Ifs 101

[dnsfailure]

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.

I think road race cars don't really see the kind of regular abuse that offroad racing buggies do. And they are usually alot lighter weight too, and much lighter weight tires.

My neighbor has several drag cars, a few of them tube chassis. It amazes me how small the suspension and steering components are, even compared to "bolt on" type jeeps and light trucks. And also most of the chassis is built from tubing that's a wall thickness thinner than .120

I usually build things probably a good bit stronger than they need to be, mostly because I don't know how to figure out exactly how thick to make something, or how much bracing it needs, or whatever. I'd love to learn more about this, to keep from over-building things that don't need to be.

 

[michael.gonzalez]

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.

1. You might be able to use the 3500 knuckle as well. Or fab a knuckle with the UB bolt pattern.

2.

3. I haven't seen aluminum used for front lower control arms. I would say .120 DOM steel at a minimum, .180 and .250 if you want to go full rock donkey. For aluminum, solid billet would be a safe bet.

 

[Weasel]

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.

It's what effects the Anti-dive on IFS. I cannot remember the term right now but "kick" doesn't seem correct. It works great in absorbing direct impact as the tires moves backward with the direction of impact. But it also creates bad anti-dive so when you hit the brakes the front end drops. This can be bad as now you are using up suspension travel every time you hit the brakes which leaves less travel for what it's supposed to do. Another drawback is it exaggerates "bucking". Front end does move up as much and starts to drop by the time the rear hits (which if flat will pop) and you get a bucking.

Packaging could be an issue or a whole host of other things.

 

[Weasel]

1. 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.

Steel is always my choice. It's easy to weld, stiffer, easier to tap, mount tabs on, etc then Aluminum. If you are machining then Aluminum might be worth looking at. If your fabbing then stick with steel.

 

[NickM]

1. 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.

My lowers are aluminum, but they are solid cast aluminum ... Also running balljoints instead of uniballs

 

[patooyee]

1. You might be able to use the 3500 knuckle as well. Or fab a knuckle with the UB bolt pattern.

The reason I asked is because I have full 3d models of the entire front suspension of the 3500 trucks already. I got them with the intent to input dimensions into some calculator at some point to see what kind of numbers GM is running. (I intend to do that eventually no matter what.) But having the actual GM model of that knuckle would be a huge head start for me as half the fun of building is having it all drawn up in SW before I ever cut metal.

And just to reference what I'd be building with this suspension, it is a light-weight turbo Ecotec buggy with 42RH and D300. Definitely not a race car. My goals for it would be to simply get out into the woods and be as mediocre at climbing rocks as it would be going as fast as the engine and gearing will take me.

Again, I don't mind all the race talk, I find it interesting and it surely cross-applies to what I want to do. But I didn't want people to think I was personally going racing.

 

[SLOWPOKE693]

It's what effects the Anti-dive on IFS. I cannot remember the term right now but "kick" doesn't seem correct. It works great in absorbing direct impact as the tires moves backward with the direction of impact. But it also creates bad anti-dive so when you hit the brakes the front end drops. This can be bad as now you are using up suspension travel every time you hit the brakes which leaves less travel for what it's supposed to do. Another drawback is it exaggerates "bucking". Front end does move up as much and starts to drop by the time the rear hits (which if flat will pop) and you get a bucking.

Packaging could be an issue or a whole host of other things.

This explanation is great, thanks!

 

[michael.gonzalez]

What diffs do you plan on using? Narrowed 3500hd diffs?

The Ford IRS 9.75 from ~2006 expeditions is another good option. Already narrow.

Ford IRS 8.8 also but that is weaker.

 

[Treefrog]

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.

👍

As far as outers go, plenty of 4x4s with IFS out that you could use.

 

[SLOWPOKE693]

My lowers are aluminum, but they are solid cast aluminum ... Also running balljoints instead of uniballs

Custom parts or stock stuff?

 

[SLOWPOKE693]

What diffs do you plan on using? Narrowed 3500hd diffs?

The Ford IRS 9.75 from ~2006 expeditions is another good option. Already narrow.

Which option is stronger stock vs stock? That would be the one I'd start with.

