Rear roll center

[Pete]

Got a question. What would it do the handling if you moved the rear roll center to the right 2" roll center height stayed the same? On a rocket blue front.

[MasterSbilt_Racer]

Car would squat RR less during cornering and hike lr more.

[SuperEight]

It should increase drive and make the car calmer, but a lot depends on how you do it... If you do it by shortening the j-bar then forget what I just said, the car will be wilder and hike up more. If you somehow shift your current j-bar 2" to the right and everything else stays the same(length, angle and heights), then what I said at first would apply. Many variables play into this depending on how you do it.

[Rogue1]

I thought the upper pick up points of the springs determined where the roll center was from left to right, and the jbar determined the height

[Matt49]

Correct, Rogue1

[billetbirdcage]

Car would squat RR less during cornering and hike lr more.

I'd agree with this.


As to how the rear roll center is figured well: I have issues with the newer method that roque and matt are talking about. While I do think it helps people visualize what moving the frame side of the j-bar does as far as raising or lowering the roll center, I think it's vastly wrong on left to right.

That's my opinion and I'll leave it at that

[Dirt2727]

Good to see ya back, Billet

[let-r-eat]

Good thread.

[Matt49]

I didn't have much time when I posted before but here goes my best effort at trying to explain what I THINK is going on here.
Unfortunately, there isn't a lot of literature out there on this and most of it is in automotive engineering text books which when dealing with panhard bar beam axle suspensions, are dealing with very long bars and equal spring rates on both sides of the car. This greatly simplifies the roll center determination because almost invariably, it will be at the center of the car. For example:
http://www.timskelton.com/lightning/race_prep/suspension/images/panhard_displacement.jpg
In this crude but common example, the roll center is in fact on the point midway between the ends of the bar. I think this is where a lot of people get the notion that the roll-center on a late model is the point midway between the ends of the j-bar. But it simply isn't so. That roll center would be so far to the left and so high that the car would never transfer weight to the right side.
In modern dirt cars, we use a much shorter bar with a lot more angle and very often have a difference between the spring rates on each side. This complicates things.
With a beam axle configuration, spring rates and their lateral mounting location certainly play in part in determining roll center. In general the roll center will be closer to the heavier spring. Think of how the car would roll if you had no spring on the LR and a solid rod where your shock is on the RR. Left side would go up while right side stayed basically in place. Then think the opposite. Solid LR and no RR spring. Left side would stay and RR would go down. Obviously, the roll center isn't in the same place in these two scenarios.
Roll center height is still dictated by the points of the ends of the j-bar but you have to draw an imaginary line between the points and extend that line BEYOND the ends of the j-bar. In many cases, the roll center may not actually be between the ends; it may be past one end (e.g. further to the right of the pinion mount).

People talk about front roll center migration a lot but my goodness can you imagine how much the rear roll center migrates with all of the hike up the rear end gets?

[MasterSbilt_Racer]

Both shock mount and panhard/j bar location affect lateral roll center location. Don't ask me to show the exact location, but I have plenty of experimental data to see it.

[hpmaster]

Like others here I have heard several ideas/theory on what puts the roll center where in the rear of the car over the years of reading and classes I have taken. I do not have enough confidence after all this to say X makes Y happen for sure so I look at these roll center talks on the rear as good ones to sit out. Who here has what they think is a good cause and effect chart on changing the rear roll center by changing the different components that affect rear roll center location?

[billetbirdcage]

I couldn't find the picture of the system to find the rear roll center I was talking about, so I had to remake it. I think it used to be on afco's tech section as well as many others but seems to be wiped from the internet as it should be, lol. That is the one I was talking about, which I believe to be idiotic and not correct at all.

That one basically said the roll center left to right was at the top of the RR spring.

[billetbirdcage]

In my view, the most accurate is this one. However as you can see it leaves open a large area that it could be, which I think is really a mute point anyways. What I care about is tire loading more so then where the roll center actually is. You have a lot more forces going one with a current LM set up, then just roll loading of the tires. Where the J-bar is attached compared to the tires and the angle of the j-bar has a huge effect on tire bias loading.

I also think this is basically what matt was referring to also, I just wanted to makes sure people weren't using the method that I posted above with with intersection of the RR top of the spring as the defining place of the rollcenter.

