One of my improvements to be accomplished while the snow is on the ground is to add a panhard rod to my rear axle setup. Curtis has a very neat looking setup on his car, and I think that that is the way I'm headed with mine. Curtis, do you have ant photos of the axle end of the rod? How about dimensioned drawings for the frame end? Chris in Salt Lake.
Thanks for kind words Chris. I actually don't have a photo of the axle bracket. It's just a short piece of 2" by 2" by 1/8" wall mild steel box tubing, cut with a fishmouth at one end and MIG welded to the Ford axle housing (outboard of the leaf spring). The centerline of the rod end ended-up about 5.75" behind axle centerline.
The rod itself is nominally 37" long (spherical bearing center-to-center), and it runs with its centerline parallel to the ground and about 4" below the trunk floor. The height could easily be moved 0.75" higher or lower at the chassis-bracket end by enlarging pilot holes that are kinda hard to see in the snapshot below.
PanhardBrkts.jpg
Moderator Wrote:
-------------------------------------------------------
> Thanks for kind words Chris. I actually don't have
> a photo of the axle bracket. It's just a short
> piece of 2" by 2" by 1/8" wall mild steel box
> tubing, cut with a fishmouth at one end and MIG
> welded to the Ford axle housing (outboard of the
> leaf spring). The centerline of the rod end
> ended-up about 5.75" behind axle centerline.
>
> The rod itself is nominally 37" long (spherical
> bearing center-to-center), and it runs with its
> centerline parallel to the ground and about 4"
> below the trunk floor. The height could easily be
> moved 0.75" higher or lower at the chassis-bracket
> end by enlarging pilot holes that are kinda hard
> to see in the snapshot below.
>
^Hi Curtis,
I have a B GT V8 with a 4.6 liter engine and I need to modify my rear axle as well and I quit like your design! Would it be possible to get a few more pic from the complete Panhard rod design?
Cheers,
Volker
(Moderator: Volker, I removed your personal e-mail address from your post because it was an invitation to spammers...)
The two parts shown above look like this installed:
(http://www.britishv8.org/MG/CurtisJacobson/CurtisJacobson-G.jpg) (http://www.britishv8.org/MG/CurtisJacobson/CurtisJacobson-H.jpg)
I don't have pics of the axle end... and anyhow, if I did it again I'd make it look more like this: (on Les Gonda's car)
(http://www.britishv8.org/MG/LesGonda/LesGonda-CJ.jpg)
Curtis:
Hate to be critical, but the double reinforcement of the trunk floor doesn't look like it would be nearly butch enough to handle a panhard that really had to work. You are still limited by the strength of the trunk FLOOR (now 38 year old metal?).
Our racecar runs a 1.5" square tube welded to the chassis rail (in that corner where yours is attached.) It drops down to provide the chassis mounting point. It's then a 3/4" pipe with LH and RH rod ends at each end for easy adjustment. (Long turnbuckle, basically.) It then had a small gusset (sheet metal) from the back of the floor to the square tube (triangulating about 5".) There is a bracket that attaches with longer bolts to the back of the brake backing plate for the axle location (longest run, basically). All this on a stock MGB axle. It ran parallel to the ctrline of the axle, behind it. (Low things get HIT on racecars!)
Well, after 4 years of "racing" (say, about 3000 miles) we started to RIP OUT THE TRUNK FLOOR. And rub the LR tire in the fast right handers at Road Atlanta. While we couldn't make it flex or see it flex, it obviously was. All we had as evidence were stress cracks in the trunk floor and paint removed from wheel wells!. The "sheet metal" aspects of the installation were letting us down. :-(
We've now BOXED the trunk floor with 1" tubing between the chassis rails and there is a much longer 1/2" tube for trangulation, from lower on the 1.5" tube to the 1" box tubing. (Thus, the FLOOR has NOTHING to do with the panhard anymore.) This, 1000 miles on, has been fantastically better! (Has held it's 'adjustment".)
So, don't trust your trunk floor. It has, by now with it's age, virtually no structural stiffness whatsoever. You really want to make the attachment contingent on the two chassis rails that run either side of the trunk floor. This is the strongest part of the car that you'll find back there...
