At some point your
project is going to go on its wheels. You can save yourself some
work hours (and make the car feel pretty decent the first time
you start it up) by pre-aligning the front suspension previous
to putting weight on the tires.The bushing style control arms
(A-arms to you hotrodders, wishbones to you Brits) of book-built
Locosts are straightforward enough, plus there's not much you
can do to adjust them. The only adjustments are camber (by moving
the rod end on the upper control arm; thread in for more negative
camber) and toe (thread the tie rods in for toe in, out for toe
arms add some complexity, but the benefits are well worth the
trouble. Replacing the bushings with ball rod ends can significantly
reduce "compliance" -- the effect of suspension geometry changing
under load, due to frame flex, control arm flex, and suspension
bushing elasticity. Ball rod ends also allow straight load paths
(indeed they pretty much demand straight load paths) from their
attachment points on the wheel spindles to the suspension brackets
on the frame. This reduces control arm flex, and allows lighter
control arms for any given strength and rigidity.
And so, finding
the advantages outweigh the disadvantages*, we've departed from
The Book (that's Ron Champion's Build Your Own Sportscar for
as Little as 250 £; the book that started this Locost
thing) and changed to straight control arms and ball rod ends
for the Whippet.
Here's an early CMC
iteration of the Whippet-style upper control arm. It's for a narrow
track Locost (using an early Toyota Corolla rear axle) and the
tubes are 44 degrees from parallel. To avoid binding and to keep
the loads on the ball joints as radial as practical (radial because
ball rod ends are considerably weaker in axial loads than radial
loads -- 85 to 90 percent weaker in most applications; practical
because wide track cars have tube angles as tight as 28 degrees
from parallel) the chassis pick-up points (suspension mount brackets
on the frame) are canted toward each other. It is our understanding
that all CMC Locosts shipped after May of 2004** had the Whippet
style*** front suspension.
Before that, CMC
made interim kits that had ball rod ends instead of bushings on
otherwise "book" control arms, which fit "book" suspension brackets
and bracket placement. I've set up one car that used that style
suspension (the Grassroots Motorsports three-day-build Miata Seven)
using the technique described below and it worked pretty decent,
though I favor the Whippet (straight arm) style. For "book" suspension,
skip steps as appropriate; this will still get you in the ballpark.
- 1) Put your chassis
on four jackstands, on a flat floor. Shim the jackstands as
needed to make the car parallel to the floor. The accuracy of
your alignment will be directly proportional to the flatness
of your floor and the levelness (is that a word?) of your car.
- 2) Thread a locknut
onto each rod end; run the nut all the way to the ball end of
the threads (finger tight). Use real lock nuts. Using conventional
full nuts will cost you some adjustment range.
- 3) Using a felt
pen, mark the threads of each 1/2" rod end at 3/4" from the
threaded end, and the 5/8" rod ends at 1" from the threaded
- 4) Thread the
rod ends into the control arms, until the felt pen marks are
just barely visible. Now turn them in a little more (if needed)
so the balls will line up with the bolts in the frame suspension
brackets (aka "chassis pick-up points").
- 5) Bolt the control
arms in place on the frame. Don't bother putting nuts on the
bolts; you'll be taking them out again several times.
- 6) Bolt the wheel
spindles (with hubs but no wheels) to the control arms. The
techniques vary depending on which donor car sourced your spindles.
Finger tight is plenty for now. If your spindle-to-control-arm
mounting system uses nylock nuts for the upper attachments,
put the nylocks aside for now and use plain nuts (otherwise
you'll wear out the nylocks during the adjustment process).
- 7) Mount the brake
disks on the hubs. For some donors, the wheel holds the disks
on; if so for yours, put a short length of plastic tubing (or
use lots of washers) over each wheel studs so you can hold the
disks in place with lug nuts.
- 8) Tie the lower
shock mount to the upper shock mount with a piece of sturdy
twine (or flimsy rope), so the lower control arms are parallel
with the floor. (hey, it's easy to measure and it's close to
where your ride height will be when you're ready to roll).
- 9) Using two straight
edges, a tape measure, and some tape to hold the straight edges
to the brake disks, set the wheels so they point straight ahead.
A leftover length
of 1" square tube makes a good straight edge, but the very best
straight edge is a beam of light. A laser level taped to each
brake disk is very handy. Don't bother with the bubble, just
make sure the base of the level is held flush against the disk.
