fatbillybob

Agreed! Once Bill reported that there were matching rings cut into the smart fore and aft rods it all made sense, not only my question about non-parallel strings but the fact that you really are square to the centerline with car equidistant everywhere in an ideal box. Bill also mentioned trying to make smart strings from plastic pipe but did not know how to solve the non-ideal box. But based on bill's report of the concentric rings on the shafts one could make 2 equal length plastic pipes with pipe caps on the end. The caps would be where to wrap strings and make the ideal box.

fatbillybob

I can feel 2lb changes in tire pressure and that is a number most drivers are comfortable with. 3lb changes almost anyone can feel. I have not tested enough alignment variation to feel changes. I have set things to where the faster friends tell me and try and learn to drive the car. Can we comment on how much change and what kind of change might we use to optimize at different places in a corner, under braking , and on the gas? For example some front toe out helps corner entry turn in. If you wanted more corner entry turn in how much more should one try, 1/8" 3/16" so you can definitely feel it? I think we need to know things like camber gain/loss for the vette as the suspension travels before we can answer those questions? I've never looked into those changes either. For example I found out rear camber changes really mess with thrust. What happens to rear toe under braking vs. acceleration?

Bill Dearborn

Due to play in the suspension bushings under hard braking front and rear toe will tend toward toe out. The braking force is being at the tire contact points and the body of the car is pushing forward against the suspension members connecting the body to the tire contact patches.

Of course there will be some camber changes that will affect things as well. Weight transfer to the front will cause some increased negative camber while the rear will see some decreased negative camber. Those changes will affect toe as well.

As for suspension settings I have noticed I like a fair amount of rear toe in when on the track. I don't like driving a loose race car so more rear toe tames the rear and allows me to add more power going through turns. I can tell when it isn't set right. One time at the Glen I went under the rear and adjusted both tie rods two flats each to increase the 1/16 toe in that I had set in to a total of 1/8. The car seemed to handle the Esses much better especially Turn 3 where the rear of the car had been twitching to the right as I went by the Apex. With the increased toe in I was able to go through the turn almost wide open with an appropriate increase in speed at the end of the back street. I thought about adding another 1/8 to see if I could go through Wide Open like I used to do with my previous cars.

Bill

froggy47

Reply to myself,

I think you could pretty easily measure the 4 angles that are formed by the rods & strings & if all are 90 deg. then you do NOT have a trapezoid. Yes?

froggy47

We all have different bushings, sway bars, tires, shocks etc. Plus the "measuring different" thing (rim vs. tire). I'm not sure comparing would serve much purpose, but I'm not saying don't do it.

For myself I just last alignment went from zero toe F, to 1/8 out & it CLEARLY did not feel worse, I "think" it's a little crisper turn in (corner entry). The rear I went from 3/8 total in to 1/2 total in and my rear grip was great, almost to not being able to rotate the car with power.

fatbillybob

"Flats"...you mean you loosen the rear tierod nut allowing it to sit on the rod. Then moving the rod looking for movement of 2 flats on the passive nut going along for the ride correct?

fatbillybob

I have no idea what is too much rear toe-in because I have never tested it and do not know if it can be empirically derived with math like calculating chassis frequency to guess at empirical spring rate starting points. For anyone else reading thinking more is better, like tire pressure, "I think" there is a sweet spot to rear toe in where too little toe-in (towards toe out) causes oversteer or too much toe-in also causes oversteer. So don't be surprised out on track getting unexpected results that can put you in the weeds. Tip-toe.

Bill Dearborn

No, I watch the rod turning right where the wrench is on it. I watch the very end of the rod to see how much it moves as I turn the rod. If it moves I don't count the movement of the rod until the very end stops turning. That makes sure I take up the slop in the ball at the end. That can move as much as one flat of the rod which means I turn the rod 1 flat and the end moves with it the rod didn't actually turn in reference to the end.

I mark the flats on the tie rod with red fingernail polish so I can reference how many turns I have made.

Bill

Bill Dearborn

It is more of a feel type of thing. I think as long as you have some toe in the car will be stable enough. However, some people, like me, don't like the feel and won't push the gas pedal hard enough when the back end feels uncomfortable to them. You hear the Cup guys talk about it all the time. Some like driving a loose car and others don't.

When LG added a lot of rear toe in to my car at the Glen if felt much better to me on the track. When I took the car home I left it adjusted to his setting. However, on the street leading to my house the pavement was so rough the back end of the car was lifting off the pavement. If the left rear lifted the back end would jump that way and if the right rear lifted the back end would jump that way. Driving straight on that street was an exercise in flipping the steering wheel back and forth. It also rapidly wore the outside edges of my brand new EMTs and I got just over 3K miles before they corded. Once I reduced the toe from Lou's setting to close to zero the hopping around went away.

Bill

fatbillybob

It seems that you are talking about the important theory of "most important part of turn is apex to exit" getting on gas as hard as possible. How much toe did LG run on you? I do not know what happens to our rear end alignment settings under power. We know if we toe out we rear steer and are unstable into oversteer. So if LG is adding toe in my guess is that under power the rear squats improving grip and maybe loosing tow in and squatting could reduce the contact patch from camber gain? I have never put the rear through its travel and register what happens to camber and toe so that's a complete WAG. Your off track cruising wheel hop makes perfect sense because you have proven that the rear end is doing something completely different on power vs. coasting. Comments?

