I could use some direction on this subject. first a back story. My project 31 that uses cowl steering (bad subject I know but I am living with for the moment) has some issues. First the bone and the connecting link from the pitman arm to the steering arm are not parallel. From the center of the bone to the center of the pitman tie rod end is 13 inches where as up front from the center of the steering arm tie rod to the center of the bone is 10 inches. These need to be the same to avoid adding to the bump steer. I know I can extend the length of the pitman arm but that would leave me with a 16 inch long pitman arm or I could fab up a new steering arm that is 3 inches higher for the front. It already has an arm with a 1 inch rise so adding three would make it 4 inches. Pitman arm would be the easiest way to go but the length is going to make the steering quicker and less turning. I am told that a 4 inch rise up front is not going to work as the wheels will not want to turn with the higher 4 inch rise. I know many of you have had a lot more experience with this geometry stuff than I have. What is the best way to go forward on this other than ripping out the cowl steering at this time. That subject is on the drawing board for a winter project since it means a serious amount of surgery and expense. Pic of the steering arm for reference:
They should not be parallel. That is an incorrect ***umption. The suspension link and the drag link would only be parallel if you were running a 4-bar suspension setup. You cannot eliminate bump-steer with wishbones, or other rigid links, and cowl steering. You can only minimize it.
And to add what @gimpyshotrods said about minimizing........................I have said this before, my OT 2000 Ranger Daily had worse bump steer than my old T with cowl steering! With such minimal travel on these cars you gotta have things really messed up to notice much bump steer.
About as close as you can get to eliminating bump steer with a suspension link that is solidly anchored to the axle (wishbone, split bone, etc.) it to have a drag link that is as close to the same length as the suspension link as physics will allow, with the the pivot of the tie rod on the pitman arm dead-center over that of the suspension link. That will not make it go away, but with the limited suspension travel that these cars have it will keep it to a minimum. While it is not technically possible to fully achieve this, the idea is to have the arc of the swing of the suspension, and the arc of the swing of the steering be the same. You either can get as close as you can, or live with it. And yes, before anyone points it out, I have built cars that do not follow this rule. They all have some degree of bump-steer. I am not happy about that, but it is what the customer wanted. Thankfully, the average one has about 2-3" of suspension travel, so the driver can manage it.
The drag link is usually set to be level when the car is sitting static, or as it would be cruising down the road. Trying to set the angle to accommodate bumps in the road, or wheels turned one way or the other will only make the straight ahead driving worse. Why set it up for the things that are occasional instead of setting it up for where it is the vast majority of the driving?
@vtwhead , if you want a prime example of side steer cars that get driven hard EVERY year across the US and back look at The Rolling Bones cars Ken and Keith build as an example. Whether you agree with cowl steering or not you can not dispute the amount of high speed miles that group puts on their cars on some of the worst Highways and Interstates we have.
I know Pete it is not the best. Far from it but I am saddled with it for the moment. I would like to just minimize the bump steer for this year so I can get some ride time. I had planned to do a cross steer in the next phase. This has been a ten+ year project so many things were cast into the build a long time ago. I was reluctant to change this since we were so far into the build. Now I will deal with it to see if I can make it a little better for the time being.
Tman, very familiar with Ken's builds. Here are a few more shots as best as I can get with the android.
Cowl steering is not "bad subject" here. Yes Mr. Eastwood has his minions that follow his every post on the subject here but many cars have been built that drive fine with it. And FWIW I respect his contributions to the hobby over the last few decades. Here is a question? You did not say if you even have this car on the road? If so, What it is doing? OR, are you just re-engineering something that isn't even driving due to things you have read?
The pitman arm and the rear of the wishbone pivots are in alignment. My concern was with the slope of the link to the steering arm based on this post a while ago on another thread: I don't care about level, just parallel with whatever locates the axle. If the radius rods run downhill from the frame to the axle at 20 degrees the drag link should do the same. If the split wishbone runs uphill the drag link should too. I have done the popsicle stick/cardboard link deal many times (and now use Wm. C Mitchell's software) but the fact remains that the vertical separation between the steering link and the axle locating medium needs to be close to the same at each end, even if the pitman arm is a little to the rear of the frame location of the suspension mount. ****py quick sketch but the geometry is right. If the bars are parallel the axle A and the steering arm D swing in the same arc and both points move back the same amount. If the steering arm runs down hill and starts at point C it moves forward and the axle still moves back--lateral relativity of points B and D. The reverse occurs if the drag link runs uphill as the steering arm is already partway around the arc and as thus moves back faster than the axle.. The drawing is the ideal scenario with equal length links and having the pitman arm a little further back simply flattens the top arc out a little due to the longer axis (which would actually help with non parallel links). For illustrative purposes I did not build in the fact that the steering arm axis is generally a little to the rear of the axle axis due to castor considerations.
