Anybody ever run a Split I beam set up?

A few years ago there was an article in Street Rodder. Fat Man Fabrications had "Invented the independent I beam axle". I remembered that I had seen the set up in a Tex Smith book 10 years before, so Im guessing that the Fat Man was full of ****.

Anyway, my buddy has a chance to pick one up and we're wondering if it's worth snaggin. Anybody have any experience with them?

Thanks for the info guys!

 

Hi Crease, We should just call each other. Anyway I have a poor opinion of the split wishbone thing. With a solid axle the spring does not know it is sitting on an axle and not the ground. When you split them the axle becomes a lever and the spring must have maybe twice the capacity, The load on the spring goes up by the lever ratio. The spring rate goes down by the lever ratio squared. Ford used long overlaping axles. I think the short axles will create bump steer issues.I talked to fat man at a show about this and he refused to admit any problems. He said his rig would not change ride heigth. I mentioned that the axle was now a lever. He said the springs were so stiff it would not make any difference. LMAO.

 

I think the Fatman setup is designed to work with tube type front axles. The set up in your picture may be home fabricated.

The Cad Allards of the 50s ran the same kind of front end. They were considered "tricky," "odd," and "excentric." But, for apparently good reason, never caught on.

I'd p***.

 

Poms were doing this **** on their odd-ball things back in the 40s and 50s too.

 

Years ago a friend took the front end out of an Allard that was being s****ped and put it in a '32 three window. He said it rode just fine. The local stock car guys used the basic setup when they were riding the county of 1933-40 Ford coupes.

 

That picture is on the front end of a Pop, yes?
Grenville Grenfell devised the overlapping split beam, oh I'd say yay years ago to overcome the m***ive camber changes displayed by the Allards and their like with split beams. He used his system on a number of specials, from Triumph powered Formula 500 to Flathead V8 all of which cornered remarkably flat according to motoring tests of the period. Each beam was attached to the opposite side of the ch***is.

Unfortunately his patents didn't stretch to the USA, and Ford used it on the Econoline without giving him a bean...

Here's a link to an old article - there's a picture or two in there.
http://www.500race.org/Marques/Granviille.htm

 

I wouldn't do it (thought about it) This has been tried a bunch of times all with the same results, it just don't work. Excessive tire wear, bump steer, are amoung the reasons.
I put it in my notes of REALLY GOOD IDEAS that just don't work.

 

I wouldn't bother..... but... I disagree that it is a bad idea. Ford pickups used a twin I beam up into the 80's.

 

Nothing in this world is new.
Heres two examples of pre war IFS for british small fords.

 

I think the biggest problem with the I-bheam cut in half is that you will get excessive camber change. Even the Ford "twin-I-beam" set-up with the beams anchored at opposite frame rails was susceptible to excessive camber change, the shorter "half-I-beam" would be even worse. I do not think bumpsteer would be such an issue, bump steer is caused by the drag link and radius rods swinging at different arcs, the "half-I-beam" would not necessarily change this vs a solid I-beam. maybe if you used cross-steer it would definitely have an effect, but for drag link style it won't have much effect.

 

[ QUOTE ]
I wouldn't bother..... but... I disagree that it is a bad idea. Ford pickups used a twin I beam up into the 80's.

[/ QUOTE ]

Yep - that's the Grenfell rip-off, twin overlapping beams.

 

I dont like the one in the pic you posted, Crease.
These split I Beam front suspensions can work extremely well, but the length of the I Beams and the height of the pivot points are very critical.
If the I beams are too short or the pivot points are too high the outside wheel will try and tuck under during hard cornering. ( the setup in the pic has both...)
But if you would build one that is setup correctly ( with the beams overlapping, like monkeybiker was talking about ), and the right spring rates, it really is a great system...
And if setup right there will be absolutely no Bumpsteer.
Here is a pic of the two I beams overlapping in my Mallock U2 Race Car...

 

Pic...

 

And a pic of the car...

 

Thanks Alex, I was trying to remember where I saw that. I
thought it was on a Birkin (Lotus 7 clone) or some car like
that.

Mallock, I love that car, it fit me well too, when do I get
to run it on the track?

