Shorten the Front LCA on a Macpherson strut?

[CrisAnderson27]

Hey guys!

I've been doing some searching in the forums this morning (and for the last week via the internet as well), and can't seem to find any information on my specific issue. I think it's probably because the terms required to search are pretty generic...lol. I mean the words, 'Macpherson strut', 'LCA', 'lower control arm', and 'shortened' bring back millions of hits, no matter how you mix them.

Anyhow, what I'm building is a 1968 Cougar. It's currently a street/strip build, but as I'm going I'd like to make sure there's some future utility for other forms of performance driving in there. The engine is a 347, and should put out somewhere north of 700 naturally aspirated horsepower on out of the pump E85. The car will be street driven far more than it is raced (probably daily or close to it...I live in Phoenix, AZ lol). I'm starting out here talking about the engine because that's where the entire front end redesign started. The heads are monstrous...and the 2" primary headers aren't so tiny either. I first tried the standard big block 'notch the shock towers' thing...which was necessary just to get the valve covers on the heads. Unfortunately it was still a no-go for the headers. Some calculation showed me that even lowering the upper control arms by 2" wouldn't provide enough room. So I started researching front end options. First of course was the Mustang II setup, but I didn't like the additional weight, particularly on the nose of an already nose heavy car. I also didn't like that in order to provide the kind of structural integrity I wanted/needed...I'd need to run down bars from the cage to the front frame section. Next came the strut based kits...Fatman, AJE, Gateway, RRS. I've heard good and bad about them all...but the one big universal downfall was the ridiculous pricing. In looking over pictures, searching out install threads, and finding the less than a handful of guys who went their own way...I decided to design my own setup using 96-04 Mustang GT spindles and brakes, Strange 10 way adjustable struts with coil overs, and stock car type tubular LCA's with tubular adjustable strut rods to replace the factory setup.

This is where (finally) my question begins to come in. The rack I'm using is a Pinto/Mustang II setup. I originally intended to narrow it by approximately 3" per side to line up properly with the strut and LCA mounting points...but my headers are in the way if I narrow it at all. This led me to the option of cutting the LCA's down from the approximately 13.5"-15" they are currently (I've got about 1.5" of adjustment in the rod end), to somewhere between 11"-12.5". The LCA mount would be moved outboard roughly 3" from the center of the stock location, and up about 3/4". With the current setup, the LCA is just about parallel to the ground, and by raising the mounting point I figured it would help raise the instant center...which on a lowered MacPherson strut system can only be to the good. The problem is, I don't know if there will be any negative effects of shortening the lower control arms. I can grasp that it will shorten the arc the spindle travels in, but with the strut setup, I can't quite get a grasp on what problems that might cause, if any.

Let me post up some pictures to help illustrate both what I've done so far, and to help clarify my question:


https://static1.pt-content.com/images/pt/2014/04/20140411215803-1.jpg
LCA's and coilover setup.


https://static1.pt-content.com/images/pt/2014/04/20140415172308-1.jpg
https://static1.pt-content.com/images/pt/2014/04/20140415181017-1.jpg
https://static1.pt-content.com/images/pt/2014/04/20140415184446-1.jpg
Caster/camber plates.

https://static1.pt-content.com/images/pt/2014/04/20140415181140-1.jpg
https://static1.pt-content.com/images/pt/2014/04/20140415181117-1.jpg
Ride height is about 13.5" from the center of the wheel hub to the fender lip...which is about an inch lower than stock.

https://static1.pt-content.com/images/pt/2014/04/20140415181051-1.jpg
This picture's a little deceptive because of the angle. There IS a bit of negative camber, but it's nothing that the caster/camber plates and the adjustable LCA's won't be able to tune out. Track width seems to be just a hair wider than the original stock setup.

https://static1.pt-content.com/images/pt/2014/04/20140415182325-1.jpg
https://static1.pt-content.com/images/pt/2014/04/20140415182220-1.jpg
https://static1.pt-content.com/images/pt/2014/04/20140415181826-1.jpg
https://static1.pt-content.com/images/pt/2014/04/20140415181817-1.jpg
She's got a long way to go...but once the steering is finished, it's mostly going to be about lowering the engine, getting the cage in, and putting it back together.

