Pablo

iTrader: (1)

In the span of a couple of weeks I've replaced just about the whole suspension on the (relatively) cheap. I picked up this Z28 specifically to scratch a corner carving bug.
Springs are 5664/5665 moogs, half coil cut front, full coil rear (no isolator)
stock sway bars
poly bushings except for the back end of the rear ctrl arms
howe .5 taller extended ball joints
Koni Yellows full stiff front, one click from full stiff on rear

I had to weld up steering box frame rail cracks and then replace a bent tie rod (looks like a previous owner curbed it pretty good)

So after the tie rod, I had to do an alignment. I decided to do it in my garage with my caster camber gauge from racer parts wholesale. I used some contractor garbage bags with WD40 sprayed inside for slip plates.

With the strut towers all the way in and back I only got .875 negative camber on the drivers side and .75 negative on the passenger.
Caster was 5.0 drivers side and 5.5 passenger (I'm not sure I measured caster at the correct wheel angle. I just checked the difference lock to lock. So I think this number is higher than what it is supposed to be. I was mainly concerned with the difference between the two sides).
I decided that this was good enough for me for now. I was however disappointed at the lack of negative camber.

So with that settled we moved on to toe. I think you can only do this with help if you don't want to take 3 years to pull it off. With the help of a buddy we very very carefully aligned our string reference to the rear wheels. The string is attached to a jackstand in the front and a jackstand in the rear next to the car. We are talking about taking measurements down to a 64th of an inch difference. From there squeezed under the car and started turning the tie rod adjuster till we had the slightest amount of measurable toe possible. I was probably close to 1/64th. I repeated this process on the other side. I was surprised how well we could accurately get it down to an exact measurement.

As for the amount of toe, I couldn't find where people were measuring from to determine where they would come up with a number for toe like "1/16th". Since the distance from the spindle axis would magnify any measurements and since I was taking measurements from the rim edge I decided to get it as close to 0 toe as possible and still be toe in slightly.

I skipped a bunch of complicated steps that most of the online diy alignment guides give you. They seemed kind of like a waste of time... so after all this I wasn't expecting much.

I went out and drove the car and much to my surprise the car tracks PERFECTLY and the wheel is PERFECTLY centered. I'm still kind of in shock over it. Doing this at home de-mystified the alignment process for me. I kind of had it in the back of my head that you really needed a very sophisticated alignment rack to pull it off.
My settings might be off slightly but for my purposes they are working quite well.

I went for a long canyon run and the car is handling quite well. I pushed it pretty hard and found that with the above components, the car basically refuses to oversteer outside of doing something stupid like jamming on the brakes and yanking on the wheel.

I'm concerned that I may be giving up some ultimate traction (overloading the outside front) and wanted to know what you guys think I should do to compensate

I have a few options
1)Adjust the rear swaybar mounts- IIRC if you move the mounts outward you effectively stiffen the bar? Should I worry about moving the clamps off the locating tabs on the rear?

2)Adjust the rear shocks to full rebound dampening- I'm one click away.. though I believe this would only matter on initial turn in

3) Cut the rear springs slightly for more rate - I still have the stock isolators I can put in to make up for a slightly shorter spring.


The only other observation I can make is that on long sweepers the car feels much more neutral then on tight sections. I can hear both rear and front tires start to squeel on a sweeper vs understeer on very tight sections.

What do you guys think I should do? high speed wide radius turn to low speed tight radius turn difference has me thinking about more rear dampening but I'm still new at this.

As for the alignment thing, I just wanted to share my experience in case anyone was thinking of trying it.

Pablo

iTrader: (1)

I just thought of another thing.

Is the behavior I am describing also the result of an inclined roll axis?

I suppose if i lowered the PHB it would help. I do also seem to spin the inside tire very easily powering out of a turn (pretty much an open rear) but then wouldn't the greater lever arm from cg make me understeer more?
I guess I would have to lower the phb, and add spring or bar all together.

Guest

On the contray, lowering the panhard would tighten you up more so yes the greater leverage would tighten you up and make the car steer more as you discribe later in your paragraph is see.

From your first post, you say that higher speed sweepers the car is more nuetral. However, it pushes more on tighter corners. This is a result of too much front compression damper. I would recommend upper the Koni rear rebound to help turnin and as you ask, YES widen the rear sway bar mounts off the tabs. THis will stiffen the rear overall spring rate and balance you a little more a steady state.

Guest

Also, toe readings are taken at the radius of the tire diameters both front and rear of the tire. Toe plates that race car shops sell are generally for the diameter tires run in the series and are made to that aprox width so as to read lower on the tire uder the most front and rear reaches of the radius'.

So in other words, if you set a 25.7" tire at 3/32" toe in, and then swappped the car to 28" tires, the toe would then probably be 4/32" or 1/8"

Pablo

iTrader: (1)

ah, always wondered that. It would seem then that the actual toe angle is the only true measurement when comparing vehicles with different tire sizes and whatnot.

As for the rear susp. I'll be trying the increased rebound dampening on the rear and widening the swaybar clamps.

