How to relocate steering rack, maintain suspension geometry?

Calling all members knowledgeable of suspension setup.

I want to move the steering rack forward 3-5" and can change other components of the LGT front suspension to get the geometry to line up. I have access to a good machine shop and a good fabricator, so anything can be made within reason. I just have no idea where to start. If I move the rack forward and change nothing else, then toe will be a mess.

The alternative scenario is to drop the steering rack as much as 4", but that is not ideal for a number of reasons.

I am also open to swapping suspension parts from various other Subaru's to get everything to mesh well without bump steer... Though I don't see that being beneficial.

One idea was to move the tie rod ball joints forward an inch to buy a little more space, but that will shrink my turning radius...

One idea is to modify the rack so the main rack moves forward, and a bracket on each end reaches backwards to put the rack end pivot point in stock location. I have not looked into doing this exact solution except as an idea, and I don't know enough to say more about it.

Don't ask why I would want to do this, please just help my lack of suspension understanding

Build a tubular subframe.

What are you trying to accomplish by moving the rack that far?

He is building a bump steer demo car

Everything I've come up with so far would be exactly that, except moving the rack forward and having brackets on each end that would reach backward to the stock inner tie rod ball joint point, keeping it unchanged. Could perhaps use shorter secondary rail guides to keep everything lined up...

Always a solution to a problem, which gets progressively easier and simplified with time.

Reading the Modified Magazine - Suspension Geometry article, will see if I can't learn something.

I'm assuming you know what causes bump-steer, and what type of setup minimizes and eliminates it. Arbitrarily moving the rack forward 4" isn't going to do a lot. Remember, to solve bump steer, you need the tie rod to track the path of the wheel through it's movement. We are at an immediate disadvantage, because our wheels do not move linearly in the vertical direction as the suspension cycles. Moving the rack forward, but keeping the inner rod joint point fixed is going to net you a zero change.

Another sticky wickett? When you move the rack forward, the splined shaft that currently mates to the universal joint attached to the steering column will now, no longer, be able to meet up with the rack. You'll need to either double-u joint it, or change angle of the rack and extend that shaft.

I've worked on the design of a steering system and front suspension for an off-road race vehicle that utilized perfect ackerman and practically zero bump steer. If you formulate a list of real questions, I'd be happy to help answer them. I'm a little rusty, but I'm sure I can shake that and come up with correct answers.

If you just want to move the rack, though, a tubular crossmember is the way to do that.

Reading the Modified Magazine - Suspension Geometry article, will see if I can't learn something.

Why not just pour a gallon of gasoline on your car and start it on fire.

Thank you for the good response

Arbitrarily moving the rack forward 4" isn't going to do a lot.

Doing this to get it out of the way of stuff that will eventually be in the way of it as it sits in stock location. Not arbitrary

Remember, to solve bump steer, you need the tie rod to track the path of the wheel through it's movement. We are at an immediate disadvantage, because our wheels do not move linearly in the vertical direction as the suspension cycles.

Yeah, I have trouble seeing this in my mind because it's not MacPherson, but when I have the struts off next, I'll move the hub through it's axis and get a vivid idea of what it looks like.

Moving the rack forward, but keeping the inner rod joint point fixed is going to net you a zero change.

This is the goal I don't want to mess up the geometry, unless purposefully changing it for the better.

Another sticky wickett? When you move the rack forward, the splined shaft that currently mates to the universal joint attached to the steering column will now, no longer, be able to meet up with the rack. You'll need to either double-u joint it, or change angle of the rack and extend that shaft.

No problem. I figure this will be the easiest part.

I've worked on the design of a steering system and front suspension for an off-road race vehicle that utilized perfect ackerman and practically zero bump steer. If you formulate a list of real questions, I'd be happy to help answer them. I'm a little rusty, but I'm sure I can shake that and come up with correct answers.

I will have an exact question, sort of. Once I change the ride height (lower than stock, maybe 1" - 1.5"; right now it's lower than that, way too low by most measures), I would love to take a fresh look at the suspension geometry with and without the Whiteline rollcenter alignment kit, and make any obviously beneficial changes, custom if needed. Re-positioning the inner tie rod pivot points with full 3D options while relocating the steering rack anyways, this would be a freebie since it would be getting set in a new custom crossmember mount. Beyond that, LCA mount points and outer tierod positioning would be on the table, since everything would be apart anyways, and it would be a good time to do it. I have the Whiteline 'ROCK', but I have not yet sat down to draw out the geometry it changed and results in. I would value your help with that. It would probably end up more an academic exercise than a practical one, but would be interesting and fun.

If you just want to move the rack, though, a tubular crossmember is the way to do that.

That's the plan. Stock crossmember will get cut up and re-worked like a rich housewife in Beverly Hills. Interested to see if any meaningful weight savings can be had. Some guy on NASIOC made a tube crossmember, and it looked super minimal compared to stock. But that's not the aim, just a possible incidental.

Any time.

Think about this - you are moving the rack forward and not moving the hubs forward. You can make a subframe out of tubes, angle iron, cardboard or anything else, but you can't get around that fact.

I take it that you want to clear a low-mount turbo?

