Tires

[SPARKY]

none of the tire companies want to talt to you about running a drag tire even a mile let alone 5

[salt27]

I am currently building a 64 Dart to begin my journey into land speed racing. My current plan after I have observed as a spectator is to run the car first in the 130 MPH moving later to 150 MPH. What would be the recommended tires (15") to run at thoise speeds?

Go to the U.S.F.R.A. site to check the rules.
130 club H minimum, 150 club V minimum, I would contact them about the drag radials.

Don

[Interested Observer]

Ref: Robfrey 4-bar suspension

While "X-ing" in the bottom two links of the suspension makes for a compact way to transfer the lateral and anti-roll loads, there is a reason that most 4-bar suspensions make use of a Panhard bar or Watt's linkage for lateral location of the axle, and a dedicated anti-roll linkage (if that is desired).  From the photo posted earlier, it is apparent that the link pivots make use of Heim type joints.  These ball joints are designed to carry only axial loads.  By X-ing in the lower links, the large lateral location and anti-roll loads will be forced laterally onto the Heim joints, creating large bending stresses in the threaded shank of the joint.  Large bending stresses located at stress concentrations (thread roots) are not a good idea.  It would be good to re-think this method, or at least use ball joints that are suitable for carrying the lateral components of the loads.

Secondly, when in "anti-roll" mode, the only way that load is passed from one side of the X to the other is via torsion of the intersection at the center of the "X".  From the CAD drawing it is apparent that this intersection is quite small in cross-section, and likely unable to effectively carry the load.  It constitutes a largely ineffective and non-adjustable anti-roll function.  A torsional failure at this point is merely a matter of time.

While pioneering "new methods" is to be encouraged, appreciation of the merits of the "tried-and-true" also has its place.

[robfrey]

Ref: Robfrey 4-bar suspension

While "X-ing" in the bottom two links of the suspension makes for a compact way to transfer the lateral and anti-roll loads, there is a reason that most 4-bar suspensions make use of a Panhard bar or Watt's linkage for lateral location of the axle, and a dedicated anti-roll linkage (if that is desired).  From the photo posted earlier, it is apparent that the link pivots make use of Heim type joints.  These ball joints are designed to carry only axial loads.  By X-ing in the lower links, the large lateral location and anti-roll loads will be forced laterally onto the Heim joints, creating large bending stresses in the threaded shank of the joint.  Large bending stresses located at stress concentrations (thread roots) are not a good idea.  It would be good to re-think this method, or at least use ball joints that are suitable for carrying the lateral components of the loads.

Secondly, when in "anti-roll" mode, the only way that load is passed from one side of the X to the other is via torsion of the intersection at the center of the "X".  From the CAD drawing it is apparent that this intersection is quite small in cross-section, and likely unable to effectively carry the load.  It constitutes a largely ineffective and non-adjustable anti-roll function.  A torsional failure at this point is merely a matter of time.

While pioneering "new methods" is to be encouraged, appreciation of the merits of the "tried-and-true" also has its place.

Interested Observer,
You need to observe closer but it might not show in the pics. The "X" is not the only way that the bottom bars are tied together. There is another 1.25" bar running across the front of the "X". It is quite rigid.

We tried flexing it by jumping up and down with only one shock mounted and we probably could run it that way if we wanted to. It is that rigid.

Now for the side loading issue. One of the latest ways that many drag cars locate their rear axle is with a devise called a wish bone.

http://www.competitionengineering.com/catalog/CategoryDisplay.asp?CatCode=10049

I run one on my 63 8 sec Lemans for a couple of years now. It puts one rod end in the same kind of load as we put two. I have not heard of one failing so far. I did think of this when I designed the system and bought the highest quality joints just to on the safe side.
Of all the ideas we implemented on this car, I feel this was one of the best. I wouldn't hesitate to do this again. Car drives great. I tried zig zag real hard when we were pushing the car and I couldn't feel any body roll.

