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Lower control arm lenght?? #568372
12/31/09 11:00 PM
12/31/09 11:00 PM
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Mooresburg, Tn
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'72CudaRacer Offline OP
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Mopar lower control arms are much longer than upper.Why? Is it because of torsion bar placement?
In a all drag car, is it possible to fabricate some that are closer to upper cont arm lenght, and still be stable at speed.
It would seem to me that if the upper and lower cont arms were the same lenth and spaced apart the same distance as the spindle height, you would have a lot less problem with bump steer.
Or am I missing something? Any chassis guru's have thoughts on this?
Thanks, Brian

Re: Lower control arm lenght?? [Re: '72CudaRacer] #568373
12/31/09 11:11 PM
12/31/09 11:11 PM
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Romeo MI
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Its done all the time with a chassis car that runs a
A-arm set up... set the inner pivot points as the
same length as the steering rack pivots

Re: Lower control arm lenght?? [Re: '72CudaRacer] #568374
01/01/10 09:25 AM
01/01/10 09:25 AM
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Posts: 2,128
sweden
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sshemi Offline
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Quote:

Mopar lower control arms are much longer than upper.Why? Is it because of torsion bar placement?
In a all drag car, is it possible to fabricate some that are closer to upper cont arm lenght, and still be stable at speed.
It would seem to me that if the upper and lower cont arms were the same lenth and spaced apart the same distance as the spindle height, you would have a lot less problem with bump steer.
Or am I missing something? Any chassis guru's have thoughts on this?
Thanks, Brian




If they where equal in length you would get a whole lot of camber change throughout the susp travel. about the bumpsteer read Pbodys post

Re: Lower control arm lenght?? [Re: sshemi] #568375
01/02/10 04:45 PM
01/02/10 04:45 PM
Joined: Sep 2005
Posts: 2,442
LOWELL IN
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LOWELL IN
http://www.heidts.com/support_suspension_101.html

here is the answer to all your questions

i made a home made weld in MII setup for my duster based on this info abd it has worked perfect since day one

5706197-front3.bmp (48 downloads)

WAXER
Post deleted by Defbob [Re: QWK_ENUF] #568376
01/02/10 06:44 PM
01/02/10 06:44 PM

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Re: Lower control arm lenght?? [Re: '72CudaRacer] #568377
01/02/10 09:59 PM
01/02/10 09:59 PM
Joined: Dec 2003
Posts: 22,695
Bitopia
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jcc Offline
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I believe the answer you are looking for, they are unequal lenght becuase they want a certain amount of camber change, reason being as the car turns and body rolls, you would get positive camber, not good for turning, with negative camber as wheel compresses, additional negative camber keeps the tire in better road contact. Its all a big set of compromises anyway. bump Steer refers more to Toe changes as the wheel raises and lowers, due to cornering, braking, or accelerating or some combination.


Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
Re: Lower control arm lenght?? [Re: jcc] #568378
01/02/10 10:15 PM
01/02/10 10:15 PM
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Posts: 2,036
Mooresburg, Tn
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'72CudaRacer Offline OP
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Quote:

I believe the answer you are looking for, they are unequal lenght becuase they want a certain amount of camber change, reason being as the car turns and body rolls, you would get positive camber, not good for turning, with negative camber as wheel compresses, additional negative camber keeps the tire in better road contact. Its all a big set of compromises anyway. bump Steer refers more to Toe changes as the wheel raises and lowers, due to cornering, braking, or accelerating or some combination.




Exactly. In a drag race only car, none of that (except bump steer), matters, right? If I'm going to go to the trouble to do away with K member and torsion bars and use lighter upper and lower control arms and coil overs with a braced front frame section, wouldn't this be a good time to address the geometry? Most everyone that offers tubular K's have basicly duplicated the factory geometry (for street use, I assume?).
Or am I WAY out in left field?
Thanks, Brian

Re: Lower control arm lenght?? #568379
01/02/10 10:22 PM
01/02/10 10:22 PM
Joined: Aug 2009
Posts: 2,036
Mooresburg, Tn
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Hemi Fred,
I also like the way that your car has the added bracket to put the lower control arm in double shear. Your's is the only one I've seen so far that has done that. Just hanging the LCA out there on a stud with a bushing (and no torsion bar to keep it in check), don't look right to me.
Thanks, Brian

Re: Lower control arm lenght?? [Re: '72CudaRacer] #568380
01/02/10 10:25 PM
01/02/10 10:25 PM
Joined: Dec 2003
Posts: 22,695
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jcc Offline
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Posts: 22,695
Bitopia
I don't think so, but not sure what you are going to gain, and I'm not one to advise what direction you should go, but I watch from the sidelines, I would though not toss all handing assumptions aside becuase you are only doing a 1/4 at a time, evasive or crossedup situations it might be useful to have.


Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
Re: Lower control arm lenght?? [Re: '72CudaRacer] #568381
01/02/10 10:30 PM
01/02/10 10:30 PM
Joined: Nov 2004
Posts: 4,330
Lynchburg, VA
Leon441 Offline
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My lower control arms are shortened. The length is identicle to the upper control arms. And like Pbody said the tie rods are the same length also.

The length of the rack is longer than the distance between the pivot points of the lower control arms. This works to be an advantage. When you make up the steering arm the tie rod end needs to be further out from center of the car than the ball joints in order to have proper ackerman. This control which wheel turns shorter than the other when turning. How much is not criticle but if you have negative ackerman you are hurting the handling of the car. In a drag car if the steering whell needs to turn you are already in trouble. So it is important to have a car that will have stable manners. My car is narrower than the later A-bodies so it all works out fine. This is not going to be the case on 67 and later A-bodies as well as the others. So you may want that lower control arm a little longer. Builders of strut cars have a measurement between frame rails they use for all of the cars. The measurement has to do with the length of the rack. This is not written in stone because you can get a shorter rack it just cost more.

A drag car does not need as much suspension travel as a factory built car. You need to limit how much compression the front end has so you don't flatten your oil pan or headers. Depending on how much power you have you may not need a lot of extension either.

Leon


Career best 8.02 @ 169 at 3050# and 10" tires small block power.
Re: Lower control arm lenght?? [Re: Leon441] #568382
01/02/10 10:49 PM
01/02/10 10:49 PM
Joined: Aug 2009
Posts: 2,036
Mooresburg, Tn
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Well, back to the drawing board for me.
I'm starting to believe an OLD racer friend of mine when he said, years ago I might add, "forget the weight, just build a bigger motor!"

Thanks, Brian

Last edited by '72CudaRacer; 01/02/10 10:53 PM.
Re: Lower control arm lenght?? [Re: '72CudaRacer] #568383
01/02/10 11:21 PM
01/02/10 11:21 PM
Joined: Nov 2004
Posts: 4,330
Lynchburg, VA
Leon441 Offline
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Leon441  Offline
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Posts: 4,330
Lynchburg, VA
Bondobob he's got a nice kit. Bob's pro fab I think is the name.


Career best 8.02 @ 169 at 3050# and 10" tires small block power.






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