Car physics: ARBs and load transfer (calling Doug M and other gurus of RAS)

Hi, Please can anyone with the necessary background and experience please help me and a friend settle an ongoing debate about the weight transfer effects of ARBs? The discussion started when I claimed that fitting front and rear ARBs would not affect the handling balance of a car provided that the _percentage_ increase in roll stiffness at each end was the same. My friend (an experienced test driver) says that it is common knowledge that ARBs increase overall lateral load transfer, and refers to respected sources for backup. The trouble is, this seems to be at odds with the basic physics. In steady state, the weight transfer must be determined by track width, C/G position and cornering radius/speed only. A car that rolls less will not lean its C/G so far towards the outside of the turn, which will slightly *decrease* the weight over the outside wheels, the opposite of what my friend argues. So, where have I gone wrong? And if I haven’t gone wrong, why do so many people confirm that ARBs *increase* the lateral load transfer? For example, here is a quote that Simon sent me from Carroll Smith’s “Tune To Win”... “The greater the resistance of springs, the less roll will result - but there will be no significant effect on the amount of lateral load transfer because the roll couple has not been changed and there is no physical connection between the springs on opposite sides of the car. The same cannot be said of the resistance of anti-roll bars. In this case, because the bar is a direct physical connection between the outside wheel and the inside wheel, increasing the stiffness of the anti-roll bar will both decrease roll angle and increase lateral load transfer.” This just seems plain wrong to me, as any attempt at lifting the inside wheel by the ARB will just cause the car to “settle back” onto that wheel until the loadings are in keeping with Mr. Newton’s requirements for the cornering acceleration, C/G location and track width. This will lead to less body roll, which is just what we expect. All makes perfect sense to me – only problem is, I’m arguing against a legend! Help! TIA -= mike =-

Hey, You're buddy is correct. ARBs will add to the weight trasnfer. You just about got it with the explanation of it picking the inside wheel up to help keep the car level, but i think you're putting to much stress on the effect of it keeping the c/g planted. In essense, ARBs are is trying to pick the inside wheel up, but that takes weight off that wheel...the weight has to go somewhere, so it gets transferred to the opposite side. The way i learned to keep it straight in my head was to think of a go-kart with no suspension and a solid rear axle. If we could apply enough lateral force to tip the kart on two wheels, what would we have just done? We put all the weight on the two wheels remaining on the ground. Take the same kart only this time instead of the rear axle being a rigid part of the chassis, free it up with only a single swivel point in the axle's center connecting it to the chassis and apply the same lateral force to tip it on it's side, this time both wheels will remain planted and we'll still have weight on the inside wheel. Extremely simplistic look at it, but i think it's a good way to "see" it. -- In memory of DE, - Will - M1MS - http://mach1.simhq.com "Mike Nunan" <[email hidden]> wrote in message news:[email hidden]... > Hi, > > Please can anyone with the necessary background and experience please > help me and a friend settle an ongoing debate about the weight > transfer effects of ARBs? The discussion started when I claimed that > fitting front and rear ARBs would not affect the handling balance of a > car provided that the _percentage_ increase in roll stiffness at each > end was the same. My friend (an experienced test driver) says that it > is common knowledge that ARBs increase overall lateral load transfer, > and refers to respected sources for backup. > > The trouble is, this seems to be at odds with the basic physics. In > steady state, the weight transfer must be determined by track width, > C/G position and cornering radius/speed only. A car that rolls less > will not lean its C/G so far towards the outside of the turn, which > will slightly *decrease* the weight over the outside wheels, the > opposite of what my friend argues. > > So, where have I gone wrong? And if I haven&#8217;t gone wrong, why > do so many people confirm that ARBs *increase* the lateral load > transfer? For example, here is a quote that Simon sent me from > Carroll Smith&#8217;s &#8220;Tune To Win&#8221;... > > &#8220;The greater the resistance of springs, the less roll will > result - but there will be no significant effect on the amount of > lateral load transfer because the roll couple has not been changed and > there is no physical connection between the springs on opposite sides > of the car. The same cannot be said of the resistance of anti-roll > bars. In this case, because the bar is a direct physical connection > between the outside wheel and the inside wheel, increasing the > stiffness of the anti-roll bar will both decrease roll angle and > increase lateral load transfer.&#8221; > > This just seems plain wrong to me, as any attempt at lifting the > inside wheel by the ARB will just cause the car to &#8220;settle > back&#8221; onto that wheel until the loadings are in keeping with Mr. > Newton&#8217;s requirements for the cornering acceleration, C/G > location and track width. This will lead to less body roll, which is > just what we expect. All makes perfect sense to me &#8211; only > problem is, I&#8217;m arguing against a legend! Help! > > TIA > > -= mike =-

