Ifs 101

[patooyee]

Hello everyone. I feel like I got lost in a time travel vortex and when I came back to Pirate I was all alone. :) It's good to know that the tech spirit lives on here and I look forward to my membership.

I posted this over there and wasn't getting any activity. I hope it gets some traction here.

I'm interested in learning more about IFS design theory for a few reasons.

A, I'm bored not being able to build anything for years and hoping to get back to a point where I can sometime in the next year or two. I can use this down-time to learn.
B, I kinda wanna build one.
C, it's probably more applicable to the style of wheeling I have in my future.
D, I've always been curious about it.

I've been doing prelim research using several sources. Of course, Herb Adams' Chassis Engineering book, and some great YT videos that I made a list out of here:

https://www.youtube.com/playlist?lis...iBb_WxXdUF4raB

There's also several threads here about it, but sadly not nearly as in-depth as I'd wish. I think a lot of people keep their secrets for racing now days. Nevertheless, I've developed an outline of topics and questions that I have. I'd appreciate any light anyone is willing to shed on them. My goals are not racing, just general off-roading. If I ever built anything I would want it to be basically as close to a Polaris as I could get while still using an automotive drive train. Feel free to share thoughts about any venue though.

1. Camber
   1. Def: Vertical angle of tire when viewed from front.
   2. How important is this within reason for general off-roading? I feel like camber is going to be all over the place in uneven terrain. Beyond the suspension's movement, the terrain itself would cause camber changes even if the suspension stayed stationary. I get that a small amount of negative static camber is generally good for road racing when some camber gain is built into the suspension for turns. But isn't that all kind of out the window when going over whoops, rocks, berms, hills, ditches, ruts, etc.? Not saying that this should be ignored, but maybe just not as obsessed over as it might be on a road-car?
2. Toe
   1. Def: Angle of front of tires when viewed from above / below.
   2. Again, my hunch is that, so long as toe is relatively neutral, for general off-roading this isn't going to be hugely impactful to stress over given the lack of traction and reduced need for tracking perfectly straight?
3. Scrub Radius
   1. Def: The distance from where the king pin inclination axis touches the ground to the center of the tire.
   2. I suspect that this is a big concern given tire sizes and the effects that excessive scrub radius can have on handling.
   3. Assume this needs to be minimized if not negative?
4. King Pin Inclination
   1. Def: Angle of steering axis when viewed from front.
   2. Herb Adams recommends 7-9* but this is for race cars.
   3. Not sure if off-road implies any special considerations here?
5. Caster
   1. Def: Angle of steering axis when viewed from side.
   2. How much positive caster?
   3. Herb Adams recommends 10* as a rule of thumb.
6. Roll Center
   1. Def: The intersection of both a-arms, when viewed from front, with imaginary line drawn from that point to the center of the opposite tire patch.
   2. This is what I imagine to be one of the most important design focuses of an IFS for any car, but especially offroad vehicles that have higher chances of rolling.
   3. COG acts like a weight on the end of a pole with roll center being the pivot point on the opposite end of the pole.
   4. Theoretically one would like their COG to be as low as possible with RC to be equal to COG. This would induce the least amount of roll angle in turns and weight shifts. It would also induce a large amount of jacking, which means the COG is moving all around in a semi-unpredictable fashion.
   5. So my understanding is that we want RC to be slightly above the road surface and to design CoG as low as possible to reduce the lever arm. Of course, everything is a compromise.
   6. RC will move around throughout the movement of the suspension. RC change should be minimized for a predictable suspension.
7. Pitch Center
   1. Def: Same as roll center only viewed from side.
   2. A shorter PC will allow the CoG to have more leverage, and therefore, for fore / aft movement under both braking and acceleration, correct?
   3. I would think that a longer PC with minimal change would be a desirable goal? Herb Adams calls pitch center "side view swing arm." Swing arm either directly correlates to, or actually is ...
8. Anti-Dive
   1. Roughly equivalent to anti-squat in a rear suspension.
   2. It's been a long time since I've done suspension research. The last time I did it was the general consensus that anti-squat should be relatively neutral and the shocks / springs should be tuned to handle most of the suspensions resistance to movement.
   3. I assume the same applies to the front / anti-dive? This is Herb Adam's general recommendation for race cars.
9. Ackerman should abide by all the general rules as any other front suspension as far as I know. Thus, I won't go into great detail here as there are threads about that already. Tell me if I'm missing something.
10. Of course, bump-steer should be minimized.
    1. When viewed from front, if your steering arms intersect with a theoretical point where your upper and lower a-arms intersect, IE all three at one point, theoretically you would have zero bump-steer.
    2. How realistic is this in an off-road rig?
    3. I suspect that using a steering rack helps with this by allowing longer steering rods than would otherwise be possible with just a normal ram?
11. CV plunge
    1. Should be minimized to avoid heat / wear / tear.
    2. In order to minimize plunge the center point of the CV joints will need to be close to the suspension pivots?
12. Calculators:
    1. Haven't come across many. I'd be willing to pay for one if someone can recommend it.
    2. Suspension Geometry Calculator

