Rear Sway Bar vs. Front+Rear

[Dr Ronald]

I took my car out to my first AutoX event a couple weeks ago, and it seemed like I was having a terrible understeer problem. I know I was probably too aggressive into the turns, and I was on cheap all weathers, but still seemed to not handle like I would have liked. I just got my car, so I haven't done anything to it except for maintenance related stuff. Anyways, my question is this: Should I go with a larger front and rear sway bar, or just rear? I am looking to get coilovers, but I can't afford them right now. I'm hoping to get up to near 300-350 hp at some point down the road. I'm going to be competing in AutoX more next year, but what I would really like to get into is road racing. Any thoughts/brands/other mods? Thanks

p.s. My car is a 2g TSi

 

[Nasty Dream]

From my experience, lowering a car reduces handling and increases understeer, but can make a car more stable (sometimes significantly so, especially if the suspension is stock, wimpy, or damaged).

Lowering a car lowers the center of gravity. A lower center of gravity is always a good thing, until your car or suspension bottoms out!

However, upgraded suspension components can also make the car more stable, without the negative effects.

 

[jtmcinder]

I have stock 98 GSX sway bars front and back but with Koni adjustable and Eibach sport springs and it handles like a go cart.

You've obviously never actually driven a go-kart, then.

To the OP: before anything else, please tell us whether you plan to run in a particular class so we don't suggest mods that won't be legal. But regardless of class, you probably already hit the core problem: you were driving too aggressively. You absolutely have to follow the slow-in/fast-out rule with a 2G DSM. You must have patience. Even after modding it to the SM level, you have to have patience when driving these cars.

 

[jtmcinder]

I dont no all of the technical terms and all but I do no from exp that a 2g that is lowered too much does handel like crud (my car now from previous owner).

It is a very technical issue, but it comes down to the front roll center height. When you over-lower a 2G (and the definition of "over-lower" is lowering it to the point where the lower lateral control arm angles up from the chassis to the knuckle, instead of down, as it was stock), you have moved the front roll center way too far down. It can even end up below ground level. A roll center below ground level greatly increases body roll because a roll center below ground level means a super-long roll moment arm, which is just a really pompous way of saying that the force which you are using to make the car turn (i.e., the force pushing in on the outside tire) is now also being used to roll the car to the outside. More body roll is almost always worse, since it means you either go positive in camber on the outside wheels or you have to run a boatload of static negative camber to keep the outside tires happy and there goes straight-line braking and now your inside tires are completely useless.

 

[jtmcinder]

From my experience, lowering a car reduces handling and increases understeer, but can make a car more stable (sometimes significantly so, especially if the suspension is stock, wimpy, or damaged).

Lowering a car lowers the center of gravity. A lower center of gravity is always a good thing, until your car or suspension bottoms out!

However, upgraded suspension components can also make the car more stable, without the negative effects.

Bah! Non-technical babble. Of course bottoming out is bad, but upgraded components aren't going to address the core problem with over-lowering a 2G, which is the front roll center. And assuming that you don't bottom out or ruin your roll center, lowering is otherwise always good. Finally, depending on the suspension design, over-lowering can cause either understeer or oversteer; it's not the lowering that matters; it's the geometry.

 

[Nasty Dream]

Yeah, I have a lot to learn when it comes to suspension. Thanks for the correction. I had to look up front roll center and looked at a graph of the lines. That was really helpful, thanks.

I can't wait to read through this thread when I get home. Setting up suspension always been a bit of a mystery to me and I would love to finally understand.

 

[snowborder714]

When you over-lower a 2G (and the definition of "over-lower" is lowering it to the point where the lower lateral control arm angles up from the chassis to the knuckle, instead of down, as it was stock), you have moved the front roll center way too far down.

Would having the lateral arm parallel to the ground then be the lowest you'd want to go? Or do you ideally want to have some downward angle?

 

[Nasty Dream]

Would having the lateral arm parallel to the ground then be the lowest you'd want to go?

That's what I was wondering too. I had fantastic results with them parallel to the ground (and also at a slight angle down) on single wishbone suspension professional R/C cars. The stock configuration was for clearance, I guess, and the arms were greatly angled down. The car would roll over (flip) at high speeds until I modified the suspension as described. The center of gravity was too high and the grip was too good for those speeds.

I also don't yet understand how you could sometimes get oversteer from over-lowering a car with double-wishbone suspension.

But I have lots to read already, maybe this has been explained already; sorry.

 

[jtmcinder]

Would having the lateral arm parallel to the ground then be the lowest you'd want to go? Or do you ideally want to have some downward angle?

