Leading arm attachment

jphoenix
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Leading arm attachment

Post by jphoenix »

Here's another question for the FV folks who would know: I saw this axle flange arrangement on an FV (Protoform I think) and I was wondering what the advantage is of this arrangement - that is where the zero-roll rod attaches to the axle flange (machined aluminum part bolted to the axle housing flange) - well below where the rod would normally attach - and normally is attached to the leading arm.

Does picking up that axle housing pivot point below the leading arm afford some better geometry to the zero-roll setup? Note the small clearance between the wheel inner flange and the machined part attaching the rod and leading arm.

Two other items of note -

The leading arm-to-frame attach points appear to be level with the axle housing attach points - is that the best location or is there some distance above or below the axle housing attach point that is optimum for the leading arm-to-frame attach point?

There is a triangular brace above the transaxle attaching to the frame between the leading arm-to-frame attach point - just below the rain light. That small triangular from goes forward and is attached to the zero-roll support - would that small frame be present to provide some support for the rear portion of the frame - or is it supporting the zero-roll structure?
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Jim Phoenix
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hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

jphoenix wrote:Does picking up that axle housing pivot point below the leading arm afford some better geometry to the zero-roll setup?
1) If we assume you have fixed wheel rate setup number.. all this arrangement does is decrease the force pulling out on the axle housing to side cover bearing surface. Hard to say if this is net good or bad. In a corner the axle housing is pushed inward do to cornering forces so an outward pull might help reduce net suspension movement friction. The arrangement shown would increase net friction in a turn... I believe.

I think you might have to change spring to maintain your original wheel rate setting.

Note: The only think most zero roll mechanism do is maintain rear ride height. Some might have a some form of spring rate variability but nothing significant and of questionable importance. The zero roll mechanism plays no roll in how a the rear suspension performs other than to provide a spring/wheel rate and of coarse no roll resistance.

2) The attachment point height determines the amount of bump/roll steer. You determine what you need for your car.

3) The small rear triangular bracing is to provide support for the braking force being transferred in from the control arms. The zero roll mechanism does not need additional support.

Brian
jpetillo
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Re: Leading arm attachment

Post by jpetillo »

I pretty much agree with Brian's response. I see two benefits in that location point on the rear axle. The first as Brian mentioned is that the side force on the axle can be reduced. This happens any time you move the attachment point out while keeping the suspension rod at the same angle, or keeping the axle attachment point the same and making the rod angle more vertical. This side force will add to (on the outer side) or subtract from (on the inner side) the side forces due to cornering.

The other advantage is it lowers the whole rear suspension (including the shock) while while leaving the suspension action the same - so decreasing COM. From the picture it looks like everything was lowered a good number of inches. Very nice!
jphoenix
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Re: Leading arm attachment

Post by jphoenix »

thanks for the info guys, I've never seen an arrangement like this one. It's interesting.
Jim Phoenix
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FVartist42
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Re: Leading arm attachment

Post by FVartist42 »

It's a copy of a Ron Chuck design. The design has evolved, you'll have to contact him for more information. The second design is only on one car that I know, but will probably be on another soon.

Bruce
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Re: Leading arm attachment

Post by hardingfv32 »

jpetillo wrote: This side force will add to (on the outer side) or subtract from (on the inner side) the side forces due to cornering.

The other advantage is it lowers the whole rear suspension (including the shock) while while leaving the suspension action the same - so decreasing COM. From the picture it looks like everything was lowered a good number of inches. Very nice!
Not so nice..... Not a well thought out modification



2) You do not want to add side force to the already highly loaded outside wheel. It only reduces the freedom of the suspension to move while in the turn. This modification does not provide a contracting force (while in the corner) normally seem by the standard FV rear suspension. The standard design actually reduce the side force of the outside wheel in a corner... I believe.

3) This modification does not change the position of the rockers or shock... so the CG is not lowered. It does add unsprung weight to the rear wheel assembly. The mounting bracket on the axle flange has to be massive to handle the the terrible force path that is being used.

The negatives out way the positives with this design. Unfortunately designs like this are a very common occurrence in FV.

Brian
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Re: Leading arm attachment

Post by jphoenix »

Does the lowered droop rod attach point (is that the correct terminology for the rod that goes up to the spring bellcrank?) allow some of the braking forces to be captured by that rod? Unlike my "normal" FV which has all braking loads transferred to the leading arm first, then to the droop rod attached to the leading arm.
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Re: Leading arm attachment

Post by hardingfv32 »

No

The brake forces are best controlled by an arm that is parallel to the wheel such as the original VW rear suspension design. The rear control arm design becomes progressively more compromised as you move away from this original design.

