Light Unsprung Weight Solid Axle Set Up

[Bysch]

I have been reading every thread on here in regards to making a light solid axle vehicle (think class 10 truggy) because I am building a class 3000/7-2 bajalite/trophylite type vehicle currently. I am still in the design stage of the rear suspension and chassis.

The question I want to throw out for discussions sake is would the advantages of making my 4-link be only links and mounting the shocks on the axle to save 50 to 60 pounds of unsprung weight (12lbs per link versus 35-40) on the lower links be significantly better than the 3-4" of travel lost in the rear (23" leveraged versus 19-20" on axle) Making the 4 link system only links also enables me to achieve a significantly better roll axis than if I had the shocks mounted on the links because I can't mount them in front of axle centerline without compromising upper link strength

I am thinking about angling the shocks backwards also to get more weight to the rear of the car because I want to build the car light and its going to need some sprung weight to control the live axle and instead of building it heavier, I will put everything I can on the back. I have looked into doing a linkage setup but it just adds to many parts and to much weight.

The front of the car is already designed and it has 19" of travel. I want to make 2500 pounds but it may be closer to 2600-2700, but I am going to try everything within reason to get it to be 2500.

I can build 20" shocks for it and get to 22-23" of travel but I'm thinking 20" with 18" travel shocks will be fine

Thoughts???

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[Ramsey_ElWardani]

You might want to think about the advantages of "motion ratio" - it is very hard to setup what you are talking about. I raced a Class 8 years ago that was like your plan, very hard to get spring rates that worked, and shock valving was a pain, think about the shaft speeds. We ended up redesigning the truck and it became a great truck with 50% more wheel travel.

[scottm]

Short course trucks run the shocks right on the axle.

[Bysch]

I have kicked that around because we work on quite a few rigs at KOH with King Shocks that for the majority of the cars is a standard to have the shocks on the axle. We can get those things working good in the rough but you do need pretty soft springs and it makes it difficult.

I worked on, I think it is the truck you are talking about, Steve Krieger's class 8? when I worked at DR, I thought I remember it working pretty good but I was quite the rookie at the time so maybe I don't remember as clear as I think.

As far as the shaft speeds, the way I am thinking is this, the wheel needs a certain amount of force acting on it to damp the suspension. If the shocks are leveraged, the valving needs to be thicker creating more heat because of the valving stack but the shaft is moving slower so that creates less heat than on the axle where the shock valving will be light creating a smaller amount of heat but it will be traveling really fast creating more heat. However, when all is said and done, the wheel still needs the same amount of energy from the shock to control it so wouldn't it be somewhat of a push?

[Zambo]

the wheel still needs the same amount of energy from the shock to control it so wouldn't it be somewhat of a push?

Yep as far as I know. X amount of damping equals X amount of heat. Energy is neither created or destroyed. Only caveat I would think is that a longer shock holds more fluid however so it is able to absorb more heat before it fades.

Like Ramsey said, I'd worry more about getting the travel you want and making sure you have a rising rate rather than put the shocks in a bad spot just for weight bias.

[Ramsey_ElWardani]

I worked on, I think it is the truck you are talking about, Steve Krieger's class 8? when I worked at DR, I thought I remember it working pretty good but I was quite the rookie at the time so maybe I don't remember as clear as I think.

You have the right truck and it was OK, but it is so much better now, not even in the same league. Think again about flow and volume.

[Bysch]

10-4, I think after this thread and alot of thinking/brainstorming today at work, I am going to leverage the shocks, I am pretty sure I can make a trailing arm that is light enough to not be that big of a deal, I'll get the unsprung weight back somewhere, thanks!

[Zambo]

10-4, I think after this thread and alot of thinking/brainstorming today at work, I am going to leverage the shocks, I am pretty sure I can make a trailing arm that is light enough to not be that big of a deal, I'll get the unsprung weight back somewhere, thanks!

If you're going to build trailing arms, now they should be strong enough to use a little sway bar mounted up near the forward pivots with end links attached to the arms rather than run a full size traditional deal attached to the axle housing. Maybe you can save some weight there.

[Bysch]

Yup, already snatched that idea up from RG's SST trucks, it will probably pivot through the tube that the lower links pivot from on the chassis (if that makes sense) and catch the arm about 12" out from the frame pivot.

[Zambo]

Yup, already snatched that idea up from RG's SST trucks, it will probably pivot through the tube that the lower links pivot from on the chassis (if that makes sense) and catch the arm about 12" out from the frame pivot.

Those SST trucks have the smallest end links I've ever seen on any vehicle. I think the ones in the front are 5/8" aluminum tubing with 3/8 heims.