I suppose lowering the phb will require both of these and more spring rate and/or bar to get everything back in balance right?

Thanks for the tips.

Guest

Yes, lowering the panhard would require either lowering front spring rate, or increasing rear spring rate.

Its is solely based on body roll desire based on grip of tires. If the roll rate does not roll enough then mechanical grip is loss on the tires. If the body rolls too much, then the car is not nimble and agile in transition. Its your call whether the front needs lowered in rate, or the rear needs increasing based on your liking. Shock valving needs to be taylored to the spring rate. Since you are using fix valved compression shocks, you will have to make that choice based on feel of the car right now whether you thing the front is too stiff or the rear is tto soft.

Pablo

iTrader: (1)

Thanks, makes sense. So if you had really grippy tires you could get away with a stiffer susp. to improve transitory response, and if you had crappy tires you'd have to sacrifice transitory response for grip?

Everything is a balance I guess. I think with the lower PHB and decent tires I'll need to stiffen up the rear rather than soften the front.

Now at what point does a soft spring setup end up making the sprung weight act like a pendulum? I would think that another factor is all this inertia rolling and eventually stopping on the outside suspension. I would think this could basically throw the car once all the weight hits the outside. Porsche actually has magnetorheological engine mounts now to cope with this kind of thing- when you start pushing the car the computer stiffens up the engine mounts. I thought that was a pretty neat concept.

BTW I guess my post could have been worded differently, by tighten the rear suspension I mean stiffen. Someone might think that by tighten I mean to reduce oversteer. That's not what I meant (I'm sure you gathered that)

Norm Peterson

Sometimes you can get a little more negative camber by using up all of the hole clearances in the knuckle and strut holes.


Just guessing that you actually steered the wheels a little less than 30° (the wheels tend to relax away a bit from the hard stop), you probably have closer to +3.5° and +3.9°. Half a degree of cross is probably OK, and in your case it is in the "good" direction since it's trying to steer you out of the gutter.
http://www.tirerack.com/tires/tirete...e.jsp?techid=4


I strongly recommend that you measure the distance between the strings ahead of and behind the car, as that is what will guarantee that they are parallel (as long as they aren't actually touching the rear tires). The error that this avoids is the assumption that rear toe is zero (as it frequently is not). It's fine to start your setup measuring off the rear wheels, though.

I think most toe specs for newer cars are given in angular measure to avoid the problem that you noted - where to take the "inch" measurement. FWIW, I'll make all measurements off the wheel flanges rather than the tires and scale the difference in measurements up to 25" when I'm working with the Malibu.


I'm curious - which "steps"? And which online guides?


Once you know how to set the car up for and make the measurements, the rest is not much more than turning wrenches and maybe doing a little math.

It's good to hear of successful first attempts at this stuff so that people understand that you don't have to be an engineer or a crew chief to pull it off. The $$$$$ racks in the shops are a bit intimidating.


Norm

Guest

I missed answering the part on caster/camber gauge. Sorry.

Anyways, you do not go lock to lock. What you do is on the side you are checking (Lets say the left side first) you turn the wheel left 15* and center out the bubble levels. Then (I like using laminate floor tile squares with sand inbetween them- kindaof like a linoliem sam'mich- sorry about the rednekk slang, I digressed for a moment) then turn the wheel to the right 15* (total movement of 30*) and check the caster reading.

Then on the right side you start with the wheel turned right first and center the gauge, then turn to the left.


Yes home alignments can be done, but with the tools and time involved it is fine for the racer to do on a car that sees mostly lateral wear of tires and a tire lifespan of 100miles rather than on a street car where you are trying to get 25,000 miles out of a set of tires and 1/16" mistake can mean wearing out in 20,000 rather than 25,000. For the time and perciseness of a street car? I just spend the $100 rather than going through all the work even though I own the gauges and have the knowledge.

Norm Peterson

Not to be argumentative, but you can use lock to lock if you know how many degrees that it takes to get there and how to compute the factor. It's needless extra work to do so, though.


I figure the time spent DIY'ing it is at least partly offset by the time it takes to get to the shop and hang around waiting for them to get it in the bay and done. I'll write the time to go home off against the time spent on the test drive that I'd be doing to check my own work.

The big DIY benefit is that you can set what you want without having to argue with anybody. You won't ever have a service writer tell you one thing (promises that the car will be set to your specs) and then have the tech go off and do something different (does a toe-n-go, or calls it good once nothing is in the red and the cross isn't huge).

You absolutely do have to take full responsibility for the downstream results when you DIY this. Just like you do with any other DIY project, except that with this there is some judgment involved if you're going to set anything other than "factory preferred".


Norm

383fbod

iTrader: (2)

What are the best caster/camber gauges? I am in the market for one with toe adjustment. I found one from Longacre but I dont like the idea of it attaching magnetically. What are your experiences with them? Should I go digital? Cost is a factor.

Guest

As long as your magnetic attachment surface is flat and stable to hold the gauge then I highly recommend this gauge working perfectly fine. Its the gauge we have and use on the racecar.


