SUSPENSION GEOMETRY AND GULDSTRAND MOD-PAGE

THIS PAGE CONTAINS INFO ON SUSPENSION GEOMETRY, AND CAMBER CURVES.


SHOULD I DO THE "GULDSTRAND" MOD?

(plan "A")

If you don't corner your Camaro hard, I doubt you need to do this modification. You can get a lot of improvement by changing springs, shocks, swaybar, bushings, tires and more aggressive alignment. If you have done all of these and still are wanting more cornering power, then consider doing it. The wider the tire you run the more it will help.

PROS:

  1. 1 Better cornering power due to improved negative camber gain. Outside tire will sit flat on pavement especially helps on full out cornering.
  2. 2. Higher front roll center. Adds some stiffness in roll due to geometry changes, that is independent of springs or rollbars.
  3. 3 Less wear on the outside edge of the front tires.
  4. 4. Can run a less aggressive front end alignment (neg camber). Less tire wear.

CONS:

  1. 1 Your car will not be "Factory stock"
  2. 2 You will have to re drill the upper mounting holes, or use plan "B" below.
  3. 3 You will have to trim off the upper mount area down to the old holes for A arm clearance. You will not be able to go back to the old holes unless you weld material back on.
  4. 4 You will have to trim the front and rear of the bracket braces for A arm clearance.
  5. 5. You will need to have your Camaro's front end aligned.

The other way to do it is to cut 3/4" off the bottom of the mount and re weld it to the frame about a half inch (my best guess if you need a better number, call Guldstrand) to the rear to increase caster, and reduce the thickness of the alignment shims. The upper A frame usually has an interference problem with the header pipes on the rear bushing (RH side).

It's interesting to note the Mustang guys are doing the "Shelby mod"! It's the same kind of mofification but for the Mustang!


67 upper A frame mountRELOCATED UPPER MOUNT

(PLAN "B")

This is an upper mount that has been cut off, trimmed on the bottom, and re welded slightly to the rear.

You can see that if you were to drill the rear lower A arm mounting hole according to the Guldstrand template, you will have a problem with the rear shim hitting the angle change in the bracket and preventing proper seating of the shaft. You must trim the first alignment shim to prevent a problem.

#Top

 HERE IS MORE DISCUSSION ON THE GULDSTRAND MOD, AND CHANGING THE CAMBER CURVE.

 

Here is a magazine article on how to do the Guldstrand mod

PART 1 - PART II  


DSE UPPER CONTROL ARMS (Upper A frames)

Detroit Speed sells a really neat tubular upper A frame that uses a varation of the Guldstrand mod. I understand this upper A frame has slightly different dimensions from stock (shorter requiring less shims) and will allow setting more positive caster. The A frame uses frame mounting holes in a slightly different location than the Guldstrand mod.

If you are planning on using these A frames, don't do the Guldstrand mod. Order the kit, and drill the holes as instructed by DSE.


PRO MOTORSPORTS SPINDLE EXTENDERS 

Plan "C"

Here is a link to an article on them.

I don't like these as far as streingth, possible 14" and 15" wheel clearance problems with the upper A frames, it raises the roll center too high causing excessive camber change and resulting side scrub on the tires. They raise the upper A frame 1 15/16" and that's too much unless you have a specific problem you are addressing.

I have been in contact with several people who removed them because they were wearing out the front tires.

 
DROP SPINDLES

Plan "D"

The drop spindle kits use second gen parts, on a cast iron spindle similar to a second gen spindle with caliper mount cast in. The steering arm is two inches lower than a stock Camaro and the caliper mounts two inches higher in relation to the upper A frame, which can cause caliper to A frame clearance problems.

Several problems develop when you use drop spindles.

You can't fit some wide tires, the tie rod end winds up two inches lower in relation to the wheel so forget wide front rims.

Geometry stays stock which is not good on a Camaro.

Just trimming the springs to lower the car will put the geometry in a slightly better position as far as camber gain.

You may have clearance problems with the upper ball joint to caliper.

You can't use any aftermarket disc upgrades, they won't fit.

Steering arms are cast in, so you can't bend them to fix bumpsteer. You would have to use a rod end and spacers on a stud.

I have to apologize for using this photo. I took it from a web page of someone I exchanged E-Mails a fiew years ago. I can't find the E-Mail or web page or I would just provide a link to his page. I think this is the only image on my page that I don't have the owners permission to use. I feel the photo shows the problem so well, that I'll leave it here for a while.

