How important are Penske front shocks?

[Hardingfv32]

So just how much extra performance do those expensive front Penske shocks being to FV's?

The 2022 national FV champ had a front shock fall off during the Runoff race, as many of us have.

I spoke to B Farnham, the winner mentioned above, and he thought it cost him .5-1.0 sec per lap. You can kind of see when it happened if you look race time sheet. Maybe around 5 laps to go. It is not perfectly clear about the delta because the other lead cars also fell off at this same time. 1 sec per lap represents a .7% loss in lap time performance.

So, as some of you like to say, track performance is the true measure of things. Then how do you justify the great expense of the Penske shocks? Now some are going to claim a great improvement when you first put them on, but was that really caused by the Penske shock? Or is this just in your head.... spent the money and it has to make a difference.

It is hard to refute what is being demonstrated by the Farnham result. And NO, his performance and that of his car were not the best during the race. Andrew Whitston was generally turning laps .75-1.0 sec faster during the race. So no unusual performance on the part of Farnham, just mistake free.

Brian

[Matt Clark]

I again am hesitant to post in one of these threads... but I will just throw out there that Brians car sits VERY low & stiff, similar to Varacins & Weishiet. Other cars who do ride higher & let the chassis move more will probably see a bigger benefit to good shocks than the guys that are slammed on the ground. That only makes sense, since you would be using the shock more.

That being said, basically the damper curves are damper curves no matter what shock it is, and as long as you have that right, you should be fine. But having the quick & easy adjustability of the current Penske is very handy, instead of having to tear shocks apart for changes. Being able to quickly make those changes on pit lane during practice or qualifying is absolutely worth it when track time is at a premium.

[problemchild]

Very expensive droop limiters!

[Hardingfv32]

That being said, basically the damper curves are damper curves no matter what shock it is, and as long as you have that right, you should be fine. But having the quick & easy adjustability of the current Penske is very handy, instead of having to tear shocks apart for changes..

But the whole premise being demonstrated by the Farnham example is that the car was very good with one shock missing. Shock curves, low speed dampening for chassis control, and easy of those adjustments are all irrelevant if the shock is missing.

Farnham stated to me that he adjusted his driving style to compensate for the missing shock. So as far as chassis control is concerned this would indicate that the drivers inputs have more importance than shock valving when it comes to chassis dynamics.

Of course this pretty much applies only to the FV suspension system.

Brian

[E1pix]

I’d thought the shock issue was on the right front, on a clockwise track, and for just the last few laps.

My impression was that Brian drove like a man possessed and wasn’t to be denied over a simple “bouncy” front corner (regardless of shock type), after coming really close to winning in nearly all of his Runoffs to date. It looked like a slick race and I imagine a broken shock in higher-grip track conditions would have greater ill effect.

Winning the Runoffs, and especially by commanding most of it in a Vee in really tough conditions, is by definition an “unusual performance” to be admired and aspired to.

Thanks for the insight on the Penskes Matt, makes good sense to me.

[jpetillo]

But the whole premise being demonstrated by the Farnham example is that the car was very good with one shock missing. Shock curves, low speed dampening for chassis control, and easy of those adjustments are all irrelevant if the shock is missing.

Brian, I agree with this to a point. Since we run an ARB in the front, even when the damper on one side fails, through the ARB that side will get some damping from the remaining shock on the other side. I'm guessing if Brian Farnham ran totally independent front suspension - no ARB - that it might have been more of an handful with a truly bouncy or bouncing tire. That Brian's car was still very good does suggest perfect damping rates in the front of a vee are not paramount, since at best his overall effective damping rate in the front changed by roughly a factor of two. John

[BLS]

Even when everything is perfect, I'd guess there is still enough frictional dampening that the loss of the shock is not total loss of dampening.