I'm sure I'm missing a ton, please enlighten me.

 

[patooyee]

I'm DuckDuckGo-ing for suspension calculators right now. I've not used any of these yet, just linking them for future reference. I'll update it as I find others:


Free:

https://www.racingaspirations.com/ap...ry-calculator/
http://vsusp.com/

Paid:
http://susprog.com/
[url]https://optimumg.com/product/optimumkinematics/
http://www.auto-ware.com/software/asgp/asgp.htm
http://performancetrends.com/[/URL]

 

[rockmup]

Good to see you and I have nothing to offer but interested in it.

 

[SLOWPOKE693]

Is Isdtbower here? This kind of stuff is right up his alley.

 

[YotaAtieToo]

Good to see you and I have nothing to offer but interested in it.

Basically this

I was trying to play with ifs a little on a suzuki sidekick, but it was a McPherson strut, so basically garbage.

I also have a mild 3rd gen 4runner I'd like to mess with a little, but need to maintain drive ability. It's dual a arm with coil overs for those who aren't familiar.

I've also thought about scratch built full independent rig. Ie: sxs killer/wannabe. Seems like flat, equal a arms is kinda the go to. I'd be curious about laying the a arms back like an rc stadium truck, basically so the tire moves back under compression.

Is there a reason why making 8 identical a arms, then building a little caster and camber into the chassis mounts wouldn't work pretty damn decent?

 

[Treefrog]

Finally, the fun begins.

1. It can't be too bad to have or else there wouldn't be solid axles building it in. Looking at desert suspensions they seem to do what they can to keep it constant.
2. Above not front. Same as camber, it doesn't hurt to run a small amount
3. Depends. Desert guys seem to like to run as little as possible. Crawlers seem to like it. Allows you to try to grab traction by turning. Depends on use. Higher means more force on the steering. Negative should probably be avoided.
4. Higher means more return to center at low speed. Depends a bit on design, but Race-dezert says 10*-15* is the normal range. Clearance and scrub radius guide it.
5. Geometry governing the straightening of the wheels at speed. I've heard 12* from a solid axle racer on PBB.
6. Its the intersection of the line from the center of the tire patch to the front view IC of the suspension locating that wheel with the same line on the other side.
7. Yes. But its higher/lower not longer/shorter. Lower it is , the more pitch the vehicle will experience during acceleration. Its more of a point of interest rather than a design point for most people. The current 4-link calculators don't determine it.
8. Pretty much. The lower the value the more it will dive when braking. But it will also be softer in rough stuff when braking. With outboard brakes, the line for it goes from the center of the tire contact patch to the side view IC.
9. Correct
10. In combination with the outers.
11. Nothing missing here
12. From a technical standpoint, its only at that moment in travel. At any other point it will not be pointing at the IC. Road cars can handle this because they have such little travel. From a pure design standpoint, you can create an axis in 3D space along which there will be no bump steer at full droop, ride, and full bump. A steering rack makes it easier to get the rod end on that line.
13. Pretty much
14. That one is okay, but doesn't account for caster change. Same with vsusp. CAD that can handle 3d parametric design is by far the best option, just requires some hand (excel) math for stuff like finding shock install ratios and stuff.

