Relation between lateral weight transfer and roll
12-22-2003, 02:24 PM
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Relation between lateral weight transfer and roll
I've been reading Carroll Smith's "Tune to Win" lately, yet I've become a bit confused on the topic of lateral load transfer.
Total weight transfer at the front or rear is a function of the CG height, track, weight, cornering acceleration (seen at the CG), and thus is independent of the roll resistance. WT = (CG height)(weight)(cornering G's)/(track) or something like that.
So the only reason we want high roll resistance is to prevent unwanted camber/toe changes and because it is inherently difficult to drive (much less quickly transition) a car that wallows about. I would also guess that the roll stiffness has an effect on how quickly the lateral load tranfer happens, but did not find enough info. in Prepare to Win or Tune to Win.
C. Smith then goes on to say that the lateral load transfer is dependent upon spring compression. I'm assuming that this is because the compressed spring changes the roll center height and thus the roll moment will change and this should have an effect on the distribution of load transfered front and rear, correct? Larger roll stiffness in the front means more lateral load transfer between front wheels? But in terms of the actual load tranferred, it shouldn't matter, right?
Edit: I just read descartesfool's post here (the big one), and it definitely answered some of my questions. I haven't considered or thought about load transfer through the suspension links (geometric transfer) or that the unsprung portion experiences load transfer and the only "spring and shock" is the tire...also, besides my stumbling across this particluar topic, I feel like I need more technical based reading. Can anyone offer book suggestions that get more in depth?
Anyone care to discuss? or at least tell me where I am thinking incorrectly?
Modified by GSpeedR at 7:01 PM 12/23/2003
Total weight transfer at the front or rear is a function of the CG height, track, weight, cornering acceleration (seen at the CG), and thus is independent of the roll resistance. WT = (CG height)(weight)(cornering G's)/(track) or something like that.
So the only reason we want high roll resistance is to prevent unwanted camber/toe changes and because it is inherently difficult to drive (much less quickly transition) a car that wallows about. I would also guess that the roll stiffness has an effect on how quickly the lateral load tranfer happens, but did not find enough info. in Prepare to Win or Tune to Win.
C. Smith then goes on to say that the lateral load transfer is dependent upon spring compression. I'm assuming that this is because the compressed spring changes the roll center height and thus the roll moment will change and this should have an effect on the distribution of load transfered front and rear, correct? Larger roll stiffness in the front means more lateral load transfer between front wheels? But in terms of the actual load tranferred, it shouldn't matter, right?
Edit: I just read descartesfool's post here (the big one), and it definitely answered some of my questions. I haven't considered or thought about load transfer through the suspension links (geometric transfer) or that the unsprung portion experiences load transfer and the only "spring and shock" is the tire...also, besides my stumbling across this particluar topic, I feel like I need more technical based reading. Can anyone offer book suggestions that get more in depth?
Anyone care to discuss? or at least tell me where I am thinking incorrectly?
Modified by GSpeedR at 7:01 PM 12/23/2003
12-23-2003, 01:21 PM
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Re: Relation between lateral weight transfer and roll (GSpeedR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR »</TD></TR><TR><TD CLASS="quote"> I feel like I need more technical based reading. Can anyone offer book suggestions that get more in depth</TD></TR></TABLE>
Allan Staniforth's Competition Car Suspension book, Chapter 8
Total load transfer is independant of suspension. Portion of load transfer at front "axle" compared to rear "axle" is what is affected by suspension. This determines oversteer/understeer balance based on tires and centre of gravity location, moment of inertia, etc.
Allan Staniforth's Competition Car Suspension book, Chapter 8
Total load transfer is independant of suspension. Portion of load transfer at front "axle" compared to rear "axle" is what is affected by suspension. This determines oversteer/understeer balance based on tires and centre of gravity location, moment of inertia, etc.
