Recently we asked you guys to post your questions about sway bar and bushing upgrades to be answered by Scott Bennett, the Product Manager at SuperPro. Scott has gone through the questions and replied with some very informative answers, which you can find right here.
Now, let’s get the info flowing!
Can you explain why people say to put a big front bar on my WRX to combat understeer? Doesn’t making the front end stiffer lead to more understeer?
Does adding a stiffer anti-roll bar REDUCE that axle’s grip? I believe that it does, and lowers the ‘theoretical grip’ on that axle, but when approached in the right way, can make the car easier to drive on or close to the limit.
As far as sway bars go, what amount of a performance increase can you expect from aftermarket sway bars vs. stock on a stock or lightly modified vehicle? Also is eliminating all body roll the goal, or is some okay?
These are great questions and highlight the dilemmas faced by you guys in selecting the best solutions for your vehicles. Answering these three questions as a group is best explained by firstly explaining the basics. A tyre contact patch at static position offers maximum theoretical grip. Body roll either increases the grip or decreases it depending on the mass load transfer in a dynamic situation. Mass produced vehicles are designed with understeer for safety reasons. Modifying the wheels, tyres or increasing the power output creates a situation that when a vehicle corners, the body roll characteristics change. For example, with a Subaru WRX the understeer will actually get worse. Grip can be changed with too much or too little weight transfer. A Subaru WRX in standard form when driven aggressively is best improved by front and rear sway bar upgrades. This controls camber change, roll center geometry change and grip footprint, while maintaining the original balance to keep the grip correctly distributed on all four wheels.
Too much weight transfer produces plough understeer. A front upgraded aftermarket sway bar will control that situation. If there’s not enough weight transfer due to higher spring rates, then a rear upgraded sway bar will control understeer in this situation. Aftermarket sway bars are generally thicker which means less twist to give less body roll and ensure the grip footprint stays within maximum contact. So to summarize, bar size is generally thicker when vehicle is heavily modified with tyre, engine upgrades and body strengthening packages or can be actually thinner with spring/damper kits with high spring rates and dampening rates.
If we’re constantly being told polyurethane bushings are a superior replacement alternative to rubber bushings, then why do all car manufacturers continue to use rubber over poly bushings? Why is it that aftermarket bushings are almost always polyurethane and not, say, a hardened rubber compound instead?
It all comes down to cost. It is cheaper and more cost effective to mass produce a rubber suspension component than it is to produce a polyurethane component. Also, the vehicle manufacturer is predisposed to appeal to a mass market in making their cars feel good travelling under the speed limit! A better, more durable and resilient material than rubber is polyurethane. This is why PU is the go-to replacement material for performance and handling. However, it is all in the mix. PU material is used to make everything from skateboard wheels to carpet underlay! SuperPro is a class of synthetic isocyanate resin base material converted with various curing agents to become a more durable product with the best features of both rubber and PU.
The secret formulation and molecular structure of our material ensures that it is energy absorbent; a bushing incorporated into a suspension system has to accommodate geometrical interference and reduce the impact of energy transmission. It also has to be lightweight and strong, resulting in a product that is superior to OEM rubber products. We think of our blend of polyurethane as an elastomer, or synthetic rubber. The best way to think of SuperPro versus rubber is the same as engine oil, mineral oil versus synthetic oil. Ours is a synthetic rubber with all of the undesirable characteristics of rubber eliminated and all the desirable ones enhanced. Having said all this, it must be remembered that not all brands of PU suspension bushes are the same!
Say you have an OEM sway bar, replace the bushings with polyurethane units and then use shorter adjustable end links. Is it the same in theory as those adjustable sway bars with multiple holes, as in, by shortening the lever arm, rigidity increases?
Adjustable sway bars with multiple holes are effectively changing the distance from the fulcrum point of the sway bar where it mounts to the chassis to where it attaches to the suspension, in the same plane. This is what changes the rate of a sway bar. Adjustable links are used to make this possible. Changing rubber bushings to SuperPro will eliminate any undesirable movement in an OEM bar and force it to work at the original OEM rate. Adjustable sway bar links allow each side of the vehicle to be neutralized. This will not result in achieving anything like the same rate increase as a larger diameter, adjustable sway bar.
Could you explain the various optimal sway set-ups in a racetrack environment for AWD, RWD, and FWD? It’s always been a great debate amongst friends on either getting fronts, rears, or both depending on the drivetrain and type of car. We’ve even been back and forth on the best settings such as medium or full stiff. Thank you!
Neutralizing understeer is a primary factor in selecting sway bars; this is sometimes best achieved by having the rear at a higher rating than previously. Going too hard on the rear bars will induce oversteer. Finding the balance for each type of vehicle is the key – assessing the feedback and only changing one thing at a time is the best way forward. Having adjustable sway bars in a matched pair is paramount to being able to balance the car.
What would you look for in the car’s handling to determine if the poly bushings are creating stiction or binding? Is there a hierarchy of checks to rule other things out (that could potentially be causing handling issues) that you can recommend before pointing the finger at the bushings?
