Lengthening the LCA

[rb70383]

Was researching on what front suspension to use in our Challenger and came across a site that stated the A-body's LCA was about 3/4 inch longer than the Challenger's. What effect will lengthening the LCA have? Also FWIW, I am planning on using the "tall" Cordoba spindle for the disc brake conversion.



So from a generic standpoint what will a longer LCA do?

[Bryce]

changes your camber gain as well as many other things.

[David Pozzi]

Check what you have now. I was told one of the Chrysler cars had a huge amount of neg camber gain stock. I don't recall if it was Challenger or Cuda.

[kp.touring]

I plotted out E-body suspension a few years back for a Cuda project. Don't use a taller spindle! As Dave stated Mopar's have a huge amount of neg camber gain stock and the tall spindle will add to this. The 1 of biggest problems with the front suspension is the lower ball joint/steering arms they're junk when new.

Kevin

[JRouche]

Ideally you want a nice long lower control arm. It gives you a slower ratio on the circle. Think about all suspension components on a circle. Short arms have a smaller circle. Faster changes that arent good for dialing in the curves. Specially the lower control arms. In an ideal world they wouldnt be on the circle. They would travel lineally up and down on a straight line. Long arms. As the suspension travels through the circle short arms produce too much movement. Pulling the spindle in and pushing out. So a long lower arm is good, a lil shorter upper arm is needed to compensate for how high it is, at the frame mounts. If we could lower the upper arms frame mounts then a longer upper arm is good too. To the point where we like the camber change.

It would be nice to have some really long lower and upper arms. With the upper arm frame points low.

Problem starts up with packaging and bump steer. With really long lower arms the steering arms dont have any room. No place to put them. So they end up being too short. BAD. Bump steer issues.

It really becomes a packaging issue, and Im dealing with that right now. Give and take a lil here and there.. Its a juggling experience. Compromise and some really careful measuring. You end up with something that fits within a 1/4" on all the travel and doesnt touch. Cant have any touching of the members.. Its difficult.. JR

[kp.touring]

Yes longer upper and lower control arms are a good thing, but here is the rub if you lower the upper control arm mounting on a E-body Mopar you will increase the neg camber gain curve!

Kevin

[autoxcuda]

Was researching on what front suspension to use in our Challenger and came across a site that stated the A-body's LCA was about 3/4 inch longer than the Challenger's. What effect will lengthening the LCA have? Also FWIW, I am planning on using the "tall" Cordoba spindle for the disc brake conversion.

So from a generic standpoint what will a longer LCA do?

That's originally off my old website, 68 Cuda Autocrosser. AOL killed it.

That info was used by a circle track guy in Nebraska and it worked out perfect. I know when we ran Hobby Stock circle track Chevelles years ago, we all ran lots of negative static camber. We'd max out the shims. Some people were cutting and lengthening control arms (illegal) That was a flat 3/8" oval. I figured the info could help a fellow roundy round and sure enough it did.

[autoxcuda]

I plotted out E-body suspension a few years back for a Cuda project. Don't use a taller spindle! As Dave stated Mopar's have a huge amount of neg camber gain stock and the tall spindle will add to this. The 1 of biggest problems with the front suspension is the lower ball joint/steering arms they're junk when new.

Kevin

Bill Reilly plotted on a suspension geometry program the camber curves on the taller spindle (only 3/8"). He got camber gains. He used an A-body for the analysis though. Not an E-body/71-72 B-body front clip.

Article on that here: http://www.bigblockdart.com/techpages/spindles.shtml

What's the issue with the LBJ/steering arms?? What do we need to look out for?

[autoxcuda]

Check what you have now. I was told one of the Chrysler cars had a huge amount of neg camber gain stock. I don't recall if it was Challenger or Cuda.

Same exact front end between Cuda and Challenger. Think Camaro and Firebird. Only difference chassis wise is the Cuda is 2" shorter than the Challenger between the front and rear seats. The body platform is called E-body.

