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MGB MOTORSPORTS - MGB Anti-Sway Bars

tony barnhill

Great Pumpkin - R.I.P
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Asked these questions elsewhere but thought I'd run them by this group also:

1) Wonder what the effect would be to put a late roadster rear anti-sway bar under an early GT?

2) Then, wonder how that would be magnified by replacing the stock front anti-sway bar with a larger one?
 

Nunyas

Yoda
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well, i reckon it'd take a lot of experimentation to get it down "just right". I've thought quite a bit on this. If the rear anti-sway bar is too strong/stiff you'll run the risk of having one of the rear tires losing contact with the ground while diving into turns (like you see in a lot of action photos of front drive cars diving into turns), and that's not a good thing in a rear drive car.

One of the Spridget guys (Aeronca I think it was) mentioned in a thread I had a several months back, that none of the folks he knows that races uses a rear anti-sway bar. Instead, they've found/felt that pan-hard bars were much more beneficial on the track.

Here's the thread I mentioned (ok ok ok... so it was 10 months ago that I asked): https://www.britishcarforum.com/ubbthread...true#Post105441
 

Joe Reed

Jedi Warrior
Country flag
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If your GT has the same approximate front/rear weight distribution as a late RB tourer, I would think using both stock RB bars would be a good place to start - since it would maintain the same balance front-to-rear. I'm pretty sure the front bar on a late RB is stiffer than a CB bar.
 
OP
tony barnhill

tony barnhill

Great Pumpkin - R.I.P
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Hmmmm....as the early GT never had an anti-sway bar, maybe I'll take a stock front bar & attach it to the rear axle & the rearmost part of the car body (i.e., pointing rearward instead of to the front like stock)....I could even make a bracket with adjustable points on it.
 

Nunyas

Yoda
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sounds like a good idea... friend at work just installed an "adjustable" rear sway bar on his Saabaru station wagon. The setup was adjustable. The ends of the bar had 3 different mount points for varying degrees of roll stiffness.
 

200mph

Member
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Tony,
Going to a larger (stiffer) front bar reduces understeer. A larger rear bar reduces oversteer.

Current short-oval track trend is soft springs, big sway bars at both ends... not sure how this owuld translate to autocrossing.

The best bars are those with an adjustable link... where you can slide the link along the bar and tighten at different places. Shortening the bar is stiffer, longer bar has more flex... increases your tuning options.
 

Bob Claffie

Jedi Knight
Country flag
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Tony: Depends on what handling characteristics you want to get. Generally adding on a rear bar or stiffening an existing bar will increase understeer. Most racers like the ability to let the rear end hang out (within reason). Lots a luck, Bob
 

mattmacklind3

Jedi Hopeful
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I use the 5/8" front sway bar, and nothing in the rear. As I was told, a front sway bar any larger than that and you're back to too much understeer for driving on the road. It feels really good on the car, slightly tighter than the stock size.
 

Dave Russell

Yoda - R.I.P
Gold
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Hi 200 & Bob,
Quote 200; Going to a larger (stiffer) front bar reduces understeer. A larger rear bar reduces oversteer.

Quote Bob; Generally adding on a rear bar or stiffening an existing bar will increase understeer.

If the references cited above by Kenny are valid, & I think they are, increasing a front bar will increase understeer. Likewise, adding a rear bar or stiffening one, will increase oversteer.
D
 

Bruce74B

Jedi Knight
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Is this on the BGT that you resprung to much lighter springs in the rear? Seems to me that the sway bar would compensate for the lack of stiffness in the rear end and lessen the oversteer, without the resulting understeer associated with the standard suspension with the swaybar added. It's gonna give you a snappy ride...are you sure you are quick enough to react to that boattail type of driving? /ubbthreads/images/graemlins/jester.gif

If you have ever driven an early 911, you will know what I mean. One heck of a set up if you are driver enough to handle it...or want to be bothered to learn how to drive it! /ubbthreads/images/graemlins/driving.gif

Or if you're doing this with the V-8 project, I wanna join the line to drive it /ubbthreads/images/graemlins/cowboy.gif

Bruce /ubbthreads/images/graemlins/cheers.gif
 
OP
tony barnhill

tony barnhill

Great Pumpkin - R.I.P
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Bruce & All..I'm thinknig about this for the GRM GT that I've lightenend & repowered strictly for Auto-X....I'm trying to figure out how to get the most power to the wheels & then keep those wheels planted firmly on the ground while allowing quick, nimble footedness around the cones.
 

lawguy

Jedi Knight
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I understand you want a starting point, but the only way to get a really good setup is to see where you stand with everything in place (competition wheels, tires, etc.) and see where you need to go from there.