- 10) Using a carpenters'
square, adjust the rod ends as needed to put the brake disks
perpendicular to the floor and parallel with each other. This
can be done with measurement***** and math, but at this stage,
trial fittings go fast and if you're within a turn of spot-on,
you're good enough for now. Two important points:
--Turn the rod
ends in (clockwise) only. If the spindle has camber (the top
of the disk is outboard of the bottom of the disk) shorten the
upper control arm (by turning its rod ends in); if the spindle
has negative camber, shorten the lower control arm. If you adjust
the rod ends out of the control arms, you'll have insufficient
--Turn the 1/2"
rod ends on each control arm as a pair; that is, if you turn
the front rod end in 6 turns, do the rear rod end on the same
control arm 6 turns too.
Put the suspension spacers in place on the rod-end-to-chassis-pickup-point
bolts (the bolts installed in Step 5) and install shims (thin
washers) as needed for symmetry******. With one each 0.20"
and 0.10" long, 5/8"OD, 1/2"ID stainless steel
spacers, and three thin (they call them 'light' in the av biz)
AN washers, one can go from one side of the bracket to the other
by relocating spacers and washers. The photo below shows the
rod end centered in the bracket. Note that our quick adjust
control arms don't need shimming; a pair of 0.20" spacers
is all they need (see Works in Progress--Suspension).
- 12) Set the caster
so it's the same on both sides of the car. Since driving is
what's going to tell you if you want more or less caster, don't
aim for any particular absolute in this preliminary set-up.
Looking at the
side of the car, caster is the off-of-upright angle of the steering
axis of the wheel. Your car needs positive caster, with the
top pivot point rearward of the bottom pivot point (like the
front forks on a motorcycle). More caster increases straight
line stability (and thus, increases steering effort) and less
camber has the opposite effect (less stability, lighter steering).
How much caster you'll want is a matter of taste (it generally
runs between 4 and 6 degrees), but it's a good bet your taste
will run to similar steering effort and feedback for left and
right turns, so set both sides the same.
You may find the
caster angle easier to measure with the disk off the spindle
(you're looking for the line between the two ball joints that
pivot when the wheel is steered); I tape the disk to the spindle
and eyeball a line on the disk; marked with masking tape or
felt pen depending on which one's closest. I usually measure
the angle with a prop pitch protractor from Warp Drive Inc (a
carbon fiber aircraft propeller manufacturer), but a carpenter's
angle finder did a good enough job on the Grassroots car, and
simply whacking a matching angle (the floor to pivot line angle)
out of a big piece of cardboard is perfectly acceptable, since
you don't need to know what the angle actually is right now,
just that it's the same for both wheels.
Find the caster
angle of one wheel, and match the other to it by adjusting the
1/2" rod ends in one (or both) control arm(s) for the wheel
you're adjusting. Moving the outboard end of the upper control
arm back increases camber, as does moving the outboard end of
the lower control arm forward; reversing those directions decreases
To move the outboard
end of a control arm back, thread the forward 1/2" rod end out
and the rear 1/2" rod end in; the same number of turns for both.
arm should you adjust? The one you shortened the most during
Step 9. That way you're least likely to overextend a rod end
-- which will show itself because the felt pen mark (Step 3)
will be exposed. If that happens, you'll need to go back in
until the mark disappears (and out the same number of turns
on the other rod end you're adjusting) and finish the job by
adjusting the other control arm the opposite way.
- 13) Are any of
the marks made in Step 3 exposed? No big deal; just thread the
marked rod end in (and count turns) until the mark is just on
the edge of the control arm (or disappears completely, if you
prefer). Now thread in the other three 1/2" rod ends on the
control arms for that side of the car, the same number of turns.
This shortens both control arms equally, and gives adequate
thread contact for all the 1/2" rod ends on that side. This
maneuver won't change camber or caster, though it will bring
the wheel slightly closer to the car, narrowing the track insignificantly
(about 1/4" for six turns), and you'll have to redo the shimming
of Step 11..
- 14) Repeat Step
10, using only the 1/2" rod ends, and moving them in pairs (as
you did in Step 10) so you don't change the caster. Get as close
to perfect as you can, which won't take long because:
--Step 10 should
have put you darn close already, and Step 12 won't have changed
within 1/4 turn of a ball joint from where you want it, you're
as close as you can get. If a half turn (the smallest adjustment
you can make) one way puts the disk out from vertical, and a
half turn the other way puts the disk in from vertical, pick
the one that looks closest and call it good.
