austincrx

I am debating removing the rear swaybar. This isn't a street car, only runs on track with SCCA. I have spring rates of 900F and 750R and am looking for a little more grip in the rear, but can't make my mind up if should remove the rear swaybar. I ma thinking I will need to increase the rear spring rate a little so the increased compliance in the rear doesn't cause an understeer scenario, maybe up to 800#. I know a lot of people run 900 or 1000 on all corners, but you can't really make a spring rate comparison without knowing the swaybar setup. I'm running the factor swaybars F&R right now, and the front has some wash-out on corner entry sometimes, but I think that is either the driver or setup (a little more front toe-out should help that).
What are your opinions?

spdracerut

I'm running 12k front / 10k rear springs. Thicker Whiteline front bar, no rear bar. -2.8 front and rear camber, 0 toe front, 1/16" total toe-in rear, AP2. I'm really happy with the handling balance. No aero work.

So it sounds like you're have a bit of understeer on turn-in? I would probably just adjust your rear toe-in and reduce it 1/16" and see how you like it. I'd leave the rear bar alone for now. However, it's easy to disable the rear bar by just removing one endlink, so you don't have to remove the whole thing if you just want to see how it handles. But from the sounds of it, you're already understeering and removing the rear bar will just make it worse.

Mrsideways

It will be a push machine. Run a MX5 bar

Afterfire

I went from doing autocross to tracking and left my rear bar unhooked with the mindset that I would want that roll for more grip since I have a 16f/r spring rate, non staggered 200tw's, no aero and big fsb with factory 06 rear bar. The rear seemed to wallow and roll more(obviously) and I couldnt really compare the feeling from autox to track because of the speed differential but, long story short, when I reattached my rear bar it made a pretty significant difference on turn in. It became easy to rotate under braking but not so much it was uncontrollable. Brake hard before entry, slight turn in gets the rear to come around, point and shoot. With the bar unattached I felt like I could roll into the power before the apex (depending on corner) and still have some roll to give but after the change I prefer the rear bar on. Everybody is different. Play with it and see what works for you.

DavidNJ

Which class? Which corners on which tracks does the front wash out on? Are you trail braking on those corners? Are there corners where the car handles ok?

If it is a generic push on entry, shifting the roll stiffness to the rear will change that. Bars vs springs are a function of how much roll stiffness is needed vs pitch/squat control vs. ride stiffness. A lot of S2000 racers seem to like stiffer springs over stiffer bars, from some posts in order to increase platform stability (reduced pitch and squat). Some formula cars and sports racers take that further by adding a third heave spring that only works when both wheels are in bump or rebound.


There are a lot of factors including tires, geometry (in this case, dependent on ride height), spring rates, bars, wedge, and shocks. And aero, whether or not it is stock or not; if it is washing out on fast turns it could be aero lift. Some things are easier to adjust that others. Springs are a PITA requiring disassembly of the suspension and setting the cross weights and ride height. Alignment changes can be complex, minimally requiring a toe-in check; some aftermarket upper control arms use shims for camber adjustment, making quicker and simpler. Many anti-roll bars are easily adjustable in the field (Karcepts, Gendron, Ankeny). Shocks often have an easily adjustable low-speed rebound adjustment. How linear it is depends on the shocks.

Bilstein has a guide to adjusting the shocks on page 7: http://www.bilsteinus.com/fileadmin/...g_2015_web.pdf

austincrx

The front does wash on corner entry, but I feel that may be a driver issue. Heck, the whole thing may be the driver. The car will oversteer anytime you want, not hard to get it to do that. Mid corner to corner exit is where it oversteers most often, but like I said a little heavy on the throttle and the car will oversteer almost anywhere, even at 40 mph in 3rd gear on corner exit with race tires. That's what has lead me to think removing the rear swaybar could help, especially given the soft springs in the rear.
The understeer happens on corner entry, slow speed corners where aero isn't helping, and it probably has more to do with the steering input being too fast than the car actually being prone to understeer. Although, once it starts to push, it has a hard time 'un-pushing'.

Anyway, I'll start with the camber and toe settings. I'm wary of adjusting the rear to have too little toe-in because the car is already a little hairy in high-speed 'kinks' like the one at Carolina Motorsports Park. Coming through at 115 and going into a full drift isn't what I want to become the norm.

austincrx

The drop from 400 lb/in deflection (2002 MY s2k factory rear bar) to 130 lb/in deflection (sourced from a quick google search for MX5 factory swaybar stiffness) seems like a big jump. Are any MX5 bars around 200-300 lbs, or is there a way to stiffen the factory bars (I've seen people drill extra holes in them)? Or maybe just a 2008-2009 non-cr rear bar (~350 lb/in).

Or perhaps it would be better to try a slightly stiffer front bar, as my codriver commented that the car seems to have a lot of body roll. I never noticed it in the past, but now I can tell that it does roll somewhat significantly.

spdracerut

Ah.... if it's oversteering from mid-corner, yeah... It's an easy 5 minutes to jack up the rear of the car and disconnect one end-link to the rear sway bar effectively disabling it. Drive it like that and see how you like it. If you don't like it, it's easy to reconnect. It will at least tell you if you're heading in the correct direction or not.

As for the corner entry push, you're probably just going too fast. You can trail brake a bit to get the front to turn in better too.

ZDan

If you're running a lot of rear toe, you might knock that down first and see what that does for you. I was worried when I went from 0.64° total rear toe to 0.15° total, but the handling became more consistent and linear, while also being more responsive.

Regarding rear sway, you could disconnect one end link (eliminating swaybar function) and see what that does for you.

thomsbrain

I'm an advocate for using spring rates tuned for ride frequencies that produce synced movements at a target speed, ditching the rear bar, and using the front bar to fine-tune handling balance based on available front/rear grip.

High-speed handling with no aero will always be tricky, as the car will get looser the faster you go due to the natural rear lift. You have to choose what balance of neutral low-speed handling and neutral high-speed handling you want. My car can get the power down full throttle coming out of corners in 2nd so it has plenty of rear mechanical grip but it gets a little spooky at 100 MPH due to the lift without any aero mods. I could dial in more push but then the car wouldn't rotate through lower-speed corners. There isn't a perfect solution without a wing.