The guy on NASIOC that made a tubular crossmember, did so because he mounted an LS1 under the hood and didn't want to cut and weld the oil pan. Unless there was someone else.

Personally, I suggest designing your system around the existing rack and it's location. That will absolutely be easier than relocating the steering rack assembly.

Use your imagination to see this:

Steering rack in its original location. Now take a saw and cut out the middle section of it, maybe 20". So now you have the tie rod, tie rod mount and the sliding cylinder on each side, with the rack and pinion missing.

Well we need to steer, so mount a 2nd steering rack 5" forward of the first rack's location. This 2nd rack can span the whole length as intended, and has no tie rods installed. Weld a tube in to connect the left tie rod mount of rack A to rack B. Same on other side. So forward rack does the steering, and rear rack handles the tie rods. So the tie rod-to-rack ball joints are in their original location.

However, since my car is lowered and a little caster is added, wider tires w/ offset, etc, I could move the tie rod pivot points on the rack in or out or forward / back / up / down, a small amount to dial in geometry.

I take it that you want to clear a low-mount turbo?

No, but the idea is right under your nose.

The guy on NASIOC that made a tubular crossmember, did so because he mounted an LS1 under the hood and didn't want to cut and weld the oil pan. Unless there was someone else.

Then someone else did it too, as I was thinking of the RS that dis not receive the LS1, just a Subaru turbo motor.

Personally, I suggest designing your system around the existing rack and it's location. That will absolutely be easier than relocating the steering rack assembly.

I wish. I'm lowering the engine/trans/driveshaft angle substantially, all of it pivoting at the rear axles, so engine will be lowest relative change, trans less, front of drive shaft less still and rear of driveshaft almost nothing. I think I calculated 5* angle change probably more. Will tilt the diff too so pinion angle is similar to stock, though someone has mentioned that it is not as critical on IRS rear ends

The steering rack would have to go through the torque converter once powertrain lowered, but I like my torque converter and hope to keep it. Alternative is to weld the trans input shaft to the crank shaft. Stop signs would get ugly.

Enough about the WHY, that's not important

I have no problem visualizing what you are TRYING to do.

But I'm telling you that you will have shit steering if you actually do it. Why? Those connecting rods are going to flex like freaking CRAZY when you steer, or when you hit a bump. Steering feel and accuity will go to shit, and no amount of over-built extension rods will be able to reasonably counteract this. You'll still have some degree of flex, and you will almost assuredly introduce some amount of vagueness into the steering. Plus, your welds could break and then you'd be properly F'd.

What you SHOULD consider is... not moving the rack. Or, if you are die-hard on moving the rack... still dont. 5" forward will put the rack in the middle of the oil pan.

If you would give a little hint (either publically, or via PM) as to WHY you HAVE to move the rack, there might be some other solution. But as it stands, moving the rack will unquestionably ruin your steering feel and overall handling.

Now, if it's clearance you want, just order the subframe spacers from an Outback, install them, then make engine mounts that lift the engine back up to the appropriate level. That'll give you another almost 2" of space under the engine, and the Whiteline RCK will bring your steering geometry back in line with where it is now.

Are you trying to stuff an LSX into the car, and use the stock transmission to keep AWD?

Shorten the driveshaft, and push the motor and trans backwards a little.

The WHY is the most important part of this. No one ever engineered a correct solution to a problem without the WHY.

http://www.uras.co.jp/2008image/kb_adp/IMG_2233.jpg

http://www.driftworks.com/forum/technical/73184-steering-knuckle-modification-7.html

I will find a way... hopefully.

http://zilvia.net/f/tech-talk/296725-roll-center-suspension-pickup-steering-angle-modification-thread-3.html#post3208115

I am thinking putting Forester spacers between the frame and crossmember will further change the resting angle of the lower control arms in the way lowering springs do. Since I can do a cardboard crossmember, I can move that to correct things there as well... so much to learn still...

What motor are you planning on stuffing into your LegGT????

You visited Frank_ster...... Are you planning a "Frank-en-mod" of sorts???

Something like that. It all depends on the steering rack. Literally.

I'm going to have fun with my EJ255 for a while, see if that won't grow on me.

Something like that. It all depends on the steering rack. Literally.

 

I'm going to have fun with my EJ255 for a while, see if that won't grow on me.

Uh, yeah! There are lots of us waiting for you to really start testing stuff before we start blowing up our own stuff.

I've got a BNR hta68 installed now, running on waste gate boost (his upgraded actuator). Waiting for you to install your FMIC and up your boost and see where you take the VB records..............

Anticipation!

Geometry change? Nothing substantial. Your big concern is going to be ball-joint stiffness.

You could always remove the torque converter, and install a clutch and flywheel for launching. Tilton makes smaller diameter multiplate clutches that have their own hydraulic TOB system (no need for a clutch fork).

Then you could clearance the bellhousing as necessary. That, coupled with Outback spacers, and you'd be in good shape. Getting the starter to work is childsplay compared with moving the steering rack.

Geometry change? Nothing substantial.

Can you explain what would get changed geometry-wise by lowering both the rack and the outer tie rod ball joint proportionally so the angle of tie rod and LCA from pivot to pivot for each respectively is maintained? I see thet are supposed to follow the same arc, but why not follow the same arc on different parallel planes?