Leading arm attachment

jpetillo
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Joined: August 26th, 2006, 2:54 pm

Re: Leading arm attachment

Post by jpetillo »

hardingfv32 wrote:2) Rear suspension jacking happens in all FV's... all cars using a swing arm suspension for that matter. That is not to say that the amount of jacking can not be controlled or limited. I would say that the CoG has nothing to do with jacking.
I agree with that - CoG has nothing (or little) to do with jacking.

Probably the fact the Vees are not nearly as softly sprung is the main reason they don't jack excessively - compared to a Beetle. John
brian
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Joined: June 26th, 2006, 12:31 pm

Re: Leading arm attachment

Post by brian »

Brian's right about the FF approach to connecting the shocks on a cross compensating bracket. Like that name? It's not really zero roll or mono shock, and I don't know what to call it. He's right about the use of anti roll bars as well. I have seen a DB-1 with both shocks going down into the bell housing and being attached to a common rocker and another car with the two front shocks linked inside the frame. Neither is a mono shock system like the front VD approach a few years ago but are clearly trying to transfer forces across the car.

Am I correct in thinking that this is an attempt to transfer weight and get better bite on the inside?
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
jpetillo
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Joined: August 26th, 2006, 2:54 pm

Re: Leading arm attachment

Post by jpetillo »

I'm not sure it's an attempt to transfer weight - I would think the opposite. But, it depends on what you mean. So, let me say it differently, the zero roll resistance is an attempt to transfer the minimum weight possible, and if you can keep the tires at the optimum camber, you maximize grip. As you add in roll resistance, you add more weight transfer, you lose grip. But, roll resistance in many cases is required to keep the tires near optimum camber, so you lose some grip to weight transfer, but gain from improved camber. I'm thinking that's what you meant. John
brian
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Joined: June 26th, 2006, 12:31 pm

Re: Leading arm attachment

Post by brian »

Thanks John, this part is confusing for me. I recognize that the weight transfer is less since it is transferred via the mono spring and the higher the spring rate, the more the transfer but it's much less than via a anti roll bar. If a car has too much anti roll, the inside tire will raise off the ground. To me as a tire is lifted from weight transfer can't have grip. Since we rely on front roll bars to control roll on our vees, we end up varying the load on the outside front tire. There must be a compromise between load and lifting the inside tire. I have never liked droop cables on the front since they tend to lift the inside tire as well.

I think the key is to limit rear roll without resorting to anti sway bars.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
jpetillo
Posts: 754
Joined: August 26th, 2006, 2:54 pm

Re: Leading arm attachment

Post by jpetillo »

Brian, I agree with everything you said, except "the higher the spring rate [for a monoshock], the more the transfer" In a zero roll resistance monoshock like we run in the back, the rear spring rate does not affect the rear weight transfer. That is why with this zero roll resistance monoshock system, the rear weight transfer is essentially the minimum possible, all other things remaining the same. Would you agree? John
brian
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Joined: June 26th, 2006, 12:31 pm

Re: Leading arm attachment

Post by brian »

I guess I am assuming that some weight is transferred across via the spring. If there is an upward push on the outside tire doesn't that translate to a downward push on the inside tire. The spring is pushing on something to be resist compression.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
hardingfv32
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Joined: June 9th, 2015, 8:04 pm

Re: Leading arm attachment

Post by hardingfv32 »

1) Simply stated the rear spring of zero roll rear suspension is only maintaining the rear ride height.

2) A) There is about 110 lb front and 160 lbs rear weight transfer on the average FV in a 1g corner. Zero roll resistance does not mean zero weight transfer.

B) The front FV sway bar is a camber control device. The traditional sway bar system on a std race car varies the the ratio of front to rear resistance to make balance adjustments. Without some form of roll resistance in the rear of the FV you cannot use the front sway bar in a traditional manner. The key take away from this is... you are missing a significant chassis balance tuning system if you do not have a rear sway bar.

C) "Since we rely on front roll bars to control roll on our vees, we end up varying the load on the outside front tire." You can change the rate or timing of the front load transfer but the total (amount upon reaching steady state in a turn) is always the same regardless of the front sway bar size. How can the front load vary if by definition the rear zero roll system is not accepting any load transfer? Where would it go??

D) Balance is determined by front and rear grip levels. Front roll bars are just one tool of many that can be used on the front or rear suspension to modify grip levels. Loose car: Nothing wrong with degrading the front end when it is required to achieve balance... this assumes that you have maxed out the rear end performance.

Brian
hardingfv32
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Joined: June 9th, 2015, 8:04 pm

Re: Leading arm attachment

Post by hardingfv32 »

brian wrote:I guess I am assuming that some weight is transferred across via the spring. If there is an upward push on the outside tire doesn't that translate to a downward push on the inside tire.
The spring has nothing to do with weight transfer. Chassis roll is just an indication of weight transfer but is not necessary for there to be weight transfer. A gokart has weight transfer with no body roll for example.

