More Caster/Alignment/drivability ideas?

[ksagis]

I’d love some critique from folks like @lars @jamesroney @toddz69 @Apogee @Yeller @nvrstuk @ntsqd @Broncobowsher on below comments (its a long list, I missed a bunch of ya)

My understanding:

1) castor helps straight line tracking, but going around a corner or hitting a pothole with insufficient castor doesn’t seem it would create a pucker butt response if castor is reasonable Particularly if north of 4 degrees of castor.

2) loose suspension components or sloppy steering box would contribute to poor handling due to relative movement

3) different geometry on track bar and drag link seems bad too since it can produce a toe reaction

4) Insufficient toe, especially with big tires or offset wheels, makes a bad situation worse

5) these trucks are never gonna drive like a 2020 vehicle. When I drove them in highschool in the 1980s, I had low expectations, and I was reasonably happy. Todays tech has raised the bar of what we think is “normal”

Kevlar donned. Fire away!

Edit: PS. Short wheelbase makes all above accentuated

 

[DirtDonk]

So we’ve already been discussing this? I seem to remember going through all this before. Or at least some of it. Why not continue in an existing thread?
Although, now that this one’s up to two pages, I guess the point is moot now.

As mentioned already, your angles are too steep. Or at least look like it in the picture.
You should correct those before it’s going through all the other stuff.
I know it’s not standard practice to use drop Pitman arms and track bar brackets when only 2 1/2 inches of lift is involved. But in your case, I think it would be the exception that would help.

Can you get a picture from a little farther away, so that it includes the tie rod ends and steering knuckles, as well as where the track bar and drug link sit in relation to each other?

 

[Glass Pony]

I know the 2½" lift isn't much, but I still see steepish drag link and steering angles. While this is good for traditional bumpsteer, there is another bumpsteer (I don't know if there is a special name for it) where the front axle shifts side to side.

Torkman66, are you using any trackbar drop brackets and/or a drop Pittman arm? The angles do look a little steep.

 

[Yeller]

Made me go find a PC to respond to this LOL those are some hard hitting questions that will be nice to have answered in one post.

I’d love some critique from folks like @lars @jamesroney @toddz69 @Apogee @Yeller @nvrstuk @ntsqd @Broncobowsher on below comments (its a long list, I missed a bunch of ya)

My understanding:

1) castor helps straight line tracking, but going around a corner or hitting a pothole with insufficient castor doesn’t seem it would create a pucker butt response if castor is reasonable Particularly if north of 4 degrees of castor.

This is true, but there are a lot of factors. Ball joint condition is a big one, too tight and it gets sticky and darts, too loose and it gets floppy and darts. Shocks are another, soft springs need the right shock, too soft valving results in darting, too stiff rattles your teeth. Tire condition is another, I've seen tires cause a lot of issues that were chased for a long time because they "looked great" were new 5 years ago, etc. Tire pressure is an issue as well, just this week my bronco drives like its on rails (with coils all around, soft springs and no sway bars) however it was darty in corners, I always run 20-24 pounds of air in the front, somehow I air'd them back up to 29, dropped 5 pounds and it was back to its happy self. IMO bronco steering geometry is poor at best when stock, really needs a TRO and track bar riser to really dial in any amount of lift, even stock the drag link has too much angle on it, again this is my opinion. For ultimate drivability the drag link, tierod and track bar need to be parallel at ride height, just not happening with the confines of a bronco, it physically won't fit and the drag link will bind with the tie rod during compression if it was.

2) loose suspension components or sloppy steering box would contribute to poor handling due to relative movement

100% correct if the mechanicals are worn it will drive like poo.

3) different geometry on track bar and drag link seems bad too since it can produce a toe reaction

different geometry is bad, it induces "bump steer", literally hit a bump and the steering wheel moves. With how short the links are on a bronco this is critical to drive well. This does not cause a toe reaction, that is fixed with the tie rod, it physically turns the tires through suspension motion. However this can be covered up with proper shock valving, I have a truck that is far from perfect but everyone that drives it compliments on how nice it drives, it is 100% due to the shocks, changed them (and yes they were new) and it went from "I'm reworking everything, this horrible" to being very nice.