[BLS]

In 1978 I was at a national race in Gainesville, Florida, trying to make the runoffs that year (did, barely) and every point counted. That track was the famous dragstrip and used the "strip" as the straight and the return road through the swamp as the road course. It was actually a fun track. It had those round concrete "bumps" to define the road edge in several places. Those things were about a foot in diameter and maybe 8 inches tall. I hit one on the outside of the track with 3 laps to go. It broke my VW transporter steering stabilizer I used for a shock, and it bent the outer rim over the lug bolts. Because I was very, very cheap (read that as has no money) and had damaged the left front tire sidewall earlier, I had put a tube in that particular tire to keep using it. The tube kept the tire up and I finished the race in 5th place and got two points. In '78 there were at least 20-25 V's in that race so it wasn't that there were only 5 of us

Our front suspension is pretty crude and forgiving IMO.

[Matt Clark]

But the whole premise being demonstrated by the Farnham example is that the car was very good with one shock missing. Shock curves, low speed dampening for chassis control, and easy of those adjustments are all irrelevant if the shock is missing.

Farnham stated to me that he adjusted his driving style to compensate for the missing shock. So as far as chassis control is concerned this would indicate that the drivers inputs have more importance than shock valving when it comes to chassis dynamics.

Of course this pretty much applies only to the FV suspension system.

Brian

Are we just ignoring the main point in the first half of my reply, where I address literally what you are talking about?

A car that is built to sit 1" off the ground & doesn't pitch or yaw does not need much of a shock. The curve doesn't matter when the car does not move.
A car that does move the chassis more & transfers more weight is going to be way more sensitive to that. For better or worse, my car does use a lot of shock dampening to control weight transfer, especially off the corner to prevent understeer. Then people cry about cheating when I am faster on the straights.... it's because I didn't push & scrub my corner exits.
Friction was also mentioned, and I have seen some of that with bushed beams vs. bearing beams. The needle bearing beam was freer, and bounced more, so the shocks were more influential to feel.

We (or really, Dad) helped a couple people the past couple years with setup some, based on what we have learned & do. A couple of the guys immediately felt better & went faster. Some others said they couldn't notice a difference. So maybe it is in peoples heads, or maybe some guys just can't feel a car.
Either way, this is our experience with the topic. Perhaps this was also influenced by the different tires we have been on over the years... I know the old Challenge Cup Falkens were really dependent on setting up to reduce understeer compared to slicks, but the principles are the same.

Bottom line is that Brians car, and a couple others like I mentioned, are special compared to the vast majority of FVs. I cannot speak for Gregs experiences with his because it was a little before my time, but I seem to remember his cars sitting lower & flatter than others as well.
* Side note- I wish the guy that has Shirley now would get the car on track again. That car is a legend in the FV world.

[problemchild]

I don't know how you guys go through paragraphs and paragraphs through 9 posts talking about FV front shocks, without talking about their droop limiting properties. That is 95% of their benefit if used properly.

[Hardingfv32]

Are we just ignoring the main point in the first half of my reply, where I address literally what you are talking about?

A car that is built to sit 1" off the ground & doesn't pitch or yaw does not need much of a shock. The curve doesn't matter when the car does not move.

I ignored it because it is completely wrong.

First, the 1" clearance is at the floor which is about 14" wide at the beam. The car is if fact really 2X as wide when measured at the wheel. Now assume the chassis pivots around a point at the center of the floor, For the floor's corner to bottom out in roll the wheel has to move up 2". A 1" compression at the wheel in roll is about average for a FV. Do not forget the other side of the of the front suspension is rising just as much.

So, if you really believe chassis control do to shock low speed valving is actually important with FV's, then there is more than enough movement for the valving to function.


A warning about low ground clearance: it creates aero drag under the car. Yes, down force is created but at the expense of additional drag. So there is a compromise to be developed here.

Brian

[Hardingfv32]

I don't know how you guys go through paragraphs and paragraphs through 9 posts talking about FV front shocks, without talking about their droop limiting properties. That is 95% of their benefit if used properly.

I know you find front roll droop control handy, but I have never had any call to use it.

Maybe expand exactly what issues it can help resolve and what you think dynamically is happening, weight transfer, etc.

Brian

[Matt Clark]

I ignored it because it is completely wrong

Ok. Whatever.
I am in the paddock, talking to the guys with these cars, then on track & winning races/championships. You are in your garage pontificating.

I'm out.

[Matt Clark]

I don't know how you guys go through paragraphs and paragraphs through 9 posts talking about FV front shocks, without talking about their droop limiting properties. That is 95% of their benefit if used properly.