And couple pictures to show what I mean, regarding my question:

https://static1.pt-content.com/images/pt/2014/04/20140418190610-1.jpg
This first pictures shows the rough centers of where the arms are going to be moved to. About an inch higher than the center of the stock location, and 3" outboard per side. This will leave my control arms somewhere between 11.5" and 13.5' long per side from the center of the rod end mount, to the center of the ball joint. I will actually mock it up backwards (mount it to the spindle first then measure inwards) to determine the right length. If I'm right, this should help substantially with the front roll centers, but I'm not sure if there's any negative side effects I should be aware of. Hitting corners at speed isn't the main concern here, but I want a stable, predictable car regardless of any reasonable amount of horsepower I throw at it. A car with stable geometry is a hell of a lot easier to get back in shape, if/when it decides to get out.

https://static1.pt-content.com/images/pt/2014/04/20140418190654-1.jpg
A picture showing the current control arm geometry. Not horrible for a lowered Macpherson strut from all I've read.


https://static1.pt-content.com/images/pt/2014/04/20140418191300-1.jpg
Here I'm just showing roughly where the strut rod mount will be placed to keep things properly triangulated. The strut rod will be an adjustable roller setup.

Anyhow, I just thought these might help explain my question a little...and thanks in advance for any help!

[CrisAnderson27]

Any thoughts guys?

In reading, basically I've learned that the shorter arm will bring the wheel up on whatever camber change is going to happen...more quickly. Since I'll have moved the arm upward (and have a bit of static negative camber...probably something less than 1°), the arm will have to move outward through the lower part of the arc...increasing negative camber first in order to even reach horizontal with the mounting point of the control arm (which may be nearly at the limit of upward suspension travel anyway). This would be right at the point where the camber curve would begin to turn positive...so it works. in addition, I'm relatively sure that the amount of caster I'm running (unmeasured as of yet...but visually it appears to be relatively substantial) will be a serious help with negative camber gain on turn in.

I think I'm putting way too much thought in for what is primarily going to be a straight line car (for the time being lol), but I do enjoy driving my vehicles regularly, and would very much like the option of swapping caliper brackets for larger rotors, changing springs, wheels tires, and a few settings...and being able to do serious damage on at minimum an auto-x course. So, if any of you all have any input...I would very much appreciate it!

[Jetfixr320]

I hoped you would get some input.

Sorry Chris

[CrisAnderson27]

I hoped you would get some input.

Sorry Chris

No problem brother! I expected to as well...but it all worked out ok. It's entirely possible that people simply didn't know. It's not a common question to ask, you know? Most people don't have the fitment requirements I do, and so probably don't even get why the LCA's need narrowed in the first place. Either way though...the arms I have cost me nothing, and I've got a backup set I can install at the longer length if things don't work as planned, and just figure something else out for the steering (240z rack is looking promising). I'll just refrain from cutting out the factory bracket until this has been proven to work.

[Twentyover]

This is interesting because I'm going the othr way, trying to make the track arm llonger while still maintaining the same track width (want to keep the tires in the fenders). Using a true Mac Strut (Swaybar comprises part of the lower control arm. Building a longer track arm, shortening the rack, making tie rods longer, need to build a steering linkage to move connect the column to the rack. I feel the current track arm length (about 10") is just too much a compromise when the car starts to lean

[CrisAnderson27]

This is interesting because I'm going the othr way, trying to make the track arm llonger while still maintaining the same track width (want to keep the tires in the fenders). Using a true Mac Strut (Swaybar comprises part of the lower control arm. Building a longer track arm, shortening the rack, making tie rods longer, need to build a steering linkage to move connect the column to the rack. I feel the current track arm length (about 10") is just too much a compromise when the car starts to lean

That really is interesting.

What does your LCA look like at ride height? The biggest factor for me is positive camber gain on bump. Shortening the arms on the same plane (meaning where the LCA mounts to the frame) will help negate this, but raising it as well will help even more, while making the camber curve more aggressive. You will be fighting the other side of that issue. Any additional length on the same plane will tend to reduce negative camber gain, while raising it will at best maintain the camber gain you currently have. The one nice thing though, is that the additional length will make the camber curve less pronounced, so overall it will be less an issue.

My question for you though, is what do you feel the issue is with the too short control arm? What is the compromise? My shortened arms won't be a whole lot longer than your arms as/is, lol.

[Twentyover]

First, the car is a European Ford (my avatar, a Ford (Mercury) Capri). I've had the car since February 1979.To get the stance I wanted, in 1983, the front suspension is in solid stack, with the track arms pointing up. I'm looking at cutting up the crossmember and redrilling it to move the inboard pivot up. Will need to revise the steering arm height to counter bumpsteer, and relocate the upper strut mount higher in the inner fender to provide some suspension in addition to the tire sidewall.

Reason I'm lengthening is to minimize transverse movement of the track arm balljoint. When the car rolls in to a turn is the reduced transverse movement balljoint should reduce positive camber gain.