Hi Make, you are absolutely correct. The ARBS might decrease body roll, and as such responsiveness of the car, but, given a fixed lateral acceleration, and under the assumptions you put forward, the total weight left-right weight transfer will not be affected, as that is just a function of the c.g. height and track width. If you, however, are using different ARBs, what will change is the relative front to right load transfer, meaning that, while the total left-right transfer is the same, the front tire may take a larger part of it should the ARB be relatively stiffer at that end. I think the load transfer in the quote you used refers to only the rear or only the front part of the car, and not the car as a whole. -Gregor Mike Nunan wrote:

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> > Hi, > > Please can anyone with the necessary background and experience please > help me and a friend settle an ongoing debate about the weight > transfer effects of ARBs? The discussion started when I claimed that > fitting front and rear ARBs would not affect the handling balance of a > car provided that the _percentage_ increase in roll stiffness at each > end was the same. My friend (an experienced test driver) says that it > is common knowledge that ARBs increase overall lateral load transfer, > and refers to respected sources for backup. > > The trouble is, this seems to be at odds with the basic physics. In > steady state, the weight transfer must be determined by track width, > C/G position and cornering radius/speed only. A car that rolls less > will not lean its C/G so far towards the outside of the turn, which > will slightly *decrease* the weight over the outside wheels, the > opposite of what my friend argues. > > So, where have I gone wrong? And if I haven&#8217;t gone wrong, why > do so many people confirm that ARBs *increase* the lateral load > transfer? For example, here is a quote that Simon sent me from > Carroll Smith&#8217;s &#8220;Tune To Win&#8221;... > > &#8220;The greater the resistance of springs, the less roll will > result - but there will be no significant effect on the amount of > lateral load transfer because the roll couple has not been changed and > there is no physical connection between the springs on opposite sides > of the car. The same cannot be said of the resistance of anti-roll > bars. In this case, because the bar is a direct physical connection > between the outside wheel and the inside wheel, increasing the > stiffness of the anti-roll bar will both decrease roll angle and > increase lateral load transfer.&#8221; > > This just seems plain wrong to me, as any attempt at lifting the > inside wheel by the ARB will just cause the car to &#8220;settle > back&#8221; onto that wheel until the loadings are in keeping with Mr. > Newton&#8217;s requirements for the cornering acceleration, C/G > location and track width. This will lead to less body roll, which is > just what we expect. All makes perfect sense to me &#8211; only > problem is, I&#8217;m arguing against a legend! Help! > > TIA > > -= mike =-

Gregor Veble <[email hidden]> wrote in message news:[email hidden]... > Hi Make, > > you are absolutely correct. The ARBS might decrease body roll, andas > such responsiveness of the car, but, given a fixed lateralacceleration, > and under the assumptions you put forward, the total weightleft-right > weight transfer will not be affected, as that is just a function ofthe > c.g. height and track width. Agree with Gregor, but note that adding ARBs will increase the roll stiffness which will make the load transfer more *rapid* during transients... Jonny

Will DeRivera <[email hidden]> wrote in message news:CDbe7.9345$[email hidden]... > The way i learned to keep it straight in my head was to think of ago-kart > with no suspension and a solid rear axle. If we could apply enoughlateral > force to tip the kart on two wheels, what would we have just done?We put > all the weight on the two wheels remaining on the ground. Take thesame kart > only this time instead of the rear axle being a rigid part of thechassis, > free it up with only a single swivel point in the axle's centerconnecting > it to the chassis and apply the same lateral force to tip it on it'sside, No, sorry. If you apply the *same* lateral force, at the *same* height above the ground, it will still lift the inside wheels. You can't 'lose' force except by using inertial dampers (a la Star Trek) ;-) Jonny

