Suspension Set Up I decided to write this primer on suspension set-up, as a byproduct of implementing full independent front suspension and the new tubolare rear trailing arms on my own car, in preparation for the 2010 season. In thinking about what had to be accomplished, I realized that the techniques I was planning to implement would be of value to others as well. Most of the materials to do this can be purchased from the local hardware store. I find that in doing this work myself, rather than entrusting it to a suspension shop (who WILL not be familiar with the suspension of the Fiat 600), will ensure that the job is done thoroughly and completely. One thing that I find ABSOLUTELY mandatory, is a square ruled notebook to record your measurements. Without it you will be lost in no time, and simply have to repeat the work. I know that my memory is not good enough to remember all the data, so I make copious amounts of notes. As such, there are two thought processes that have take place simultaneously. First, the objectives to be achieved with the vehicle; and a second, formalizing the process dealing with the mechanics of achieving the first objective. A. Squaring the chassis. When installing new suspension, or reinstalling existing suspension after an accident repair, it is not sufficient to simply hang the new pieces in place, do a wheel alignment (caster, camber and toe-in in that order), and then call it a day. You must first establish the various datums (reference lines) for the chassis that will allow you to do the work systematically and accurately. The four basic datums are as follows: 1. Base Plane This may be a horizontal plan on the vehicle itself, or more commonly the floor beneath the vehicle is used as a base plane datum. 2. The Longitudinal (Z datum) This is generally the front axle centerline, with all measurements to the rear of the front axle centerline being positive (+) and to front of the front axle centerline being negative (-), as viewed while sitting in the driver s seat. 3. The Lateral Line (X datum) This datum establishes the location of various items in relation to the center line of the vehicle. This centerline can be established by measuring known, hard locations on the RT and LT side of the chassis, and then taking half this measurement. This establishes the centerline. Lateral displacement from the centerline is noted as positive (+) to the left of centerline and negative (-) to the right of the centerline, again while seated in the driver s seat. 4. The Vertical Line (Y datum) A vertical projection, generally at the intersection of the X and Z datums (this would be the front axle and the centerline of the vehicle, if only for convenience, with all numbers being positive (+) upward from the Base Plane. This is used in conjunction with the X and Z points to dimension a three dimensional point in space for the various components of the chassis and the suspension.
These datum lines, and the corresponding suspension component locations derived from them, will help you in determining and adjusting the suspension components so that the wheel locations are equidistant from the X and Z datums and at equal height above the chassis floor, With reference to the Y datum. During the process you may have to readjust the vehicle to the datum lines more than one time, particularly if you have to remove suspension components in order to make adjustments. You will also see the tracking distances indicated on the above drawing. I will get into that a little later. B. Leveling the measurement platform. The first order of business is to find a flat (or nearly so), bare floor. In my particular case, as I have a carpeted floor in my workshop (don t ask why as it is a long story), I purchased three 4 x 8 foot sheets of 1 pressed wood panels and laid these on the floor side-by-side. In between the sheets I used lengths of T extrusion 1 x 1 (25mm x 25mm) to join the sheets together to insure they did not move relative to each other. I also put 1 x 1 (25 x 25mm)aluminum angle along the edges to make sure that rolling the car on and off did not damage the sheets of wood. Instead of marking the datum lines in chalk, I chose to mark them using a permanent marker for future reference. The main reason for this is that once I get the entire project finished I am going to digitize in 3D the entire suspension system for entry into the SUSProg program, so that further modeling of the suspension can be done. This complete Floor Datum can be dismantled and stored for future use. Next roll the car onto the Floor Datum and position it so that the car in is the middle of the surface. Mark the tire locations with a square box for future reference. Check each wheel location with a level (in both the X and Z direction, to determine if you have to deal with a significant slope. Jack up the car so that the tires are 2-4 (50-100mm) or more from the ground. The chassis on the standard 1000TC is quite low to the ground, so making suspension adjustments will be difficult unless you get the car off the ground by some amount, or you have a very small helper to slide under the car. I used solid concrete pads to build four wheel locations that are 50mm high and then put a piece of 1 (25mm) ground granite on top of the bricks. This lifts the car 3 (75mm). Next, I leveled the four wheel platforms, using a long bubble level. A 6 ft level is long enough to stretch between the front and rear platforms for side-to-side level adjustment, and a long, straight piece of wood will be required to span the distance between the platforms in a fore-aft direction. Two photos showing the bubble level used to level the four platforms.
