Hank,
You can check for square with plumbbobs, measuring diagonally from wheel to wheel. Mine seemed pretty close, as well as I could measure (tough to do accurately), and you can't adjust it very well anyway, except rear track width, and that only slightly. Here are my notes:
DIY Four Wheel Alignment of the FFR Roadster
Tools and equipment needed:
(2) 7 foot lengths of 1” I.D. Schedule 40 PVC pipe
30 ft heavy monofilament or string
(4) elastic shockcords
machinists scale, dial calipers or tape measure
level
large carpenter’s square
camber/caster gauge
wrenches
blocks to support frame (IRS cars)
Specs:
Front caster 3 degrees (5 if using power steering)
Front camber –1 degrees
Front toe 1/16” total
Rear camber (IRS) –1 degrees
Rear toe (IRS) 1/16” total
REAR ALIGNMENT--IRS
To make adjustments to the IRS control arms, you will have to unbolt the rod ends when you twist them in or out as needed, which obviously cannot be done with the weight on the rear wheels. IRS alignment is a somewhat tedious process of trial and error, but it only has to be done once. The process is made much easier if the rear cockpit panel, the upper trunk floor, and body shell are not yet mounted, so do this early in your build!.
First thing you need to do is sit the frame on blocks, at ride height, on perfectly level ground (check and shim with masonite, cardboard, etc). The wheels need to be exactly level from side-to-side. Measure with a long 2x4 across the tops of the tires, or a long clear plastic tube filled with water. Or park them on a flat surface that you have confirmed as level. Most garage floors are close to level, but you may need shims. The car need not be level fore-and-aft. Remove the rear coilovers or back the spring way off. This way the control arm angles will be as at ride height, with the frame weight resting on blocks, and the tires resting on the ground, and you can still move the suspension arms as needed to adjust the rod ends. [If the body is on, you may want to put the frame on jackstands, and block the wheels up so that the suspension is at ride height, so that there is enough room for you to get underneath the car to turn the rod ends. Be glad that it will only need to be done once, or maybe again if you change ride height]
You will need a camber gauge to set rear camber accurately--Behrents has one for $40 (get the rim type, not hub type) (
www.behrents.com). You can set it by eyeball for now, top of tire leaning "in" by about 1/2" relative to bottom of tire. We will do the final camber adjustment AFTER rear toe-in has been adjusted, since changing toe-in will change camber, while camber changes will not affect toe-in. To adjust camber, twist the UPPER control arm Heim joint in or out of the control arm until it is right. This will be a process of trial and error.
Next we need to string two strings, one on each side of the car, perfectly parallel to the 4" frame tubes, and to each other, at about mid-axle height. The best way to do this is to build trammel bars across the front and rear of the car, so that the strings will maintain their relationship to the car even if it rolls or moves. The quickjack bumpers supplied by FFR are ideal for this purpose. If you are in go-cart stage you will want to mount the quickjacks onto the frame now. Next take the two 7 ft PVC pipes and mark notches about 3” in from each end, so that the length between the notches is EXACTLY the same on each pipe; this will ensure that the strings remain parallel to one another. Next, put the PVC pipes under the quickjacks, so they are wedged into the notch on the bottom of the quickjack, secured by wrapping the quickjack and pipe with an elastic cord, centering from side-to-side, by eyeball for now. The pipes will now run across the front and rear of the roadster, more-or-less centered. Now tie a length of monofilament along each side, from the front trammel bar (pipe) to the rear, using the notches to insure that the strings remain parallel to one another (i.e., the ends of the strings are equally far apart at each end of the car).
Now we need to make sure that the strings, which are parallel to each other, are parallel to the frame. Do this by measuring carefully from the 4” frame tube, using the square or a plumb bob, sliding the pipes in the quickjack notches from side to side as necessary. They should ideally be equidistant from the 4" tubes on each side, or very close, so that we can be sure that the wheel track is centered on the midline of the frame. This is probably the hardest, or at least most tedious part; but accuracy here is important. The 4” frame tubes should be parallel: if slightly off, just use one side for a reference. Once you have the monofilament parallel to the frame, I recommend marking the pipe at the quickjacks, and being sure that the elastic is firmly holding the pipe. This is insurance, so that when you accidentally bump the string or trip over the pipe and knock it out of place, it will be easier to reset it accurately.
Now we are ready to check rear toe-in. You may use either use the wheel rim, if you are sure they are straight (spin'em to check), or wrap a big piece of masking tape around the tire and mark a line around it while rotating the tire, in the plane of rotation, to use as a reference.
Now simply measure from the string to the rim (or mark on tire). We want to have the distance, from the string to the rim, equal on both sides of the car. Measure toe-in as the difference of the front of tire versus rear of same tire or rim: 1/16” total, or 1/32” for each rear wheel..