The E-body is basically a shortened 71/72 B-body (Charger/Satellite). The E-body and 71/72 B-body share the entire chassis from firewall forward. The angle of the steering box is slightly different for a slightly different steering column angle between the two chassis styles.

[rb70383]

So will there be any adverse effects? I saw the big block dart info. Yes it was ur old site about the LCAs. LOL So far I am thinking Hotchkis UCA's, various XV chassis stiffening (easy for me to buy and weld then try to bend up stuff for now). Still on the fence about the rear. Keeping the rear leafs though. Of course with the longer LCA I will need an adjustable strut rod to prevent the LCA bushing from binding. Any one got a suspension program that then could change the LCA length to see the basic affect it would have?

[autoxcuda]

So will there be any adverse effects? I saw the big block dart info. Yes it was ur old site about the LCAs. LOL So far I am thinking Hotchkis UCA's, various XV chassis stiffening (easy for me to buy and weld then try to bend up stuff for now). Still on the fence about the rear. Keeping the rear leafs though.

Up to your budget on the rear leafs. I don't get overly excited about trailing arms. It's not a leaf car is worthless. And some of the bolt in stuff has to take in for packaging issues and not 100% optimized.

When we were over at Hotchkis at their open house this summer, they were working on an A-body platform (71 Dodge Demon). So hopefully they'll have a rear leaf spring set for those too.

Of course with the longer LCA I will need an adjustable strut rod to prevent the LCA bushing from binding. Any one got a suspension program that then could change the LCA length to see the basic affect it would have?

The only reason I mentioned the longer LCA was for someone wanting to run lots of camber. When I mean lots, I mean like over 7+ degree. That was common for us to run in the right front of a hobby stock car. The circle track guy I mentioned only ran the longer LCA on the right front tire. It was more of trivia deal and maybe in very particular situations a person could take advantage of.

I don't think someone should run a longer A-body arm on an E/B body on the street. Not neccesary.

[High Plains Mopars]

I plotted out E-body suspension a few years back for a Cuda project. Don't use a taller spindle! As Dave stated Mopar's have a huge amount of neg camber gain stock and the tall spindle will add to this. The 1 of biggest problems with the front suspension is the lower ball joint/steering arms they're junk when new.

Kevin

Huge is certainly a subjective term. 1.5* negative gain isn't too bad a thing to have, IMO. Especially when you consider other some cars that are the opposite, like a first gen camaro that generates positive camber under compression. So, 1.5* negative camber gain during body roll is a good thing for keeping the tire face perpendicular to the road.

Yes, shortening the upper control arm length by lowering the mounting point would have a big impact on this. Whether or not that is a good thing depends corner banking and body roll and those are big factors in how much you actually need. For a street car it is always debatable

Similarly, the taller spindle does raise the roll center slightly as well, which reduces the moment lever arm length, which increases resistance to body roll, another good thing. If the car has been signifcantly lowered, than this raised front roll center height can also be a good thing.

The stamped steel, pressed fit lower control arms are not great, but boxing them up does firm them up considerably, thus alleviating a significant amount of flex. So, I'll grant you they are not great in stock form, but they aren't awful and can be fixed easily for cheap. I'll agree that I don't particularly like the stock lwr balljoint/steering arm arrangement, but hey, some crosses you have to bear.


Now, just putting an A body lower arm under a B/E body would also necessitate a longer upper arm, or else you will end up in a situation where you have the upper arms adjusted all the way out and you still have too much static negative camber. You might be able to make it up by juggling the install of some offset bushings, but that might take some trial and error and may still limit your caster adjustment. The only real advantage I could see to making all the arms longer is like JRouche pointed out, larger arcs. You also could run a rim with more rear spacing on it too, if that is your goal.

Adverse effects of the tall spindle, IMO, not enough to worry about.

If you want to add some adjustability to the rear leafs, you can put pivots in the front eyes and add a panhard bar. This will allow you to change the rear roll center height to adjust the corner exit bite.