4) Insufficient toe, especially with big tires or offset wheels, makes a bad situation worse

Everything plays a variable, some broncos like 1/16" of toe and some like a 1/4" of toe, everything is a variable that contributes to that. Many here will set toe and make some small adjustments and drive it to find the sweet spot, 1/8-3/16" is usually where that is at.

5) these trucks are never gonna drive like a 2020 vehicle. When I drove them in highschool in the 1980s, I had low expectations, and I was reasonably happy. Todays tech has raised the bar of what we think is “normal”

exactly correct, they are not a 2020 mustang, different expectations should be expected but it should still feel safe.

I'm not a sway bar fan, but many find they are mandatory for a bronco to drive nice, and if that is what works for your comfort level great, however, I feel they just cover up geometry and shock issues. As an example, I drive my bronco with friends on their Harley rides, yes, they can run away in the straights, but in the corners, I can run away from them. It is completely on paper not supposed to do that, but with good geometry, shocks and a driver not afraid to push it does it and does it comfortably. They are dragging foot boards and bags and I'm going around the corner.

Kevlar donned. Fire away!

no need for that LOL

Edit: PS. Short wheelbase makes all above accentuated

this is correct, it speeds up all of the motion and amplifies all of that motion. With modern springs and lifts these trucks also have more suspension travel than they did in the past, which aggravates all of that. Longer wheelbase does help slow all of that down so it feels better.

Hope this all helps. When it comes to suspension and steering, everything is a compromise. The key is to get the compromises to work together so it is smooth and predictable. Like my Email signature said for a long time "If it was easy, everyone would do it".

 

[Johnnyb]

I wanna chime in here because I have a similar setup and it is shocking how well mine handles on the road (and off)!

After making a ton of updates on my EB, first stop was the alignment shop. I would suggest getting a set of numbers (before/after) and posting them here.

I would also like to echo all of the other people on this thread saying make sure there are no worn or mis-configured components like ball joints, bushings, or wheel bearings.

Lastly, the trac bar (riser or drop) might be the missing component. I went with James Duff riser, but it is not adjustable and hits my frame (pending a new hole, cut top of riser, install extended bump stops). I wish I had used the Wild Horses riser or a drop instead. And make sure the axle is centered under the EB. Even a 2.5" lift can push the axle out the the drivers side and needs to be re-centered with an adjustable trac bar.

-JB

 

[Torkman66]

I have had several folks now suggest a drop Pitman and TB drop bracket. Considering how easy those would install, I’ll go ahead and get both. My understanding is I still will want parallel bars but they will be much closer to horizontal after install. Planning on both pieces from WH given they also supplied all front steering components.

 

[serial car restorer]

And make sure the axle is centered under the EB. Even a 2.5" lift can push the axle out the the drivers side and needs to be re-centered with an adjustable trac bar.

My old school lift is 3-3.5" in front. With the factory track bar that was on it when I bought the Bronc, my front axle was offset almost an inch to the left side. The adjustable bar got that to less than ⅛" offset at empty ride height.

 

[ntsqd]

I'll try a different tack with this as I too think the existing trac-bar and drag-link angles are too steep to achieve the desired results.

Say that your trac-bar is at a 25° angle relative to the ground. A bump that causes the front suspension to compress 2" will cause the axle end of the trac-bar to move laterally ~0.7" I'm sure that most can feel that! And very few will like it.

Say that you install a trac-bar riser on the axle. Now the trac-bar is at a 15° angle with the ground and you hit that 2" bump again. The axle end of the trac-bar only moved ~0.36" laterally. Can likely still feel it, but it is way less awful now.

Except that you didn't change the angle of the drag-link. Oops. With the 15° trac-bar and the 25° drag-link that 2" bump now STEERS the Bronco. The drag-link has more lateral movement than the trac-bar does, and that is Bump-Steer. A 0.34" movement of the steering linkage to the right is huge for a 2" bump. Serious road racers use .001" increment dial-indicators to measure their bump-steer.