We see similar problems with the aftermarket rear swaybars that mount with 'sandwich" brackets through the trunk floor. Ultimately, they tear out the metal in those corners. :-(
Anyone intending to run bigger tires and corner hard *should* run a panhard! (Note Ingram's MGC tires rubbing extensively while doing the Dragon!) Also note that use of panhard means MUCH smaller rear bar is needed (if ANY at all!) The racecar, for instance, runs a 1" front bar but only a 9/16" rear bar in conjunction with the panhard. :-) The rear bar is for tuning OUT the "push" of the front bar. Running a 7/8" front bar needed NO rear bar, but the car still had some initial roll into tight corners.... (This despite being a good 2" lower than stock C/B!)
$.02
Max
Good point Max, but the cornering forces on a race car running slicks is far more than most street tires can generate. Curtis took me for a ride when we were in Wisconsin and I never noticed any sort of unstableness from the rear, it stayed firmly planted even in some pretty heavy corners so his installation seems to be working without problems for now and he's running some pretty sticky tires for a street car as well. As you know his GT doesn't have any sort of "interior" carpets so visual inspection of that area is very easy. I'd like to see photos of the race car trunk area to see exactly how you guys reinforced that area though, sounds like a relatively easy thing to do and good insurance.
Sincere thanks for some really constructive comments, guys!
Max, this community/website would benefit hugely from mixing more with racers (like you and your team)... so I'm keen to start publishing something similar to "How It Was Done" articles in a racecar-specific photo gallery (with no restriction on engine type). I know you've got a lot on your plate already, but any help you can give with that would be greatly appreciated.
Just one idea: "How many Gold Cup Race participants could we possibly lure down to Durham for some sort of a show-and-tell-social on the first day of our upcoming meet?"
How can we get a "critical mass" of racers to switch over to our message board?
There are probably a thousand things I'd do differently on my car if I were building it today. The Panhard rod has been one of my favorite mods because it made an immediate and quite noticeable difference. Still, I'd construct it differently based on your feedback and also based on looking at cars like Les Gonda's (http://www.britishv8.org/MG/LesGonda.htm):
(http://www.britishv8.org/MG/LesGonda/LesGonda-CK.jpg)
When my Panhard rod went on (over ten years ago now!), I didn't have any access to welding equipment or any personal welding skill. I cut and bent the parts, made a little fixture to hold them together, and took them to a professional welding shop. The Panhard rod bracket could certainly be stronger, better anchored, and even lighter - especially if it were welded-in instead of bolted-in.
I can't testify if its effectiveness is diminishing (e.g. with metal fatigue in the trunk floor) but it certainly hasn't stopped working! I fitted much wider/stickier tires last year and they're not rubbing. (Yet! Knock on wood.)
Also, last winter I removed the bracket and doubler, and sent them to Pete Mantell (Mantell Motorsport) for powder coating. While I had everything apart, I didn't note any distortion in the trunk floor or any cracked paint. Probably I'm not driving hard enough!!! Another point - if I slid sideways into a curb one day - all bets would be off as to whether the trunk floor would take the load. Lots to think about!
Wow, time flies. It's been almost a year since this thread was started. I finished my Panhard rod and traction bar improvement last spring, and the improvement was fantastic. I would recommend this modification for anyone planning to add power and larger tires. I had previously centered my fuel tank, so I had less boot floor mounting area to work with. Realizing that the strength of this location is in the box corner of the boot I devised a doubler that would work in all three planes of the corner. I believe this will reduce the flexing of the boot floor which will lead to cracking from fatigue. I built the floor section to ride up and over the embossed reinforcement that Curtis cut-out to clear. On the underside, I notched the doubler to clear the rebound strap bracket. I used 1/8" mild steel plate for the doubler and 3/16" for the rod mounting bracket. 1/2" Heim joints were mounted to 1" dia. chromemoly tubing. I cut a section from a piece of 3" x .120 steel tube and welded a bracket with a rod end pocket devised to get the bolt in double shear. All parts were thedn powder coated. Since I didn't want to pull and drain the axle to weld to it, I raised one end to allow the axle lube to drain away for the weld area and TIG welded the 3" tube section to the axle. I touched up the area with chassis paint.
Very, very nicely done Chris!
Can you please post some more pictures of the brackets?
Pictures of the traction bar installation too?
Here are some more photos:
67MGBV8suspensionimprovements014.jpg
67MGBV8suspensionimprovements026.jpg
Here are some pictures of the traction bars I built and installed at the same time. These are modeled after the Cal-Trac concept and incorporate larger 1/4" thick retainer plates to better fit the larger diameter of the Dana 44 axle tube and larger u-bolts. The front pivot has a nylon take-up block to allow the bar to float without any effect until increased torque twists the axle under strong acceleration. The front of the bar is a simple tee joint and is bushed with Nylatron bushings of the same type used in the rear spring shankle. The amount of take-up slack is adjustable in the Hiem joint at the rear of the 1" diameter chromoly tube.