Bill Dearborn

T3 at the Glen isn't exactly that. The idea is to be wide open all the way from the exit of Turn 1 through Turns 2, 3 and 4. It can get a little hairy when the back end kicks out in Turn 3 over 110 mph. Part of the issue is that is where the steep hill you are climbing starts to level out and there is a crown in the track surface that sucks the car over to the right side of the track. Adding more toe in definitely settled the car down a lot and let me get closer to my goal of running wide open with the C6Z. I was able to run wide open with my 86, 97 and 03Zs with about 1/16 total toe but they didn't have the torque the C6Z has.

By the way I started changing my alignment from street to track this week. I have the Van Steel camber plates in the front. When I flipped them over to move the bolts out the camber went from -.4 to -4.7. I was able to use the Smart Strings to measure toe at each wheel and found it had gone from close to zero toe in to several inches. Using the measurements at each wheel I was able to determine how much I had to adjust each tie rod (1/32 per flat) to get the car to steer straightly. The left front would have required 15 turns plus 5 flats.

I also checked the thrust angle with my laser and knew what direction I had to move the rear wheels to get zero thrust but the string measurements showed me the left rear required no adjustment and all adjustments should be made at the right rear wheel to get the proper total toe and close to zero thrust angle.

Bill

naschmitz

Richard Strout at Leading Edge Motorsports and I did my car. He had me measure the center of the bottom ball joints to each other, resulting in a trapezoid with both diagonals. Using those dimensions we set up his three headed laser so we could cast a laser line down the chassis center. Using that laser, we found places near the front and rear on an aluminum cross member where we could drill and tap a hole to put in a long screw. Put those screws in and you can string a chassis centerline pretty quickly.

That was all done rolling around on a garage floor. Today I use lasers and digital levels like FatBillyBob and David Farmer so I don't use those holes.

jimtway

THIS!

I once spent a half hour setting up my strings, after working on the car all day already. Finally got them all set right, when my big lab came running into the garage, knocking over a jack stand. She made it up to me with a big lick of the face.

Bill Dearborn

Well I finished the alignment using the strings.

Front
left camber -3.0 == right camber -3.5
left caster +9.0 == right caster +8.4
left toe 0.0 == right toe 0.0

Rear
left camber -1.- == right camber -0.9
left toe 2/32 == right toe 2/32

Toe was measured at the rim edge. On the rear the rim edge is 19.5 in diameter.

So rear toe at each wheel in degrees is ~ .18 degrees using the Smart Strings conversion chart. Total toe is ~.36 degrees.

When I drove the car I ended up with a very slight steering wheel offset to the left. This may have been due to the crown on the road, the slightly lower right front caster which would pull the car to the right of just due to the inability to resolve adjustments any better than 1/32 of an inch. It is possible the right front is toed out by 1/64 but I knew I wasn't going to get any closer to 0 since I had to raise the car to make an adjustment, drive it back and forth in the driveway several times and then remeasure. It wasn't worth the time or effort to get it any closer.

The MacTool guy who lives on the other side of the hill stopped by to talk and watch for a few minutes and said the Cup teams he worked with would set up a string arrangement from the car center line to one side of the car and do their adjustments on that side, followed by using toe plates to get the other side. He said it was quicker that way although I would think it would be less accurate just due to tolerance stack up. He also talked about setting rear toe on solid axle cars. It is possible to adjust rear toe by bending the housing a certain amount and the full floater axles they use permit some bending. To get thrust angle they just move one side of the axle or the other.

Bill

froggy47

Did you want the front camber different by .5? Setup for your home track?

If/when my steering wheel is off (but car is tracking good) I just put it back up the ramps and adjust the LF/RF by a couple of flats equal each side & don't even bother with any more measuring. Just make sure you go the right way both sides.

Bill Dearborn

I didn't want the camber to be different but I have that much difference from side to side with the camber plates and shims behind the UCAs being set equal.

I had the number of shims behind the front dog bones maxed out on both sides of the car and I had 2 shims behind the rear dog bones. If I added two more shims on the passenger side rear dog bone I may have been able to equalize camber but I would also lose a fair amount of caster on that side which would make the car pull more in that direction.

Bill

fatbillybob

Don't you have to add shims to front "and" rear UCA dogbones to lower camber "without" changing caster?

froggy47

Bill, I have always let the caster "go off" a little side to side in favor of getting close to equal camber.

In my experience, a small caster difference does not make the car pull much/at all.

Toe difference will.

Bill Dearborn

Correct. My Van Steel Camber plates give me -4.7 degrees camber on the driver's side and -4.8 degrees of camber on the passenger side with no shims behind the upper dog bones. Caster was about 4 degrees on the driver's side and 3.5 degrees on the passenger side.

I am running Continental Slicks so want about 3 degrees camber. I installed the maximum number of shims I could get behind the front dog bones and half of that amount on the rear dog bones which reduced the camber on both sides but also increased caster.

If I add shims to the passenger side rear dog bone I may get camber closer to the driver's side but will also reduce caster on the passenger side which will increase the pull toward the right. It all depends on what I want to sacrifice.

Bill

fatbillybob

FWIW, I cannot feel a difference in 1/2* of camber on the front either in turning or braking. I thought there might be a stability issue with threshold braking but did not find that to be the case. Others more sensitive or skilled might feel it.