I used a Sears rotary laser, set in the middle, to double check the results with the bubble level. Make notes in your notebook of what pieces you used at what corner of the car, and the next time it will be much faster. Place at least one linoleum floor tile on each of the platforms upside down (smooth side down either against the granite surface or another linoleum tile) and coat the tiles with some axle grease before putting them down. The reason for this is that as the car settles down on the four platforms the tires will sideways tire thrust. If the two tiles do not have grease between them, then the suspension will not fully settle. When working on platforms such as this we cannot roll the car back-and-forth to settle the suspension. You may see as much as an inch (25mm) of side thrust when lowering the car on to the platforms. Note: In case you have to jack up the car to make adjustments, or later when doing caster measurements, the greased tiles will allow the tires to slide/turn friction-free. Of course alignment turn plates would be best, but this is a very good alternative. Here is a good shot of a car on the concrete platforms with additional linoleum shims to adjust the height. The next thing is to set the ride height and rake of the vehicle, as we would want it on the track. This should be done with the fuel tank full of fuel, all fluids, and with a number of the concrete bricks in the driver s seat to simulate the weight of the driver. If you do not have adjustable ride height suspension (coilovers), then you may be limited in what you can do. For the standard rear coil springs you can use rubber spacers under the springs to modify ride height and rake. If you have independent, coilover suspension, then you can use the adjusters to set the height/rake precisely. You now have a car s attitude as you want on a horizontal plane. If you have corner scales (or a weight jacker) then you can check the car for weight distribution.
Corner scales and a corner weight guage If you have corner scales, now would be the time to look at weight distribution and adjust the chassis as required, because changing it later would change the final camber settings. This is the point where you need to transfer the three datums to the floor plane and mark/notate then on the Floor Plane Datum. The Longitudinal Datum and Vertical Datums are relatively straight forward to establish. Normal procedure is to use the front axle centerline as the Lateral Datum The vertical datum is at the intersection of the Lateral and Longitudinal Datums. Mark all of these datum lines/points on the floor and draw a diagram of them in your notebook. C. Locating the Lateral and Longitudinal position of the Front Axle. Normal convention is to use the front axle as the Lateral datum. Do not use the front Stub axles as the determination of the center of the front axle. This will vary as you turn the steering. Instead find a fixed point to reference the front axle centerline. Adjust the front lower a-arms as required, if you have independent front suspension, to get them centered on the front crossmember. If you have a leaf spring car, then use the center of the leaf as you location. With a leaf spring front end there is little that can be adjusted. The aim is to make sure that each lower a- arm is in-line with the centerline of the front axle and an equal distance from the Longitudinal datum (centerline of the car. The normal wheelbase for the Fiat 600 is 78.7 (2000mm). Having the rear axle too far forward, perhaps with a shorter than standard wheelbase, will also affect the fore/aft weight distribution of the car. If the measured wheelbase is different than 78.7 (2 metre), then decide which axle needs to be moved to attain the desired measurement. E. Locating the Centerline and Longitudinal position of the Rear Axle. Everything that you have done up to this point has been purely preparatory, for the real work that you are about to begin. You will need a notebook at this point to make detailed notes NOW. The more information you write down, the less information you will have to remember. The first issue is making sure that the rear axle is located centrally and at precisely 90 degree angle to the centerline of the car. The easiest way to do this is to measure the location of the axle, at a fixed, hard location in relation to both the Longitudinal and Lateral datums. So, with a plumb bob, drop the locations to the Floor datum, mark it, measure and note these in your notebook. After you have done both sides, this will tell you whether the axle is skewed in the chassis, and/or if it is off-center in the car. You will note that I speak of the axle as if it were a beam. However, as the Fiat 600 has independent rear suspension, the swing arms (or trailing arms for tubolare or pendolare suspensions) can be adjusted, individually on each side, to minimize any discrepancy. Perfectly equidistant spacing, from the Longitudinal datum, would be nice, but if the LH and RH numbers were within a ¼ (6mm) of each other I would not consider this a problem. Note: The homologated wheel track width was listed as 1160mm +/- 2%. This would make the maxium track width for FIA purposes 1183mm for one tire centerline to the
