Tubed Chassis and Suspension...

ZedEx · #1 02-09-2005, 10:28 AM

So we're pondering doing a full tube chassis for our next project... But the only problem that I am ramming my head into... Is how am I going to set-up the suspension?

Would it be simpler to make it 100% stiff (i.e no coils, no shocks... Just straight attached to the frame)

... I am drawing a blank.

-Wes

mike@af · #2 02-09-2005, 11:46 AM

You can use coil overs and such. Just look up some reference pics on tubed chassis, and tube rollcages. Like look at the drag muscle cars where the roll cage is the chassis, and the chassis is the roll cage.

For the coilovers, just make some bracket for them to bolt to. Then reinforce the brakets and such. Its not really as hard as you make it sound. The design is easier than the build.

If you make it stiff you will run into problems.

duplox · #3 02-09-2005, 03:59 PM

I'm in the process of workin up a front suspension system for my '69 mustang. Shock towers are a bitch for turbo headers, so they've gotta lose a few inches. I recommend buying some spindles, Mustang II 2" drop spindles place upper and lower ball joints pretty even to the wheel center, allowing the suspension components to be mounted lower on the chassis. There are plenty of brake components available cheap for MII. Fabricating the arms is a bit tricky, but nothing too terribly difficult - if you're building a tube chassis, arms shouldn't be too much of a challenge. The only real difficult part is making them mirror images of each other.. which is easier if you make them symmetrical, besides the steering linkage.
Rear suspension is pretty basic. Go with a live rear axle, unless you really care about ride quality in your tube chassis car... I have a feeling you don't. Handling capabilities are just as good with a live axle and launch is much better. I recommend a Satchell link 4-link rear suspension type, although they can be tricky to make without binding. I recommend Chassis Engineering by Herb Adams for the project. It covers chassis, front susp, and rear susp design and building. Very good book.

mike@af · #4 02-09-2005, 07:14 PM

Just some food for thought. To keep things symetrical, as well as keep motivation, as soon as you build one thing on one side, immediately do it on the other side. Other wise you will end up with one side of a chassis, or a asymetrical chassis.

ZedEx · #5 02-10-2005, 01:54 PM

Excellent information guys, thanks a lot!

Ride quality is not really a concern... Track only car. We're taking doner parts from Zed32 (1990-1996 300ZedX), such as suspension components, steering system, brake system, rear differential, etc etc.

But I think over all it should be a good project... Lots of math, lots of cutting, lots of welding, lots of bending... But should be fun.

I'll keep you guys updated

-Wes

mike@af · #6 02-10-2005, 06:05 PM

Quick tip while its on my mind. Try to make as few cuts as possible in the tubing. Say you need to have some tubing go through a firewall, dont cut it to get it through and reweld it, but instead cut the damn firewall and make a patch panel for it.

I dont know if that situation will occur, but its food for thought.

duplox · #7 02-10-2005, 06:47 PM

What made you decide on a tube chassis? There are other stiffer chassis than tube. Backbone frames are stiffer than a tube chassis based on a laddar frame.

ZedEx · #8 02-11-2005, 03:05 PM

Well... Lets say we're building this thing in our back yard with no other machines than an air compressor, a mandrell bender, and a welder. Is a backbone frame still something that can be done?

And if so, how much more difficult would it be?

-Wes

duplox · #9 02-11-2005, 04:26 PM

I'm not sure, I've never built either. I don't imagine it would be incredibly difficult, it just focuses the structural support down the middle of the chassis instead of out at the sides. Its basically an extremely reinforced driveshaft/transmission tunnel, with a ladder type front and back attached to it. I'll scan a picture of one for you. Its from Chassis Engineering.

ZedEx · #10 02-12-2005, 11:45 AM

Nah, thats ok...

Im trying to track down the book... I cant seem to get a hold of it. Any ideas where I can find it? I think I should try Amazon.com right quick.

-Wes

duplox · #11 02-12-2005, 12:00 PM

http://www.amazon.com/exec/obidos/tg...books&n=507846

ZedEx · #12 02-13-2005, 11:59 AM

Thanks a lot Duplox... A lot cheaper than I had in mind.

-Wes

astroracer · #13 02-16-2005, 06:01 AM

Check out this link...
http://www.gmecca.com/byorc/index.html
There is a lot of info to be had here so look it over carefully. One of the first tips you will see is to design your chassis last. Good advice. Trying to incorporate a viable suspension onto a chassis that won't support it can be a project killer. Design the suspension first then design a chassis that will work with it...
Mark

curtis73 · #14 03-08-2005, 02:54 AM

I highly suggest a book called "Race Car Vehicle Dynamics" by Milliken. It is a 900-page engineering textbook on all vehicle dynamic properties and its an incredible reference.

One of the things they discuss is suspension compliance. The best suspension you could design starts with the chassis being as rigid as possible and then the suspension being tuned for the proper compliance. Stiffer is not better when it comes to suspensions. The proper spring rate will provide far better handling and reliability.

Basically, as you stiffen a suspension, you can improve weight transfer qualities to a point. After that point, you just increase ride harshness and DECREASE handling.

Buy that book before you start welding and you'll be totally empowered to build a complete custom suspension from concept to design to execution and have confidence in your choices.

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