Suspension Options for Light Vehicle: Help for Building Off-Road Vehicle

[fatcat]

Can anyone help me? I want to make a light vehicle (4 wheel, steering column not quad-type) capable of going on and off-road. I am confused.
Quad bike people are getting excited because apparently they have only just heard of independent suspension, it being the big new 'feature' that is available. Road users would be surprised at anything but. Yet off-road 4WDs/SUVs seem to be predominantly solid axles with leaf springs and archaic ladder chassis. Toy off-roaders have independent suspension (Freelanders et al), real off-roaders use solid axles.
(a) Why do some vehicles persist in the use of solid axles? I presume there must be a reason...? IRS must give some advantage somewhere along the line, or it never would have been adopted? Have I missed something elemental? I naturally thought it would need IRS, am I wrong?
(b) Why are off-road vehicles undesirous of the chassis developments seen as essential in other vehicles? Ie the ladder chassis, apparently as solid as a sheet of margarine, seems to be alive, well and positively brushing off newcomers. Is the chassis flexing like mad seen as a good thing? Do I forget the nifty spaceframe backbone chassis I've been doodling, and just order a big rectangle from an agricultural engineering co.?
(c) If so, do I hang the bodywork from the chassis on bungees and hope for the best? Engines don't bend very well either - does the engine hold the thing together? I'll be needing some bigger engine mounts (on the engine) then!
(d) Is it obligatory that the 'traditional' chassis weighs 2 tons?
(e) What is the verdict on the leaf-spring v coil-over debate? I presume the coil-over wins, but you never know. Toughness with articulation is what I'm after - is IRS just too weak when it comes down to it? Vehicle weight or just the stress of hitting rocks?

I have no problem either way - I like simplicity, and it fits in with the ethos of my idea perfectly. I am just confused as to how I decide which to go for. I am not building a hot-rod, I am not going for prettiness first. Latest technology is no good if there is no requirement for it. Which system? I have a target max kerb weight of approx 400kg unladen, engine power options from 50-120 bhp. Must be able to roll/slide/drop 20ft and brush it off, be capable of towing its own weight, max off-road speed 60mph. 9'x5' outside dimensions.

This is an idiotically simple problem, yet it affects the whole chassis design, obviously. I can see the wheels, the seats, load facilities, everything. But the undercarriage - at first I had no idea, now I know about several potential candidates suspension-wise I am even further from an answer.

If anyone can give me any pointers I would be most grateful. This is beginning to drive me nuts. I had an idea, have spent a long time looking into all the options, have driven my family mad with it. I just have to decide the underpinnings to sit beneath the concept I want to sit on top of it SO ONE CAN ACTUALLY BE BUILT AND I CAN RELAX!

Help? This could really send me to the wall soon. Thanks.

 

[wimms]

I'm not exactly qualified, but I'll give my opinion.
Off-road vehicles are meant to last.
a) solid joints are stonger. Less moving parts, less things to brake apart. When climbing over rocks, quite some stress on axles to tear them apart. But if you build it, you can rebuild it, so performance might be your focus.
b) not sure, but guess that (re)flexible stuff is less prone to crack, spreads loading more evenly over whole frame, thus avoids hotspots of unbearable stress. If you have solid chassis, more work to suspension.
c) its not individual feature, imo. Its all about balance. tensegrity comes to mind. Engine obviously must not face any of the body stress.
d) no, its exploiting of stupid consumers. Confidence that it rusts longer due to sheer mass.
e) coil wins performance, imo, but its not that needed for slow off-road. There might be more benefit in simple things, that are possibly "fixable" by handy stuff when you manage to brake it.
Independent suspension has one issue - when you hit smth at speed with one wheel, its prone to turn over the chassis. Not good. Completely independant suspension should be damn smart (active?), well over target of traditional offroaders.

There is a lot of science in it all, so google more. From what I've seen, I liked Hummer design, and also saw a funny vehicle on tv made by McPherson for Dakar, they had quite fancy suspension. Look at buggys.

 

[ravenprp]

Hello there,

I can understand your confusion and frustration when it comes to choosing the right suspension for your off-road vehicle. It's a crucial decision and can greatly affect the overall performance and capabilities of your vehicle.

To answer your questions:

a) The reason some vehicles still use solid axles is because they have been proven to be reliable and strong. They can withstand rough terrain and heavy loads without bending or breaking. However, independent suspension (IRS) does have its advantages, such as better ride comfort and handling. It also allows each wheel to move independently, which can be beneficial in certain off-road situations. So, it really depends on the intended use of the vehicle and personal preference.

b) Off-road vehicles often use ladder chassis because they are strong and can handle heavy loads. However, they can also be quite heavy themselves, which can affect the overall weight and performance of the vehicle. As for why newer chassis designs have not been widely adopted in the off-road industry, it could be due to cost and the fact that ladder chassis have been proven to work well in off-road environments. Again, it comes down to personal preference and what works best for your specific needs.

c) When it comes to hanging the bodywork from the chassis, it's important to consider the weight distribution and balance of the vehicle. The engine does play a role in holding the chassis together, but it's not the only factor. Proper suspension and chassis design are crucial for ensuring stability and safety.

d) It is not obligatory for a traditional chassis to weigh 2 tons. There are many factors that can affect the weight of a chassis, such as materials used, design, and intended use of the vehicle. It's important to find a balance between strength and weight for optimal performance.

e) The debate between leaf springs and coil-overs is ongoing, and both have their pros and cons. Leaf springs are known for their toughness and durability, while coil-overs offer better articulation and ride comfort. Again, it depends on the specific needs and preferences of the vehicle.

In the end, it's important to consider all these factors and do thorough research before making a decision. It's also helpful to consult with experts or experienced off-road vehicle builders for their insights and advice. I hope this helps and good luck with your build!