67MGBV8suspensionimprovements020.jpg
67MGBV8suspensionimprovements023.jpg
67MGBV8suspensionimprovements013.jpg
Chris,
Nice work there. Even though this started out as a "panhard bar" thread, I don't think it hurts to add some notes on traction devices. I just wanted to include here another variation of the Cal-Trac that you patterned off of. I ended up using the Slide-a-Link system. They're both good choices. I can't remember why I ended up with the one and not the other. If anyone is interested, have a look at the exploded view in the "instructions", item #C2100.
http://www.competitionengineering.com/catalog/CategoryDisplay.asp?CatCode=13116
Totally eliminated the wheel hop. Keeps the fillings in my teeth.
(http://i488.photobucket.com/albums/rr246/dynobeast/IMG_4982.jpg)
(http://i488.photobucket.com/albums/rr246/dynobeast/IMG_4981.jpg)
(http://i488.photobucket.com/albums/rr246/dynobeast/IMG_4980.jpg)
(http://i488.photobucket.com/albums/rr246/dynobeast/IMG_3814.jpg)
The biggest difference between the two is the sliding shock bushing and the front mount. The front mount requires a free floating assembly attached to the spring only and a solid alluminum eye bushing.. According to Bill Guzzman, the solid eye bushing has it's drawbacks but I'm living with it.
(http://i488.photobucket.com/albums/rr246/dynobeast/IMG_3806.jpg)
(http://i488.photobucket.com/albums/rr246/dynobeast/IMG_3807.jpg)
(http://i488.photobucket.com/albums/rr246/dynobeast/IMG_3894.jpg)
Negatives: Took alot of measuring and it does add weight.
Ken,
Does the c2100 Slide-a-Link fit the MGB?
Thanks,
JB
John,
The actual item, Slide-a-Link #C2100, I'm most certain would not be a straight bolt on affair to anything other than what they list in the cataloge as fitting. There's alot of suspension variations out there, let alone the LBC family, but the design concept will work.
Just work with the dimensions you have in your application.
Ken
Here are some picture of the Group 44 MGB rear Suspension set up.
MGB3a.gif
MGB5a.gif
It has some wild traction bars, sway bar ans watts-linkage arrangement!
Pretty cool. I might try some variation of that swaybar on the Jag IRS if I can figure out a way to fit it in.
Jim
QuoteHere are some picture of the Group 44 MGB rear Suspension set up.
Thanks for posting those VERY interesting photos. I understand that car will be at "The Mitty" race, at Road Atlanta in May. I'd love to be there and photograph the heck out of it for the proposed new "race car" section of our photo gallery.
Here's my bracket for the axle end of my panhard rod. Mounted to the back right side axle flange.
PanhardRod13.JPG
Panhard2.jpg
Phil, that is an interesting construction you have there! Seems like the pivot point is considerably higher that the axle center, is that correct? That would raise the roll center considerable as well, Im very curious how that influenced the handling of the car!
Or, is hthere anybody else on the forum who has raised the roll center on the rear of an MGB?
QuoteOr, is there anybody else on the forum who has raised the roll center on the rear of an MGB?
I actually went the other way. My panhard rod is mounted so the roll center is about 2.5" below the rear axle center. I don't think you want to just raise the roll center on the rear of a B unless you do other suspension changes.
Scott
It just so happens that I've been working on a new Panhard rod installation lately, and I got the bracket welded-in this weekend. I put the bar 3.5" below axle centerline. To me, that doesn't seem terribly aggressive. But obviously I haven't driven with it yet.,
I'll post a snapshot... but I'm not ready to talk about it yet.
CHJ-NA.jpg
I will also be doing a 3 or 4 link in the coming weeks and have been thinking about how I could simplify the design. I'd rather not use a panhard rod if I can avoid it with the construction of the top link(s). I'm aware that a pair of top links can be mounted at an angle in order to provide the side to side locating function and the concern there is with binding. But what about a 3rd link that is a triangle? Central joint to the body at the top of the tunnel and another joint on either side of the pumpkin? The central joint would have to be able to rotate in 2 axis and resist side motion and the axle points would have to rotate in one axis and also resist side motion. Why wouldn't this be a good idea, other than the structure above the driveshaft?