Brian
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Re: Leading arm attachment

Post by brian »

This design has been around for quite a few years. Ronnie made an aluminum plate for the bracket, but several cars have had the push rod out to the wheel vs. somewhere on the trailing arm for a long time. My understanding is the design allows the spring and wheel rate of travel to be closer to one another. If you look at most more technically inclined cars, all have the push, or pull, rods going all the way out to the wheel. A push rod that goes to say the mid point of the trailing arm will only move the shock and spring half the distance that the wheel is moving. I have been told by shock folks that moving the shock more will make it more responsive.

I converted my car to this concept last year and am still developing it. The effective spring rate changes and I'm still chasing the perfect spring set up. It appears to have made my shock more responsive to changes and that was a target for me. The project is far from finished but a track record this year at Buttonwillow has bolstered my belief that it is worthwhile.

The bracing you see in the picture provided was installed by Jess Heitman, also the guy from whom I got my aluminum plates. He added bracing to the Protoform cars he was preparing primarily to reduce general flexing witnessed with the cars. He had not mentioned braking specifically, but I know there's a lot of issues regarding braking and reward trailing arms.

An additional benefit of mounting the push rods at the wheels is that I am no longer using the trailing arms as mounts and am considering a winter project to convert my car to forward mounted arms. I've driven both types of cars and consider the front mounted cars capable of anti dive geometry and much more stable under braking
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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Re: Leading arm attachment

Post by hardingfv32 »

The motion ratio is changed to create more travel at the shock. This makes the compromises made by this modification even more interesting. I learned a new trick today.

Did you re-valve your rear shock to compensate for the change in motion ratio? Did you calculate or model what the actual number would be? I have the change on the order of 40% increase indicating a change in the shock valving to get back to baseline.

Better tire/wheel compliance is the ultimate goal of any suspension change. This is better measured with back to back testing using sector times on a test day. A new track record is a pretty broad measure with a lot of variables involved. I think there can be a bias involved when one has an opinion that some change is beneficial or the see others using the modification. It is easy to do when it is difficult to quantify the pros and cons of a modification like this. As an example I have never seen any data or research on a shock that is allowed to travel more for a given situation. Should be beneficial.. but is it a statistical significant number that translates into more grip?

Brian
jphoenix
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Re: Leading arm attachment

Post by jphoenix »

brian wrote:T
An additional benefit of mounting the push rods at the wheels is that I am no longer using the trailing arms as mounts and am considering a winter project to convert my car to forward mounted arms. I've driven both types of cars and consider the front mounted cars capable of anti dive geometry and much more stable under braking
Brian, when you say forward mounted arms - do you mean trailing arms as in a Womer? Or are you talking leading arms mounted on the forward side of the axle flange?

Is you car currently leading arm or trailing arm?

I see what you mean about more shock travel - interesting.
Jim Phoenix
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brian
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Re: Leading arm attachment

Post by brian »

I apologize for the language issues. To me, if the arms are in front of the axle it's called a trailing arm and the rear mounted arms should be called leading arms but in general usage both are called trailing arms. I have been able to design most of the short comings out of the rear mounted style but still experience issues under hard braking. Hence the desire to go to front mounted arms this winter.

I stayed at a Holiday Inn, but it didn't really help my math Brian. I am an accountant by training so anything beyond adding and subtraction is a challenge. I cannot do the math to calculate most engineering issues. I tend to ball park and then tune by performance and feel. The Penske compression procedure is to start at full soft and eliminate bleed until the car gets skittish then back off one or two clicks. In the case of my shocks, using a cockpit adjustable shock really helps. I change the bleed settings and get an idea if the valving is high or low. In other words, if I completely close the bleed and the shock still is not dampening enough, I know to go up a step in shim pack. Likewise, if I back off all the bleed and the shock is getting better, but not there yet, I know I need to go down in shim pack. Not really scientific but it works pretty well unless you're changing springs at the same time. I prefer to do one thing at a time. The rule of thumb I have been taught is that if you go up in spring rate, you go down in compression and up in rebound with the shim pack. The basis is that the higher spring will do some of the compression control that the shock had been doing and since there will be more energy stored from the higher spring, you have to go up in rebound.
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.
jphoenix
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Re: Leading arm attachment

Post by jphoenix »

I may be wrong, but it sure seems like trailing arms would be a simpler installation in that you don't need a lot of structure aft of the transaxle mounts. Looking at some Womer photos, it looks like some structure is required above the lower frame rail to attach the trailing arms at the same level as the axle flanges - and the rear shock and bellcranks bolt to the transaxle.
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Re: Leading arm attachment

