Hot Rods Cowl Steering . . . just stop !

Great thread and great info.

 

It works in 900hp Sprint cars.

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That's because they steer with the throttle and stagger!

 

The Cop Shop Coupe is my favorite rod of all time. It looked so malevolent. The kind of look that would have mothers gathering their kids and hustling them into the safety of the house as the car went by. I had a two page photo of it from Street Rodder Magazine(?) hanging on garage wall for years. It only came down when it got so grubby you couldn't see what it was.

 

....with 4-bar front suspension. Not the topic of this thread. Pete is referencing hair pins or split wishbones.

 

Jeepers, Rootie! Looks like 'caster steer'!

 

No idea what caster steer is, but that is a bell crank of sorts which locates the pivot point of the secondary drag link in line with the pivot point of the radius rod eliminating bump steer. Just food for thought, using some Imagineering it could configured several different ways.

 

But, he also says to not use cowl steering no matter what. Was just asking.

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Of course you guys are right about the pitman arm moving as the wheels are turned, which does relocate the pivot point, but I'm not sure that changes the geometry with regards to bump steer. Look at the attached pic from the Pete & Jakes catalog. Re image 2, you can move point D forward and back and up and down a slight amount, as would happen in a turn, and that doesn't substantially change the arcs A & C, not enough to induce bump steer. I verified that last night myself, taking a nice sweeping left hander (transition connector from the north bound 55 fwy to the west bound 91) at about 70 mph. This connector goes up and over the 91 fwy, makes a wide sweeping left hand turn, then drops back down to grade level as it merges onto the fwy. Unfortunately for us living and driving here in So Cal the road surfaces of most of our highways are in exceptionally poor condition, due to the failures of our state gov't to properly maintain them, and this transition connector is no different, with several really nasty grade separations in the middle of the turn. But steering was rock solid, no bump steer at all. Consider this myth busted....

 

If the "he also says to not use cowl steering no matter what" is referring to me, that is not what I said at all.
If that is what have come away with reading this thread, you have missed the point.

 

"Bluse 4U" thanks for enlarging this Image,

These are the two most important side steer concepts to understand
#3 explains the whole cowl steer / split wishbone / hairpin deal.

If you want it perfect put "D" & "B" at the same point
The farther you move "D" away from " S / B " line, the more bump steer you introduce.
pretty simple.

 

not to hijack anything but I would like to ask a question
we are preparing to start the chassis build for our 'caddy roadster' at school
the front suspension will be suicide style. More than likely a tube axle with hairpins. The mock up looked like we would have to run the drag link in front of the axle but I have read some negatives about doing this. I see a lot of T buckets like this.
is this bad or not?

anyway, thanks for the geometry lesson. I have some nice ammo now to show the students why getting the geometry correct is important when we start the chassis set up and some very nice visuals to demonstrate this to them.

 

I guess you mean "tie rod" in front of the axle. if so, yes it can be done but look into Ackerman angle, you will have to bend the steering arms to get the geometry correct. Sometimes it can be hard to get it right so plan it out first.

 

Wasn't Trying to be a dick, Im curious, Never done Cowl Steering before, but am working on a 34 Ford PU and wanted to to Cowl Steering, but If I can't do it properly, then I want to understand why or how to make it correct. I was going to use a Sprint Car steering box, so I could get Power Steering, and since we build sprint cars I have a bunch of racing junk laying around.

 

Yes tie rod
Sorry
Thanks for the info. Just found a diagram for checking Ackerman angle and bending arms

 

so what you're saying is the geometry doesn't have to be perfect and you still end up with no bump steer. the real question is how far off perfect can it be before experiencing bump steer. and then how far out of whack does it have to be where it becomes a life and death issue.

pete keeps bringing up the geometry and how he can declare by just looking at the pivot points that the car definitely has bump steer. i believe there's other factors that come into play. i'm not doubting bump steer. it is real. i'm saying there are steps you can take to minimize it. one is suspension travel. look at the diagram above. 4 inches of upward travel? really? does your buggy spring suspension allow a full 8 inches of travel? that car would be the poster child for bump steer. that fucker would be bouncing all over the road. now take that same set up on car with maybe only 2 inches of up and down movement, it would still have bump steer, but not as bad as the first car. how else do you explain cars like the rollin bones with 3000 mile cross country treks, being driven on the salt and then another 3000 miles back home.
next they'll be coming after our bias ply tires.

 

Amazing after reading through this thread, started by one of the most knowledgable builders, that the argument comes back to building "traditional" or "it doesn't bother me that much on my car". Far too often I have seen setups that make me wonder how well they work. Forgiving poor engineering because it is a hot rod seems lame to me.

 

What I'm saying is that your claim that "in a long sweeping turn, bring on the bump steer." is not accurate. That's all. So we can put that line to bed and move on in the discussion.

Now, if you look at the picture I posted from P&J, in a turn the pivot point D doesn't deviate away from the S-D line very much, and it is deviance from that line that results in bump steer. The further away from that line, the greater the bump steer.

Id does seem that the greater the suspension travel, the more the bump steer effect would be amplified, because the difference in the A & C arcs grows the further the suspension travels. So minimize suspension travel and you minimize bump steer. But that doesn't eliminate it. And then you have another bad affect when the suspension bottoms out. Doesn't really seem like a good strategy to avoid bump steer.