 

I think Fat Man just copied the twin I beam setup off a Ford Ranger if I recall.
There's a guy in Modesto that makes a real neat setup along the same principal using a buggy spring. If it isn't hangin' out in the breeze you can make it look old skool and still take advantage of long ibeams.
The trick to making one ride and handle is to put you pivot points on opposite sides of the ch***is instead of in the middle. The beams cross eachother.

Here's a pic of a high zoot car with his split setup on coiul-overs. I thought I had a pic with the cross leaf, but as usual I can't find it. You'd never guess its independent.

 

That's it in a nutshell. The shorter the axle sections, the smaller the pivot radius is going to be, and the more radical the camber changes will be. That is why Ford overlapped them (metalshape's racecar too), so the axle length could be as long as possible. The easiest way to visualize many suspension setups is to draw the frame on a piece of construction paper in a head on shot (sometimes a profile shot depending on the situation). Next, cut out the suspension pieces and locate them with push pins, all on a cork bulletin board. That way you can actually, carefully, move the suspension through it's paces. You will clearly see the advavtages and disadvantages of almost any setup.

 

Check out the Rear end of a C2/C3/C4 corvette.

They use a horizonatally mounted leaf spring, mounted to some trailing arms. Braced against the differential case with a couple of rods.

Camber changes a good bit, but it gives you a semi-independant suspension. My two cents, shorten the lever!

I'd mount the arms farther out... not dead center of the car. The big deal is keeping the wheels from floppin around. The big name racers (**** Gulstrand) created a 6 link suspension. It had a trailing arm mounted to the frame with tierods going from the top of the arm, to the top of the differential! In addition to the tierods that were already there.

 

The pic above, is lacking the differential/half shafts...

If my brain is workin correctly... you'd be mounting a tie rod to the top of the ***embly, going to a stationary point on the frame, parralel to the lower arms.

Then, you'd mount the spindle/mount just like on your standard straight axle.

Hope thats all clear...

 

[ QUOTE ]

Camber changes a good bit, but it gives you a semi-independant suspension. My two cents, shorten the lever!

I'd mount the arms farther out... not dead center of the car. The big deal is keeping the wheels from floppin around. The big name racers (**** Gulstrand) created a 6 link suspension. It had a trailing arm mounted to the frame with tierods going from the top of the arm, to the top of the differential! In addition to the tierods that were already there.


[/ QUOTE ]

I'll give you your $.02 back. If you look at the rear end of the corvette, jag whatever it keeps the tire/wheel pretty much vertical through the suspension travel. Where if you moved the pivot point out wards on a front end it would increase the change in camber through the suspension travel to dangerous levels. You math doesn't work with a spindle on a front end as it is at a fixed angle to the axle. The spindles geometry stays the same and doesn't change. You would need to put a second arm and a pivot to achieve the same thing as the rear ends at which time you may as well went with a truely independent front anyway.

 

[ QUOTE ]


Camber changes a good bit, but it gives you a semi-independant suspension.

[/ QUOTE ]

As far as I know there is no such thing as Semi- independant suspension.
The system you descibe is independant and so is the cut I-beam suspension system we were talking about.
But a double A arm suspension will move through an arc, and race car builders will still talk about "swing arm lenth"
This is the the length an imaginairy swing arm would have to have to make the wheel move through the same arc as it does with a given double A arm set up.
Of course, being 2 completely different systems, the arc will only be the same over a short portion of the total travel...

 

Just to let everyone visualize here is a quick illustration of the difference in how the wheel travels in a split axle vs. a double a-arm. Notice the double a-arm keeps the wheel pretty close to vertical throught the suspension travel as the split axle keeps the wheel at the same angle in relationship to the axle.

 

Its worked well for Ford on their Ford pickups since 1965......its the poor sunofa***** that bought em and had to pay for the tire eatin *******s, that it didnt work out for.....
Id say if a staff of OEM engineers cant fix it in 40 years of tryin -I would not spend one dime on one.

 

Well the thing is the longer the link is the less of an angle it takes for a given suspension travel. But still it is inferior to a parellel arm setup that can keep the tire pretty much square with the road..