Found this playlist a while back, been meaning to watch it: https://www.youtube.com/playlist?list=PLYqLI7C2KoSaHxSJRNur0uReYyZATRACB

 

[Treefrog]

Basically this

I was trying to play with ifs a little on a suzuki sidekick, but it was a McPherson strut, so basically garbage.

I also have a mild 3rd gen 4runner I'd like to mess with a little, but need to maintain drive ability. It's dual a arm with coil overs for those who aren't familiar.

I've also thought about scratch built full independent rig. Ie: sxs killer/wannabe. Seems like flat, equal a arms is kinda the go to. I'd be curious about laying the a arms back like an rc stadium truck, basically so the tire moves back under compression.

Is there a reason why making 8 identical a arms, then building a little caster and camber into the chassis mounts wouldn't work pretty damn decent?

Usually, the upper arm is a bit shorter than the lower.

The big limitation of 8 identical arms is the lack of tunability of the values as the suspension moves.

 

[rockyota83]

im glad you got my message

 

[Mr Stubs]

Good to see you here

 

[Toreadorranger]

im glad you got my message

I beat you too it yesterday.

 

[Sterlingfire]

Hell yeah pat! Nice first thread. This will get good imo.

I know you want shorter upper control arms than lowers so your camber is less effected by suspension travel.
Another problem is that you'll never be able to delete toe, and will be less under compression, and higher under droop.

 

[SLOWPOKE693]

While not 4wd, here is a decent picture of a go fast front suspension on a pre runner i saw a couple weeks ago at a local fab shop.

 

[gt1guy]

I have the Performance Trends suspension program. It's an impressive tool. I think I bought it in 08-09, and it was around $500. You can't compare it to the 4-link calculator everyone on here is familiar with. They are worlds apart, even though I'd guess PT is Excel based too.


If you don't have it already, you need the Milliken brothers book Race Car Vehicle Dynamics. It's an SAE college level book that's basically God's word on all things vehicle dynamics. It's thick and it ain't cheap.

The most important thing to always remember is that everything affects everything else. Getting tunnel vision on something like keeping the RC movement as low as possible, will always bite you in the ass somewhere else.

 

[arse_sidewards]

While not 4wd, here is a decent picture of a go fast front suspension on a pre runner i saw a couple weeks ago at a local fab shop.

I wonder why they chose to package the upper control arm that way. Seems like you could get same-ish strength to weight with the mounts on either side of the shock with possibly more steering angle. My best guess is they wanted to leave room in case they wanted to angle a shock to the rear.

 

[SLOWPOKE693]

I wonder why they chose to package the upper control arm that way. Seems like you could get same-ish strength to weight with the mounts on either side of the shock with possibly more steering angle. My best guess is they wanted to leave room in case they wanted to angle a shock to the rear.

I think alot of it has to do with steering. Im thinking once the rack and tie rods are mounted and turned full lock left, there wouldn't be much room to push the coil over forward from its current position before there would be interference with the spring and tie rod. I could be wrong though. This is all just a guess.....

 

[SLOWPOKE693]

Here is my IFS question........

Why do most builders mount their front upper and lower arms level in relation the the chassis, like my above picture, vs rc cars where the front suspensions are generally tipped up in front with the arms angle back when viewed from the side?


Im sure there is a technical term for this but I R dumb.

 

[Treefrog]

Here is my IFS question........

Why do most builders mount their front upper and lower arms level in relation the the chassis, like my above picture, vs rc cars where the front suspensions are generally tipped up in front with the arms angle back when viewed from the side?


