Hot Rods Cowl Steering . . . just stop !

Radials? is there a panhard and a damper. These all pacify but he (Pete) also did say geometry and I know you are very in tune with it. As Ludd said if you really understand there are ways...But guys like me I'll just eat popcorn and try to understand...

 

Yes radials, yes panhard bar, no dampener

 

Have any issues with left turns?
maybe tire hitting drag link?

 

If the front drag link end on the spindle is a couple inches above the spindle's kingpin (like in 31Vicky's photos), can you raise the back end of the drag link too? Basically making two parallel planes? Assuming the drag link and the hairpin/wishbone are the exact same length to allow equal arcs.

 

Darrell Zipp built my Zipper 19 years ago using quarter elliptic suspension and a Schroeder box. The drag link is parallel to the ground and within a couple of inches of being on the same arc as the hairpins. Unlike many cars posted here with 4" dropped axles, I'm use a '32 heavy with a 2" drop. I think that the quarter elliptic suspension and lack of a deep dropped axle may be one of the factors that has eliminated the bump steer issue on my car.

 

There are a lot of cars with bump steer, being driven plenty of miles, that doesn't make it good, ( or safe ).
Pictures have been posted & descriptions detailed, none of it correct.
I would guess some of the cars with bad geometry are masking the bump steer with stiff suspension.
There is the possibility that some owners don't know what bump steer is, and assume what their car does is normal.
If you are not sure, go to the front of your car, if it has frame horns, stand on them & jump up & down.
While you are doing that watch your steering wheel, if it's rocking back & forth you have some bump steer. If it is rocking wildly back & forth you probably have cowl steering & split wishbones / hairpins.

 

Good explanation.....

 

No. The steering arm on the spindle travels through an arc centred on the rear pivots of the hairpins/wishbones. The front end of the drag link travels through an arc centred on the bottom end of the pitman. The two centres are at different points, so if the arcs are going to cross they'll only do so at one point. Everywhere else they are going to pull apart. The greater the distance between the centres, the more the arcs are going to diverge, the more bump steer for any given suspension movement.

Colin Chapman famously said that any suspension will work if you don't let it. You won't have enough bump steer to worry about if you've only got ¼" of suspension travel for most intents and purposes. I suspect that this was the case with a lot of early builds. Colin was still experimenting on various Austin Seven specials etc. when the definitive hot rods happened.

At that time adding spring rate was considered a sort of suspension panacea. Hence the bone-jarring ride which survives on Morgans, for instance. Yet more people than Colin Chapman were thinking about the performance benefits of soft, long-travel suspension at the time, doubtless the result of trains of thought begun while trying to find ways of traversing hostile terrain during WWII. So long-travel suspension was very much part of the theory, if not the practice, of the "traditional" era.

 

Pete, I couldn't agree more, it's funny, you can take a ride in a guy's car and he'll explain that it's a hot rod.....like it's supposed to be that way. The geometry behind bump steer is simple and anyone can learn what causes it, trouble is, most don't care to know. When I see a car with cowl steering and a foot long pitman arm, I wonder how they can drive it, must steer so fast.

 

Fist a bit of comic relief, someone told me that you are really Pete Eastwood. For the longest time I just figured you were someone using the name. :eel:

So now you have opened this can of worms, perhaps you should take the time to educate us. Split bones and Cowl steer has been around longer than either of us and there is a correct way to do it, unless I am mistaken.

 

How about on the T modified I'm building with parallel springs on the front? Here's a pic of a project by an esteemed builder with similar proportions:





I realize the arc length of the drag link is going to be different than than the arc length of the axle on the shorter spring. What's a guy to do? And, would mounting the shackle on the front of the spring make any noticeable difference to make the axle/spring move in the same directional arc as the drag link?

 

Oh my More fun to come.
Good luck.Have fun.Be safe.
Leo

 

That is exactly what makes bump steer & will only make it worse.
It's geometry.
Forget about components / axles / draglinks / wishbones / etc.
it's points in space. Two points make a straight line, it doesn't matter if they are connected by a pretzel or a hairpin.
The drag link is steering the spindle.
The drag link is controlled by where it attaches to the pitman arm
The spindle is controlled by where it attaches to the chassis (the back end of the wishbone / hairpin )
Soooo . . . looking at the car from the side . . ( because that is the view you need to consider because of suspension travel )
Draw a line, from the point where the split wishbone / hairpin end attaches to the frame, to the point where the drag link attaches to the spindle arm ( yes that's right! )
Draw a second line, from the point where the drag link attaches to the pitman arm, to where the drag link attaches to the spindle arm ( you may have a drag link with a zig zag in it, so that is why we are drawing a straight line )
Those two lines share the same front point.
Now draw an arc, pivoting from the rear of the drag link, through the point where the draglink attaches to the spindle.
Draw a second arc pivoting from the rear of the wishbone / hairpin, where it attaches to the frame, through the point where the drag link attaches to the spindle.
At the point at the front of the draglink, check what the arcs are doing.
If they are laying right on top of each other you are golden
If they are moving away from each other,
The quicker they are moving away from each other the worse the bump steer.
I hope this wasn't to hard to follow.
You don't have to drive a car to tell if it will bump steer, you can tell just by looking.

