Chris
I'm not sure that the rear camber is as bad as you state. I would say that 1 deg of chassis roll might yield a 1/4 deg of camber change at the rear.
Why would you say we don't have much control in the rear?
Brian
Rear Roll Resistance Never Needed
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hardingfv32-1
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Re: Rear Roll Resistance Never Needed
Rewinding to the subject from last night - the effect of droop & droop control over rises when cornering - over the rise, the rear wheels will be limited to how far they are alowed to drop, and momentarily will have a loss of downforce, like was mentioned. Jacking force will be reduced for the reasons you folks mentioned, but the tires will drop while the car is waiting to come back down to put full weight on the pavement due to gravity, and at that time you could be running near your max droop camber.
But, I guess we're onto the next topic... John
But, I guess we're onto the next topic... John
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CitationFV21
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Re: Rear Roll Resistance Never Needed
Brian,hardingfv32-1 wrote:Chris
I'm not sure that the rear camber is as bad as you state. I would say that 1 deg of chassis roll might yield a 1/4 deg of camber change at the rear.
Why would you say we don't have much control in the rear?
Brian
What I mean is compared to a suspension with upper and lower wishbone. Our geometry is pretty fixed compared to most other race cars, including ones with struts. Only one worse is a solid axle, but even they get links, trailing arms, panhard rods, etc.
Chassis roll affects rocker pivot points so the effect might be exagerated. Since I don't have a computer program to do it, I need to go back the the old push pin cardboard cutout models where you can simulate all the movements.
ChrisZ
Re: Rear Roll Resistance Never Needed
Brian H
You suggest “everything you might want to accomplish with car balance can be achieved with modifications to the front end.” However, this thread seemed focused on the rear end.
Are you speaking of legal modifications?
Could you expand on the options available to improve front lateral grip?
Once front end options are exhausted, and front lateral grip is less than desired, would you then say enhancing front grip through placing some roll resistance at the rear is acceptable?
Finally, at one time you advocated moving weight forward towards 50/50 weight distribution. How did that work out?
You suggest “everything you might want to accomplish with car balance can be achieved with modifications to the front end.” However, this thread seemed focused on the rear end.
Are you speaking of legal modifications?
Could you expand on the options available to improve front lateral grip?
Once front end options are exhausted, and front lateral grip is less than desired, would you then say enhancing front grip through placing some roll resistance at the rear is acceptable?
Finally, at one time you advocated moving weight forward towards 50/50 weight distribution. How did that work out?
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hardingfv32-1
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Re: Rear Roll Resistance Never Needed
The best, but not easiest, way to increase front grip is to change the camber. IF you agree that the FV outside front wheel's camber is positive in most turns, then it would seem that we have a lot of camber range to work with, say 1-2 deg. It will require offset bushings machined to the correct angles. You might have to have a set of different angle bushings available to do the job right. A ball joint front end would be a simpler solution.
Personally, I am sure any balance issue can to solved working with the front. You always have the wide front tires as a option.
My 49/51 weight distribution car work fine. Could make it loose by using 1.75 deg front camber. That is why I say a regular FV can do everything with the front. The 49/51 handled as good as any Nat car we encountered, but not noticeably better. I have built a new car with a priority on cooling and aero. For packaging reasons the weight distribution is comparable to a normal FV.
Brian
Personally, I am sure any balance issue can to solved working with the front. You always have the wide front tires as a option.
My 49/51 weight distribution car work fine. Could make it loose by using 1.75 deg front camber. That is why I say a regular FV can do everything with the front. The 49/51 handled as good as any Nat car we encountered, but not noticeably better. I have built a new car with a priority on cooling and aero. For packaging reasons the weight distribution is comparable to a normal FV.