Hey, I think you missed the point of the explanation, or i didn't explain it very well. See, the first time, the axle is rigidly bolted to the chassis...the axle doesn't move. If you could then mount the rear axle by a single mounting point in the center and allow it to swivle around that point this would leave the axle free to stay planted squarly on the ground as the kart tipped over. Hard to explain apparently...the book i read it from dedicated a whole chapter to explaining the effect of weight transfer, so i can hardly go into depth in a mere paragraph. -- In memory of DE, - Will - M1MS - http://mach1.simhq.com "Jonny Hodgson" <[email hidden]> wrote in message news:Azde7.12735$[email hidden]... > > No, sorry. If you apply the *same* lateral force, at the *same* > height above the ground, it will still lift the inside wheels. You > can't 'lose' force except by using inertial dampers (a la Star Trek) > ;-) > > Jonny > > >

Mike Nunan wrote:

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> Hi, > > Please can anyone with the necessary background and experience please > help me and a friend settle an ongoing debate about the weight > transfer effects of ARBs? The discussion started when I claimed that > fitting front and rear ARBs would not affect the handling balance of a > car provided that the _percentage_ increase in roll stiffness at each > end was the same. My friend (an experienced test driver) says that it > is common knowledge that ARBs increase overall lateral load transfer, > and refers to respected sources for backup.

Your friend is right....IF... he means the RATE of change in lateral load transfer, not the total amount of rate transferred. ARBs are torsion springs connecting an inside wheel to an outside wheel for the purpose of reducing chassis roll and thereby increase the rate at which weight is transferred, not the total amount transferred. But in terms of the MAXIMUM transfer of weight from inside to outside wheels, you are right. ARBs do not effect the factors that determine the maximum lateral weight transfer which are track width, center of gravity height, and roll axis height, at a given corner speed (lateral acceleration). > The trouble is, this seems to be at odds with the basic physics. In > steady state, the weight transfer must be determined by track width, > C/G position and cornering radius/speed only. A car that rolls less > will not lean its C/G so far towards the outside of the turn, which > will slightly *decrease* the weight over the outside wheels, the > opposite of what my friend argues. True, but a negligible amount.

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> So, where have I gone wrong? And if I haven&#8217;t gone wrong, why > do so many people confirm that ARBs *increase* the lateral load > transfer? For example, here is a quote that Simon sent me from > Carroll Smith&#8217;s &#8220;Tune To Win&#8221;... > &#8220;The greater the resistance of springs, the less roll will > result - but there will be no significant effect on the amount of > lateral load transfer because the roll couple has not been changed and > there is no physical connection between the springs on opposite sides > of the car. The same cannot be said of the resistance of anti-roll > bars. In this case, because the bar is a direct physical connection > between the outside wheel and the inside wheel, increasing the > stiffness of the anti-roll bar will both decrease roll angle and > increase lateral load transfer.&#8221;

Looks like poor editing. Seems to be contradictory unless the the last sentence is referring to increasing only one (front or rear) ARB rate, in which case the lateral weight transfer will increase only at that end of the car, reducing the weight transfer on the other end, but not changing the total weight transfer of both inside wheels to both outside wheels.

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> This just seems plain wrong to me, as any attempt at lifting the > inside wheel by the ARB will just cause the car to &#8220;settle > back&#8221; onto that wheel until the loadings are in keeping with Mr. > Newton&#8217;s requirements for the cornering acceleration, C/G > location and track width. This will lead to less body roll, which is > just what we expect. All makes perfect sense to me &#8211; only > problem is, I&#8217;m arguing against a legend! Help!

Not to worry. You and the legend are in total agreement. Marty

Will DeRivera <[email hidden]> wrote in message news:1efe7.9826$[email hidden]... > > No, sorry. If you apply the *same* lateral force, at the *same* > > height above the ground, it will still lift the inside wheels.You > > can't 'lose' force except by using inertial dampers (a la StarTrek) > > ;-) > I think you missed the point of the explanation, or i didn't explainit very > well. See, the first time, the axle is rigidly bolted to thechassis...the > axle doesn't move. If you could then mount the rear axle by a single > mounting point in the center and allow it to swivle around thatpoint this > would leave the axle free to stay planted squarly on the ground asthe kart But you wouldn't be *able* to apply the same force, since the kart would simply end up spinning around this pivot in a continuous barrel roll. If it had limited travel, it would hit the stops before the force built up and *then* it would lift wheels. Ultimately, any force applied to the vehicle (including, for these purposes, imaginary ones like centrifugal force) has to be resisted by the tyres. There's just no way round this. Jonny

