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    1. #1
      Join Date
      Aug 2004
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      PHB vs. Watt's Link

      I am planning for a new rear suspension for my Chevelle. I have read a substantial amount of past posts here and over at CC.com. I am looking for some opinions and some more clarification on the differences between running a Panhard Bar vs. a Watt's Link.

      Here are the positives that I have found for each:

      PHB mounted to the chassis on the left and the axle on the right...
      The asymmetrical behavior of the PHB will help counteract driveshaft torque and aid in rear wheel traction.
      Fewer parts to build and buy and less weight.

      Watt's Link with the pivot mounted to the chassis...
      Zero lateral movement of the rear axle.
      RRCH does not move in bump/roll relative to the sprung mass of the vehicle. Therefore the Rear Roll Moment does not change.
      More parts = more to build/buy and more weight.

      All of that being said, I am looking at this from a clean sheet of paper approach. And money and time to build are not my primary concerns at this point. Can anyone add to the positives or negatives of either. And can anyone give me their reasoning of why one would be preferred over the other in practical terms. I know that Katz mentioned that he liked the Watt's over the PHB back in Dennis's 3-link thread from this summer, but I haven't seen allot of direct comparisons between each.

      As always, thanks for you wisdom and assistance.

      R.J.



    2. #2
      dennis68 Guest
      Time and money are not a primary concern, how about packaging? that would be the only negative to a Watts. If you can fit it and don't mind having to buy/replace the added parts, I cannot think of 1 reason why not to run the Watts over a PHB.

    3. #3
      Join Date
      Jan 2004
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      NW Suburbs, Chicago
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      560
      well... packaging is one issue, and what about weight...

      now if its not going to be a full out racecar i dont see any major issue with weight either. but ive read a lot about this on CC.com and many of the guys use PHBs because of packaging and weight.

      along with that the gains from a watts arent anything majorly significant over that of a PHB

    4. #4
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      I'm assuming that it's either a torque arm or 3-link arrangement that we're discussing, rather than the addition of another means of lateral constraint to the OE 4-link or a Satchell . . .

      How about first deciding on where you want the rear roll center to be, and on how much ground clearance you need to maintain. That, in turn, depends on how much rear axle roll steer you want to end up with and the LCA inclinations (both plan and side views), and should be slightly higher than the front RCH. You may even want to start with some desired amount of anti-squat to get started from the LCA side view inclination.

      100% anti-squat is your likely target if the dragstrip is particularly important, and perhaps half that for road course/auto-x/open road (in the interest of avoiding brake hop without giving away any rear braking contribution). Maybe shoot for 3% - 5% roll steer (vehicle understeer). IIRC, Katz's car has 2% and if your Chevelle's OE geometry is anywhere close to the G-body's it's about 8%. As a general guideline, 7% has been considered too high for best slalom performance. BTW, all of these numbers are at static ride height, and will vary somewhat over suspension travel.

      If you're not quite sure where to spot the RCH, or want to retain the ability to fine-tune it later, a PHB that's adjustable for height would probably be easier to work up than a properly-done Watts with a similar feature.

      Packaging is likely to favor the PHB, though the diagonal brace to the passenger side frame rail that you should be using* isn't without its own effects on things like exhaust routing.

      *Without this brace your driver's side frame rail would be picking up a torsional moment in addition to the entire lateral force. With it, the lateral force is shared between the two rails (not quite equally, though) and the torsion is replaced by vertical forces.

      Norm
      '08 GT coupe, 5M, suspension unstockish (the occasional track toy)
      '19 WRX, Turbo-H4/6M (the family sedan . . . seriously)
      Gone but not forgotten dep't:
      '01 Maxima 20AE 5M, '10 LGT 6M, '95 626, V6/5M; '79 Malibu, V8/4M-5M; '87 Maxima, V6/5M; '72 Pinto, I4/4M; '64 Dodge V8/3A

    5. #5
      Join Date
      Aug 2004
      Location
      CA
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      452
      While I agree that PHB setup is lighter overall, I kinda have a doubt about the actual advantage.

