As I have mentioned, you cannot eliminate bump steer on this configuration, only minimize it. To illustrate this for yourself, perform the test and record the change in steering wheel position. Then, turn the wheels half-way to the steering stop, and perform it again. You will then see that your minimization efforts had the greatest benefit only when the wheels were pointing straight forward. Any deviation will cause the bump steer to return, increasing with steering angle. Again, if you get to a point where you are comfortable with the steering, drive it.
Remember that lengthening the pitman arm comes with issues of its own, IE it's gonna steer harder and the ratio is going to be faster. If you look at my drawing, I could have solved the bump steer issue by moving the pitman arm/drag link attachment point either by lowering the box or extending the pitman arm. Neither of which were acceptable solutions, which is why most of these setups suffer from bump steer; there is no great solution to achieve proper geometry. The best you can hope for is a situation of compromise but the geometry won't be 100% correct.
Something like this is what I was referring to when I mentioned "acceptable solutions". While it may or may not work, I'm not a fan of the design.
I agree, the look pictured is not ideal, but the concept will work to minimize bump steer. The top arm and link could be on the inside of the cowl with just the bottom ***embly on show, and maybe not so glitzy 'look at me' looking. It does add more moving parts and potential weak/flex points into the system, but it could be done. If you want the cool factor of cowl steering and you want it to work as well as possible, your going to have to be prepared to put in the effort. If not, maybe frame-mounted side steer or cross steer is for you. They are both a better option when set up right.
Well, I wouldn't exactly call that "cowl steering" in the traditional sense. More like an Early Ford side steer setup with a bunch of weird linkage to hook it to a Schroeder box. Not sure what the point is, as they could have easily mounted an early box and side steered the car without all the bell crank nonsense. I think the whole point of cowl steering is to emulate the early Indy cars with the drag link running from the cowl to the steering arm. This doesn't do that. /thread derail
The radius rod angle has little to do with things and with a dropprd axle it is even leess. The angle you need to know is from the radius rod pivot (where it pivots on the ch***is) and where it intersects in the center of the spindle, that line runs up not flat. Your drag link and spindle are moving in two very different arce's, on a road bump the steering arm will move forward and the spindle will move backwards. Another thing to lookout for is on a 2 1/2'' axle with spring over axle perch bolts and 35 and up radius rods is that the perch bolts are not long enough to have good purchase in the axle (2/3-3/4 on average). The axle drop has a lever affect on the radius rods and in particular the perch bolts. My set up on my RPU, no issues at all and on NZ roads that's something! JW
This is the cowl steering on my HA/GR. The rear end is solid mounted so bump steer is accentuated but in a straight line you can let go of the steering wheel and it tracks true. Get on a ****py return road and it's all hands on the wheel to hold it straight. The pivot is to make it steer left when you turn left.
That is irrelevant as the pivot is the same as the pitman shaft if a steering box was mounted there and that is where the pivot point is. The cowl part doesn't matter. JW
Update! Sort of. I sent my axle out to Kohler Customs in PA back in early June and am still waiting for to it to return. Andy was out a week with Covid just about that time and has not been able to catch up since. He thought he was going to get to it last Saturday and he may have but I have not heard from him, nor can I reach him as no one is answering his phone. Little aggravating to say the least as summer is quickly sliding by up here reducing the amount of time I have to do these changes and try this out. I did make a longer pitman arm (12 inches long) to get the connecting link even or parallel with the bone. It has helped immensely but does steer harder as suspected. I am now making a new higher steering arm to see if I can reduce the length of the pitman arm back to around 8 1/2- 9 inches. This new steering arm will need to be 8 1/2 inches long and around 5 inches high. We will see how that turns out. I will update this thread as we progress forward.
The longer pitman arm will also steer quicker, which you may or may not like. You are going down the path that many have gone down before in an effort to make a cowl steering setup "work". There's a reason the setup didn't catch on after the Doane Spencer roadster and why guys like Pete and Jake, et al went a different route on the cars they built and drove coast to coast. I planned on a cowl steering setup on a roadster that I'm building as it's early Indy inspired, even went so far as to have Ididit go through the box that Gary Schroeder had set up for me back in the early '00s, but the geometry just wouldn't work out and I wasn't interested in building a car where function followed form. Ended up with a cross steer setup and haven't looked back. Something to think about, sometimes we get tunnel vision with these ideas of how things got to be that we forget that there are alternatives that might work better.
