Leading arm attachment

hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

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Last edited by hardingfv32 on October 12th, 2015, 2:10 pm, edited 1 time in total.
FV80
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Re: Leading arm attachment

Post by FV80 »

hardingfv32 wrote:
FV80 wrote:It wasn't DIVE .. he was just LEANING the car. Negative camber on the outside, positive camber on the inside - no camber straight ahead. 3 position valve.
I would question whether this was ever possible....

Brian
Brian,
You are confusing cars. Harvey's FF Cigar car is the one that had the leaning front suspension - not any of his vees. I have edited my original post - I didn't really make that very clear.
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Re: Leading arm attachment

Post by FV80 »

brian wrote:I am under the impression that Harvey Templeton first used the zero roll concept on his one off car the Shadowfax. It may have been on his first car the Ringwrath as well but I'm not sure. Bill Caldwell had a version on the D-13 that took the concept to a production basis.

As for the leading arms I'm not sure who did it first since it showed up on several cars around the same time. The Vista, and James Brookshire's Agitatior were very early examples. Donnie Isley ran the very same Agitator at Daytona a few weeks ago. It's neat to see a car that's old enough to drink in the top ten at the Runoffs.
Brian (M),
You are correct. I just THOUGHT the Ringwraith was also ZR.

However, Donnie is not in JB's original car - JB has that in his shop at home. JB built this car for Donnie about 15 years ago .. or so. Donnie's as far as I know is the most recent (and likely the LAST) Agitator to be built. I'm not certain who had the oldest car at Daytona this year, but it was most likely Mark Edwards, although I'm not sure how much of the original Glamdring he was able to save after his horrendous crash a number of years ago.. Phoenix, I think it was - head on into the concrete at speed. Harry Schneider likely had the second oldest in his Adams Aero.
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hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

FV80 wrote: I'm not certain who had the oldest car at Daytona this year, but it was most likely Mark Edwards, although I'm not sure how much of the original Glamdring he was able to save after his horrendous crash a number of years ago.. Phoenix, I think it was - head on into the concrete at speed.
M Edwards' car had surprisingly little chassis damage form the Phoenix accident. The front roll hoop was cut away for driver removal. His ankle damage was really caused by driver movement in a chassis that does not have any space for leg movement. Now this is a very old car patterned after the Stan Towns' Sting. I am sure that the lower frame rails have been change once or twice.

Edwards runs both Major and Regional events. I think it would be safe to claim that is probably the highest milage individual FV that ever was built. I will check and see when it was built and first used. Possibly an interesting topic.

Brian
jpetillo
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Re: Leading arm attachment

Post by jpetillo »

hardingfv32 wrote:
FV80 wrote:With regards to one of Jim's original questions .. what is the purpose of the triangular structure that mounts at the tail with the heim joint? I believe its purpose is to control the fore/aft forces on the shock bell cranks that mount to the chassis. The pivots at the chassis have a SEVERE fore/aft load...
1) This is not correct. I am assuming a traditional rocker base bearing system. The brace we are talking about would travel in an arc (horizontal) and if attached to a moving (vertical) rocker would cause binding.
Agreed - it took me a few reads to understand what you were describing.
hardingfv32 wrote:2) If the axle pushrods off the rockers are parallel to the shock axis then there is almost no fore/aft force. This is part of the compromise you make when mounting the pushrods to the leading arm.
I think I agree with this.
hardingfv32 wrote:3) The vertical force acting on the base of rockers where they meet the chassis is not as great as most people think. A great deal of the vertical load is carried by the axle tube pivot area at the side plate. The purpose of the rocker is to help form the truss made up by the complete zero roll rocker assembly.
If the pushrods are at 45 degrees, and went all the way out to the wheel center, then the vertical force at the base of each rockers is 1/sin(45) = 1.41 times that of the sprung corner weight. That would be around 320 lbs. If the angle is about 30 degrees, then the vertical force is about 450 lbs. That should be right - what do you think? I don't think on the design in the picture that there is much vertical force on the axle tubes at the fulcrums.

John
hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

You are correct. My statement about the vertical force is incorrect.

Brian
Rickydel
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Re: Leading arm attachment

Post by Rickydel »

The Ringwraith did and does have ZRR rear suspension.
DFC17
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Re: Leading arm attachment

Post by DFC17 »

Just a little note on rear Motion Ratios.

Over the last 30+ years I have tried high and low motion ratios with the zero roll rear suspension. My conclusion is it doesn't matter. In fact my current rear suspension system (Modified BRD) has the lowest motion ratio of any system that I have ever made, or used, and it performs the best.

The fastest FV in the nation has the worst rear motion ratio of any Vee, or frankly any race car, I have ever seen.

The zero roll design is very unique and can not be engineered like a conventional suspension system.
Scott
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Re: Leading arm attachment

Post by FV80 »

I agree with you Scott. Although I haven't actually TRIED nearly as many setups as you, my car has bascially ZERO motion "ratio" and it seems to work pretty well. I've seen quite a number of cars with widely varying ratios.. some push, some pull, but basically they ALL *CAN* handle pretty well. It seems to just come down to proper shock valving and that adjustable NUT behind the steering wheel.
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hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

DFC17 wrote:The fastest FV in the nation has the worst rear motion ratio of any Vee, or frankly any race car, I have ever seen.

