And that makes them unsuitable for serious off road use, as side angulation is seriously limited, and traction is lost as one rear wheel will lift. IFS on 4WD vehicles means dirt roads and snow, but no serious off roading. It is not the beam axle that causes bump steer, it is the difference in radius of the axle and the drag link, and it is possible to move the steering box right over the leaf spring shackle so that they would have the same radius. It is also possible to eliminate any bump steer with a beam axle by mounting a rack and pinion steering gear to the beam axle. This design is now being done on a lot of older trucks and a lot of hot rods. It only requires a universal joint arrangement on the steering shaft. All later model 4 x 4s used "cross steering" where the steering box moved the tie rod by pushing a long link to the passenger side spindle. Up and sown motion had no effect on the steering. This is what my '53 has in it, a '77 Ford Hi-Pinion Dana 44 with cross steering, a power steering box which is mounted on the left frame rail almost to the front of the leaf spring. Works great. I will soon post a picture of a beam axle with a rack and pinion mounted on it.

Alan

 

Alan, I really don't want to get into a long discussion, but a beam axle itself is what causes bump steer, althought the effect can be mitigated with the steering geometry and limiting the suspension travel to a small movement. With a beam axle, the wheels are fixed to the ends much like a simple rod axle on a toy car. when one end goes up, the camber on that side increases and the camber on the other side decreases to the point where it can reverse and become positive. On both sides you are reducing the contact patch between the pavement and the ground different amounts.
IFS is not suited for off road use??? Show me one serious off road racer that uses anything but IFS. The military doesn't use a solid axle on their Humvees or sand buggies. LAST thing they want is the travel on one wheel on an axle affecting the geometry of the other wheel. They take great pains to develop geometry that will allow a large amount of single wheel displacement without shooting their vehicle off in an unexpected direction. Take a look at the front end of a monster truck (the extreme of an off road vehicle) sometime, you certainly won't find a beam axle under there!

 

Bump steer is purely an IFS phenomenon (at least in the context of stock Ford trucks covered by this forum). Read here: http://www.longacreracing.com/articl...mp_Steer_p.pdf

It's not possible for a straight axle to have bump steer the way our trucks' steering linkages are made. The linkage elements all move with the axle, with the sole exception of the drag link. Its pivoting point was designed to be as close as possible to the front spring's rear perch, so the two swing in equal arcs as the left front suspension goes up/down.

Our trucks can be and are affected by bumps, but it isn't "bump steer" in the true sense.

 

Wade,

Was your truck over at Alb Tire last week, on Wednesday? I had a late afternoon in that area and driving down Menaul I thought I caught site of a Bonus Built truck in one of the bays. Was that yours?
Man, if I'd have known I would have stopped in

Bobby

 

If your steering axis is the same as one of roll centre axis' you will not get bump steer.
The issue occurs when they are not on the same axis, and vertical movement of a tire will translate into the steering arm experiencing horizontal movement about its rotational axis (the king pin), and you will feel (and see) "bump steer".

Bump steer occurs independantly of any type of suspension system, be it IFS, solid beam axle, or even having wheels that hover... it is in the way that the suspension system is set up that can eliminate it.
Few road vehicles are ever setup to eliminate bump steer.

 

Who told Adrian he could come out of his room?

 

I am not out of my room - I am still typing this from inside the padded cell


(Morris is a bit busy currently, and he asked me to keep an "eye" on you folks in the mean time - thats all )

 

Bobby, Yeah that was me. Had it over there trying to figure out the alignment. I about got her on the road so well need to hit a cruise night.

 

What specs are they using for toe and caster?

 

Dang, all I did was catch a glimpse of the tailgate.

I guess I better excavate my truck out of the garage and get her going. We'll look like a before and after pic if we park next to each other....lol

Bobby

 

[quote=AXracer;7654729]Alan, I really don't want to get into a long discussion,but I am making statements that will cause one. but a beam axle itself is what causes bump steer, this is an incorrect statement. althought the effect can be mitigated with the steering geometry and limiting the suspension travel to a small movement. It is not necessary to limit the suspension travel with correct suspension geometry. With a beam axle, the wheels are fixed to the ends much like a simple rod axle on a toy car. when one end goes up, the camber on that side increases and the camber on the other side decreases to the point where it can reverse and become positive.Not true. The camber goes negative on the wheel moving upward and positive on the wheel being tilted. The effect on the opposite wheel is much smaller due to the radius of the beam width. On both sides you are reducing the contact patch between the pavement and the ground different amounts. Exactly why this type of axle would not be used in racing, particularly on rougher pavement. This is why solid axles in the rear should not have track bars. The roll stiffness should be all at the front, so that you do not pull up an inside rear wheel.