      All lateral loading is transfered through a long single tube on PHB, therefore rod ends, PHB tube, mounts and everything else have to be pretty stout on 3000+lb cars.

      Assuming each linkage for Watt's is half the length of PHB, the linkage made of same material & cross sectional area will take 4 times more compressive axial loading w/o failure. Actually, it will probably be less than 4 b/c shorter links will increase angle per inch of suspension deflection, but shorter links still take a bunch more loading than longer ones. With two linkages to share the loading (one in tension and the other in compression), you can use lighter linkages and rod ends than PHB. Linkage mounts on axle also can be made lighter, especially if you don't make them height adjustable like on most PHB setup. I think, this will cut down on unsprung mass over PHB setup.

      The heaviest part of the Watt's (center bell crank) will be mounted relatively low at the centerline of the vehicle. More than likely it's way below the overall CG height of sprung mass, so I wouldn't worry about it. I really don't think the bell crank mount will be any heavier than PHB chassis mount. The Watt's mount can be integrated with crossmember for behind-axle coil over mounts (if you're running C/Os) to further reduce the weight.

      In terms of suspension geometry, chassis-mounted Watt's is theoretically better, as roll moment stays constant. Typical road race style PHB does change roll moment, usually 0.5" per inch of suspension travel. On a related note, RC moves in the opposite direction on some sprayed 4-links.

      Besides the obvious things like cost & packaging, the downside of Watt's is lack of adjustability as Norm already stated. You can only lower it so far before bell crank starts dragging on ground, and you'll still have RC 6~8" above the ground. But this may not be a consideration if you need 10" RC height to maintain good roll steer. It depends on skew angle, side view angle, as well as height of LCAs.

      I run PHB on my Riviera. Primary reason is the cost. Secondary reason is that it's my current R&D car so I needed lots of adjustability. BTW, Norm is correct that my design Roll steer is 2% understeer at 9" RCH. But due to large skew angle of LCAs, it varies from 7.7% roll understeer to 0.5% roll oversteer over the range of 8 ~ 12.5" RCH. Smaller skew angle will make roll steer less sensitive to the change of RCH. On the other hand, large skew angle will let you raise IC height therefore higher AS number.

      I am very happy with the PHB setup on my car, but I'd use Watt's on my next car if money's no object.
      The first step of becoming a better driver is to attend a track event, time yourself, and realize the fact you really suck.

      Signed,
      A driver who laps Big Willow at 1:42.6 in a 134hp BMW - and I am still considered mediocre.

    6. #6
      Join Date
      Aug 2004
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      McMurdo Station, Antarctica
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      Guys as usual thanks for the help.

      Dennis, Packaging is a potential problem on my car, but I think it could be accomplished without major surgury. That is part of the reason for the questions. I'm trying to decide if I should take the time to mockup a Watt's for the car, or just go straight to the PHB.

      Norm, Yes this is for a 3-link. As I mentioned I have been doing allot of reading and I was hoping to simplify things a bit by looking at one component at a time. And as I already knew and you have pointed out, they are all so very interconnected. I need a bigger head to stuff all of this info in.

      Well if I may I would like to revise my question then. I am confident that I can determine the Anti-squat and RRCH however I really don't know how to determine the roll steer. And now it is obvious to me that determining the amount of roll steer is related to the RRCH. My current thoughts are to use the stock LCA mounts on the frame, and I am building a new rear axle for the car so the axle mounts are open at this point. The stock A-bodies have a 21.750" long LCA and they are angled in towards the front similar to the G-body. The are at a 8.8 degree angle to the centerline of the car. Also currently the LCA's are level at ride height, and the pivot is 4.500" below the centerline of the axle.

      Can anyone describe for me how to determine the roll steer % or send me to a link or a book that describes it well. My current library of chassis books doesn't cover this.