[b1driver]

Here`s my 2 cents. Roll center on rear is middle of both ends of panard bar. Shock angles and placement only locate cg in relation to that roll center. Moving your roll center 2" to the right will make your rocket handle like a rayburn, reeally good inthe mud and terrible in the slick.

[zeroracing]

The CG is 100% independent of any linkages, shocks, springs or roll centers on the car. It is only the center of the sum of all the masses.

[hpmaster]

I just spent/wasted 2 hours reading my notes, various books and a couple old RaceWise note books on rear roll centers. After reading that and these posts by guys I respect I officaly refuse to even think about where this make believe point is from here forward. I now think it doesn't do anything but add a piece of pretty much useless poo that can't be proven to me in a definitve way to do anything positive in tire loading adjustment.JMHO

[MasterSbilt_Racer]

Here`s my 2 cents. Roll center on rear is middle of both ends of panard bar. Shock angles and placement only locate cg in relation to that roll center. Moving your roll center 2" to the right will make your rocket handle like a rayburn, reeally good inthe mud and terrible in the slick.
You can move a left mounted panhard to the right side of the car and move the roll center to the left. Observation of roll angle and change in wheel travel confirms this.

[b1driver]

Then i guess we should all be running rabuds purple bar

[b1driver]

The only way any of this gets proven is with some data aquasition on one of these cars and whoever does it sure ain`t going to share it unless you got a fat wad of cash.till then its just guesswork in a firesuit

[b1driver]

Acording to this theory, would moving shock mounts on frontend also change moment center?

[MasterSbilt_Racer]

Then i guess we should all be running rabuds purple bar

Not what I was referring to.

[FlatTire]

One night I found the roll center to be on top of my roof! The car wasnt too pretty after that.

[hpmaster]

One night I found the roll center to be on top of my roof! The car wasnt too pretty after that.

That is the most definitive explanation of the existence of "roll center" so far in this thread! Now someone will say that was more related to center of gravity.........

[Matt49]

Acording to this theory, would moving shock mounts on frontend also change moment center?

No. Front end is independent wishbone suspension which is a completely different mechanical model than a beam axle suspension which is what we're dealing with in the rear end.

[Matt49]

Regardless of what theory we subscribe to on how to find the roll center, it is important to know that you are finding the STATIC roll center with the car at ride height. So if you're interested in knowing how the car will handle while you're following the pace truck, this is very useful information. But our cars are hiked up the majority of the time which drastically raises the CoG and shifts the RC to the left. It also changes shock angles, etc.
Oh yeah and by they way, when you apply the gas and the lift bar moves up, the j-bar pinion mount moves up also. Don't forget to factor that in :-)
In seriousness, the important thing to know if you wanted to understand it from an engineering standpoint, is the moment arm. The moment arm is the line between the CoG and the RC. Ultimately, its length and angle is what affects handling. This is what we are really changing when we move RC.

[JustAddDirt]

Regardless of what theory we subscribe to on how to find the roll center, it is important to know that you are finding the STATIC roll center with the car at ride height. So if you're interested in knowing how the car will handle while you're following the pace truck, this is very useful information. But our cars are hiked up the majority of the time which drastically raises the CoG and shifts the RC to the left. It also changes shock angles, etc.
Oh yeah and by they way, when you apply the gas and the lift bar moves up, the j-bar pinion mount moves up also. Don't forget to factor that in :-)
In seriousness, the important thing to know if you wanted to understand it from an engineering standpoint, is the moment arm. The moment arm is the line between the CoG and the RC. Ultimately, its length and angle is what affects handling. This is what we are really changing when we move RC.


I think my head just exploded.

[b1driver]

Couldn`t agree more matt49.

[Bcollins82]

No. Front end is independent wishbone suspension which is a completely different mechanical model than a beam axle suspension which is what we're dealing with in the rear end.

If your solid rod theory applies to the solid rear axle in changing the effective roll center, why would it not change the effective roll center up front? If you move the upper shock mount it can change dynamic roll rate, making the car feel like it has a softer or stiffer spring, charging how fast and far that corner travels. Obviously it doesn't change the RC statically, but it doesn't change the rear RC statically by having a solid rod in place of a shock. I've heard many differing opinions on this, just curious on your take..

