Solid Front Axle Fascination (SFAF): Help Me Understand
- Thread starter RichinRidgewood
- Start date
thennen
New member
I don't have a dog in this fight - I'm not a trail buster nor a rock crawler, nor am I a suspension expert. That said, I'm reading explanations around the benefits and drawbacks of IFS/SFA in this thread. While there may be a few who are fascinated with the solid front axle, I mostly see guys explaining why it's better in severe off-road situations versus current IFS configs. I can't say that I really see any 'fascination'.
Independent suspensions have their place. One of the benefits is that they tend to reduce the transfer of force from one wheel directly across to the other. So hitting a pothole may be less jarring than it would on a SFA. But from all I gather, I would want a solid front axle if I ever went severely off road. A lot less to go wrong, a lot sturdier, and a lot stronger. Never mind the increased wheel travel, etc. It wouldn't be fascinating to me, it would just be the wiser choice if available.
I imagine that independent suspensions could eventually be designed to 'compete' with solid axles' strong points, but I don't think manufacturers have the incentive to do so. A very narrow band of buyers would find such a robust IFS/IRS to be important - not enough to warrant the manufacturers' investment in time, money, and manufacturing capacity, IMO.
So again, I don't see the fascination. I think solid axles just make sense in many instances.
Independent suspensions have their place. One of the benefits is that they tend to reduce the transfer of force from one wheel directly across to the other. So hitting a pothole may be less jarring than it would on a SFA. But from all I gather, I would want a solid front axle if I ever went severely off road. A lot less to go wrong, a lot sturdier, and a lot stronger. Never mind the increased wheel travel, etc. It wouldn't be fascinating to me, it would just be the wiser choice if available.
I imagine that independent suspensions could eventually be designed to 'compete' with solid axles' strong points, but I don't think manufacturers have the incentive to do so. A very narrow band of buyers would find such a robust IFS/IRS to be important - not enough to warrant the manufacturers' investment in time, money, and manufacturing capacity, IMO.
So again, I don't see the fascination. I think solid axles just make sense in many instances.
Jetboy
New member
Name calling? I think it's just identifying your behavior. You asked why people prefer solid axles. The answer is that they work better for some uses. You then seem to challenge that answer with nothing other than typical trolling responses. The premise of your comments is that it must be an irrational or ignorant person who prefers a solid axle. Then when confronted with the facts that demonstrate otherwise you're could have simply said "interesting, I wasn't aware of that reason". Instead you've demonstrated that you had no intent on learning, just being a troll.
Last edited:
jbtvt
New member
There's nothing to correct here. Possibly you just don't understand it. Also no idea what you're talking about with "belt drive" Subarus. Granted I haven't worked on any lately but never seen any that had a belt anywhere that would qualify them as belt driven.
If you don't like the SRA then good news - you have about 800 other choices! Buy a Highlander and move on.
He's definitely trolling you, then trying to play victim accusing you of name calling.
That being said, thank you for the information you provided despite the weak trolling.
RichinRidgewood
New member
Dependent Suspensions (Solid Front Axle Fascination)
Here are a few things out of a couple hours of reading I did lately
Dependent
On dependent systems with large displacements the camber angle becomes so severe on both tires and the tire contact patch on both tires so small that the benefit of claimed “more articulation” is greatly reduced or worthless. (see the picture of that cartoonish white Jeep thing with the front axle vertical and the tire sitting on its sidewall.) Also you have the front axle between the wheels so you really only have less than the radius of the wheel assembly as ground clearance.
Front dependent systems have high unsprung weight and they are susceptible to shimmy and steering vibrations.
“Shimmy of the front axle had become a serious problem by the 1920s. General Motors (GM) engineer Maurice Olley’s description of the problem
“On a smooth road with front wheels carefully balanced, the car might be traveling at 60 or 70 mph. Suddenly, for no apparent reason (perhaps a small dip or pothole passing under one front wheel), the steering wheel would be wrenched out of the driver’s hands, and would start oscillating violently, while each front wheel would leap along the road in giant ten foot jumps. The front axle would be tramping at 550–600 cpm [cycles per minute], each front wheel jumping three inches into the air.” (1)
“Olley and his colleagues at GM determined that a solution to the shimmy problem was the switch to the independent front suspension (IFS), which “suppresses shimmy by connecting the mountings of the two wheels through the entire sprung mass of the front of the car”. The IFS also had the advantage of allowing for softer front spring rates, which decreased how much the car would pitch over bumps — this flat ride proved pleasant.” (4)
I have personally seen this and had it happen to me in a solid front axle F-series.
