Help with engineering project

[zach]

Good Morning,

I'm hoping you can help me. I am conducting research on 4x4 enthusiast's opinions on certain subjects for an engineering project. I have cast my net far and wide across many different marques and varying subjects.

If some of you can spare you time to give me a few words on your opinions on the differences between solid axle trucks and independently suspended trucks i would appreciate it.

The areas or questions i am investigating views on are.

1. General robustness? Is one more robust than the other and how much of this is opinion vs fact? Can anyone provide specific examples for me?
2. Where does one system excel over the other?
3. Extreme offroad use vs offroad touring use?
4. Why do you think manufacturers are now erring on the side of independent systems?

What i'm trying to get to is a general opinion amongst varying offroad communities about this and then assess this against how much actual evidence there is about the conclusions?

Thankyou very much for your time.

Zach

 

[Lorin]

Just opinion nothing more...

1. I think the suggested robustness issue is largely founded on little more than unfounded/uninformed opinion.... Maybe the first IFS systems were weaker than their solid axle counterparts but more recent ones do not seem to lack for robustness (e.g. Hummer) and there are more than a few weak solid axles out there....
2. Articulation! Solid axle articulation is usually, and most definitely able to be, considerably greater than an IFS counterpart
3. Extreme offroad probably favours solid axle, largely due to the articulation advantage. Offroad touring depends on the terrain. There is a point at which either/or would suit and where one would excell over the other but generally, assuming offroad tracks as the terrain IFS would be favoured for it's superior ride and driving characteristics (i.e. more like a car)
4. Safety and driving characteristics. Offroad vehicles spend little if any time offroad and need to meet ever more stringent safety standards. In addition, the buying public expect their 4x4s to go, stop and handle as near as dammit like a car.

 

[OG.]

1. By its very nature a live axle will be more robust under most circumstances than IFS. Its simpler and the joints tend to move only in one plane. Compare ball joints on the IFS with swivel bearings on a live axle for example.
2. Ground clearance/articulation. A live axle effectively pivots about the opposite end hence can move vertically a significant amount without running into issues with joints binding up. Ground clearance is also a benefit (please note this is effective ground clearance not necessarily static ground clearance). As a live axle equipped vehicle encounters a bump the whole axle pivots about the opposite wheel thus raising the entire axle over the obstacle by an amount dependant on the distance from the wheel encountering the obstacle. An IFS vehicle will not gain a significant amount of clearance from an obstacle encountered by one wheel. An IFS will give better ride characteristics as a result of less unsprung weight.
3. As Lorin said.
4. As Lorin said.

 

[clivehorridge]

Hi Zach! Welcome!

I don't disagree with any of the above.

You talk about an engineering project, but you give no clues as to direction, meaning either overland and/or offroad.

Again only opinion, but as said, for offroad I favour live axle. It's arguably more complex inside, but once set up, it's simpler on the car, meaning you've got versatility on which springs/dampers to choose and fit to suit your needs.

There are plenty who might contradict me, but when reading recent threads, a lot of discussion ensued over lifting a 90 whereas most 80 owners do a lift on a Saturday and are out enjoying it on Sunday.

The main draw-back for me on the 80 is the steering box vs the more efficient rack and pinion steering.

Ultimately, if you were building an offroad, then I would seriously look at live axle with power steering, not power assisted, but full hydraulic steering.

Of course, for long asphalt driving, there is benefit to be had from independent suspension, as has been said above.

Please give us some clues which direction you're aiming at, I'm envious and eager to know!

 

[Jon Wildsmith]

The main draw-back for me on the 80 is the steering box vs the more efficient rack and pinion steering.
[SNIP]
Of course, for long asphalt driving, there is benefit to be had from independent suspension, as has been said above.

The steering on a 100 seems less positive/direct than an 80 to me, strange. I don't find any benefit or deficit either way for long asphalt driving which is more likely to be affected by other factors like noise levels, tyre and modified suspension choices etc.