Im sure there is a technical term for this but I R dumb.

Its called kick. Good for getting the IC low. But has a backward movement when it hits a bump. Some think it slows you down. There was some debate over if it causes lift when climbing.

 

[Tech Tim]

I've been doing prelim research using several sources. Of course, Herb Adams' Chassis Engineering book

The Herb Adams book is a great primer and my go to when I have a simple question.

Theory of Ground Vehicles by Wong and Fundamentals of Vehicle Dynamics by Gillespie are to two hard core engineering books if you have the math skills.

- All the items you list are important to keep track of and optimize the best you can. Often making a change to one, screws up another, so just like a 4-link suspension, you are often making compromises to get everything as close as you can within your parameters.

- Due to the longer travel most are shooting for on an off road car, you have to track all these items throughout the range of travel of the suspension. Many designers/builders do not do this. When you look at their car sitting at static height, the geometry may look decent, but when you watch them in action, you'll see things go funky.

- Width is everything. The longer the A-arms are, the easier it is to control all the parameters though a given travel range.

1. Camber
   1. Def: Vertical angle of tire when viewed from front.
   2. How important is this within reason for general off-roading? I feel like camber is going to be all over the place in uneven terrain. Beyond the suspension's movement, the terrain itself would cause camber changes even if the suspension stayed stationary. I get that a small amount of negative static camber is generally good for road racing when some camber gain is built into the suspension for turns. But isn't that all kind of out the window when going over whoops, rocks, berms, hills, ditches, ruts, etc.? Not saying that this should be ignored, but maybe just not as obsessed over as it might be on a road-car?
   
   - Controlling the camber is very important. Keeping the tire tread flat on the ground, especially through a turn will help make your vehicle easier to control.
   
   - The thought that onroad suspension geometry is out the window off-road makes me chuckle, it seems to be a bygone conclusion by so many designers and it shows in their suspension designs. Geometry is geometry, you can't get away from it. The big differences between road cars and off road cars is the traction and the travel. A high performance on road car might have 3-4" useable travel and 6-7" of total travel. It is fairly easier to control and plot all the necessary geometry. Stretch that out to 15" of travel or more, design it with big enough components to stay together and package it as narrow as you can and you have so much more to keep track of.
2. Toe
   1. Def: Angle of front of tires when viewed from ABOVE/BELOW.
   2. Again, my hunch is that, so long as toe is relatively neutral, for general off-roading this isn't going to be hugely impactful to stress over given the lack of traction and reduced need for tracking perfectly straight?
   
   - In general, Toe is Toe. You adjust that according to the wheel offset/backspace and scrub.
   
   - Controlling toe change through the travel (bump steer) is one of the biggest handling improvements you can do to an off road car. Again the whole it's off road, all that goes out the window....
3. Scrub Radius
   1. Def: The distance from where the king pin inclination axis touches the ground to the center of the tire.
   2. I suspect that this is a big concern given tire sizes and the effects that excessive scrub radius can have on handling.
   3. Assume this needs to be minimized if not negative?
   
   - Same as a live axle off-road rig, keep your scrub down to a minimum, but not zero, you want a little.
4. King Pin Inclination
   1. Def: Angle of steering axis when viewed from front.
   2. Herb Adams recommends 7-9* but this is for race cars.
   3. Not sure if off-road implies any special considerations here?
   
   - This is often dictated by many other of the items in this list.
5. Caster
   1. Def: Angle of steering axis when viewed from side.
   2. How much positive caster?
   3. Herb Adams recommends 10* as a rule of thumb.
   