I have a matching photo with the same wheel and tire but on a stock spindle, the tie rod end is two inches higher with that combination.

Another point, this is a Stainless Steel Brakes drop spindle, I don't know if other drop spindles are better or worse than this one. I don't know if Superior spindles makes all the drop spindles or if they are all making their own. If your 17" wheels have 4.25" backspace or less, they should clear, with "drop" spindles, according to posts on Team Camaro forum.

TALL SPINDLE UPDATE

2008

New drop spindles are being produced by Heidt, Fatman, and others. They are taller by 1.5" and correct the poor camber gain curve. However they are still drop spindles and still put the outer tie rod end in contact with the tire sidewall. If they were just taller it would be great.


BUMP STEER

"Bump Steer" refers to an incompatability between the steering linkage and a cars A frames.

The A frames and their relative relationship control the camber curve of the front wheels.

The lower A frame is usually level or close to it. The upper A frame is usually inclined down toward the center of the car a couple of degrees.

As the car goes into bump (frame gets lower) as when braking hard on corner entry. You want the tires to steer straight ahead. Many Camaros have toe out under bump. I have seen as much as 1" of toe out at three inches of bump travel. This will make the car dart left and right under hard braking.

When the car is leaning in a corner, one side is experiencing bump (down, the loaded side), the other is in rebound (up, the unloaded side). If you have a lot of toe out bump steer, the car will steer itself out of the turn. The inside tire will steer out of the turn due to additional toe IN, the outside loaded tire will experience toe OUT, turning out of the turn.

The fix is to get the steering linkage to travel the same arc as the spindle. On an early Camaro you MAY need to bend the steering arm (bend template) down or raise the inner mounting point. Here is a handy FORM you can use to fill in the needed dimensions to properly draw out your car's suspension.

NOTE: Adding more positive caster will usually reduce bumpsteer, it lowers the outer tie rod end. Try aligning with plenty of positive caster before measuring and attempting to correct bumpsteer.

 

 BUMP STEER GEOMETRY

bump steer drawing.gif

Here is a link to another explanation of Bump Steer

Click here for a link to more info on front suspension geometry.


GULDSTRAND MOD TEMPLATE

guldstrand template

If you print this template out, it most certianly will NOT be exactly the correct size. Right click and select save, then you can try printing it out.

My measurements off my template are lower ft bolt 1.060" lower rear bolt .775" To measure, draw a line through the top hole centers, the cross hairs are accurate reference points, the circles are a bit off center so don't use them. Measure down from this line. The lower holes are also offset 1/4" to the rear to increase positive caster adjustment. My template was aquired by me when I visited Guldstrand sometime arond 1973, I talked to an engineer there who said they developed this template for Penske. My version shows some alternate holes that were tried, these holes were higher and lower than this "final" version.

NOTE Chicane67 was an employee of Guldstrand Ent and says his hole lowering measurements are: F .875" R .775"

I used to have a link to a Pro-Touring.com web discussion on this topic, but I found out the dimensions I posted there were wrong. The dimensions posted here are from my template.

All I can say is, I used the top measurements and they worked well on my 67 Camaro.

This is the template, "the Guldstrand Mod" that is used to improve the front suspension geometry. The Camaro front susupension has too low a front roll center, and almost no negaitve camber gain in bump. If you do this modification to your Camaro, make shure you trim the bottom of the first thick alignment shim you place on the rear bolt. The A frame mount face changes angle and the shim will hit and prevent the upper shaft from properly seating on the mount.

In addition, if you use stock upper A arms, the upper part of the mount must be trimmed off to about the height of the holes to allow enough clearance. The mount braces will also need to be trimmed or the A arm will hit in the middle.

 

If you use tubular upper A arms, the mount does not need to be trimmed near the holes, the braces may, or may not, not need trimming.

If you call Guldstrand ent, they will send you a template


HERE IS THE CAMBER CURVE GENERATED AFTER THE GULDSTRAND MOD

Negative height numbers are for bump = suspension compressed. positive numbers are for droop.

To my eye these charts are upside down, but my chart software won't do it any other way, and I haven't had time to figure out how to reverse it.

guldstrand camber curve67 camber curve - stock

GULDSTRAND MOD

Measured from my 67

HEIGHT CAMBER

-3" ...............-2.6 (bump, with springs compressed)

-2" ...............-1.5

-1" ................-.7

0" .................0 NR (Normal Ride height-for a lowered car)

+1" ............+.4

+2" ............+.7 (rebound, with springs extended)

+3"............. NA

*PRO MOTORSPORTS SPINDLE EXTENDERS Data from their web page

http://www.drgas.com/promotor/

 HEIGHT CAMBER

-3"...............NA

-2".............-2.375 bump compressed

-1".............-1.