While I did not directly mention droop limiting, I thought I kinda was with my weight transfer and limiting corner-off understeer references.

[problemchild]

I know it makes for a much better story that Brian won the Runoffs despite the RF shock falling off, but losing the RF droop limiting was of very little consequence, and may have actually been helping. As the drizzle picked up, he had an unintended "rain setup" on his RF on a track with many right hand corners. Perhaps not as fast ultimately, but rolling over onto the left front may have made the car easier to drive in tricky conditions.

There are many ways to tune a race car, so my opinion is just that, but if I was helping tune a FV, then I would start with finding the "sweet spot" of the rear suspension, then finding the best rear shock settings, then configuring the ideal roll steer. Then I would be optimizing the front droop limiting. If front droop was #6 on my worklist, then front shock valving would be about 100 on that worklist.

Again, these are just my opinions. Your results may vary.

[Hardingfv32]

Can you expand:

1) Find the sweet spot at the rear', Is that both static camber and droop setting? May we assume that shock settings relate mostly to chassis control? Did you find a relationship between static camber and the low speed shock settings? Along the lines of more static camber requires more travel and time to reach the droop setting.

2) Roll steer at the rear: what would be been your most common outcome in roll, toe-in or two out? How did you integrate the effects of the rear suspension roll and jacking during this roll steer?

Thanks
Brian

[S Lathrop]

At the rear of a FV, I believe that every car has some form of droop limiting. This is necessary because the geometry of the FV rear has a missive jacking tendency as the car is loaded laterally. As it is in a corner.

Some years ago, I took the time to model the FV suspension in Bill Mitchel's WinGeo software. I have always been told that the front roll center of a FV was at ground level. Not so according to Mitchel. The front roll center is at a similar location as the rear, very high. This in turn causes the front to jack up as the car corners, just the same as at the rear. The shocks limit the droop of the inside wheel and thus control the roll at the front to some degree.

Many years ago we were testing a front shock setup that I di where I could adjust the droop length of the front shocks. The shock shaft had a long threaded end. I used to nuts to clamp the top of the shaft to a rod end where the shock top would fasten. During the testing, we found that the car responded positively to limiting the front droop. We ran out of adjustment to shorten the droop so we eliminated the bottom clamping nut and moved the top nut down to the end of the threads. Tis setup gave maximum droop limiting but with no shock function. That was the best performance we got from the setup.

I have never tried it, but based on that test, I think you don't need a front shock, other than to meet the FV rules. And what you do need is a much better droop limiting system at the front.

We are also talking about roll toe. There is a second effect of tuning roll steer. And that is what it does in terms of squat and jacking effects under acceleration and braking. Example roll toe out also has a anti squat force under acceleration. This is because the trailing arm angles upward as it goes to the pickup point on the chassis. So as the car accelerates, the driving force from the rear tire lifts the rear of the car. Under braking it pulls down on the rear of the car. the down side here is that you pay a bit of a price in terms of mechanical grip. That should be confusing enough.

[Hardingfv32]

... I took the time to model the FV suspension in Bill Mitchel's WinGeo software. I have always been told that the front roll center of a FV was at ground level. Not so according to Mitchel. The front roll center is at a similar location as the rear, very high.

This is a completely ridiculous position for you to be taking. Either you applied the program incorrectly or the program cannot process the FV variables correctly.

1) There has never been a requirement to set the front droop in the history of FV similar to what is required with the rear suspension. Front shock displacement data (wheel travel) shows no indication of jacking. Simple head on viewing of a FV in a turn shows no jacking. The ground clearance at the center of the front floor does not change.

2) If there was jacking in the front then there would be no need for zero roll, a mainstay for rear FV suspension. FV's would use similar weight transfer setups as all other race cars that have low angle roll axis.

The whole reason for zero roll and its weight transfer dynamics is because of the very steep roll axis the FV's trailing arm front and swing axle rear suspensions produce.

3) If front suspension droop limiting was if fact really necessary then there would have developed a simple external adjustable control system. No such system is found on the vast 'majority' of FVs.

Brian

[S Lathrop]

This is a completely ridiculous position for you to be taking. Either you applied the program incorrectly or the program cannot process the FV variables correctly.

