A custom front suspension can be built using modified GTS struts. A similar design could be used with other front stut donors. Here's a of the front suspension components with a modified strut.
The GTS design uses bracket locations similar, but not exactly the same as those in the book. The intent is to retain a matching track between the front and back of the car, and to allow the use of the the same wheel offset and bolt pattern on all 4 wheels. There are other suspension designs, and not all arms will work in the locost chassis - check carefully before purchasing if you aren't making your own.
A comparison of various front suspension geometries, including the book version, can be found here: Locost Front Suspension Geometry.
McPherson struts, cut to length, with a cap welded in place to hold bolt receiving an upper spherical rod end. After machining, I chucked the cap in a drill by passing a bolt through it and used a file to finishing fitting to the cap to the strut, final diameter was 1.795". I used a 3/4" high strength spherical rod end from McMaster-Carr. The spherical rod end is held to the cap using a 3/4" grade 8 bolt fit through the bottom and welded in place before the cap is welded to the strut. Strut was cut off square 3 1/4" (you may want to cut at 3 1/2", see the 12/2000 update below) up along the tube portion in line with the bolts holding the steering arm in place. I used a hacksaw to cut the strut, a hose clamp serving as the saw guide. Struts were swapped from side to side to allow for a front steer steering rack.
Note that this strut cap design, using ball joints rather than large tie rod ends, is very sensitive to the angle of the upper a-arm relative to the strut. Suspension travel will be limited within a narrow range dictated by the maximum offset angle allowed by the upper ball joint. It is critical that you fully design your suspension to determine the length of the struts needed to keep the range of travel desired. My design allowed for setting the shocks up with 1" of compression at ride height (lower a-arm horizontal), allowing the shocks to compress 2" or extend 1" from this point. The tolerances are rather tight, the travel allowed by the ball joint was just sufficient.
I've used some 3/4", grade 8 bolts and appropriate sized spacers, and welded the bolts to the caps. The nut seen in the photo will be replaced with a nyloc nut upon final assembly. Note in that photo that I've used 1/4" spacers UNDER the ball joint as well as over. This was necessary to get the correct bump/rebound motion. I would recommend that you cut your struts as above at 3 1/2" rather than 3 1/4", allowing you to skip the spacers. It's always easier to take a bit more off than add a little more on :-).
My original design utilized cutouts from the doner lower control arm, welded into 2 1/2" OD, 1/8" wall tube. The original ball joints were then pressed into these cutouts, and locked in place with a ring. After reflection on the advice I received from Geoff Hollins, I decided that this was just not a good idea. The issue is that the ball joints on the GTS don't support any load, and are used only for location (the spring load is through the top of the strut). In our use, the ball joints are in tension, from the springs to the lower arms through the wheels. In actual fact, the original design is quite strong, the ball joint designed to be held in tension in the press fit ring, so all of the forces where directed correctly. The only concern was that if a wheel were to move to full droop under force, it might be possible for the ball joint to be forced from the retaining ring and popping free. Unlikely, but possible (it would take some sort of jump or very large bump.
I broke apart one of the stock ball joints, and I think that it's quite capable of supporting the weight of the car in tension - it comes apart by pushing the ball joint out (violently) through the bottom. But I didn't know this till I took it apart, so I decided to go ahead with a new design.
Lower ball joint supports are made from a 3/4"" length of 1/8" walled 2 1/2" OD tube. Lower control arms are made by welding the tubes making up the a-arms to this ring. A plate is added between the a-arms to support the arms and hold the shock bracket. When I made mine, I modified them slightly from the drawing in the downloads section, the tube being flush with the top and bottom of the control arms.
Inspired by Phil's design (see below), I strengthened my own lower control arms in a similar fashion. I cut two lengths of 3/4" square tube, and profiled them to fit between the tubes up against the ball joint support. The welded side of the square tube was filed down to fit as tight as possible against the support. Then the square tube was welded in place.
Next, a threaded sleeve to hold the ball joint is pressed into the ring, leaving 1/4" protruding from the bottom (the sleeve is 1" long and 2 1/4" in diameter), and welded into place. I believe the control arms could be welded directly to the threaded sleeve, but I was concerned with damaging the threads.
The lower ball joints are from a racing application (see New Parts), and provide a lot of additional strength. The first step is to ream out the lower strut bracket (the piece with the control arm for the steering) to accept the new ball joint. I used an 12":1 1/2" (8:1) ball joint reamer. The holes are reamed carefully until no more than 1" of the ball joint thread protrudes through the top of the hole - there's only 1" of clearance inside the strut tube.
Phil Dale has improved on my design by incorporating more of the donor's lower control arm steel. This gives more welding area to attach the tubes, providing additional strength. A plate across the top holding the spring mount will be attached to ball joint ring holder, providing even more strength. Check it out here: Phil's Front Suspension.
These are very similar to the book version. If you can use curved arms, do so, as this will provide more room for any choice of shock and spring. As designed, the shock/spring diameter is really limited to about 2 3/4", though there may be a little more space available - measure carefully before ordering! For the threaded bush to hold the spherical rod end, I used 1" OD 0.156" walled tube, tapped to 3/4"-16NF from the Chassis Shop. See new parts.
