cowl steering geometry questions.

I have been searching for a week and can't seem to find info on proper cowl steering geometry setup, as it relates to a beam axle front with split wishbones.

I understand that with traditional drag link steering that the proper setup is to draw an imaginary line from the tie rod end mount hole on the steering arm to the center of the pivot point of the wishbone on the frame, and that the drag link mount hole on the pitman arm should fall within this plane. In this way the drag link and the split wishbone both travel the same arc during suspension movement.

I don't think I've seen a cowl steering setup yet that puts that drag link hole in the pitman arm in that invisible line. By nature the cowl steering setup puts that point MUCH above the proper point. To achieve the proper geometry you'd have to lower the steering box down a bunch, at which point you might as well run F1 steering or the like, OR, you'd have to make the pitman arm LOOOONG, which would mess with your steering ratio, not to mention looking kinda dumb.

So, what about this solution--- currently the invisible line in my setup runs downhill to the rear. could I bend my upper steering arm down toward the axle, pie cut my wishbones, and raise the wisbone rear pivot point on the frame, in order to make my invisible line run uphill to the rear? This should make it easier for the drag link hole in the pitman arm to intersect the line.

Does it matter that conventional drag link steering places the pitman arm in front of the wishbone pivot, and that cowl steering places it behind?

 

Make the drag link as close as possible to the same length of the wishbone, and as close to parallel as possible. This will give the 2 similar archs through suspension travel and reduce bump steer.

You probably wont get it perfect, but thats life. Just do the best you can.

 

no one else has thoughts about this?

 

from what I understand about steering geometry (which the more I learn, the more I realize I don't know) I think 52pickup has pretty much put you in the right direction. You will end up either with something that has a way off ratio, or bump steer. Personally I'd avoid the latter. Its just like everything else in life: "you gotta pay to play" In other words, minimize bump steer as much as possible, and make it safe to drive, but live with whats left if you want cowl steer. You ever stop to think there has to be a good reason why henry didn't put cowl steer on these things from the get go?

 

A properly designed cowl steering is WAY better than any of Henry's Model A thru '34 designs. There are quite a few basic rules that need to be followed however. It starts with a bunch of math and another bunch of measuring before you even begin to mount anything.

 

You're right that the axis of the radius rod and that of the drag link should be the same. That would be ideal but not practical with a cowl mounted box. I hear people say all the time that the radius rod and drag link should be parallel...thats not true with a split wishbone (or hairpin) setup...that's the way to set up a four link because the axle dosn't rotate through an arc. And keep in mind that the bumpsteer will be a lot less in a hot rod with a couple inches of total suspension travel than in a stocker with more travel.

 

so where do I find these rules, math and measurements? I want to get it as close to "right" as possible BEFORE I weld everything together.

The whole bit about "just get it close and live with it" doesn't cut it for me. I am building this car because I want BETTER, not stock or worse. All hot rods should have a loftier goal than "Awww... fuck it, it's JUST a hot rod."

I realize that I may not get it perfect the first time, especially based solely on the science of it to begin with, and I'm cool with that. I intend to make things changeable where necessary, but I really would like to at least start in the right direction.

 

find an old Pete & Jakes catalog...before they started building complete chassis's

it explains side steering , how to set it up...and has diagrams

the drag link parallel to the wishbone is not always correct

 

I have that info, just wondering if there are other factors to be considered, such as the pitman arm being behind the wishbone pivot point, rather than in front of it like conventional side steer, or if that's it.

As far as the parallel thing, it seems to me that you'd do better with the drag link parallel to the imaginary line from the upper steering arm to the wishbone pivot point, than parallel to the wishbone itself. It'd be closer to a 4 link type geometry then.

 

Here is where I found my information -

Tex Smiths Book How To Build Hot Rod Chassis

There is not alot on Cowl Mounted Boxes however there are some tips in this diagram. I would recomend this book to everyone, it has been extremely helpful. It is not full of Bolt-On Billet parts. It is full of real garage build tips!

 

You won't get it perfect the first time, the second time, or the third time. It's cowl steering. By it's very nature it's nearly impossible to build it with zero bump steer. I look at the problem for weeks before deciding that the best way to go about things was as previously suggested, run the draglink parallell to the hairpin, and as close to the same length as possible. That results in as little bumpsteer as is possible given the packaging limitations of cowl steer.

It isn't perfect, and that drives me nuts since I used to build road race cars for a living, but there's not much to be done about it. 90% of what you're worrying about is paper theory anyhow, doesn't really translate to a real world problem.

 

Yours seems to be the prevailing theory. I asked a couple old timers around town that used to race sprints- they all said, and I quote--- "HUNH?". Thanks for the pic of your ride- it's quite inspirational and LOOKS KILLER! I got with the waterjet guy this week, I should have my pitman arm and other pieces in a week or so. I gotta get an upper steering arm and the box next week too.

BUT... I want to at least start with paper theory. Geometry works and makes sense to me. It always seems better to me to study a bunch before hanging my neck out, y'know?

the four pics/descriptions posted from the chassis book are the same as in the front of the Pete and Jake's book.