   - Just like toe change, you have to plan for caster change throughout the travel and do everything you can to put the caster where you want it. Many like to have some caster gain as you go into bump, it'll help you come through a landing easier.
6. Roll Center
   1. Def: The intersection of both a-arms, when viewed from front, with imaginary line drawn from that point to the center of the opposite tire patch.
   2. This is what I imagine to be one of the most important design focuses of an IFS for any car, but especially offroad vehicles that have higher chances of rolling.
   3. COG acts like a weight on the end of a pole with roll center being the pivot point on the opposite end of the pole.
   4. Theoretically one would like their COG to be as low as possible with RC to be equal to COG. This would induce the least amount of roll angle in turns and weight shifts. It would also induce a large amount of jacking, which means the COG is moving all around in a semi-unpredictable fashion.
   5. So my understanding is that we want RC to be slightly above the road surface and to design CoG as low as possible to reduce the lever arm. Of course, everything is a compromise.
   6. RC will move around throughout the movement of the suspension. RC change should be minimized for a predictable suspension.
   
   - Roll center is one of those things that you try to optimize, but it is often very affected by other items.
7. Pitch Center
   1. Def: Same as roll center only viewed from side.
   2. A shorter PC will allow the CoG to have more leverage, and therefore, for fore / aft movement under both braking and acceleration, correct?
   3. I would think that a longer PC with minimal change would be a desirable goal? Herb Adams calls pitch center "side view swing arm." Swing arm either directly correlates to, or actually is ...
   
   - Same as above.
8. Anti-Dive
   1. Roughly equivalent to anti-squat in a rear suspension.
   2. It's been a long time since I've done suspension research. The last time I did it was the general consensus that anti-squat should be relatively neutral and the shocks / springs should be tuned to handle most of the suspensions resistance to movement.
   3. I assume the same applies to the front / anti-dive? This is Herb Adam's general recommendation for race cars.
   
   - You are correct, anti-dive is anti-squat for the front and yes, you want it to be fairly neutral.
9. When adjusting suspension points, outer a-arm joints control:
   1. KPI
   2. Caster
10. When adjusting suspension points, inner a-arm joints control:
    1. Roll Center
    2. Pitch Center
    
    - No, all those can be change at any of the pivot points.
11. Ackerman should abide by all the general rules as any other front suspension as far as I know. Thus, I won't go into great detail here as there are threads about that already. Tell me if I'm missing something.
    
    - The same arguments apply with a live axle. Do you go for true Ackerman or do you plot Ackerman to do what you want.
12. Of course, bump-steer should be minimized.
    1. When viewed from front, if your steering arms intersect with a theoretical point where your upper and lower a-arms intersect, IE all three at one point, theoretically you would have zero bump-steer.
    2. How realistic is this in an off-road rig?
    3. I suspect that using a steering rack helps with this by allowing longer steering rods than would otherwise be possible with just a normal ram?
    
    - Controlling toe change through the travel (bump steer) is one of the biggest handling improvements you can do to an off road car. Notice the bold on "through the travel".
    
    - If you are planning to use a ram, mount it to a slider so you can optimize tie rod end placement for your suspension.
    
    - Spend some time watching videos of the IFS U4 and desert race rigs cars going through the rough at speed and watch closely for the toe changes. Few designers have figured it out.
13. CV plunge
    1. Should be minimized to avoid heat / wear / tear.
    2. In order to minimize plunge the center point of the CV joints will need to be close to the suspension pivots?
    
    - Yes, minimized plunge through the travel.
    
    - Rule of thumb is to keep the CV centerlines inline with the inner and outer A-arm pivot points. It doesn't have to follow this rule exactly, if you know what you're doing, but it is a good rule to follow.
14. Calculators:
    1. Haven't come across many. I'd be willing to pay for one if someone can recommend it.
    2. Suspension Geometry Calculator

I'm sure I'm missing a ton, please enlighten me.

- WinGeo was one we used when the kid and I first got into designing IFS suspensions.

- Eventually he figured out to just track it all through Solidworks.

 

[arse_sidewards]

All the road car literature is worth reading. IMO it's more important in an off road vehicle because we spend much more time much closer to the limit of available traction than road cars do. We also tend to care much more about behavior characteristics at the extremes of compression/droop because that is how we do/don't get over obstacles.