12-23-2003, 10:36 PM
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Re: Relation between lateral weight transfer and roll (descartesfool)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool »</TD></TR><TR><TD CLASS="quote">Allan Staniforth's Competition Car Suspension book, Chapter 8</TD></TR></TABLE>
Will check that out. Thanks.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">Total load transfer is independant of suspension. Portion of load transfer at front "axle" compared to rear "axle" is what is affected by suspension. This determines oversteer/understeer balance based on tires and centre of gravity location, moment of inertia, etc.</TD></TR></TABLE>
That makes sense. I found a few interesting articles here: http://www.ozebiz.com.au/racet....html (and I know there is a good amount of stuff out there too), that answered some other questions. So, the rate at which the sprung load is tranferred is determined by the suspension roll stiffness...and the unsprung and sprung transfer through the roll center depends on the suspension type, though they typically happen quickly and are far less than that of the sprung mass (I believe you stated that elsewhere).
Can't wait to start playing around with ADAMS (FSAE team).
Will check that out. Thanks.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">Total load transfer is independant of suspension. Portion of load transfer at front "axle" compared to rear "axle" is what is affected by suspension. This determines oversteer/understeer balance based on tires and centre of gravity location, moment of inertia, etc.</TD></TR></TABLE>
That makes sense. I found a few interesting articles here: http://www.ozebiz.com.au/racet....html (and I know there is a good amount of stuff out there too), that answered some other questions. So, the rate at which the sprung load is tranferred is determined by the suspension roll stiffness...and the unsprung and sprung transfer through the roll center depends on the suspension type, though they typically happen quickly and are far less than that of the sprung mass (I believe you stated that elsewhere).
Can't wait to start playing around with ADAMS (FSAE team).
12-29-2003, 12:25 PM
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Re: Relation between lateral weight transfer and roll (GSpeedR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR »</TD></TR><TR><TD CLASS="quote">
I would also guess that the roll stiffness has an effect on how quickly the lateral load tranfer happens, but did not find enough info. in Prepare to Win or Tune to Win.
</TD></TR></TABLE>
The speed or rate at which load transfer occurs is a much more complex subject. It depends of course on the roll moment of inertia, which is a little difficult to measure. The Yaw moment of inertia can me measured by placing a car on a suspended platform and seeing how fast it oscillates, but this is a little more difficult to do for the roll moment about the roll axis. Another factor is of course the dampers. The outside front wheel is going into bump (low speed bump damping) while the inside rear wheel is going into rebound (low speed rebound damping) and the other two corners are compressing/extending as well. Jacking has to be considered. The damping force depends on how fast the rear and front are rolling which depends on roll axis inclination and roll resistance balance. Another factor is that for an inclined roll axis, with the front roll centre lower than the rear, the body moves to the outside at the rear as the car corners causing a yaw moment. The real process of cornering needs a far more complex model than those used for steady state cornering. Plus you need a good tire model, since that is what counts in the end.
I would also guess that the roll stiffness has an effect on how quickly the lateral load tranfer happens, but did not find enough info. in Prepare to Win or Tune to Win.
</TD></TR></TABLE>
The speed or rate at which load transfer occurs is a much more complex subject. It depends of course on the roll moment of inertia, which is a little difficult to measure. The Yaw moment of inertia can me measured by placing a car on a suspended platform and seeing how fast it oscillates, but this is a little more difficult to do for the roll moment about the roll axis. Another factor is of course the dampers. The outside front wheel is going into bump (low speed bump damping) while the inside rear wheel is going into rebound (low speed rebound damping) and the other two corners are compressing/extending as well. Jacking has to be considered. The damping force depends on how fast the rear and front are rolling which depends on roll axis inclination and roll resistance balance. Another factor is that for an inclined roll axis, with the front roll centre lower than the rear, the body moves to the outside at the rear as the car corners causing a yaw moment. The real process of cornering needs a far more complex model than those used for steady state cornering. Plus you need a good tire model, since that is what counts in the end.
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