Technical Need Pre- war race car handling help! Understeers badly

1/8 In toe in, 3 or 4 long leafs up front and in back, 4 to 6 Degrees of caster up front.

 

I'm a little late to the party.
A very interesting thread that I've just read through. I've been road racing my '36, among others disciplines, for nearly 10 yrs and the picture below, exiting the Goodwood chicane in May, is where I'm currently at with the car.



I've spent most of time making small improvements (tyres, shocks, driving style etc) , but the car has always suffered from understeer.
A couple of years ago I made a complete U-turn with my approach to car set-up and the improvements have been huge.
The first was to soften the suspension. I fell into the trap of piling on stiffness, more spring, more shock, more anti-roll bar. You need to let the suspension do its thing and then control it i.e shocks. Shocks, shocks, shocks! Such an important part. I think Early fords are over sprung from the factory. If your running stock springs with a lightweight body/car, you need to be softening it up. This leads me into the split wishbone. Bad move. You've created way to much stiffness in the rear suspension.
The other is front end set-up. The wrong or excessive toe will cause understeer issues, but the biggest factor I've found is camber. All Early Ford front beams have positive camber. You will never get a beam suspension to handle with positive camber. I bent my beam in a 10ton press and at great effort (I never want to do another one!) to give me 1.5 degrees negative camber, which transformed the car and has almost eliminated the understeer. I saw you mention earlier that you had 1.5 neg., are you sure? Did you mean positive camber? This is about right for a well used original Ford beam.
If you have 1.5 degrees negative you'll know as the suspension looks broken, but man does it go round corners!

 

In all the years I've been running race cars, I've often wondered the "whys and wherefores" of the "Back Markers" or constant "Also Rans"! Both on dirt and pavement. Ovals and Road Courses. ears, NOW I KNOW! By reading of all the use, or lack thereof, of reasonable chassis design on this thread with geometry that considers tire "Grip" in all regimens, I see why there are a lot of perpetual losers. I like to ponder the event many years back where at the USAC Phoenix 150 when Geo. Follmer and crew-chief Howard Gilbert called on my highschool chum, Bruce Burness to set up the chassis for Follmer's Iron block SBC race car. Bruce set it up for a turn with exact geometry that had no undo "scrub" on any of the four tires. No weight offset, no differential tire pressures, no "Stagger" (leave that for the drunks)."Akerman Principle" used so that both front wheels had their own turn radius (the car was not slowed in the turn by a dragging right tire). Follmer won going AWAY (not fast on the straight;but very quick in the turns). The "Naysayers" told Bruce that George 'Backed into the win, 'cause Mario (Andretti) dropped out!" Bruce replied: "We backed in from the Pole Position when Mario ran out of gas!" "Bottom Line"! Dust or Asphalt, nothing is better than good engineering!

 

I go along with softening the suspension on a hot rod "airport racer".
I built several 32 and model A roadster "sports car" road racers in the 50's and 60's.
They were all winners and while I would have liked to have gone south and ran against Livingstone, Balchalski and
Miller I knew I could not compete with the kind of horsepower they had with my 315 flathead.
I had a lot of fun blowing by C Jags and Mercedes 300SL's in the corners though.
All of my cars had and still have 100 lb per inch or less, spring rates both front and rear and at least 5 inches of compression travel. Stock type wishbones front AND rear. I use sprint car type shocks so there is a wide selection of compression/rebound rates available and I have them set up with quick change pins at each end so it is possible to change 4 shocks in less than 3 minutes if need be.

 

If competent constructor were to build a vintage race car that used period correct parts but with 2019 knowledge , it would certainly have an unfair advantage. [eg: antiquated ideas like positive camber for the curvature of the road, simply don't cut it anymore]

The OP needs to corner weigh the whole car [with driver]
The unsprung weight at each corner.
Then also calculate the front CGH and rear CGH with the scales
Then the roll centre heights Fr and Rr.
And Fr and Rr track widths.

Once this is done, it is easy to calculate Fr and Rr weight transfer and also how much of this weight transfer is via "overturning moment" [which is the tune-able part]
There are other factors to consider such as motion ratios etc.

So all these recommendations are just a moot point

You can never build a car too low, too wide. or too light.

 

I can go with Enbloc's advice. The car needs to be freed up so the components actually work. On the stock cars I ran, it was normal to have a lot of - camber on the RF, maybe as much as -3*. It looked bad, but it worked. The figure-8 guys did this on both sides as the car had to be ready for RH and LH turns. If I had a handling problem that stymied me, an old timer showed me how to find a bind in the chassis. Put the car on 4 jack stands, remove the wheels and check everything, granted the OP's car is a lot simpler in design. In my case, make sure the upper and lower control arms move, look for a frozen or jammed ball joint. Look for a bent sway bar. Probably the simplest and having the most impact were shocks. I found one on the RR corner once, the rod somehow had a slight bend in it, not letting the car down fast enough and the chassis was loaded the wrong way.

 

It'd be handy to see how your quarter elliptics are mounted - typically they'll give you roll steer as they effectively lengthen and shorten your wheel base either side as they flatten out.

 

It would be good to see the whole car's set up [otherwise we're all taking a stab in the dark]
His car has a cross leaf model A spring in the rear and 1/4 elliptic springs in the front only.

