Springs, braces or swaybars? Which is best?

[dailybean]

Does this help?

http://arrc.ebscohost.com/ebsco_static/repair-tips/8852CH23_Rear_Suspensions.htm


Dave

Awesome Dave, thank you.


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[dailybean]

[MENTION=8487]Zombie[/MENTION] OP I don’t even know if we’ve asked you this but what is your budget for whatever you would like to do?


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[LargeRubberFist]

But racecars sit low! Yes, but they don't use the factory pick-up points. While my Mustang may be old, the physics and statics still apply. In order to lower my Mustang to get a lower CG, but keep the proper suspension geometry, I had to do the following. First was move the control arm pick-up point the same distance I was lowering the car. The subframe that mounts the control arms has the pick-up points raised in the chassis. Next was to move the steering rack. I had to use special aluminum bushings to move the rack in the chassis. Then I had to articulate the suspension while measuring toe change. The distance between the spindle knuckle and the tie rod end was then adjusted with shims until the toe change was minimal and never toe-in in bump.

Something else worth noting. The suspension bushings are typically in a neutral position at static ride height. Lowering the ride height preloads the bushing in one direction.

I've heard of people raising the mounting points of their control arms and spring perches creates a similar effect to a drop spindle but haven't 100% understood this. Can you explain the differences between the two a bit and how the steering rack adjustments relate to it all? I try to understand all this suspension stuff but most of it is magic/voodoo to me, having it all laid out and explained like you've been doing is super helpful and interesting. Thank you

 

[BRGT350]

[MENTION=1313]BRGT350[/MENTION] I have a question regarding another post of yours. Ideally the suspension should be at the factory height as it was designed. You said the Mountune springs you had were a great upgrade but they changed the ride height. Is that because of the minimal change in height? I went with swift because they also were tuned to match the factory dampers but offered a linear spring rate which I prefer the feel of and comparing my past experiences when switching from progressive springs, linear rated always felt much better on the track while putting down mildly faster lap times. This car is not a track car, but I like the feel of linear springs on the road and in normal driving as well. After many FiST owners and companies that offer suspension upgrades stated that the swift springs were the best springs for a performance upgrade, based on that and my experience it was an easy choice for me (I am admittedly biased as stated). With Swift offering a similar drop as the Mountune springs with a higher and linear spring rate, would you say they offer the same upgrade or more in performance? I haven’t had the car at a track with these springs yet, but testing the handling after installing them and an alignment it feels much better on all types of turns I’ve pushed it through so far. Also from my experience experimenting with the front end on my truck and MS3, and adjusting the sway bar back to its original position by swapping the endlinks, I never noticed any ill effects from dropping from the stock height. The truck was never put on a track with any turns (1/4 mile only), but the numbers were there from the Mazda which to me showed an improvement. I always ran the same wheel and tire setup so it wasn’t a difference in grip. Is the information you shared FiST specific or does that apply to every vehicle every time?


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I went with the Mountune springs since the drop wasn't too much and the spring rate worked well with the factory dampers, so it made the upgrade very affordable. Going with a stiffer spring, either progressive or linear rate, would have required upgraded dampers. I could easily see the Swift springs and a set of Bilstein dampers outperforming the Mountune springs with factory dampers. A lot of the suspension geometry stuff I brought up is true for any McPhearson Strut. I haven't dealt enough with an IRS or SLA IFS to be able to comment with any real authority. I have some experience, but not enough. As for linear vs progressive, I have used both and would say it comes down to preference. I like a progressive rate on the street since it gives a little softer ride over a lot of the minor bumps on the road. It also allows me to feel more of the weight transfer.

 

[BRGT350]

I also want to know this. I recently purchased Eibach Pro Kit springs, which only have a mild 0.8" / 0.7" drop. Is that enough to bring the suspension geometry past optimal range?



That's good to know. I hope that means that the Eibach Pro Kit springs are still at optimal range.

Suspensions are all about compromise. Without doing a complete layout and articulation study, it is impossible to really know how much lowering is too much and how much is just enough. The general thought has been to say under an inch. Mostly because the amount of change in the suspension at the first inch of travel is minimal. With lowering springs, you give up a little of the optimal suspension geometry for a lower CG and reduced fender gap. It is a compromise.

 

[BRGT350]

I've heard of people raising the mounting points of their control arms and spring perches creates a similar effect to a drop spindle but haven't 100% understood this. Can you explain the differences between the two a bit and how the steering rack adjustments relate to it all? I try to understand all this suspension stuff but most of it is magic/voodoo to me, having it all laid out and explained like you've been doing is super helpful and interesting. Thank you

