From: Jay Kempf [jkempf@tds.net] Sent: Saturday, July 20, 2002 11:15 PM To: 928 Subject: [928] Alignment 101a (long, reeeeeeaaaaaaallllllllly lllllooooonnnnnnggggggg) OK here goes. Three variables.... 4 corners. That is the sum total of the subject. Well, except for height :) First variable... Toe in or out at each wheel. Most important to tire wear of the three variables. Tires that are scrubbing will wear. Too much toe out and the insides will wear. Too much toe in and the outsides will wear. Wear won't be even for this variable. The tires will chamfer or bevel for the first couple beads because the tire is basically rolling in under the strain of the steering input. 928s like to be real straight ahead or slightly toed with factory camber settings (about 1/6° is stock+. Toe is adjusted by lengthening or shortening the tie rod at the end of the rack. You use a 22mm and a 17mm open ended wrench to adjust. Even chubby people like me can do this by lying next to the car and reaching under. No need to lift. This is the simplest of the variables to adjust. To measure there are several methods including rigging parallel strings next to the car and then measuring to the front and rear edge of the wheel or to the tire. Another method is to put two needles in the tire and measure between them with a tape measure side to side first in the front then roll the car backwards till the needles point back and measure again. Difference plus trig plus tire size equals total toe. Total toe (in or out) does not relate to the steering wheel position. The car can be properly toed with the steering wheel wacky. Some cars like mine will not align in the center once the toe is properly set and the tie rods must be adjusted to center the wheel. Adjusting the toe of the rear wheels is done by rotating the eccentric at the front lower control arm attachment. You need to loosen the outboard nut on the long eccentric bolt and then rotate the head of the bolt to adjust and then retighten the nut to lock. These can be schmegged up and require disassembly and cleaning to do a good adjustment on older cars. My favorite method of measuring toe is to put a straight edge on the wheel with a laser mounted parallel with the straight edge. This allows you to extend the measurement for accuracy. mark on the wheel where you start with tape on two opposite spots on the wheel until you know your wheels are true. Tape or clamp the laser to a straight edge that only contacts the wheel rim. Use a shortened bungee cord to hold this in place to make it hands free. A small spring clamp or clothes pin to hold the button of the laser on. Measure and make a chalk mark at 10 feet or so in front of and behind the rear wheels. Aim the laser behind the front left at the 10 foot distance. Then repeat in front. Then do the same on the other side. Don't move the car. Use a tape measure to check the distance between the two rear and two front marks. Now you have something like 75" front and 76" rear. That means you have a total difference of 1". Divide this by 4 and you have .25 per wheel at 10 feet. Using tangents you can find that this equates to .119366° per wheel or a total of double that. Tangent is the little measurement divided by the longer measurement then inverse tangent on a trig calculator or [arctan(.25/120]. Roll the car back so that the marks are horizontal again or half a tire revolution and repeat. If the numbers are the same that spot on the wheel is true and can be used in the future. If it is by the stem that is all you need to remember. If the numbers don't stay the same you need to average your measurements to take out the wobble in the wheel. When I measure toe or anything else I block my steering wheel by wedging two pieces of wood between the bottom of the s4 wheel's lower hub edge and the carpet just below the wheel in front of the seat. I also sit in the car so that the wheel looks right to me. After I finish measuring adjusting toe I then use the same laser to sight a mark near the center cap of each rear wheel. The measurement from the laser spot to the rear wheel should be the same each side. If it isn't you need to shorten one side's tie rod some and lengthen the other side. If you move each side the same but in opposite directions your total toe should not be affected. Next variable camber. First changing camber changes toe so you need to do these things in order. Get camber close first before dialing in toe (or caster). Camber is the tilting away from vertical of the face of the wheel. If the top of the wheel is canted in toward the center of the car that is negative camber and that is desired by us. The factory setting is around .5° for the fronts and around .66° rear. Using trig and a 16" wheel as an example this means that if you put a level on the wheel so it contacted the bottom center of the rim the top center of the rim should be .139 from the level. The rear should be .186 from the level. This is an easy way to measure camber. Levels and shims. If you have a .186 shim and a 24" bubble level and a flat spot on the ground to measure you can approximate camber enough to drive to the alignment shop. If you are good you can use this simple technique to set camber closer than a guy with $500,000 worth of equipment. Actually you will do less harm to your car than probably 95% of the so called qualified shops out there. Another way to do this and very accurately is to use a plumb bob. A good plumb bob is probably the MOST accurate tool for setting camber if it is on a fixture that can be set on the wheel properly. I used a 39" high mast plumb bob for several years with great accuracy. At 39"... 