whats needed for ultimate handling?

[greengoblin]

Well the pictures make it pretty clear why the offset ball joints won't fix the roll-center on a lowered car. They would do nothing but change wheel position, lowering the car a bit but not affecting the angle on that lateral arm.

Might it work for the anti-dive restoration on the compression arm?

I pretty sure it would have an effect on the roll center. This picture shows the effect of moving the out board pick up points. If I have it wrong then please tell me. I'm not an authority on this by any means.

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[TSiAWD666]

Your diagram is wrong. Assuming the ground is the reference, the entire suspension would move downward. You've left out the shock and the shock fork, which are what are controlling the angle on the lateral arm and thus the roll center. Those don't change when you move the ball joint down at the knuckle. They would on an Evo though.

Of course maybe I'm wrong but that's what it looks like to me.

edit - not the entire suspension would move downward in the diagram. the knuckle and upper a-arm would remain stationary.

 

[greengoblin]

My understanding of how to find roll center is this.

Draw a line through each suspension link axes until they form a instantaneous center.

A straight line is then drawn between the contact patch and the instantaneous center.

Where this line intersects with the centerline of the car is the roll center.

Kevin

 

[snowborder714]

Kevin, it sounds like we'd really benefit from a suspension modeling program (I keep searching and still haven't found any)

 

[Ludachris]

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Found this image...

 

[TSiAWD666]

I'm not questioning your method of finding roll center. I'm questioning your diagram of our suspension. Also, it's not an effect on roll center in general we want, but a return to an orientation that gives us roll resistance. Let me find MS Paint...



Of course I'm waiting for someone to tell me to back to my corner and that I'm completely wrong

 

[greengoblin]

The book Tune to Win has a great little 1/4 scale suspension model in it that you can copy and cutout. Then play with different pick up points and suspension pickup points, arm lengths etc and see what they do in bump and drop along with roll center ETC. It really pretty cool. It will also drive you insane when you realize just how many options you have and how they all have comprises.

Kevin

 

[jtmcinder]

Of course I'm waiting for someone to tell me to back to my corner and that I'm completely wrong

Sorry, dude, but you're completely wrong. In your picture, you have the lower ball joint moving down relative to the wheel when the car is lowered, but, unless you rework the knuckle, that ball joint stays where it was. This is what causes the lower control arm to start angling down from knuckle to chassis and that's when you trash the roll center.

 

[snowborder714]

By lower do you mean inner?

 

[TSiAWD666]

Sorry, dude, but you're completely wrong. In your picture, you have the lower ball joint moving down relative to the wheel when the car is lowered, but, unless you rework the knuckle, that ball joint stays where it was. This is what causes the lower control arm to start angling down from knuckle to chassis and that's when you trash the roll center.

Isn't that what we are discussing, offsetting the ball joint on the lateral control arm downward at the knuckle?

 

[jtmcinder]

Oh. Then, yeah, that's the idea. By lowering the lower ball-joint relative to the knuckle, you keep the lower lateral arm pointing down from chassis to knuckle and the roll center stays up. Not as high as it was originally, due to the change in the angle of the upper arm, but better than sinking to ground level or worse.

 

[greengoblin]

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Here this is a bit closer to the arm alignment. Still it does move the roll center up. I left out the strut since it does not come into play with this.

 

[jtmcinder]

As the old saying goes, once it's been updated: a picture is worth a thousand internet posts. Nice.

 

[gixxerdrew]

I use several different suspension modeling programs. For simulation I use Chassis Sim, which is amazing.

The robispec subframe raises the front roll centers and this allows you to lower the front without having the same geometry issues you would with the factory part.

Robi also cut my shock towers and raised them up an inch (max allowed by rules) and now I have control over droop/compression travel with shims. This is all part of a system that was worked out for my car, one of the reasons we wanted a hood with extra clearance.

 

[Ludachris]

This makes me appreciate how easy it is to change the roll center on a 1g in comparison.

 

[greengoblin]

Drew,

Did you guys just move the cap section of the tower where the upper hat bolts?

How are the camber curves on our cars once we but them down super low?

Also do you feel that the rear pickups need to be moved?

I know, I know I always have question.

Thanks in advance

Kevin

 

[jtmcinder]

Drew -

Did they try to move the inboard end of the compression arm, too?

- Jt

 

[gixxerdrew]

Drew,

Did you guys just move the cap section of the tower where the upper hat bolts?

How are the camber curves on our cars once we but them down super low?

Also do you feel that the rear pickups need to be moved?