 

I think to draw this full circle.

Split Beam is an independant front suspension, but has poor
camber change characteristics.
The longer the arm the less camber prob you will have

Straight beam is not independant but maintains consistant
camber geometry.

If you want your cake and eat it too, you need a paralell
arm independant setup.

Anybody want to talk about DeDion and unspring
weight??

 

You are right Zman, when the A arms are the same length an parralel,the Camber doesn't change.
The old Lister Jags were like that. ( and I have heard that called infinite swing arm lenth, Trailing link suspension like a VW Bug front behaves the same way...)
The reason that doesn't get done much anymore is because when the car goes through a corner the body will roll and the wheels will change camber by the same amount.
If a wheel will get some Negative Camber on bump and some Positive Camber on droop, it will make up for some of that.
Most Double A arm suspensions will have a shorter A arm on top that is angled down slightly from the spindle.
The difference in length and angle will produce the amount of arc, or swing arm length ( maybe they called it instentanious swing arm length, I cant remember...)
The pivot point ( that exists as a geometry point only ) can be far outside the actual car...

 

I had a 74 Econoline van with the split I beam...loved it!
My uncle STILL owns a 78 Ford van he customized back in 79 and he has no tire wear issues...even with 8" mags and wide tires!
A very good system for a 2wd commercial vehicle in my opinion.
Now 4x4 might have some serious issues due to the added height and travel of that configuration!!!

Fatmans setup is basicly for trailer queens in my opinion. Just another waste of money to add to your mirrored sign at the car show so people can ohhh and awe at your ability to find and buy useless ****.

The race version (that alone says it can be capable!) of this setup on the Mallocks and others who used it successfully had the pivot points very low and very wide...so wide that to reapply it to a full size Hot Rod you would possibly have to sacrifice TWO axles to get the same beam length ratio!
I believe (True Alex?) the axles were actually mounted upside down so that the curve of the stock drop and the king pin angle would combine to make the low pivot point possible, without having to heat the **** out of the axle and bend it radically.

The result would be a very low roll center and a better camber curve when combined with small diameter race tires and limited suspension travel.
In basic terms...a SLOT CAR for the m***es.

Personally I think this is the most advanced use of early I beam axles your ever likely to see.

But unfortunately, the "Big Guy" missed it by a mile in the interest of "ease of ***embly"!

[ QUOTE ]
Anybody want to talk about DeDion and unspring
weight??

[/ QUOTE ]

Sure! Be a real interesting post considering the new people we've picked up since the last time it was discussed!

 

[ QUOTE ]

I believe (True Alex?) the axles were actually mounted upside down so that the curve of the stock drop and the king pin angle would combine to make the low pivot point possible

[/ QUOTE ]

True...
plus the way the Cut Wish bones bolt up you can easely get more Caster as well that way...

 

[ QUOTE ]
You are right Zman, when the A arms are the same length an parralel,the Camber doesn't change.
The old Lister Jags were like that. ( and I have heard that called infinite swing arm lenth, Trailing link suspension like a VW Bug front behaves the same way...)
The reason that doesn't get done much anymore is because when the car goes through a corner the body will roll and the wheels will change camber by the same amount.
If a wheel will get some Negative Camber on bump and some Positive Camber on droop, it will make up for some of that.
Most Double A arm suspensions will have a shorter A arm on top that is angled down slightly from the spindle.
The difference in length and angle will produce the amount of arc, or swing arm length ( maybe they called it instentanious swing arm length, I cant remember...)
The pivot point ( that exists as a geometry point only ) can be far outside the actual car...


[/ QUOTE ]

Absolutely. I guess ina way I over simplified it to try and make it easier to understand the inherent design flaws. BUt yes the unequal length A-arms actually address the flaw in the equal length design. Most all suspensions are a compromise on some point or another. But merely splitting a straight front axle has to many critical flaws to make an option to those of us who like to go fast through the turns...

 

Don't know anything about the technical side of things but thought you might like this picture of Sydney Allard's car taken after a failed attempt to climb the UK's tallest mountain Ben Nevis. The independent front end was produced by a company called LMB and obviously didn't hold up to the abuse Allard threw at it that day!