Roll stiffness: Springs vs anti-roll bars?

[Dimman]

So the rear bar removal has to do with the nature of a Torsen where a completely unloaded side ends up getting all the power like an open diff, and the nature of aggressively hitting curbing is putting that wheel in the air?

[fatoni]

Originally Posted by Dimman

So the rear bar removal has to do with the nature of a Torsen where a completely unloaded side ends up getting all the power like an open diff, and the nature of aggressively hitting curbing is putting that wheel in the air?

basically. you see this all the time in the miata world simply because of the lack of droop caused by the sway. you are bound to see this a lot more in an autox setting though and while i dont have any track experience with the frs but i would suspect improper rebound or inadequate spring travel to be the primary cause while the sway removal is a really good bandaid

[7thgear]

Originally Posted by fatoni

that doesnt make any sense. if there was more roll and now there is less roll, it reduces roll.

it reduces the visual roll, it does not address the underlying problem

or i guess i should say the underlying goal, which is to increase grip

but people prefer to deal with the easy stuff first so whatever.

[fatoni]

Originally Posted by 7thgear

it reduces the visual roll, it does not address the underlying problem

or i guess i should say the underlying goal, which is to increase grip

but people prefer to deal with the easy stuff first so whatever.

visual roll as opposed to what? sway bars can absolutely increase grip but i think what youre trying to say is that sways are often used as a bandaid and frequently poorly executed. if that is the case than i agree but sways are important, especially for cars that are designed to use them

[Element Tuning]

Remember what i said about generalizations and realize i am speaking about our setup which is what you would see on a professional race car, not a dual purpose street/track car.

With that said I'm not very low at all because race cars need suspension travel and I'm on a relatively tall tire package. At the Ultimate Track Car Challenge you need to be fast out of the gate and i didnt want to risk tire rub or a cut tire.

Droop is important and sway bars reduce that ability when turning. This is why i had to pull the bar (pulling inside wheel up). It was already happening with stock suspension and slicks and oem droop is huge.

I have a couple friends that race professionally, one was Auberlins teamate at Turner and Joey Atterbury who races Cameros for Mitchum and now for Roush was at VIR this weekend. Its nice to be able to bounce your findings and ideas with those involved in higher forms of motorsport because information isn't shared much in that realm. Sometimes you need the rear bar for certain tracks and other times you don't. Sometimes you run super soft springs and sometimes really stiff. You do what sets the fastest lap times.

At VIR i was running 2:19.xx with the bar on. Tweaked front and rear suspension clickers in a effort to tame the inside rear lift. Given I've had this problem on our other race car i knew taking the bar off would help but would it cause push or require excessive steering input? Nope the rear inside grip was there allowing the Torsen to work, therefore i was on the gas much sooner and harder plus hitting the curbs was no longer a death sentence. The result was a low 2:17.

[Element Tuning]

Originally Posted by Matt Andrews

2 seconds where?

that is a ton of time on just about all east coast tracks. I wonder how much of that could be made up with a clutch pack diff. Tuning around a torsen sucks.

A lot of this comes down to driver preference and what makes them comfortable. I like rwd cars that roll in the back. generically, guys that come from karting seem to like a really stiff rear.

Yeah I was really hoping this diff would work for us but we may have to go with a clutch type.

As far as rear roll stiffness the fastest and I mean rediculously fast rear wheel drive cars typically pull the front inside wheels up. I will have to wait and see some action shots of the car but at this point i can afford to go softer in the rear because my front end is phenominal. We are not yet running downforce however so we may be where we need to be. I was dancing with the devil in the uphill esses and exiting turn 10. Front aero is good but the rear is clearly getting light around the 100 MPH turns.

[jamal]

Originally Posted by Element Tuning

Droop is important and sway bars reduce that ability when turning. This is why i had to pull the bar (pulling inside wheel up). It was already happening with stock suspension and slicks and oem droop is huge.\

How does your droop travel compare to stock?

[mla163]

For reference, I removed the rear swaybar from my STR miata. It was too tail happy with the sway. I took it off and I dropped time. Not because the suspension was better, but because the car didn't want to swap ends as much. Techincally, my original setup could have been faster, but when you are backwards you don't go any faster.

OP, to answer your question, both sways and springs reduce body roll (or fight it, I'm not sure there is a difference). A sway bar is basically a torsional spring. Typically these two are used in conjunction with one another to tune the suspension. If you wanted to change just one element, changing sways is easier to live with and cheaper. The suspension isn't any more harsh in straight line driving, but it is stiffer in turns. The down side is that if you hit a bump in mid corner, the suspension isn't as independent as a car with stiffer springs and a lighter bar.

In tuning racing suspensions, there are differing opinions between stiff springs, soft sways or soft springs, stiff sways.

Changing springs opens up a new list of items - are shocks still adequate for the stiffer springs? do you have adequate suspension travel? how is geometry and camber curve affected? etc.

Sways are the easy button. These are typically a first suspension modification

[Element Tuning]

I've mentioned this elsewhere but the oem setup is very good and I think much of the aftermarket parts can make it worse. There are a few people/companies that are out there testing on the autocross or race tracks to make sure gains are made.