[MasterSbilt_Racer]

If your solid rod theory applies to the solid rear axle in changing the effective roll center, why would it not change the effective roll center up front? If you move the upper shock mount it can change dynamic roll rate, making the car feel like it has a softer or stiffer spring, charging how fast and far that corner travels. Obviously it doesn't change the RC statically, but it doesn't change the rear RC statically by having a solid rod in place of a shock. I've heard many differing opinions on this, just curious on your take..

You answered your own question. On the front, it only affects wheel rate.

On the rear, the point that the mass of the car contacts the rear axle assembly is the upper coilover mount.

[let-r-eat]

Matt's example of taking the spring out on the right side is a perfect example of BilletBirdcages illustration. The intersection of the top spring mount and the line between the panhard bars mounting locations will determine the lateral roll center. If you don't have a right spring then the roll center will automatically be at that left spring mount intersection with the line drawn through the panhard bar mounting points.

I agree that Matt's example of the rear ends *contact patch* lateral location underneath those mounting points as migrating would certainly be accurate.

Everything there is definitely dynamic for sure and getting this roll center coupled correctly with the front lateral location is most certainly an important concept to wrap your head around IMO.

[drtrkr244]

You answered your own question. On the front, it only affects wheel rate.

On the rear, the point that the mass of the car contacts the rear axle assembly is the upper coilover mount.

MBRacer, do you think that is the main reason chassis builders designate rear spring lengths?

[Matt49]

Spring length is not what he means when he says upper coilover mount. The car doesn't load the top of the spring, it loads the top mount. Spring length doesn't affect handling in any way unless you are so short that you're in a coil-bind situation or so long that you are in a spring bow situation causing interference with the shock body.
But pretty common spring lengths are LF-10, RF-12, LR-14, RR-12. Longer on the LF if you're down pretty low (like under 350).

[Matt49]

Bcollins82,
Good question because I have thought about that also. If you had a 1000 pound spring on the RF, it would certainly decrease roll rate and visually it seems that it would change roll center also but this is never taken into consideration in front roll center calculations. I think the reason that it doesn't is because front roll center has to do with how the two moment centers (or front view swing arms) interact with each other. And for lack of a better way to put, the left hand doesn't really know what the right hand is doing.

[drtrkr244]

Spring length is not what he means when he says upper coilover mount. The car doesn't load the top of the spring, it loads the top mount. Spring length doesn't affect handling in any way unless you are so short that you're in a coil-bind situation or so long that you are in a spring bow situation causing interference with the shock body.
But pretty common spring lengths are LF-10, RF-12, LR-14, RR-12. Longer on the LF if you're down pretty low (like under 350).

Im not sold 100% that spring length doesn't affect handling. When computing roll angles of front and rear suspensions, you have to measure from the top of each coil spring to the ground. I do know from experience that trying to match roll angles from front to rear, produces faster and more consistent handling, esp when the track slicks off.

[MasterSbilt_Racer]

Im not sold 100% that spring length doesn't affect handling. When computing roll angles of front and rear suspensions, you have to measure from the top of each coil spring to the ground. I do know from experience that trying to match roll angles from front to rear, produces faster and more consistent handling, esp when the track slicks off.

I believe it was carerra that did testing with data acquisition at Eldora and proved to themselves that spring length didn't matter.

[let-r-eat]

Top mounting location on coilover should be used in roll angle analysis. Length of spring doesn't matter. The mounting location is where the force is transferred through. You can turn the coilover up side down or however. The location of the mount is all that matters unless like Matt49 says you are rubbing somewhere.


A heavy front spring as described would add resistance to roll. The easy way to look at this is by roll angle effects on the wheel rates. The roll center and center of gravity location relative to the center of the contact patches.

[fastford]

Regardless of what theory we subscribe to on how to find the roll center, it is important to know that you are finding the STATIC roll center with the car at ride height. So if you're interested in knowing how the car will handle while you're following the pace truck, this is very useful information. But our cars are hiked up the majority of the time which drastically raises the CoG and shifts the RC to the left. It also changes shock angles, etc.
Oh yeah and by they way, when you apply the gas and the lift bar moves up, the j-bar pinion mount moves up also. Don't forget to factor that in :-)
In seriousness, the important thing to know if you wanted to understand it from an engineering standpoint, is the moment arm. The moment arm is the line between the CoG and the RC. Ultimately, its length and angle is what affects handling. This is what we are really changing when we move RC.