Jim
From a handling point of view, I think you'd get much better results by flipping your idea upside down but using coilovers a la Lotus Seven.
ref: http://www.lotus7register.co.uk/images/7%20story/Series%20Two%20Rear%20Suspension.jpg
(The Ginetta on BritishRacecar is basically a Seven with different bodywork.)
btw: here's an MGB with a triangle link: https://www.britishracecar.com/JerryRichards-MG-MGBGTV8-40.htm
I have always heard that part called a wishbone, as in, wishbone 3-link.
I have seen the wishbone oriented in both directions & top or bottom.
Question for Scott & Curtis: What was your reasoning for mounting your panhard rod that distance below axle center line?
What is the reasoning behind putting the wishbone under the diff giving better handling? Also is there any reason why the single pivot point being at the differential instead of at the body any better?
Jim
I do not know for sure, but I do not think it matters. Certainly not with your chopped up grocery getter & your emergency tires. :)
QuoteQuestion for Scott & Curtis: What was your reasoning for mounting your panhard rod that distance below axle center line?
I wanted to play around with reducing the roll axis inclination to see how things would react. The car seems to corner really flat now with minimal body roll so I think it was a positive change. It's basically a stock suspension with a 3/4" roll bar up front. I was enjoying it this afternoon going around a roundabout.
Good suspension tuning, Scott!
Without a rear sway bar, that is correct direction. Lowering the panhard rod below the axle centerline will more the car towards understeer.
Curtis can likely go a little lower since he has more weight on the rear wheels.
Even among MGBs, we have a great variety of set-ups and great differences in how we intend to use our cars. These cars left the factory with front roll center height close to ground level and rear roll center height close to axle centerline. (Front roll center was defined mainly by the relative inclination of upper vs lower wishbones. Since MGB didn't have Panhard rods from the factory, rear roll center was defined mainly by leafspring mounting points.) It's been roughly 45 years since the last MGB left Abingdon, so things have changed. At the front... if a particular MGB has been lowered by sagged or deliberatly shorter springs, its front roll center height is likely significantly below ground level. Fitting Killer Bees style dropped spindles (as I did) will move that upward, but not as much as Headley style dropped spindles. Entirely different front suspensions (e.g. FastCars) likely place the roll center even higher. But at the rear, regardless of whether you've got leafsprings or coilovers, until/unless you deliberately move the rear roll center it's probably still near axle centerline. A line drawn from front roll center to rear roll center defines roll axis. On MGB, it's pretty steeply inclined compared to other cars and particularly ones known for good handling.
Carl's first question: (paraphrased) "why did I choose to lower mine 3.5 inches?" I've long felt that if you're going to the trouble and expense of fitting a Panhard rod anyhow, it'd be silly not move the roll center down significantly. It doesn't cost any extra! I expect the bigger roll-couple (i.e. height difference between center oif gravity and roll axis) will provide me more feedback and the flatter roll-axis should make handling more consistent in various cornering situations. You can read a hundred better explanations than I'll write about how roll center height affects load transfer and tire grip. Most credible sources are however discussing "real racecars" or more modern sporty cars that have some sort of independent rear suspension. Where class rules allow, roadracing cars usually have much lower rear roll centers than MGBs. Nearly all cars with independent rear suspension much lower rear roll center heights too. Even so, you'll see people discussing the relative merit of shifting roll center lower.
I'm gonna decline to digress into discussions of spring rates, anti-sway bars, etc.
Jim asked "Why put the pivot on the diff rather than the car's body?" The most obvious reason is that doing so puts the pivot point a very predictable and stable height. A pivot on the body would bounce around, relative to tire contact patches. (Jim: you could use your project car's existing leafspring mounts to mount the wishbone. Installing the wishbone would thus be easy. And don't you want to ditch the leafsprings anyhow?)
(edited to correct grammar and improve clarity)
Carl wrote: "Curtis can likely go a little lower since he has more weight on the rear wheels."
We'll see about that;o)
I was thinking the simplest lower links would duplicate the front half of the leaf spring with a tubular link to a pivot below the axle. Since I'm using a banjo housing welding on brackets is easy of course, but I have to be mindful of vertical limitations since the suspension has to collapse into the body for loading. To the point where there is about 1/2" clearance between the body and the ground and I may even need to revert to CB front spring hanger locations and shave the jacking points and driveshaft pan. With a 22.3" tire this means using every fraction of available space. We had already removed the filler panels over the axle on the '74-1/2 tub and it'll need every bit of that space and possibly a bit more. Plus I'll need perches for the air bags. The original plan of mounting the bags where the bump stops went doesn't give enough compression, so they will probably need to go outboard if the tire allows clearance. I have one of the wheel/tires on the way.