 

[NickM]

Custom parts or stock stuff?

I used stock LCA's from a 2010 ish GM 1500

 

[NickM]

Which option is stronger stock vs stock? That would be the one I'd start with.

The GM AAM 9.25 is high pinion, but it's an aluminum housing and 33 spline. The Ford 9.75 is low pinion, steel housing, 34 spline shafts. The other bonus is Ford sells E-lockers for the 9.75 for about $500

 

[patooyee]

What diffs do you plan on using? Narrowed 3500hd diffs?

The Ford IRS 9.75 from ~2006 expeditions is another good option. Already narrow.

Ford IRS 8.8 also but that is weaker.

Ford 9 probably. I already have new 5.40 locked third members and there's tons of aftermarket housing options. It will be rear-engine, so the dif will be upside-down.

 

[SLOWPOKE693]

I used stock LCA's from a 2010 ish GM 1500

Ok, I'm curious now. What did you build with that stuff? Got any pictures?

 

[patooyee]

👍

OK, now you've pissed me off. How did you do that? :)

 

[KrisKYK]

Does anybody offer control arms and uprights off the shelf instead of fabricating everything from scratch?

 

[NickM]

Ok, I'm curious now. What did you build with that stuff? Got any pictures?

2005 Colorado. 8.8 F-150 High pinion IFS front diff that's narrowed up with 31 spline OX locker. GM 3500 hubs, spindles, brakes. GM 1500 lower control arms and steering rack.

 

[Treefrog]

OK, now you've pissed me off. How did you do that? :)

 

[SLOWPOKE693]

2005 Colorado. 8.8 F-150 High pinion IFS front diff that's narrowed up with 31 spline OX locker. GM 3500 hubs, spindles, brakes. GM 1500 lower control arms and steering rack.

Bad ass!


You should post a build thread here. I'm sure alot of people would be intrested in what you got going on under there.

 

[patooyee]

👍

 

[Ghetto Fab.]

It's what effects the Anti-dive on IFS. I cannot remember the term right now but "kick" doesn't seem correct.

Wheel recession, or something like that.

When I was researching this 6ys ago I found some good old threads on Racedezert so you might want to go over there and search in the tech section. I wanted to build a budget IFS buggy, but I realized I wasn't going to be going that fast and a buggy that gets used once a year wasn't really worth it. In the end a solid axle has a much better cost to benefit ratio for the bulk of the wheeling that I do so that idea never went anywhere.

Looking at and watching U4 IFS trucks it doesn't seem like many are built with much camber change throughout the range of travel. This is one of the major benefits of the double wishbone suspension but most only seem have a few degrees of camber change. I don't know if this is on purpose or not.

Steering is always fun. While most use a rack of some kind, they don't technically offer the best bump steer performance. Using a swinging style steering you can really get the bump steer numbers down. Racks are typically used because of their strength, easier to package and good enough bump steer performance.

It is really neat that you can build your own subframe, arms, knuckles and even steering. The downside though is that axle shafts and joints are very expensive if you want the good stuff. I don't know about these days, but back then there really wasn't an off the shelf OEM shaft that could pull the high angle numbers that you would need and still be strong enough to go wheeling with a largish sized tire. You'd also be stuck to whatever half shaft length the OEM made, which is usually pretty short. If you can find and afford a set of hummer portals you might be able to use those and either the stock hummer shafts or the cheaper 930 series joints and they might hold up just fine with the portal reduction.

Kevin

 

[patooyee]

Another thing ... why do people use heims at the chassis end of the a-arms? You don't need any of that misalignment there and bushings of some sort I would think would be way more durable and longer-lasting?

 

[Weasel]

Wheel recession, or something like that.


Looking at and watching U4 IFS trucks it doesn't seem like many are built with much camber change throughout the range of travel. This is one of the major benefits of the double wishbone suspension but most only seem have a few degrees of camber change. I don't know if this is on purpose or not.

I think it's cause no one thinks it does anything and would hurt more then help. I disagree if you watch the Ultra4 corner none of them can turn if there are no berms. Plow city.

Another thing ... why do people use heims at the chassis end of the a-arms? You don't need any of that misalignment there and bushings of some sort I would think would be way more durable and longer-lasting?

