Front axle material for spindle mounts and questions

[Jonny Hotnuts]

How thick of tube is needed, the bosses are about 1.5" and will only have a span of about 24" (total) and off the frame (the cantalever) only about 2".

Is it common to use a solid bar?


----------ALSO------------

Because the axle bar is going to be straight I am considering a way to mount the axle so you can adjust the castor angle by being able to loosen mounting blocks and roll the axle into different angles changing the king pin angle. Is this worth doing or should I just assume that a number like 15 degrees negative will be acceptable and hard mount it.

[Stan Back]

Boy, you got me lost.

One, it's cantilever.

And two, castor is a bean.  Caster has something to do with front-end geometry.

I know we're not supposed to be critical anymore, but at 200 mph you ought to have a good grasp of the terms.

Is your new front-end solid mounted?  Why? 

I don't build front-ends.  I have a beam axle, because it is simple, like me.  I have about 13º of what I think is positive caster.  And it goes over 200, mainly straight.  I'm not sure what negative caster is -- maybe that's what I have.  My axle and kingpins lean with the top back 13º from the vertical.

I'd suggest you let someone who knows how to assemble a safe front-end do it, or engineer it for you.  Taking the best answers off this forum -- as good as it is -- may be dangerous.  I've learned through the years that certain things are best left to the people who do them everyday.

Like I can't weld.  I can stick things together, and have a bunch of good ideas on how to fabricate things, but when it comes to welding it together, I trust someone who does it on at least on a weekly basis.  Most of the time is spent in designing it, and making the elements.  But the failures can come when the parts don't stick together as intended.

Stan Back

[maguromic]

Since axle configuration is open for roadsters, I used a 0.180 wall 2 1/2" diameter tube and made a set of dies to press it into the aero shape I wanted, works out to a little over 3 1/4" (aero tube does not come in the thickness I wanted).  The results were the center would collapse.  We played around with different methods for about four months until finally giving up and going to a solid axle (not solid mounted) and milling the shape into it. 

I am also using Anglia spindles and it worked out great.  My axles is 3.372” wide and because it is solid I couldn’t run my wiring for the wheel speed sensor inside it, instead I am running them in my tie rod links. Done correctly you should have no problems with a solid axle. 

[edweldon]

I'd use minimum 1/4" wall low carbon steel; but listen better to guys with actual experience than me. Engineering opinion generally takes a back seat to actual experience when it comes to Landspeed racing.  Use the same quality tubing you'd use for your roll cage.  Solid bar will get you little but more unsprung weight (bad on a rough course) and possible welding problems unless you're a really good welder.  Have the welds magnaflux checked for any voids or bad spots in the weld.
I'm not thrilled with the idea of simple clamps around the tube to maintain your caster.  This is more than just a bit of engineering experience with heavy machinery talking here.  Everything may work fine until the day you have a rough course or hit a bump of some kind.  As long as a special axle is being fabricated I can think of more than one clever way to set caster with positive keying without hurting the strength of the axle with the mechanical stuff needed to do the job. 4 bar and wishbone type linkages come to mind here, of course.  Any of you other guys have actually done this please comment on your method. 
Ed Weldon

[Jonny Hotnuts]

I'm not thrilled with the idea of simple clamps around the tube to maintain your caster.  This is more than just a bit of engineering experience with heavy machinery talking here.  Everything may work fine until the day you have a rough course or hit a bump of some kind.  As long as a special axle is being fabricated I can think of more than one clever way to set caster with positive keying without hurting the strength of the axle with the mechanical stuff needed to do the job. 4 bar and wishbone type linkages come to mind here, of course.  Any of you other guys have actually done this please comment on your method. 
Ed Weldon

I would not have just have simple clamps holding it....but if I tried to explain in detail the concept would be blurred with too much info. The question should have been "is it a good idea to make an adjustable caster set up?", I mentioned the clamps to keep it simple but still convey the concept. Here is a crude model and rendering of how things could really go.
I am very confident that a locking mechanical turnbuckle (along with lateral shaft locks) in conjunction with locking blocks will be more than enough to support the shaft from unwanted forward or aft roll.


Stan:

I understand your concern but can assure you that if I never did anything because I did not have experience in it, I would have never gotten anything done. You could easily say “don’t build your roll cage if you don’t have experience” or “don’t put a Mazda Rx7 rear end in a Fiat” or “Don’t put a motorcycle motor in your car and let someone with experience do it”……. Where do you draw the line?
For me…I don’t, unless it requires tools or experiece I do not have the means to acquire, and subsequently I did 99.9% of the work on my car without having to have someone else bail me out. I made mistakes, but by god I wont make the same mistakes again and my future projects will be even better. If you do not have confidence in your own abilities than you should find someone to do it…..I personally feel that I am the best at everything I do. 


Here is a pic of the my new axle shaft:
1.25 (same a king pin boss) and 3/8" wall!
I figure it will be plenty stout!

[4-barrel Mike]

Adjustable front axles are fairly common in the street rod world using a single traverse "buggy" spring and adjustable spring perches such as http://www.peteandjakes.com/parts/parts_dept/SBspringPerches.htm and a 4-bar setup.



Probably not what you're looking for though.

Mike

[edweldon]

Jonny -- Nice CAD drawing.  Kinda thought that's where you were going.  Looks like the axle will be stiffer than most.  You'll want to make sure there's enough flexibility in the setup to keep all 4 wheels in contact with the Salt.
Ed