>Please can anyone with the necessary background and experience please >help me and a friend settle an ongoing debate about the weight >transfer effects of ARBs? The discussion started when I claimed that >fitting front and rear ARBs would not affect the handling balance of a >car provided that the _percentage_ increase in roll stiffness at each >end was the same. I agree with your claim. As (I think it was Marty) pointed out though, the time it takes for the load transfer to happen would decrease, but the handling balance and total weight transfer would remain identical. The first thing that comes to mind that would mess all this up is that with increased roll stiffness, you may end up with a different tire camber situation that could change the handling balance, but if your friend and you are not including this in the argument, I agree with your claim about equal load transfers. >My friend (an experienced test driver) says that it >is common knowledge that ARBs increase overall lateral load transfer, >and refers to respected sources for backup. > As the others pointed out, increasing anti-roll stiffness at only one end of the car will do exactly what your friend says, but doing it to both ends the same amount will keep everything identical as you argued. This is a common argument. >The trouble is, this seems to be at odds with the basic physics. In >steady state, the weight transfer must be determined by track width, >C/G position and cornering radius/speed only. A car that rolls less >will not lean its C/G so far towards the outside of the turn, which >will slightly *decrease* the weight over the outside wheels, the >opposite of what my friend argues. Exactly right, although as someone else pointed out, it may be a negligable effect and unrelated to the point your friend seems to be arguing anyway.

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>So, where have I gone wrong? And if I havent gone wrong, why >do so many people confirm that ARBs *increase* the lateral load >transfer? For example, here is a quote that Simon sent me from >Carroll Smiths Tune To Win... > >The greater the resistance of springs, the less roll will >result - but there will be no significant effect on the amount of >lateral load transfer because the roll couple has not been changed and >there is no physical connection between the springs on opposite sides >of the car. The same cannot be said of the resistance of anti-roll >bars. In this case, because the bar is a direct physical connection >between the outside wheel and the inside wheel, increasing the >stiffness of the anti-roll bar will both decrease roll angle and >increase lateral load transfer.

This may interest you. From the same book, page 36: " One of the most widespread misconceptions in racing is that the amount of load transfer taking place is directly related to chassis roll. Two opposing theories are revalent: (1) The car that rolls a lot transfers more load and develops more cornering force. (2) The car that is strongly restricted from rolling doesn't transfer as much weight and so develops more cornering force." Neither of these exactly pick out what you're arguing about, but close. A couple of paragraphs before this, Carrol Smith lays out the formula for lateral load transfer: Load transfer = (Lateral Acceleration(g) * weight(lbs) * c.g. height(inches)) / track width (inches) Where are the anti-roll bar settings and spring constants? Not there, because they don't matter when looking at overall load transfer as you described. That only matters when the front/rear settings are different. >This just seems plain wrong to me, as any attempt at lifting the >inside wheel by the ARB will just cause the car to settle >back onto that wheel until the loadings are in keeping with Mr. >Newtons requirements for the cornering acceleration, C/G >location and track width. This will lead to less body roll, which is >just what we expect. You've got it right. If the car generated more load transfer than dictated by cg height, track width, and cornering acceleration, it would continue to roll forever. The torques are in balance once steady state is reached if the car has no rolling velocity. The only thing I can say on your friend's behalf is that he is right if he means at some specific roll angle, total weight transfer is higher with the ARB's. At say 3 degrees, the load transfer is higher, for instance. However, it doesn't sound to me like that's what the argument is about, but rather, it's about total weight transfer through a given corner, letting roll angle fall where it may. Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com

Ok, you're putting to much critical thought into this, put all other important factors aside for a minute. Like i said, it's an extremely simplistic look at it. =) -- In memory of DE, - Will - M1MS - http://mach1.simhq.com

