Rear Anti Roll Bar aka Swaybar - LotusTalk - The Lotus Cars Community
 
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Old 11-25-2012, 03:33 AM   #1 (permalink)
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Rear Anti Roll Bar aka Swaybar

Anyone has this?
????????????????????????????????????TOYBOX48?????? ??--????????????????????? ??????????????

Too pricey though

I have BWR 1" front swaybar (medium setting) and ATS 1.8way carbon LSD, Nitron 46mm Single 550/700lb. Have to use -8/-2 settings in track and yet the low speed corners are understeer. This rear swaybar from ARC might help with the understeer???
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Old 11-25-2012, 05:38 AM   #2 (permalink)
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Might help with the understeer, but it would likely "enhance" snap oversteer. I would rather deal with low speed understeer.
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Old 11-25-2012, 05:49 AM   #3 (permalink)
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You really want to avoid the rear swaybar if at all possible. It reduces wheel independence side to side and in the rear that can cause you to hang a wheel over bumps etc. How low speed are you talking about? Is it corner entry push or corner exit? There are a couple of possible causes in your set up.
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Old 11-25-2012, 05:52 AM   #4 (permalink)
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Mine is corner exit push...even when I'm on the throttle...
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Old 11-25-2012, 09:33 AM   #5 (permalink)
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Mine is corner exit push...even when I'm on the throttle...
IMO - it is always best to balance the car by adding grip to one end instead of taking grip away from the other so that you end up with both balance and grip.

Understeer on corner exit is common and makes sense since when you get on the power to pull out of the corner you unweight the front tires and they grip less. If one is really heavy handed (footed?) they can put a lot of power down and overwhelm the rear tires and bring the car into oversteer but in most cases this isn't all that quick either as you've gone from static friction on the rear tires (a very good thing) to sliding friction (fun in this case but not as quick).

So it comes down figuring out how to get the front to grip more and this can be done by adjusting the shocks in many cases. Increase the bump damping in the rear (so less weight transfers to it) and adjust the front rebound damping so less weight comes off the fronts and you will have more weight on the fronts during corner exit. This isn't always easy as the shocks often adjust rebound when the adjust damping but if you have two way shocks it can be done.

You can also address this with the alignment - no toe-in in the front, and little toe-in in the rear - and as much camber and caster as you can muster in the front.

In the end a rear-mid engine car will almost always be prone to corner exit understeer because of the great grip the rear inherently has with the engine being back there and the weight shift with acceleration. The upside of course is that the rear grip is so good that you can put power down and pull hard out of corners without wheel spin or throttle-on oversteer. If the driver brakes late into the turn and only turns the steering wheel as the brake is released the front end will bite hard and the car will turn in very well...........then if the driver gets the car lined up properly so that the car can push slightly on corner exit while under throttle he can get on the gas early and be quicker on corner exit. The combo of late braking and early throttle is why rear engine cars can be so quick if exploited to the full.

I hope that helps and doesn't muddy the waters.

Dave
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Old 11-25-2012, 11:08 AM   #6 (permalink)
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I would drop front ride height by 5 to 10mm. This worked wonders for me, although, my set-up is very different. I found Nitrons have very limited droop travel.

What is the wall thickness of the front sway bar?

Take a look at Speedway Engineering or HRPWorld for racing sway bars. Much easier and cheaper to build and you know what you get.

Unlike the common opinion on this forum, rear sway bars are NOT the source of all evil. 911's run them (they have the same weight bias)... and the rear is bigger than the front... Did Porsche get it sooo wrong??? Lotus got away with light car, open diff and a lot of understeer for the street, so the average Joe does not kill himself on the way to Walmart. Beeing able to tune both ends of the chassis is not such a bad thing....

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Old 11-25-2012, 11:37 AM   #7 (permalink)
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Unlike the common opinion on this forum, rear sway bars are NOT the source of all evil. 911's run them (they have the same weight bias)... and the rear is bigger than the front... Did Porsche get it sooo wrong??? Lotus got away with light car, open diff and a lot of understeer for the street, so the average Joe does not kill himself on the way to Walmart. Beeing able to tune both ends of the chassis is not such a bad thing....