I know, I know I always have question.

Thanks in advance

Kevin

Kevin,

Robi just moved the shock mount to gain ride travel and I use shims to adjust back as needed. I have enough travel for the tire to go into the frame rails.

We discussed and decided to keep the UCA mounts intact.

The compression arm we also discussed and would like to move it but its not possible within the rules and budget.

Our camber curve is not that agressive, I was not too impressed I think its one of the few compromises of our setup, which is why I opted to keep the UCA pickups as factory as I could trade off some other things a bit for some more camber curve. That was the nature of the tall spindle but the rest of its compromises work hugely in our favor.

I worked around the dive geometry problem elsewhere in total the system was OK with the compromises and overall beneficial with the other things we do on the car a lot of which I would not apply to an AWD.

 

[jdsoza]

Drew, you inspired me to post this thread so i got a couple questions for you. Im not going to be building this car to certain rules and regulations, i just want to see what i can build. i want to experiment. theres talk of the geometry being fixed by a custom knuckle and a custom subframe but some arms may go through the floor. how true is this talk? also is it necessary to lower the car to the extent that it needs all this extra chassis and suspension tuning? i know center of gravity and also roll center is a key tuning point, you proved that. i dont want my car slammed, just lowered a little more than an inch. with lowering it just more than an inch will this affect geometry enough to cause problems? another question, if going to the extreme of building new knuckles and subframes, why not build a conventional double wishbone? the fabricator i use builds trophy trucks and some cantilever suspension sand rails and does build knuckles and subframes. do you think a conventional wishbone suspension could benefit our cars?

 

[gixxerdrew]

Travel is the biggest problem for lowering 1". Watch your bump steer as well

On the inboard pickup for the compression arm to raise that arm you will have to cut into some structural stuff. you need someone good to do that job. My rules disallow modification to "frame rails". WIthout that rule in play I would have probably done that.

I custom spindle is a good solution, but for FWD especially and probably AWD I would like to retain the tall spindle mode for reasons of steering axis geometry. Going to a racing style upright was considered and ruled out for this reason. Something that extended the ball joint mounts down would be a nice addition. I dumped all my knowledge on this stuff to Andrew at Frontline Fab but I dont know what ever came of it all.

 

[jdsoza]

Thanks for the input! I see how running out of travel can become a problem. Now a question for all. I hear talk of ball joint replacement being common. Some people use the stock ones and others i've hear use the 3g ball joints. Which will benefit the most for a road race suspension?

 

[jtmcinder]

Our camber curve is not that agressive, I was not too impressed I think its one of the few compromises of our setup, which is why I opted to keep the UCA pickups as factory as I could trade off some other things a bit for some more camber curve. That was the nature of the tall spindle but the rest of its compromises work hugely in our favor.

Are you allowed to extend the bolts that connect the UCA to the chassis? Moving the eyes of the bolts downward will not only add a little static camber, but will steepen the curve. I know the question of whether is legal came up in autocrossing; I have no idea what your rules are.

 

[greengoblin]

Thanks for the input! I see how running out of travel can become a problem. Now a question for all. I hear talk of ball joint replacement being common. Some people use the stock ones and others i've hear use the 3g ball joints. Which will benefit the most for a road race suspension?

It is common on other cars but not ours. There are no replacements that are taller that I have seen. I have looked in this quit a bit too. You are going to have to either build custom arms that have taller ball joints or build a spacer that bolts to the spindle to move the pickup points down.

Are you allowed to extend the bolts that connect the UCA to the chassis? Moving the eyes of the bolts downward will not only add a little static camber, but will steepen the curve. I know the question of whether is legal came up in autocrossing; I have no idea what your rules are.

It will also raise the roll center even further too. I don't know if that would be good or bad though.

 

[gixxerdrew]

Are you allowed to extend the bolts that connect the UCA to the chassis? Moving the eyes of the bolts downward will not only add a little static camber, but will steepen the curve. I know the question of whether is legal came up in autocrossing; I have no idea what your rules are.

Yes, up to 1" is allowed. However, at the moment I am happy with my roll center stability vs dynamic camber compromises but that may change in the future. I have other lower hanging fruit at the moment.

 

[jtmcinder]

Wow. This is a great example of how you have to think "system" not individual part, isn't it? If your lower LCA is angling down, as on a over-lowered 2G with OE subframe, then lowering the eyes of the upper LCA actually helps the roll center, as well as steepening camber. But if your lower LCA is still pointing where it should, then lowering the eyes hurts. I never connected those dots before. Thanks.