Ifs 101

[Weasel]

^^^^^ 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.

too much though can cause odd steering behavior. It's been a loong time but iirc too much cause very slow return to center until it gets about half way through the radius, then the return to center speeds up, that was on a non power/hydro steering system though.

 

[DMG]

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?

I think fender clearance would be a problem if it moves back inter travel.


I have thought about making a SxS-sized buggy with irs/ifs by making a jig and doing 4 identical uppers and 4 identical lowers. I have even thought about building with junkyard control arms from a full-size truck. I am glad this thread was started, I am enjoying the ifs in my tundra and land cruiser with bolt on upper control arms, coil overs, etc.

 

[Weasel]

Robby's Speed UTV has the something like that all the way around doesn't it? To reduce the number of spare needed.

 

[dnsfailure]

For folks who are building their own IFS, when it comes time to do the final alignments, are yall doing it yourself? Or taking it to a place with laser alignment setups and telling them the specs you want? Is it not as critical to get some of the angles as it is in a road vehicle?

 

[patooyee]

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.

Here's a screen shot I grabbed from a YT video of TC's current IFS rig, which has won first place in like everything this year. His upper a-arm is highly offset like your pic is. Is it just as simple as making room for the shock package?

 

[Weasel]

your getting into where the engine sits and possible steering as well if you wanted to go with the upper mounting behind the shocks.

 

[arse_sidewards]

Here's a screen shot I grabbed from a YT video of TC's current IFS rig, which has won first place in like everything this year. His upper a-arm is highly offset like your pic is. Is it just as simple as making room for the shock package?

Think about the geometry. The arm pivots about a line. The knuckle moves about the ball joints. In terms of handling it doesn't matter what shape your arm is or if it's offset forward or rear. It pivots about the same line.

 

[YotaAtieToo]

Think about the geometry. The arm pivots about a line. The knuckle moves about the ball joints. In terms of handling it doesn't matter what shape your arm is or if it's offset forward or rear. It pivots about the same line.

Yes, but I think the question was strength. If you hit something, there is a lot more stress on the front of that a arm vs one that was centered. Obviously it's still pretty strong if it's holding up to a year of rock bouncing.

 

[TRINDU]

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.

The way the shocks are set, theres no way in hell the air bump would ever contact the strike pad on the upper a arm. What am I missing? Is knuckle farther out that what the pic shows?

 

[Weasel]

The way the shocks are set, theres no way in hell the air bump would ever contact the strike pad on the upper a arm. What am I missing? Is knuckle farther out that what the pic shows?

just the angle of the picture. The arm is going to to out in an arc and up towards the picture direction.

 

[Tech Tim]

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.

Depending on whether it is a vertical or horizontal swingset. Vertical is what you see the most in the desert rigs and they are not good for steering performance. Horizontal can get steering down to the gnats ass as long as you don't want to steer too sharp. We did some early designs for both of Scheerererers cars and Farravanti's car, but they proved to be problematic especially at full lock, so it was just back to a straight rack. Definitely one of those "it looks good on the computer, not in real life" things.

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.

Not true, there are a couple that corner very well.

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.

Scherer's LCAs are using bushings on the inboard side.

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.

For what you are doing, OE type bushings will be fine.

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?

We need to get Ben Bower in on this thread, I sent him a link, he is the guy when it comes to pics and vids of the IFS cars doing things right and wrong.

He is also building a pretty damn cool billet aluminum IFS/IRS for a play rig. Maybe he'll post some pics up.

 

[Isdtbower]

Haven't seen this. Lots of good stuff. I have a ton of stuff that might lend clarity. Presently out "get'in it."

 

[Weasel]

Not true, there are a couple that corner very well.

Yeah okay maybe well, not sure I'd say very well. Yes there are a few but as a whole they don't. As for the bushing it's similar to bushing in links, they can work or they can be a giant PIA. Most don't want to deal with that whatever reasons. Hence the reasons most run hiems style joints.

