Leading arm attachment

Moderators: Dietmar, smsazzy

Re: Leading arm attachment

Postby Speedsport » November 1st, 2015, 11:58 am

John's comment is spot on. The only real issue with a high motion ratio (short shock travel) is getting a shock to work well in that situation.

Other then that, i don't think it's possible to say a higher or lower motion ratio is better. What really matters is what the motion ratio does throughout the travel. Try plotting wheel movement vs. Shock movement on some of the standard bell crank systems and you'll get some funny looking graphs.
Speedsport
 
Posts: 167
Joined: October 20th, 2006, 7:45 pm
Location: Burlington, WI

Re: Leading arm attachment

Postby FV80 » November 1st, 2015, 12:09 pm

jphoenix wrote:Why is zero roll only found on an FV? Is it not a suitable design for other class open wheel cars?


The reason zero roll works well on a vee and not most other cars, is the SWING AXLE. MOST other chassis have CV type joints for totally independent suspension. IIRC the early small prod Sprites (or some cars like that) also had a swing axle and a few of those also sport ZERO Roll mods.
The Racer's Wedge, FV80
To sign up in the FV Registry for updates about SCCA Formula Vee, please go to http://www.FormulaVee.us/fvregistry_interface2/eEditor.asp?action=insert and enter the appropriate info.
User avatar
FV80
 
Posts: 1123
Joined: June 27th, 2006, 9:07 am
Location: Near Athens, GA

Re: Leading arm attachment

Postby brian » November 1st, 2015, 5:10 pm

The real demon in vw rear suspension is the tendency to hike up and reduce camber. Once positive camber is achieved, the car becomes diabolical. Zero roll tends to control hiking better than just limiters like the z bar or droop control. The Triumph Spitfires had swing axles and some experimented with zero roll. Had a customer with a 356 roadster that contemplated zero roll before retiring.

I know of a couple of FF that have run zero roll rear suspensions on the QT. They had a rocker installed on the pivot points inside the tranny spacer. Think of a DB-1 with two shocks mounted on one rocker. It apparently helped running smaller front tires on the rear. Word has it that a zero roll FF made it to the podium this year at Daytona.
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.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Leading arm attachment

Postby DFC17 » November 1st, 2015, 11:02 pm

brian wrote:The real demon in vw rear suspension is the tendency to hike up and reduce camber. Once positive camber is achieved, the car becomes diabolical. Zero roll tends to control hiking better than just limiters like the z bar or droop control. The Triumph Spitfires had swing axles and some experimented with zero roll. Had a customer with a 356 roadster that contemplated zero roll before retiring.


Brian, I don't think that rear suspension jacking happens on all Vee's. I believe the COG of a Vee, compared to a beetle, is to low. My FST has a droop limiter, however, it does not engage until the rear camber exceeds +5 deg of camber, which never happens on the track. I think Brian H. proved this years ago.

brian wrote:I know of a couple of FF that have run zero roll rear suspensions on the QT. They had a rocker installed on the pivot points inside the tranny spacer. Think of a DB-1 with two shocks mounted on one rocker. It apparently helped running smaller front tires on the rear. Word has it that a zero roll FF made it to the podium this year at Daytona.


I doubt the FF was a zero roll, maybe a mono shock. The FF's I have seen that have mono shock front suspensions are definitely not zero roll.


Scott
Scott
DFC17
 
Posts: 14
Joined: July 27th, 2015, 9:42 pm

Re: Leading arm attachment

Postby hardingfv32 » November 2nd, 2015, 12:57 pm

1) 'Zero Roll' is a colloquial term used in FV to describe a mono shock system that does not use any form of roll resistance. It is extremely unlikely that a mono shock FF suspension would not have some form of roll resistance... thus it is not correct to call it a zero roll system. I have never seen a mono shock system on any race car other than FV that did not have some form of roll resistance.

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.

Brian
hardingfv32
 
Posts: 93
Joined: June 9th, 2015, 8:04 pm

Re: Leading arm attachment

Postby jpetillo » November 3rd, 2015, 12:34 am

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
jpetillo
 
Posts: 740
Joined: August 26th, 2006, 2:54 pm
Location: MA

Re: Leading arm attachment

Postby brian » November 3rd, 2015, 2:46 pm

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.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Leading arm attachment

Postby jpetillo » November 3rd, 2015, 10:18 pm

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
jpetillo
 
Posts: 740
Joined: August 26th, 2006, 2:54 pm
Location: MA

Re: Leading arm attachment

Postby brian » November 4th, 2015, 4:49 pm

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.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Leading arm attachment

Postby jpetillo » November 5th, 2015, 1:20 am

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
jpetillo
 
Posts: 740
Joined: August 26th, 2006, 2:54 pm
Location: MA

Re: Leading arm attachment

Postby brian » November 5th, 2015, 2:39 pm

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.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Leading arm attachment

Postby hardingfv32 » November 5th, 2015, 2:41 pm

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
 
Posts: 93
Joined: June 9th, 2015, 8:04 pm

Re: Leading arm attachment

Postby hardingfv32 » November 5th, 2015, 5:52 pm

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
hardingfv32
 
Posts: 93
Joined: June 9th, 2015, 8:04 pm

Re: Leading arm attachment

Postby jpetillo » November 6th, 2015, 1:00 am

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: 740
Joined: August 26th, 2006, 2:54 pm
Location: MA

Re: Leading arm attachment

Postby jpetillo » November 6th, 2015, 1:17 am

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: 740
Joined: August 26th, 2006, 2:54 pm
Location: MA

PreviousNext

Return to Tech Tips, Rules, and Safety

Who is online

Users browsing this forum: No registered users and 1 guest