Im sure many of you are here because you want to learn a bit more about the black art of suspension geometry. More specifically roll center, and if you really need to install extended balljoints or (roll center adjusters) on your car. I’ll try my best to explain it as simply as possible, and help you better understand how impactful these extended ball joints can be on your cars handling characteristics.
Do you need these for you car? The short answer is yes, if you don’t need any more reason than that, just go order yourself some right now. But if you want to learn about the science of why this will help your car so much, please continue reading…
What is roll center? Roll center is a theoretical point around which the chassis rolls, and is determined by the design of the suspension. Front and rear suspensions have different roll centers. Put simply, the roll center is the point the chassis rolls around when it leans around a corner. Roll center is one of the most under-utilized adjustments on a car, but one of the most powerful. This is because roll center has an immediate effect on a car’s handling, whereas anti roll bars, shocks and springs require the car to roll before they produce an effect.
To find your cars roll center first you must find the “instantaneous center.” The Instant Center is the intersection point between the upper and lower wishbone/arm axis, or with a Macpherson strut arrangement the lower wishbone and a plane set perpendicular to the strut axis. Instant centers are critical as they help define the roll centre as well as the geometry of the steering to help eliminate unwanted bump steer and excessive roll center movement. Note this is done with the car at ride hight.
Hopefully the image above will help clarify what I wasn’t able to explain well enough. Now that you have found your Instant center (its the dark red dots) you are now going to make some more hypothetical lines from the center of the tire (contact patch) to the instant center (dark red dot) draw a line from the right center tire to the left IC dot, and then a line from the left center tire to the right IC dot. Where those lines intersect is going to be your roll center (the bright red dot). Now I seriously doubt any of you are ever going to measure any of this, and why would you? Aftermarket companies have done all this for you and designed their product to best suit your needs. I just wanted to explain it to you so that you know what a roll center is.
Now that we know what the roll center is let’s discuss how it effects your car, and its overall handling. Lets talk about your cars center of gravity (CG), Im not going to explain how you find your cars center of gravity because frankly its to much for my basic brain to try and explain. But there are plenty of ways if you just search google you can find out the formula, or a good round about estimate is the crankshaft of the engine is usually where the CG is. Again though none of this is necessary for people like us or are just enthusiast, and I’m only talking about the CG because this is how I’m going to explain the effects that raising your roll center will have on the cars handling. The CG is almost always going to be higher than the roll center, and now that we know where our roll center is and your theoretical CG is, now let’s take a vertical line and connect them. This will give you the “roll moment arm” The roll moment arm works like a lever when your car rolls in turns. the longer it is the easier it is for the car to “roll over” into turns (not actually flip over) Think of a roll moment arm as a lever where centrifugal force works to lean the car over. the longer the lever (lower the roll center) the easier to roll the car and the shorter the lever (higher roll center) harder it is to roll
As you can see above if you connect the roll center dot and the CG dot on the top “stock suspension” it will be substantially shorter than if we were to make line connecting the roll center and CG on the “lowered suspension” so remembering that the line is called the Roll Momentum Arm, and also remembering that it acts as a lever and that the longer/larger the distance is between the two dots the more leverage and easier it is for the body to roll. I know this image is blowing your mind because you are seeing that when you lower your car it actually makes the roll center worse, and you just can’t quite grasp why your car feels like it handles better when you lower it, when technically you’re making the suspension geometry worse. Well let me explain… It’s simply because when lowering the car you have installed springs that are stiffer, quite possibly shocks that are better, and you have in-fact lowered the cars center of gravity. All of these things do in-fact make your car feel better, but you have effectively ruined the geometry of the suspension since you have now altered the roll center in a negative way (moving it lower and further away from the CG). This causes bump steer, and other suspension issues that can negatively effect your cars handling.
Let’s take it to the extreme now, let’s say that we managed to get our roll center to be the same level as our center of gravity. Technically the car wouldn’t have any body roll as it goes around a corner since there wouldn’t be a lever and therefore nothing for the centrifugal force to push on. Obviously this would also have negative side effects but this should help you understand why you want a short roll moment arm. (the distance between the roll center and the center of gravity). Anytime you lower a car you are going to increase the distance of the roll moment arm. Again, think of the roll moment arm as a lever that centrifugal force uses to lean the car in a corner. The longer the lever the more roll. Raising the center of gravity will lengthen the lever as will lowering the roll center. Lowering the car lowers both the center of gravity and the roll center, but the roll center moves more than the center of gravity which lengthens the roll moment arm. This is why it becomes an issue with lowered cars.