Post by jpetillo »

hardingfv32 wrote:Not so nice..... Not a well thought out modification

2) You do not want to add side force to the already highly loaded outside wheel. It only reduces the freedom of the suspension to move while in the turn. This modification does not provide a contracting force (while in the corner) normally seem by the standard FV rear suspension. The standard design actually reduce the side force of the outside wheel in a corner... I believe.
I agree that you don't want to add any additional side force, for the reason you mention. I'm confused by you saying that this is not the standard design. It is, in that it's a shock over the tranny design and the suspension links push down and out where it attaches to the axle/wheel. What I was saying was since the link is connecting to the axle further out, then it has more leverage over the axle and the force along the link is less, and so the force out parallel to the axis is less.
hardingfv32 wrote: 3) This modification does not change the position of the rockers or shock... so the CG is not lowered. It does add unsprung weight to the rear wheel assembly. The mounting bracket on the axle flange has to be massive to handle the the terrible force path that is being used.

The negatives out way the positives with this design. Unfortunately designs like this are a very common occurrence in FV.
Brian
Perhaps you're right about the shock being in it's original position on this car, and so not lowering the CG. However, on my car such a design would lower my CG. I'm not sure about the rest, but without seeing it in person, it would be hard to argue for or against what you say.

John
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Re: Leading arm attachment

Post by brian »

The rear structure and tranny mount is much stronger than just hanging the tranny off the end of the chassis. I've seen trannies ripped off the chassis in serious accidents.
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.
gbrianmetcalf
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Re: Leading arm attachment

Post by gbrianmetcalf »

brian wrote:This design has been around for quite a few years. Ronnie made an aluminum plate for the bracket, but several cars have had the push rod out to the wheel vs. somewhere on the trailing arm for a long time. My understanding is the design allows the spring and wheel rate of travel to be closer to one another. If you look at most more technically inclined cars, all have the push, or pull, rods going all the way out to the wheel. A push rod that goes to say the mid point of the trailing arm will only move the shock and spring half the distance that the wheel is moving. I have been told by shock folks that moving the shock more will make it more responsive.

I converted my car to this concept last year and am still developing it. The effective spring rate changes and I'm still chasing the perfect spring set up. It appears to have made my shock more responsive to changes and that was a target for me. The project is far from finished but a track record this year at Buttonwillow has bolstered my belief that it is worthwhile.

The bracing you see in the picture provided was installed by Jess Heitman, also the guy from whom I got my aluminum plates. He added bracing to the Protoform cars he was preparing primarily to reduce general flexing witnessed with the cars. He had not mentioned braking specifically, but I know there's a lot of issues regarding braking and reward trailing arms.

An additional benefit of mounting the push rods at the wheels is that I am no longer using the trailing arms as mounts and am considering a winter project to convert my car to forward mounted arms. I've driven both types of cars and consider the front mounted cars capable of anti dive geometry and much more stable under braking
Brian
This was an idea I had for the next generation Lazer suspension. I had a couple of customers break the leading arm at the attachment point half way down the arm. I designed an arm that had a longer "duck foot" that accommodated the suspension attachment.
G.
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Re: Leading arm attachment

Post by FV80 »

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 in addition to the side to side loads of normal suspension travel. Ideally, the shock is (and stays) PERFECTLY centered along its load axis.. but that is generally not the case. A very minor move of the loads through the shock in fore/aft puts extreme force on those lower pivots. The triangular section back to the rear will significantly 'control' the fore/aft loads, thereby reducing the wear on the lower pivots. This has nothing to do with braking forces .. it's just the general 'pitching' of the shock on those long arms back to the frame at the bottom.
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Re: Leading arm attachment

Post by jphoenix »

That makes sense Steve. Any movement of that shock and its bellcranks fore and aft would be uncontrolled (un-dampened and un-sprung) "slop" so to speak in the suspension.

I'm currently trying to understand the advantage of leading arms (seems most popular in the zero-roll setup) over trailing arms. Seems trailing arms would be simpler to fabricate with less load carrying structure behind the tranny bellhousing mounts - ala Womer and the vintage cars.