In my case the car felt great with our without the sway bar and wasn't appreciably different in terms of balance. The only real issue was the inside pulling up and the differential unloading so I couldn't accelerate.

I might go a little softer in the rear without a bar until I add downforce. This type of rear suspension gains a substantial amount of negative camber as it compresses which can help with grip. A softer spring is also going to give me a little more droop but if not I'll have to try and squeeze a helper spring in the rear but the shock is just so short the spring it will have to be short.

[Element Tuning]

Originally Posted by mla163

For reference, I removed the rear swaybar from my STR miata. It was too tail happy with the sway. I took it off and I dropped time. Not because the suspension was better, but because the car didn't want to swap ends as much. Techincally, my original setup could have been faster, but when you are backwards you don't go any faster.

The difference here is that you had too much rear bar and this reduced grip causing the car to be tail happy so either your setup was off or removing the bar was ideal on the FRS the issue is that the sway bar causes the differential to unload but the chassis had grip (off the curbs) but poorly put power down.

We can be hypothetical all day long but we pulled 8 seconds a lap out of the FRS with no power adders so clearly we are on to something. In race trim with the oem diff this is working but my setup is too much for street tires or street use. There is a compromise in there for a street car which I'm going to explore.

[Matt Andrews]

I suspect the up hill Essex felt spookily without the rear bar and no rear aero. What slick were you running? Any specs on the car? Those are quick times at vir with stock power. Really curious about e rest of the setup. I haven't been there is while, I'm envious.

I'm testing at buttonwillow this weekend, definitely not the same caliber of track, and we'll be on rs3's so while there are some low speed off camber tight turns, I'm hoping the Torsten limitations dont show up...

[jamal]

You going to have the ASTs for it?

[Sam Strano]

There always have been, and always will be two schools of thought on this. I'm a more moderate type. I see validity in both big springs and at times big bars. It's not absolute, and can vary on the car, and the use. At times I use big bars and softer springs at one end, but will use a moderate/moderate mix at the other.

I don't believe that either extreme is the right answer. Bars help a lot with roll stiffness and are quite effective and keep you from having to run massive rates meaning you can have a things work better on imperfect surfaces. But bars do try and lever up on the inside tires, which is not ideal in a perfect world (good thing we don't live in one). Also remember that the stock bars on this car as quite small and some stiffness will be gained with very little harm. It's not like we are starting with say, 32mm fronts or 22mm rears, etc.

Add to this what you guys do with springs. BOTH springs and bars add wheel rate, you have to consider the total amount of each and watch yourself.

Now, RWD cars with diffs, I'm used to. I know what I think is best, and I think a little bigger front bar is part of that. I'm currently working on a 22mm front bar. Eventually, I will also offer different links and an adjustable version as well. I'm not as hot on a bigger rear bar, but I'm exploring options and likely will do something in the 16mm range *to be used with the bigger front, not on it's own*.

I live in PA. I will not run ballistic rates on springs, no way on a street car, and I have never had to go as nuts as it seems 80% of the world does even on dedicated track and autox cars.

[Element Tuning]

Originally Posted by Matt Andrews

I suspect the up hill Essex felt spookily without the rear bar and no rear aero. What slick were you running? Any specs on the car? Those are quick times at vir with stock power. Really curious about e rest of the setup. I haven't been there is while, I'm envious.

I'm testing at buttonwillow this weekend, definitely not the same caliber of track, and we'll be on rs3's so while there are some low speed off camber tight turns, I'm hoping the Torsten limitations dont show up...

The esses felt better to me without the rear bar since I didn't have to avoid the curbing and therefore I was going straighter. I typically race a high downforce car and I could feel the aero lift at the rear in the high speed stuff. I think for a lot of weekend track guys that don't want a wing a huge diffuser will do the trick. Take if off for daily use. None the less I was WOT from the exit of turn 4 at VIR to the entrance of turn 10 so no time to be gained there with more DF, just a little more stability. The DF will help elsewhere though.

GRM photoshoot at the Ultimate Track Car Challenge:



18x10 wheels on 285/645-18 Hoosier slicks, Element custom valved BC BR Coilovers, Brembo STi front brakes, Hawk DTC70 front, Carbotech XP-12 rear. Junk in the trunk removed, cat-back replaced with dump pipe, and the battery replaced with Odyssey.



Sorry guys not trying to make this a "me" show here.

As Sam mentioned you have to take your application and make compromises to get the best overall setup. If I'm building a street car we typically will run soft springs, higher valving, and bigger sway bars. For a race car much higher spring rates, and conservative on the rear bar. Like Sam, I find front roll stiffness needs to be controlled more than the average person thinks especially with the MAC strut. A stiffer front end will help push down the rear and will also control the camber curve up front.

If you are running tires with the grip level I've got I think running a rear bar at all is going to be tough keeping the Torsen. For my personal race car my next step is to drop down a little softer on the rear spring and squeeze in some helpers to increase droop. I also want to go about .5-1" lower but for me to do this I will have to cut my rear fenders (but I have flares so it will still look fine).

8 seconds a lap is a huge amount of time to accomplish with some good estimations on spring rate, valving, and only 3 sessions to sort it out. No doubt more time can be shaved if I can power on sooner.