I wish I had a good way to show this visually, because it far easier to see it than read it. A drop spindle moves the axle centerline up in the vehicle, which in effect, lowers the vehicle since the radial distance between the center of the wheel and the ground doesn't move. The spindle should keep the proper control arm and tie rod geometry since they stay in the same location. I say should, because I am sure there are many drop spindles that alter the arm positions. Moving the suspension pick-up points upward in the chassis while lowering the ride height is also done to maintain the suspension geometry with a lowered overall height. If you look at the vehicle from the front and peel back all the body work until you are looking at the suspension. You will see the lower control arm and steering tie rod. The tie rod, control arm, and ground should all be parallel. When the suspension articulates, it moves in an arc that is controlled by the length of the control arm and tie rod. When the arc of the control arm and tie rod move the same, the steering is unchanged. When the arcs are different, the tie rod either pulls in or pushes out the spindle, causing the steering to be altered. This is bump steer. So, if you raise the control arms upward in the chassis, install a drop spindle to lower the ride height, you need to move the steering rack upward in the chassis so the tie rod and control arm are parallel and move in the same arc. There are ways to trick the tie rods and control arms to move in the same arc by using shims and steering knuckle geometry. Off-road racing trucks have crazy front suspensions with huge amounts of travel. Getting those to work right is a pretty big challenge. A road race car is easier since the amount of suspension travel is so much less.

One of the best ways to see how this works is to make paper dolls. Make a box to represent the chassis, add a lower control arm, spindle, tie rod, and strut as independent pieces. Pin the control arm and tie rod to the chassis, and then move the spindle up and down to see how it changes. If you have CAD, you can do this with a line drawing. You could probably do the same with some Legos too. The idea is to see how the suspension moves and how you can alter it by changing pick-up points and ride heights. Even if you don't have any real car measurements, you can still model the basic shape and get the idea. I haven't looked, but I would bet there are probably videos on YouTube. I learned the trick from a suspension book by Carroll Smith. His books are a little dated, but the physics are all the same. They are great books and really helped me out.

 

[SirThomas88]

Suspensions are all about compromise. Without doing a complete layout and articulation study, it is impossible to really know how much lowering is too much and how much is just enough. The general thought has been to say under an inch. Mostly because the amount of change in the suspension at the first inch of travel is minimal. With lowering springs, you give up a little of the optimal suspension geometry for a lower CG and reduced fender gap. It is a compromise.

That's a relief. Thanks for the helpful info! Eibach Springs going in this weekend.

 

[BRGT350]

That's a relief. Thanks for the helpful info! Eibach Springs going in this weekend.

no problem, hope the install went well!

 

[wraith]

Just trying to understand, are front sway bars (also called anti-roll or stabilizer bars) accomplishing the same thing as xx point front harnesses on our Fiestas? I assume you cannot run both sway bars and xx point harnesses at the same time since I think they use the same mounting points and might occupy the same spaces under the car?

As D1JL previously mentioned, my plan already was to get BC Racing BR coilovers (I like the adjustable height and damper in both front and back) and then the H&R sway bars front/rear unless anyone has a compelling argument for otherwise. I do plan to do track lapping days a few times a year as well as daily drive it.

Also, I've been curious why I don't hear much about using adjustable camber bolts (like H&R Triple Cs) on a lowered fiesta. What is the likelihood I would need them in my planned setup?

 

[alexrex20]

The front sway bar and the chassis braces are unrelated and can be used in conjunction. The front sway bar is just like any other anti-roll or anti-sway or stabilizer bar that you're used to. The basic 2-point lower brace ties the lower control arms together so there is less deflection. The 4-point further ties into the crossmember, and the 6-point further ties into the unibody. The braces are not a suspension component, though they do allow the suspension to work more efficiently and be more responsive and predictable.

I think you may be confusing the front sway bar with the rear "sway bar" as the Fiesta ST aftermarket has rear torsion braces which are also sometimes called sway bars. Because of the torsion beam design of the rear suspension, a simple brace achieves the same result as a traditional sway bar. There are multiple designs of rear sway bars and some of them can be used in conjunction. For example, you could use the Pierce Motorsports rear torsion brace and the Eibach rear sway bar together, though I don't know why you would want to... lol

Some folks will use camber bolts to get more negative camber. On a lowered car it naturally will have more negative camber so unless you want something crazy, you shouldn't need camber bolts. I certainly wouldn't get them until you know you need/want them.

 

[wraith]

Thank you, it's good to know I have the option to add in the brace later if I'm not satisfied with the sway bar.

The camber bolts I thought I might need in order to get into a camber setting closer to factory spec for even tire wear rather than try for even more camber than it already will have with the coilovers. I remember on my STI when I got an alignment and was lowered I had to get the camber bolts because the top of the wheels was so cambered inward and the factory bolt couldn't flatten it out and bring it back in to spec enough.

 

[Zombie]

[MENTION=8487]Zombie[/MENTION] OP I don’t even know if we’ve asked you this but what is your budget for whatever you would like to do?


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Thanks for asking. I didn’t know when to ask a follow up question due to all the technical discussions going back and forth.

I’d like to stay well under $1k for everything suspension related. I’ve only installed lighter 17” wheels but gave back some ultimate grip when I replaced the OEM Bridgestone’s with the Firestone Indy 500s.

The car feels lighter on its feet but definitely
has less grip and squeals a lot easier.

Regarding the Swift springs, I’d like the lower appearance but don’t want to give up suspension compliance, which stock is not much. I only want to make changes that improve handling. Aesthetics are secondary.

In regards to driving experience, I actually have a fair amount of HPDE experience in the past with higher power RWD cars.

Thanks again for all the input guys!