Warning - thread drift - who developed the first zero-roll suspension in the FV; I don't believe I've ever heard the story of its invention and have never seen it on any other race or street car that I can recall?
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Re: Leading arm attachment

Post by FV80 »

jphoenix wrote: Warning - thread drift - who developed the first zero-roll suspension in the FV; I don't believe I've ever heard the story of its invention and have never seen it on any other race or street car that I can recall?
Jim,
I guess, since it's YOUR thread, we can let you squeak by on this one.
The general lore of FV says that Harvey Templeton designed and constructed his first FV .. The RingWraith - named after a character from The Lord of the Rings Trilogy by J.R.R Tolken I think that was 1968. Harvey's second car was the first zero roll car. He was assisted in the conception by Ed Zink - another historical name and the designer of the Zink series of Vees and Fords.

The current owner of the RingWraith ... as well as the Shadowfax, is Mike Jackson - president of the VSCDA (http://vintagevees.com/) I believe. More about these cars can be found on the formulavee website at http://formulaveeusa.org/gallery45/Ringwraith.pdf. Harvey's 2 cars are the ONLY zero roll cars allowed in vintage racing .. a true tribute to an historical figure in FV. I sat in the Shadowfax once .. didn't think I would ever get IN .. or OUT. A myriad of bars in there.

Interestingly, although Harvey's cars were wildly successful.. he never managed to win the Runoffs, despite several attempts. His cars DOMINATED every where he ran .. except at the Runoffs. He and I shared a birthdate (Sept. 15) except that he was 40 years ahead of my time :lol: . He died in 2003 IIRC at the age of 94. His son, Harvey Jr. raced in SCCA a couple of times in Harvey's 'cigar car' FF, before Harvey's nephew, Handley, took it over and ran it off and on for several years in SEDIV. I presume the car has finally been retired - I have not seen it in quite a few years now. Probably still parked in Handley's garage. Another tidbit .. the Cigar car (Harvey's FF car he built after leaving FV) started life with a front 'PITCH' suspension. Harvey designed the car to LEAN into the turns using hydraulic pressure to move suspension mounting points (WOW). Although it technically worked, the car pitched quite savagely initially, making it quite a handful to drive. Harvey slowed it down and it was more manageable, but he eventually canned the idea and went back to normal suspension -- too much complexity and maintenance for the minimal advantage gained. That car also had the radiator mounted HORIZONTALLY along the left side .. like a STEP... but he wouldn't want you to step on it.

Harvey's wife, Jewell, CLIMBED MOUNTAINS for kicks. Not sure when she stopped .. or if she is still around (not likely), but she was still climbing after Harvey moved to FF and the cigar car .. and he was close to 75 I think at that time. He, like Paul Newman, used to always run his AGE as his car number. He named his FF as the HR7260 - the House Resolution that passed the bill creating Social Security.
Ah.. I found an Apex post when he died. It confirmed at least some of my fading memory :lol: http://www.apexspeed.com/forums/showthread.php?t=179
Wow.. memories .. faded or not
wish I could find that picture of him in the cigar car with the red balls, decreasing in size running down the back of his car .. the first ball was on his helmet
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Re: Leading arm attachment

Post by FV80 »

Found another pdf about the Shadowfax at http://teamtac.org/e107/e107_files/publ ... dowfax.pdf
Also found a small pic of his FF with the balls :lol: down near the bottom of the page http://www.thekentlives.com/index.php/photos/
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jphoenix
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Re: Leading arm attachment

Post by jphoenix »

Very cool, great reading, thanks Steve! Can't imagine the hydraulic dive front suspension - and I've restored a Citroen (including the insane hydraulic system) recently!
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Re: Leading arm attachment

Post by FV80 »

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.
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hardingfv32
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Re: Leading arm attachment

Post by hardingfv32 »

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.

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.

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.

Remember there are zero roll rear suspension systems that do not have rockers mounted to the chassis. They use towers mount to the axle tube to help form the suspension truss.

Brian
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Re: Leading arm attachment

Post by hardingfv32 »

jphoenix wrote: Seems trailing arms would be simpler to fabricate with less load carrying structure behind the tranny bellhousing mounts - ala Womer and the vintage cars.

Warning - thread drift - who developed the first zero-roll suspension in the FV; I don't believe I've ever heard the story of its invention and have never seen it on any other race or street car that I can recall?
1) Trailing arms are not necessarily easier to fabricate. Depending on the length... they could be lighter in general. Mounting to the chassis forward of roll hoop can be a challenge depending cooling duct location and a number of other variable. I have reviewed these comprises for both leading and trailing arms for each car I have built and it really does not matter which system you use. The overall design of the car plays the largest roll in deciding which way you go.

2) The leading arm and zero roll are actually two separate developments. The leading arm system was first developed by Stan Towns for the Sting.

Brian
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Re: Leading arm attachment

Post by brian »

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.
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.
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