What rear suspension and why?

Knurled wrote: Knurled has been on the 3-link train since 2006 or so

Iiiintersting...... Did you do any sort of math/modeling of the geometry, or did you go with "looks good, and fits the space" to end up with such grip?

I have always tended to think along the same lines of Driven5, if easy/simple has some appeal, why introduce all kinds of toe control and camber curve problems by going with IRS? For a homebrew car, I'm happy to take on some minor concerns to manage binding and roll-steer in exchange for simplicity and wheels/tires that are always square to the road.

ae86andkp61 wrote:

Knurled wrote: Knurled has been on the 3-link train since 2006 or so

Iiiintersting...... Did you do any sort of math/modeling of the geometry, or did you go with "looks good, and fits the space" to end up with such grip?

I kept shortening the link/lowering the front pivot until I ran out of room. It kept getting better and better.

Next time, I'd probably just do a torque arm like a Chevette or Camaro. Or truck arms, if I had to start with a car that wasn't a Chevette.

I kind of want a Chevette, if this isn't obvious. Nice combination of headroom, long front suspension travel, decent rear suspension as-produced, and WTF factor, all rolled into one.

In reply to Knurled:

Knurled for president.

In reply to Dusterbd13: Jaguar IRS. $300-$500 and for that you get a full sub frame. For racing you weld it in. for street driving you mount it on the rubber mounts. It has a Dana (or it's Salisbury twin) capable of handling up to 700 horsepower and whatever size tires you want (Chevy Bolt pattern 4&3/4") Inboard disk brakes (or Outboard on later ones) Positraction in most of them, common ratios are 3.54,3.31, 3.08
Narrow from the XK-E or wider from the sedan.. coil over shock absorbers (4 or later ones had 2)

ae86andkp61 wrote: I have always tended to think along the same lines of Driven5, if easy/simple has some appeal...

Oh sure, I may publicly make recommendations for reasonably easy/simple things for other people. But late at night, in a dark corner of the house lit only by the enchantingly soft glow of my computer screen, I secretly indulge in my one true vice...Coming up with unnecessarily difficult and overly complicated ideas.

What about a 4th gen fbody rear. Comes with torque arm. 2 control arm mounts, a torque arm mount and a panhard mount should be easy.

They are cheap because they blow up all the time in fbodys but 1k light are a little less hp, would prolly survive.

Ps if you want a watts link the mini truck guys make cheap kits, way cheaper than the 1k kits for fbodys. Have no idea how durable they are outside of hard parking

Edit: toeque arm not panhard

Knurled wrote: I kind of want a Chevette, if this isn't obvious. Nice combination of headroom, long front suspension travel, decent rear suspension as-produced, and WTF factor, all rolled into one.

What long suspension travel and a rear suspension that articulates well may look like.

Not pictured: Apparently I was three wheeling it through certain corners, after dabbing the brake the inside front tire would not turn until corner exit. With 8" of front travel. On dirt. With an open rear diff.

Can a torque arm mix with leaves? Maybe offset from center and making it reach far forward if needed?

In reply to pres589:

I don't see why not. The torque arm doesn't locate the suspension, it just defines the instant center. It would just be a centrally mounted, extra-long traction bar.

If I were doing it, I'd remove or loosen all of the leaf spring clamps so the setup wouldn't bind. The front half of the leaf spring would still need to locate the axle fore and aft, but you'd want the spring to be able to wrap freely so the torque arm could define the axle's position rotationally.

In reply to Knurled:

What about a monoleaf and coilovers with that torque arm?

Factory leafs and shocks are junk. Both ends of the leafs where they mount to the body are rotten to the point i can poke my fingers through without even much feeling it.

In reply to Dusterbd13:

Isn't that more or less what some circle track suspensions have? Monoleaf springs and then torque arms, or torque arms and pull bars for different instant centers for acceleration and braking?

I'm not a circle track guy, but I like the parts catalogs. A lot of interesting ideas in those catalogs.

The original Ford Escort 4-link suspensions retained the leaf springs (rules probably required they be kept) and the front spring eye was cut off and a slider mounted to the body, so the spring's only job was holding the car up, the 4 link located the axle. Some time later they were allowed to ditch the leaves and go with coilovers.

By the way. Doing a Google Image Search for escort 4 link will send you deep into a rabbit hole of fabricator porn. Beware. An example...

Three link with a Watts link and the center pivot attached to the car adjustable up and down to alter roll center.

Prepare for a fairly steep angle on the upper link, using a non-centered drive shaft facilitates the third link installation.

Also for brakes a dual master with a balance bar will be smart.

Mumford vs Watts Link

Knurled wrote:

gearheadmb wrote: Truck arm and coilovers would be cheap and easy, but not awesome.

Truck arms are the most awesome suspension ever. They work great for traction and handling and are simple. And they make sidepipes practical. How is any portion of that not awesome?

I agree with truck arms. The axle becomes the sway bar. Its a pretty common way for old-school hot rods to get traction with handling. I'll likely be doing it on my 67 Lemans.