 

[AgitatedPancake]

I'm in for the discussion. It's been a long time since I've had time to properly digest a tech heavy forum post like this vs the average social media crap, so I'm just going to lurk until I can put my thoughts together a little more comprehensively.

One of the best downright tech threads just about grasping some of the dynamics of anti squat/anti dive was by ThinAirDesigns back at the old place years ago, I'll be excited to rehash those topics here. One of the biggest ah-hah lightbulb moments I had back then was the fact that your antis (Anti dive and Anti squat) are actually comprised of two significant geometries/forces that work together to create the effect you feel. Torque based anti squat, and thrust based anti squat. Thrust based anti squat is your wheel recession/kick/whatever term you want to describe the wheels front to rear motion through travel. An example of this would be in a rear axle, where the wheel moves rearward in compression, and forward in droop. As you accelerate, the fact that the tire is trying to drive forwards against the chassis causes it to force the suspension into droop, cancelling the squat from weight transfer to whatever degree (based on AS %). When it comes to torque based anti squat, it's the actual rotational force of the axle housing that causes the suspension to unwind under torque, even if the tire is moving perfectly vertically at that point in travel. The reality is 99.9% of the time you're working with a combination of the two which create your final AS number, but the proportion of which is which is rarely touched upon. But it directly impacts what I would call "compliance" of the suspension, how resistant it is to compression when you hit an object at speed, as that directly changes. The more your AS is based on thrust, the more compliant your suspension is to impacts at speed because the wheel regresses through compression. While AS that's primarily based on torque doesn't have that inherent compliance because the wheel is moving vertical.

The easiest way to see it on paper and your standard calculators, thrust based AS is when you have an extremely long IC. For example, if you have 100% AS but your IC is set near infinity, essentially your links are exactly parallel to your AS line so your wheel has a silly amount of front to rear movement through travel. Compared to torque based AS, where to acheive the same 100% you have an extremely short IC that rests on the AS line at the same height as the centerline of your axle. So you still have 100% AS, but your axle is moving directly up and down with no progression/regression (at that static point). Those are the two extremes of the example, but help me visualize the concept.

 

[patooyee]

Sorry for being an idiot, but what about that pic shows good cornering? I don't know what I'm looking for ...

 

[patooyee]

Is there a rule of thumb for how high the front dif is mounted in an IFS car with a solid rear? IE, level with the rear dif? Higher?

 

[arse_sidewards]

Is there a rule of thumb for how high the front dif is mounted in an IFS car with a solid rear? IE, level with the rear dif? Higher?

Everyone seems to get it as high as they can for their packaging situation.

 

[Sterlingfire]

Since you're looking to swap in stock ifs components, have you looked into raptor front control arms and center section. This might make it easier to get more travel reliably.
I would like to get a lower control arm in my hands to check measurements against a stock chevy ifs control arm.

 

[Ghetto Fab.]

Is there a rule of thumb for how high the front dif is mounted in an IFS car with a solid rear? IE, level with the rear dif? Higher?

To me, diff height depends completly on half shaft cv angles and how much comp/droop you want in the car. The cvs dictate how much travel you have for a given width. If you want the diff to sit higher for more clearance then you need to run more bump travel than droop travel. If you want 50/50 bump/droop travel then your half shafts should be horizontal to the ground and the CV angle should be zero. My guess is most U4 guys are running in the 60/40 bump/droop split range for more clearance and travel for the big hits. Just like with a solid axle, diff clearance matters. You also loose clearance as the suspension compresses. Obviously a good solid subframe and skidplates are a must.

I haven't heard any mention of tire scrub from suspension travel. You can play with camber change to help minimize tire lateral scrub as the suspension cycles, say in a jump. This is somewhat counter to what you want to do to help minimize cv angles though.

Kevin

 

[YotaAtieToo]

To me, diff height depends completly on half shaft cv angles and how much comp/droop you want in the car. The cvs dictate how much travel you have for a given width. If you want the diff to sit higher for more clearance then you need to run more bump travel than droop travel. If you want 50/50 bump/droop travel then your half shafts should be horizontal to the ground and the CV angle should be zero. My guess is most U4 guys are running in the 60/40 bump/droop split range for more clearance and travel for the big hits. Just like with a solid axle, diff clearance matters. You also loose clearance as the suspension compresses. Obviously a good solid subframe and skidplates are a must.