Roll steer is only a rear suspension problem due to the wheels always being perpendicular to the axle.

During body roll a front beam axle and the tie-rod parallelogram themselves and the steering angle doesn't alter.
The front only has bump steer [generally wheelbase variations are corrected with steering geometry. Eg: draglinks on cowl steering etc]

 

Depends if the quarter elliptic is used to locate the axle, without a shackle, like on GN's. This thread needs pictures!

 

Only if on the rear axle........... Front axles don't roll steer [if the bump steer is correct]
If one side lengthens , the Axle and Tie-rod stay parallel, and the L and R wheels stay parallel [ they all become a parallelogram shape ]
It only becomes a problem if the front wheels are fixed perpendicular to the axle [or there is a bump steer issue ]

 

At the risk of going off at a tangent, I wonder if positive camber on front axles persisted because they were empirically found to trim out oversteering tendencies. The early-Vintage Leyland Eight famously ran positive camber on its rear axle, on the curvature-of-the-road theory; but positive camber on front axles seem to have outlived that view. I'd expect that the combination of narrow front spring base, wide rear spring base, and slight rearward weight bias would have made the typical car of the era a recipe for oversteer at the limit, which was found for reasons not quite understood to be tempered somewhat by positive camber at the front. In fact a lot of the early history of chassis development suggests an emphasis on getting rid of oversteer as if it were the only dynamic vice.

But, as I think you're saying, all that becomes almost moot once you grasp the load - pressure - slip (or rather twist) angle interrelation.

 

if you are going left and right maybe you could increase spring rate to load the front end

 

Pictures

 

Again thanks to all of you that provided insight as to rectifying my understeer. I spent a good deal of time trying to sort out the good advice from the less good.....
I'm back to working on the race car again. Kids and grandkids all safely back to they're respective homes and quiet here again.
So; thinking the suspension is too stiff I disconnected the shocks and bounced it up and down and side to side(pushing and pulling on the roll bar up high)/. Yikes. Like no movement; it wasn't like that before! I committed a cardinal sin by changing the rear radius rods and adding a panhard bar at the same time.
I then disconnected the rear panhard bar. Holey shit she moves now like a baby buggy. Apparently my rear end doesn't like the radius rods somewhat parallel with a panhard bar. For what ever reason the panhard bar put the rear in a total bind.
Up front with the shocks disconnected it bounces nicely. No binding at all.
So at this point and not wanting to change too much at one time I'm going to Road America 7/19-21 with all else the same but no rear panhard bar. R/A is not at all as tight a track as Blackhawk Farms but I should learn something.

 

Some more pictures with hopefully more detail
Picture jacking in the rear after removing the rear panhard bar. With the bar in place the r/r was almost not touching ground

 

Please keep us informed, as I'm interested, and I'm sure others are of the same mindset. At 81, Im not planning to go road racing, but there are still times when I get a bit "enthusiastic" on some of these twisty roads here
On edit: Going back and looking more closely at the pics, Your rear spring shackles are at a near ideal angle and I think a rear panhard bar isn't needed.

 

Front springs and front panhard bar. I believe the front bar is required for this front suspension. It sits dead level at rest.

 

If I find the shocks are too stiff I can change to lower vis oil.

 

Can't change wheelbase due to wishbone.

 

Well this is an entertaining thread!...the number of people who fail to realize that the end of the car with more roll resistance (" roll couple ") will slide out first is amazing! The one thing that baffles me however is a straight rear axle with split wishbones certainly should have the most roll resistance due to the axle acting like an" antiroll bar" ....

 

Yes; I think too much antiroll in the rear, just pushes the front.

 

I may have too much front spring. The 1/4 elipticals look and function like each 1/2 of a stock Model A cross spring. I know my car is lighter than an A but the stovebolt engine is heavier than a Model A . Then again my engine sits rearward more... something else to fool with!

 

Panhead, I think your on the right path there!

 

As I said earlier the split rear radius rods all the way outboard to the frame like this car put things in a binding mode. And like bottoming out, bound up suspension can cause very different reactions to what you would expect, pretty much unpredictable. With the lever action shocks it makes it more difficult to measure wheel travel. With tube shocks a zip tie around the shaft of the shock will give you an indication of travel after a couple of "hot laps"

 

Dirty, I hear you loud and clear. After I test a bit more I will move the end points closer to the center of the car. I can get the rears to within 6" of the center line. Fronts not sure yet. As for the shocks....some guys have hid tube shocks inboard.....not as effective there but maybe better than the Armstrongs. Maybe I can rig something to check for travel with the lever shocks

 

My comments in post #86 were directed @ King ford in response to his comments about how spring rates affect under and oversteer. They are accurate when the suspension moves freely, but all bets are off with binding or bottoming involved.
I think if you can figure out a way to measure suspension travel, it will help a great deal in deciphering what's wrong and correcting it. I also agree with the suggestions for negative camber on the front.

 

In addition, I would be sure not to change too much stuff at the same time. As you get closer to what you want/need in handling then you can fine tue with small thingslike tire pressure, wheel offset and all sorts of tricks
Maybe leave the rear radius rods as is till you try it without that rear panhard bar.

 

The rear bodyroll could be twisting the frame and unloading the outside front. The whole frame will be pivoting around the ladder bar front pivots when it does this.