[Interested Observer]

Robfrey,
All I had to go on was the drawing that you submitted earlier in the topic which, if YOU will observe closer, does not have the cross piece at the front.  While that addition will considerably stiffen the frame, it moves the area of concern to the bending strength of the X tubes just aft of their intersection, as well as the various weld joints in the frame which are undergoing tension/compression/bending/and torsional loads.  The “new” configuration is an improvement, and if adequately executed will probably work, but is rife with concerns that other solutions eliminate.  If you are happy with it, continued good luck. 

My original and primary intent was to point out the mis-application of the rod ends.  And again, while it may “work” as used here, it is not good practice, and is tantamount to asking for a failure.  (The “wishbone” just gives me the willies.)  Fortunately, drag racing and LSR are substantially one-dimensional activities in which lateral loads are minimal until one is in a heap of trouble, after which it is difficult to determine just what happened.

Regards,
Interested Observer

[robfrey]

Even if we got our car really sideways, I doubt we could ever generate enough side loads to hurt the joints. The pencil roll would probably happen long before.
Ultimately, I would of liked to use watts link but packaging on this car is a nightmare. It just wouldn't fit.
All in all, I thank you for your concern and because of this exchange, I will be keeping a closer eye on the lower front rod ends.

[thundersalt]

Even if we got our car really sideways, I doubt we could ever generate enough side loads to hurt the joints.

Incorrect. In 2007 when we first built the Fairlane we only had a drag race style diagonal link (half of your x ). Spun at +/- 200 and found all 4 bar mounts and shock mounts bent. Have since added a watts(on a narrowed housing)

[joea]

interesting to read through this dialogue....

some well intended engineering principles.....and some "I doubt..."....

[robfrey]

Even if we got our car really sideways, I doubt we could ever generate enough side loads to hurt the joints.

Incorrect. In 2007 when we first built the Fairlane we only had a drag race style diagonal link (half of your x ). Spun at +/- 200 and found all 4 bar mounts and shock mounts bent. Have since added a watts(on a narrowed housing)

That single diagonal link is not nearly as strong what we got now. They always scared me. My favorite is the watts link link you have but impractical for quick change rear.

[SPARKY]

wouldn't it work horizonaly, on top of the housing? 

[Rick Byrnes]

I have used another variation on the WATTS link on my liner wannabe.
It is based on parts available from Streetrod Manufacturing in Castle Rock Co. which I have greatly modified and adapted to my application and packaging issues in both the front and rear.  It works.  Centers the axle and provides stable +-1.00" jounce and rebound that I allow.  "That is in the shop"  Proof will of course  will be in the LSR pudding.

This design also puts the roll center considerably lower.

[thundersalt]

I must be seeing something wrong. Wouldn't the X in you pic or a single diagonal put the same stress on the forward 4 bar mounts and rod ends?

[Blue]

You need to observe closer but it might not show in the pics. The "X" is not the only way that the bottom bars are tied together. There is another 1.25" bar running across the front of the "X". It is quite rigid.

Yes, the "X" is extremely rigid.  Although if we go with only one diagonal instead of the "X", we can tune the alignment of the four link much easier.  I have seen an "X" setup like this before and it took them MUCH longer to get the other linkage lengths set up to go straight at all speeds and torques than it would have with only one diagonal member on heim joints.

Yes, it has to be over-built.  If set up properly all the bars are only in compression or tension and heim joints allow for precise tuning of all alignment angles;  there are NO bending loads in a four-link.  If there are, we missed something.

[robfrey]

wouldn't it work horizonaly, on top of the housing? 

I think it would but would move the roll center much higher. Right now the roll center is the at the height of the bottom links. This desirable for how stiff our springs are. If springs were softer, it might be good to move the roll center higher.

[Cajun Kid]

I like Thundersalts  watts link... works good on most rear ends.. but on a Quick Change  you can not do a rear mounted watts,,, if you mount it high you change the roll center,, so for QC rears you mount the watts in front ,,,they make a pinion housing mount for the QC... I will look for the pics (can't find right now)  it is one cool set up,,, I was going to use it,,, but cost and fab time was more, so we decided to use the tried and true panhard bar for the Stud.

Charles