I haven't heard any mention of tire scrub from suspension travel. You can play with camber change to help minimize tire lateral scrub as the suspension cycles, say in a jump. This is somewhat counter to what you want to do to help minimize cv angles though.

Kevin

I could be wrong, but aren't most set ups limited by the skid hitting the ground vs the CV's on compression? I thought this was a big reason why portals are getting more and more popular, even with trophy trucks.

 

[Weasel]

To me, diff height depends completly on half shaft cv angles and how much comp/droop you want in the car.

I haven't heard any mention of tire scrub from suspension travel. You can play with camber change to help minimize tire lateral scrub as the suspension cycles, say in a jump. This is somewhat counter to what you want to do to help minimize cv angles though.

Kevin

That is the approach I've worked through before as well. And yes on the travel scrub. Robbie talked about that on his new Sxs quite a bit and one of the things he's pretty proud of.

I could be wrong, but aren't most set ups limited by the skid hitting the ground vs the CV's on compression? I thought this was a big reason why portals are getting more and more popular, even with trophy trucks.

I would want the suspension to bottom before the skid plate can touch, in general terms. I thought that was the normal practice as well?



Really Robbie's Speed SXS design presentation (youtube) are interesting to watch. He does some good explanation on why they build things they way they did and why he feels it's better. I agree with some of it.

 

[Weasel]

Sorry for being an idiot, but what about that pic shows good cornering? I don't know what I'm looking for ...

So I can't really tell either here on this pic but the outside tire looks to be turned more then the inside which is fine/good for speed. But the camber doesn't seem to be great, can't tell the roll of the vehicle but the tire seem to be hooking with the outer edge of the tread/sidewall. But I can't quite tell either.

 

[patooyee]

Seems like, if it bottoms before the suspension, you've wasted useable suspension.

 

[YotaAtieToo]

I would want the suspension to bottom before the skid plate can touch, in general terms. I thought that was the normal practice as well?

Well yes, in theory. What I'm saying is that the skid will hit the ground before the CV's run out of angle, hence the portals. This is my impression at least.

 

[Sterlingfire]

Well yes, in theory. What I'm saying is that the skid will hit the ground before the CV's run out of angle, hence the portals. This is my impression at least.

If you're bottoming out, and your skid plate is the bump stop, you've built it wrong, sa or ifs...
There should never be less than 6" of clearance to your skid plate from terra. Maybe my opinion, but i wouldn't go any closer than that with the bottom of my rig.

Considering portals may help with this, but your skid plate is not an effective bump stop.

 

[patooyee]

Well yes, in theory. What I'm saying is that the skid will hit the ground before the CV's run out of angle, hence the portals. This is my impression at least.

When did portals become popular? I assume you're talking about HMMWV portals since we're taking about IFS? Besides JHF where do you even find HMMWV portals these days?

 

[Tech Tim]

Yes there are a few but as a whole they don't.

I agree, most don't.

I'm in for the discussion. It's been a long time since I've had time to properly digest a tech heavy forum post like this vs the average social media crap, so I'm just going to lurk until I can put my thoughts together a little more comprehensively.

