Swaybars vs. Coilovers

[rwh11385]

First place I'd look to reduce understeer on these cars is a larger front bar......

Excuse me? A larger front bar will promote more understeer.

-Erik

I'm with DSP74. Only because Brian Watts is as well. Basic theories cannot always explain reality as simply as you would like. There are factors not always included that DSP and Bwatts understand in this counter-logic.

Depending on your car a swaybar can have different effects I think. If you have tons of understeer and body roll a stiff front bar might help it turn better. Because it can keep the footprint of the tire properly on the pavement. But for a car that already has a good tire footprint a stiff front sway bar could actually hurt(more understeer). I think it has to do with how the car is before you install the sway bars.

The natural effect of a front bar is to induce understeer, jsut as the natural effect of a rear bar is to induce oversteer.

But there are many more variables, as elh alluded to. With our massively camber challenged cars (Subarus are very much like BMWs in the front strut department), a bigass front bar controls body roll which helps transitional response and keeps the front tire(s) gripping without absolutely stupefying camber settings. Ergo, a front sway decreases understeer for most BMW suspensions.

And so on and so forth...

Anti-roll bars are just a different kind of spring. They add spring rate. Depending on your camber up front, a little extra spring rate can actually increase grip by keeping the tire happy instead of allowing the suspension to roll too much into the bad portion of the camber curve where very little camber is gained. With sufficient camber and spring rate from your coil springs, a stiffer front bar will generally produce understeer as you would normally expect.

Looks too soft on the front to me. Considering your limited front camber, I would think about stiffening the front spring rate or front bar to see if that helps. Seems counter-intuitive, but it has proven to work on these cars at times due to limited camber, poor camber curves, and roll centers that fall quickly when lowering the car.

Not everything in life can be summed up by simple equations and rules.

[JeffRR]

Sorry I tend to ramble. I'll try to keep focused.

Last year for the FSAE competition we ran our car with no front or rear swaybars, only superstiff springs. We got hammered by the judges for that reason, that although our car was responsive and felt good driving, it was not anywhere near as good suspension-wise as the other teams that combined good sways and springs. Although our car was far more responsive without the sways, it was a bitch and a half to drive well at the limit due to the lack of sways-- we were relying on the springs to do the job of both spring and sway, and that really did not work.

Stiffer springs make the car more responsive to driver inputs, but does not necessarily make you quicker. Stiffening one end will increase lateral weight transfer on that end, which in turn results in less grip on that end but more on the other end. They will also decrease body roll and pitch. Stiffer springs also have the disadvantage of making the car more difficult to drive and much less forgiving of errors when pushed to the ultimate limit.

Similarly, stiffening the anti roll bars (ARB, swaybars) will again increase weight transfer on the stiffened end, but will decrease grip accordingly. You will have less body roll again. The bars will make the suspension much less compliant and more susceptible to bumps.

For the stuffer = under/oversteer argument, here's what actually happens:

Take an bone stock car. You decide that you want to increase the rear ARB stiffness for no particular reason. What happens dynamically is the rear wheels have an increase in weight transfer, a reduction in body roll, and less grip. By stiffening the rear bar, you increase grip on the front. Since the front tire contact patches have more grip than the rears, the car tends to oversteer.

Now you return the car to stock and then swap the front bar for a stiffer one. You now have the reverse situation: more weight transfer up front, less front grip, and less body roll. You have also increased the rear grip to where the rears can overbalance the front contact patches, resulting in understeer.

As for DSP74 and JeffRR's example of an FWD car increasing front bar to decrease understeer, my only guess(shooting in the dark so bear with me) is that they matched the front sway to the springs in the OE Sport package, which would tune out the understeer.

I'm going to say that especially on a tight auto-x type course (such as FSAE) a car with shorter delay (response to driver inputs) will always be faster than a softer car with longer delay. A simple test is a slalom, assuming you have 2 different balanced set-ups drive each one and pay attention to the time between you turn in for the gate and the delay to the front response and then the rear response. It might be difficult to detect subjectively if you can't evaluate back to back, but you will be faster with the stiffer, balanced set-up.

As for my example of the production sport package, the reduction in understeer was noted with only a front bar increase. Going back to what DSP74 pointed out that if you reduce the total roll you'll also reduce the amount of camber change during that roll.

Some general rules of thumb for non-aero cars:
Front ride rate: ~2hz
Rear ride rate: ~Front Fn + 15%
Bars: Approx 50% of total roll stiffness

[Charlie]

Excuse me? A larger front bar will promote more understeer.

-Erik

Yes and no. In a purely textbook world, yes, a larger front bar will simply cause more understeer. However, with the lawyerriffic front suspension designs of many modern cars and their weird camber curves & geometries, a lot of them will actually experience better front bite & turn in with a larger front bar, it's part of the reason that the SCCA allows a front bar in "stock" class autoxing.