The body moving on the suspension is unnerving enough even though it doesn't alter the actual direction of travel. Bump-Steer does directly change the direction of travel, and that can really make a vehicle spooky to drive.

Ideally the drag-link and the trac-bar are exactly parallel and exactly the same length. An aspect that hasn't gotten a lot of attention is that ideally they need to be parallel as viewed from the top as well as the commonly accepted as viewed from the front. The reason is that with a radius arm the axle housing move fore and aft as it cycles thru it's range of motion. If you're really trying to dial out all of the bump-steer this needs to be looked at. It's not easy to change and fortunately they're pretty close already. For most it won't matter, but that doesn't mean it's not a factor.

Compromises. When the trac-bar and the drag-link can't be the same length or angle, or both, they still can be made to travel in curves that are complementary. That is to say that over a small part of the travel range that the difference in the curves can be made to be small enough to not cause any trouble. This is a lot harder for most to grasp, but it tends to be more real world.

The direction that the Bronco turns in compression bump-steer will tell you a lot. If it steers to the left that says that the steering linkage is moving laterally less than the trac-bar. If it steers to the right it means that the steering is moving laterally more than the trac-bar.

Then you get into adjusting the Caster. Do the cut and turn. Get away from using the angled C bushings and go back to rubber if at all possible.
Dropped radius arm brackets would increase the Caster, except that they are an unsafe, poorly designed and built 'solution'. I can think of no reason strong enough to ever consider using them.

Someone brought up Akerman. No live axle 4x4 that I've seen yet has good Akerman or has the ability to have it adjusted to be good. The fundamental problem is that live front axles, for the most part, use a tie-rod in front of the axle and there is a wheel and/or tire sidewall right where the TRE wants to be to have good Akerman.

 

[Yeller]

@ntsqd well said!

I agree about akerman, trying to improve that is why the 76/77 EB steering knuckles get very close to the wheel, and it still isn't enough. However, I'm not convinced for normal road driving it is a huge factor.

 

[DirtDonk]

Perhaps why the Ford 2wd pickups back in the day had their tie-rod assemblies behind the A-arms? Necessitating that wildly short steering shaft and a gearbox just in front of the firewall!
Makes messing with the steering stuff a lot of fun.

Paul

 

[Torkman66]

This will be a great experiment. I think a lot of folks have a similar setup as mine. With 4.3* caster, you’d think driving would be acceptable, not like a modern car, but not spooky. So I’ll add the pitman and drop bracket and let folks know exactly how it affected the ride. After, might also add a front AntiSway and again see if there is a noticeable difference. @ntsqd provides interesting diagnosis in terms of the geometry at play. Hoping these two changes result in noticeable improvement.

 

[lars]

Attaching a photo of my Bronco's front axle, taken this afternoon. I've spent over two decades trying to get this thing to handle/steer/drive like a modern-ish vehicle. Most of that started 24 years ago when I drove my boss's 78 big Bronco that seemed to truly drive like a modern vehicle. Because it did. Despite having a radius arm front suspension nearly identical to mine- in fact radius arms were interchangeable. Looking up specs, the obvious difference was the caster spec. I attacked that with the cut n' turn, accomplished in 2003. Big improvement.

Moving on, extended radius arms 6 inches. Added about 3/4° caster, now up to about 6-1/2°.

Fabricated a track bar mount on the right inner C that let me run a track bar nearly the same length as the drag link, though the latter angle was still too shallow compared to the former. That helped with bump steer but didn't eliminate it.

Played with front coil springs. At my current lift of 2-1/2" I tried Duffs progressive coils. They gave a squishy ride but it moved around too much on the suspension. Switching to higher spring rate WH progressive coils helped

I had been running Duff knuckles for 25 years, for an OEM style disc brake conversion. Nothing wrong with them but with the TRO conversion the tie rod was way high. A couple of years ago I obtained a pair of early 70-ish F-150 knuckles with lower arms. Moving the tie rod down put the track bar and drag link almost exactly parallel. Killed residual bump steer.

