Too much caster ?

[stringfellow_po]

I got around to doing a proper alignment at the weekend but I seem to end up with too much caster (aiming for 5 deg positive caster, 0.5 deg negative camber). I have installed PST non-adjustable tubular upper control arms (checked they are installed the right way round with ball joint level with floor) and adjustable strut rods (adjusted as per instructions with 3/4" thread of eye bolt threaded into rod). I have no binding over full suspension travel.

When measuring caster (on left side) I get +3 deg camber at 20 deg steering angle to the left and -2 deg camber 20 deg steering angle turning to the right (pretty much lock to lock). This means I have 7.5 deg caster (taking the difference and multiplying by 1.5) ?

If I move the rear cam bolt outward to decrease the caster I cannot compensate enough moving the front cam bolt inwards to get enough camber as it is already fully in board (aiming for 0.5 deg negative). I could lengthen the strut rod but would have thought I could get the correct adjustment with the UCA ? Pretty much same readings on right hand side.

I have set the front end ride height fairly low (23.75 in floor to wheel arch) to match the rear (hotchkis rear springs)

I have power steering (for now) so no issues with turning. Just checking my methodology is correct before I look at adjusting the strut rod length ?

 

[moparleo]

Your ride height affects the alignment settings.The strut rods are not where you make your caster adjustment. You are just moving the lower control arm closer or farther from the rear.
Caster was also known as King pin angle.

WHY THE PROPER RIDE HEIGHT IS SO IMPORTANT​

Ride height determines where the control arms operate within their normal range of travel. This is especially important with SLA and wishbone strut suspensions. When a suspension is designed by the vehicle manufacturer, the control arms are positioned to operate at a specified ride height. That position determines the amount and direction of camber change that occurs as the suspension moves from jounce to rebound. If the springs are weak and the suspension has sagged two or more inches below the specified ride height, the arms are forced to operate above their normal plane and beyond their normal range of travel - which can cause undesirable changes in camber and toe. Unequal camber can cause a vehicle to lead to one side.

Differences in ride height front-to-rear can also upset the steering geometry of the front suspension. Raising or lowering the rear of the vehicle will change the angle of the steering axis (caster). Depending on the amount of change, it may have an adverse effect on steering stability, effort and returnability.
Other clues to look for that may tell you a vehicle has a bad attitude problem:

• Caster readings out of spec. Depending on whether the front or rear of the vehicle is low, a certain amount of caster will be added to the front wheels (unless both ends are equally high or low, in which case there is no net change). If the nose is low, negative caster is added to the front wheels. If the rear end is low, positive caster is added to the front wheels.
• Camber readings out of spec. Changes in front or rear ride height can alter front camber alignment (and rear camber on vehicles with independent rear suspensions) especially when there's a difference in ride height side-to-side. How much the camber readings change will depend on the amount of sag and suspension geometry.
• Increased tire wear. Changes in ride height that alter wheel geometry can accelerate tire wear - particularly on suspensions where toe is sensitive to changes in ride height.
• Suspension bottoming.

 

[stringfellow_po]

Thanks moparleo for the useful info, I have played with varying ride heights but still does not get me within range. I am going to have another look at it tonight.

 

[cuda joe]

with wheels on turn tables you move the wheel out 20 deg then zero the bubble then turn in 20 deg . where he bubble is that is your caster measurment

 

[moparleo]

Have a picture of what equipment you are using to get your alignment readings ? Stock size and offset rims front and rear ?

 

[stringfellow_po]

Here is my setup.

I have a laser level so first ensured all 4 wheels are level on the ground
Checked ride height is even left / right and where I want it
Front rims are 17x9, 5in offset + 1/4" spacer to clear brakes (spindles are swapped left to right as Baer Track 4 setup has calipers to rear of spindle). Rears are same, also with 1/in spacer to match front
Camber gauge reading verified against phone angle app (I understand I am not going to be to 0.1 deg but should be possible to get within 0.5 deg)
Homemade alignment jig is checked square and reads 0 deg on true vertical, (verified with laser)

Experimenting with strut rod length, I pulled them off the car and measured against the originals. I needed to add around 1/8" length. This made noticeable difference to the caster so I am now around 5 deg caster with 0.5 deg camber (with possibility of additional 0.5 deg camber). As I am planning to use the car on the track I will probably keep it there.

Edit; after looking at my photo the 20 deg tape lines did not look correct so checked these and they are closer to 30 deg, doh! so looks like it could be a simple fix and I need to go back to school !

 

[Chryco Psycho]

IMO I am not sure you can have too much caster , it will just help the car steer straight & return to straight after cornering , , it will make it harder to steer but with power steering this is no issue & will increase steering feel .

 

[stringfellow_po]

Sorted now with 5 deg caster and 0.5 deg camber. That was a learning exercise, but should be straightforward next time round! Thanks all for your help and replies