THSCC Forums

I have run into a bit of a quandary about a handling set up. The track car recently broke a rear sway bracket. I was going to replace the Brackets, but decided to try something since the car has been somewhat tail happy if any aggressive power was applied. Instead of replacing the brackets, I just removed the Aftermarket JR rear bar all together to see how much it would change the set up. The results were mixed. The car now handles great as far as balance and rear traction. I can not get the car to do anything wrong midturn unless I really am aggressive with either on or off throttle applications. The downside is now I have noticeable rear lean, and I have loss some of the sharpness in turn in.

Now, I guess I could go to a stock bar and find a middle ground, but the truth of the matter is its just feel that’s different. I am definitely getting faster exit speeds and the car will do pretty much anything I ask it to now, including a slight drift and/or over steer with either throttle or off throttle applications. It’s just the extra lean that really feels weird mid turn, even though it is still flatter than a stock version. I am trying to decide which is more important to me, actual traction or feel. Given that I bought the car set up and I have limited information of the actual components used, I don’t really have any way to ask about the setup as is.

Thoughts?

Last year at VIR-S, my (now Ryan's) Miata was rather tailhappy, especially going down the Spiral. Traction on corner exit was not great, and it was not the neutral car I was used to. I had coilovers with a pretty stiff rear spring rate (342#) and JR bars front and rear. After being unhappy with the car after day 1, I switched to the stock rear bar on Saturday evening and never went back to the bigger rear bar. Big rear sway bars and stiffer rear springs on a Miata tend to make for a squirrelly car. In an auto-x contect, Les has a similar suspension setup to my old car, and he also went back to the stock rear bar.

If you like the way the car feels with no rear bar, I'd get used to the lean and enjoy your higher exit speeds.

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Tom Freeman
'98 M3/4/5 | '93 Spec3 325i | '12 TSX sport wagon | '03 Tahoe
Team Silver Bullets '91 240SX

That seems to match my experience with the car. It's a 93 Miata

The setup seems to be Koni Adjustables with red springs that feel like 280F/240R. The Front and rear sways were JR red solids. I am concerned about transitions though.

Acctually, by mid-season, I was running no RSB at all, and finished out the season that way. Now that I've softened my rear springs, I did put the stock RSB back on because the car was a bit pushy for my tastes after spring swap. Not sure if it will stay there or not, but I will start the season with a stock RSB, one thing is certain, I will not go back to a large aftermarket rear bar. It was "entertaining" at autocross speeds to be that loose, but I'd think it would be downright scary to have a car that loose at HPDE speeds.

In GENERAL, more rear spring and less rear bar CAN be a good thing. Especially since in many cases rear bar wheel rates are relatively low so it is practical to add enough rear spring rate to make a difference. When I increased spring rates drastically both front and rear on my formula car I disconnected the rear bar. Car kept it's balance just fine and put power down at least as well as before.

One thing to watch out for when removing a rear bar (or going much softer) without adding wheel rate with springs is allowing enough camber change that the car still has oversteer.

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Dick Rasmussen

FS 50 2018 Mustang GT

What is your setup?

FSB?
Shocks?

My setup at Rockingham was 343/343 F/R on Bilstein SPSS's with a 1.125" FSB and stock RSB. With the front shocks full stiff/rear shocks full stiff it was loosey goosey (I didnt mean to have it set like that ). My first session was a bit un-nerving. I ended up with full stiff F/Full Soft rear and it was pretty good.

Im switching to 457/286 for next year (copying Les) with the same sway setup. It should allow for me to not run the shocks full ANYTHING (I have been told its not optimal to run at Max stiff or soft on any shock). At Rockingham, if conditions changed and I needed to tighten the car up, I would have had to take the RSB off, this should allow me some room to play.

The big JR RSB is NOT the way to go if you have stiffer springs than stock. I know Kevin Butler uses a big RSB on his E Stock Miata on track and seems to like it. He runs stock springs though.

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02 Focus SVT
STF 9

I wouldn't worry about it. If it is faster and more predictable, run without the rear bar.

My racecar (probably one of the fastest ITA miatas in the country) is set up as follows:

Front: 650lb springs, shortened and revalved Konis, big ST sway bar
Rear: 350lb springs, shortened and revalved Konis NO sway bar

It just worked better that way. I always had trouble getting power down with a rear bar. Now, this season I am going to put it back on the car for ballast purposes, but I am only going to connect one side.

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Bowie
President, Conover Motor Sports
http://www.raceconover.com

Yeah, with stock rear springs rates at ~100 lb/in you have to do something to loosen up the car. Otherwise you'll never be able to get it to rotate. Believe me, I tried every thing before plunking down for the Racing Beat 5/8" RSB.

This car I'm currently preparing is all new territory to me. I have no idea were to begin with setting up a coil over suspension, but it should be fun. I guess it's time to see what kind of springs I have on the car. I guess I'll start out with the stock RSB and if need be, I can always remove it.

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“I feel safer on a racetrack than I do on Houston's freeways.” - A.J. Foyt

Kevin Butler
Mobetta Autosport Spec E30 #612
2003 C5 Z06 Corvette
AFR Miata, SM2 61, '93 w/200 SC'd RWHP - soon to be resurrected
Waaaay too many other projects....

Looks like the spring rates on my '93 are 375 F, 250 R. It's got an Adco 7/8" FSB and stock on the rear. If I can get a '95 15/16" FSB to fit, I'll try it out. Since I've barely driven this car, I have no idea where the shocks are currently set. They're Koni SA's.

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“I feel safer on a racetrack than I do on Houston's freeways.” - A.J. Foyt

Kevin Butler
Mobetta Autosport Spec E30 #612
2003 C5 Z06 Corvette
AFR Miata, SM2 61, '93 w/200 SC'd RWHP - soon to be resurrected
Waaaay too many other projects....

I'm far from the expert, but a couple of things to keep in mind .... you pick springs based on the stiffness you desire. If you want to mimick the factory balance then use the same relative front to back spring rates and the same bar sizes. Stock Miatae have a roughly 1.5:1 front to rear spring ratio (150-/97 lbs/in IIRC) so keep that 1.5:1 ratio if you want the stock bars to be close. The springs on mine are something like 505/324 (9/6 kg/mm) to keep the same 1.5-1 ratio. I use the FM front bar (1") full tight and the FM rear bar (5/8") full loose . The car will tend to drift the rear end under power when turning in fairly aggressively at relatively high speeds. A touch of countersteer and its back to neutral. If you take stiffness out of the rear (smaller or no bar) the car will tend to push more on slow corners.
You can certainly increase the front springs above the 1.5 ratio and decrease the rear bar stiffness to help getting power down as Bowie suggests. Its the total spring plus bar stiffness ratio thats important from a balance perspective. And remember that bar stiffness is a function of the diameter of the bar to the fourth power (i.e. a bar that twice as thick is sixteen times as stiff). If you're tuning something that's close, then adjusting the length is typically easier. Assuming you can get the darn holes to match the end links. Mazda comp has heim jointed adjustable length end links if you need them.
I tend to try and get things close, then appreciates Ron's advice to "deal with it" . Imagine jumping into a something like a 911. My first track day was at a rainy Roebling. My instructor took me for a ride in his 911 on slicks. The only time the steering wheel was pointed straight ahead was during the transition from countersteering left to countersteering right ,,,

Frank