- 15) You can break
out your trigonometry textbook from yesteryear, or trust me
on this: three full turns in with a 5/8" diameter 18-thread-per-inch
rod end will put you very close to 1 degree of negative camber,
which is a good place to start. So, once you're happy with Step
14, screw the upper control arm outboard rod ends (the ones
that attach to the spindle) in as desired for your chosen negative
If your suspension
is more flexible than ours (you have curved control arms instead
of straight, or rubber bushings instead of metal ball rod ends)
give yourself another half turn or so. If you're running racing
tires and are convinced you should start off at 1-1/2 degrees
of negative camber, then turn the rod ends in 4-1/2 revolutions.
But if it's a street car, try it at one degree (three turns)
and see how you like it before you go wild and crazy.
- 16) Look for exposed
felt pen marks on the rod end threads; if so, deal with them
as per Step 13. Double check the shimming (Step 11) to avoid
side load on the rod ends in the chassis pick-up brackets. Snug
down the lock nuts on all the rod ends, install and tighten
the locknuts on the chassis pick-up point bolts, tighten the
control arm attachments to the spindles (Nylocks? Cotter keys?
Now's the time to use them), replace the twine of Step 8 with
coilover shock absorbers, and you're dang near ready to roll.
Thus endeth the oddball
aspects of the Whippet front suspension. All you have left to
set is toe, which is adjusted the same as any other car. Toe in
(the fronts of the wheels closer together than the rears of the
wheels) makes a car more stable in a straight line, toe out (the
fronts of the wheels farther apart than the rears of the wheels)
makes a car quicker to go into turns. Too much of either one is
a Bad Thing; too much toe out and you're driving a train, too
much toe in and it'll go into turns all by itself.
Cars are rarely run
with no toe at all, but that's my recommendation for initial setup;
loosen the locknuts on the tierod ends, install the tierods in
the steering arms of the spindles, use the straight edges (or
laser levels) and thread the tierods in or out as needed to make
the brake disks parallel to each other in toe. You can set your
toe before you take the chassis off the jackstands (if so, do
it before you replace the twine with the shocks; sort of a Step
15-1/2) or after the car is on the ground.
Mark the tierods
so you can get back to the no-toe position without remeasuring,
and after you've driven enough to get used to how it handles with
zero toe, try some small adjustments both ways. And speaking of
adjustments, if/when you readjust either caster or camber, you'll
have to readjust toe and your tierod marks will have to be redrawn.
*The only real downside
(IMHO) to straight tube control arms on Locosts and the like is
that with curved upper control arms, one can squeeze in larger
diameter coil-over shock absorbers. There's a fake downside too;
the fact that curved tunes are weaker than straight tubes means
that, in a mishap on street or track (a curb strike, for example),
one is more likely to bend a control arm and less likely to bend
a frame tube. That's the theory. I ain't buyin' it.
**We're not complaining,
mind you. Kinetic was a CMC dealer back then, at least on paper,
and it was an improvement I insisted on (and built the tooling
for). We swapped some (non-exclusive) suspension design rights
for some (equally non-exclusive) fiberglass design rights, and
everybody was happy.
***Well, we need
to call it something, right? It's not how Colin Chapman was building
Lotus Sevens fifty years ago, or how Ron Champion built the Locost
fifteen years ago, or how CMC built Locost kits before we brought
them our Whippet fixtures, so we'll pat ourselves on the back
for coming up with radial load control arms for Locosts.
rule of thumb is a rod end should be inserted at least 1-1/2 times
its diameter; that's 3/4" for the 1/2" rod ends and 15/16" for
the 5/8" rod ends. I round the 15/16" up to an inch because the
outboard rod end gets a bit of beam loading under heavy braking,
and shorter = stronger and stiffer.
*****Each turn of
the 1/2" rod ends moves the control arm roughly .045"; the 5/8"
rod ends bring the end closer to the frame by roughly .050" per
placement will cause camber changes as the suspension travels,
which is possibly a good thing (though if so, it's way beyond
my current level of understanding) but still not appropriate for
initial suspension setup.