 

[NickM]

Copying this comment over from the Pirate thread. I really hope this thread gains traction. You're right, a lot of this information is not laid out in one place in an organized thread. I'll add a few notes to possibly help clarify... or confuse more...

1. Camber
   1. Def: Vertical angle of tire when viewed from front.
   2. How important is this within reason for general off-roading? I feel like camber is going to be all over the place in uneven terrain. Beyond the suspension's movement, the terrain itself would cause camber changes even if the suspension stayed stationary. I get that a small amount of negative static camber is generally good for road racing when some camber gain is built into the suspension for turns. But isn't that all kind of out the window when going over whoops, rocks, berms, hills, ditches, ruts, etc.? Not saying that this should be ignored, but maybe just not as obsessed over as it might be on a road-car? Camber change can potentially be used to "cheat" some extra suspension travel by reducing the angle on balljoints/uni-balls and CV joints.
2. Anti-Dive
   1. Roughly equivalent to anti-squat in a rear suspension.
   2. It's been a long time since I've done suspension research. The last time I did it was the general consensus that anti-squat should be relatively neutral and the shocks / springs should be tuned to handle most of the suspensions resistance to movement.
   3. I assume the same applies to the front / anti-dive? This is Herb Adam's general recommendation for race cars. (Some Anti-dive can be good so you don't have to rely on shocks/springs to prevent the nose dive when braking. Most OEM IFS suspensions have anti-dive. Adding anti-dive can be accomplished by angling the upper a-arm downwards towards the center of the vehicle when viewed from the side. Or I supposed angling the lower control arm up. It is calculated by finding the intersection point of the upper and lower a-arm axis when viewed from the side. On my Colorado, I angled the upper a-arm a few degrees back. You have to be careful with long travel suspension to not add too much anti-dive. As the suspension droops, it will move the caster angle towards zero, or possibly passed zero... which can probably make things pretty unstable.)
3. Of course, bump-steer should be minimized.
   1. When viewed from front, if your steering arms intersect with a theoretical point where your upper and lower a-arms intersect, IE all three at one point, theoretically you would have zero bump-steer.
   2. How realistic is this in an off-road rig?
   3. I suspect that using a steering rack helps with this by allowing longer steering rods than would otherwise be possible with just a normal ram?
   4. Generally the outer steering pivot will not land directly on the KPI axis when viewed from the front because of ackerman (I think) as well as tire and wheel clearance. You should be able to get pretty close to zero bump-steer though by moving the inner steering pivot towards the center by the the same distance that the outer joint is off of the KPI axis. You also want the height location ratios to be the same for the inner and outer pivots.... Take the the ratio of the distance that the outer steering joint is between the ball-joints, and make the inner steering joint at the same height ratio between the inner a-arm pivot points. On my Colorado, I am using a 2010 GM 1500 steering rack, so I was stuck with a fixed width rack. I plotted points in CAD from the steering knuckle throughout the suspension travel to determine the best height of the steering rack to minimize the bump steer and I think it ended up at like .030" bump-steer at the outer tie rod joint....... The other way that desert guys are getting good steering geometry is with a steering box, but by using "swing-set steering". This type of steering causes the relay rod that the tie-rods attach to to move in an arc motion. This arc can be fine tuned to follow or match the arc that the steering knuckle moves in caused by caster. I have never attempted this. Kibbetech has built some pretty crazy setups, but I think only one was in a 4wd.
4. CV plunge
   1. Should be minimized to avoid heat / wear / tear.
   2. In order to minimize plunge the center point of the CV joints will need to be close to the suspension pivots?
   3. It is definitely important to minimize CV plunge . This can be done similarly to how I described the bump-steer. At least in my GM knuckle & outer CV joint combo, the outer joint pivot lies directly inline with the KPI axis. The best way to minimize the joint plunge is to place the inner joint pivot directly on the axis going through the upper and lower a-arm inner pivot points.... As well as place it at the correct height by keeping the same height ratio as the outer joint. in my application, I was able to get inner CV plunge down to about .375", but I was limited by packaging constraints with the oil pan and front diff.
   4. I'm excited to see some of the fancy technology become more popular. Ball spline shafts have existed for a while. They can be used as a telescoping CV center shaft (sort of like a driveline). This can allow the inner joint to be a higher angle, non plunging joint. I'm curious if we will start seeing these used in more places. Check out some of the Youtube videos from automotive journalists showing the new GMC Hummer EV. They use some beefy CV axles with ball spline shafts. Pretty cool to see on an OEM vehicle.

