Roll Center possible fix

[logr]

Ok, this probably isn't legal on public roads but it might be an inexpensive fix for roll center/bump steer/steering ratio. I cut the lower part off an extra S13 spindle and welded it onto a good spindle 1.25 inchs lower. I used a bolt through the tie rod hole to align things. I then cut off the original tie rod end and welded it to the new arm 1 inch in. I think this should give me 2 turns lock to lock of the steering wheel. I will let you know how it works for me. The suspension is open in SM so this should be legal for that.

[BeerBringer]

I am surprise I have not seen this before. I have thought about it but I'm a bit to scared it will break.

[Matt93SE]

Seen it done several times among the real road race crowd, but most everyone here seems to poopoo welding on the spindles so I don't bring it up.

[racepar1]

I've seen it done on an old speed touring car s-14, posted here somewhere. They spaced the joint down MUCH more then that though, it looked like 2-3". They also dodn't re-use the factory balljoint, they used a rod end and a 5/8" bolt.

[Def]

It's hard to get a ton of penetration, so effectively you're at less than stock strength on most welding jobs. I'd much rather drill and use a 3/4" bolt with a spherical bearing versus welding and being fixed to that much adjustment.

[logr]

Whatever makes your boat float. I think this is safer for my money.
I figured out how much space I needed and moved it that much. If I change my ride height somewhat, I will still be very close.
If the welding is done right, it is close to stock strength and stronger than the ball joint mounting hole. The thing is that doing it this way there is no leverage to break anything. Spacing away from the mount makes leverage and it makes the bump steer worse. Because the ball joint is pointed towards the top of the shock and the tie rod end is vertical, the more you space them down, the more apart they become. This is the strongest way I have seen to do this and it kills 3 birds with one stone. I set everything up myself and paid a friend that is a fantastic welder 50 bucks to weld it. I then decided to add the extra tie rod hole back in the arm so I can use it or not. Cast steel welds very nicely and if you saw how thick the part we welded was, you would never doubt it. Taper the parts to get all the way to the middle with the welding and you couldn't break it if your life depended on it.

[racepar1]

My primary concern with your setup is repeatability. Did you build a jig of some sort to align everything? There is no reason that a good welder could not weld that back together strong enough so I'm not really worried about that. I'm just worried that not enough precautions may have been taken to ensure that all the critical measurements are 100% correct.

I actually think that doing it your way is technically better (if executed correctly), though it doesn't matter in the front. Remember the balljoints do not sit flat, they are angled. If you space the joint with a spacer, you will end up with a longer control arm to put the spindle in the same place because of how the balljoints are angled. Our front suspension is a strut setup so it really doesn't matter much up there, but our rear is multilink. If you end up with a longer lower control arm in the rear you will likely end up changing the camber and toe curves. By moving the pivot point like you did you move the pivot straight down without moving it out and the control arm length is closer to correct. In a perfect world I would only want to use spacers to fine tune the roll center heighth.

[logr]

It is not perfect by any means. It is just a different option. I used a bolt through the tie rod ends to hold and align everything. Since the tie rod hole is vertical I felt this was the best option. By doing that it moved the ball joint mount in(towards the car). I then used the flat outer portion to decide how much to move it in and keep the ball joint on the same plane. By using this method it has to be pretty darn close. If it doesn't work very well for me, I will tell you.

I'm not much of a fan of the long rods or bolts and rod ends. I used to do tech a lot and the number of rod ends I saw wobbling was crazy. I'm sure higher quality ones would be much better. I use rod ends on my logging equipment and they have to be replaced regularly to reduce slop.

Like I say this is just one option. I almost didn't post it because I figured there would be controversy.

[SoSideways]

I'd like to use this method, and Def's method combined, for ultimate adjustability and steering angle.

[Def]

Whatever makes your boat float. I think this is safer for my money.
I figured out how much space I needed and moved it that much. If I change my ride height somewhat, I will still be very close.
If the welding is done right, it is close to stock strength and stronger than the ball joint mounting hole. The thing is that doing it this way there is no leverage to break anything. Spacing away from the mount makes leverage and it makes the bump steer worse. Because the ball joint is pointed towards the top of the shock and the tie rod end is vertical, the more you space them down, the more apart they become. This is the strongest way I have seen to do this and it kills 3 birds with one stone. I set everything up myself and paid a friend that is a fantastic welder 50 bucks to weld it. I then decided to add the extra tie rod hole back in the arm so I can use it or not. Cast steel welds very nicely and if you saw how thick the part we welded was, you would never doubt it. Taper the parts to get all the way to the middle with the welding and you couldn't break it if your life depended on it.

Cast iron welds are notoriously difficult to get up to the strength of the parent material because of all the "impurities" that ate introduced for casting alloys.

Not sure why you think making a larger spindle I'd a lower stress than spacing the spherical bearing down. A lever arm is a lever arm, on the spherical bearing it is taken by the bolt, in your setup maximum bending is going to be right around your weld joint. Typically the last place you want a load is right across the plane of a welded joint.

It might work fine, but in my engineering opinion it is not even close to the best choice.

[logr]

It is cast steel.

[Def]

It is cast steel.

I know that. Most people refer to cast steel as cast iron in my experience.

All my points still stand.

[hispanicpanic]

doesn't somebody make aftermarket balljoints that you press into the lower controll arm that lowers the Roll center? I think they come with spacers so you can adjust how you want it.

Or am i just dreaming??

If not, i should design one and mass produce it.....

[a_ahmed]

^Yes but they are overpriced and not worth it. Especially when for the same price you can now get the godspeed LCAs modified.

mmdb went with balljoints and modified knuckle to achieve roll center change (i think the knuckles also changed toe and kingpin angle if i recall).

[Def]

doesn't somebody make aftermarket balljoints that you press into the lower controll arm that lowers the Roll center? I think they come with spacers so you can adjust how you want it.

Or am i just dreaming??

If not, i should design one and mass produce it.....

You cannot space a balljoint down a variable amount. The nature of the press fit makes it non-adjustable(unless you have obscenely expensive conical spacers machined, and even then the adjustment isn't likely to be much).

Most balljoints that say they adjust the roll center up don't do anything, or at most it's a very small movement that isn't worth the cost. The only ones I've seen that definitely do at least something were the most expensive Moonface ones, and I think they were $300+ for a pair. That's way over what I have in completely adjustable modified Godspeed arms with good rod ends and spherical bearings. I know which one I'll choose.

The welding the spindle is good on a steep budget or if the outer balljoint can't be replaced with a different one due to class rules. I still think I might try to reinforce the spindle via bolts in shear(and also in bending due to geometry unfortunately).