Tension rods vs. Compression rods

[desert dog]

Is there any inherent advantages to tension mounting?

 

Nissan changed from compression to tension on the S130, and all Z's since are tension rod design front suspension.

 

What I can see, the tension mount would be a sturdier design...

 

Any thoughts?

[Guest Phil1934]

AISC steel design reduces the yield strength for compression members significantly as they can buckle, so a series of calculations determines the length of the sine wave and the associated reduction in strength. That being said, if it works there is no point in reengineering the car. Auto designers have armies of engineers looking at such things so they rarely miss. (Stylists are another story.)

[JMortensen]

In the Datsuns, the ZX and 510 tension rods seem to be more prone to snapping, especially when used with poly bushings. There is a thread by afshin from about a year and a half ago called something like "Scary tension rod failure" and MOST of the people who had broken rods had them in tension, although there were a couple from Z's as I recall.

[JMortensen]

Here, I looked up the thread for you: http://forums.hybridz.org/showthread.php?t=87758

[JMortensen]

You got my brain working a little bit on this subject so I just took a looksee in the garage. Looks like the other major issue is that the tie rods would be right where the TC rod would have to go. There was another thread about using a 240Z steering rack and struts in a 510 and that setup used front mounted TC rods. Here is that thread: http://forums.hybridz.org/showthread.php?t=108113

 

It MAY be possible for someone to set it up this way and have it work out. The 510 and 280ZX TC rods mount to the bottom of the control arm, which just barely allows for clearance for the tie rod. In my case I was planning on running a bumpsteer spacer kit on the outer tie rod, and that would move the tie rod down, maybe allowing for the TC rod to mount in its normal location on top of the control arm. It's too close and there are too many ifs for me to consider changing to the front mounted setup but you did have me thinking pretty hard!

 

Advantages would be that it would be easier to fabricate the mount, since the TC rod mount wouldn't have to cross the frame rail as it does in the 240 design. Also the rods would be longer. Quick tape measure eyeballing puts the rod at about 19" or so long with a front mounted setup, where it is only about 17 with a rear mounted setup. Disadvantages are that the front mounted style LOSES caster as the suspension compresses and the TC rod goes to level, where the rear mounted style gains caster as the TC rod goes to level. I think running a rod end would eliminate the failure aspect of having the rod in tension. I believe that the failures we've seen have more to do with the bushings used than an inherent weakness created by having the rod in tension.

[260DET]

Its also worth noting that the later Nissans went from a pad type bushing setup, like on the S30/130, to an eye bush type at the chassis end of the tension rod. Makes using an adjustable rod setup much easier, just substitute a rod end arrangement for the eye bush.

 

The only question about the tension rod setup may concern the front chassis Xmember which has to bear suspension loads and being at the front is a bit more exposed to crash damage.