Now as you probably know, many cars built by Ford, all those with coils over the upper A-arms had positive camber curves(bad engineering) which means that when the chassis loaded, you lost the contact patch. All of these cars could not compete in autocross until they had modifications to lower the upper A-arm or replace the upper A-arm to correct the geometry and give the suspension a negative camber curve. In fact, if an IFS does not have a negative camber curve it will not do well in handling, particularly at higher speeds. The negative camber curve maintains a good contact patch when the tire is rolled inward by cornering forces. Nascar setups are to use stagger (different tire sizes on each side), negative camber to the limit, and putting negative camber in the rear end, 3/4 degree is allowed and the full floating wheel bearings allow it.


IFS is not suited for off road use??? Show me one serious off road racer that uses anything but IFS.Fella, just pick up any 4WD magazine and open your eyes. The military doesn't use a solid axle on their Humvees or sand buggies.Why? because they are first engineered to run in mud and sand with a fairly long wheelbase, and they need high ground clearance, the ability to run high entrance and exit angles, less important is side angulation. The sand buggies started out as high dollar vehicles, now they are buying normal sand buggies based on v-dub technology. Sand does not require side angulation, just good ground clearance. LAST thing they want is the travel on one wheel on an axle affecting the geometry of the other wheel. They take great pains to develop geometry that will allow a large amount of single wheel displacement without shooting their vehicle off in an unexpected direction. Take a look at the front end of a monster truck (the extreme of an off road vehicle) sometime, you certainly won't find a beam axle under there!No, not with the extreme lift that they use with the huge tires, but then a monster truck is a totally fabricated vehicle and is not an off road vehicle for rough country. Its entire purpose with the huge wheels is to jump things, cross over logs, drive through mud pits. It does not do side angulation. /quote]

This is where you are totally wrong about both rock crawling and side hill and rough country 4 x 4ing. I also take exception to the comment that the beam axle causes bump steer. This is untrue. Yes, when one wheel has a lot of movement, it causes decambering of the other side, but that is all. When a cross steering setup is used, the steering arm radius is the entire frame rail width. If a rack and pinion is mounted to the beam axle, there is no change in steering at all. Now why are solid axles preferred for serious off roading? because when one side is in a rut and the other side is high, IFS does not allow the body to angulate sufficently toward the low side without pulling up a wheel because the wheel cannot move far enough without holding the body via the track bar and the reduced wheel travel with IFS. If a vehicle were sidehilling, the same is true where there is a real danger of capsizing with tighter angulation and reduced wheel travel. It is not as simple as removing the track bar, as the reduced wheel travel and shock travel is also too limiting. Humvees, the real ones made by AMGeneral, have very high wheel travel which negates the problems with IFS, but this was the result of engineering which also eliminates transfer cases by using hydraulic motors to run each wheel assembly allowing tremendous wheel travel and variable lockup 4WD. My Silverado 4WD which uses torsion bar IFS is not worth a **** in rough country. Hell, anybody around here knows modern 4 x 4s are worthless past a point. You;re not from around here are you? Most of us have new trucks for driving on dirt roads where there may be ruts, mud or snow, and have an older rig with solid axles or jeeps for hunting or driving mining roads for fun and exploration. Looked under a new Jeep lately? Dirt roads are just that, roads which get plowed once or twice a year, but may have wet spots, mud, snow, hills which if towing require 4WD.. Rough county means roads that may not have seen a plow in 20 years, have ruts from runoff, high angles of side angulation, high entrance and exit angles from creeks or dry creek beds, (many non lifted trucks can't do these) (most extended cabs, long beds, etc can't do these) You hit a lot of snow in early summer and late fall, mud, rocks, etc. The road my have big dropoffs, steep switchacks, and steep grades. Rockfalls may have crossed the road, so you may have had to dig some.

Most of our rigs have flatbeds for real hauling. You see, out here if we buy a refrigerator or need a load of wood or pipe, there is no lumber yard closer than 140 miles, and Reno is 200 miles to 250 miles from where anyone may live. Yoiu need pipe, electrical conduit, etc. plus one or two months groceries, auto parts, you haul it.

Alan

 

And the econoboxes have torque steer as well......And stock 4WDs do not have locking front ends, but racing ones do, front and rear, ooh dangerous! There is very little bump steer on Ford Beam Axle trucks from 48-60. Starting in 76 on 4WD trucks they used cross steering, not drag links. Shimmy problems with Ford solid axle trucks are usually caused by tires which do not have a center raised rib for highway driving, or by an axle that needs bending. Too much rake (excessively lowered front end) may have eliminated enough caster as well. For strong wheel return you should have 1.5 degrees (I like to have 2.5 degrees) of caster. I also like 1/2 degree of negative camber. (Specs are 1.0 degrees Positive, but thats partially due to the inside wheel going negative in a hard turn) This will wear the tires a bit, but I corner hard enough and I use radial tires.

Regards,

Alan

 

So Adrian,

When Morris asked you to fill in, did he forget to mention that you are supposed to give Alan his Prozac?

 

 

If you would like to see what a Power Rack and Pinion box looks like on an F-1, go to the following URL: http://nolimit.net/Instructions/PS-SA_Instructions.pdf This will take a while to load because it is in .pdf format, but if you have broadband it won't take long. If you have dialup, I will send you the file via e-mail.

Alan