Somewhere in all that I obtained a pair of offset upper ball joint bushings, which I used to adjust camber (NOT caster!) to less than 0.5° per side. That ties into a comment I saw here recently about Ackermann angle. The F-150 knuckles are still wrong, and it's audibly obvious in a parking lot at full lock when the front tires screech. But with less camber the outer tire wear went away. And who cares. It drives straight. Little old ladies and liberal studies professors (sorry, I live in a college town) flinch when I'm turning into a parking spot.

I don't recall the toe setting but I do it as an angle rather than a length measurement, though it probably translates to 3/16"-ish.

Other details.. 4x4x2 steering box, excellent condition. Meticulously maintained ball joints and tie rod ends. Extended radius arms have Johnny joints maintained carefully (no more OEM style rubber bushings or equivalent). Track bar uses spherical rod ends but they are replaced when ever inspection reveals slop. 35" BFG AT tires running around 25 psi.

All that said, does it drive like a modern vehicle? Nope, not exactly. But close. My totally non-technical wife drives it without comment about twitchiness. Until she finds herself going too fast into a corner (dang 408 stroker). Then the steering is too light for her.

 

[jamesroney]

I’d love some critique from folks like @lars @jamesroney @toddz69 @Apogee @Yeller @nvrstuk @ntsqd @Broncobowsher on below comments (its a long list, I missed a bunch of ya)

My understanding:

1) castor helps straight line tracking, but going around a corner or hitting a pothole with insufficient castor doesn’t seem it would create a pucker butt response if castor is reasonable Particularly if north of 4 degrees of castor.

2) loose suspension components or sloppy steering box would contribute to poor handling due to relative movement

3) different geometry on track bar and drag link seems bad too since it can produce a toe reaction

4) Insufficient toe, especially with big tires or offset wheels, makes a bad situation worse

5) these trucks are never gonna drive like a 2020 vehicle. When I drove them in highschool in the 1980s, I had low expectations, and I was reasonably happy. Todays tech has raised the bar of what we think is “normal”

Kevlar donned. Fire away!

Edit: PS. Short wheelbase makes all above accentuated

OK, I'm back...

1. Caster helps tracking and centering at all steering angles. 4 degrees of caster is inadequate for a 93 inch wheelbase live-axle vehicle. 7 degrees is correct for a Bronco on 33's, and 6.5 degrees is pretty good on 35's.
2. Well generally yeah. But I don't know what "poor handling" means to YOU. Loose components doesn't always equate to "undriveable." I've driven plenty of trucks with horrid sloppy components that still manage to go down the road straight.
3. Sometimes, but not always. Take a look at a 1987-96 F350 with monobeam Dana 60 front axle. The track bar is about 15 inches long, and the drag link is at least double that. So there's that.
4. Big tires and offset wheels makes every bad situation worse.
5. Your Bronco can drive as well as any 2020 Jeep Wrangler JL 2 door. And about the same as a 2024 Ineos Grenadier. My Bronco certainly drives better than my 2006 Cummins 2500. But yeah, an IFS Subaru tracks pretty well.
PS...pretty sure that a Samurai sits right at 80 inch wheelbase. A VW Beetle has about the same wheelbase as your Bronco. Some people say they handle pretty good.

Not 100% sure what we are trying to solve. If you want your Bronco to drive like a passenger car, then install low profile, smaller tires with highway tread, increase spring rate, and increase damping. Add IFS, sway control, and precise (rack & pinion) steering. Move the drive train rearward for better weight balance.

Ackerman angles are a bunch of hooey. Totally irrelavant at any speed over about 15 mph. My Sunbeam Tiger has horrid Ackerman. It does just fine on the street, and at the track.

 

[ksagis]

Really appreciate all the guru's feedback as I'm trying to get my Bronco to drive as good as I can. I've done all the usual play with toe, bounce the front end and look at steering wheel to see if it moves, etc, and still feel like it darts more than I would like.