Wow, thanks to everybody for the comprehensive replies! Will, which book did you read for the weight transfer stuff? I'm glad in a way that you picked the kart example, as I have used that as a reference point in recent discussions. You mention the effect of tipping the vehicle up onto the outside wheels, but that will happen regardless of roll angle when there is enough cornering force to "pull the wheels out from under the car". Body roll only plays a part insofar as it moves the C/G towards the outside, which will increase the tendency to overturn. I'm willing to bet your book contains a diagram that shows the various forces and moments involved in this process. Gregor, Jonny, Marty and Todd, glad to see you all think I'm on the right track. Also glad that people mentioned the transient effects. There was a much longer message that I was originally going to post that included some of this stuff, but Simon reviewed it and said it was overlong so I cut it down to the raw essentials. These were my original comments on the transient behaviour changes if you simply add "balanced" ARBs to an existing setup: 1. Initial transient weight transfer increased on turn-in, because the higher roll rate means that the outside wheels will load up harder and faster in comparison with the softer setup. This would also be true if the same roll rate increase was obtained by upping the main spring rates, however. 2. If the suspension is under-damped in roll, you get a delayed weight transfer effect to the outside following turn-in as the springs halt the outward swing of the body. A softer setup allows the body to swing further, so that it builds up more momentum, while the stiffer ARB-equipped setup will exhibit this effect to lesser degree. 3. Transient effects resulting from braking/tractive forces while cornering will follow the same basic patterns. Dabbing the brakes mid-corner will load the outside front more suddenly in the ARB-equipped car for example. This last point is interesting, because Simon is willing to agree on the pure steady-state situation but says that it is never applicable in real life because there is almost always some braking or acceleration going on, even if a minute amount, which alters the situation. In his words: "as soon as weight shifts forward or backwards the ARB at the unladen end will cause more weight transfer even if the roll resistance at both ends are the same." I don't agree with that. I think if you achieve the same roll rates by means of the main springs, you will see the same corner loadings, because front/rear load transfer is governed by C/G position, wheelbase and longitudinal force. The only difference is with ARBs and softer springs, you will have more pitch movement which will lead to the similar transient weight transfer effects to those we have already agreed on in the roll situation. I.e., an increase in the "negligible" movement of the C/G due to pitching, plus slower load transfer and perhaps (if we're low on damping) a higher peak magnitude. Camber angles and other aspects of the geometry might also be influenced by the larger wheel displacements, but I think it's fine to treat those as a separate issue for now. Simon, I think the "accepted truth" about ABRs and weight transfer is out of context here, because it is only true if you increase the rate at just ONE END. This is a point I tried to make earlier, and has been confirmed by others here. Guys, who here is a dynamics engineer with practical experience who can maybe give some anecdotal evidence or other information that establishes the truth of all this in real-life situations as well as just theory? -= mike =-

Hi Chaps I'm Mike's friend (who's getting a slating!! :-)) The main cause of the difference of opinion between Mike and I has been the difference between the isolated and incredibly limited discussion of true steady state cornering and the application of the effects of ARBs to the HUGE subject of the entire handling package. In true steady state (if such a thing exists in the real world) I agree that load transfer is not a function of roll resistance except to say that the *difference* between front and rear roll resistance will obviously affect it. But.. Roll resistance describes the amount of force required to roll the sprung weight a given amount. So if you had exactly the same roll resistance (through ARBs) front and rear and perfect 50/50 weight distribution, horizontal roll axis and true steady state cornering.. The car would roll equally at both ends, and weight transfer would be equal at both ends.. But.. Move the load rearward (acceleration, etc) and you will roll the rear suspension more than the front = front inside wheel lifts = more load transfer at the front. The more roll resistance created in this way, the more greater this effect and the greater the load transfer. Handling is unfortunately (or fortunately otherwise it would be boring) substantially more complicated than steady state cornering. All the best Simon

Simon de Banke <[email hidden]> wrote in message news:[email hidden]... > Hi Chaps > > I'm Mike's friend (who's getting a slating!! :-)) Welcome aboard ;-) > Move the load rearward (acceleration, etc) and you will roll therear > suspension more than the front = front inside wheel lifts = moreload > transfer at the front. Aha - I've just spotted the aberrant assumption! The chassis is generally regarded as torsionally stiff for the purposes of suspension analysis, so *roll angle is the same at both ends*. Wheel lifting happens when one end either has less travel than the other, or is significantly stiffer in roll such the the load on one wheel drops below zero (in practice the latter doesn't happen with coil springs, since they're not designed to load in tension). This assumption may actually be false for '60s GP cars, but I don't know whether or not it holds for GPL... ;-) HTH, Jonny