1) There has never been a requirement to set the front droop in the history of FV similar to what is required with the rear suspension. Front shock displacement data (wheel travel) shows no indication of jacking. Simple head on viewing of a FV in a turn shows no jacking. The ground clearance at the center of the front floor does not change.

2) If there was jacking in the front then there would be no need for zero roll, a mainstay for rear FV suspension. FV's would use similar weight transfer setups as all other race cars that have low angle roll axis.

The whole reason for zero roll and its weight transfer dynamics is because of the very steep roll axis the FV's trailing arm front and swing axle rear suspensions produce.

3) If front suspension droop limiting was if fact really necessary then there would have developed a simple external adjustable control system. No such system is found on the vast 'majority' of FVs.

Brian

Brian

I guess that in my old age, my experience will have to bow down you you understanding of FV suspension geometry. By the way, how many SCCA national championships do you have on your record?

Currently I am working on a major update of one of my old FVs that has back to back national championships.

The only thing that makes the FV front suspension unique when modeled in the Mitchell is the axis rotation of the front suspension control arms. Most cars have axis of rotation at some angle to the center line of the car. The FV us unique at having that angle 90 degrees. Other than that the FV is the same as any double a-arm car when modeled in WinGeo3. The A-arms just happen to be unique in their design.

There are several reasons the front behaves as it does. One is the way the wheel rate changes as the ride height changes. This changing motion ratio contributes to jacking of the front at it responds to lateral forces.

[Hardingfv32]

By the way, how many SCCA national championships do you have on your record?

As if that has not been said before. It is the common retort for those who cannot respond to the my precise and logical technical positions.

The above post is actually not technical at all. It relies on the logical conclusions drawn from the observation of FV history. Please feel free to challenge these conclusions.

I have a very big 'technical' ego, but what makes me very special is that I do not mined being proven wrong. I can learn something from that. I am thick skinned and do not mind in the slightest.

'This changing motion ratio contributes to jacking of the front at it responds to lateral forces.' But first you have to prove that jacking does in fact take place. You acting like it is a given when no physical evidence exists to demonstate that.

Brian

[S Lathrop]

'This changing motion ratio contributes to jacking of the front at it responds to lateral forces.' But first you have to prove that jacking does in fact take place. You acting like it is a given when no physical evidence exists to demonstate that.

Brian

The physical evidence I had was the the test we did with the front shocks that led to my conclusion that droop limiting was a valuable thing to do. We started with sufficient droop travel that the we did not encounter any limiting to the droop travel.

As to the jacking effect, that is related to the roll center location. Any car with an above ground roll center experiences some amount of jacking forces as the car corners. It is a fact of the physics and geometry of the car.

We did not have a data logging system that could them monitor suspension position. The only performance monitoring system we had as a stop watch. The driver was someone who had a lot of experience ands had many FV wins on his resume.

I have worked for many decades as a race car engineer in the Indy Lights through multiple generations of chassis designs. Understanding what a car does on the track has been my profession for over 30 years and simultaneously designing and build race cars.

Droop limiting suspension travel is something I have a lot of experience doing with many different race car types and I have done it at both ends of the car. I have been able to see the results no only in interviewing the driver after a run where wwe change the droop limiting but also in the data logging systems that we had on those cars.

[E1pix]

It’s extremely educational to discuss suspension theory, and can only help us all. Thanks to those who know this stuff.

But it’s equally uncool to systematically insult contributors having the most education to give on this forum. They’re a gift.

The well-presented thread and its products leading to this spiteful knockoff thread was by a first-time poster whose reputation preceded his ever coming here.

Great welcome, Harding. Now you’re insulting a 50-year chassis builder?

We’re way better than this.

[problemchild]

[problemchild]

if I had to choose between having front shocks or front droop limiters, I will take the limiters thank you.

[problemchild]

While I am not an engineer, I would suggest that the front roll center would move based on the height of the beam assembly, just as the front roll center moves on conventional cars when we move the pickup points.

[Hardingfv32]

But it’s equally uncool to systematically insult contributors having the most education to give on this forum. They’re a gift.

