GTD front suspension settings

Gents,
I am in the process of realigning my front end and would like to establish what the factory settings were. I believe they were posted on a previous thread long ago but couldn't come up with much using the search function. I know it depends on usage; track or street, wheel and tire choice, tuning to personal tastes, etc. but would like to reconfirm the factory build as a baseline. In particular the following settings; castor/camber/toe-in and especially KPI. I know KPI is non-adjustable, but knowing this value helps when verifying castor measurements.
thanks
 

Mike Pass

Supporter
KPi is 4 degrees as it has the Granada Mk2 upright. I have sent you a message with my email address. If you send me your email address I will send you a copy of the GTD build manual which has the original suspensin settings.
Cheers
Mike
 
Is there a rule of thumb for the GT40 replicas? A base thats pretty common on all?.
I am rebuilding one of three KVA "B" chassis and offcourse there's no building manual or instructions.
 
I'm not sure what uprights were used on your KVA but it all starts with them. The following comments are based on a Granada Mk2. I know that was the donor vehicle as I removed them myself in the scrap yard many years ago!
After Mike Pass's kind help I decided to go back to basics and remeasure/recalculate everything.
I started by measuring the angle between the axis through the upright swivels and the hub front face. It's an awkward measurement but came up with a value of 6.1 degs. To find KPI you need to add the camber you are planning to use. In my case it's -0.6 degrees so KPI becomes 6.7 degrees. There are a range of values/designs mentioned on other threads so it may be worth checking this first. The next two things are the castor and scrub radius. I noticed when I was dismantling the scrapped Granada that the wheels had a large negative offset. I assumed that was to keep steering effort reasonable as there was a heavy old lump of iron between the front wheels and the negative offset would reduce scrub radius. By comparison the front end of the GT would be very light so it was a bit difficult to work out steering weight with scrub radius and castor angles. In the end I settled on 2.9 degs castor and scrub radius of about 75 mm. See attached photo showing offset I used. The steering is nicely weighted but is a bit weak for self-centering. I have decided to increase castor to about 5 degs and see what happens. I plan to take the car into an alignment shop with a castor/KPI gauge to confirm the values I've calculated/measured. Hope this helps a bit but there are so many parameters to play with, I don't think there is one perfect answer. If I was starting with a clean sheet, I would go with uprights with a larger KPI (>10 degs) but am hoping that a bit of tweaking can improve this issue.

DSCF0035.JPG
 

Mike Pass

Supporter
GTD

Ground clearance to chassis Front 4" Rear 4.5"

Front castor 6.5 degrees
Front camber 0.5 degrees negative
Front toe in 1.6mm

Rear camber 0.5 degrees negative
Rear toe in 1.6mm


Cheers
Mike
 
Gents,
As I have far too much time on my hands I've written a Excel-based program that includes the effects of KPI/castor/camber combined and calculates camber gain and vertical jacking as a function of varying steering angle for different front-end geometries. With a small addition it could also calculate variation of scrub radius with steering angle. Unfortunately, although the math is textbook its a bit involved. If there is any interest out there I could put together a few diagrams and some text to explain the worksheet. I have tested it against my own workshop measurements and it seems to give results close to what I observed. I am planning to take the car into a shop soon to get a more accurate front-end alignment to confirm/refine my measurements.
cheers,
Trevor
 
Top