      Thanks.

      R.J.
      R.J.


    7. #7
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      Look at post #11 (by Jon A) in this thread. Your roll steer % is the slope of dotted line AB identified as 'roll axis'. Downward sloping toward the front of the vehicle is vehicle roll understeer.

      Just to try to ward off the confusion that this picture from Millikens' RCVD may be bringing with respect to terminology, the 'roll axis' in this picture is the rear suspension's own roll axis, not the roll axis of the vehicle as a whole (Milliken refers to the vehicle roll axis as "Neutral Roll Axis", probably to provide some distinction between the two).

      Norm
      '08 GT coupe, 5M, suspension unstockish (the occasional track toy)
      '19 WRX, Turbo-H4/6M (the family sedan . . . seriously)
      Gone but not forgotten dep't:
      '01 Maxima 20AE 5M, '10 LGT 6M, '95 626, V6/5M; '79 Malibu, V8/4M-5M; '87 Maxima, V6/5M; '72 Pinto, I4/4M; '64 Dodge V8/3A

    8. #8
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      Post resubmitted after "page not found" message came back.

      Norm
      Last edited by Norm Peterson; 12-09-2004 at 01:33 PM. Reason: duplicate post
      '08 GT coupe, 5M, suspension unstockish (the occasional track toy)
      '19 WRX, Turbo-H4/6M (the family sedan . . . seriously)
      Gone but not forgotten dep't:
      '01 Maxima 20AE 5M, '10 LGT 6M, '95 626, V6/5M; '79 Malibu, V8/4M-5M; '87 Maxima, V6/5M; '72 Pinto, I4/4M; '64 Dodge V8/3A

    9. #9
      Join Date
      Aug 2004
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      Thanks Norm. I will read this over this weekend a likely come back with 6 more questions on Monday.
      R.J.


    10. #10
      Join Date
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      Have you seen the story in Hot Rod Magazine (Jan 2005 issue) about Peter Castellana's '67 Chevelle? Talk about coincidental timing . . .

      Norm
      '08 GT coupe, 5M, suspension unstockish (the occasional track toy)
      '19 WRX, Turbo-H4/6M (the family sedan . . . seriously)
      Gone but not forgotten dep't:
      '01 Maxima 20AE 5M, '10 LGT 6M, '95 626, V6/5M; '79 Malibu, V8/4M-5M; '87 Maxima, V6/5M; '72 Pinto, I4/4M; '64 Dodge V8/3A

    11. #11
      Join Date
      Aug 2004
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      No I haven't yet, however I have heard allot about it this week. Sounds like I'm going shopping during lunch break. :icon996:

    12. #12
      Join Date
      Aug 2004
      Posts
      957
      R.J,



      First, good for you in attempting to design and build your own setup, there is no better way to learn this stuff than to tackle it on your own. You are asking some good questions, and it seems like you are coming along well in your understanding of how things interact. But, those interactions are TERRIBLY important and cannot be taken lightly. At some point you are going to need to determine where the compromises you will be forced to take will come from, because you just can't have it all.



      Also a good choice, in my opinion, on the three link approach. It is simple, easy to fabricate, and has terrific theoretical advantages over most of the other link type setups. Some of the things that battle each other in this arrangement are the SVSA, A/S, and roll steer charcteristics. If you poke at one, something else will basically have to give. Where you choose to make the compromise will depend upon what you are really going to do with the car. For a high speed road course application, I'd sacrifice a bit of A/S for a suitable SVSA and roll steer behavior, for a street car that see some drag use, or cone killing, you might want to slip a bit the other way, and focus a bit more on A/S.



      Then there's the whole packaging issue. The temptation for most folks is to use the stock location for the LCA forward mounts, because it is already "there." At first glance, it seems like this is possible on your car from where you describe they are (I had a Chevelle years ago, but never thought too much about the rear suspension), but "may" be a bit on the short side. Also, the rear mounting point for the LCA is 4.5" fromt he axle centerline, or the bottom of the axle tube? Important distinction.