Mostly because bushing deform with those kinds of loads and blow out too quickly. Bushings also have more bind in them due to friction, are harder to keep aligned so they are all square.

 

[patooyee]

Mostly because bushing deform with those kinds of loads and blow out too quickly. Bushings also have more bind in them due to friction, are harder to keep aligned so they are all square.

Chevy control arm bushings are hard as a rock. So are Ford. Or bronze bushings? I bet all of those are more durable and possibly cheaper than heims.

 

[SLOWPOKE693]

I think it's cause no one thinks it does anything and would hurt more then help. I disagree if you watch the Ultra4 corner none of them can turn if there are no berms. Plow city.

I'm a believer that it helps more than hurts. Its how much is needed for what we do that is the big question.. SxS front suspensions are built similar and from what I see at the short course races do exactly as you describe. Look at dirt circle track racing as a very loose example... The cars run negative camber on the right and positive on the left to get them to turn on dirt. If keeping the tire 90° +/- to the track was a better method they would all be running it like that. I believe Timmay from the old board was the first one in U4 to do it to his solid axle car. I dont remember how much he added but I remember him posting "game changer" after getting it finished and testing it out. It has to have the same positive effect in an IFS car.

IFS cars with long travel suspensions suffer from another situation that effects camber, chassis roll/pitch when cornering at speed. If you run a big sway bar to keep it minimal it will make it plow no matter what the front camber is, and if to soft the chassis may roll to much and fuck up the camber curve that is built in.

I used to think dealing with all these issues when building our circle track chassis was difficult and we were only playing with 5" of suspension travel and a 3" ride height. U4 and desert suspensions are an entirely different level of complexity.

 

[patooyee]

Can you guys who keep talking about U4 cars, etc post some vids of what you're talking about if you have any good examples, please?

 

[vetteboy79]

I believe Timmay from the old board was the first one in U4 to do it to his solid axle car. I dont remember how much he added but I remember him posting "game changer" after getting it finished and testing it out. It has to have the same positive effect in an IFS car.

He put in 3* negative camber on each side, and we made sure to align it such that the inner axle shaft wasn't tweaked at all. Basically the u-joint just had a 3* operating angle when going straight. I was the crew chief for a bunch of his Ultra4/Dirt Riot races and it was always fun to have it come into the pits and have everyone thinking that he bent it

I never drove it with the camber change so I can't tell you first-hand how much of a difference it made, but he certainly picked up some time (and more importantly, confidence) from it. No negative effects on handling or wear that we ever could find.

I will say that the inherent camber change in my TTB front end feels pretty good from the driver seat, both crawling and going fast. When you corner and the body rolls to the outside, the camber on that side goes further negative which helps keep the tire from rolling under. TTB has its own set of compromises but I do not miss having a solid front axle at all.

I remember Isdtbower had a picture of Rick Deremo's IFS car, which was one of the first in XRRA, that showed an example of what happens when you *don't* have camber change...think making a corner with a berm, and the outside tire rides up on the berm but the camber stays vertical. You end up riding the berm on basically the outer tread block and some of the sidewall, trying to roll the tire under, rather than maintaining a good contact patch.

 

[gt1guy]

^^^^^ This is also where running lots of caster can help. When you turn the wheels, the caster adds neg camber on the outside tire and positive camber on the inside. Helps the tires bite.

 

[Weasel]

Its how much is needed for what we do that is the big question.. U4 and desert suspensions are an entirely different level of complexity.

Ideally you'd match your body roll in the corner you are designing for (where you can get the most time). That's not always doable though. The window of operation is larger on the U4 and what not, but the idea's are the same and really the design window is the very similar. Design so it handles really well on the places you can make the most time and understand it will wokr well enough everywhere else.

Can you guys who keep talking about U4 cars, etc post some vids of what you're talking about if you have any good examples, please?

Find the drone footage of places like the infield at KOH, or the Finals at BFE. The sweeping corners, nearly everyone runs 30-40 foot wide way up into the berms, instead of in closer to the corner where you could gain time. Not to say they are slow. Of course camber isn't the only issue there, more on that later.