I wouldn't say they excel at everything, but they're simple, bulletproof, and a major upgrade from leaves. Nice thing too, you can remove two bolts and change IC by moving the arms up for traction or down for twisty things.

Another benefit is that you can run a wee bit softer spring (but not too soft... see below) and not give up the handling. This further aids weight transfer for launches.

One thing with truck arms: Be sure to really research the right spring rates. Since the axle is effectively the sway bar (and its very stiff) you don't want springs that are too far off the target. Springs too stiff and you'll have oversteer problems. going way too soft puts too much stress on the tubes. Its just like any rear suspension that you have to match spring rate and bar stiffness, you're just starting with a REALLY stiff bar.

Trackmouse wrote:

Jumper K. Balls wrote: This has me wondering again if there is a way to significantly lighten up the ubiquitous Explorer 8.8. Perhaps some careful removal of extra casting on the center pumpkin or stuff the guts into a lighter car based housing? When I did the 8.8 swap on my falcon I was able to lift the old rear end out by myself, it took two people to lift the 8.8 back into the cradle. It feels like I am dragging a boat anchor. I am very aware of the extra weight in a way I didn't expect.

I've heard you say this before... I completely disagree. I put a ford 8.8 (with drum brakes at that!) into my 2300lb Celica. It's incredible. Best mod I've done yet. Weight difference was 50lbs compared to the old t code axle I had. I drift that car all the time. It didn't change the dynamics of handling at all. (Aside from the lack of a rear sway bar) I did my ford 8.8 swap for about 150$. That includes the axle (50$), the passenger short side axle(10$), and a full brake rebuild and fluids (the remainder$). I could not be any happier.

While i have a bit more money in my 8.8 swap and its a factory foxbody housing i also didnt notice a diffrence between the stock 7.5 and the 8.8 in driving. My car even has the same engine as the falcon.

I started wondering what the Group 5 Ford Capri racers did in the rear. The stock car uses leaf springs in a multi pack. Here's what some internet research tells me;

"The Capri's rear suspension is famous for its curious way of beating the Group Two rules which state that the car must retain its standard suspension medium (leaf springs in the case of the Capri). Therefore the car has been fitted with a plastic leaf spring which would have no effect whatsoever while normal coil spring fitted to the Bilstein shock absorbers once again provide the effective rear wheel control. The coils are officially termed as "additional springs" - just for the record, of course.

Four trailing arms control the beam axle, along with an adjustable transverse Watts linkage which allows the rear roll center to be adjusted."

I like your idea of a slightly simplified setup. Maybe just the top spring from the factory AMC leaf pack, some motorcycle rear coilovers with the right spring rate (somehow), the torque arm to control axle wrap, and the longest Panhard you can fit under the car for simplicity, weight, and cost considerations.

I have always been told that a 4 link wants to Bind in tight turns, Oddly the c4 I am building Has 4 link and a Torque arm? and on a ridged mounted rearend housing,sure the rubber mounts allow some Deflection but darn that thing looks like a Girder beam from a hi-rise,Thinking about moving the 4 links to the rear to get some Length and tire clearence. Maybe take out the Girder beam and make a top link like a 3 link would use.

You guys keep saying with the right spring rate but how do you define it? Is it an experimenting? Axle diameter factor in there?

Thats a good question. How is it determined? Gotta be a way to get it in the ballpark on the first try.

So the idea of truck arms is now stuck in my head. Any good info for challenge car purposes?

stay with truck arms I Know a Little 'Bout em. Yea spring rates So Nuff Rocket Science. And all I can Say Is Billy Shopes, Find his site read it absorb it read it again. Put Scales under each wheel, a spring is rated in Inch's of Travel/resistance,or spring rate. you want the spring to hold the weight of the car at approx. 1/2 way through its travel or Jounce, Squeeze a 200 inch pound spring 4 inches and it can hold 800 pounds add 200 more it will go down 1 more inch In reality the resistance increses a bit more the more you squeeze it, Newer steel compounds are combating this.so now you got to know ride height and susp. travel.

pres589 wrote: I started wondering what the Group 5 Ford Capri racers did in the rear. The stock car uses leaf springs in a multi pack. Here's what some internet research tells me;

That description is an Escort 4-link. Capris were just longer Escorts so it makes sense that they just copied what the rally guys did.

In reply to Knurled:

Yeah, seems to be. Escorts never interested me as much as the Capri.

Knurled wrote: I am a firm, FIRM, proponent of solid axles. They allow you to incorporate more anti's in your handling than you can with an IRS. IRS allows you to play games with toe on bump/droop but that makes for inconsistent handling if you allow the suspension to move much. Camber is not to be considered because solid axles by definition keep the tires planted regardless of body position. Camber curve is a crutch independent suspension needs for chassis roll.

Is it possible to get even tire wear out of a live axle though? Pretty well all the live axle cars I've driven/worked with wore the outside edge excessively.

I have been led to believe that it was an inherent quality of live axle cars, but have no real data to back that up.

check out a cup car rear end they have a crazy amount of camber and toe,and you can buy em cheap round charolette and Kannapolis