The ''steering link'' (drag link) even or parallel with the ''bone (radius rod). This is not correct. You need to work out the arc of the drag link from its pivot on the pitman arm and then work out the arc from where the radius rod pivots on the ch***is and through the front pivot of the drag link. These two arcs must travel in an arc the same or very close to each other. The angle of the radius rod has no bearing on how this works. JW
I think you keep using this phrase and that makes it appear you don’t understand the concept. Thus the repeat comments. Not criticizing, just observing. Please run a string from your front left spindle nut back to the bone pivot at the frame and maybe refer to that angle rather than just “the bone”. It would sure give a better idea of what is going on. Thankful this isn’t using a later wishbone! D
Thanks fellas for all the input. This is my first straight axle build so it has been a learning experience for sure. And yes, terminology does get away from me at times. Good news is that I got a text from Andy this morning and he is shipping my axle out to me on Thursday. I should have it on Monday. I will work on these angles then. I may draw them out on the floor to get an idea of the differences in the two arcs. At least that would give me an idea at what is happening and a base line. I am going out of town now for the remainder of the week so I will revisit this on my return and post my findings.
One of these days I am going to build some models of all of the different side-steering models, and explain this once-and-for-all.
That will only convince the converted and a few others. There will still be many that say their cowl steer with radical angles works fine because (to them) it looks cool. JW
I really have no need to jump into this pool but ... here goes ... AIGHHHHHHHHHHHHHHH (splash) I believe there are three camps on this subject. Those who understand the geometry issue and avoid cowl steering, those who don't understand the geometry issue and build anyway, mistakenly believing having things "parallel" is correct, and then there are those who actually do understand the geometry issue and decide/choose to live with flawed geometry simply due to the argument that, with limited suspension travel, the bump-steer issue is so minute as to be almost non-existent. I will now attempt to explain what I believe is the stumbling block for those who don't truly understand why parallel is NOT correct for bones and cowl steering. On a parallel bar four-link REAR suspension, ALL FOUR ENDS of the two locating bars (one side of the car) are pivot points. Raise or lower the rear end (when installed in a car) and the pinion angle (whatever it happens to be) will NOT change if the bars are parallel and equal length. In the case of parallel four-bar rear suspension, parallel bars can be viewed as a good thing simply because the pinion angle is maintained through suspension travel. Both bars swing on IDENTICAL but SEPARATE ARCs and, due to the FOUR PIVOT POINTS, the pinion angle doesn't change. In this scenario, travelling on separate arcs works just fine. I believe people incorrectly ***ume "parallel four-link rear good so therefore parallel bone and drag link good too" and that is NOT the case. Now, speaking of cowl steering, here is the big issue (again, as I see it) with the drag link and split bone being parallel (viewing the side of the car the cowl steering box is mounted on) ... all four locating points of both bars (again, "both bars" meaning the drivers side bone and the drivers side drag link) are NOT pivot points ... only three are. This means the front axle swings on the same arc as the bone BUT THE AXLE DOES NOT SWING ON THE SAME ARC AS THE DRAG LINK. THAT right there is the problem and the difference between a four-link rear suspension. Simply because the axle is fixed to the bone. In order to eliminate or should I say "minimize" bump steer (as much as is humanly possible) the bone and the drag link need to SHARE THE SAME ARC. If there are two different arcs, the result will be the drag link pushing or pulling the steering arm, when the suspension is compressed or extended, with the end result being the dreaded bump-steer. Picture this .... a parallel bar, equal length four-link rear suspension with the rear axle bolted solid to the lower bar (removing one of the four pivot points). Now try to move the rear up and down ... nothing happens, the entire suspension is in a bind and locked solid. Now, do the same with a front axle, bones and a drag link ... mount the axle solid to one end of the bones (as is obviously done) and try to move the suspension ... in this case the entire suspension DOES NOT BIND because the spindle is able to swivel on the king pin ... unfortunately, this results in unwanted movement of the spindle when travelling down the road (even when driving in a straight line if the road is bumpy). The end result of "unwanted spindle movement when the suspension is going through normal travel" is ... bump steer. The more suspension travel, the more bump steer. I am available to speak at weddings, funerals and birthdays
I'm going to build car with cowl steering and start a thread about it just to give you all something to argue about...
If I recall, there were a few animations posted in Pete Eastwoods thread about cowl steering. Heck, I recall saying to myself “I get it now”.
They didn’t run it? How do you put a side or cross steer setup in a single seat midget? It was a setup of necessity, not a moral decision. D
Ha. Just that members jump on this as if it’s a great infraction. There are always such topics in all hobbies. No dog in the fight but there is history of cowl steering s actually working in well engineered cir***stances and particularly in racing. Not a fan of it myself but the comments get pretty dogmatic. That is all. D
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