So the wishbone would set the roll center height? Is that what you are saying? If that is the case I can see the point. And a bracket on the bottom of the banjo bulge doesn't really affect anything important here. But if that's the case why is it common practice on a 4 link to triangulate the top links rather than the bottom ones?
Jim
I don't know if the wishbone always set the roll center. Best I can tell, nothing is simple about suspension design.
I don't think any of this much matters on your little clown car. :)
This looks to be right up your alley, Jim:
https://www.lotuscortinainfo.com/?page_id=1799
High tech wishbone:
https://youtu.be/cjZRhL0WMlg?si=JRt2qs3DzF6ChYrf
https://www.youtube.com/watch?v=SibLgsG__-I
Curtis, funny how similar our approach to the panhard bar is.
Scott
20250805_1403371.jpg
My panhard rod is adjustable on the body side. I see Scott's is, as well. Can't tell on Curtis'.
I believe it is important to have the panhard rod level with the full weight of the car & driver. To accomplish this, I drove my B up on Les Shockey's trailer that has an open center. Les sat in the driver's seat while I crawled underneath & leveled it up using a bullet level. Trailer was very close to level.
Coilover shock absorbers...
What shocks are you using, Curtis?
Sometimes, I wish I had studied mech. engineering with slant towards vehicle dynamics & suspension design, instead of electronics. It can get complicated in a hurry with trigonometry & calculus.
As a starting point in suspension tuning, the front roll center height should be about 15% of the height of the center of gravity. The rear roll center height should be about 30%.
Raising the rear roll center height from there aids turn-in, but also starts inducing oversteer.
Lowering the rear roll height moves towards understeer.
Everything affects everything dynamically. So, each vehicle will likely need slightly different tweaks.
The above is for RWD cars with no aero aids.
QuoteMy panhard rod is adjustable on the body side. I see Scott's is, as well. Can't tell on Curtis'.
I believe it is important to have the panhard rod level with the full weight of the car & driver. To accomplish this, I drove my B up on Les Shockey's trailer that has an open center. Les sat in the driver's seat while I crawled underneath & leveled it up using a bullet level. Trailer was very close to level.
Carl, mine is adjustable on both ends. You can kind of see it in the picture if you look closely.
I tried to adjust mine so the rod is level at the halfway point of suspension travel. I think that is supposed to minimize the deflection the rod causes.
I wonder where the roll center is for the Jag IRS?
I also wonder how a triangulated 3rd link affects roll center? Might as well optimize it if I'm building it.
Jim
"I tried to adjust mine so the rod is level at the halfway point of suspension travel. I think that is supposed to minimize the deflection the rod causes."
With our long panhard rods & limited suspension travel, any lateral deflection is minute. We will never feel it.
QuoteI believe it is important to have the panhard rod level with the full weight of the car & driver.
By the same token, this approach is a waste of time in my opinion. You will feel no difference with it in that position.
Everything that I have read indicates the panhard rod is to be placed level at ride height. Adding weight to the driver's side, tends to make the bar not level. Not being level will increase the lateral deflection. As you said, probably will not feel it with such a small amount. A larger angle with certainly move the rearend.
A better approach is to ditch the 3-link set-up and go to a 4-link and scrap that problematic panhard rod!
"I wonder where the roll center is for the Jag IRS?"
You will have to find it like for the front suspension.
"I also wonder how a triangulated 3rd link affects roll center?"
No easy answer for finding that roll center, either.
Problematic panhard rod, Graham? I have been using my DIY panhard rod for 20 years without issue.
Your rear roll center is fixed at what ever Bill Guzman designed into his triangulated 4 link. They are known to bind. Probably not an issue with the limited articulation of your rear suspension.
As Scott has shown, rear roll center can be adjusted with a panhard rod.
Quote"I also wonder how a triangulated 3rd link affects roll center?"
No easy answer for finding that roll center, either.
Not really that hard. First I'll point you in the general direction:
3_link_inverted_with_A.jpg
from "Race Car Vehicle Dynamics" by Milliken and Milliken
And then I'll give you my 2 cents:
In practice, whether (a) an A-arm converges at a spherical bearing (or equivalent) that's secured to the rear axle housing as shown in the figure, or (b) a pair of links converge toward some point in space behind or ahead of the axle (as on many 4-link suspensions) doesn't need to confuse the issue.