* When the RC is far away from CG (lower RC), when the car corners the CG has more leverage on the RC, so the car will roll more.
* When the RC is closer to CG (higher RC), when the car corners the CG has less leverage on the RC, so the car will roll less.
Adjusting your roll center will also help the suspension arms be more level which will allow them to all work as the engineers of the car had designed, it will allow for less bind in the CV (constant velocity) joint of the axle, allow the suspension geometry to work in its optimal range, and increase shock travel so your shocks are working in their optimal range, and not always bottoming out on large bumps because you are low.
Effects of Front Roll Center Adjustment: Front roll center has most effect on on-throttle steering during mid-corner and corner exit.
LOWER front roll center
* More on-throttle steering
* Car is less responsive
* Better on smooth, high grip tracks with long fast corners
HIGHER front roll center
* Less on-throttle steering
* Car is more responsive
* Use in high grip conditions to avoid traction rolling
* Use on tracks with quick direction changes (chicanes)
Effects of Rear Roll Center Adjustment: Rear roll center affects on- and off-throttle situations in all cornering stages (entry, mid, exit)
LOWER rear roll center
* More on-throttle grip
* Less grip under braking
* Use to avoid traction rolling at corner entry (increases rear grip)
* Use under low traction conditions
* Increases traction, reduces rear tire wear
HIGHER rear roll center
* Less on-throttle steering
* Car is more responsive
* Use in high grip conditions to avoid traction rolling
* Use on tracks with quick direction changes (chicanes)
these are all subjective, and will just be a rough guide for how Roll Center effects the car. Please also understand that there are many different ways to set up a car, and this whole article is merely an explanation of what roll center is, and how it effects a car. The goal of this article is to help clarify why extended ball joints are such a good modification, and as with anything in life too much can be bad. So of course you can make the roll center too high, that is why I say that the manufactures of the parts have already done all the R&D so you don’t have to.
To sum up all this overly complicated talk about Roll Center and why it’s an important aspect of suspension tuning. Let me just say that raising you roll center will make the car roll over less easily, it will put the suspension back into is optimal operating range, it will allow you to run a softer spring and sway bar since you won’t have to combat the excess body roll with stiffer springs and sway bars, and it will also help eliminate bump steer.
Let me talk of my personal first hand experience that I immediately noticed after I installed these.
- Car turned in easier, and with less steering input.
- when switching lanes and going over the dots in the road there wasn’t as much feed back in the steering wheel.
- less understeer.
- since there is less body roll I found myself going much faster through corners than before. because the car isn’t rolling as much so it doesn’t seem like im traveling that fast through a turn
- under hard braking the car was less unstable.
Now mind you when I’m talking about going faster through corners, I’m talking about corners where I felt the car was at the limit at 80-90 mph I can now take at 100mph and have it not even feel near the limit. I would probably have to go 110-120mph before my butthole would pucker. When I talk about hard braking, Im talking from 80 down to 20 as late as possible to enter or exit freeways. The car just feels so much better, but its hard to put fully into words, and trust me when I say everyone should do this to their car. Even if it’s not that low, even if you don’t want to track your car. This will just improve the over all driving experience, it will go over bumps and uneven surfaces smoother than before, it will allow you to soften the dampening on your shocks, run softer sway bars or springs, which again will improve the overall ride quality. When I posted that I was installing these on my Instagram some one commented that this mod was “one of the most slept on mod for double wishbone cars” and I couldn’t agree more. When I look back at how long I have been driving lowered Hondas or just lowered cars in general. (20 years now) Im mad at myself for never wanting to install extended ball joints/roll center adjusters. I have been driving around with stock ball joints for ever thinking that it couldn’t get any better, boy was I wrong! Do yourself a favor and order yourself a pair, it doesn’t have to be the buddy club ones like I got. It can be any brand, they will all raise the roll center.