[David Pozzi]

1.5 deg neg camber gain is a lot. I'd be concerned where the roll center height is, and where it moves to.
David

[autoxcuda]

1.5 deg neg camber gain is a lot. I'd be concerned where the roll center height is, and where it moves to.
David

I assume that's camber gain is in bump/dive only. So wouldn't that be mostly pure straight line braking and chassis raise and dive under aero effects?? That would effect straight line braking contact patch.

What about dive AND roll?? Also it's interesting to see the roll center movement under bump and roll.

David, what's your opinion of the roll center plots for the two different height spindles: http://www.bigblockdart.com/techpages/spindles.shtml

You could make them even taller with bolt in Howe upper balljoints. Remember they will just screw into our Mopar upper contor arms. They are based off a Mopar UBJ.

[David Pozzi]

Well, maybe I didn't understand what was posted. 1.5 deg neg camber gain PER INCH OF BUMP is a LOT of gain. If the travel is something else, then I assumed incorrectly.

Steve, The neg camber gain per inch of bump is very small on your page, but RCH is very very high. Normally RCH is ground level to 3" above ground. I would think a RCH in the 6" to 8" range would cause jacking effects big time and when cornering hard on a flat surface or slightly off camber surface the car would start hopping sideways.

Is the plot for the actual Roll Center or the Instant Center???
David

[autoxcuda]

Well, maybe I didn't understand what was posted. 1.5 deg neg camber gain PER INCH OF BUMP is a LOT of gain. If the travel is something else, then I assumed incorrectly.

Steve, The neg camber gain per inch of bump is very small on your page, but RCH is very very high. Normally RCH is ground level to 3" above ground. I would think a RCH in the 6" to 8" range would cause jacking effects big time and when cornering hard on a flat surface or slightly off camber surface the car would start hopping sideways.

Is the plot for the actual Roll Center or the Instant Center???
David

That's not my page. The measurements were taken and were plotted on a computer suspension program by Bill Reilly that designed the Alterkion tubular/fabricated front end.

David, to get you up to speed...

The "73-76 A-body Spindle" table are the results from stock height spindle measured on a Mopar A-body platform (Dart, Duster, Demon, 67-69 Cuda).

The "73-up B Spindle" table are the results from slightly taller height spindle that will bolt on and measured on an Mopar A-body platform

But either way, you are saying the roll centers seem high? And the taller spindle is about an 1+" higher throughout suspension travel.

Now those spindles will bolt onto a 66-72 B-body (Road Runner/Charger) and 70-74 E-body (Cuda/Challenger) platforms as well. Those all share the same chassis geometry pick up points and same critical suspension arms/linkage dimensions. I have not seen a table/graph done like the one above for that platform.

I remember Guldstrand saying you want the roll center axis between the rear and front roll center a little pointed down. Is this right? But I forgot the amount? Your opinion?

[High Plains Mopars]

The 1.5* of gain was through 2.25 inches of travel, so no, it is not 1.5* per inch, which is a lot.

We don't know the rest of the parameters that were used to set up the table on Bill's site, but they likely were set up in a stone stock configuration. So a 6" roll center height in a stock vehicle would not seem out of line. This could easily be dropped to an under ground roll center height by turning down the ride height just a few inches. Since changing rear roll center is much more difficult on a leaf spring car, the underground front RCH creates a longer moment lever arm and subsequent body roll. Raising this back up with a taller spindle helps put the equation back to a better point.

When I ran hobby stocks, we tried to get the front roll center between 3-4" above ground and the rear roll center in the 10-12" above ground range. This provided a reasonable amount of roll resistance while still allowing some weight transfer for bite on the hard tires we had to use.

[David Pozzi]

The GM stuff is either ground level or near it.
That's a high RCH. 3" is a pretty common goal. At 6" the RC may be moving laterally a lot too, but it's hard to say. Rear is usually a housing center which is OK.
David