Car and Driver refers to this as “…Ox-cart technology….” (5)
Independent
With an independent front or rear you can have zero camber angle change throughout the travel range, what ever range you choose to design to, and maintain full tire contact patch or you can design in the camber angle required for the job the vehicle has to do. You can also design in zero bump-steer as well.
Here are some of the benefits of the TAK-4 and TAK-4i independent suspensions used on our military vehicles.
“Equipping the TAK-4 suspension on HMMWVs provides numerous benefits, including:
–A 70 percent off-road profile capability and 14 inches of independent wheel travel to overcome obstacles and navigate rugged, mountainous environments
–Ground clearance increased to 17 inches to improve mobility and occupant visibility while also helping to counter underbody blasts, such as IEDs, by enabling more stand-off distance
–A 40 percent increase in the vehicle’s maximum speed and a 46 percent improvement in braking
–Restoring a 2,500-pound vehicle payload capacity when the crew is embarked with all current add-on armor installed, which allows for consideration of an under-vehicle armor vee-shaped panel solution to further improve survivability
–Improved ride quality, with a reduction in suspension vibration and harshness for less crew fatigue” (3)
“The new Oshkosh TAK-4i intelligent independent suspension system suspension provides 20-inches of wheel travel ..
TAK-4i intelligent independent suspension system suspension is an ‘intelligent’ independent suspension, providing variable ride height through gas springs.
“In all cases the operating profile of the system is 70% off-road, 30% on-road.” (2)
If the 4Runner had an independent rear suspension it would be a much better vehicle imho. Actually a BOF with 4 wheel independent from a major automotive manufacturer like Toyota would be pretty ‘effn awesome. SRS is not going to stop me from buying a 4Runnner.
The Sport of Rock Crawling amounts to micro percents of the 4 wheel drive vehicles used in the world. I doubt I will ever do it again. It was fun in a rented Jeep in Hawaii for a day. Here are some purpose built vehicles that have interesting articulation
Spider excavator
All Mountain Inc.- All Mountain Construction Spider Excavator Services
YouTube
Turbo diesel Hexapod Walking Machine
YouTube
Conclusion: I haven't seen anything in my reading to convince me that Solid Front Axle systems on a 4 wheel drive vehicle are anything I would want to have (again). This was almost a stupid waste of time since I knew this all ready however since I did get to read a 200+ page paper on vehicle suspension design it was probably worth my while. Thanks to everyone who replied.
1) W. Milliken and D. Milliken. Chassis Design: Principles and Analysis. Society of Automotive Engineers, Inc., 2002.
2) Oshkosh TAK-4 Independent Suspension System - Wikipedia
3) Oshkosh TAK-4 Independent Suspension System Enhances HMMWV Capabilities | DefenceTalk
4) Geometric Design of Independent Suspension Linkages D.E Kline
5) https://www.caranddriver.com/news/a15340751/explained-the-five-most-common-automotive-suspensions/
Here are a few things out of a couple hours of reading I did lately
Dependent
On dependent systems with large displacements the camber angle becomes so severe on both tires and the tire contact patch on both tires so small that the benefit of claimed “more articulation” is greatly reduced or worthless. (see the picture of that cartoonish white Jeep thing with the front axle vertical and the tire sitting on its sidewall.) Also you have the front axle between the wheels so you really only have less than the radius of the wheel assembly as ground clearance.
Front dependent systems have high unsprung weight and they are susceptible to shimmy and steering vibrations.