One of the best downright tech threads just about grasping some of the dynamics of anti squat/anti dive was by ThinAirDesigns back at the old place years ago, I'll be excited to rehash those topics here. One of the biggest ah-hah lightbulb moments I had back then was the fact that your antis (Anti dive and Anti squat) are actually comprised of two significant geometries/forces that work together to create the effect you feel. Torque based anti squat, and thrust based anti squat. Thrust based anti squat is your wheel recession/kick/whatever term you want to describe the wheels front to rear motion through travel. An example of this would be in a rear axle, where the wheel moves rearward in compression, and forward in droop. As you accelerate, the fact that the tire is trying to drive forwards against the chassis causes it to force the suspension into droop, cancelling the squat from weight transfer to whatever degree (based on AS %). When it comes to torque based anti squat, it's the actual rotational force of the axle housing that causes the suspension to unwind under torque, even if the tire is moving perfectly vertically at that point in travel. The reality is 99.9% of the time you're working with a combination of the two which create your final AS number, but the proportion of which is which is rarely touched upon. But it directly impacts what I would call "compliance" of the suspension, how resistant it is to compression when you hit an object at speed, as that directly changes. The more your AS is based on thrust, the more compliant your suspension is to impacts at speed because the wheel regresses through compression. While AS that's primarily based on torque doesn't have that inherent compliance because the wheel is moving vertical.

The easiest way to see it on paper and your standard calculators, thrust based AS is when you have an extremely long IC. For example, if you have 100% AS but your IC is set near infinity, essentially your links are exactly parallel to your AS line so your wheel has a silly amount of front to rear movement through travel. Compared to torque based AS, where to acheive the same 100% you have an extremely short IC that rests on the AS line at the same height as the centerline of your axle. So you still have 100% AS, but your axle is moving directly up and down with no progression/regression (at that static point). Those are the two extremes of the example, but help me visualize the concept.

Good post AP and good to see you in this thread AP. Heck good to see all the usual techheads in this thread, patooyee, Weasel, and others, really makes this place feel like the old days.

Sorry for being an idiot, but what about that pic shows good cornering? I don't know what I'm looking for ...

How sharp the tires are turned, most of the U4 IFS cars don't turn very sharp. Though I gotta admit, that's not a great pic of that car turning.

Scherer's LCAs are using bushings on the inboard side.

Do you know what kind?

Last we talked, he was running an AlumiBronze type material with a few other tweaks. He has played with a few different materials over the years, so not sure what he is running now.

Running bushings instead of heims allows you to get the bottom pan higher up against the front diff.

Is there a rule of thumb for how high the front dif is mounted in an IFS car with a solid rear? IE, level with the rear dif? Higher?

As posted by others above, placement depends on where in the travel you want/need it to be.

Seems like, if it bottoms before the suspension, you've wasted useable suspension.

Yep, G-Outs are painful in any sport.

When did portals become popular? I assume you're talking about HMMWV portals since we're taking about IFS? Besides JHF where do you even find HMMWV portals these days?

Jesse is the one who has made Hummer portals so popular these days. Where to find boxes? Military surplus auctions and scrap yards. Watch eBay closely, craigslist, al the usual.

There is a desert racer, Brad Fallon, who built a IFS hummer portal'd race truck. Even ran it at KOH one year. Not sure where my hard drive with those pics are, Isdtbower probably has some.
Don't know if Brad is still racing or not, I met him through Race Desert forum years ago and had a couple chats with him on hummer portals.

Just like on live axle suspension, portals do change a bunch of geometry in IFS too.

There is a new portal'd IFS being designed for KOH, still in design, so doubt it will be running KOH 2021, but you know how some of these builders are, design one day, full car built the next. Can't wait to see this one, it should be interesting.

 

[Ghetto Fab.]

Peligrino and Cody Wagoner run mog based IFS and IRS cars in U4. I thought that Armada Engineering or someone else was trying to adapt 74welds portal parts to trophy trucks?

The hummer stuff is just more common and I would imagine a bit cheaper, if you want to call any of it cheap.

Kevin

 

[Wilson]

Well yes, in theory. What I'm saying is that the skid will hit the ground before the CV's run out of angle, hence the portals. This is my impression at least.

Some chased those numbers until they found themselves planting the skid into nuisance rocks more than they predicted.

Portals gain clearance and decrease the shaft angles, which allows for more balanced travel and or much tighter steering angles. With ifs, the travel and steering angles are added together (or subtracted from) the total operating angle of the joint.

 

[Wilson]

“Mosebilt” on the old board was building some neat mini buggies with junkyard parts as well as some higher end customer projects. I got to go through his shop a couple times.