The well-presented thread and its products leading to this spiteful knockoff thread was by a first-time poster whose reputation preceded his ever coming here.

These are not attacks. They are just very strong statements about a product and a statement that are COMPLETELY wrong. I have clearly stated how the history of FV does not support either the product or the statement. Anyone is free to correct my observations of FV history, but please note no one has at this point.

That popularity or track record of someone means nothing when they are flat wrong. You clearly do not appreciate that you are being 'educated' with incorrect information.

Brian

[problemchild]

While perhaps not the first, certainly the first to aggressively limit the front of a FV, was a certain Dan Binks, whose brother-in-law won the 1995 FV Championship. Dan has won a few other races while working for Ford and Chevrolet factory sports car teams over the years. That success motivated me to give it a try.

[Hardingfv32]

if I had to choose between having front shocks or front droop limiters, I will take the limiters thank you.

Yes, you picture a very good and a simple example of a front droop limiting hardware. IF...droop limiting was actually require for the correct handling balance of a FV, why has this not became commonly adopted in FV over the last 60 years?

Brian

[Hardingfv32]

The physical evidence I had was the the test we did with the front shocks that led to my conclusion that droop limiting was a valuable thing to do.

You could be Adrian Newly and I would still call you out for a position that is so contrary to common engineering and FV history.

1) One test without data and only a track times does not prove the point in anyway. This important, how do you know that the improvement you saw was not from weight transfer control, which is a common use for droop limiters.

2) There are NO examples in engineering literature that show the roll center of a beam trailing arm suspension not being at ground level. Rice's statement about possible roll center movement: That is also not to be found in any engineering literature. Guy's, feel free to post something, from the literature, that says otherwise.

3) Again, your race history brings no science or engineering to this discussion other than the one test. Please expand on why nothing in the development of FV suspension design supports your belief that the front end jacks.

Brian

[Hardingfv32]

While perhaps not the first, certainly the first to aggressively limit the front of a FV, was a certain Dan Binks, whose brother-in-law won the 1995 FV Championship. Dan has won a few other races while working for Ford and Chevrolet factory sports car teams over the years. That success motivated me to give it a try.

Not unusual, you are not being clearly about what is being posted. Lathrop's post in talking about suspension jacking, not wheel displacement do to chassis role and/or weight transfer. I would be my position that you have 'never' discussed front suspension jacking. When you have posted about on the subject of front droop limiters, it has always related to controlling weight transfer.

The whole front suspension (beam) jacking IS NOT the same as one corner intending, going into rebound, or if you like jacking. I am sure you would agree that opposite side ii in compression and in no way jacking.

I have no argument with someone thinking they need front drop limiting to control weight transfer.

Brian

[problemchild]

You could be Adrian Newly and I would still call you out for a position that is so contrary to common engineering and FV history.

Mr Newey does a lot more than stay home and study engineering papers. He goes to race tracks!
Reportedly, he is very open to new ideas, even when they conflict with his ongoing beliefs.
Just sayin.

[S Lathrop]

I have no argument with someone thinking they need front drop limiting to control weight transfer.

Brian

There is a second reason that the front end of a FV jacks and it has to do with the motion ratios of the front torsion bars. If you have a rising rate on the outside and a declining rate on the inside, the front end will jack up as the car rolls. The motion ratio change is a lot more pronounced if the spring is in the upper tube vs. the lower tube.

Droop limiting on the front ends some formula cars, like FF and FC, is quite popular on cars with rising rate front motion ratios. That is when the springs get stiffer as the suspension goes down and softer as the suspension goes up.

I do have the bad habit of follow the results of my experiences when I test cars and continuing to do what works.

[problemchild]

Yes, you picture a very good and a simple example of a front droop limiting hardware. IF...droop limiting was actually require for the correct handling balance of a FV, why has this not became commonly adopted in FV over the last 60 years?

Brian

I thought it had over the last 25 years.

[jpetillo]

I am intrigued, Steve, by your modeling of the front suspension showing the roll center not being located at or near ground level. Although I don't currently see how it would manifest itself not to be at ground level, I'd be interested in seeing how what you mentioned can come about. I'll think about it more.