      As for the Watt's versus PHB, the PHB is incredibly simple, but doesn't necessarily have any weight advantage over a Watt's. I am doing the Watt's approach on my package, and I can tell that there is probably very little difference in overall weight, and unsprung weight probably goes to my advantage. Very tough to sneak tailpipes around though. I read a previous post on the bellcrank dimensions, there is no magic here as I have discovered. In relative terms, the longer the distance between the pivot and rod ends, the less relative rotaion angle as a function on bump, etc. But, it doesn't really rotate that much anyway. For the record, mine has a 2" distance (four inches between the rod ends). Make a scale model out of poster board, and use thumb tacks as the pivot points. You will be amazed at how simple, and effective the system works once you see it work with your eyes. Further, as far as the lateral downfall of the PHB, don't sweat it. The rear does not move laterally under bump very much at all, with a suitably long bar, you'll never probably notice. Either approach is very effective if exectuted correctly.



      Just as the layout of the overall system is important kinematically, the construction of the setup is also critical. If you are not a mechanical engineer, make certain you consult with one to determine if the brackets, etc, that you employ are up to the task. Don't compromise, you could end up getting hurt or hurting someone else if it fails at the wrong time.



      If you are really serious about doing this, I'd strongly advise getting fully up to speed on all aspects, which basically means reading Milliken about six times, and as many other relevant references you can get your hands on. In the end, I will tell you, you will be really proud of yourself, I know this first hand.



      Keep the good questions coming!

      Mark

    13. #13
      Join Date
      Aug 2004
      Location
      McMurdo Station, Antarctica
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      Mark,

      Thanks for the help and encouragement. As far as the mounting for the LCA, I am quite sure that it is 4.5" below the axle centerline. I will double check this weekend.

      As far as the comprehension of the design and interaction of all of the components, my goal is to get up to speed on the definition and determining all of the calculated points on the system. And then I can come up with what I think is a good start of a system and come to everyone for input. My goal is not to just come to the group and ask people to design my system for me, but just for assistance and direction.

      Currently my collection consists of:
      Chassis Engineering by Herb Adams
      How to make you car handle by Fred Puhn
      Paved Track Stock Car Technology by Steve Smith

      I have heard many people recommend Milliken many times, so I just ordered it from the local library. This way I can save a few $$$ before X-mas, and maybe I will get a copy under the tree.

      As far as the construction, no I am not a ME, but I have two that are more than willing to help. I actually am a Mechanical Designer so I am looking forward to solving any of the packaging issues. Also, I have a welder fabricator/ car builder that will be assisting me and watching over my shoulder during the process. And as far as the safety factor, I have been a firefighter for many years, and I have seen first hand the effects of high speed crashes. I like my body parts attached to their OEM places. :icon996:
      R.J.


    14. #14
      Join Date
      Aug 2004
      Location
      CA
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      452
      Quote Originally Posted by airrj1
      .... My goal is not to just come to the group and ask people to design my system for me, but just for assistance and direction....
      :icon996: That's why I like helping people like you, Dennis, baz67, and few others.

      With 8.8* skew (per side, I assume), you can probably drop down the LCA axle pivots slightly for increased AS. It can be done by either fab'ing new LCA brackets, or by making simple drop down brackets like in the pic below (excuse me for crappy pic quality).



      Figure out the ride height and RCH, set the LCA angles (for good roll steer characteristic), and let the UCA fall where it needs to be for desired SVSA. That's the simplified version of my typical 3-link design approach. I'm doing one for one of members here as we speak.

      Mark, how's your Camaro coming along?
      The first step of becoming a better driver is to attend a track event, time yourself, and realize the fact you really suck.

      Signed,
      A driver who laps Big Willow at 1:42.6 in a 134hp BMW - and I am still considered mediocre.