opposite tire centerline with the wheels VERTICAL. It is however just as important, and perhaps even more important, to get the fore/aft distance from the Lateral datum to within a ¼ inch (6mm), otherwise one side of the axle will lead the other, and it will have a thrust angle that is not parallel to the Longitudinal datum, making it handle quite differently in RH and LH turns. Make a notation in your notebook as to the final adjusted distance for LH and RH sides of the rear axle, as well as the distance above the floor datum for the axle center. Once the axles are in the correct position with a wheel base of 78.7 (2 metre), or longer, and you have double checked that the car is once again on the lateral and Longitudinal datums, then you need to take measurements and note any location that you may need in the future to repeat the process up to this point. E. Cross Chassis Measurement If you now drop identical locations on the front and rear axles on the RH and LH sides with your plumb bob, and mark them on the floor, then you can do a cross measurement from RF to LR and from LF to RR, and the measurements should be very close to identical. This means that the car s suspension is square and also square to the chassis it self. F. Centering the Steering Before checking and adjusting the steering, make sure that all of the tie rod end joints are in good condition, and that the rubbers in the idler arm bracket are not sloppy. The next job is to center the steering in the middle of the travel. Turn the steering all the way to one side, and then all the way to the opposite side, counting the number of turns of the wheel. Now turn the steering wheel back half the total number of turns. If the steering wheel is not centered, remove it and center the wheel, and then lock the wheel so that it cannot turn. Next, adjust each tie rod so that they are approximately of equal length and the wheels are generally pointed straight ahead. At this point you do not have to be exact, but they should be close. You will eventually check the toe-in with parallel string lines, but for the moment they are just going to get in the way. F. Setting the Caster. Now you will need a Camber/Caster gauge, or at least a camber gauge and pencil and paper. First let s talk about making a camber gauge. Here is a commercial gauge that you can purchase for around USD$200. However, if you are handy with a drill and a saw you can make your own. I would make one out of a little digital level indicator and a piece of 1 inch steel, thin-wall steel tubing and three, 2 inch long pan-head ¼ x 20 screws. The level you can purchase from Sears for between $20 and $40. What you will end up with is something like this. Alternatively, if you own an I-Phone and a piece of straight wood, there is a neat little inclinometer application for it that will allow you to use it to measure caster and camber.
Now this is only a camber gauge, but we can compute the caster angle from the two camber angles at 20 degrees of wheel turn to the right and left. The formula is as follows. [(Camber RH 20 Degrees) ( Camber LH 20 degrees) ] x 1.5 = Caster [3.0 (-1.5)] x 1.5 = 6.75 degrees caster. Since the digital level is accurate to 0.1 degree, this would give an accuracy of =/- 0.06 degree, which is probably quite good enough for our types of cars. It is important to set the caster FIRST and have it the same on both sides of the car. As we earlier set the distance from the Lateral datum to the lower a-arm/leaf spring eye, you should try to adjust the caster using the upper arm adjusting shims between the a-arm trunnion and the chassis. Only if things are very far out of adjustment will you have to make more heroic adjustments. G. Setting Camber. Camber must now be set for both the front and rear axles. Front I recommend about negative 1.0 of static camber. Adjust the upper a-arm trunnion by adding/subtracting shims of equal thickness on both sides, so as not to upset the previously set caster adjustment. If not enough adjustment is available, then modifications to the leaf
spring/lower a-arm are required. If you are setting up a car for FIA racing, be careful that you do not exceed the maximum track specification on the Homologation papers. Rear The standard Fiat suspension is a swing arm type suspension, and there is little that can be done in terms of camber adjustment with the standard arms. As you lower the car you will automatically gain negative camber. Being a swing axle, remember that as the chassis rolls in a corner that the will be a natural camber gain. This means that the amount of negative camber will increase. Photo courtesy of Ad Van Ling Ad has made a lot of changes since this photo was taken. Here is a fantastic example of too much rear camber. The chassis is highly loaded in a RH turn, with very close to the maximum 3 degree chassis roll. The RH rear wheel is extending, and still has 2-3 degrees of negative camber. So much so, that the tire probably only has 50% of its usable contact patch on the road surface. The LH wheel is probably at something like negative 6 degrees, and may also only have a partial contact patch available for both forward and cornering forces. If the tires stood up straighter, even with the same 3 degrees of chassis roll, there would be larger tire contact patches for each wheel and the car would be able to generate higher cornering speeds. At this point this car is suspension-traction limited, which is limiting how much of the available horsepower can be put to the ground. This is however a result of the standard trailing-arm design. There is a solution. You could put tapered shims between the bearing carrier and the trailing arm face (where the bearing carriers mount) which are thicker at the top than at the bottom. This would allow the tire to sit more upright (even though it has been lowered a great deal in the rear), without generating massive negative camber. Caution! You will have to make some tapered washers as well, so that when the four mounting bolts for the bearing carrier are inserted, they have a flat surface to tighten up against. I used this configuration and tack-welded the washers in place on the inside of the trailing arm face, where the bearing housing mounts.