The zero roll design is very unique and can not be engineered like a conventional suspension system.
The same engineering that is used for a 'conventional suspension system' is used for a zero roll... or mono shock system.

Are you certain Varicins' mono shock system has a bad motion ratio? You have accurate knowledge of his shuttles dimensions?

Motion ratios are just one part of the suspension design puzzle. Not holding any more significance than any other part. Motion ratio is not an end target goal. Any valid research regarding changes in motion ratios would require appropriate spring and shock modifications made during a same day back to back test. Is that the type of testing you did?

Changing motion ratio without spring and shock mods is just basically a gross setup change. It could be better or worse than what you had before.

Brian
hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

FV80 wrote: It seems to just come down to proper shock valving and that adjustable NUT behind the steering wheel.
Spring/wheel rate.... and shock valving.

Brian
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Re: Leading arm attachment

Post by FV80 »

hardingfv32 wrote:
FV80 wrote: It seems to just come down to proper shock valving and that adjustable NUT behind the steering wheel.
Spring/wheel rate.... and shock valving.

Brian
Yep ... I MEANT to say that - spring/shock valving. The wheel rate is FIXED (pretty much). Can't change the wheel rate itself - just it's relationship to the spring.
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DFC17
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Re: Leading arm attachment

Post by DFC17 »

hardingfv32 wrote:
The same engineering that is used for a 'conventional suspension system' is used for a zero roll... or mono shock system.
I don't necessarily consider mono shock and zero roll to be the same. Even though they both use one shock they are different.
hardingfv32 wrote:Are you certain Varicins' mono shock system has a bad motion ratio? You have accurate knowledge of his shuttles dimensions?
I should have used the term "low" not "worst" my mistake. Yes, I would say that it is a low ratio. I might be wrong because I have never measured it, its just an educated guess based on my observations of the angles and the spring size.
hardingfv32 wrote: Motion ratios are just one part of the suspension design puzzle. Not holding any more significance than any other part. Motion ratio is not an end target goal.
Completely agree, especially when it comes to zero roll, that was the point of my original post.
Scott
DFC17
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Re: Leading arm attachment

Post by DFC17 »

FV80 wrote: Yep ... I MEANT to say that - spring/shock valving. The wheel rate is FIXED (pretty much). Can't change the wheel rate itself - just it's relationship to the spring.
Actually the wheel rate is not fixed. it is a calculation of the spring rate and the motion ratio and will change depending on both factors.
Scott
hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

FV80 wrote:... my car has bascially ZERO motion "ratio" and it seems to work pretty well.
I have thought on this and I am interested in how you physically accomplish your motion ratio... if it is not a big secret.

I assume ZERO means 1:1 ratio. I have found that getting to 1:1 is a very challenging packaging problem. About the only way I can think of is either a very high shock location or rockers that hang downward and have a pivot point in a very high location above the transmission on a special sub-frame. Either would make for a interesting exhaust system layout.

Brian
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Re: Leading arm attachment

Post by FV80 »

It depends on how you define "motion ratio"..
In my car, there is a single rod connecting the ends of the shock to the ends of the axles (actually, a triangular structure that attaches to the axle near the trans and another point at the end of the casting closest to the wheel). There are no other rocker arms and there are no bell cranks. So.. as the wheels move up, the shock moves IN and UP. Yes... it has been quite a challenge to get a decent exhaust system on it, but we have managed to do pretty well with this setup for .. oh... 30 years or so.
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hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

Your system would be similar to the Agitator? If so then you have a motion ratio on the order of 2:1... 2" travel at the wheel equals 1" at the coil over shock.

Motion ratio being the wheel travel movement vs the coil over shock travel.

Brian
jpetillo
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Re: Leading arm attachment

Post by jpetillo »

I like this discussion. Much of the reason to find the right motion ratio dependents on what your shock tolerates. You want the shock to move enough that its function is not dominated by stiction for small wheel movements where you want the shock to work for you, but on the other extreme not so much movement that you run out of travel. Then the valving needs to work for the piston speeds expected from that motion ratio. You can change motion rations, but where your shock transitions between low speed and high speed damping changes. I think that matters, and we should be concerned with that.

There's nothing magical about very large motion ratio suspensions (much lower shock movement - using Brian's definition of motion ratio) - it may just require a better engineered shock that will not have a stiction problem for small movements.

Although there is a big difference to me of how a single shock system compares in action to a double shock system, there is no reason I see where the motion ratio is any less important in a single shock design. Does anyone feel otherwise? John
jphoenix
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Re: Leading arm attachment

Post by jphoenix »

Why is zero roll only found on an FV? Is it not a suitable design for other class open wheel cars?
Jim Phoenix
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jpetillo
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Re: Leading arm attachment

Post by jpetillo »

Zero roll resistance in the rear puts the anti-roll duties to the front tires, which helps balance the front to rear grip. But, with the swing axle rear end and the standard single shock design, it helps control the rear tire camber better during cornering.
Last edited by jpetillo on November 1st, 2015, 3:38 pm, edited 1 time in total.
Speedsport
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Re: Leading arm attachment

Post by Speedsport »

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.
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Re: Leading arm attachment

Post by FV80 »

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.
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Re: Leading arm attachment

Post by brian »

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.
DFC17
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Re: Leading arm attachment

Post by DFC17 »

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
hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

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
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