1/16" is 1/10° Very useful. So, what I did was to put a flat piece of plywood up against the rim about 6" x 16". I attached the mast to the outer edge so that the string on the plumb bob sort of swing accross the plane of the front of the plywood. I put a piece of paper on the plywood with marks so that I could see how far the string moved from vertical as the plywood leaned against the wheel. 5 x 1/16" equaled .5°. Actually the string on my rig was a stranded piece of wire about .005 thick so I could see tenths of sixteenths or HUNDRETHS of a degree. That is more accurate than anything out there no matter how much you spend. Just recently I bought a digital level that is accurate to 1/10°. I also made some sliding clamps that allow me to use it on different wheel sizes. With this level bungee corded to the wheel I can set camber directly to 1/10° which is accurate enough for me. I can see the display when I am lying on the ground next to the car making the measurements so it is very convenient. Camber is adusted on the front wheels by rotating the eccentric washer under the clamp nut on the balljoint attachment stud closest to the wheel. The one furthest away from the wheel is the caster adjuster. Both nuts need to be loosened in order to make the adjustment. An 8mm allen wrench, the long handled variety, is the best tool to do the adjustment. Rotate the eccentric washer to adjust camber monitoring the measurement with your level, plumb bob, digital meter. If the measurement will not move in the desired direction move the caster eccentric. These can be misadjusted and will limit the travel of the caster adjuster. Cars with the older style aluminum ball joint carriers have the adjusters reversed so the caster adjuster is closer to the wheel. If you have this you should change them out anyway so no need to explain the differences. The rear wheel camber adjuster is the rear inboard attachment of the lower control arm. There is a nut to the rear of the pivot and the front is the head of the eccentric bolt. Loosen the nut and adjust the camber with the adjuster. Check during adjustment and after final tightening. They move as you tighten them. Camber does not wear tires quickly. Even a ton of it. Race settings can be in the 3° range and it doesn't necessarily wear tires unevenly for that application. Camber tire wear is even accross the entire tire not just at the edges. Wear from large non stock camber can be minimized by rotating a set of tires half way through it's life from side to side keeping the direction the same. The camber number that you set is far less critical than making real sure you have it the same side to side. Unbalanced camber feels like a dragging brake but the feeling gets stronger proportional to speed. <<<<<<<<<<<>>>>>>>>>>>> Jay Kempf 79 US 5ish speed From: Jay Kempf [mailto:jkempf@tds.net] Sent: Saturday, July 20, 2002 11:16 PM To: 928 Subject: [928] Alignment 101b (long, reeeeeeaaaaaaallllllllly lllllooooonnnnnnggggggg) <<<<>>>> Last variable.... Caster. The tough one. Caster like in a bicycle is the tilting of the steering axis. This is done in our cars and many others by having the upper ball joint farther back than the lower with respect to a vertical line. The inboard eccentric on the lower ball joint pivots the ball joint carrier on the camber adjuster making the ball joint move fore and aft to adjust. Most cars need to have their ball joints adjusted all the way forward to get anywhere near a proper measurement. For most this means that you can look at the ball joint carrier move and make it go as far forward as the eccentric will make it go near the eccentric. This drives the ball joint by the wheel as far back as possible. Most cars will steer well and not wear tires or act weird backing up using this technique. Cars that have had damage, Scott M's Cab, cars that have differing measurements from the centers of the wheels side to side may not do well using this method. Caster is a derivative measurement. It cannot be measured directly. It is important to have it be balanced side to side and it is not really important what the actual value is especially with a strong power steering system. Caster is measured and set using turn plates and camber measurements at a set steering angle from straight ahead. Most ways of measuring caster require turning the wheel from 10, 15 or 20° each side of straight ahead and then measuring the camber