<Ninja edit, damn, I should read the whole thread before posting>

-Charlie

[uofom3]

anyone running something like 600f/750r care to comment on handling and ride quality?

firm, damn firm.

and it handles like mad compared to anything else I've run on it... particularly once you get it dialed in with the koni's

[nando]

firm, damn firm.

and it handles like mad compared to anything else I've run on it... particularly once you get it dialed in with the koni's

streetable?

are your konis OTS or custom valved?

thanks

[DSP74]

There is an important point to make and that is you can't always read a book and apply everything in it to go faster.....

What camber angle requires a stiffer bar? You know that is damn hard to say. For one tire size will VERY, VERY heavily influence how much negative camber is actually needed. On top of that spring rate, track width, ride height, vehicle weight, and lots of other factors....I'd guess that for most folks -3 to -3.5 is about right. Maybe a little less for stock sized street tire type tires.

[DSP74]

streetable?

are your konis OTS or custom valved?

thanks

IMO custom valved Koni's are a waste....Most shock dyno charts I've seen show that they simply are very non linear in adjustment. On top of that the compression adjustment does almost nothing and almost all of that nothing comes at high speed displacements......So basically you are paying a bunch of money for DA's or adjustable DA's for NO reason....

What I've settled on is 450lb fronts with a 25mm I/E adj bar. Nothing much to write home about here. A simple short body Koni SA will do the job fine. We aren't trying to do anything dumb with the springs.....And the stock SA's will have plenty of damping to handle those springs. The car will be PLENTY responsive with 450's the big bar, and rebound cranked up.

Out back WE ARE TRYING TO DO SOMETHING DUMB WITH THE SPRINGS. We are trying to get all of our roll resistance from the springs, and none to only a tiny amount from the bar. We don't want much of a rear bar because it will tend to lift the inside wheel off the ground. A wheel lifted is a wheel spinning. And a spinning wheel doesn't give any forward thrust.:!:

Since we are using all spring and no bar the car will be much more sensitive to compression damping. And we need a shock that has a workable ajustment range, in LOW SPEED compression. Options include some REALLY EXPENSIVE race Koni's, Ohlins, Penske, Moton, and less expensive Advanced Design, and AST.....

For the rear I'm going to start with 600lb springs and no bar and drop down as HP goes up. And who knows I may even stay at 400/600 even with big power, simply because of rear tire choice.

[Bimmerman325i]

IMO custom valved Koni's are a waste....Most shock dyno charts I've seen show that they simply are very non linear in adjustment. On top of that the compression adjustment does almost nothing and almost all of that nothing comes at high speed displacements......So basically you are paying a bunch of money for DA's or adjustable DA's for NO reason....

Out of pure curiosity and ignorance on my part, are the compression and rebound high or low speed adjustable on the SA/DA Konis? Are the Koni's you mention the same as is sold by TCKline in their kits?

We are trying to get all of our roll resistance from the springs, and none to only a tiny amount from the bar. We don't want much of a rear bar because it will tend to lift the inside wheel off the ground. A wheel lifted is a wheel spinning. And a spinning wheel doesn't give any forward thrust.:!:

I agree with you that a wheelspin is counterproductive to forward travel. Is it possible/practical to use a soft tender spring in addition to the stiff spring so that your wheel will not raise under cornering?

Since we are using all spring and no bar the car will be much more sensitive to compression damping. And we need a shock that has a workable ajustment range, in LOW SPEED compression. Options include some REALLY EXPENSIVE race Koni's, Ohlins, Penske, Moton, and less expensive Advanced Design, and AST.....

Again out of curiosity, are the race Koni's you mention the same as the DA's commonly sold? There is bigger car-setup tuning changes that can be done with low speed comp/rebound damping than with high speed.

[Bimmerman325i]

I'm going to say that especially on a tight auto-x type course (such as FSAE) a car with shorter delay (response to driver inputs) will always be faster than a softer car with longer delay. A simple test is a slalom, assuming you have 2 different balanced set-ups drive each one and pay attention to the time between you turn in for the gate and the delay to the front response and then the rear response. It might be difficult to detect subjectively if you can't evaluate back to back, but you will be faster with the stiffer, balanced set-up.

As for my example of the production sport package, the reduction in understeer was noted with only a front bar increase. Going back to what DSP74 pointed out that if you reduce the total roll you'll also reduce the amount of camber change during that roll.

Some general rules of thumb for non-aero cars:
Front ride rate: ~2hz
Rear ride rate: ~Front Fn + 15%
Bars: Approx 50% of total roll stiffness

Thanks for the guidelines. By front/rear ride rate, what do you mean?

We did try both with and without antiroll bars in the two days we had to test before going to comp. I was not a driver at that point so I have no feedback on how I think it felt with the bars, as I have only driven it without them.

When we were testing the car the drivers said it felt faster without the bars and that the car worked amazingly well in slalom(which it did). They said the car felt much more balanced without the bars, and tuned the suspension using the damper rebound and compression adjustment only. We did not do any timed runs to quantify the drivers' feelings on the car setup, so it is purely subjective.