Technically, roll center height is found by projecting the convergence point back to the vertical plane the rear tire contact patches are on. Other links that constrain the axle's movement affect the correction. However, that correction is small beans! On any car I care about, the height of the point of convergence is
very nearly equal to the actual roll center height. And, because it's a close enough approximation, it's fair to generalize that:
(1) Attaching an A-arm to the axle ABOVE the 3rd member (as on some dragracing cars and some rock crawlers) would put the roll center VERY high. Bad for cornering.
(2) Using converging links above axle center line (as on many 4-link suspensions) puts roll center height above axle centerline. Not great, although other aspects of the suspension might be good.
(3) Attaching an A-arm wishbone to the axle BELOW the 3rd member (as on a Lotus Seven or on Jerry Richards' MGB GT V8 racercar) puts the roll center height quite low.
QuoteWhat shocks are you using, Curtis?
Shock travel seems to be my more pressing concern. In the photos above, jackstands held the axle at static ride height. I bumped the axle straight upward, and found that the shocks would compress 3.25" before the spherical bearing of the top link contacted the (unmodified) body. (If I modified bodywork there as done on Ken Biermann's car, there could obviously be more suspension travel.) Then, however, I put brakes/wheels/tires on and bumped one wheel at a time upward, simulating roll. In this check, my hypothetical shock on the bumped side compressed about 4.25" before contact between axle and body. Based on this - not thinking yet about extension requirements - my initial reaction is that 7" shocks probably would be more suitable for my suspension than the 5.2" ones I already have. I'm investigating some longer spring options accordingly. The good news is that I don't have clearance issues between the coilovers and anything else. They'll be pocketed up neatly into the back seat area in any event, and on account of my roll cage I've got lots of options for attachment.
Sounds pretty good on your shocks Curtis, more travel will give a better ride and make the spring and damping rates less critical. Ground effects may become less but we don't really get much of that anyway. I base the needed stiffness on what it takes to prevent bottoming out the suspension after becoming airborne. A foot or so of air generally seems adequate for testing. More than that risks loss of control if there is any turning involved, and of course you can't accelerate while airborne.
So if the wishbone is attached at the bottom of the bulge this is generally going to give it an upward angle towards the front of the car. Sounds like that might not be a good thing. Or do the side links, being located higher then become the controlling element? I don't want any bracketry dropping below the body. Also, the closer the body ends are to the same level the more the pinion angle will change during travel. That one shown would effectively be like ladder bars. I'm beginning to see the attraction of the angled 4 link. Binding must be avoided of course.
GM was using an angled 4 link back in the 60's on their mid sized cars. (GM A body platform, from which all other platforms were derived.)
Jim
Quote...from "Race Car Vehicle Dynamics" by Milliken and Milliken
I guess not, if you have that book. I do not. I have read over the years, that it is a very good one. Quite expensive, these days.
Yes, much different results dependent whether the wishbone is on top or bottom. I have read that for some reason it makes a difference which way the wishbone is pointed.
Certainly not as easy to calculate as a panhard rod.
QuoteA better approach is to ditch the 3-link set-up and go to a 4-link and scrap that problematic panhard rod
Sorry, Graham. Your 4-link is fine for cruising & drag racing, but the 3-link is superior for road racing, track days, & autox.
Jim, having the lower links angle slightly upward somewhat from axle-end to body-end is normal and desirable for both 3-links and 4-links. The convergence of upper links and lower links (in side view) provides some anti-squat. There are four 3-link suspensions in the MG photo gallery section (Terry Schulte's, Dan Masters', Ivan Collins', and Ken Biermann's). I think it's fair to say they're all similar in this respect, although Ivan's is more adjustable than the others. Here's a rendering Ivan provided with his HIWD:
(https://www.britishv8.org/MG/IvanCollins/IvanCollins-DC.JPG)
The mechanics of anti-squat and a visual method for approximating the amount of anti-squat effect is illustrated in the write-up on Dudiak's McKee Formula 5000 car on the BritishRacecar site. (That car has independent rear suspension, but basic principles aren't so different because radius links function similarly...)
The dynamics of pinion angle is indeed another thing to think about. You'll note they're affected by the relative length of upper links versus lower links in side view. For this reason, upper links should be shorter than lowers. But how much shorter?