at that point. The difference between the camber measurements can then be mathematically converted to camber. Suffice to say without showing the derivation that at 14.3 degrees of turn left then right caster is 2.0 times the difference between the two measured cambers at the left and right positions. So if the camber with the wheel turned right is 2.0° negative and the left is .5° negative the difference would be 1.5° and the caster would be 3.0° simple enough to describe. The wheel must be steered straight ahead before turning left and right to make this work and very accurately. A turn plate is a platform that you drive the wheel onto that is a ball bearing floating table. This also has a pointer and a scale that shows center and say 45° both left and right. The platform floates laterally and for and aft as well so that tire scrub won't effect measurements. Some people use two sheets of steel or plexiglass with grease in between to allow the tire to float as the measurements are being taken. In order to measure the angles left right and center a pointer or axis has to be rigged near the edge of the upper plate as it slides on the lower. It can be done but it takes a little understanding of the task. Caster like in a bike is a centering force, the more caster the stronger the centering force, and is necessary for good stable, non divergent, steering feel. Bad caster is especially noticeable when backing and turning tightly. It can be manifest and jumping or tire scrub noises. A couple comments about related height issues: Height at each corner is critical to a good alignment. Some will tell you that height has to be correct to align a car properly but that isn't necessarily true. The car is somewhat tolerant to height changes as long as they have been stabilized before final setting of alignment variables. The front of the car is notorious for not settling for many reasons. It is less the height value and more the settling. A car can be wacky and be aligned and handle very well. A car with somewhat wacky corner balancing can handle well also. Yup, most drivers can't tell the difference if you gave them a car that was noticeably wacky but you didn't tell them. Then you gave them a perfect one assuming a perfect aligment on both they wouldn't notice. The reason the front needs to be settled is that the car toes out as a result of and increase in negative camber as it settles. That means that the tires will wear bevels on the inside edges rather quickly after a bad alignment and it won't feel hooked up to a sensitive driver as the tires are not evenly loaded and so not generating their max grip. Wow, that was a bunch...... I am sure I am forgetting some things. Wally will correct me or Jim or somebody if I got something messed up. I think it is mostly on target. Thanks to Kurt Gibble for giving me some insight to get me started. The rest is shear messing with the subject and thinking of better ways to take good measurements and increase accuracy. Next maybe handling variables and why you might want to stray from stock settings :) Jay Kempf 79 US 5ish speed 1.2° camber front 1.5° camber rear no toe front slight toe in rear 3.75ish° caster with slightly screwed up heights because of non adjustable perches front. Handles like slot car on PCP ask the trackmeister..... From: Jay Kempf [mailto:jkempf@tds.net] Sent: Sunday, July 21, 2002 7:32 PM To: 928 Subject: [928] Alignment (further comment) One lister sent me a message about camber and tire wear that makes and excellent point. It is possible for tire wear to be more pronounced with large camber settings. All things are a compromise. Large camber, tire pressure and intended driving purpose are all interrelated. If you put large negative camber on a car, don't change the toe to compensate, go beyond what the tire likes to run at, continue on with high tire pressures, etc... you can offset one variable without complimenting with another. I tried to make that point but it wasn't clear. But that being said it is also for tire wear to be normal with large camber settings. Good point. Higher than stock negative cambers can give more even tire wear if the car is setup and used for VERY aggresive cornering. This is how some of us have set our cars up and with proper adjustment of all of the factors the tire wear is normal. It depends on the tire, the setup, the weight, the use, shock/spring, bars, the pressures, etc... It would be wrong to set a car up with large camber with stock toe in and 90% highway use with no rotation strategy and no alteration of tire pressure you can wear tires abnormally. The way camber is set is by targeting a handling variable outcome and monitoring things like tire lateral heating until you get the compromise you want. Changing something, anything, without a plan to monitor the outcome is just a shot in the dark. Handling variable explanation/experimentation next installment :) Jay Kempf 79 US 5ish speed (36psi front on 225/45/16, 34psi rear on 245/45/16 Kumho Ecsta 712) with even tire heating/wear.