I don't have any special tools, just a tape measure and a plumb bob, but I did some testing a while back on this subject, with no shocks on and the car at ride height on jacks, I used the method of determining the rear roll center to be half way between the pan hard mounting points, then dropped a plumb bob from chassis down through that line, as I jacked the car into dynamic roll, left side up and right side down, the plumb bob moved to the right, which to me means roll center moved to left, using the between pan hard mounting point theory. my question is, how do you incorporate the spring mounting points into this?

[Bcollins82]

Bcollins82,
Good question because I have thought about that also. If you had a 1000 pound spring on the RF, it would certainly decrease roll rate and visually it seems that it would change roll center also but this is never taken into consideration in front roll center calculations. I think the reason that it doesn't is because front roll center has to do with how the two moment centers (or front view swing arms) interact with each other. And for lack of a better way to put, the left hand doesn't really know what the right hand is doing.


Yeah, that is what I had always been taught. And I know most people subscribe to that theory. But I've also had people in the industry who are much smarter than me argue that theory. Lol I asked one to please clarify this when he mentioned it. He simply said if you have 500s across the front, then put a 300rf and 700lf in the car will it change the point the car actually rolls around? Yes, obviously it does... He then said OK, any argument that front spring rate doesn't change the dynamic roll center is invalid. It was hard for me to argue against that point... Definitely an interesting subject.

[Matt49]

There is definitely something to the fact that we are dealing with independent suspensions up front. That being said, the engineering books that teach where front roll center is also usually assumed symmetrical suspension all the way down to spring rates. So my argument for why it matters in the rear could certainly be extended to the front.
That got me thinking...These days, most folks agree that a softer RF spring helps the car turn on entry. This is contrary to the old school thinking "heavy spring gets the weight" that was applicable when the cars ran much flatter. But it does seem to work today. My theory on WHY has been 3 pronged:
1) More RF travel allows for more RC migration to a lower position
2) More RF travel usually yields more camber gain
3) More RF travel usually means the LR stays in hike and gets more rear steer
All of the above would help turn the car and supersede any losses in tire loading due to the softer RF spring.
But now I'm wondering if we should also consider the theory that the softer RF is moving the "real" roll center to the left (toward the stiffer spring) which is giving the moment arm more leverage on the RF contact patch.
Thoughts???

[MasterSbilt_Racer]

There is definitely something to the fact that we are dealing with independent suspensions up front. That being said, the engineering books that teach where front roll center is also usually assumed symmetrical suspension all the way down to spring rates. So my argument for why it matters in the rear could certainly be extended to the front.
That got me thinking...These days, most folks agree that a softer RF spring helps the car turn on entry. This is contrary to the old school thinking "heavy spring gets the weight" that was applicable when the cars ran much flatter. But it does seem to work today. My theory on WHY has been 3 pronged:
1) More RF travel allows for more RC migration to a lower position
2) More RF travel usually yields more camber gain
3) More RF travel usually means the LR stays in hike and gets more rear steer
All of the above would help turn the car and supersede any losses in tire loading due to the softer RF spring.
But now I'm wondering if we should also consider the theory that the softer RF is moving the "real" roll center to the left (toward the stiffer spring) which is giving the moment arm more leverage on the RF contact patch.
Thoughts???

What happens when the lf leaves the racing surface?

[Matt49]

My hope is that it doesn't. But if it does, I hope I'm done turning. My feeling is the roll centers further to the left are assisting in keeping the LF down all the way around the track as opposed to the older setups where it was sometimes never on the track. To lift the left front, the roll center would have to be pretty far to the right assuming you aren't getting a lot of help by squatting the RR...something else we're seeing less and less of.

[save the racers]

I tried these theorys on a car.The problem is when you change r/c it will change other things.Camber curve ,bump steer etc in the front,motion ratio it the rear.The car responded in the rear like the spring mounting points set the r/c.If you are going to offset the rear r/c be ready to put springs in it that are outside the box to normal.You want to now where the r/c is mostly because you don't want it to be in an odd location causing the car not to respond in a predicable manor.