 

Completely different dynamics & geometry than split wishbones / hairpins
Which is what this thread is about.
Let's save this for another day

 

Pete, I am sorry, I am more of a visual person...could you draw something showing this? Specifically the arcs?

 

I hear you but cowl steering still looks cooler.... and deep down isn't that what traditional hot rods are all about? If you wanted best performance for your money we would be driving either a Lotus Exive or a Honda Civic R. No one would put a flathead in anything when they could fit a Zetec.

Sent from my SM-A520F using The H.A.M.B. mobile app

 

Pete, what would be your ideal steering solution on a traditional high boy hot rod?

 

I understand what your are trying to say, but suggest you are combining two different principles into one.
Choosing to use vintage components and styles does not necessarily require unsound principles of either engineering or geometry. It mostly requires an interest in understanding the fundamentals of what one is intending to do and being careful how they are applied. The difference in sophistication of a 'B' banger vs a Zetec has nothing to do with insuring how either is utilized in a particular application. Same for suspension principles that merely require attention to geometry when utilizing an older format.

Ray

 

So the only way the steering will actually be perfect is if the bottom joint of the pitman arm (the rear end of the drag link) is at exactly the same pivot point as the hairpin, right? Everything else is a compromise.

I know these next questions are going to be non-answerable, but here goes: How far off perfect can it be before it becomes too bad? How much shorter can the drag link be if it's on the same plane? Or how far above the plane can the drag link be if it's the same length?

 

and then it's only going to be spot on perfect going straight. so in a long sweeping turn, bring on the bump steer.

everything is a compromise, we aren't building street rods here.

 

Good discussion as long as we don't get too big-headed or get our panties in a bunch...lol.
My 0.2 cents worth. Just thinking out loud...because it IS interesting. Btw...I'm always open to being wrong...especially since many of you guys have waaaaaaay more experience than me.
But geometry is geometry, so it is what it is, geometry has no opinions.
At first, when you guys brought up the idea of quick steering and bump-steer coexisting, I thought to myself, wow, the quick steering would really increase the bump-steer problem. You know...tend to yank the steering wheel from your hands. But I'm thinking that the opposite would actually be true. With quick steering, a small amount of movement at the steering wheel causes a larger change in direction at the tires. In reverse, bumps in the road, causing movement in the suspension, and the subsequent bump-steer would act upon the steering wheel to a smaller degree.
Yes? Or am I just over-medicated?

 

Until you encounter a pothole or railroad tracks!

 

I have to agree with the Beaner ,I never knew Eastwood was a real guy , I just thought that was the name of a Badass model A sedan. Seriously I think I can speak for a lot of people ,feel free to show us ,some of us are slow but we can can understand pictures, Thanks for the post.

 

I can assure you I know what bump steer is.
And the car drives fine- not perfect but perfectly acceptable
So look here- Soft axle, check it out.
https://www.jalopyjournal.com/forum/threads/soft-axle-whats-going-on-here.1022965/


Drawing up the arcs this is what is developed.
Full size draw up at actual measurement.
There's other stuff drawn up too but try to ignore it.


Crossing of the arcs at steering arm



The variation at pitman arm.
This would show the amount of pitman arm movements needed to keep the car straight and counteract the bump steer.

Like Pete says it should not drive fine, and be a bump steer mess,
However, check out the soft axle link ant these 2 pics
That axle wiggles around between the perch and the King pin enough to cover up the bump steer. I'll have to ponder more but I think that axle is the reason the bump steer is masked.
These pics were taken with tension to turn left and tension to turn right.
Compare that axle movement to the draw up pics.
If my thinking is correct, the axle gobbles up the first 3/8" of any bump steer.

 

These are the drawings from the "Pete & Jake's " catalog
#2 is the typical early hot rod set up & it's pretty good.
#3 "Mustang with wishbone" set up shows the same geometry as cowl steering with
split wishbones / hairpins & why it's not good.
Find a "Pete & Jake's " catalog & read these pages
Take a class in geometry.

 

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One I'm building. Ninety-nine percent of the vintage sprint cars I've seen used it. I realized the effect cowl steering was going to have and I tried to mitigate its effects on bump steer by using a relatively slow Gemmer box with a relatively long pitman arm to try to get the drag link connection down nearer the pivot point of the hairpin. I'll be using it for track time as well as occasional street driving. Not expecting much suspension travel - that will help too. In a perfect world the pitman arm would be further forward and lower and the hairpin pivot would be further rearward. I'll be adding a panard bar to stabilize the axle shackles.

 

Is this how the Israelites felt when Moses brought down the commandments?

 

Very well said !!!!!!!!!

 

You got it !