“Shimmy of the front axle had become a serious problem by the 1920s. General Motors (GM) engineer Maurice Olley’s description of the problem
“On a smooth road with front wheels carefully balanced, the car might be traveling at 60 or 70 mph. Suddenly, for no apparent reason (perhaps a small dip or pothole passing under one front wheel), the steering wheel would be wrenched out of the driver’s hands, and would start oscillating violently, while each front wheel would leap along the road in giant ten foot jumps. The front axle would be tramping at 550–600 cpm [cycles per minute], each front wheel jumping three inches into the air.” (1)
“Olley and his colleagues at GM determined that a solution to the shimmy problem was the switch to the independent front suspension (IFS), which “suppresses shimmy by connecting the mountings of the two wheels through the entire sprung mass of the front of the car”. The IFS also had the advantage of allowing for softer front spring rates, which decreased how much the car would pitch over bumps — this flat ride proved pleasant.” (4)
I have personally seen this and had it happen to me in a solid front axle F-series.
Car and Driver refers to this as “…Ox-cart technology….” (5)
Independent
With an independent front or rear you can have zero camber angle change throughout the travel range, what ever range you choose to design to, and maintain full tire contact patch or you can design in the camber angle required for the job the vehicle has to do. You can also design in zero bump-steer as well.
Here are some of the benefits of the TAK-4 and TAK-4i independent suspensions used on our military vehicles.
“Equipping the TAK-4 suspension on HMMWVs provides numerous benefits, including:
–A 70 percent off-road profile capability and 14 inches of independent wheel travel to overcome obstacles and navigate rugged, mountainous environments
–Ground clearance increased to 17 inches to improve mobility and occupant visibility while also helping to counter underbody blasts, such as IEDs, by enabling more stand-off distance
–A 40 percent increase in the vehicle’s maximum speed and a 46 percent improvement in braking
–Restoring a 2,500-pound vehicle payload capacity when the crew is embarked with all current add-on armor installed, which allows for consideration of an under-vehicle armor vee-shaped panel solution to further improve survivability
–Improved ride quality, with a reduction in suspension vibration and harshness for less crew fatigue” (3)
“The new Oshkosh TAK-4i intelligent independent suspension system suspension provides 20-inches of wheel travel ..
TAK-4i intelligent independent suspension system suspension is an ‘intelligent’ independent suspension, providing variable ride height through gas springs.
“In all cases the operating profile of the system is 70% off-road, 30% on-road.” (2)
If the 4Runner had an independent rear suspension it would be a much better vehicle imho. Actually a BOF with 4 wheel independent from a major automotive manufacturer like Toyota would be pretty ‘effn awesome. SRS is not going to stop me from buying a 4Runnner.
The Sport of Rock Crawling amounts to micro percents of the 4 wheel drive vehicles used in the world. I doubt I will ever do it again. It was fun in a rented Jeep in Hawaii for a day. Here are some purpose built vehicles that have interesting articulation
Spider excavator
All Mountain Inc.- All Mountain Construction Spider Excavator Services
YouTube
Turbo diesel Hexapod Walking Machine
YouTube
Conclusion: I haven't seen anything in my reading to convince me that Solid Front Axle systems on a 4 wheel drive vehicle are anything I would want to have (again). This was almost a stupid waste of time since I knew this all ready however since I did get to read a 200+ page paper on vehicle suspension design it was probably worth my while. Thanks to everyone who replied.
1) W. Milliken and D. Milliken. Chassis Design: Principles and Analysis. Society of Automotive Engineers, Inc., 2002.
2) Oshkosh TAK-4 Independent Suspension System - Wikipedia
3) Oshkosh TAK-4 Independent Suspension System Enhances HMMWV Capabilities | DefenceTalk
4) Geometric Design of Independent Suspension Linkages D.E Kline
5) https://www.caranddriver.com/news/a15340751/explained-the-five-most-common-automotive-suspensions/
Jetboy
New member
Ultimately there's no substance to what you've posted. If you think it is meaningful to you - then you should find a vehicle that has IFS and IRS and they will probably be better suited for your needs. Your needs are not what the 4Runner or Jeep products are built for.
it's already been explained to you multiple times. If you want to be ignorant about things then be prepared to be called out for it.