[let-r-eat]

I agree with your comments Matt49 but why do you think the old saying of "the stiff spring gets the weight" actually happens?

Wouldn't it happen because of the reasons you just described?

[7uptruckracer]

A LF oriented Roll Center puts more weight jacking into the LF the extra RF travel we are seeing would raise the dynamic RF upper control arm angle which will tend to migrate the RC right as well which would take off some LF loading BUT at the same time the RC is dynamically lower which will help load the front end.. So by moving it farther left you are in a way accounting for that migration. I do think MATT hit on the tendency for it to travel lower which a lower roll center will definitely make the front end steer and load in a more positive manner good point. Another thing that was hit on was the Camber gain. With the extra travel we are seeing you tend to see more dynamic gain and you don't see the RF bleed back as much height as we use to on the straights the RF stays pretty pinned. We use this on asphalt front ends a lot. You don't have a tire transitioning through a camber curve as you are trying to turn it you are already at optimal camber for corner entry at the moment you turn in. Also higher camber settings like matt has discussed in other threads with Camber Thrust theories. I think we are seeing the higher camber to 1) Load the tire more and 2) Like we use on asphalt to stretch our contact patch which i think helps fight a dirt tires tendency to deflect which will roll up under the tire and distort your contact patch You are seeing more LF rebound and softer compression so you aren't rolling the front ends as much as before either that helps with Roll Center Migration. Just my 2 cents. I don't pay attention to all the rear design i just tune how it was built for the power and package I have lol You can really make that act so many different ways it ends up being a mute point just know how to tune it for where you need to be

[FlatTire]

Track width hasn't been mentioned, but it also plays a role in how the lateral roll center migration effects chassis roll.

[Matt49]

Right on, FlatTire. How far the right rear contact patch is from the moment arm has a tremendous impact on the loading of that corner of the tire.

[save the racers]

7up, if you would, how much caster are you running?What are your thoughts on caster gain?

[billetbirdcage]

A LF oriented Roll Center puts more weight jacking into the LF the extra RF travel we are seeing would raise the dynamic RF upper control arm angle which will tend to migrate the RC right as well which would take off some LF loading ***BUT at the same time the RC is dynamically lower*** which will help load the front end..

Just want to point out this isn't always true:

Here are 3 brands of cars RC both static and with dive and roll typically seen (I know this from data acquisition)

Brand A: RC hieght 1.8" and 2.5" left - During roll and dive: RCH 1.3" and 29.1" right

Brand B: RC hieght 5.8" and 1.9" left - During roll and dive: RCH 6.0" and 8.5" right

Brand C RC hieght 2.8" and 0.8" left - During roll and dive: RCH 3.5" and 13.9" right

Only one has a lower RC during roll and dive, something to think about

[billetbirdcage]

These days, most folks agree that a softer RF spring helps the car turn on entry. This is contrary to the old school thinking "heavy spring gets the weight" that was applicable when the cars ran much flatter.
Thoughts???

I'm gonna play devils advocate here, lol.

I will argue that heavy spring gets the weight is still true even in this situation so the RF has less weight and therefore less traction then with a heavy spring in theory.

So why under many situations does the car turn better? Guess that depends on where you are talking turns better? On gas or Off gas.

Lets start with off Gas, as Matt said if the old system is true softening the RF should take weight off the RF and apply some of that to the RR and LF. So if the RF has less traction how can it turn better? My argument is it doesn't turn better because of more RF traction, but a function of other things going on like:

1. Not upsetting the car and causing excessive hike down
2. Added Roll steer
3. Much smoother entry and transitions for the driver therefore less driver errors
4. Very possible that the extra travel on the RF finally gets into the progressive curve of camber gain and finally gets to the optimal camber needed for fuller contact patch

Like I said playing devils advocate here and not picking on anyone or there ideas as I find matt49, mastersbuilt_racer, and other always give good advise.