 

[Wilson]

In

 

[michael.gonzalez]

Here is my IFS question........

Why do most builders mount their front upper and lower arms level in relation the the chassis, like my above picture, vs rc cars where the front suspensions are generally tipped up in front with the arms angle back when viewed from the side?


Im sure there is a technical term for this but I R dumb.

The main goal of suspension is to absorb loads in the Z direction (up and down).

Tilting the arms back allows the suspension to absorb a slight amount of front and back motion. This also reduces the theoretical efficiency as the wheels have to travel forward again after being pushed back with each compression of the suspension. Too much tilt-back is no good. Some builders/designers think no tilt back is ideal.
Having some tilt-back would also allow the suspension to work a bit more when the truck is pitched downward (front down, rear up). It's all trade-offs.

Take a look at the Vildosola trophy trucks. They have LOTS of tilt back. Probably 10* or more. No right or wrong way to do it, just different ways.

 

[patooyee]

Thanks again everyone welcoming me.

Replies came in faster than I was expecting, which is awesome. I want to digest them more before I keep asking questions. But other questions I have that haven't been touched on yet:

1. Links to good IFS knuckles as a starting point?
2. Static angle of lower arms? Flat gives up ground clearance, which is one of the benefits of IFS, angled gives you a bit more clearance. I feel like I've seen both in rigs these days.
3. What materials are generally considered strong enough for the a-arms if not fabbing them from scratch?

 

[michael.gonzalez]

Thanks again everyone welcoming me.

Replies came in faster than I was expecting, which is awesome. I want to digest them more before I keep asking questions. But other questions I have that haven't been touched on yet:

1. Links to good IFS knuckles as a starting point?
2. Static angle of lower arms? Flat gives up ground clearance, which is one of the benefits of IFS, angled gives you a bit more clearance. I feel like I've seen both in rigs these days.
3. What materials are generally considered strong enough for the a-arms if not fabbing them from scratch?

1.
These are builder bells. You still need to weld in your lower and upper pivot but it provides a base for your hub to mount to.
http://www.spidertrax.com/products/Builder-Bells
http://www.spidertrax.com/products/Unit-Bearings
If you don't need something so strong, you can maybe adapt an OEM knuckle/CV.

2. This mostly involves your ride height and desired droop/bump travel. You can have "angled arms" that are built "flat" and then kick down to the uniball. Those allow more ground clearance while leaving more bump travel.

3. Not sure what you are asking here. Steel?

 

[SLOWPOKE693]

3. Not sure what you are asking here. Steel?

I think he means making them out of something other than gusseted plate steel. Is DOM tube acceptable to use? Kind of like how sport quad and SxS arms are designed. Would that be strong enough in an offroad application? Building arms out of tube would be alot easier for the DIY guys vs having parts plasma or lazer cut at an outside facility.

 

[SLOWPOKE693]

Who was the guy on the other board that built the tiny little IFS/IRS U4 car in his garage using a bunch of GM truck parts? That car was the definition of home built IFS/IRS.

Side note: Laser Nuts IFS/IRS U4 car is pretty freakin crazy!

 

[patooyee]

Finally, the fun begins.