All good and much appreciated but now we are back to looking at the wishbone vs twin top links. If the wishbone is on the bottom then the side links by necessity have to become the top links. If using the spring hangers as the pivot points this will give a rather steep downwards angle I think and the convergence point will have to be somewhere near the spring hangers as well just because there isn't room to put them any lower. Unless I'm mistaken I think this will cause a jacking effect on acceleration due to counter-rotation of the housing. Good coming off the line but not so good coming out of a corner.
Now if the wishbone is above the axle it can have a more gradual downward angle and the side links now being the bottom links the convergence point can be moved further forward, decreasing the jacking or anti-squat effect. This all depends on where the end points are located of course and is limited by interference between the body and the bulge on one end and the driveshaft on the other. With the 4 link the upper attachment points can be below the bulge and near the top of the rear shelf area, creating a line that can project almost level I think if that is desired. IIRC this is somewhat consistent with the A body rear suspension which was actually surprisingly good for an American car of that era.
The effect of a shorter upper link upon articulation is to rotate the housing downwards. I think this should tend to increase the jacking effect or anti-squat whereas equal length arms, especially parallel ones should minimize it and some anti-squat being a desirable trait this perhaps explains current designs. Just throwing assumptions out there while trying to work my way through the theory. So raising and lowering pivot points changes the convergence point and allows tuning of the anti-squat, seen much more often in drag cars to control jacking off the line. I have ridden in a drag car that I would swear raised the rear of the body a good 3 inches when the owner hit the gas.
With the Jag IRS it seems the anti-squat is essentially neutral as far as I can tell and that's fine with me. The LCA pivot points are very close to parallel with the ground. I do not know what the effect is on roll center but the typical RC for a Jag IRS seems to be about 5-6" up which is an improvement for the most part I think. I don't know if that is dependent on half-shaft angle or LCA angle though.
Still and all I'm definitely leaning towards the 4 link just because there is more room to locate the attachment points. As Bill's kit evolved I understand he solved the early binding issues and following his approach might be the best tactic. I should probably take a closer look.
Jim
Alternatively, you could build a traditional 4-link complete with a Panhard rod. Probably easier to avoid binding issues. Put roll center wherever you want it.
I cringe every time you mention 60s GM A bodies. Those aren't sportscars. First generation RX-7 is a sportscar with a 4-link incorporating parallel and widely speced uppers. Interestingly, it uses a Watts linkage instead of a Panhard rod though.
No. you are right they were not sports cars. However in some ways they were really quite good when push came to shove, and all of my education in the fine art of the 4 wheel drift came at the wheel of a somewhat prepped A body. Done right they were extremely controllable if a bit slow in response, could easily achieve neutral handling and gave great feedback to the driver. This leads inevitably to the old term of "setting the chassis" which is just another way of saying that you had to anticipate the handling and prepare in advance. Transitions were wonderful exercises in timing. But the cars were forgiving so that was a plus. Not being a sports car certainly did not mean you couldn't take everything it had to give and maybe then some. I suspect more than a few of us did just that.
Incidentally, although brakes were inadequate and the steering atrocious the suspensions were advanced enough to be considered state of the art at the time. All the right parts were there and even by today's standards they could be competitive. Curb weight was 3400 lbs which was considered heavy, not so much today. Separate frame and body was not especially stiff but wasn't bad. Mainly they were big, which it turns out isn't necessarily a bad thing either. It gave them the advantage of being able to blast over curbs and such with impunity. For a rugged driver of a car they were really quite good and an aggressive driver could make time.
So I think using their high points as an example is more than appropriate, and the double wishbone and 4 link combination did work well. They certainly were anything but delicate and were far more refined than the MGB setup. Most people never had any reason to wonder what was under there. Disc front brakes at the end of the 60's and into the early 70's certainly helped, but they never did get beyond the recirculating ball steering which was a pity, and then all the fun went away. Too bad, those cars were a blast.
I do not like the panhard rod. I feel it is adding weight, failure points and complexity when the same job could be done in a simpler way. If not running leaf springs (ox cart technology) I just don't see the sense in it.
Jim
QuoteI do not like the panhard rod. I feel it is adding weight, failure points and complexity when the same job could be done in a simpler way. If not running leaf springs (ox cart technology) I just don't see the sense in it.
Leaf springs? I resisted using a panhard rod because, IMO, they weren't meant for leaf springs. The leaf spring are supposed to provide lateral support. For the most part. ;) Panhard rods were meant for 3&4 link suspensions, not leaf springs. Then, I grew tired of my butt feeling the rearend move around. Bit the bullet & built a panhard rod. Certainly does the job.