As you know better than anyone, you hardly have the common GT. With all the sprung and unsprung weight removed and the far from standard suspension, what may work on a GT closer to stock is of very limited application.

Test and test and test some more.
 

swift6

Yoda
Offline
[ QUOTE ]
Hi 200 & Bob,
Quote 200; Going to a larger (stiffer) front bar reduces understeer. A larger rear bar reduces oversteer.

Quote Bob; Generally adding on a rear bar or stiffening an existing bar will increase understeer.

If the references cited above by Kenny are valid, & I think they are, increasing a front bar will increase understeer. Likewise, adding a rear bar or stiffening one, will increase oversteer.
D

[/ QUOTE ]

That's correct, Larger front bars on rear wheel drive cars will induce/create more understeer. An understeering car is tight and easy to control, an oversteering car is loose and on the edge of out of control. Understeer is deemed safer than oversteer because it is easier to control and correct through driver control. When understeering you turn the wheel but the car keeps going staight. Oversteer is when the rear of the car no longer follows the front but comes around on its own. Oversteer is considered less safe because it is very easy to lose control of the car when oversteering. If you lose control while oversteering, the driver becomes a passenger and a whole lot of physics start happening. The 911 problem, before they engineered it out, was "snap oversteer", sometimes referred to as 'exiting a corner backwards'. Though this is primarily a 911 (or other rear engined cars) trait and has to do a lot with weight transfer from lifting off the throttle too quickly while deep in a corner. 911 drivers often call it "chickening out". Spend some time at a PCA event and you will see plenty of rookie 911 drivers doing just that. /ubbthreads/images/graemlins/grin.gif

Cars are designed to understeer from the factory as a safety measure. Sway bars/Anti-roll bars increase roll stiffness. Anything you do to increase rear roll stiffness will reduce the designed in understeer. This includes adding rear sway bars but can also be done by stiffening the rear springs, reducing chassis/body flex in the rear (as in rear strut bars etc...) or increasing rear axle placement and control (panhard bars etc...).

When understeer and oversteer balance out you achieve a neutral handling car. Which can be really fun but can also be a nightmare under common street driving conditions, especially if roads are wet. Race cars are rarely set up absolutely neutral. The particular race course determines the amount of understeer/oversteer in the set up and is why they try to have as much adjustability as possible.

Front wheel drive cars have strong understeer characteristics. So strong that the factory often places equal size front and rear bars or slightly larger rear bars on the car to reduce the understeer by inducing a small level of understeer. They will still be understeer biased but much more driveable.

Tony, on your GRM car, since you have already altered so much of it you can only really start by guessing. For Auto-Xing you might think that an oversteering car would help you rotate around the cones better, which it would, but could make chicanes a nightmare. Ideally you would want a more neutral car. With the lighter car and the increased torque you should be able to induce oversteer with your right foot on the vertical pedal and steer the rear of the car with the throttle (throttle steering /ubbthreads/images/graemlins/thumbsup.gif). If you have ever heard someone refer to balancing the car with the throttle, it means they can transiton the car from understeer to oversteer and back simply through throttle control.

Tire Pressure is another large contributing control factor in this and something you should test as well. Variances as little as a pound or two can make all the difference in fastest time of the day or losing control in a corner. Some auto-Xers will gaurd their tire pressures like top secret knowledge.

If you have time, try taking the car to some local auto-X events. By practicing on competitive courses you can learn so much more and you will probably get plenty of advice from more experienced auto-Xers. You will only really find the answer to your question through application. Auto-Xing is a different enough form of motorsport that circle track and road course set ups might give you a good starting point but will be far from ideal for the short low speed coned course of auto-X.