As for the understeer lessening with the addition of front bar, I'm quite surprised by that being the sole change. The bit about less camber change in roll with a stiffer bar, thus more grip, does make sense though. Strut suspensions really have some odd issues with the geometry.

[DSP74]

Out of pure curiosity and ignorance on my part, are the compression and rebound high or low speed adjustable on the SA/DA Konis? Are the Koni's you mention the same as is sold by TCKline in their kits?



I agree with you that a wheelspin is counterproductive to forward travel. Is it possible/practical to use a soft tender spring in addition to the stiff spring so that your wheel will not raise under cornering?



Again out of curiosity, are the race Koni's you mention the same as the DA's commonly sold? There is bigger car-setup tuning changes that can be done with low speed comp/rebound damping than with high speed.

I'm not sure how Koni markets the sport shocks but the rebound adjustment is low speed.....Compression adjustment doesn't seem to be. And this is at least on two entirely different cars. 3300lb Camaro vs 2800lb E30. Same basic design from TCK. The initial valving may differ from say a standard Koni sport or a Ground Control sport, but the actuall adjustment is the same. Low speed rebound, medium to high speed compression.

Yes juggling spring length, ride height, spring seat, and tender spring rate and height is one area I'm going to give some serious attention to. For one thing these car WILL lift an inside front and there isn't much of anything to do about it. But as soon as you lift a rear you are on two wheels. Not confidence inspiring to be sure. Much less fast.

I beleive it's the 28 series Koni, and again I think TCK sells those for the rear of BMW products. They 'may' sell the rebound adjustable only version however and I can't be sure without checking. They are not the standard sport version but an aluminum body large piston monotube design.

[nando]

IMO custom valved Koni's are a waste....Most shock dyno charts I've seen show that they simply are very non linear in adjustment. On top of that the compression adjustment does almost nothing and almost all of that nothing comes at high speed displacements......So basically you are paying a bunch of money for DA's or adjustable DA's for NO reason....

What I've settled on is 450lb fronts with a 25mm I/E adj bar. Nothing much to write home about here. A simple short body Koni SA will do the job fine. We aren't trying to do anything dumb with the springs.....And the stock SA's will have plenty of damping to handle those springs. The car will be PLENTY responsive with 450's the big bar, and rebound cranked up.

Out back WE ARE TRYING TO DO SOMETHING DUMB WITH THE SPRINGS. We are trying to get all of our roll resistance from the springs, and none to only a tiny amount from the bar. We don't want much of a rear bar because it will tend to lift the inside wheel off the ground. A wheel lifted is a wheel spinning. And a spinning wheel doesn't give any forward thrust.:!:

Since we are using all spring and no bar the car will be much more sensitive to compression damping. And we need a shock that has a workable ajustment range, in LOW SPEED compression. Options include some REALLY EXPENSIVE race Koni's, Ohlins, Penske, Moton, and less expensive Advanced Design, and AST.....

For the rear I'm going to start with 600lb springs and no bar and drop down as HP goes up. And who knows I may even stay at 400/600 even with big power, simply because of rear tire choice.

A) I don't have a 325i, so your chosen spring rates don't really apply to me ;)

I was more interested in if konis would be able to handle my chosen rates - short body housings, DAs, 25mm front bars, and all that stuff doesn't help me at all.

B) I've never seen an E30 lift a rear wheel - even my car lifts front wheels when provoked. Every E30 I've seen lifts the inside front, I'd like to know what you're doing to lift the inside rear! (although wheel lifting is definitely a problem)

[DSP74]

Cusom valved Konis will 'handle' those rates. Pretty much all the autox E30's have at one time or another lifted a rear wheel. The two most serious cars I know of do/have, E30Racer's car and Alex's car. Both with 285/30/18's and E30RACER with 275/35/15's. Don't know if the car on 15's does it since it is much lower.

[rsafier]

Actually it seems wide wheels help keep the 3 wheeling more under control. if you see the well setup cars with 245s running they lift even higher then Alex's & E30 Racer's.

[nando]

IMO custom valved Koni's are a waste....Most shock dyno charts I've seen show that they simply are very non linear in adjustment. On top of that the compression adjustment does almost nothing and almost all of that nothing comes at high speed displacements......So basically you are paying a bunch of money for DA's or adjustable DA's for NO reason....

I wasn't speaking of DAs at all - what I meant was, were the shock's valving matched to his spring rates. AFAIK, Koni SAs are only valved up to about a 450# spring. And rebuilding/valving is like $80.. it's not really a bunch of money. :p

[JRKOUPE]

I wasn't speaking of DAs at all - what I meant was, were the shock's valving matched to his spring rates. AFAIK, Koni SAs are only valved up to about a 450# spring. And rebuilding/valving is like $80.. it's not really a bunch of money. :p

Nando...I have GC valved koni SA's....and I spoke w/ GC last month.....mine are good for up to 700-800#'s.....but it does appear that some SA's may be different than others...GC confirmned this via my part nos on my invoice.