended more). Longer will give less change, but overall it may be dictated more by the length of the upper link than the lower.

A side on drawing, some ice-cream sticks and thumb tacks can be very good for seeing how it's going to run.

Originally Posted by Dougal

Yes.
Consider AS at ride height level as well as ride height climbing (rear compressed more) and descending (rear extended more). Longer will give less change, but overall it may be dictated more by the length of the upper link than the lower.

A side on drawing, some ice-cream sticks and thumb tacks can be very good for seeing how it's going to run.

I used to plot wishbones out in half scale on huge sheets of cardboard with thumbtacks and string just to see where changes in camber curves and roll centres would end up.

Quick and easy to get a visual on what's going on.

Originally Posted by Dougal

Yes.
Consider AS at ride height level as well as ride height climbing (rear compressed more) and descending (rear extended more). Longer will give less change, but overall it may be dictated more by the length of the upper link than the lower.

A side on drawing, some ice-cream sticks and thumb tacks can be very good for seeing how it's going to run.

Since AS is a combination of link geometry, wheelbase and COG....everything changes on a climb.

Climbing as you say may compress the rear, which on level ground would decrease AS, but as the COG has shifted on a climb, it will increase. Throw into the factor real world wheeling and rutted tracks etc, plus the axle wanting to crawl down and forward due to higher AS.

I think it can be controlled alot more with the TA than the A frame. as the A Frame and ball joint will change the pinion angle, but the TA control the axle arc.

at the end of the day, it is the relation of the A frame to the TA's...the more parrallel they are to each other the less the AS.

I have submitted my 1854 form to Qld DOT for vehicle modification.

PSimpson was generous enough to give me some of his time and chat about doing some CAD for the cutouts and folds. I will supply him with full scale tech drawings to the best of my abilites. I have started drawing Version 2.0, but looking at the end elevation of TA side, im not happy with the size of this thing.

Im going to source a used TA chassis bush and cut the rubber off so I have the physical part that bolts to the mount. I can place this on my drawing and see where it fits and what can be done. All of coarse, keeping in mind the TA height....

This whole project is not going to be a quick process. I am greatful for anyone that has and will help along the way. The knowledge and experience of some of you guys is invaluable to me.

Thanks

Originally Posted by uninformed

Since AS is a combination of link geometry, wheelbase and COG....everything changes on a climb.

Climbing as you say may compress the rear, which on level ground would decrease AS, but as the COG has shifted on a climb, it will increase. Throw into the factor real world wheeling and rutted tracks etc, plus the axle wanting to crawl down and forward due to higher AS.

I think it can be controlled alot more with the TA than the A frame. as the A Frame and ball joint will change the pinion angle, but the TA control the axle arc.

at the end of the day, it is the relation of the A frame to the TA's...the more parrallel they are to each other the less the AS.

The COG when climbing only moves due to compression/extension of the suspension. Climbing a hill and accelerating are exactly the same thing to suspension. The force vectors move in exactly the same way.

Accelerating at 1g (fast landrover) and climbing a 45 deg slope give exactly the same forces and suspension reaction.

Originally Posted by Dougal

The COG when climbing only moves due to compression/extension of the suspension. Climbing a hill and accelerating are exactly the same thing to suspension. The force vectors move in exactly the same way.

Accelerating at 1g (fast landrover) and climbing a 45 deg slope give exactly the same forces and suspension reaction.

hang on a second.....are you saying that all the geometry is the same if the vehicle is sitting on flat level ground, or flat 45 degree incline?

lets say both parked and both at 7km/h???

From what I have read, or thought in my head I would have said different. To me gravity does not act perpindicular to a surface. So if its mostly in a vertical plane then there has to be a difference between the 2. If your wheelbase is 110 inch on level ground, does it not become 78 inches at 45 degrees (no the wheels dont get closer togther but the points ploted do..the engine and tranny is now much high than the rear axle than on level ground.

I would have said that COG definitely be different from level ground to 45 degree incline, even with suspension at same postion relitve to vehicle....

Originally Posted by uninformed

hang on a second.....are you saying that all the geometry is the same if the vehicle is sitting on flat level ground, or flat 45 degree incline?

lets say both parked and both at 7km/h???

The geometry isn't the same, as the suspension extends/compresses at each end due to the load shift. Accelerating at 1g on the flat will give the same load shift and same geometry as 45 deg incline.

The load shift from being stationary (or at steady speed) on an incline is the same as the load shift from acceleration.
Squat/Antisquat and force vectors are exactly the same.

The reaction on the tyres is perpendicular to the surface, weight isn't just gravity, it's gravity plus acceleration.
Gravity acts downwards, acceleration acts forwards (in this example). The result on a flat surface is the weight/inertia vector swinging backwards with acceleration.
The result is exactly the same as being stationary (or at steady speed) on an incline.

I started down this path 15 years ago nutting out mountainbike rear suspension and climbing vs acceleration. It is a mind-bender and it might take a few years to accept.

Is the COG the same for level and inclined?