Norm Peterson
Corner Barstool Sitter
Grant - I think I found the disconnect that caused a bit of commotion in the other thread. I couldn't reply in the other thread because it had already been closed, so I just forgot about it. But I stumbled back on this thread while looking for a different topic.
I think you were looking for my opinion in part on this:
Let me get something out of the way first. Aside from within this paragraph, I'm going to be using terms like 'lateral load transfer' and 'total lateral load transfer' and their acronyms exclusively. I know that most of the car enthusiast world likes to use "weight transfer", but the only weight that actually transfers (i.e. physically moves around in the car) is that due to fluid slosh and poorly restrained cargo and passengers. Maybe a couple of lbs from engines and transmissions rocking in their mounts. We're going to ignore those effects, just like anybody who talks in terms of "weight transfer" does as well.
Lateral load transfer can be broken down into three distinct components. LLT through the geometric roll centers (where you get LLT but no roll), LLT through the elastic elements of the suspension (which is where most of your visible roll comes from), and LLT coming from the unsprung masses (wheels/tires/brakes/etc.).
So, if you leave the CG height the same, the total lateral load transfer remains the same. Note that this says nothing whatsoever as to how it gets distributed among the above components of LLT. It could be all going through the roll centers, where you'd get no roll in the suspension (though you would still see a bit due to vertical tire stiffnesses being what they are and the LLT obviously changing the inside and outside tire loadings). Or it could all be going through the elastic suspension elements (the geo-RC would be at grade), where you'd certainly get roll in the suspension. Or in any other combination. But the TLLT would stay the same.
That means if you were to hold the CG height constant, and vary a roll center height, as you get less LLT through a roll center because you lowered the RC, you have to be getting more LLT through the suspension. And that means more roll. This is really just a slightly different way of looking at it than watching the vertical distance between the CG and the RCs increase and computing a larger roll moment. Whatever works, just that sometimes looking at things from a different direction helps.
The effect on handling is more involved, as the transitions from geometric LLT to combined geo+elastic LLTs are no longer the same as before (have to think in terms of force variations with respect to time here). And axle roll steer varies with PHB height as well as with rear LCA plan and side view inclinations.
(truth be told, I was looking to see if Billy Johnson had posted any PHB vs Watts link thoughts).
Norm
I think you were looking for my opinion in part on this:
No flame intended, but it looks like you're confusing lateral load transfer with roll, like X amount of LLT can only cause Y amount of roll. It doesn't quite work that way.But mechanically, if the CG height, spring rate and sway bar rate stays the same, there shouldn’t be more roll.
Let me get something out of the way first. Aside from within this paragraph, I'm going to be using terms like 'lateral load transfer' and 'total lateral load transfer' and their acronyms exclusively. I know that most of the car enthusiast world likes to use "weight transfer", but the only weight that actually transfers (i.e. physically moves around in the car) is that due to fluid slosh and poorly restrained cargo and passengers. Maybe a couple of lbs from engines and transmissions rocking in their mounts. We're going to ignore those effects, just like anybody who talks in terms of "weight transfer" does as well.
Lateral load transfer can be broken down into three distinct components. LLT through the geometric roll centers (where you get LLT but no roll), LLT through the elastic elements of the suspension (which is where most of your visible roll comes from), and LLT coming from the unsprung masses (wheels/tires/brakes/etc.).
So, if you leave the CG height the same, the total lateral load transfer remains the same. Note that this says nothing whatsoever as to how it gets distributed among the above components of LLT. It could be all going through the roll centers, where you'd get no roll in the suspension (though you would still see a bit due to vertical tire stiffnesses being what they are and the LLT obviously changing the inside and outside tire loadings). Or it could all be going through the elastic suspension elements (the geo-RC would be at grade), where you'd certainly get roll in the suspension. Or in any other combination. But the TLLT would stay the same.
That means if you were to hold the CG height constant, and vary a roll center height, as you get less LLT through a roll center because you lowered the RC, you have to be getting more LLT through the suspension. And that means more roll. This is really just a slightly different way of looking at it than watching the vertical distance between the CG and the RCs increase and computing a larger roll moment. Whatever works, just that sometimes looking at things from a different direction helps.
Actually, lowering the RC height tends to slow down the load transfer. That's because LLT through the roll centers happens almost instantaneously, while LLT through the suspension has to wait for the roll to finish developing (spring and bar forces reflected out to the tires) or at least develop a velocity (damper forces). Even a stiff coilover suspension is relatively soft in comparison to the stiffness of the geometric load path (through the geo RCs), assuming that the suspension linkage and the associated pivots and bracketry are up to snuff.But as I’m suggesting, the transfer will happen faster. And again, that’s just for the panhard setup.
The effect on handling is more involved, as the transitions from geometric LLT to combined geo+elastic LLTs are no longer the same as before (have to think in terms of force variations with respect to time here). And axle roll steer varies with PHB height as well as with rear LCA plan and side view inclinations.
(truth be told, I was looking to see if Billy Johnson had posted any PHB vs Watts link thoughts).
Norm
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