With regard to conventional theory about roll centers, Brian is right that conventional theory says that it should be right at ground level for the trailing arm front suspension. If you start with an A-Arm whose mounting points are parallel to the axis of the car and then rotate the mounting points to being 90 degrees from the centerline where its becomes a trailing arm like we have, the instantaneous roll point for one wheel moves from, say, close to outside the opposite tire for the A-Arm to infinity when you get to the trailing arm like the Vee has in the front. That puts the roll center on the ground. The way everyone explains for determining the roll center for trailing arms has always bothered me - I'm not sure I believed it for trialing arms, although I believe it for A-arms - but reading some papers today I think the conventional theory is still correct. I'll read more.

With there being differences in the two torsion arms on the beam front end and how they are located on the beam and their static angle with respect the ground, I can believe the roll center could move up or down, but it's hard to see how it can be as much as reported here. More later. John

[Hardingfv32]

Mr Newey does a lot more than stay home and study engineering papers. He goes to race tracks!
Reportedly, he is very open to new ideas, even when they conflict with his ongoing beliefs.
Just sayin.

You clearly can not read. I posted above:

'I have a very big 'technical' ego, but what makes me very special is that I do not mined being proven wrong. I can learn something from that. I am thick skinned and do not mind in the slightest.'

You don't seem to be answering any of the quest\ions I put forth. Could it be you don't know the answers and I do?

Just saying

Brian

[Hardingfv32]

[QUOTE=S Lathrop;650007]There is a second reason that the front end of a FV jacks and it has to do with the motion ratios of the front torsion bars. If you have a rising rate on the outside and a declining rate on the inside, the front end will jack up as the car rolls. The motion ratio change is a lot more pronounced if the spring is in the upper tube vs. the lower tube.[QUOTE]

Clear state what you consider to be jacking of the front suspension. For me jacking is the role center height changing in the vertical plane. NOT wheel displacements caused by weight transfer.

In your test, how did you discern between between jacking control and weight transfer control?

Brian

[S Lathrop]

[QUOTE=Hardingfv32;650016]

Clear state what you consider to be jacking of the front suspension. For me jacking is the role center height changing in the vertical plane. NOT wheel displacements caused by weight transfer.

In your test, how did you discern between between jacking control and weight transfer control?

Brian

What do you mean by weight transfer control? And are you talking about pitch or roll weight transfer?

Maybe there is the problem. I am saying a car is jacking up when the ride height as measured in the center of the car rises as the car corners. I take it we would agree that the inside of the chassis will rise and the outside of the chassis will go down if the car just rolls.


One thing I will point out is that until I did the Mitchel analysis, I had always assumed that the roll center was at ground level at the front. Now it may be that Mitchel is wrong. And I did say at the beginning of this that the roll center location was as Mitchel calculated. But if the roll center is at the ground level, the car would not be as reactive to droop limiting as it is. And given my experiences, I think they confirmed Mitchel's analysis.

[brian styczynski]

Why do people continue to engage the troll?

[jpetillo]

I think the thread is mixing two different forms of "jacking".

First definition: Steve mentions "As to the jacking effect, that is related to the roll center location. Any car with an above ground roll center experiences some amount of jacking forces as the car corners. It is a fact of the physics and geometry of the car." This is what I understand to be the conventional definition of jacking and how it is discussed. This form of jacking has to do with the instantaneous roll center for each tire as it is deflected vertically. This roll center is from the tire changing camber - tilting/rotating with respect to the chassis - as it moves vertically. You find the center of that for each tire. Those centers - one from each tire - are usually symmetrically opposed (although perhaps not for a car running on ovals). Since each tire rotates around its roll center, the bottom of the each tire rotates around the same center. The side force of the bottom of the tire when cornering is lateral - parallel to the ground and at the bottom of the tire - and that is the force used for this definition of jacking. Since the whole tire rotates around its instantaneous center ("instantaneous" is used because the centers may change with suspension movement and then the roll centers may change) you can draw a line from the bottom of the tire to the roll center and that roll center is the point that will move due to the torque on the tire (when viewed from the back - not acceleration torque). The opposite tire will do that same but will try to move its roll center, which is symmetrically opposite from that of the other tire. The real roll center is the one that comes about because of these two constraints of motion, and is the point where the two lines drawn from the bottom of each tire to its instantaneous role enter intersect.