    15. #15
      Join Date
      Aug 2004
      Posts
      957
      I'm with Katz, it is really fun and makes me feel good to help out others, just I have gotten help from so many others in the past. Feel free to bounce anything you'd like off us, we're here to help. And by the way, Milliken is a funky book, I think it could be a bit better organized, and is defintely good material to help put you to sleep, it is pretty dry. You mentioned cc.com, you should post there, we'll be nice! Seriously though, there are some really talented racers on that site, you can learn a lot.

      I just got my copy of Hot Rod, and that 67 Chevelle is just awesome, and really simple in terms of the design approach: just the way I like it. It won't win any beauty contests either, which is just fine by me. The pic in there with the inner front wheel off the ground, while not the fastest way around the track, shows the incredible value of a good set of tires.

      Katz: The Camaro is coming along really, really well. I am assembling the engine and should be ready to drop it back in within a few days. All of the rear is complete and needs final assembly, although I am making one change to the bellcrank that should be done this week. Then, the only thing left is plumbing, I installed a fuel cell, and the brakes need new lines due to the floater rear end. I hope to be driving the car by x-mas. Like everything, lots of little setbacks here and there that kill the momentum of getting it done. I can't wait!!!!

      Mark

    16. #16
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      Last night I took the time to sit down and draw out my cars points and try to figure out the Roll Steer, AS, etc. Not exactly and not to perfect scale, but I must say that brought everything into perspective in my head. It is all much clearer now, I am amazed how much that helped.

      So it is time to got out in the snow and take exact measurement from the car, and then Monday at work I can start inputing it into Pro/E. Looks like there won't be allot of toys being built on Monday. :D
      R.J.


    17. #17
      Join Date
      Aug 2004
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      CA
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      Quote Originally Posted by Mean 69
      ...Katz: The Camaro is coming along really, really well. I am assembling the engine and should be ready to drop it back in within a few days. All of the rear is complete and needs final assembly, although I am making one change to the bellcrank that should be done this week. Then, the only thing left is plumbing, I installed a fuel cell, and the brakes need new lines due to the floater rear end. I hope to be driving the car by x-mas. Like everything, lots of little setbacks here and there that kill the momentum of getting it done. I can't wait!!!!

      Mark
      Excellent!! I'm planning to head down your way at least twice next year (El Mirage and OT event). I gotta hook up with you so I can check it out, or better yet, we can do an OT event together if schedule works out!
      The first step of becoming a better driver is to attend a track event, time yourself, and realize the fact you really suck.

      Signed,
      A driver who laps Big Willow at 1:42.6 in a 134hp BMW - and I am still considered mediocre.

    18. #18
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      Race Car Vehicle Dynamics

      Well I picked up a copy of Race Car Vehicle Dynamics by Milliken and well, I will get back to you about this subject in about 3 months when I reattach my head.

      It actually looks quite interesting and I look forward to digging in. I am sur that I won't be even close to catching it all, but anything is a good start.

      It is kind of interesting, several of the Techinal Contributors studied at University of Buffalo and/or worked at Calspan Corp. They are both a few miles from me. And I have several friends that work at Calspan, now General Dynamics.

      Thanks for the sugestions guys.

      Now all I want for Christmas is 1200 free hours to read this book. :icon996:
      R.J.


    19. #19
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      westchester county new york
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      Does anyone have photos of peter castellanas chevelle? I tried to search, but no luck.

    20. #20
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      I was going to toss in my opinion but looks like you guys have it covered. A PHR is an inexpensive, simple way to keep your rearend centered, However, in every other way a Watt's link is superior (except cost, weight). The biggest plus is that with a Watt's you car won't care if it's making right or left hand turns.
      "A ship in port is safe, but that's not what ships are built for."

      1968 Track Rat Camaro:
      https://www.youtube.com/watch?v=SGHJ5c1yLIo&t=2s

      1971 Chevelle Wagon with a few mods:
      https://www.youtube.com/watch?v=WBVPR3sRgyU

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