0"..............-0

+1".............+1

+2".............+1.75 rebound

Their figures start at .75 deg neg camber, I subtracted that amount to start out at zero deg.

* I'm not endorsing or recommending the Pro-Motorsports spindle extenders, the data is just provided for your comparison. I feel the roll-center may be raised too high with this mod and it may cause Porpousing- front bobbing up and down in the corners. I have talked to a couple of people on the net who have experienced this. People who have used this mod report wearing the heck out of the inner edge of the tires!


Below is my response to a suspension geometry question from the Team Camaro Forum

The question relates to the Guldstrand mod and if lowering the upper A frame more than Guldstrand recommends, or using a taller spindle plus the Guldstrand mod to get more negative camber gain is a good idea.

Please understand that you can't focus ONLY on camber gain.

 As they say, a little knowledge is dangerous, and in the case of suspension geometry I feel it's VERY true. If you are going to change anything from stock, it's a good idea to understand all the ramifications of your "improvements". Since most everything concerning your suspension is interelated, one change usually affects other aspects of your suspension.

Changing upper A frame mounting location will change:

The roll center height affects driver feel, roll stiffness, how much of the cornering roll torque is fed through the springs, shocks, sway bars, vs how much is fed directly via the geometry to the tire.

EXTREME EXAMPLE: If the roll center were raised to the same height as the center of gravity, NO roll torque would be fed through the suspension at all! The car would not be tuneable by changing sway bars or springs!

SO lowering the upper A frame usually will raise the front roll center, increase the neg camber gain, increase tire side scrub, the higher roll center will move more - the more you lower the upper A frame mount. If it get's too high, the tires will tend to break loose if small bumps or undulations are hit in a corner. The suspension- springs, shocks, swaybar, should be softened to accept the resulting lowered roll torque generated.

The starting point "should" be the tires, and what they require for best performance. Some tires need more negative camber than others.

You should temper tire requirements with the application, street, track, drag, roadrace, autocross, type of track, type of pavement, banking, bumps, etc.

They all have specific requirements from geometry to setup, and how much wear can be tolerated. I assume you would be concerned if your front tires wore out the inside edge in 500 miles?

You would then set up your suspension geometry, springs, swaybars, shocks, alignment, to best work with "that" tire.

The Guldstrand mod lowers the upper mount about an inch or just a bit under that.

It retains low tire side scrub, stable roll center movement and height, some beneficial negative camber gain.

Consider that my 89 IROC camaro had 1/2 to 3/4 degree static neg camber with the adjsters moved all the way in. The McPherson strut suspension added little in negative camber gain during roll.

Late vettes have similar neg camber gain much less than the Guldstrand mod. I don't have the figures, but the A frame angles I see lead me to that conclusion.

The newer radial tires have SOME ideal requirement for camber. But I don't know what that is! THAT is the burning question, and the starting point for the suspension geometry improvement proccess.

That data is generally only known by suspension and tire engineers.

TRADEOFFS.

Why not lower the holes more than Guldstrand did?

More negative camber gain might be better, but it could easily be worse in other areas.

You brake hard at the end of a long straightaway, now the tires are unevenly loaded on the inside edge during straight ahead braking! Result-poor braking, wheel locking.

Example two, you brake hard and turn into a corner, - all is good, you then get past the middle of the corner, get on the gas, the front end raises up under acceleration, now the camber curve goes the other way! The tire will lean out more! Your increased neg camber curve cranks camber out of the outside front tire, is that good? Result- corner exit understeer.

You enter a long high speed sweeper, the car is under power, front lifts a bit higher than static ride height due to power applied and aero lift. BUT you need to corner hard, you are on a flat curve going 90mph. How much negative camber did you lose? how much understeer are you going to have?

The best I can say is "dont' get greedy", people do break the rules sometimes, I've seen some crazy stuff work and win, especially on a circle track sprint type car. Those guys have some wierd ideas! But, circle tracks do not have flat or off-camber corners.


TUBULAR ARMS VS THE GULDSTRAND MOD

The Guldstrand mod increases negative camber gain, when the car leans (rolls) in a turn, the tire will not lean out as much as it does with stock geometry. It will also raise the front roll center making it more compatable with the rear roll center height.