Ideally, the roll center is pretty high, so a downward angle is best. In the case of a car with a true lower A-arm, you can get a fancy after-market lower ball-joint (from a place like Whiteline for Evos) and that fixes the roll center. For a 2G DSM, with those ridiculous, twin, offset, lower balljoints, I don't see a solution. But the gains due to a lower CG are also attractive. Upshot: stop at level is my advice. Your only other option is to move the roll center using the upper A-arm. Since a 2G is double-wishbone, this is doable. My slightly shortened upper arms helped a bit. Those funky, giant, adjustable balljoints are not helpful in this regard. This is why I never used those and did the cut upper A-arm, instead.

 

[jtmcinder]

That's what I was wondering too. I had fantastic results with them parallel to the ground (and also at a slight angle down) on single wishbone suspension professional R/C cars. The stock configuration was for clearance, I guess, and the arms were greatly angled down. The car would roll over (flip) at high speeds until I modified the suspension as described. The center of gravity was too high and the grip was too good for those speeds.

Yeah, when it's a strut and the lower lateral arm angles up from chassis to knuckle, you are totally screwed. That's why companies that really know suspensions, such as Whiteline, but not Ingalls, have kits to fix the roll center on Evo Xs, for example, because everyone lowers their Evo X since the thing is a bit of a wallowing pig when stock (ask me how I know ), but you trash the roll center as soon as you lower it.

Reading is good. Your attitude is great. Ask any question you wish.

 

[snowborder714]

Another option (if you haven't seen/heard of it) is to send the front subframe to Robispec and he will cut/weld where the lateral arm mounts to account for really lowering a car.

See posts #345 (modded) and #348 (stock) in this thread. Let me know if you can't see the picture and I'll copy them here.

 

[jtmcinder]

Wait. I knew that you can raise the lower rear inboard pick-up points. There's a way to raise the lower front inboard pick-ups, too? Wicked.

 

[jtmcinder]

See posts #345 (modded) and #348 (stock) in this thread. Let me know if you can't see the picture and I'll copy them here.

Just finished all 60+ pages. Very nice. Few questions/comments:

When you put a spherical at the inboard end of the compression arm, did that allow it to flop down in the middle? That's what I've always worried about if a bearing were put there.

Did you consider moving the inboard pick-ups for the compression arm forward a tad, to get more caster?

I saw that you ran into the problem of those adjustable upper A-arms hitting the shock tower. That's why I dislike those pieces. If you fabbed new A-arms from scratch, you could not only get more camber, but could also add caster that way. I thought about trying for 5* caster when I cut my arms, but couldn't get them to rotate smoothly when twisted a little, so I went with a straight shortening.

No matter what. Very sweet project.

 

[hypergenesis]

Just wanted to say awesome thread I don't think I have actually understood the complete physics behind suspension till now. I was actually curious the other day about if they had equations for all of these different aspects out there good to know. Seems like a lot of mechanical engineers get into cars honestly im planning to be one too ha.

Btw Does the owner of that build still have the car? Thats one amazing build.

Armin

 

[PieEyedPiper]

If I were to assign a homework at this point (which would make this post not only pompous, but seriously condescending, as well), then I'd ask you to use these idea to deduce why you want the roll centers to be at different heights at the two ends of the car. Fortunately for everyone, I won't bring this up.

- Jtoby

Stink bug mode.

 

[jtmcinder]

Bingo. Full points.

 

[snowborder714]

Just finished all 60+ pages. Very nice. Few questions/comments:

I'll send Kevin a PM and see if he can pop in here to answer those.

Btw Does the owner of that build still have the car? Thats one amazing build.

Yes he does. He just started to test fit Drew's (gixxerdrew) aero kit. It's a long project coming and still has a while to go. But it's amazing.

 

[greengoblin]

Just finished all 60+ pages. Very nice. Few questions/comments:

When you put a spherical at the inboard end of the compression arm, did that allow it to flop down in the middle? That's what I've always worried about if a bearing were put there.

Did you consider moving the inboard pick-ups for the compression arm forward a tad, to get more caster?

I saw that you ran into the problem of those adjustable upper A-arms hitting the shock tower. That's why I dislike those pieces. If you fabbed new A-arms from scratch, you could not only get more camber, but could also add caster that way. I thought about trying for 5* caster when I cut my arms, but couldn't get them to rotate smoothly when twisted a little, so I went with a straight shortening.

No matter what. Very sweet project.

Yes the arm did want to flop. I'm going to build a soft crescent shaped poly insert that will mount between the dog bone and the outer sleeve to prevent that from happening and still allow the unit to move freely when under load. That is what I hope anyway.

The inboard compression arm mount where left alone. I figured I was gaining plenty of caster from the adjustable upper arms.

On the upper arms. I think Im going to do a bit of cutting soon to make more room.


Kevin

 

[jtmcinder]

I'm sorry (for you) that the compression arm flopped, but at least (for me) my model was able to predict that.