OK now that you want to order some, let me show you how easy it is to actually install them. (I never did these for fear of how difficult I thought it would be to install them) so if you’re anything like me and you hesitate to do this modification because you are scared that it might be too difficult. Trust me its super easy!
Break the lugs loose, jack the car up, place on jack stands, and remove the front wheels.
You’re going to completely remove the spindle off the car so you can easily remove/install the ball joint.
Start by removing the 32mm axle nut
then remove the brake caliper, and rotor.
Above are the holes where the brake caliper bolts to the spindle
Now remove the lower balljoint, the upper ball joint, and the tie rod end
use a hammer to smack against the spindle to “shock” the ball joints, and tie rod loose. as you can see I flip the castle nut upside down and thread back on to help protect the threads from damage when swinging the hammer. don’t be afraid to hit very hard a lot of times until they come loose.
Once you get the upper and lower ball joint loose the spindle will come out, just slide the axle out of the hub carefully not pulling to hard on it or the axle might come out of the transmission, this will cause some of your fluid to leak out.
you should be left with a wheel well that looks like this. Notice that everything can still stay connected you just take everything off the spindle.
removing the old ball joint. Locate the Circlip
Now take Circlip pliers and remove it.
Now the ball joint is ready to be removed. Simply position the spindle like so, and hit the ball joint hard a few times with a hammer and it would just fall right out.
As you can see, there is a difference in the ball joint lengths. this is what raises the roll center. One thing to take note of is that the extended ball joint will place the lower arm closer to the brake rotor, and you might have to remove the brake dust shield so it doesn’t get pushed into the brake rotor when the suspension sits at ride height, or under compression while cornering. It’s pretty close, I don’t have a dust shield and there is still only about .5 inch of clearance. It is kinda scary but I haven’t had any issued with brake rotor to lower arm contact, and neither has anyone else that I know who runs these.
Installing the new ball joint. Make sure to throughly clean all debris out of the spindle where the ball joint gets pressed into, and I lubed it with some grease to aid in proper seating. You will also have to use a ball joint press tool, I just went to Autozone and rented one.
This is what it looks like in action
The new ball joint should slide in pretty easily, you shouldn’t have to use much torque when tightening the clamp. Once the balljoint is fully seated you will now install the NEW Circlip that came with the ball joints. Make sure you install the Circlip or eventually the balljoint will just press back out of the spindle, and you will most likely crash.
be careful when installing the Circlip that its doesn’t come of the pliers and snap on the boot possibly causing damage to the boot, and for sure you’re going to mess up the stickers like I did too.
Reinstall the spindle on the car. It should just go right back on the same way you took it off.
- As you place the spindle back in, line up the axle and slide it through (spray some WD-40 or some other lubricant to help the splines slide into the hub easier),
- once all the balljoints are in you won’t be able to slide the axle in.
- Re install the upper and lower ball joints, and the tie rod and tighten completely.
- Then install the suspension fork onto the shock and lower arm, but don’t fully tighten.
- Put the brake rotor back on, then the brake caliper, and the brake line bracket and tighten it all completely.
- Tighten the axle nut and take a punch to lock it in place in the notch at the end of the axle.
- Now take a jack and place it under the lower arm, put some tension on the suspension so that the fork properly seats tight against the bottom of the shock, and tighten the bolt clamping it to the shock, and on the lower arm.
- Lastly double check that you have tightened everything that you had originally loosened.
You will repeat the same removal/install process for the opposite side and once both sides are done reinstall the wheels and lower the car back down.
Since installing theses is going to raise your roll center its going to lower your car more so you will most likely want to jack the car back up and adjust your ride height. as you can see below in my before and after photos it will be about an inch lower.
You are going to for sure need to get an alignment again because the toe will be off. I have covered previously HOW TO do you own garage string alignment, if you’re feeling good and want to try something else that is actually pretty easy. If not just make sure you go get an alignment before doing any hard driving.
Here’s the link on how to do your own alignment.
Hopefully this article helps you understand why roll center adjusters are such a worth while modification. I also hope that the way I explained it was easy enough for you all to understand. As always thanks for reading, and I hope this article can help inspire you to do some work on your own car this weekend. If you like what you’re reading please feel free to share, like, or comment. Or if you have any questions please don’t hesitate to ask.