Tie rod angle question...

[A930Rocket]

Years ago, when I had a mustang, we used to install offset steering rack bushings or a bump steer kit to level the tie rods for better handling.

When I installed a 3” leveling kit on my 2014 F150 awhile back, my tie rods angle down now. It seems to ride well, but I wonder if it would be better to have them level.

I found one set online, but the cost is $600 and I don’t think it would level them near enough.

I remember my friend having Robinson Racing in ATL make him some adjustable control arms with heim joints at each end.

Would a machine shop be able to make me a set?

Mustang bump steer kit.


My truck.

[masraum]

I always thought it was ok for the tie rods to angle down some, but it's not ok for them to angle up. The problem is usually for cars that have been lowered so the tie rods angle up.

[A930Rocket]

You might be right. When the car is lowered and the tie rods angle up, toe in is affected as the wheel goes up I believe.

Originally Posted by masraum

I always thought it was ok for the tie rods to angle down some, but it's not ok for them to angle up. The problem is usually for cars that have been lowered so the tie rods angle up.

[masraum]

Originally Posted by A930Rocket

You might be right. When the car is lowered and the tie rods angle up, toe in is affected as the wheel goes up I believe.

Right, that sounds like what I remember. When the suspension compresses on a lowered car where the tie rods are angled up from the rack to the knuckle, it's bad. If the tie rods are angled down, when the steering compresses, they may go near or to flat, but that's not a problem. I don't remember the exact "bad" result.

[wdfifteen]

Toe is going to be affected whether they go up or down.
In the pictures above as the wheel moves up in a bump the wheel will tend to toe out.
You can calculate how much the toe changes. On a truck I would worry about the strength of a rig like the one in the top photo.

[masraum]

Here's some good info from the 911 tech board. There's more in the thread, but these posts seemed to be the most informative to me.

https://forums.pelicanparts.com/porsche-911-technical-forum/436855-do-i-need-bump-steer-kit.html#post4255788

Originally Posted by Flieger

It is more the change in toe than the change in camber. Toe change is affected by the relative movements of the tie-rod to the A-arm (different arcs).

If the A-arm is pointing down and the tie rod is level (stock suspension setting), then under compression, the hub/A-arm moves out but the tie rod gets shorter. Therefore, the toe turns out under compression. This is bump-understeer.

If you lower the car: A-arm level, tie rod up, zero toe-alignment at this ride-height.
Under compression, the tie-rod still causes toe-out.

If you add dropped tie-rod pickups, the tie rod will not get shorter at a faster rate than the A-arm. Therefore, less toe-out bump steer.

Theoretically, you could make the tie rods angle down while the A-arm was level. This is bump over-steer. The toe turns inward on the wheel in bump, causing steering input tightening the turn.

Camber effects complicate the severity of the bump steer.

Originally Posted by Bill Verburg

Yes & No, at static loaded rest the steering arm is presumed to be at the mid point of it's travel range and this is ideally the point were camber and toe changes are linearly correlated to wheel travel, out of this sweet spot the changes in camber and toe are non linearly correlated to wheel travel and cause excessive extraneous steering inputs to be even more undesirable. Ideally the steering arm and lower control arm will always be parallel and move thru the same arc minimizing camber & toe changes(which cause bump steering) but that can't happen because the pivot points for the 2 arms are in different planes both horizontally and vertically. So you can only minimize the difference in arcs over the relatively narrow sweet range of travel, to limit travel you use big springs and stiff shocks, to minimize arc difference you start in the middle of the travel range and start w/ parallel to the ground for the steering arms and as close to that as possible for the A arms.

Here is a '73RS that could stand to be lowered a tad, you can see that the steering and A arms are at different heights and have different pivots so they move in different arcs, a washer type bump steer kit will lower the steering arm pivot to be nearer the plane of the A arm pivot but they will never coincide.






??? bump steer is caused by a vertical suspension movement on one side of the car that cause the wheel on that side toe toe in or out causing a corresponding change in vehicle yaw, in a turn the same effects are still in extent, but now the turn is causing one wheel to move up and the other to move down, one wheel is trying to turn more than the other,the 2 wheels will steer in different arcs because of built in ackerman and because of the camber/toe changes caused by wheel movement

I agree w/ the latter but the former is misleading, the A arm has max Y axis displacement when it is parallel to the ground, the arcs can only move horizontally inboard from there, The effect is to shorten the effective length of the arm at the lower end of the steering axis, the steering arm is doing a similar thing in a slightly different arc but if both start horizontal then you have a better chance of staying in the linear ranges for camber/toe changes


camber curves are typically S shaped w/ a relatively linear portion at the middle of the S that is where you want your ride height to stay in the linear middle portion of the curve

The spindle is raised to maintain full shock travel, at the same time it allows the A arm to start in a more horizontal position on a lowered car again, starting at horizontal is good because you stay in the sweet spot for camber/toe changes more of the time

You will always have some bump steer, it is in the nature of the suspnsion design used, all you can do is minimise it.