The spring like the sway bar dictates the amount of roll and the timing of the weight transfer. The total amount of weight transfer is not effected by either the spring or sway bar. There is no spring variable in the weight transfer formula or calculation.

Brian
jpetillo
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Joined: August 26th, 2006, 2:54 pm

Re: Leading arm attachment

Post by jpetillo »

hardingfv32 wrote:1) Simply stated the rear spring of zero roll rear suspension is only maintaining the rear ride height.

2) A) There is about 110 lb front and 160 lbs rear weight transfer on the average FV in a 1g corner. Zero roll resistance does not mean zero weight transfer.

B) The front FV sway bar is a camber control device. The traditional sway bar system on a std race car varies the the ratio of front to rear resistance to make balance adjustments. Without some form of roll resistance in the rear of the FV you cannot use the front sway bar in a traditional manner. The key take away from this is... you are missing a significant chassis balance tuning system if you do not have a rear sway bar.

C) "Since we rely on front roll bars to control roll on our vees, we end up varying the load on the outside front tire." You can change the rate or timing of the front load transfer but the total (amount upon reaching steady state in a turn) is always the same regardless of the front sway bar size. How can the front load vary if by definition the rear zero roll system is not accepting any load transfer? Where would it go??

D) Balance is determined by front and rear grip levels. Front roll bars are just one tool of many that can be used on the front or rear suspension to modify grip levels. Loose car: Nothing wrong with degrading the front end when it is required to achieve balance... this assumes that you have maxed out the rear end performance.

Brian
Brian, I agree with everything you said here - well said. John
jpetillo
Posts: 754
Joined: August 26th, 2006, 2:54 pm

Re: Leading arm attachment

Post by jpetillo »

hardingfv32 wrote: The spring has nothing to do with weight transfer.
In zero roll resistance with our standard rear setup - yes.
hardingfv32 wrote:Chassis roll is just an indication of weight transfer but is not necessary for there to be weight transfer.
Agreed.
hardingfv32 wrote:A gokart has weight transfer with no body roll for example.
But, this is for a different reason. Two things affect weight transfer, 1) the force on the center of mass, which is the weight transfer in the rear of a zero roll resistance single shock rear ends, and 2) whatever force resists the body roll around an axis connecting the front and rear roll centers. Our front ends have both forms of weight transfer. The springs and anti roll bars in the front keeping the car from rolling add weight transfer. For the go kart, the "rigid" chassis becomes the spring.
hardingfv32 wrote:The spring like the sway bar dictates the amount of roll and the timing of the weight transfer. The total amount of weight transfer is not effected by either the spring or sway bar. There is no spring variable in the weight transfer formula or calculation.
The first sentence is true, and we need to add in the shock for the timing. However, I don't believe either of the last two sentences is true for a standard suspension, like what we have in our fronts with separate springs and an anti roll bar. Anything that resists roll (rigidly mounted separate springs or ARBs) adds weight transfer. Your statement B) above is correct, though, where the ARBs are used to balance the car by affecting weight transfer at one end vs. the other. Do you agree? John
jpetillo
Posts: 754
Joined: August 26th, 2006, 2:54 pm

Re: Leading arm attachment

Post by jpetillo »

brian wrote:I guess I am assuming that some weight is transferred across via the spring. If there is an upward push on the outside tire doesn't that translate to a downward push on the inside tire. The spring is pushing on something to be resist compression.
I go along with Brian H. on this, yes, definitely, some weight is transferred across the spring, but only so far as it's the means to hold the car up. If you replace the spring with a bar in the zero roll resistance setup, the weight transfer is identical, so it's independent on spring rate.

With the zero roll resistance single spring suspension, the spring can only apply the same force to each tire. If you hit a bump with one tire, the other one feels it as the force is equalized (I'm taking about a zero mass component suspension). Here a different spring rate will soften the jounce differently, but the tires get the same force added by the jounce. In this case, the effect of the jounce is shared across the spring to each tire equally. Maybe this is what you've been talking about.

But, this is different than weight transfer due to cornering. If we consider cornering being similar to tilting the car (it's not the same, just similar), the COM comes through at an angle, and the additional weight transfer is provided mechanically through car. In other words, if we just consider the joint between the transmission and the axle tube of the outer tire, when the car is not cornering, there is no sideways force along the axle (let's neglect the suspension arms being on angle because the suspension arm on each side has the opposite force, or we can make them vertical, in actuality so they do not contribute to side forces). Once we go into a corner there is now a sideways force along the axle tubes. This force is what causes the weight transfer. It adds on the outer side and gets less on the inner side. The spring, as Brian H. said, is just holding the car in position, and its role has not changed, nor has the force on the spring changed if the car is on a flat surface.

Again, this is only for zero roll resistance monoshock suspension we run.

John
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