Also, keep in mind that ulitmate Auto-X set ups are not ideal for 1/4 mile times either.

BTW, I think it's awesome that your doing this and allowing us to live vicariously through your exploits. Keep it up and keep us informed. /ubbthreads/images/graemlins/driving.gif

If anyone is wondering, my knowledge on the subject comes from much research, some practical application and instruction from professional racing drivers, mechanics and engineers.

/ubbthreads/images/graemlins/cheers.gif
 
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In racing Radio Control touring cars (albeit they weight 3 pounds and are 4 wheel drive and go about 45-55 mph), I kept increasing the stiffness of everything... front, rear, springs, shock fluid, shock valving, swaybars, etc. The simple chart I provided above is correct. But if you make everything stiffer, you increase both understeer and oversteer. More problems occur when everything is so stiff that you start raising tires off the ground because of chassis flex. Eventually I found a happy medium by stiffening up the chassis, and going to more in-the-middle settings on the suspension components.

You definately need to drive it as is first to know where it needs adjusted. Making suspension tuning adjustments without knowing what it does now is pointless. Rip it around the neihborhood a few times - lol. /ubbthreads/images/graemlins/thumbsup.gif

That said, for auto-X you'll want it pretty nuetral - but leaning to understeer. A touch of understeer that you can change into a touch of oversteer with the throttle. Too nuetral, or even a bit toward oversteer, and you'll be swapping ends as bad as the 911 drivers in the post above. (but the 911 problem has lots to do with the fact of the engine weight hanging out by the rear bumper.)
 

Nunyas

Yoda
Offline
I have a better idea... empty the Garagemahall and setup some cones... consider it your secret testing facility... /ubbthreads/images/graemlins/grin.gif
 

Bugeye58

Yoda
Offline
Shawn, well thought out and presented response.
I remember learning "Trailing throttle oversteer" when I had my first Porsche. OOPS! "Why am I heading west, but pointing east?"
When I was racing cars that had both front and rear bars, the first thing I did if I had to race in the rain was disconnect the rear bar. Much easier to drive in the slipperies with that done, the front bar toned down, and the shocks set full soft.
Jeff
 
G

Guest

Guest
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Right because you lift off to get it to turn in rather than staying on (and sliding off).

My favourite quote about this - and I'm paraphrasing badly - is "understeer thrills the passenger and scares the driver, oversteer thrills the driver and scares the passenger".
 

swift6

Yoda
Offline
[ QUOTE ]
Shawn, well thought out and presented response.
I remember learning "Trailing throttle oversteer" when I had my first Porsche. OOPS! "Why am I heading west, but pointing east?"
When I was racing cars that had both front and rear bars, the first thing I did if I had to race in the rain was disconnect the rear bar. Much easier to drive in the slipperies with that done, the front bar toned down, and the shocks set full soft.
Jeff

[/ QUOTE ]

Thanks Jeff, I know that sometimes the jargon can confuse people so I figured a little longer post could help clarify the concepts at hand.

/ubbthreads/images/graemlins/cheers.gif
 

Bruce74B

Jedi Knight
Offline
[ QUOTE ]
Right because you lift off to get it to turn in rather than staying on (and sliding off).

My favourite quote about this - and I'm paraphrasing badly - is "understeer thrills the passenger and scares the driver, oversteer thrills the driver and scares the passenger".

[/ QUOTE ]

That explains the look on a buddy's face when we took his 911 to lunch one day and he asked me if I knew how to drive a Porche...I took it through an "S curve" and the second curve I came out of "steering left while turning right", never backed off when it came around. The look on his face was priceless...and half a mile later he was able to say "gee, I guess you do know how to drive a Porche" LOL I learned to race in Midget Sprint cars on a dirt track and was used to the idea of oversteer, but never had a passenger in the car then.

Tony, I agree that the only way to find out is to go with the adjustable bar and get out there and find out how she handles. I bet that will be fun ;-) Good luck...and let me know if you need a volunteer to help!

Bruce
 
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