This is true, but there are a lot of factors. Ball joint condition is a big one, too tight and it gets sticky and darts, too loose and it gets floppy and darts. Shocks are another, soft springs need the right shock, too soft valving results in darting, too stiff rattles your teeth.

Could you elaborate on how ball joints being too tight and sticky causes darting? Not sure I get that one.

Soft springs seems like it conspires with poor track bar and drag link angles. i.e. infinitely stiff springs seems like they would not respond and avoid bump steer since nothing actually moves.

I always run 20-24 pounds of air in the front, somehow I air'd them back up to 29, dropped 5 pounds and it was back to its happy self.

How much do you run in rear, figuring less that 20-24 since less mass over back axle?

different geometry is bad, it induces "bump steer", literally hit a bump and the steering wheel moves. With how short the links are on a bronco this is critical to drive well. This does not cause a toe reaction, that is fixed with the tie rod, it physically turns the tires through suspension motion.

I'm still working to understand the physics and geometry of this one better. Seems like to me if one tire hits a pot hole, it moves up or down, and if the track bar and drag link aren't resulting in the same geometry changes - assuming the steering wheel doesn't move in the short period time frame, the end result is the drag link "pushes" or "pulls" the steering resulting in darting?

Say that your trac-bar is at a 25° angle relative to the ground. A bump that causes the front suspension to compress 2" will cause the axle end of the trac-bar to move laterally ~0.7" I'm sure that most can feel that! And very few will like it.

The direction that the Bronco turns in compression bump-steer will tell you a lot. If it steers to the left that says that the steering linkage is moving laterally less than the trac-bar. If it steers to the right it means that the steering is moving laterally more than the trac-bar.

Lots of good math for me to consume and consider, thanks. I get the math on the entire front axle moving up 2", but harder for me to process one wheel moving up 2" inches and how that affects things. Is the comment on compression bump steer relative to the entire axle moving up, or just one end?

Attaching a photo of my Bronco's front axle, taken this afternoon. I've spent over two decades trying to get this thing to handle/steer/drive like a modern-ish vehicle. Most of that started 24 years ago when I drove my boss's 78 big Bronco that seemed to truly drive like a modern vehicle.

And who cares. It drives straight. Little old ladies and liberal studies professors (sorry, I live in a college town) flinch when I'm turning into a parking spot.

Second generation Broncos had >100 inch wheel base, had to have helped them drive better for sure. Totally know what you mean about college town, the professors in Palo Alto have had some precious reactions when I drive around!

Not 100% sure what we are trying to solve. If you want your Bronco to drive like a passenger car, then install low profile, smaller tires with highway tread, increase spring rate, and increase damping. Add IFS, sway control, and precise (rack & pinion) steering. Move the drive train rearward for better weight balance.

I'm trying to solve for what seems like too darty to me. Otherwise rig drives great. I hear many comments like "my rig drives great" and trying to calibrate myself if I expect too much.


Thanks to all for in-depth replies, much appreciated!

 

[Yeller]

To answer the 2 questions directed at me, about the same on the rear 20-24. The thing about tire air pressure gauges, unless you have an expensive calibrated gauge they are all just a hint, I’ve seen swings as much as 20% from gauge to gauge.

I’ve seen new ball joints installed that have the preload too tight, eliminating the return to center feel. Causing things to feel darty. This unusually will pass with a few thousand miles. I’ve also seen internal leaks of the seals on spool valves in the steering box do the same thing. Not saying either of these is your issue, just sharing experiences of things I’ve seen.

 

[ZOSO]

I will ditto what everyone has said already. My front axle looks a lot like lars. Both track bar and draglink are parallel and mostly flat. I can run 80+ with no hands on the steering wheel. I can hit the train tracks at my house with no hands and it stays straight. Now I did screw something up along the way that made it horrible to drive and dart in corners. I had replaced a heim on the passenger knuckle. I never checked toe after that. I removed the heim and replaced the new one. Same spot. Well it caused a lot of toe and it drove horribly in corners. once corrected it is fine again. And last is tires. Crappy tires with amplify things 10 fold. I cant rotate my tires because I have one that is out of round. If i put it on the front it causes all sorts of issues.