Brian
Re: Rear Roll Resistance Never Needed
i fail to see where this question has gone... i think it better to either have a computer model or a proof of concept car that you can quick change design elements to find the solutions to these questions. example being if you think you need more camber than a linkpin front suspension will give you, slap on a balljoint front end for a test day and muck with the camber until you're happy and find out just how much camber that is. same with any other part of the car. will adding roll resistance to the rear decrease lap times or improve the overall grip level of the car? will a larger air intake scoop net a higher speed at the end of that long straight? unfortunately, for most mere mortals, in order to comprehend what the car is doing, we have to simplify it so much that we're no longer modeling what is actually going on. its like saying velocity during freefall is based entirely on gravity and nothing else. of course we know that's not true, wind resistance plays a key roll in establishing terminal velocity, as does any centripetal force being applied, but that makes our calculations just that much more complex and messy. the only good way of determining what can be done to improve our cars is to go out and try it (since i don't think anyone here owns a supercomputer and advanced simulation software which accounts for any and all variables you find at the track)
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hardingfv32-1
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Re: Rear Roll Resistance Never Needed
1) The roll resistance issue was not resolved and then the discussion changed to droop limiters. With droop limiters I would say that we determined that you can corner on OR off the limiter depending on the stiffness of the rear spring.
2) If we keep a discuss focussed and the variables very restricted, you can learn things that can help you better understand the car as a complete system.
2) You can get more than enough camber from a FV front end for any situation.
3) The normal Nat level FV competitor does not have the time or budget to track test every idea. Much better to develop an understanding of the properties of an FV and pre-screen ideas before actually implementing then on a car. Most the things you see guys experimenting with on race weekends should never have gone beyond the discussion stage.
4) One accept of this forum is to discuss ideas and figure out mentally if they hold any merit. It only cost you time using this technique.
5) So what is your narrow focused question?
Brian
2) If we keep a discuss focussed and the variables very restricted, you can learn things that can help you better understand the car as a complete system.
2) You can get more than enough camber from a FV front end for any situation.
3) The normal Nat level FV competitor does not have the time or budget to track test every idea. Much better to develop an understanding of the properties of an FV and pre-screen ideas before actually implementing then on a car. Most the things you see guys experimenting with on race weekends should never have gone beyond the discussion stage.
4) One accept of this forum is to discuss ideas and figure out mentally if they hold any merit. It only cost you time using this technique.
5) So what is your narrow focused question?
Brian
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maurus97
Re: Rear Roll Resistance Never Needed
Correct me if I am wrong (it's happened before 
it'll happen again I'm sure 
) but, isn't a normal, zero roll suspension on a swing trans-axle, at mid corner (discussed as the assumed variable), but with no droop limiter/limitation mechanism/stop mechanism, a near impossibility?
The discussion seems to elude to the hypothesis that the rear spring/shock can be setup and tuned in such a manner as to where one does not run the risk of jacking afoul into undesirable camber scenarios. It seems to me that such an assertion is at root, a hypothesis recognizing the importance of droop limitation.
I am not trying to sound like a smart-alek or an ignoramus; it's a serious question.
On a side note, I realize this this thread dates circa 2010 but I enjoyed it and as I said, I'm being sincere with my inquiry.
it'll happen again I'm sure ) but, isn't a normal, zero roll suspension on a swing trans-axle, at mid corner (discussed as the assumed variable), but with no droop limiter/limitation mechanism/stop mechanism, a near impossibility? The discussion seems to elude to the hypothesis that the rear spring/shock can be setup and tuned in such a manner as to where one does not run the risk of jacking afoul into undesirable camber scenarios. It seems to me that such an assertion is at root, a hypothesis recognizing the importance of droop limitation.
I am not trying to sound like a smart-alek or an ignoramus; it's a serious question.
On a side note, I realize this this thread dates circa 2010 but I enjoyed it and as I said, I'm being sincere with my inquiry.
Re: Rear Roll Resistance Never Needed
Nick,
Your question is valid and was addressed back in the earlier posts of this thread. BrianH is using a VERY STIFF rear spring that is relatively short. Rear jacking is caused by the jacking forces of the rear swing axle *AND* additional pressure from the rear SPRING. So... if your rear spring is 10" long and your spring length at rest is ... say 7.5 inches, then you will have force from the spring adding to the jacking forces until you reach the limiter (if you have one) or the maximum extension of the spring or shock, whichever is less. With no limiter, the rear will go positive (normally considered to be a bad thing) assuming the fully extended shock will allow that. If, OTOH, you have, say an 8" spring that is strong enough to hold the car up WITHOUT any (appreciable) compression, then when the jacking force is applied, there will be (almost) NO additional force from the spring (it's already all stretched out, so it comes off the perch instead). So ... Brian's feeling is that if the car is designed properly, the rear would never reach the limiter because there is not enough jacking force (due to loss of rear traction) to force the car into positive camber.