Last edited:
RichinRidgewood
New member
Well lookee here. We have a real doctor on this board. I mean a doctor maybe like a Dentist is a Doctor but any how a PHD.
My worthless Bachelor of Science in Electrical Engineering and my Master of Science in Mechanical Engineering from a couple big name schools in Michigan and 30 years of experience working as an Engineer and a Director for some of the biggest companies in the world is no match for that. I am, after all, a "troll".
So Jetboy why dont you scratch out a few force diagrams, derive the formulas, explain your constraints and compare both cases. Don't bother with Matlab it's too cumbersome. Do it on paper with a pencil. This shouldn't take you so long you have a PHD. I even gave you a head start with the formulas in the papers I posted.
(PHD) Pile it High and Deep there son. Help me understand.
Inv4drZm
Senior Member
He's talking to the wrong dudes. The dudes that like/support offroading.
Go to the Honda forum and they'll agree with you for sure.
SpeedyKevin
New member
Youre not contributing much to this discussion. Please provide your own input based on your expertise. Lets make this a fruitful conversation
See, now you turned it into a pissing contest...you've just lost all credibility.
Surprised the 3 houses, 10 car, 4 trophy wives and 11 figure bank account wasn't mentioned...
Inv4drZm
Senior Member
I'm still looking for where it says he has any actual experience with designing suspension systems.
RichinRidgewood
New member
Nope married to my first (and will be my only wife), 1 old car, 1 old motorcycle, a bunch of degrees, semi-retired, (Billions of dollars in a bank account? how is that even possible?) I have traveled a lot and will continue to do so.
This thread turned from tech discussion into a name calling and cow pie throwing contest. Too bad could have been worth something.
jbtvt
New member
Dude, your 3rd post in this thread you were saying how SFA might make sense for a "budget weekend warrior", and you're whining about some cow pies lobbed back at you? Watch some rock bouncing vids and count how many SFA vs IFS rigs you see. Want to go to one of their events and tell the 95% of guys who run SFA/SRA on the hardest courses on the planet in their $50-100k+ rigs how they're "weekend warriors" because your 20 yr old Benz has only needed a few alignments? Get real. Every one of those guys and most of the guys here have weighed the pros and cons of both, and all decided on at least an SRA if not SFA. Maybe they know some things about it firsthand that you don't?
Every truck, and really every BOF vehicle that I know of, designed by multiple PhDs with millions of data points behind them, of uses a SRA. Maybe they know some things from a century of design research and stress testing that you don't?
Every design has its place. If you don't want to off-road, don't want to tow heavy things, don't mind replacing perfectly good CVs because the boots cracked yet again, and are willing to pay slightly more for slightly better on-road handling, then buy a Highlander, buy a Prius. No one cares. I poke way more fun at mall crawlers than I do the suburban dad who drives an IFS/IRS vehicle because it suits his needs. It's your insistence on tearing down people whose different needs are met by a different design than your preference that led your thread down the road it traveled.
LandCruiser
New member
My CV axles were destroyed at 100k miles. The LCAs for the IFS had also seized up.
My alignment is okay until I start to off road it heavily and then it's just a matter of time before it gets so bad it needs to be put back.
IFS is great on highway, tho.
SFAs, ALL OF THEM, get weird at highway speeds under the right conditions.
My alignment is okay until I start to off road it heavily and then it's just a matter of time before it gets so bad it needs to be put back.
IFS is great on highway, tho.
SFAs, ALL OF THEM, get weird at highway speeds under the right conditions.
thennen
New member
Isn't the Mercedes C-Class a passenger sedan?
RichinRidgewood
New member
I haven't looked real hard but I haven't seen any Monster Trucks using IFS. Same with the rear ...all SRA
According to these guys "The wheels and tires are sessentially what make your Monster truck"...
So You Want to Build a Monster Truck – RacingJunk News
The Government is notoriously cheap and if they paid for IFS and IRS on their combat vehicles I bet there is some serious justification on it and it would be in some public documents of someone could find it.
They are even upgrading the HUMVEE with TAK-4 it looks like.
Attachments
Similar threads