Car is on the road finally. Several issues, mainly Chinese axle flexes at the top of the axle at the king pin. Very noticeable when you stand over the top of it and look down on to it with someone moving the steering. As it flexes the right tire does not move. It is not a lot of movement, somewhere around a proud 1/8 to 3/16 each way. I do not know where it came from as it was part of the project that I bought years ago. I just sent a Henry axle off to Kohler Customs so Andy can drop it for me. Fix is coming. Next if you stand on the frame horns you can see the steering wheel move back and forth. Might explain why this thing is hard to drive on our roads around here. You cannot take your eyes off the road as in motion the car is steering itself. Not as bad of course on a new paved road but still there. It is frankly just too scary to drive so I have to change a few things to see if we can get this somewhat more comfortable. I will take a side shot and post it in a minute.
Why do you have someone standing on your axle as you are driving? Toss the Chinesium, get your axle back from Andy, THEN worry if you have bump steer. What you posted in the last paragraph DOES NOT describe bump steer. It sound more like a tracking issue.
LOL! I paid that dude a handsome amount to jump and down on my frame horns as we were driving down the road. I think I may have scared him a bit as he has not come around since then Agreed! Axle first of course. I am just looking ahead to see what my options are if it does not straighten out. After reading the above attached post I started looking at the angles and then suspected an additional issue which as you say may or may not be there.
The side view angles should pay no attention to where the wishbone connects to the axle. The key item is where the kingpin connects to the back of the wishbone. Say you had a three foot dropped axle, but wishbones that reached down to meet it. Or a totally flat axle, and the wishbones ran uphill. As long as the kingpin was in the same place in relationship to the rear mount rod end, it won't make a difference in the arc. So in reality, your sketch of the arcs would probably be worse than what you have drawn. That lower front point should be the kingpin, not the wishbone, and it will be higher. I'm not sure why you think you can't build a taller upper steering arm? If you need to get that point up there to help the geometry, just use strong materials. I've seen cars with an upper steering arm that looks 4 inches tall. I can't say how they drove, but if built strong enough it shouldn't flex. I bet a whole lot of your problem is in your cheap axle. Fix that and report back. Make sure the perches and wishbone yokes are tight after it is ***embled.
@Budget36 Hold it. He probably drank it for him. After that ride his hands were probably too shaky. He would have spilled half of it.
I have yet to see a side steer car with a raised steering arm not have some degree of flex in the axle. With the axle dropped you have changed the leverage points and increased the possibility for flex. That being said, the axle Andy drops for you should be better with it just because it’s a Henry, but you may still have some. Cross steering will just about eliminate it.
Bouncing the suspension and having the steering wheel move is an indication that bump steer may be the problem, or at least a part of the problem. "Bump steer is the term for the tendency of the wheel of a car to steer itself as it moves through the suspension stroke. Bump steer causes a vehicle to turn itself when one wheel hits a bump or falls down into a hole or rut." "Bump steer can be hard to feel unless significant amounts of travel are being used. Typically it would be more of a wandering feel rather than a jerking feel." Tracking problems (or 'tramlining') are usually a symptom of alignment/offset issues, and this could very well be part of the problem. Component flex could also be playing a part, as @Nailhead Jason pointed out. Investigate one thing at a time until you see and can solve the problem.
I don't think your geometry is correct. You're comparing the arc of the radius rod at point A with the arc of the drag link at point D. Both should be based on point D (where the drag link connects to the steering arm). Do that and I think you'll see a drastic difference in the arcs and why this setup doesn't work. Here's mine as an example: Ended up with 2-inches of steering wheel movement with every inch of travel, give or take. That's bump steer. The only way to make it work would be to make those arcs start to overlap, which results in a unsatisfactory design (IE, super long pitman arm, etc.). I s****ped the Schroeder box and went with a cross steer setup and never looked back. Proper engineering and function is WAY more important to me than form and what's "cool". I don't care how many miles a guy has on his car, if it's set up wrong, it's wrong.
Compare your setup with the diagram. Your problem is fairly obvious. Even a minion can see that.... Side steering can be set up with good geometry if some thought is put into it. Cowl steering is a whole different box of frogs. Hard to manage the bump steer, and the higher the shaft exits the cowl, the worse it gets. It looks really cool, but you will always have the ***ociated negative effects.
Alchemy addressed this , I'll repeat it . It doesn't matter on the axle end where the radius rod/ split bone is , it doesn't matter where the drag link connects to the steering arm , the only salient point is the spindle center . its a single point. The arcs that the linkage travels in is defined by where the drag link connects to the pitman arm & where the radius rod/ split bone connects to the frame . Make those 2 points the same and the arcs at the axle will be the same . The more separation at those points , the more the arcs will deviate .
update: as the car sets if you jump on the frame horns the steering wheel moves side to side considerably. Today I added an extension to the pitman arm leveling the connecting link to that angle of the wish bone. Did the same test and was amazed to see that the steering wheel hardly moves at all. That is not to say that it will not on the road but in a static test there is an improvement. I may make up a longer pitman arm now to see the impact when we are on the road again after the new axle arrives. More to come.........
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