All this tells us is where the overall instantaneous roll center is for a car when lateral forces on the bottom of the tires is applied - nothing else. If you push the bottom of a tire in it will raise that roll center if it is above the road surface because the force on the bottom of the tire provides a force parallel to the ground, and if a roll enter above the ground it will cause a torque and work to raise it up. If the roll center is on the ground, nothing happens from this force as it goes through it and cannot apply a vertical force on it.

Back to jacking... when you corner there is a side force on the bottom of the tires, and the force on the outer tire is inwards towards the car center, and on the inner tire, outwards. The outer tire works to raise the car and the inner works to lower the car's instantaneous roll center. With equal grip from each tire there is no jacking. But the outer tire gets weight transferred onto it and will have more grip - more lateral force - while the opposite happens with the inner tire and it has less lateral force. This imbalance causes the outer tire to win the battle and push up harder and so the car stands up - jacks!

All this says is that a suspension that has camber change with vertical motion is what enables jacking.

In our cars the vertical motion of the front tire does not cause a camber change - at least nothing significant, I believe. When that is the case the instantaneous roll centers are at infinity off to each opposing side, which, when connected back to the bottom of the tire, sits effectively along the road surface, and we get no jacking of this sort.

This above is the textbook definition of jacking. Do you folks agree?


Second definition: Steve says "a car is jacking up when the ride height as measured in the center of the car rises as the car corners." and if it changes height "it has to do with the motion ratios of the front torsion bars. If you have a rising rate on the outside and a declining rate on the inside, the front end will jack up as the car rolls." What Steve says is exactly the way I see it; that in such a situation the car would raise. However, I'm not sure this is the conventional use of the term "jacking" when people discuss suspension.

This vertical motion has nothing to do with the instantaneous roll center discussed above, which is not dependent on motion ratios from things that bend/mov like springs and shocks and roll bars. This motion Steve mentions is dependent on motion ratios from things that bend/mov like springs and shocks and roll bars.

I would suggest that if we separate these two aspects of suspension in our discussion that it would be helpful.

The content in the thread is very interesting. I'm just trying to get everyone on the thread onto the same page with regard to terminology so the discussion is less ambiguous and we can move forward. Can we agree to use the first definition as what we call "jacking"?


Have I put everyone back to sleep? Please correct me where I'm wrong - it's early for me as well. John

[problemchild]

You don't seem to be answering any of the quest\ions I put forth. Could it be you don't know the answers and I do?

There are several reasons.

1) I have no engineering education so cannot discuss many of your topics intelligently. You would just be attacking me because of my nomenclature, etc. I have never read "engineering literature" or studied "engineering papers". I can barely read. I will let the smart people share their expertise and absorb anything useful. I would say that you are disappointing me in that regard on this topic.

2) I don't care about many of your concerns. Front roll center is determined by spec components, for example, so why should I worry about it. I am much more of a manager than engineer. I look and listen to what successful people are doing, and I follow those trends. Some people would call that imitation or copying, which is totally fair. When Dan and crew showed up at the Runoffs in the mid-90s, I was fascinated by a few revolutionary trends on their Aero. From them, I have learned that FVs need to have the front end pinned down. I have also stopped measuring rear droop and use the rear droop limiter to set preload. I believe these trends were a big part of my FV and FST success in the 2000s. My Reynard FF also liked the concepts, supporting the concept that if your car has lousy suspension geometry, minimize those flaws by reducing suspension travel.

3) I have stated my belief that tuning these FV cars with rear roll steer and front limiters is very important. FWIW, I do believe that a 4-spring car will ultimately be faster than a 3-spring car, but would require a lot of track-specific tuning. After spending 3 years working on the concept, it will take more than 8 sessions during FST races to convince me that someone else has got it all figured out. That is not a shot but a fair observation. I believe that the lazy turn-in on Matt's FV is a front droop issue rather than a rear suspension issue.

I am very intrigued by the relaxed standards of the forum. I really miss the fascinating debates from previous times, and the contributions from the interesting people who got banned for far less than your recent commentary. Perhaps we could have an absolution process and liven things up around here!