 

[Chris]

I'd add that in general, a live front axle is easier to maintain in the field with basic tools. IFS is slightly more complex and connected to the chassis at more points. Live axle sits under the chassis on springs with not much more than an arm to connect it. All of these bits can be hammered straight, bent in the crook of a tree etc. Now on the school run, there's seldom need for bush mechanics to keep them running.

Modifications to the live axle, which is what many of us do is also easier and can be taken further than can with IFS. Drive shaft angles and wishbone droop are the enemy of IFS mods. In essence, the LFA is crude, but effective.

 

[OG.]

One secondary advantage to a live axle is that if a halfshaft breaks it doesn't flail around under the engine like an IFS one does so it can still be driven (in 2 or 3 wheel drive depending on your lockers). This can be a benefit for when repairs cannot be effected on the spot. If an IFS setup breaks a halfshaft it must be worked on immediately to at least remove the broken bits.

 

[Paul_Humphreys]

Just remember you can try to make things Idiot proof and then god makes a greater idiot!!

 

[clivehorridge]

The steering on a 100 seems less positive/direct than an 80 to me, strange. I don't find any benefit or deficit either way for long asphalt driving which is more likely to be affected by other factors like noise levels, tyre and modified suspension choices etc.

Just to clarify my remark, I've neither driven a 100 nor a 90 so I was only presuming better performance from rack and pinion.

Also, about 4 years ago, the steering box on my old 80 was leaking like a sieve from almost everywhere. This prompted me to spend a fortune having it "renovated" with new bearings and seals throughout. Afterwards it worked perfectly, but recently I've noticed a slight weep from the bottom seal of the output shaft.

Here we go again, methinks.

Does anyone concur that steering racks are cheaper to maintain/replace and/or more reliable that the 80's steering box?

 

[Jon Wildsmith]

Does anyone concur that steering racks are cheaper to maintain/replace and/or more reliable that the 80's steering box?

On standard vehicles I doubt there is much difference but on modified ones racks tend to have a harder life because of the increased angles they work at on a lifted vehicle. Ease of replacement will be model specific but that's probably about the same.

 

[Julian T]

I have had more problems with the steering rack on a 83 Vandenplas SD1 than I have ever had with any car that had a steering box, a worn steering rack is not repairable in my experience.
Steering racks only work on cars with IFS but I have seen lots of cars with IFS that have a steering box.

IMO steering rack has the advantage of fewer moving parts, steering box has more moving parts.

When it comes to the decision between live axle or independent suspension then it all depends what I am looking for in a car, If I was buying a sports car then I would want the superior handling that independent suspension gives you but for a overland/off road vehicle I personally prefer solid axles, fewer moving parts, fewer bushes and so on, when you are a long way from anywhere simplicity is the best option for longevity, ease of maintenance and repair.

In my experience with IFS on 4x4's comes torsion bars and I have had a nasty experience with a failed bolt and subsequent no suspension on the one wheel.

 

[OG.]

Torsion bars are less common on IFS 4x4s than coils/airbags.

 

[clivehorridge]

Torsion bars are less common on IFS 4x4s than coils/airbags.

Is this for good reason in your opinion OG (or anyone else)?

My only experience with torsion bars suggests they're not so effective. The Nisshap Terrano used to shed torsion mounting bushes fairly regularly and the (I'm not sure what it was) Toyota like a 4 Runner / LC but not, seemed to have little travel on the front suspension. It always felt like the torsion bars were made of cheese and it made a lot of undesirable noises. Both were probably suffering from lack of maintenance because they were site vehicles in construction.

There's not much that survives construction site abuse very well, sadly.

 

[OG.]

In theory a well executed torsion bar should be no worse than a coil spring (effectively a torsion bar wrapped to make a coil) and should be better as it cannot get coilbound so allowing greater total travel. The problem with torsion bars is the anchor points at each end are subject to enormous forces and this usually generates a weakness where they fail. Failure is always catastrophic unlike coil where the remains of the coil can provide some support.

An anti roll bar is a torsion bar and they give very little trouble on most vehicles.