Anton
+1

A rear sway bar can be used in a mid engine and rear engine car very successfully. Anyone ever driven an Cayman or Boxster, for example?

I believe it's the Elise's light weight and spring choice that allows for it's elimination. I'm sure the steering response could be even further improved and the handling can be very nicely balanced by tuning with a rear bar and an adjustable front bar. Personally, I would trade ultimate grip for a little more responsiveness and adjustability, so I think I would like a rear bar and thicker front bar.
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Old 11-25-2012, 11:40 AM   #8 (permalink)
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ageshelin,

While I would agree with you about the rear anti-roll bars on heavier cars or ones that have "issues" like the 911 i.e. 70% mass cantilevered behind the rear axle. In lotus case, the independence helps put down power. It would certainly be in BWR's financial interest to do a rear anti-sway bar, but I don't think it is the best fit for the chassis in our many experiments with the cars in autox and track.

Trying the lower front ride height is an option if it doesn't go too low as to push the roll-centers below ground. Shock also is an option. IMHO the front spring rates are too stiff, but it could be "band-aided" with ride-height and shock changes perhaps.
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Old 11-25-2012, 07:02 PM   #9 (permalink)
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You can also address this with the alignment - no toe-in in the front, and little toe-in in the rear - and as much camber and caster as you can muster in the front.
Everything except the castor makes sence...I would think that less castor would make the car point better.
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Old 11-25-2012, 07:50 PM   #10 (permalink)
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Everything except the castor makes sence...I would think that less castor would make the car point better.
I would think that that max caster would allow for better camber gain and grip on turn in and that by the time the wheel is being unwound on turn exit that it would allow for a flatter tire and more grip on turn exit. No?

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Old 11-26-2012, 05:32 AM   #11 (permalink)
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How about just adjusting the front sway bar to be softer or less rear toe-in? Both are free.
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Old 11-26-2012, 06:41 AM   #12 (permalink)
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Adding caster to increase the amount of camber in a corner is like adding a stiff rear sway bar to decrease grip in the rear to get a net increase in the front. You take one step backwards to take a step forward. Increasing castor increases high speed stability at the cost of point-ability.
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Old 11-26-2012, 08:03 AM   #13 (permalink)
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Adding caster to increase the amount of camber in a corner is like adding a stiff rear sway bar to decrease grip in the rear to get a net increase in the front. You take one step backwards to take a step forward. Increasing castor increases high speed stability at the cost of point-ability.
I disagree -

With added caster one can have their cake and eat it too to a certain extent. With more caster the car can have less camber. So you get a flatter tire and larger contact patch when the steering angle is low so the car will have better grip under straight line braking as well as when you are getting back on the gas at corner exit.

And at the same time added caster will give more dynamic camber so once you turn the wheel. So you have more camber when turning and less when going straight. That seems ideal to me.

What am I missing?

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Old 11-26-2012, 05:43 PM   #14 (permalink)
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The point is largely moot in this car as the max caster available is negligible. I would check rear toe, then lower the front if you don't screw up geometry. If so, then raise the rear. Don't let the rake get over about 15mm. Then start with shocks.
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Old 11-27-2012, 03:41 AM   #15 (permalink)
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Had tried to add more castor but those shims seems to be at max castor settings already...has lowered to front slightly and add little toe out. Going to track again this coming weekend and see if the understeer has cured.
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Old 06-19-2013, 03:48 AM   #16 (permalink)
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re: rear sway bar

Since this thread got resurrected....

Does anyone know what size bars does the new V6 car use? It has both front and rear and Lotus has been exalting the use of the rear bar as part of their new latest and greatest suspension set-up.

Anton
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Old 06-19-2013, 05:31 AM   #17 (permalink)
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Did you try softening the front bar? It's a no-brainer. On my car (and every car I've ever tuned) changing the front bar setting made huge changes to the car's dynamics.

Adding a rear sway is what Lotus did to make the new cars roll less while still allowing the springs to control ride comfort. It's a compromise that we don't have to make... and that you clearly haven't by running 700# rear springs. That's a lot of rear spring. You CERTAINLY don't need a rear bar.
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