Norm- agreed for the most part to the avarage person. I personally have a very good friend (Jon of Accurate Alignment in Orange CA) that I do not have to jump through those type of hoops with. I call him and when he has time I run over there and he gets me taken care of in a very timely manor with me in the cockpit as needed.

383fbod

iTrader: (2)

If I do my own alignment how do I calculate SAI? I am using the "Adjustable Camber Bolts" from spohn.
http://www.spohn.net/shop/1982-1992-...Bolts-Kit.html

383fbod

iTrader: (2)

my rim lips are angled out slightly what Caster/Camber gauge style should I use a clamp on?

Guest

Like I said above, Its best to just take it to a shop especially if you have a friend that will work with you on getting your specs perfect.


Using these cambber bolts is changing the SAI and the IA (included angle) based on the camber you want. If you start using these bolts to change things, you damn well better have it measured accurately because if one side is off from the other the car will pull regardless of camber settings.

This is a trail and error thing on alignment racks. Lowering the car will increase the potential of negative camber, it will also increade the potential of positive caster. Here's the catch on these McPherson strut cars- when you increase the negative camber, you also increase the SAI. Increased SAI is like increased caster because when its combined with camber the IA increases as the car is lowered. This kit is a way to decrease the IA to gain more negative camber range- BUT THE "IA" HAD BETTER BE EQUAL ON BOTH SIDES .....This is done best and most pinpoint accurate with sophisticated alignment equipment. You can calculate spindle angles when you build them, but it is very difficult to measure equally both sides of the vehicle with hand tools and tape measures, etc when dealing with changing settings not normally having built in adjustment. You are walking on dangerous grounds so to speak. I would not be able to tell you how to measure these plotted points in a 3 dimensional feild around the obsitcles of the vehcile chassis and body full assembled. You are pretty much dealing with "imaginary points" when you try and physically measure these plotted points of a working chassis and suspension in tact. Its like trying to measure a straight line from the LF headlight bulb to the right rear passnger ash tray.

What you want to do is measure your strut angle to the spindle angle that this kit will change. You want to set both sides equal. What angle do you set them to? Lets start with does any body have the factory spindle angles recorded? and their +or- tolerances combined with the +or- tolerances of the slop in simply bolting together the strut and spindles using just the factory bolts (non adjustables ones)? Then lets factor in what ride hieght you will have on your paticular car- Why? because this will determine if you overall camber range is where you need it after you set the spindle angle and find out what your SAI and IA ranges are from those factors.

The more the IA is- the more the SAI will increase when Camber is set back to zero from positive, and the less positive caster needed due to increase vehicle height being lifted as the wheel is turned

In other words, SAI and caster will both act alike. Increasing one generally lends towards decreasing the other.

383fbod

iTrader: (2)

Thats my problem I don't have anyone trustworthy behind the scenes not to just do the "toe n go" The shops around here are shady at best. The reputable ones treat me like Im a doush and have no idea what I want. Doing my own alignment seems like the best idea. if I just need to be diligent with my measurements then so be it. I just need a good C/C gauge. My rim lips are not square to the hub so what gauge will work best for me?

I definatly feel the inside wheel "lift" the car when I turn from lock to lock while the car is not moving

Norm Peterson

You can work with a digital angle finder (or even a carpenter's combination square that has a bubble level in it) as long as you can hold the thing steady enough against the outermost diameter of the wheel without getting up into the tire sidewall. It's a little fussier, but still do-able. The factory Torque-Thrust style wheels on my '08 Mustang are the same way. (It's worth measuring an extra time or even two). Unless you make a fixture to fit the measuring device up to the wheel diameter precisely, you won't be measuring right at the axle line, so you'll have to watch more closely in side view that you're vertical and not "tipped" to follow the flange shape. But that's OK as long as the wheel isn't bent (which would screw the whole alignment process anyway).


That's from the caster, which lifts the car on the inside and wants it to drop on the outside as you steer. While this is happening, IA lifts the car on both the inside and outside. On the inside the IA and caster effects add, on the outside they sort of offset each other.


Norm

snowstorm

Hi guys. First I have to say I’m impressed of all the knowledge it seems like you have.

I don’t know much about wheel alignment, and I don’t have equipment to do the job my self. So I think I’m going to take the car to a local shop for the job.

My question is what are the best set points for my street car? I’ve read people talking about caster: 4 degree (.5 more on the right side, here in Norway we drive on the right side)
camber: .25 - .35 negative
toe: 0

Do this numbers seem ok for a car that never sees a race track? I think I’ll prioritise drivability at local bending roads. The car also might see high speed at autobahn in Germany.

My car is a -86 Z28
Eibach Pro-kit #3801-140, progressive rate, lower the car 1” front/rear
ROH ZS Racing 8.5” 245/45-17 in the front and 9.5” 275/40-17 in the rear

Appreciate feedback
Cheers

Norm Peterson

I think I'd set just a tiny bit of toe-in, something like 1/32" (0.8 - 1.0 mm, 0.07° - 0.10° ).


Norm

snowstorm

Thanks Norm, I'll hand the numbers over to the local shop.

ojo