1. It can't be too bad to have or else there wouldn't be solid axles building it in. Looking at desert suspensions they seem to do what they can to keep it constant.
2. Above not front. Same as camber, it doesn't hurt to run a small amount
3. Depends. Desert guys seem to like to run as little as possible. Crawlers seem to like it. Allows you to try to grab traction by turning. Depends on use. Higher means more force on the steering. Negative should probably be avoided.
4. Higher means more return to center at low speed. Depends a bit on design, but Race-dezert says 10*-15* is the normal range. Clearance and scrub radius guide it.
5. Geometry governing the straightening of the wheels at speed. I've heard 12* from a solid axle racer on PBB.
6. Its the intersection of the line from the center of the tire patch to the front view IC of the suspension locating that wheel with the same line on the other side.
7. Yes. But its higher/lower not longer/shorter. Lower it is , the more pitch the vehicle will experience during acceleration. Its more of a point of interest rather than a design point for most people. The current 4-link calculators don't determine it.
8. Pretty much. The lower the value the more it will dive when braking. But it will also be softer in rough stuff when braking. With outboard brakes, the line for it goes from the center of the tire contact patch to the side view IC.
9. Correct
10. In combination with the outers.
11. Nothing missing here
12. From a technical standpoint, its only at that moment in travel. At any other point it will not be pointing at the IC. Road cars can handle this because they have such little travel. From a pure design standpoint, you can create an axis in 3D space along which there will be no bump steer at full droop, ride, and full bump. A steering rack makes it easier to get the rod end on that line.
13. Pretty much
14. That one is okay, but doesn't account for caster change. Same with vsusp. CAD that can handle 3d parametric design is by far the best option, just requires some hand (excel) math for stuff like finding shock install ratios and stuff.

Found this playlist a while back, been meaning to watch it: https://www.youtube.com/playlist?list=PLYqLI7C2KoSaHxSJRNur0uReYyZATRACB

1. OK. My intent wasn't to say that it could be ignored. Just that maybe compromising on it instead of something like roll axis would be more acceptable in an off-road rig vs a pavement racer. Let's not get hung up on this point though. I understand its importance and that maybe I was understating it to begin with.
2. How do we not have a thumbs up emoji? Instead I'll use this one when I want to signal agreeance.
3. Didn't think about the reach out and grabbing effect. Good point and example of how conventional racing theory doesn't always apply to off-road.

Don't really have much else to say on your other points other than thank you for them and I agree / understand.

 

[patooyee]

If you don't have it already, you need the Milliken brothers book Race Car Vehicle Dynamics. It's an SAE college level book that's basically God's word on all things vehicle dynamics. It's thick and it ain't cheap.

I'm going to try to pick up a used copy of that on eBay.

 

[patooyee]

...

Thanks. Again, wasn't trying to throw anything "out the window" because off-road. I made the corrections in my OP that you pointed out. Also deleted those few adjustment rules that were wrong.

 

[patooyee]

1.
These are builder bells. You still need to weld in your lower and upper pivot but it provides a base for your hub to mount to.
http://www.spidertrax.com/products/Builder-Bells
http://www.spidertrax.com/products/Unit-Bearings
If you don't need something so strong, you can maybe adapt an OEM knuckle/CV.

2. This mostly involves your ride height and desired droop/bump travel. You can have "angled arms" that are built "flat" and then kick down to the uniball. Those allow more ground clearance while leaving more bump travel.

3. Not sure what you are asking here. Steel?

1. While those are nice, they're kind of the creme de la crop and, as far as I know, lock you into using their UB's, which are also nice, but expensive. If I decide to move forward with IFS it wouldn't be with any components that expensive. I'd love to build something around 05" Ford UB's or even '13+ GM 3500 UB's.
2. Cool.
3. I assume people use aluminum as well. Say one used round tube. Is .120 wall enough? Solid bar? I honestly have no point of reference. I see race cars that look like they're using pencils and then TC's previous IFS rig (not his current) which looks like it's used axle tubes for a-arms. LOL.