 

i'm not an expert at cowl steering ,or driven a sprint car that this setup get's it inspiration from . but i can't believe that a car that spends most of it's racing time sliding sideways on dirt that proper geometry is a big factor.

that's on dirt..and you are talking about a street driven car.

well. i don't see any way of making that type of steering have the proper geometry..i think you do what you have to and live with it

what i have driven are some hot rods with incorrect steering. sure they have some funny habits...get used to it

 

Bump steer on a sprint car is irrelevant for the most part. You're constantly making steering corrections anyway....elbows up and bearing down.

If you want to drive a street rod that way then build the thing ignoring the accepted design theories. If you prefer holding the steering wheel with a thumb and forefinger at 70 mph while holding your cell phone (cheeseburger, beer, etc.) in the other hand then it might be in your best interest to apply a few of the basics to your design.

 

I've just had a look at the picture of Hillbillyhells cowl steering setup, and I only see one potential area for improvement. If the point where the hairpins attach to the frame were moved back to a point directly below the output shaft on the cowl steering shaft, there would be some improvement in terms of bump steer. Of course, that would be a major pain in the ass, and require longer hairpins to be fabricated. I don't think that a cowl steering setup can get much better than what he has shown.---When the wheels are facing straight ahead and the Pitman arm is pointing straight down, the drag link is running parallel to the centerline of the hairpins.---And the way he has it set up does not require any modification to the front axle or spindles.

 

I agree.

 

are you nuts? I've won a few championships running midgets on dirt. Properly designed steering/suspension setups are the only way to win on a rough track. there is no way you could hold onto a wheel that had bump steer when it is half a turn lock to lock......

 

Thanks! I couldn't really go any longer on the hairpins, they're already REALLY long since the axle is in front of the radiator. I debated adding another 6" to them when I was fabbing them, but thought they might get a little flexy.

No modifications to spindle or axle, just one tall ass steering arm to get that end of the drag link in the right place!

 

I've built 4 cars with cowl steering. I try to keep the draglink parallel to the ground. None of the cars have had any amount of bumpsteer. It may not be "right" but it works. I think the geometry is more important when the draglink is short like in a conventional side steer location.
Clark

 

not only the draglink but when the hairpins/wishbones are short as well. if you have a nice long drag link that doesn't move very much through the arc of the supsension and short bones that cause the front end to swing alot through the bumps then you will get bump steer that way as well.

 

Good point rev. I don't like the A bones or 32's cause they are shorter than the later bones.
Clark

 

One of us must be nuts ! Look at any sprint car and you'll see a 4 foot draglink and a 2 foot (at best) left front leading arm (radius rod). That's as bad a design as there is if bumpsteer is a concern. Besides, the power assist absorbs almost all feedback to the steering wheel so any amount of bumpsteer is barely noticeable if it's noticeable at all.

 

When we unloaded the rolling chassis, the first thing that happened was the steering flipped from a right turn to a left turn! It took a lot of trial and error to get the pitman arm and steering arm right. This is a Schroeder sprint car box.

The steering arm is a much modified Speedway Motors hair pin. I actually used 2 of them before i got it right.

The results were well worth the work. This car handles like a slot car.

 

I believe the 32's are the longest ones Ford ever made?

Matt

 

Matt...didn't know that. I know the 42-48's are pretty long. I never had a set of 32's ...I'm too cheap for that overpriced shit.
Clark

 

this is exactly what I was trying to get at with my other posts- that armed with the proper info I should be able to build a car with as few "quirks" as possible. Finding the proper info is sometimes the hard part. Funny thing is that what I end up with may still be exactly what I am arguing is wrong- the radius rod and drag link parallel and similar in length. It may be as close to right as it gets, but I want to know BEFORE I set everything up, just what RIGHT is.

As something of an explanation of my position- One of my buddies very recently came within an inch of his life as a result of improper steering/front suspension setup on his hot rod. He did not build that part of the car, and doesn't know anything of proper front/steering geometry. The builder's negligence and the owner's lack of knowledge almost ended in tragedy. It is precisely this which I am trying to avoid. I could never forgive myself if my negligence cost someone his life.

 

my midgets never had power steering, dirt or asphalt. If I had bump steer believe me I would have known. have you ever noticed that the drag links and radius arms are perfectly level and parallel with each other? Even though its technically not a perfect setup it is pretty good. on asphalt there is so little travel that you could have the worst geometry in the world and it wouldn't matter though. If I got an inch of travel in my front end I would be amazed.

clark, if you want a 32 wishbone you can make your own. I know of three that were built using 33-34 wihbones and model A rear ball assembly flipped upside down. They were all made using my old wishbone as a pattern.

 

"on asphalt there is so little travel that you could have the worst geometry in the world and it wouldn't matter though. If I got an inch of travel in my front end I would be amazed."

That's why you weren't aware of the bumpsteer. It was there.

 

psst, I raced dirt too, 8 years worth

 

Just out of curiosity, what kind of steering box are you using?