"Jonny Hodgson" <[email hidden]> wrote in message news:<3Eze7.3746$[email hidden]>... > Wheel lifting > happens when one end either has less travel than the other, or is > significantly stiffer in roll such the the load on one wheel drops > below zero (in practice the latter doesn't happen with coil springs, > since they're not designed to load in tension). This is true, but wheel lifting can also happen in a number of other situations also. If you load up one particular wheel individually, the oposite wheel will be more likely to lift the stiff the car is in ride and roll rate. However.. the ride rate is what would have most effect on the attempted pitch angle of the car, but the roll rate (through ARBs - slightly different with springs) would have the resulting effect on the lifting of the wheel - WELL inside the maximum droop. So with ARBs fitted (even if they are equal) at any time that the sprung mass is rolled towards one single wheel, the oposite wheel loses load to it's adjacent axle partner. The stiffer the arb the greater this transfer. All the best Simon

"Jonny Hodgson" <[email hidden]> wrote in message news:<3Eze7.3746$[email hidden]>... > > Aha - I've just spotted the aberrant assumption! The chassis is > generally regarded as torsionally stiff for the purposes of suspension > analysis, so *roll angle is the same at both ends*. Sorry I forgot to answer this bit.. It is the torsionally stiff properties of the chassis which *cause* this. Although, the fact that in real life they are not completely stiff actually REDUCES this effect. I was not saying that the roll *angle* was more at the rear than the front, but that the *forces* were increased at the rear. As the front has less forces on it, but is still being forced to roll (by the chassis), it will effectively sit up higher on it's laiden spring and the ARB will lift the unlaiden wheel (admitedly not necessarily off the ground, but load will be lifted off that wheel and transfered onto the laiden one). The problem with all this is that there are very few hard and fast rules in vehicle dynamics. I know of / have been involved in situations where the spookiest things have a happened... Sierra Cosworth Race car. 1000lb springs on the front... dire understeer. Fitted 1200lb springs and the understeer went away???? Now that information isolated would be argued. If I posted a message saying "how can I reduce the understeer of my race car" and someone said "increase the front springs", they would be laughed at. But they would have also (in this case) have been right. The biggest trap you can fall into is the one where you believe you understand it all. There are very few hard and fast rules as there is such a chaotic aspect to ride and handling once a car is on the move in the real world. The maths and formulas are invaluable for making a first stab at it, and then for ideas as to what to test in order to tweak it. But after that, there are accepted truths which generally work, and LOTS and LOTS of testing. Cheers Simon

Hi Simon, now that's interesting. Just of curiosity, how much was the camber on the front wheels? Also, did the camber get out of shape with suspension travel? -Gregor Simon de Banke wrote:

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> > Sierra Cosworth Race car. 1000lb springs on the front... dire > understeer. Fitted 1200lb springs and the understeer went away???? > Now that information isolated would be argued. If I posted a message > saying "how can I reduce the understeer of my race car" and someone > said "increase the front springs", they would be laughed at. But they > would have also (in this case) have been right. >

Simon de Banke <[email hidden]> wrote in message news:[email hidden]... > So with ARBs fitted (even if they are equal) at any time that the > sprung mass is rolled towards one single wheel, the oposite wheel > loses load to it's adjacent axle partner. The stiffer the arb the > greater this transfer. Oops, I've just hit the point where I've forgotten what we were disagreeing about! :-) ('cos it's not this...) Erm... is it to do with how this compares to achieving the same, increased roll rate with springs? Now that I'm thinking about it, actually this is reminiscent of my empirical approach which says that front bar controls corner entry, rear bar controls corner exit... So what was the original question?!? Regards, Jonny

Gregor Veble <[email hidden]> wrote in message news:<[email hidden]>...

