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Old 09-17-2002, 07:15 AM
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Question ladder bar length

I recall hearing that ladderbar length should be related to wheelbase. Also, I notice that most ladderbars available are 33", but the ends are somewhat adjustable. My wheelbase on my 35 ford is 113". Will the standard 33" be ok? If you have any experience in this area, your help will be appreciated.

[ September 17, 2002: Message edited by: beetle9 ]</p>
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Old 09-17-2002, 09:09 AM
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hell yeah
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Old 09-17-2002, 11:20 AM
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the ladderbar length is determined by the center of gravity under acceleration, i would install the 33 inchers and see how the car reacts under full acceleration, if the front comes up in a funny lifting fashion, they are to long, if the rear rises under acceleration they are to short. the car should just react neutral and launch off the line.

if you nail the length the launch will feel just right
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Old 09-17-2002, 12:08 PM
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ASSUMING your frame is stiff (big assumption!) it shouldn't matter where the ladder bars attach to the frame. When a car accelerates, the pinion gear in the rear end climbs the differential gear. Three things can happen; 1) the rear end housing will rotate backward and the front wheels will come off the ground, 2) the rear wheels will begin to turn, or 3) the rear end housing will rotate backward with that motion absorbed by the springs wrapping up. All ladder bars or slapper traction bars are intended to do is prevent spring wrap-up and the resulting un-wrap that allows the rear tires to hop and thus lose traction. This needs to happen without limiting the travel of the rear suspension, thus there are several methods of attaching ladder bars that allows the suspension free travel.

In the old days when the super long ladder bars were popular it was probably due to the old buggy frames of those early Fords and Willys. Those frames weren't very stiff and the cars with 1500 hp engines would do wheelies the frame would bend around the ladder bar attaching point causing wretched handling. Super long bars put the bending point closer to the front of the car reducing the poor handling. As the cars got stronger and stiffer the bars could be shorter and still do their job.

Slapper bars are a cheap way to sort of reduce spring wrap-up without the complications of attaching the front of the bar to the frame.

[ September 17, 2002: Message edited by: willys36@aol.com ]</p>
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Old 09-17-2002, 06:03 PM
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A longer ladder bar is for a longer chassis or more weight over the front wheels,and will allow the car to transfer weight faster and not hit the tires as hard as a 33" bar.A short{33"} bar will hit the tires hard,and wont lift the front as well unless the front is very light or the wheelbase is very short.Unless it is a drag car,it doubt you will be yanking the front wheels off the ground.In a street cars Ladder bars are mostly for making a wheelhop proof rear suspention,but on a drag car the instant center is more important.Also,how you mount the bars plays a lot into how they work.The lower the front mount is in relation to the center of gravity of the car,the more the car will want to wheelstand rather then hit the rear tires{Imagine the front of the ladder bar trying to drive a path straight under the body of the car and driving it upward}.As the front of the bar is aimed above or closer to the center of gravity,the car will transfer less weight,and the rear will be more prone to rising in the rear,the best way to visualize this is imagine to the ladder bar as a fishing pole handle which is trying to yank the front of the car off the ground rather then trying to drive under it like a lower settting would do,therefore the only way the front of the car can rise is if the ladder bar helps pull it up.4 link cars work the same way,only the pivot point on the ladder bar is the intersection point where the front of both links would meet,so aiming them to intersect closer to the rear of the car,or at a point lower or higher in relation to the center of gravity effects the car the same way as moving or changining the length of a ladder bar,only with a 4 link you can make the pivot point{actaully called the instant center}as close as maybe 40 inches from the axle,or as far away as 20 feet,which will react much different then a short ladder bar.In a 4 link the relation to the center of gravity is still the point where the 2 lines cross the center of gravity,so you cant put the instant center 4 feet into the ground or 20 feet in the air,it will always be in the middle of where the 2 bars intersect the center of gravity.This is the down and dirty way to explain how suspention systems work,and if you think long enuff about it you will see clear as day why old mopar"pinion snubber" cars used to leave the line like a leapfrog while a "slapper bar" car yanks the front wheels more then it lifts the rear,and a factory 4 link car will usually have enuff abilty to transfer weight that it will appear to squart because it isnt applying any force to the rear tires,which is why they are so prone to axle twist and need airbags to keep them straight.After all is said and done,I say that even with a 113" wheelbase,you should be able to make the 33" bars work,just remeber to visualize where you want the bars to point with the car at ride height and weld in brackets with at least 2 adjustment hole upward and 2 downward in case you change you mind and have a better idea later on.If you put the ladder bars in with the front pointing at the sky you will now understand why regardless of how long they are the car will want to do more leapfrogging then weheelstanding.Good luck.
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Old 09-17-2002, 07:08 PM
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Back in the late 60's I came upon a formula that I used for 10 yrs. on the length of traction bars.( ie) 32% of the wheel base = length of bars. worked for me and every one that I built them for. I know it sounds simple but it worked. ...GK
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Old 09-17-2002, 07:58 PM
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For optimum effectiveness ladder bars should attach at the roll center on any car. Changing the offset (mounting bracket) from the roll center will affect the rate of rise or weight transfer the vehicle experiences during launch. Mostly it is a cut and try affair since getting a long enough bar under the car is hard enough but if you are interested in learning more read this guys book, this subject is to broad to cover here.

http://members.aol.com/racecartec/engineer.html
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Old 09-18-2002, 11:35 AM
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wow, ya know, this is one of those subjects that just leaves you sitting there staring at the screen with your mouth open and a glazed look in your eyes, goin "gee, i really don' know sh-- about drag racin.
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Old 09-18-2002, 03:47 PM
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It's like this: Back in the 60's we used traction bars on leaf setups (for all you recent comealongs, pro-street didn't exist yet). Knew what they were about, only one thing, good hookup with the track ,eliminating wheel hop, which was good for breaking springs, tearing our the rear end and ripping loose a whole array of things. Here I come along 30 years (actually 40 years later) and people are using the term traction bar synonomously with "ladder bars". I thought the ladder bar was a suspension part used with coilovers to bolt on the rear end and never really looked at it as a traction device. Does it not also serve the purpose of anchoring the rear as well? I am from the very old retired school (I heard the term 301 Small Block the other day and got all excited, now your're talking something I understand). Is the ladder bar a traction bar or a suspension part necessary to hold rear in place.
Lets have some discussion on this, I'm sure it's up there with the color of small blocks and by the way, given my age, orange is the only acceptable color for any small block chev.
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