As to those upper arms, I seriously would consider just tossing them. Even if you made room, those giant ball-joints aren't good. And the tower is critical, structurally, so I wouldn't hack them to get room (but, then again, I don't have the ability to weld in braces, so maybe this worry doesn't apply to you). I would plan the camber and caster, and build new arms. Probably easier in the long run than hacking the towers. I spent many hours staring at my car and playing with the model and that seemed the only good option: custom upper arms. But then I made my own arms by just cutting the originals, so all I could get is camber. If you made new arms from near scratch, you could get some caster, as well.

ps. nice to meet you. SnowB turned me on to your MM build thread. Very cool.

 

[greengoblin]

I'm sorry (for you) that the compression arm flopped, but at least (for me) my model was able to predict that.

As to those upper arms, I seriously would consider just tossing them. Even if you made room, those giant ball-joints aren't good. And the tower is critical, structurally, so I wouldn't hack them to get room (but, then again, I don't have the ability to weld in braces, so maybe this worry doesn't apply to you). I would plan the camber and caster, and build new arms. Probably easier in the long run than hacking the towers. I spent many hours staring at my car and playing with the model and that seemed the only good option: custom upper arms. But then I made my own arms by just cutting the originals, so all I could get is camber. If you made new arms from near scratch, you could get some caster, as well.

ps. nice to meet you. SnowB turned me on to your MM build thread. Very cool.

I might very well build my own arms at some point. It has crossed my mind several time. Your right about the towers too. "if" I cut them braces will be built . I've already designed a fender brace and have really been thinking about running the cage into the towers.
Right now I'm really trying to work with what I have for a bit. I would really like to drive the car someday. But with any car development one thing always leads to another and another and another.

Nice to meet you to. Your insight, knowledge, critical thinking and help are alway appreciated.

Kevin

 

[jtmcinder]

I love having someone to chat about this stuff. This was my favorite part of having a DSM: people who aren't afraid to hack it up to make it better. My new Evo X pals never do this. Heck, I can't get many of them to even rallycross their pretty cars.

In any event, here's my suggestion for the short term: take a set of stock upper arms, weld tabs on the outsides of arms, inboard end, covering the original hole. Drill new holes about 3/8" further from the end than the original holes. Call it a day.

Moving them 3/8" doesn't buy you a ton of camber and it buys you no caster, but you won't have to trim the ends off the arms to avoid rubbing the wheel-well. For you, this is an easy job and you now have all your travel back without messing with the towers, plus a bunch of new camber.

And it actually does a little bit of good for your dynamic roll center, too.

 

[jtmcinder]

Last thought (for now): I considered slotting the holes in the upper arm, so I could actually adjust camber, but wimped out on the grounds that the bolt might slide. I'll bet you could come up with a way to have adjustability there and no risk of slipping. That would be uber-cool.

 

[TunaTalon]

Last thought (for now): I considered slotting the holes in the upper arm, so I could actually adjust camber, but wimped out on the grounds that the bolt might slide. I'll bet you could come up with a way to have adjustability there and no risk of slipping. That would be uber-cool.

Maybe something like an eccentric camber bolt?
Eccentric bolts - Mechanical Database

 

[knochgoon24]

Since the bushing has a metal sleeve in it, can't you just tighten it all down with a lock washer and use some Locktite? I too have thought about slotting mine.

 

[jtmcinder]

Can't use those eccentrics; those are for the lower end of a strut.

I did think about just trusting the bolt to squeeze it all together enough, but mine was a DD as well as an autocrosser and the roads near where I lived suc ... were sub-optimal. But I may have been too cautious. The only other excuse I can think of is that, if you have pressed sphericals into the eyes of the OE inboard upper mounts (i.e., the funky bolts that hang down from the top of the shock tower), then you would be squeezing the stand-offs onto the bearing, itself, and that might not be the best. But, odds are, a slotted upper arm with sphericals in the pick-up bolts would be safe and sweetly adjustable.

 

[Nasty Dream]

From my experience, lowering a car reduces handling and increases understeer, but can make a car more stable (sometimes significantly so, especially if the suspension is stock, wimpy, or damaged).

Lowering a car lowers the center of gravity. A lower center of gravity is always a good thing, until your car or suspension bottoms out!

However, upgraded suspension components can also make the car more stable, without the negative effects.

Wow, I got a bad rep for this, and I quote "All else equal, lowering will not shift a DSM towards understeer. I can think of no car where this will happen."

I guess you haven't heard of the Scandinavian flick, or any such technique. Well that's insulting as heck. This is one of the most elementary race driving techniques. Lowering a car reduces the ability to throw the car around using the high center of gravity, hence reducing oversteer.