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> Hi Simon, > > now that's interesting. Just of curiosity, how much was the camber on > the front wheels? Also, did the camber get out of shape with suspension > travel? > > -Gregor >

I don't remember now to be honest. It certainly wasn't huge, and the amount of roll was incredibly low (this was a stiff car anyway) so it wasn't a reduction of camber thing. The only thing they could think of (bare in mind this was a group of TOP dynamics engineers from a VERY VERY well respected motorsports company (possibly the most respected)) was that it had some unusual effect on the rear and everything just fell into place during turn-in. But the most valuable lesson here was that you should respect the fact that it a spooky complex subject, and there is no harm (unless you are qualifying and do't have time) in just trying something. These guys were SO SO good at what they do, that they knew not to be fooled into thinking that they understood it all. The guys are so good that the openly admit that you can get close (a good starting point) on paper, but after that it's just guessing :-) All the best Simon

Hi Jonny, There are multiple aspects that we have been arguing the toss about, but one key one is that I believe you can calculate the load distribution based on roll rates only, without caring whether the roll resistance is provided by bars or springs. Simon contends (I think -- correct me if I'm wrong!) that in a steady turn you get more weight transfer with bars that you do with springs alone, even assuming the same roll rates. If you use ARBs then you'll have softer springs for a given roll rate of course. This will lead to handling differences due to the increase in pitch movement, which will make their presence felt during longitudinal force transients (braking, lifting, accelerating). Clearly, the less main spring rate you trade off against bar rate, the less these differences will be. -= mike =- "Jonny Hodgson" <[email hidden]> wrote in message news:<y_Xe7.4041$[email hidden]>...

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> Simon de Banke <[email hidden]> wrote in message > news:[email hidden]... > > > So with ARBs fitted (even if they are equal) at any time that the > > sprung mass is rolled towards one single wheel, the oposite wheel > > loses load to it's adjacent axle partner. The stiffer the arb the > > greater this transfer. > > Oops, I've just hit the point where I've forgotten what we were > disagreeing about! :-) ('cos it's not this...) > > Erm... is it to do with how this compares to achieving the same, > increased roll rate with springs? Now that I'm thinking about it, > actually this is reminiscent of my empirical approach which says that > front bar controls corner entry, rear bar controls corner exit... > > So what was the original question?!? > > Regards, > Jonny

Sorry, looks like I was misrepresenting Simon's opinion there. He agrees with me in the steady-turn case, but reckons that if you introduce braking or accelerative forces then that is when you will see greater load transfer with a bar than with just springs. I'm going away to sketch the situation and see how the numbers come out. Have a good weekend everybody! -= mike =- [email hidden] (Mike Nunan) wrote in message news:<[email hidden]>...

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> Hi Jonny, > > There are multiple aspects that we have been arguing the toss about, > but one key one is that I believe you can calculate the load > distribution based on roll rates only, without caring whether the roll > resistance is provided by bars or springs. Simon contends (I think -- > correct me if I'm wrong!) that in a steady turn you get more weight > transfer with bars that you do with springs alone, even assuming the > same roll rates. > > If you use ARBs then you'll have softer springs for a given roll rate > of course. This will lead to handling differences due to the increase > in pitch movement, which will make their presence felt during > longitudinal force transients (braking, lifting, accelerating). > Clearly, the less main spring rate you trade off against bar rate, the > less these differences will be. > > -= mike =- >

Slow USENET here...just tonight I'm getting the flood of posts on this topic<sigh>. Here's some more factors to make the real situation more complex still-- - the tires deflect with load change and they have a nonlinear spring rate - the tires also deflect vertically with lateral force - while the chassis is often assumed torsionally stiff, it often isn't(!) So actually determining the wheel loads with any confidence (even in steady-state) by either test or calculation is rather difficult. Simple models (as can be discussed in words without the math) are good for geting a physical feel, but fall flat when it's time to get down to work. -- Doug Milliken Milliken Research Associates Inc. On Wed, 15 Aug 2001, Jonny Hodgson wrote:

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> > Simon de Banke <[email hidden]> wrote in message > news:[email hidden]... > > Hi Chaps > > > > I'm Mike's friend (who's getting a slating!! :-)) > > Welcome aboard ;-) > > > Move the load rearward (acceleration, etc) and you will roll the > rear > > suspension more than the front = front inside wheel lifts = more > load > > transfer at the front. > > Aha - I've just spotted the aberrant assumption! The chassis is > generally regarded as torsionally stiff for the purposes of suspension > analysis, so *roll angle is the same at both ends*. Wheel lifting > happens when one end either has less travel than the other, or is > significantly stiffer in roll such the the load on one wheel drops > below zero (in practice the latter doesn't happen with coil springs, > since they're not designed to load in tension). > > This assumption may actually be false for '60s GP cars, but I don't > know whether or not it holds for GPL... ;-) > > HTH, > Jonny > > > >