[CrisAnderson27]

First, the car is a European Ford (my avatar, a Ford (Mercury) Capri). I've had the car since February 1979.To get the stance I wanted, in 1983, the front suspension is in solid stack, with the track arms pointing up. I'm looking at cutting up the crossmember and redrilling it to move the inboard pivot up. Will need to revise the steering arm height to counter bumpsteer, and relocate the upper strut mount higher in the inner fender to provide some suspension in addition to the tire sidewall.

Reason I'm lengthening is to minimize transverse movement of the track arm balljoint. When the car rolls in to a turn is the reduced transverse movement balljoint should reduce positive camber gain.

I see...so due to your current inboard mounting position and the resultant upward slope of the control arm towards the spindle...you're trying to increase the radius of the curve to minimize lateral movement. Makes sense.

I actually got my shortened arm mounted up Friday:

https://static1.pt-content.com/images/pt/2014/05/20140502195018-1.jpg

The picture shows the suspension at full droop...with the inboard mount very nearly where it will be when finalized (it needs to move up and towards the spindle about half an inch to work properly with the steering). Full droop is important to check on this car, because...well, it should see it every pass down the track. Today I'm going to be measuring for my strut rod length in the new mounting position also (strut rod needs to be shortened equally) so I can verify the travel in compression as well. Right now there's nothing controlling the fore and aft movement of the spindle so it would be a difficult thing to check, at best.

[Motorcitydak]

Cool, good to see you got it done. Unfortunately most of us on site are doing SLA (short/long arm) front suspensions so we do not have much data on strut style suspension. However they do not offer much in camber gain during travel so the length of the arm itself does not do too much to change camber gain. Your thinking is right on in that you just have to match the control arm length to the tie rod

[CrisAnderson27]

Cool, good to see you got it done. Unfortunately most of us on site are doing SLA (short/long arm) front suspensions so we do not have much data on strut style suspension. However they do not offer much in camber gain during travel so the length of the arm itself does not do too much to change camber gain. Your thinking is right on in that you just have to match the control arm length to the tie rod

Thanks...and I completely understand. I've seen a couple of really cool strut based cars here, but this kind of setup is obviously in the minority...and obviously we all don't have time to babysit everyone else's projects lol.

The initial problem I had trying to find an answer to my question, was that the terminology necessary to formulate any sort of search, is incredibly generic...while what I needed to know was incredibly specific. Lower control arm length, LCA, MacPherson strut, short, lol...the sheer number of unrelated hits is incredible.

I'm really looking forward to getting the thing down on the ground, and eventually moving under its own power. I can't wait to see how it drives with all of the changes I'm making.

[CrisAnderson27]

Got a bit more done today.

https://static1.pt-content.com/images/pt/2014/05/20140504174435-1.jpg
Suspension at ride height. My control arms are right at about 13.5" long, and I have a hair over 1" of upward travel at 4" from the mounting point before the frame. By the numbers, this should give me something more than 3" at the ball joint (in line with the strut...which has about 4" of travel left), and over 4.5" at the wheel. I'd like a hair more cushion, but I think this is sufficient.

https://static1.pt-content.com/images/pt/2014/05/20140504174501-1.jpg
This is the camber at ride height, with no adjustment. That half bubble on the level adds up to something under 1/4" per foot of slope, or about -1° (I think this number could be FAR worse with the constraint of keeping relatively close to the factory 67/68 track width). The caster/camber plate is maxxed out for positive camber, but I still have about 5/8" positive (inboard) adjustment on the rod end. Worst case...I'll shorten the arms another 1/2", just to give myself a bit more inboard adjustment, as I'd like to have the caster/camber plates a bit more centered if possible.

https://static1.pt-content.com/images/pt/2014/05/20140504174608-1.jpg
Overhead shot of the strut rod setup. It looks WAY out in this picture, but if you raise the stock LCA, they actually line up almost perfectly.

https://static1.pt-content.com/images/pt/2014/05/20140504174510-1.jpg
https://static1.pt-content.com/images/pt/2014/05/20140504174645-1.jpg
https://static1.pt-content.com/images/pt/2014/05/20140504174722-1.jpg
A few pictures showing the clearance to the frame at ride height. I think this will work to be honest...but until I drive it, I really won't know for sure.

So that's it for now. I didn't get to any of the rear end stuff, and didn't get the other side setup either...but I still feel like I accomplished something. Tomorrow I'm going to hit the local surplus store for a couple of right and left hand 1/2" rod connectors and some all thread to replicate my strut rod so I can size it properly. I'll also grab some 5/8" if its available, to simulate my outer tie rods as well. If things work out over this week, I'll be able to get all the measurements for my swedged tubing, and get the rack mount position roughed in as well.