Andre Van Koeveringe s Div. 2 winning car in action Note the straight up wheel position. If the car is equipped with tubolare or pendolare arms (as the car above), then these would have been manufactured with the bearing carrier angle revised to allow much greater lowering, without generating excess negative camber. This means that no more than negative 1.0-1.5 degrees should be required. As the car corners it will generate additional negative camber, but this should be very much equal to the additional generated camber at the front of the car. E. Setting up Perimeter Strings. The next step is to set up parallel string lines, on each side of the car, equidistant from the Longitudinal datum. These string lines should be positioned so that they bisect the axle centers of both the front and rear axles. The amount of offset from the Longitudinal datum is entirely up to you. I chose a distance 2 inches (50mm) greater than the distance to the outside edge of the rear tire, as rear axle has the widest track if you are using wider wheels on the rear than the front.. I then took two pieces of straight, electrical conduit and marked the center and also the offset distance. In the center of each piece of conduit I drilled a small hole and installed a zerk-o-bob fitting.
These drilled out zerk fittings allow a plumb line to be threaded through and provide a very accurate location. Note: I have even thought of mounting a series of these on various locations, to provide instant accurate locations of important points on the Floor datum. I then also mount two additional zerk-o-bob fitting at 90 degrees to the first one, to terminate one end of the string line. Once you have two of these conduit tubes clamped to a jackstand at each end, you can quickly position the two string lines at equal distance from the Longitudinal datum. Now the string lines will be equidistant from the centerline of the vehicle, parallel to it, and you are ready to finish the rear suspension. This diagram does not show the conduit tubes between the jack stands, front and rear of the car, but this would simply speed the set of the lines.
Now, using a small ruler, graduated in 1/32 inch or 1mm increments, measure the distance from the wheel edge to the string line, directly both fore and aft of the center of the hub. If the distance to the line is greater at the front of the wheel than at the rear of the wheel, then you have toe-in. If you have the reverse, you have toe-out. Let me say at this point, that unless you are doing a very tight, slow speed slalom or gymkhana event, you NO NOT want toe-out. A toe-out condition will make the car VERY nervous on corner turn-in with significant oversteer possible. I recommend using either a straight ahead position or about 1/32 (.75mm) toe-in per side, for a total axle toe-in of 1/16 th inch or 1.5mm. This creates a small slip-angle between the tires and the road. The initial small about of toe-in will be reduced at higher speeds by the tire drag putting the rubber bushes under tension. The net effect is that the car at high speed will have very close to neutral alignment. If however you find that the car is very nervous at high speed, with you having to make steering wheel corrections to keep it going in a straight line, then it is likely that you will need some additional toe-in. Not a lot, perhaps only an additional 1/32 inch (.75mm). As you can see, if we had not squared the rear suspension to the Longitudinal datum, then could have still adjusted the toe-in to the string lines, however one side of the car would lead the other side and affect the handling. Now go to the front suspension, without moving the string lines and set the wheel alignment settings for the front axle. Here is a general rule of thumb. If you want the car to turn into the corner quicker, then set the front suspension with a total of 1/16 th toe-out. This means that the inside wheel in the corner will be later in turning (due to Ackerman effect) and cause a slightly higher slip angle on corner turn-in. This higher slip angle will provide a slight pivot effect for the front end of the car to rotate around. On the other hand, if this makes the car too nervous (sometimes called loose ), start out with 1/16 th total toe-in. Remember that the rubber bushes in the front suspension will have some deflection, so at high speed the front end will generate some additional toe out due to tire drag. Small changes can make a big difference, so don t make any massive changes. On my own car, because much of the front suspension is located by spherical bearings, instead of bushings, I set the suspension up with 1/16 th (1.5mm) total toe-in, or 1/32 inch (.75mm) per wheel. The world s WORST situation will be where you have toe-out at the rear of the car, and toe-in at the front. This will create MASSIVE oversteer and the car will simply not be willing to go around a corner without wanting to spin out.
Part of my project in rebuilding my own race car, will be to document all of the important physical locations of the various chassis and suspension parts and recording these on paper. These will then be transferred to an engineering program called SusProg3D, so that the entire suspension can be observed dynamically in 3-Dimensional form. You will be able to identify changes that you could make to the suspension to optimize its performance. Best of luck with your chassis and wheel alignment.