THEREFORE.... a "properly designed and setup car" *COULD* perform adequately with no rear camber limiter.
At least, I THINK that's what he said
.
Ensuing discussion addressed the issues of whether the car could handle worth a flip with a spring rate that high. THEN, with spring rates that high, the 'spring rate' of the tires themselves becomes a more significant part of the equation and ... well, it gets pretty messy from there
This HAS been quite an entertaining discussion....
Steve, FV80
Your question is valid and was addressed back in the earlier posts of this thread. BrianH is using a VERY STIFF rear spring that is relatively short. Rear jacking is caused by the jacking forces of the rear swing axle *AND* additional pressure from the rear SPRING. So... if your rear spring is 10" long and your spring length at rest is ... say 7.5 inches, then you will have force from the spring adding to the jacking forces until you reach the limiter (if you have one) or the maximum extension of the spring or shock, whichever is less. With no limiter, the rear will go positive (normally considered to be a bad thing) assuming the fully extended shock will allow that. If, OTOH, you have, say an 8" spring that is strong enough to hold the car up WITHOUT any (appreciable) compression, then when the jacking force is applied, there will be (almost) NO additional force from the spring (it's already all stretched out, so it comes off the perch instead). So ... Brian's feeling is that if the car is designed properly, the rear would never reach the limiter because there is not enough jacking force (due to loss of rear traction) to force the car into positive camber.
THEREFORE.... a "properly designed and setup car" *COULD* perform adequately with no rear camber limiter.
At least, I THINK that's what he said
.Ensuing discussion addressed the issues of whether the car could handle worth a flip with a spring rate that high. THEN, with spring rates that high, the 'spring rate' of the tires themselves becomes a more significant part of the equation and ... well, it gets pretty messy from there
This HAS been quite an entertaining discussion....
Steve, FV80
The Racer's Wedge and now a Vortech, FV80
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hardingfv32-1
- Posts: 1014
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Re: Rear Roll Resistance Never Needed
Steve's summary of my position is correct. I use a 350-500 lb., 4.0" long spring with a normal rocker or motion ratio. Rear grip is not an issue on the roughest of tracks.
Brian
Brian
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maurus97
Re: Rear Roll Resistance Never Needed
(Steve)Quote- THEREFORE.... a "properly designed and setup car" *COULD* perform adequately with no rear camber limiter.
At least, I THINK that's what he said. -End quote
Re. (BrianH) confirms that Steve's interpretation of the hypothesis is accurate.
The reason I had asked if the hypothesis was a near impossibility, was because when I look at an FV, I see a swing trans-axle. With no rear camber limiter, the back end of the race car would literally be dragging along the pavement. To state that positive, or negative droop control, on a swing trans-axle is not needed just doesn't add up. To me, it would be on par with the hypothesis that our leading/trailing arms are not necessary for limiting horizontal swing.
Again, I am not trying to irritate with my inquiry. I really am trying to learn something. I truly have a hard time learning concepts that incorporate math, unless I have a visual reference (in the physical or mental picture). So, when I visualize my drum-to-drum trans-axle sitting by itself on the shop floor, I know those axles/tubes/drums have a plenty of room for "swing" if provoked by an outside physical force. In fact, we have a specially made handle (many people probably own something similar) designed so that one person on his own, can pick up and move the drum-to-drum trans-axle. The only thing that makes this handle design special, is that it controls/limits axle swing. If limiting swing is important when moving a drum2drum tranny around the shop on foot, I just don't see how NOT having axle swing limiter(s) (camber limiter/droop...however one chooses to specify it) is plausible on our cars, at CORNER SPEEDS/FORCES.
Nikolaus
At least, I THINK that's what he said. -End quote
Re. (BrianH) confirms that Steve's interpretation of the hypothesis is accurate.
The reason I had asked if the hypothesis was a near impossibility, was because when I look at an FV, I see a swing trans-axle. With no rear camber limiter, the back end of the race car would literally be dragging along the pavement. To state that positive, or negative droop control, on a swing trans-axle is not needed just doesn't add up. To me, it would be on par with the hypothesis that our leading/trailing arms are not necessary for limiting horizontal swing.