 

Woops! I stand corrected. Maybe I wasn't paying attention or I was excited about who posted this thread but I have a 4 bar suspension. I jumped up and down on the front spreader bar and nothing moved. Again this is good education from what I and a lot of others consider a professor........

 

OK , one more time
Pictured is a classic example of what we are talking about here
referring to the illustrations below,
On this car, notice how far point " D " is from the " S / B " line.
This is what creates bump steer.
In this example & with others like it, the bump steer is about as extreme as it gets.
Yes, you can look at a car & tell it has bump steer.
It doesn't take a lot of suspension travel with this type of set up to experience it.
With a set up like this, using your body weight, one can move the front suspension up and down a small amount & watch the steering wheel rock back & forth ( a lot ! )

 

Here’s one way to solve the wishbones/cowl steering problem Pete has mentioned. Use (either in the car, or outside as Hollywood Hotrods did), a lower shaft that is connected to the steering output shaft, via a vertical connector. The lower link is positioned so that B-S line is almost same as D-S line. The arcs travel almost same, and should not have noticeable bump steer as other high-mounted cowl steer units exhibit


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Well there's no way to possibly ague against the arcs and geometry.
It all clearly shows that the car has bump steer.
That point is completely settled.

However there's one contrary point left and apparently several reasons for it.
Just hear me out here, I do believe I'm on to something and going to attemp to make a clear concise point, and something else equally detrimental to be considered.

First the one contrary point- there are cars with cowl steering that get plenty of miles and no complaints. You can get as many examples as you want of this.
Next the reasons for this- one and a popular reason is that the driver simply doesn't know the difference. Another reason in any variation imaginable is the owner/builder/driver is living a lie in order to justify their poor geometry.

For the moment entertain the idea the cowl steering does drive fine without complaint, that the owner is not lying, and that they do indeed know the difference. How is that possible? Within the the pictures and drawings presented here and my own draw up, the "arc fight" as Pete put it clearly exists, it's right there in black and white. Yet those examples of cowl steering without complaint are there and should not be ignored or dismissed under the popular reasons.

So let's look closely at point "S". What happens if point "S" moves without rotation of the spindle?? Point "S" moving along the opposition arc with spindle rotation in accord with "S" movement is bump steer. Point S movement along the opposition arc without spindle rotation must have the movement someplace else, the movement absolutely does happen.
The movement of point S without spindle rotation as natural consequence results in fore and aft linear movement of the spindle and and everything attached to it including point S and the King pin and the axle with that linear movement beginning and ending at the spring perch.

For me, I take this stuff seriously and will attempt to correct it for my customer. I see things differently and as a result my points get missed. But in a nutshell, if a concep is supposed to work but doesn't there will be a reason, conversely if a concept is not supposed to work but does well there is a good reason for that as well. I will be figuring if it's a weak axle, too much scrub radius, or too tall of a steering arm. I'd like some help dissecting that issue but I understand if you'd deem it as rambling.

https://www.jalopyjournal.com/forum...r-thread-that-got-axed.1100074/#post-12477913

Btw.
I did jump on the cars front end, there was no movement in the steering wheel or the chassis, that test I'll reguard as inconclusive without any chassis movement. I did drop the suspension to full droop and back up to holding weight and the steering wheel showed a little better than 1/2 turn.

 

@31Vicky with a hemi that and the universe is an unexplainable head pondering question that just proves one can not judge a book by it's cover and exclaim "Stop". Even Richard Feynman admits, there's a time to let go to that has no definitive answer. Even if it's looking at you straight in the face.

 

It must be pretty stiff if you couldn't get the front end to move by jumping on it.
I assume you used stands & a jack to do the suspension drop.
in inches, how much suspension travel, resulted in the 1/2 turn of the steering wheel?
That is a huge amount of steering wheel movement

I've driven the Doan Spencer roadster ( heck, I did a lot of the restoration work ) . Regardless of what you may hear, cars with that type of set up have bump steer.

 

This car, when under acceleration, does it need a little 'steer to the left' to keep it going straight ?
And under deceleration, does it need a little ' steer to the right' to keep it going straight ?

 

Yes it was on stands
From ride height to full droop suspension movement is between 2-7/8 and 3" -,Hard to get dead nuts an exact measurement on that. Also that would be at the far extreme of the arc fight and just to be sure that all of that suspension movement went to steering wheel rotation, I bound the wheels.

Also with the wheels bound, using the steering wheel I can move point S linearly 3/8 from center in either direction an inch before detecting any spindle rotation. The axle moves, first right behind the King pin then at the spring perch.

 

If it does it's not enough to be noticeable or remarkable under normal street driving (don't get a ticket) conditions. I've done a few hole shots and stuck my foot in it pretty good up to 50mph from a dead stop and don't notice a needed steering wheel correction to stay straight. Getting off the throttle from 70 I don't notice it either. Not that it's not happening just not enough to be a noticeable issue. On my wife's car FWD supercharged Grand Prix you definitely notice and need to correct when you stick your foot in it.

 

1/2 turn, that's a ton of steering wheel movement for 3" of suspension travel.
The axle is anchored at the spring perch / wishbone. With the steering arm on the spindle raised way up like it is, you are increasing it's leverage to flex the axle, so yah the axle is going to flex. A tall steering arm like that on a dropped axle is not a good idea.
Remove what you have binding the wheels, & with the wheels in the air, run the steering back & forth. Probably don't see as much axle flex. The car rolling down the road will have less resistance against the steering that it does at a standstill.