 

Stock upper A arms can achieve around 3 degrees positive caster. "Properly" made Tubular upper arms allow higher positive caster alginment settings with pretty close to the same amount of shims front and rear. Increased positive caster from tubular upper arms can eleminate the tire leaning out when turning sharply. Steering effort will increase, but if you have power steering it won't matter. There are also dynamic weight jacking effects from high caster.

 

Park your Camaro on level ground and turn the wheels to the right to full lock, the left front tire will lean outward, (positive camber) by about 3 to 4 degrees, increased positive caster of around 5 degrees will keep the tire vertical. Remember the chassis will dive and roll in a turn and you need excess neg camber gain to make up for that.

 

A First Gen Camaro has 8.75 degrees steering axis inclination* (SAI) built into it, If you were able to turn the front wheels sharper to a 90 deg turn, the wheels would camber out by 8.75 degrees, minus any positive caster you have set. You can't turn your front wheels that sharply, but you can turn them around 26 degrees, which is almost 30% of 90 degrees.

 

In general, more neg camber gain via the Guldstrand mod will help most on large sweeper type corners, - generally high speed turns.

 

The tubular upper arms will allow 5 degrees positive caster with minimum shim stack which isn't achieveable with stock arms, usually 3 deg + is all you can get. Large amounts of caster tends to help most when the wheels are turned very sharply, like at an autocross, but it does help a bit on larger radius turns. The nice thing about positive caster is, it goes away when you point the wheels straight ahead, so you can use less neg camber setting

 

* SAI, Steering Axis Inclination, draw a line from top balljoint to bottom balljoint this is the rotation axis of the front wheel, a First Gen Camaro SAI is 8.75 deg from vertical with the top balljoint closer to the center of the car than the lower.


CASTER SPECS

 

Caster and Camber settings

QUESTON:

I'm wondering if anyone can share information on caster and camber settings. What is a compromisable setting for street driving, what is a good start for road racing? I am also wondering about how increasing caster effects handling. I've seen that most of GMs cars run only a degree or two, where as the Camaro is up around 4, and a Corvette and Viper run more than 6. Is it recomended to increase caster in a car that calls for say 2 degrees, to 6, 6.5? How much camber increase can be run without shaving off the insides of my tires on the way to work? I've pieced together quite a sweet chassis setup for my V8 S-10 and would like to put the suspension to work. This site has been increadible help for me in finding information. Great job, keep up the good work. Any and all responses will be greatly appreciated.

Thanks, Nick

ANSWER 

Using a lot of positive caster will help keep the tire flat on very sharp turns. The Camaro spindle has 8.75 degrees angle between the balljoints and wheel hub. If you could turn the front wheels 90 degrees, this would make the front wheel lean out that amount minus whatever positive caster you have set. Of course you can't turn the front wheels 90 degrees, but you can turn about half of that, and the tire will lean out by 4.375 deg. Try turning your wheels full lock and measure your camber or put a level up against the wheel.

On wide sweepers it would have much less benefit, but some. More caster can cause more bump kick back on the wheel especially if your wheels stick out a lot - the scrub radius.

More positive caster will take more steering effort so PS would help.

I wouldn't use over 3 degrees or so unless autocrossing or running timed events with tight corners. A lot of Caster is not needed on large radius turns. Many new cars like the Vette and Viper use 8 or 9 degrees positive caster. Mercedes uses 14 degrees positive caster.

David


TOE-IN INFO

I have a highly qualified suspension book that recomends .1 degree toe OUT reduction, (from stock setting) for every 1 degree neg camber you use.

.1 degree is almost 1/8 INCH toe out! This is total toe-out across the car, 1/16" per wheel.

 Why? -

The front wheels try to turn inward when using neg camber due to camber thrust.

Imagine the tire tilted one degree in at the top. When it is rolled, the wheel will try to run around in a circle - Imagine it were on a bycicle and you were leaning it 1 degree.

Both front wheels cancel each other out, so the car stays straight, but the tires are thrusting inward as you drive, and should be toed out slightly to compensate for any "extra" neg camber.

 

Origonal factory specs for 60's cars were developed for use with positive camber and bias ply tires required more toe in than radial tires do.

When radial tires came out, toe-in specs were reduced by half, so a Camaro with a 1/8" toe in spec was reduced to 1/16" toe in. Many front end shops may have forgotten this fact and set toe to the "book".