Kevin's suggestion actually measuring is good( and very interesting to be able to see) but unnecessary.

If you stay at RoW ride height, or ~ 25.5" at the fenders w/ stock 16" wheells and tires then the factory specs are great, they did all the work.

the lower you go from there the more other "stuff" needs to be done, go to ~ 25" and the washers are needed, go to 24.5" and raised spindles and Steering arm kits are needed

[wdfifteen]

Looking from the front of the truck, imagine a circle with its center at the joint at the tie rod end and the rack, with a radius that is the length of the tie rod. As the wheel moves up and down the tie rod end describes an arc on the circle. As it moves through the arc its distance from the center line of the truck changes and the wheel moves in toward the center or out from the center (changes toe) accordingly. Ideally you want the tie rod to be horizontal when the suspension is at its static height.

[DanielDudley]

I think in many cases it is more about the tie rod being parallel to the lower A arm, so they swing parallel to each other. You need to talk to someone who knows about your specific vehicle, but if there is no bump steer or unusual tire wear, you are OK. The bottom line is that you don't want the length of the tie rod to change in relation to the A arm under load or during cornering as the A arm swings through its arc. If the geometry is poor, you want to compensate to try to get them more parallel (or optimal), and you want to align the vehicle while weighted with the most typical load. Obviously that may not be as important in a vehicle weighing 3 tons.

Just from what I see, it looks in one of those pictures that the tie rod and A arm are parallel. . On certain vehicles we used to bend the steering arms to adjust the swing. You should find out what other owners of your vehicle do. I don't think it is a cut and dried, one size fits all solution. If there is no ideal geometry, you want to find out what the compromise solution is, and do what works best.

[A930Rocket]

Thanks guys. The top picture is one of a Mustang with a bump steer kit.

The bottom two pictures show my control arms with the tie rods parallel to the A arms. Tire wear is good and most of my driving is highway with no off road (it’s 2 WD and I just wanted a slight height adjustment with slightly bigger tires).

[wdfifteen]

Originally Posted by A930Rocket

Thanks guys. The top picture is one of a Mustang with a bump steer kit.

The bottom two pictures show my control arms with the tie rods parallel to the A arms. Tire wear is good and most of my driving is highway with no off road (it’s 2 WD and I just wanted a slight height adjustment with slightly bigger tires).

Parallel to the A arms makes no difference, it's the angle between the rack and the tie rod that causes toe to change with wheel movement.
The discussion about 911 suspension is good as far as toe changes go, but the 911's McPherson trust system is very different from your truck's double A arm suspension. Camber geometry is different.

[T77911S]

if you want to determine the proper angle of the tie rod then you have to calculate the instantaneous center (IC) of the suspension.
then the angle of the tie rod needs to tie into the IC point.
that way all 3 lines are moving one the same arc of the IC.

[asphaltgambler]

From the pics above - your angle from the inner tie-rod pivot point is too far down (vertically measured) in relation to both upper and lower control arms. With the truck on a level surface, wheels ahead - the tie rod assy should be close to the same plane as the lower control arm.

And of course - it isn't .

MO is the best way to resolve this is (hopefully) someone makes an aftermarket steering knuckle that places the tie rod arm higher so the angle is not so extreme. I'm sure there is someone out there that has these as lifted trucks are very common place.

I'm not a fan of those tie-rod end extender's - unless they are the only solution and very short - like 1" or less.

[A930Rocket]

The real solution is to install a proper lift of 4-6” for $1,000 plus. With a revised knuckle and K member, it raises the truck while keeping the suspension geometry correct.

For $100, I installed a leveling kit, which amounted to a front strut spacer and rear axle block. It’s basically at stock 4 WD height now, which is all I wanted. One day, I might install the 4” lift...

Originally Posted by asphaltgambler

From the pics above - your angle from the inner tie-rod pivot point is too far down (vertically measured) in relation to both upper and lower control arms. With the truck on a level surface, wheels ahead - the tie rod assy should be close to the same plane as the lower control arm.

And of course - it isn't .

MO is the best way to resolve this is (hopefully) someone makes an aftermarket steering knuckle that places the tie rod arm higher so the angle is not so extreme. I'm sure there is someone out there that has these as lifted trucks are very common place.

I'm not a fan of those tie-rod end extender's - unless they are the only solution and very short - like 1" or less.

[asphaltgambler]

In this situation a revised knuckle is all he needs.........