 

[ntsqd]

Re: 2" Bump. I was talking in terms of equal compression on both sides. However, because of where the trac-bar attaches to the axle housing 2" of bump on the DS will have very little movement at the trac-bar mount while 2" of bump on the PS will move the trac-bar mount almost that 2" It is extremely close to a simple percentage of the track width to the mount location. Enough so that you can treat it that way and any error will be in the noise. A trac-bar mount like Lars' will obviously move more than it is of the OEM location, but Lars' mount is the goal. It is not possible to make a trac-bar too long. It is possible to make it longer than the steering can deal with, particularly if the drag-link attaches to the tie-rod. Move it to the knuckle. Yeah, I didn't say this was easy.

Re: "Darting", if induced by a bump that is Bump Steer. Too much toe-out can also make a vehicle "darty", but dang does it "turn-in" nicely! (See Akerman below). A road racer might run somewhere between a little toe-in to a little toe-out to strike a balance between turn-in and high speed stability where an Auto-Xer will run a little toe-out to a lot of toe-out because they don't need the high speed stability but do need a car that aggressively turns-in.

Officially Samurai's are a 79.5" wheelbase. I'm sure that it's actually metric, so there's likely some rounding error there. My avatar is nominally an 80" wheelbase and it is built from a ACVW Beetle pan that has had 14" cut out of it.

Re: Tire gauges. I have one per vehicle, it lives in the vehicle. I do not move them around. Each one is unique and it takes some time before you get a good feel for what that vehicle and gauge combo works best at. Most of mine are the $10 HF inflator/gauge with the HF gauge replaced by a better gauge (not hard to do). The one in Snowball is a Tractor Supply clone because it came with a air amplifier nozzle that replaces the tire chuck and hose for blowing the dust/dirt out of things. It too has had it's actual gauge replaced. Usually by a work's cast-off gauge from McMaster.

Akerman's most noticeable effect is how a vehicle transitions from going straight to going around a curve. Not in the curve itself (other than some tire squeal at extreme steering angles), but the transition. Road racers call it "turn-in". Does the vehicle turning into a curve significantly lag the driver's input, or does it do it 'right effing NOW'? That's Akerman working or not working.
The desired geometry to achieve 100% Akerman is simple in concept. This jpg shows 100% Akerman. Going to less than 50% Akerman (50% of the wheel base) is a waste of time. Most of live axle 4x4's that I've looked at their Akerman I'd guess it to be in the 200%-300% range. 100% Akerman is defined as being equal to the wheel base. Given that, let's assume that the F-100 knuckles borrowed for the Broncos was set at 100% Akerman (something that I seriously doubt, but let's go with it), put those on a Bronco and the Bronco's shorter WB means that the Akerman is nowhere near right. The F-100 WB (according to my copy of the "Std Catalog" Robt Ackerson) is 131" for a long bed. That puts the Akerman on an EB at 139% at the best. That's awful, and it assumes that the Akerman was correct for the F-100. Based on what I've seen, I doubt that the F-100's Akerman was anything close to 100% With it's original skinny tires it wasn't a problem.
Short answer, don't worry about Akerman until you have dialed in everything else. There isn't alot that you can do about it anyway. Look at the linked image again and you'll see why the rotor, wheel, or tire sidewall are going to limit what you can do. If you're still determined to get better Akerman I'll suggest that the easiest path will be to lengthen the wheel base.

 

[jamesroney]

... I'm trying to get my Bronco to drive as good as I can.

... I'm trying to solve for what seems like too darty to me. Otherwise rig drives great. I hear many comments like "my rig drives great" and trying to calibrate myself if I expect too much.

So let me interpret this for you:

I'm trying to get my Bronco to drive as good as I can, without actually fixing the problem. To say it another way... "I am trying to reduce darty-ness in my Bronco and keep 4 degrees of caster."

Simple.