Unless you are VERY lucky, when you first measure it, toe-in will not even be close. Adjust as needed, by turning in or out on lower control arm Heim rod ends. To make the changes, I find I can just unbolt one of the Heims, then kind of cradle the wheel/control arm in my lap while I twist the rod end in or out. Then you must remount the rod end into the frame with the bolt and shims. If you need to move it a lot, try to turn one in and one out: if you do all the adjustment at one joint it will affect camber somewhat, which is not a problem at this point. Also try to keep an equal distance from the string on each side of the car, so that the rear track remains centered on the midline of the vehicle. You may need to turn all 3 (upper and lowers) in or out to adjust width. Be sure that you don't unscrew the rod ends so far that there is too little thread remaining threaded into the control arm.
After toe-in is correct, it should stay that way unless you alter ride height significantly. Recheck camber after toe-in is set, and adjust as necessary, adjusting ONLY the upper control arm. If you compete, you will want to adjust camber later according to tire temperature measurements, otherwise leave it at 1 to 1.5 degrees negative (FFR calls for –1 degree). Camber will change quite a bit with ride height changes, BTW.
REAR ALIGNMENT-- SOLID AXLE: You will still need the strings to align the front end, so follow the directions above, except that the car may rest on the tires: it is not necessary to remove the springs to align the front. If you have a solid axle, both wheels should be parallel to the strings unless your axle is not in line with the frame. It should be centered side-to-side.
FRONT ALIGNMENT: The front is easy compared to the IRS rear, but you will need a camber/caster gauge like the Behrents tool. The tool comes with instructions for using it to set caster and camber. Caster and camber adjustments tend to interact somewhat on the front of the FFR Roadster. Basically, caster is adjusted by moving the upper ball joint forward-and-aft, while camber is adjusted by moving the balljoint nearer or farther from the midline of the car. We accomplish these by sliding the upper control arm mounting bolts in opposite directions to change caster, or sliding them both in the same direction to change camber. This is much easier to do accurately if you have welded on nuts for adjusting bolts, or installed John Lisman’s widgets. It should be even easier with the new adjustable upper control arms.
Do not set front toe-in until caster and camber are properly set, because changing caster/camber will change front toe-in. You will need to set front toe-in after caster/camber, and this is easily done using the strings. Adjusting front toe-in will not change camber/caster.
Here are abbreviated instructions to use the Behrents caster/camber gauge. Others may be similar—see the instructions provided with your gauge. NOTE that adjustments will move the tire contact patch in or out slightly, distorting the tire and making adjustment difficult. To avoid this problem, you can buy an expensive set of glideplates to go under the tires, or make your own using squares of linoleum or metal with grease between, or do as I do and just roll the car back and forth a few feet each time. The big advantage of the trammel bar pipes attached to the quickjacks is that they will move with the car, so you don't lose your reference points.
To check CASTER, turn the front wheel “in” 20 degrees (about one revolution of steering wheel). Then apply the Behrents gauge and use the dial to center the bubble. Now turn the wheel “out” 20 degrees, apply the gauge, and rotate the dial to again center the bubble, counting the number of revolutions (marks) and direction that the dial is turned. Multiply the number of revolutions by 1.5 to get the number of degrees. Clockwise turns =positive caster; counterclockwise =negative caster. [For example, if you turn it 3 turns clockwise, caster is 3*1.5=4.5 degrees positive]. Caster is the amount that the wheels lean back when turned—think of a motorcycle fork. Values are not real critical, but right and left sides should be equal. More caster helps front adhesion in a turn, but may make the steering wheel effort higher; the consensus seems to be about 3 degrees for manual steering, 5 degrees if you have power steering.
To check CAMBER, set the wheel straight ahead (measure from the string). Set the Behrents gauge to zero, apply it to the wheel, turn the dial until the bubble is centered, counting the number of marks turned, and the direction turned. Clockwise =positive camber, CCW =negative. Each complete revolution of the knob is one degree, each mark is 1/8 degree.
Finally, after camber and caster are correct, set the steering wheel straight ahead, and adjust the TOE-IN at each front wheel. Front toe is 1/16” total, or 1/32” at each front wheel. Adjust with the tie-rods. Be sure ride height is correct for this, toe-in will change a lot with suspension travel unless you have properly installed a bumpsteer kit or otherwise eliminated bumpsteer.
After doing all this, you will be ready for a beer or two. Rest assured that your car should track straight and true, with the steering wheel centered, after these endeavors. If it does not, check tire pressures first, check integrity of suspension bushings, and check bumpsteer (a whole topic itself).
Note that we have not checked the frame for squareness by measuring corner-to-corner in an X pattern. You can check for square with plumbbobs, measuring diagonally from wheel to wheel. Mine seemed pretty close, as well as I could measure (tough to do accurately), and you can't adjust it very well anyway, except rear track width, and that only slightly. While I’m sure that there will be some variation from frame-to-frame, and some may not be perfect, differences should be insignificant. Any out-of-square condition will be reflected by a slight difference in wheelbase on one side relative to the other, of little consequence. After the wheels are aligned as above, all four wheels will point straight ahead, and be in line with the frame.
With thanks to a bunch of people, including Steve Alexander, Jack Rosen, Carroll Smith, James Creasy and probably others.
[email protected]
[ April 23, 2002, 11:50 AM: Message edited by: forrest1 ]