Again, I am not trying to irritate with my inquiry. I really am trying to learn something. I truly have a hard time learning concepts that incorporate math, unless I have a visual reference (in the physical or mental picture). So, when I visualize my drum-to-drum trans-axle sitting by itself on the shop floor, I know those axles/tubes/drums have a plenty of room for "swing" if provoked by an outside physical force. In fact, we have a specially made handle (many people probably own something similar) designed so that one person on his own, can pick up and move the drum-to-drum trans-axle. The only thing that makes this handle design special, is that it controls/limits axle swing. If limiting swing is important when moving a drum2drum tranny around the shop on foot, I just don't see how NOT having axle swing limiter(s) (camber limiter/droop...however one chooses to specify it) is plausible on our cars, at CORNER SPEEDS/FORCES.
Nikolaus
Re: Rear Roll Resistance Never Needed
Nik,
It would appear (TO ME) that you are interpreting fore/aft axle swing as being a significant part of suspension travel for an FV. As a (wild) generality, fore/aft movement is a minimal part of suspension travel (at least in a moderately designed suspension system). The basic discussion is about VERTICAL movement of the axle. The trailing arms control the Fore/Aft movement and the SPRING/SHOCK (should) control the VERTICAL movement(s), and the VERTICAL movement SHOULD be the majority of the action on the track. If fore/aft takes over, then all bets are off (that is TOE-Steer and should be a very minimal consideration compared to the vertical components).
The camber limiter keeps the car from getting "too far from the ground"... the SPRING, keeps it from "dragging the ground" (so to speak). The SHOCK, helps to control the issues related to unwanted OSCILLATIONS between the spring and gravity.... If I am way off base, I hope someone MUCH smarter than me steps in to set you straight.
We (at least *I* <G>) try not to involve that "silly MATH thing" in these discussions. I rely much more on my BEHIND than my brain to determine optimum parameters of my car ( my ASS skills far exceed my MATH skills <g>) .
Steve, FV80
(most likely my last post before POST Runoffs).
It would appear (TO ME) that you are interpreting fore/aft axle swing as being a significant part of suspension travel for an FV. As a (wild) generality, fore/aft movement is a minimal part of suspension travel (at least in a moderately designed suspension system). The basic discussion is about VERTICAL movement of the axle. The trailing arms control the Fore/Aft movement and the SPRING/SHOCK (should) control the VERTICAL movement(s), and the VERTICAL movement SHOULD be the majority of the action on the track. If fore/aft takes over, then all bets are off (that is TOE-Steer and should be a very minimal consideration compared to the vertical components).
The camber limiter keeps the car from getting "too far from the ground"... the SPRING, keeps it from "dragging the ground" (so to speak). The SHOCK, helps to control the issues related to unwanted OSCILLATIONS between the spring and gravity.... If I am way off base, I hope someone MUCH smarter than me steps in to set you straight.
We (at least *I* <G>) try not to involve that "silly MATH thing" in these discussions. I rely much more on my BEHIND than my brain to determine optimum parameters of my car
( my ASS skills far exceed my MATH skills <g>) .Steve, FV80
(most likely my last post before POST Runoffs).
The Racer's Wedge and now a Vortech, FV80
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hardingfv32-1
- Posts: 1014
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Re: Rear Roll Resistance Never Needed
I'm not going to the Runoffs so I will work with you. Your issue is still not clear to me. Are we talking in the context of a normal zero roll suspension with all of is linkages? My no droop limiter setup uses all the same linkages of the standard suspension. The static camber setting and spring rate are the only really differences.
NOTE: My fully extended rear shock does act as a droop limiter (set at about 0 deg droop) to prevent wheel tucking during off road excursions.
The context of the whole tread was the need to control camber at some optimum rear camber level (max jacking point) with a droop limiter.
Brian
NOTE: My fully extended rear shock does act as a droop limiter (set at about 0 deg droop) to prevent wheel tucking during off road excursions.
The context of the whole tread was the need to control camber at some optimum rear camber level (max jacking point) with a droop limiter.
Brian
Re: Rear Roll Resistance Never Needed
Brian H. - I'm still unclear what the limiting factor is on your car then. Since you have so much more grip, what is holding back your car at this time?
Stephen Saslow
FV 09 NWR
FV 09 NWR