Well, he's got that sarcastic smiley up there, so I think he may have been joking. Point is, if hair pins weren't okay on tube axles, I would think that some serious accidents would have been reported.
Well....a couple of possibilities come to mind. One is that the existing suspension (spring) is so stiff that axle movement, relative to the frame, is limited and therefore little loading of the axle occurs....presumably though, ride suffers. Or, the frame is torsionally weak and it twists instead and absorbs the forces involved.. Another could be that the spring rate is fine, but the axle, bones etc. are so strong, that rather than twisting or breaking, THEY limit axle to frame movement more so than the spring does. In other words, compensations are made, however unintended or misunderstood.
I don't doubt that the 4 bars had been used before Pete & Jack refined the style and make them a common piece in the 70's and beyond but they still are not considered traditional in the sense as hair pins and split bones. I'm certain if just a small amount of research was expended one could find a few hot rods built back in the day that used independent front suspension but I honestly don't think we say that they were the norm for the time period. JMHO. HRP
HRP, I realize the 4-bar was not the most popular until the '70s, but was used on some early racing cars and hot rods, because builders learned that just splitting the bones was not the best modification for a solid front axle. As noted above, Norm's Kookie T had a 4-bar setup, and if that car isn't traditional, I don't really know what is.
Look no further than Ak Miller's personal history... He put a G.M. front end under his '32 hiboy in '48 or '49. Ugly as sin, and I wouldn't copy it today, but history it is.
Bob,I would be audacious of me to say that I am a authority of everything related to the history of hot rods,,I agree that there were some 4 bars used in the early years and they have been used in race cars also. They is no argument with the assessment of Normans T. As a kid here in the Sunny South I never saw 4 bars unless they were the ones in town where all the older guys hung out! HRP
Hnstray has already said everything I had to say on this subject. Bottom line, you ARE going to use the tube axle, so a 4 bar is your best bet. Your car will work BETTER with a 4-bar than with the other choices.
Can you run split wishbone with a tube axle well yes if you think it out. The issue is not with the axle but the installation design. Lets take a look at parallel wishbone design under one wheel bump. Tire and axle move upward creating a swing arc radius dependent on the length of the wishbone, the longer the wishbone the longer the swing radius and the less shortening of the wheel base length. Because the cross spring is constrained by the front cross member and can only twist slightly to compensate for the movement of the axle rotation this shallow arc puts less strain on the cross spring. Construction with a short wishbone produces a steeper swing radius and therefore places additional tension on the cross spring as it twists to compensate for the increase in distance shortening. It is this twisting of the spring to follow the arc of the axle where the problems develop. The spring can only twist so much and then begins to resist twisting. It is this resistance which produces a force that acts thru the perch pin as this is the connection point to the axle lever. As forces act upon the spring during operation they are transmitted to a point of intersection. Usually the perch pin intersection. The weakest point of the perch pin is at the taper transition point or at the end of the tread run where after continually stress applied they fatigue and crack or break. To run a tube axle with radius rods you need to minimize the arc swing radius of the suspension during bump or rebound. Or the radius rods positioning needs to be convergent to help minimize the wheel base foreshortening action of parallel design application. This means limited suspension movement or longer radius rods. Radius rods should be similar in length to the original dimension or longer if possible especially if you are using soft springs for smooth ride. This reduces the bind in the spring a lessens the potential for a problem. I've added to this as the question relates to using a 4 bar setup, essentially the are similar in action but the 4 bar reduces the camber gain of the axle during bump and that is about the biggest difference.
I have 2 '32's with hairpins, a '29 Model A pickup with 4 bar and just sold my '32 Sedan with split wishbones..........other than the Sedan had wider tires and was a little harder to turn, they drove the same to me.......
Mark Dees, in A Technical History of the Racing Flathead (Part 1, April 1973 R&C) called split wishbones "an abomination" and gave reasons for that opinion.
A tube axle with split 'bones or hairpins is a bad idea. Consider what happens when you turn a corner and the body rolls. The axle stays parallel with the ground and the front end of the bones or hairpins stay the same height from the ground. Meanwhile, the chassis rolls towards the outside of the corner, so the rear end of the outboard hairpin drops closer to the ground, while the rear end of the inboard hairpin rises. So, either the axle has to twist or the hairpins have to bend along their length. Same thing happens if you hit a bump or pothole with one wheel- the chassis stays level, so the rear end of the hairpins stay the same height from the ground, while one end of the axle rises or drops, thus changing the heights of the front ends of the hairpins in relation to the ground. Once again, either the axle has to twist or the hairpins have to bend. As others have stated, beam axles will twist, tube axles will not. If the split bones or hairpins have to bend repeatedly, eventually something is gonna break.
And in spite of all that, hot rods have been using them for over 65 years. What you wrote would be true, if nothing flexed or moved, but by design, the parts that need to flex, and move, do. I'd like to see the pre war that drops one wheel in a pothole and the chassis stays level to the ground. That doesn't even make sense when I write it out.
. V8-60 tube axle with split bones. Over 5,000 miles in it's first summer with no issues. Driven hard and put away wet. Just sayin'.... .
Thirty years and about as many thousands of miles. V8 60 axle. As said their is some flex in the spring and movement in the knuckles that attach the hairpins to the frame. On most rod installations there is not much movement anyway. If I was building a "rock crawler" it would be a different story. Just have to keep things in perspective.
Exactly Gary! What it comes down to is YES, in the strictest sense it is "wrong", in actual application it's movement is so limited that with all other factors done correctly, it works. If you were doing this on a rock crawler that had to articulate over an 18" range of movement, hell no! On a hot rod with 2-3" of total movement, yup. I would (and am) very diligently keep an eye on my heim or tie rod ends at the frame for any undo wear, though.
Yup guys, weird camera angle on that shot. I don't remember the alignment specs, but it tracks straight and true and has no abnormal tire wear. Some earlier pics of the coupe did have some major camber issues. The axle was bent. We sent to Okie Joe and he straightened out for me. Front end looks better in this pic. .
So if the rods are 36" long and roughly 36" apart and the frame moves 2" how much are you asking the axle to flex? To the nearest 0.01 would be good enough. I sometimes picture a dozer blade, cocked to establish grade.
Some people live in a black and white world. Others can see grays and even colors. When I visited the Indy Car Museum I was surprised to see some old race cars with the same suspension as as my roadster. Five hundred miles on bricks.
In the just wondering department... why not use a pair of rod ends / heim joints / something similar in function, and mount them horizontally above and below the axle using slightly longer versions of the very same bolts you would normally use to attach your bones / batwings / hairpins? All it would take is a longer bolt, eh? And it would give the axle an ability to twist in more that one plane. Gary
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