Thoughts on Front and Rear Swaybars
Trying to math things out with fuzzy numbers isn’t necessarily accurate, but sometimes it’s better than nothing.
My actual measured values of OEM vs 26mm H&R bars, with 28mm front H&R bar values being estimated based off of the 26mm bar dimensions
So I decided I'd try something a little different on this car - on my last car (Mazda2), I went full-tilt on the suspension... I ran tons of spring rate and no front sway bar at all, a 25mm AND a 32mm rear sway bar in the rear, plus at one point ran a 225/9in and 195/7.5in reverse stagger. With $$ shocks the setup was tolerable but definitely STIFF on the street. Admittedly, a lot of this setup was a result of having to work around an open differential due to autocross and Gridlife Sundae Cup rules.
Trying to avoid hating myself with this car, I decided I’d test out the stiff bars/soft springs setup path.
I bought some H&R front and rear 26mm sway bars. I went with them because they're solid (I’d rather not worry about one snapping), priced decently, and according to many they use some special hotdog butter or something impregnated in their bushings and they just plain don't squeak or ever need lubed. Note: I still recommend lubing with silicone grease anyway - sway bar bind does weird stuff and ensuring everything moves freely goes a long way.
They sell the 28mm front and 26mm rear as a matched pair, and a 26mm front and 24mm rear as a matched pair.
I ran (very rough) numbers on all of them and in a nutshell the 28/26 SEEMS to be much closer to stock as far as front/rear roll couple split goes. Since I did not want to raise the spring rate significantly, I DID want to get rid of some overall body roll via the front... but I wanted to add proportionately MORE roll stiffness to the rear to try and move the bias a bit towards oversteer to make it a little more lively on turn-in.
This is how I arrived on choosing to give 26mm H&R bars both front AND rear a shot. Once I actually had them in my hands, I was able to refine the numbers to actual measured values. I’ve still not gotten a GTI 28mm bar in my hands and off the car to measure for sure, but based on the 26mm bar dimensions I think it should be reasonably close to my estimation above.
I ended up installing the rear first out of sheer laziness and lack of time before Fastivus at Summit Point in 2022. I also wanted to try and get some data (or at least a general feel for the car) on rear only vs front + rear at VIR which I got to drive on in December of 2022 with just the rear bar before installing the front over winter time.
If I’m completely honest the sway bars were more so an attempt to just minimize tire roll-over and extend their life without going to massively stiff springs.
So what kind of difference did they make?
The rear bar (still with the stock front) helped with making the car feel better on turn-in, but you can definitely feel the car “load up” the outside front tire as you’re cornering. If I’m completely honest, on the street the change was nowhere near as much as I was expecting based off of some online chatter about the 26mm bar being “too much” for the rear. I never once felt like it was too much. It did help in feel which is harder to quantify, but can’t say it added any outright grip. I ran it at Summit Point on the Jefferson Circuit in October and VIR in December of 2022 with the stock front sway bar, and 26mm H&R bar on the rear.
The 26mm front sway bar went on over winter, and was able to evaluate how it felt in February of 2023. Unfortunately there was also a difference in tires run, BUT the overall attitude of the car exiting Oak Tree from each event from very similar vantage points really speaks for itself as to WHY a front bar helps grip: It lessens the amount of dynamic camber loss in a turn.
I will add that the bigger FSB will push a bit when the tires are cold (assuming no other changes), and the front end grip is a bit more “edgy” in the rain on track. In the dry it actually grips MORE than the stock front sway bar once the tires have some heat in them. Data to follow in the next blog entry.
Time for a thought exercise:
The above comparison also illustrates something that few people seem to understand. If you lessen overall body roll up front, you’re also going to lessen body roll in the rear.
Adding roll stiffness to the rear (in an attempt to limit overall roll) is only effective up until the inside rear tire comes off the ground. This happens because these cars have a ~60/40 weight distribution. Once the inside rear comes up, any additional stiffness is not doing anything to actually help body roll, just hike the inside rear tire higher (while raising the overall center of gravity in the process). To be fair, it will add comparably more roll stiffness on initial turn in, but it’s not doing anything for overall grip in a steady state fully-loaded turn.
When you add roll stiffness to the front, the entire body of course doesn’t roll as much, and the outside rear tire does not go as far into the positive (camber-wise).
After adding a front bar, it may be ideal to remove some camber from the rear to maintain balance. For what it’s worth I did not do that, the plan is to eventually add even more camber up front.
Let’s also consider something else: Even if the car now “pushes”… if the overall grip limit is higher is it not faster?
Setup 1: Stock front sway bar and 26mm rear bar, and the rear comes around at 53mph on corner entry
Setup 2: Bigger front sway bar and 26mm rear bar, now the front starts pushing but not until 55mph
Which one is faster around the track?
Some people also like to point to wheelspin: “Wheelspin on corner exit was worse with a big front bar”.
What if you have more wheelspin because you are pulling more Gs, unloading the inside tire more?
Taking a step back and considering things like this is exactly why capturing good data (at least to the best of your abilities) is paramount to actually making the car faster. Having measurable things to assess in an attempt to take the driver’s feel or bias or consistency out of the equation.
Suspension is a fun and highly debated topic. There are a thousand different ways to set up a car (more of them are closer to wrong than not), and every person will like each one a bit differently even if it’s not necessarily the fastest.
You have to be able to adapt to the setup and potentially change some inputs to get the most out of any change because you're adjusting the shape of the friction circle. There will be more on this in the next article (linked below)… with a more in-depth look at the testing data to show why I came to the above conclusions.