[billetbirdcage]

I just spent/wasted 2 hours reading my notes, various books and a couple old RaceWise note books on rear roll centers. After reading that and these posts by guys I respect I officaly refuse to even think about where this make believe point is from here forward. I now think it doesn't do anything but add a piece of pretty much useless poo that can't be proven to me in a definitve way to do anything positive in tire loading adjustment.JMHO

If you're looking for a basic guideline, here is my opinion so take it for what it's worth

Use the 2nd diagram I posted. It starts out more in the center of the 2 mounting points of the j-bar if the j-bar is flat. As the j-bar has rake introduced, it starts moving right on that line and the more rake the more it moves right.

That is very basic and simple and I believe that shows you what is happening in general and can allow you to plan around that simple analogy

[Matt49]

I'm gonna play devils advocate here, lol.

I will argue that heavy spring gets the weight is still true even in this situation so the RF has less weight and therefore less traction then with a heavy spring in theory.

So why under many situations does the car turn better? Guess that depends on where you are talking turns better? On gas or Off gas.

Lets start with off Gas, as Matt said if the old system is true softening the RF should take weight off the RF and apply some of that to the RR and LF. So if the RF has less traction how can it turn better? My argument is it doesn't turn better because of more RF traction, but a function of other things going on like:

1. Not upsetting the car and causing excessive hike down
2. Added Roll steer
3. Much smoother entry and transitions for the driver therefore less driver errors
4. Very possible that the extra travel on the RF finally gets into the progressive curve of camber gain and finally gets to the optimal camber needed for fuller contact patch

Like I said playing devils advocate here and not picking on anyone or there ideas as I find matt49, mastersbuilt_racer, and other always give good advise.

Don't get me wrong...I'm not saying the "heavy spring gets the weight" theory is out the window. I'm saying that other things are influencing the cars ability to turn that outweigh (no pun intended) the effect of the softer spring. You have outlined a few of those as did I and I think there is probably even some overlap. I think we're thinking the same things :-)

The same discussion can be had about LR spring stiffness as it applies to "heavy spring gets the weight" theory.

[7uptruckracer]

I'd rather not say what caster I run or gain, its a really really really big topic in asphalt right now and I think overlooked on dirt. I'll instead say that you can use caster and gain to effect your camber gain and or loss as you turn the wheel you also have to think how your jacking weight into the car and on dirt you turn both directions so be careful. The trend in asphalt which mind you are more front end dominate is to always turn left. Its common to run a 12 and 3 degree spindle or in that area So you get weight jacking onto the LF when you turn to help you cut you can also use your caster split as well as a high caster setting to help dewedge the car and help turn in but you run extremely high cross (Bite) so as you straight the wheel out to come off the corner and power down you have good drive and traction. I think if you can find a way to apply it to dirt and pair it with the right shock package you can find something there

[kaij15]

7uptruckracer, Are you measuring swing caster or true caster? That is a big topic with stuff I do, old school comparison vs what it actually is. I agree with you and how much caster is over-looked on dirt. A great example is looking at a Road Course car, and the amount of caster that is ran (typically maxx). Not only is it putting "feel" in the wheel, but maintaining load in the rear tire. Also keeping camber in the front tires throughout wheel angle changes. On a side note, this has been the most productive post I have seen on here in a long LONG time. Thank you all for the comments, and providing direction. To take some of the comments on "heavy spring getting the weight" I think the thought is still correct and can be implied, just depending on what type of track you are running. From experience, stop and go tracks, this applies 80% of the time. Momentum tracks, the rear springs are all about potential energy to provide grip. I would like to hear peoples thoughts, more indepth if you will.... also the heavy spring getting the weight....what about bi-linear RF's LF's (both stacked and BS's) and LR's.....Does this tie the theory of heavy springs, with a momentum type track? Scatter brained when I am writing this, excited to hear people's take on these.

[7uptruckracer]

As far as I know true caster, I check alot of different things and compare all the numbers to see what's built into the car, why it's built into the car and see how it fits in my package, There are a lot of things that can skew numbers so you have to look at it as a package deal.

[Dirtmod13]

Don't get me wrong...I'm not saying the "heavy spring gets the weight" theory is out the window. I'm saying that other things are influencing the cars ability to turn that outweigh (no pun intended) the effect of the softer spring. You have outlined a few of those as did I and I think there is probably even some overlap. I think we're thinking the same things :-)The same discussion can be had about LR spring stiffness as it applies to "heavy spring gets the weight" theory.I have been wondering about this too. Seems like the softer rf spring is allowing that corner to roll over more which is compressing that spring. Wouldn't the actual rate be quite higher there because of that travel?500lb spring compressed 1" =500 lb rate350 lb spring compressed 2"= 700500 compressed 2" = 1,000400 compressed 2.5"=1,000So is it that the car is actually gaining wedge by dropping LR to get the RF to squat and roll more?