1. Install a set of 26 inch tall highway tread BFGoodrich tires.
2. Install a set of at least 2 Rancho RS5000 shocks on each corner. (bone jarring, super stiff please.)
3. Add an enormous sway bar on the front.
4. Add a smaller sway bar on the rear.
5. Fiddle/fart around with every conceivable joint, link, rod end, and steering component.
6. Replace you steering box with a new one.
7. Optimize steering alignment for toe and camber.
8. Play around with tire pressure and hold it to +/- 0.5 psi.
9. Drive at speeds below 60 MPH.
10. Add 400 lbs to the rear of the Bronco.
11. Spend countless hours on the internet learning, studying, and asking opinions.
12. Listen to responses from educated and talented individuals that are answering a different question than you are asking.
13. Come to learn that vehicle dynamics, slip angle, Ackerman, turn-in, camber, grip, load, and contact patch are meaningless if your fundamentals are broken.

Now, to answer a different question: "How can I reduce the darty-ness of my Bronco?"

1. Run 7 degrees of Caster.

Then: set your toe with a tape measure. throw away your tire gage. install some used tie rod ends, and used ball joints if you can find them. Get some old junk mix-matched mud tires, and install them. Find some used shocks that fit. One or two, doesn't matter. Get a steering box from the junkyard. Maybe from an old International Scout. Scab it on. Or even better, find a worn out 6 turn Bronco box that someone threw away. Drive 75 MPH with one hand adjusting the radio, one hand holding you coffee, and steering with your knee.

See how this works?

Now, let me ask a question:
Q. "how do you ride your mountain bike with no hands?"
A. You don't. You'll crash. But you can ride your road bike with no hands, no problem. What's the difference? Caster.

 

[ntsqd]

Actually, bike geometry is a bit more complicated than that. I can and do ride all of my MTB's with no hands. The road bike is actually harder to ride that way.

 

[lars]

So let me interpret this for you:

I'm trying to get my Bronco to drive as good as I can, without actually fixing the problem. To say it another way... "I am trying to reduce darty-ness in my Bronco and keep 4 degrees of caster."

Simple.

1. Install a set of 26 inch tall highway tread BFGoodrich tires.
2. Install a set of at least 2 Rancho RS5000 shocks on each corner. (bone jarring, super stiff please.)
3. Add an enormous sway bar on the front.
4. Add a smaller sway bar on the rear.
5. Fiddle/fart around with every conceivable joint, link, rod end, and steering component.
6. Replace you steering box with a new one.
7. Optimize steering alignment for toe and camber.
8. Play around with tire pressure and hold it to +/- 0.5 psi.
9. Drive at speeds below 60 MPH.
10. Add 400 lbs to the rear of the Bronco.
11. Spend countless hours on the internet learning, studying, and asking opinions.
12. Listen to responses from educated and talented individuals that are answering a different question than you are asking.
13. Come to learn that vehicle dynamics, slip angle, Ackerman, turn-in, camber, grip, load, and contact patch are meaningless if your fundamentals are broken.

Now, to answer a different question: "How can I reduce the darty-ness of my Bronco?"

1. Run 7 degrees of Caster.

Then: set your toe with a tape measure. throw away your tire gage. install some used tie rod ends, and used ball joints if you can find them. Get some old junk mix-matched mud tires, and install them. Find some used shocks that fit. One or two, doesn't matter. Get a steering box from the junkyard. Maybe from an old International Scout. Scab it on. Or even better, find a worn out 6 turn Bronco box that someone threw away. Drive 75 MPH with one hand adjusting the radio, one hand holding you coffee, and steering with your knee.

See how this works?

Now, let me ask a question:
Q. "how do you ride your mountain bike with no hands?"
A. You don't. You'll crash. But you can ride your road bike with no hands, no problem. What's the difference? Caster.

^^^this. I don't actually drive 75. My Bronco seems to prefer 80 with the big engine. Of course I have brakes that are up to the task. I have no idea what my tire pressure is right now- seriously. But meanwhile it's one thumb hooked over the steering wheel, completely stable. Ok, I don't have 7 degrees of caster either, only 6.5. Don't believe me? Come to Davis and try driving it.