Failure points, Jim? Don't think your cargo go kart has to worry about that. :D
Perhaps. But why add another link if a properly designed 3 or 4 link will do the job? I CAN see adding one to an already existing setup, but since I'm starting from scratch I don't feel it is appropriate to start out by planning for more complexity when less can serve just as well.
I'm pretty sure there will be no room for a wishbone to attach to the top of the bulge. Could be a moot point once the wheel/tire comes in and I can start mocking it up and I may end up having to cut sheet metal there anyway to tuck the tires up into the body but I hope not. I'd like to preserve the package shelf so there is at least a little bit of cargo area. What's left of the trunk will be taken over by the gas tank I fear.
That basically leaves me with two options, either the triangulated 4 link or the 3 link with the wishbone as the bottom link and parallel top links. The center pivot joint (Rose joint?) would then be either at the bottom of the bulge which I dislike for basically esthetic reasons or at the heel plate which is the low point of the body and on the RB tub sticks down about an inch further than on the CB car. I would prefer to put it there if driveshaft travel will allow it. This would also mean fabricating new top link mounts but I'd have to do that with a 4 link anyway. Putting the center joint under the diff would let me use the front spring hangers for the wishbone however, so that would be a plus. But now ground clearance is down to less than I'd like. I should take a closer look at that, it may be OK.
Those two issues are why I have to seriously consider the 4 link despite the binding issue. I should probably try to call Bill and ask him for pointers since he's been there and done that, but mocking it up will tell me a lot. I should only be days away from that.
Jim
I think the rubber bushing are what helped the Mustang 4 link work.
With rubber bushings & limited travel, binding may be a non-issue.
QuoteI do not like the panhard rod. I feel it is adding weight......and complexity when the same job could be done in a simpler way.
Exactly!..The way I view this whole suspension argument is that a 3–link + panhard = a 4-link. Why add the complexity of a panhard to control lateral movement when another short upper link will suffice.
QuoteWith rubber bushings & limited travel, binding may be a non-issue
Speaking of limited travel, you'll agree that panhards follow an arc which can impact axle lateral movement if the travel is too large.
When I installed Bill's 4-link, I articulated the axle before adding the coilovers to see if there was any linkage binding – I didn't observe any!
QuoteSpeaking of limited travel, you'll agree that panhards follow an arc which can impact axle lateral movement if the travel is too large.
Yes. With a long panhard rod, & less travel, it is a complete non-issue. I can't feel any difference left vs right. I could feel the rearend move without the panhard rod.
My understanding is that the 3–link + panhard is more tunable & possibly easier than a 4-link.
Not many road racers use 4-links.
Jim, try using the calculator; from Irate 4x4 four link calculator I am about to put my home built four link together for the last time in the next week or so. I can confirm that it has no binding at all despite still using the nylon bushes that came with the Speedway rod ends, with the axle hanging on the straps I can lift either end to the bump stops with no ill affect . Energy Suspension poly bushes are now going in.
Although most of the online info is geared to off roaders I have gone with the few recommendations for road cars;
Top bars should be 2/3 length of the lower bars, I am almost there but not quite, I didn't want to do away with the battery boxes so went with a forty degree angle to increase their length.
Having the lower bars spaced slightly closer at the front than at the axle reduces binding and roll oversteer. The calculator is very good for juggling around with anti squat and roll steer, hope this helps you if you go down this road.
Thanks Philip. I can't seem to find the right link to download it though, not sure what's up with that. Sounds like it would be super helpful.
Jim
I will post the link in full but a moderator will have to inspect it for spam before it appears, I was hoping that you might find it from the info that I posted.
https://irate4x4.com/resources/4-link-calculator.4/
I'm suspicious of this Wave Browser Pro that wants to download it... it wants to install on my computer from the looks of it. That shouldn't be needed for a download I don't think. What was your experience?
Jim
I would not do that, Jim
It is considered to be an invasive & possibly malicious web browser.
https://www.quora.com/Why-would-my-husband-install-a-wave-browser
https://www.reddit.com/r/sysadmin/comments/mlkwuj/wave_browser_by_wavesor_software/
I didn't use it Jim, I found the download somewhere else. I didn't think of any consequences of downloading from what I posted. Search elsewhere for it because it is available.
I downloaded it from here; https://www.crawlpedia.com/4_link_suspension.htm and I have always used Open office to run it.
That looks pretty useful. I'll have to take some measurements so I can input the numbers and see what it does.
Jim