[Matt49]

I have been wondering about this too. Seems like the softer rf spring is allowing that corner to roll over more which is compressing that spring. Wouldn't the actual rate be quite higher there because of that travel?500lb spring compressed 1" =500 lb rate350 lb spring compressed 2"= 700500 compressed 2" = 1,000400 compressed 2.5"=1,000So is it that the car is actually gaining wedge by dropping LR to get the RF to squat and roll more?


Spring "rate" doesn't change due to travel unless you are coil binding.
If a 500 pound spring is compressing 1 inch then a 350 pound spring would compress 1.43 inches but the load on the wheel is the same.
I think you're mixing up cause and effect here. Weight transfer is what causes the spring to compress. The load on the spring isn't different if you change the spring rate.
If you transfer 1000 pounds to a 500 pound spring, it will compress 2 inches and the additional load is 1000 pounds.
If you transfer 1000 pounds to a 250 pound spring, it will compress 4 inches and the additional load is still 1000 pounds.

[Dirtmod13]

Spring "rate" doesn't change due to travel unless you are coil binding. If a 500 pound spring is compressing 1 inch then a 350 pound spring would compress 1.43 inches but the load on the wheel is the same.I think you're mixing up cause and effect here. Weight transfer is what causes the spring to compress. The load on the spring isn't different if you change the spring rate. If you transfer 1000 pounds to a 500 pound spring, it will compress 2 inches and the additional load is 1000 pounds. If you transfer 1000 pounds to a 250 pound spring, it will compress 4 inches and the additional load is still 1000 pounds.I understand your point. What I'm asking is with the softer spring allowing more travel, wouldn't even more weight transfer because of the amount of roll thus making the softer spring compress even more than the initial higher rated spring. We know through your example that weight will compress a spring to a certain point. But with an even softer spring allowing additional roll, doesn't even more weight transfer due the the moment center/ thrust angles.

[MasterSbilt_Racer]

I understand your point. What I'm asking is with the softer spring allowing more travel, wouldn't even more weight transfer because of the amount of roll thus making the softer spring compress even more than the initial higher rated spring. We know through your example that weight will compress a spring to a certain point. But with an even softer spring allowing additional roll, doesn't even more weight transfer due the the moment center/ thrust angles.
If more roll gets the CG higher, then more weight can transfer. That is what it comes down to. But if there isn't significantly more total weight transfer, the softer spring just gives up weight to the other one on that side.

[Matt49]

^^What he said...
My example was a crude one based on a single spring accepting weight. In reality, you are transferring weight from one PAIR of springs to another PAIR of springs and then the "heavy spring gets the weight" (we've gotta come up with a shorter way of saying that) theory would actually mean the softer spring would compress LESS than in my examples as you go softer relative the the OTHER spring in the pair that is receiving weight transfer. But what you're saying also makes sense if you are considering other dynamic changes (e.g. lower dynamic roll centers, higher VCG, etc.).
So maybe it's a wash and the RF spring rate doesn't matter ;-) Of course I jest but there are cars out there winning races on anything from a conventional 225 to a conventional 425 RF and an endless list of combinations of bumps stops, dual-stage, etc. are also winning. It's more about the overall package than any magic at one corner of the car.

[hucktyson]

Matt , spring rate increases in a non lineal fashion before coil bind. You would be surprised how close all of those rf combinations are to each other in terms of coil load at full travel

[jashonhand]

http://ajhagallery.gq/6/o.pngAs far as I know true caster, I check alot of different things and compare all the numbers to see what's built into the car, why it's built into the car and watch how it fits in my system, There are a lot of issues that can skew numbers so you've got to look at it as a package deal.

[Dirtrunner35]

http://www.auto-ware.com/autoware-bin/techarchive.pl?noframes;read=33329 good reading, do a search on the site for roll center


http://www.auto-ware.com/autoware-bin/techarchive.pl?noframes;search