Our bushings in some applications are a free pivoting, bearing style bushing. In other applications there will be inbuilt resistance to the motion of the suspension arm. Stiction and binding in our bushings will normally be as a result of misaligned suspension arms, a forced fit approach from the installer or lack of grease. With PU, the application of the supplied grease during the installation is critical to ensure the serviceability and life of the bushing.
As far as diagnosing a binding bushing, it is a feel thing. The best place to start is to remove any load from the suspension arm and work it through the normal field of travel, while checking for an excessive amount of resistance.
How can lowering a car effect the preload on the sway bar and do you have any suggestions on the best ways to go about correcting/reducing this extra stress? (I have a lowered Crossfire and the rear is extra stiff/lively after dropping. I have been playing with sway link length with varying results, just trying to find a more scientific way to approach the issue.) Thanks.
I need to clear up a misconception here – lowering a vehicle will not exert any preload on a sway bar. It is hard to give an opinion here as I do not know exactly what additional work has been done or how low you have gone. If you have just installed lowering springs and not upgraded the dampers, this could explain it. Aftermarket lowered springs have a higher spring rate than OE springs; as a consequence the OE dampers that may well be slightly deteriorated with some mileage, cannot control the higher spring rate. This will cause the vehicle to feel stiffer and livelier. Installing new performance style dampers may cure your issue. But remember that when lowering a vehicle there is always a trade-off between handling and comfort.
Is it true that polyurethane bushings can’t stretch? And is it true that rally cars use a hardened rubber bushing because of this flaw of PU? If so, why do so many aftermarket companies offer them?
This is absolutely not true in the case of SuperPro PU. Our product has a high level of resilience – it will stretch but will not rip, tear or shear. In addition it has excellent memory; it will always return to its original shape every time, making it an ideal choice for every application, whether it is road, track, rally or off-road 4WD.
Hi, what do you recommend, first replace the front bushings with polyurethane bushings, or replace all of the rear axle bushings first?
I don’t think of it in terms of front or rear, more in terms of replacing the most critical bushings in either the front or the rear. This is the approach that we take in R&D. Replacing some front bushings and not replacing any rear bushings may lead to an experience that is less than ideal from a performance handling perspective. PU bushings work better than rubber – it is always best to keep the car as balanced as possible.
What effect can bushings have and how drastic is it?
I will presume by this question you mean how noticeable the upgrade to SuperPro is. The answer to this is that the handling performance is dramatically improved. Reducing unwanted movement in suspension arms is always the goal. Soft and gooey rubber bushings are the enemy of performance handling and lead to excessive tyre wear. Our whole philosophy is to maintain optimal tyre contact with the road. This is what delivers grip. The biggest improvement comes in most applications from the positive location of the control arms during high speed cornering. Adding our bushings in these locations maintains dynamic caster on any vehicle they are fitted to.
Every application we make bushings for will benefit massively from the upgrade. The end result of installing the complete SuperPro package was a car that had lost the vagueness on turning into corners and was far more predictable on the limits of cornering. It was also noted that the car was firm but still smooth to drive and showed no signs of harshness.
What’s the best set-up for a 2002 Impreza WRX for street and light track use?
The answer to this question is easy. The first step is to replace every bushing with SuperPro! In particular, have a look at our new lightweight alloy lower front control arms with antilift bushings. If you are lowering the vehicle, you must fit our Roll Centre adjustment kit. We do a complete vehicle Performance kit for this car, every bushing you need including the alloy arms. As for the rest, there is an abundance of coilover kits in the market, so it’s best to seek the advice of your local tuner. Then get out there and have some fun!
How do you do fitments on the cars you make products for? Can we see the process to making the bars and test fitting them, then do you do real world testing to the cars before and after? I’d love to see/hear about some processes.
Our process starts at our R&D department. We start with the vehicle in our R&D workshop where we look at OE design of the suspension set-up, the positioning of the bushings and their function. We then apply our knowledge of the properties of the material we developed to produce a bushing that will work the way we want it to. Our primary goal is enhance the function of the bushing with zero increase in NVH (noise, vibration and harshness). As SuperPro is an Australian company, what we manufacture predominately services the Australian aftermarket repair sector. If you have your road car repaired in Australia it will have SuperPro or some other PU fitted as the first option. This makes us acutely aware that our bushings have to be better than OE, in all respects. We enjoy the reputation as the best PU manufacturer servicing this sector of the market in Australia. Performance and handling benefits of SuperPro are an extension of what we do.
Once our engineers have looked over the car, we measure up and start the development process of both our bushings and Roll Control sway bars. We make all of our own patterns, moulds and pour our bushings in our Brisbane facility. We control the process from start to finish. Our sway bars are designed, rate tested and manufactured in the same facility. It is important to point out that we use the highest grade of Australian spring steel in the manufacture of our sway bars – this allows us to achieve better rate results from smaller diameters. Every sway bar has three layers of powder coating to ensure they have the highest level of corrosion resistance and are supplied with SuperPro bushings.
Every bushing and sway bar is test fitted to our R&D vehicles to ensure correct fitment, alignment and function. All vehicles are compared back to back against the standard car and travel a required distance and time before they are re-checked and assessed. On most development projects we are able to get track time, as we did with Harding Performance and his APR Golfs in the development of our VAG range. We are always assessing feedback, and if necessary, tweaking the design of bushings. For us R&D is an ongoing commitment.