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Are sta-bars still used for roll resistance in non-aero racing? If so, why?

Are sta-bars still used for roll resistance in non-aero racing? If so, why?

Are sta-bars still used for roll resistance in non-aero racing? If so, why?

(OP)
Following a couple of threads here on sta-bars, I understand the need to increase roll resistance (without uncomfortably high ride rate) to meet passenger comfort expectations and prevent excessive camber gain, which would reduce tire grip. In aero racing, aero devices require ride height and body attitude control at the expense of any other considerations.

Rather than allowing the outside suspension to compress and the inside suspension to droop, sta-bars compress the inside suspension, keeping passengers and tires comfortably level.

However, the load on the outside tire unloads the inside tire through the sta-bar. This increased load transfer reduces total grip available on that axle, and thus the sta-bar can “provide a convenient means of track-side chassis tuning (1999-01-2257). However, I’ve read “Generally, you want ~2/3 of your roll stiffness from springs and the remaining ~1/3 from bars for a performance oriented set-up.”
Such a large proportion of roll stiffness from sta-bars would appear to significantly increase load transfer and thus sacrifice quite a bit of ultimate grip, and a large sta-bar presents a packaging challenge, and weight and serviceability penalties. The cumulative stiffness rate also undesirably applies to one-wheel bumps rather than just cornering.

Wouldn’t it be better to achieve gross under/oversteer with tire selection? A narrower and thus lighter and cheaper tire (and thus wheel) could achieve similar restriction of lateral grip at that axle while still providing sufficient longitudinal grip for braking (my 1g braking front load is 20% lower than 1g lateral).

For suspension control (and specifically camber gain, in this question), it appears that integrated spring aids (first bump stops and now bump springs) are standard setup in stock car racing. In fact, stock car suspensions now seem to be set up to ride on the bump stops for aero and suspension control. Why not design to touch down on soft (say 80-100lbf/in) progressive bump stops to prevent excessive camber change? The total effective spring rate required to do so should be equivalent whether from springs alone, or springs and sta-bar, or springs and bump stop.

But using the bump stops for camber control would give the mechanical grip advantage of soft springs without sacrifices of lateral grip and suspension independence, and without the packaging challenge and weight and serviceability penalties. Are sta-bars just a vestige of OEM passenger applications, perpetuated by “tuners”?

I am curious to hear your thoughts.

RE: Are sta-bars still used for roll resistance in non-aero racing? If so, why?

Sta bars are used on race cars because they can easily be adjusted at the track. In theory with a clean sheet of paper there is no necessity for a sta bar, yet in almost every performance oriented program I've worked on they crept back in.

Using ride aids/ jounce bumpers or whatever is not quite as easy as you'd like it to be. The rates are typically very non linear as the bumper engages, and they tend to have a lot of hysteresis

This type of foam ones in particular are robust, but tuning them is a black art. note the compression rings in some of them

https://encrypted-tbn0.gstatic.com/images?q=tbn%3A...

Cheers

Greg Locock


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RE: Are sta-bars still used for roll resistance in non-aero racing? If so, why?

(OP)
Thanks Greg. Yes, it would seem that just enough roll stiffness from sta-bar to tune under/oversteer for the expected environmental conditions would be ideal. 1/3 of roll stiffness from sta-bars seems excessive, and I'm thinking specifically of the ubiquitous advice to fit a bigger sta-bar for better handling, and which are never adjusted.

Bump stops do seem to have an initial near-linear response before an exponential increase. If you're referring to damping them, clearly they cannot easily be damped without some sort of position-sensitive active damper. Or perhaps that's not true: with a digressive damper, the foam bumpstop would decelerate the piston velocity, eventually enough to return the damper to the high-force damping region.

Further, there is a class of (junior formula?) racing that utilizes rubber pucks for both spring and damper duty. Are foam bumpstops likewise self-damping?

RE: Are sta-bars still used for roll resistance in non-aero racing? If so, why?

Your initial Comment contains reference to passenger comfort and racing. These are two different venues.

You presume that inside to outside load transfer diminishes the net sideforce available to the axle. This is not always true, especially with 'performance' vehicles (cars and SUVs etc) which use tire sizes larger than normally specified to get the transient response AND ride comfort to be other than dismal. Because they have so much higher load capacity, adding load transfer can make the pair stickier. Meaning that their roll distribution is often backwards.

And, using bars to reduce camber is a pretty ignorant statement to make in stereotyping modern vehicles. If your car rolls more than 6 deg/g these days, and you cut that in half, the change in camber is pretty small. That couples with the low camber stiffness of radial tires means diddly squat these days.

But then, are 'racing tires' radials, or is that just what the paint on the sidewalls says ? Burn one and find out for yourself.

RE: Are sta-bars still used for roll resistance in non-aero racing? If so, why?

Quote (EricPSS)

Such a large proportion of roll stiffness from sta-bars would appear to significantly increase load transfer and thus sacrifice quite a bit of ultimate grip, and a large sta-bar presents a packaging challenge, and weight and serviceability penalties. The cumulative stiffness rate also undesirably applies to one-wheel bumps rather than just cornering.

I am sensing a mis-understanding here. If ARBs are used to stiffen both ends of the car equally, the load transfer does not increase. Load transfer only increases where roll stiffness is increased at one end of the car relative to the other. In this situation the increase in load transfer at the stiffer end is compensated by a reduction in load transfer at the other.

je suis charlie

RE: Are sta-bars still used for roll resistance in non-aero racing? If so, why?

(OP)
Thanks ciba,
Indeed, comfort and racing offer conflicting design objectives; I was trying to acknowledge the benefits of sta-bars in both while narrowly defining the present inquiry to non-aero racing.

"Because they have so much higher load capacity, adding load transfer can make the pair stickier."
And adding your explanatory quote:
"And there are cases in which the tires on a vehicle having VERY large load reserve (They are way under their rated load capacity) do just the opposite. It these cases, you will sometimes see that adding an anti-rollbar WILL increase the grip of the pair of tires up to a point. Corvettes come to mind in this case. Their tires 'like' increased vertical load up to a limit. Pressure, rim width, and construction details influence this trait. And this phenomenon can easily be lost in some (most) forms of tire math models which can not accomodate a linear or increasing stiffness tire trait. It's there in the raw tire test data but not in the analysis. Oops. From there on out, it's lies, untruths, urban legends, dogma and blatant ignorance. In God we trust, all others bring data..."
This very much seems like an edge case on a poorly-optimized "tuner" street car. I don't expect it would apply with properly-sized race tires.

"using bars to reduce camber is a pretty ignorant statement to make in stereotyping modern vehicles. If your car rolls more than 6 deg/g these days, and you cut that in half, the change in camber is pretty small. That couples with the low camber stiffness of radial tires means diddly squat these days."
I don't mean to stereotype modern vehicles; in fact, my application is quite atypical. Even if I limit roll to 5deg, outside camber swings from -2deg to +2.9deg.
So this is a substantially interesting problem.

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