from nerdy maths to predicting camber and castor angles

**oldcorollas** · 14-06-2008, 06:23 PM

following on from the "maths help" thread (thanks again DerekJay

), i've made some equations to simulate the lower control arm movement, first without radius rod, and then with radius rod pivot moving 100mm in each direction (and combinations thereof)...
case 1 is no offset, when looking from front of car to back
case 2 is horizontal movement of RR pivot
case 3 is vertical movement of RR pivot
case 4 is both horizontal and vertical movement of RR pivot
100mm is exaggerating things a bit, but good to see the effects.

bump/rebound is only 100mm from the LCA in flat position.
when looking at the camber gain curves keep in mind that normal car has lower arm at maybe 50mm droop to begin with..

the results are interesting...
although there is some effect on camber, the effect of moving the radius rod mount on camber is quite small.. (all camber curves are grouped very close together on the LHS, going through -2deg on Xaxis)

but moving the radius rod mount has a massive effect on castor...
(the largely spread out curves going through +2deg on Xaxis)

also, changing the strut KPI (steering axis inclination) from 7deg to 10deg has a big effect on camber, but almost no effect on castor......

also remember that both of these movements will affect bump steer...

next step will be to feed in real car data and see what happens... then start modelling steering geometry and changes in camber and castor and bump steer...

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**AAAAGZE** · 14-06-2008, 06:36 PM

so many pretty colours.....

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**thechuckster** · 14-06-2008, 08:02 PM

now all you need is a table of different LCA lengths to see how they affect camber for various KPIs as found in toyota struts

**RAd28** · 14-06-2008, 08:34 PM

OC - How does this answer my question???

Do i Install BLUE, or RED camber tops??

**oldcorollas** · 14-06-2008, 09:56 PM

Originally Posted by thechuckster

now all you need is a table of different LCA lengths to see how they affect camber for various KPIs as found in toyota struts

all i need is the data to input... i will make up a diagram and list for people tonight.
hopefully, we can make a "toymods library" of castor and camber curves, from which, people can plan and implement altered steering stuff.. or something like that.
i suspect motivating people to actually measure cars accurately will be harder than these equations

RaD, depends which colour is least ghey that particular month

**oldcorollas** · 15-06-2008, 12:24 AM

if you can supply me with the following dimensions (and car type) i can make graphs

radius rod offset: Bx, By, Bz
Strut top offset: STx, STy, STz
lower control arm length
KPI/steering axis inclination (this is also important)

additionally, the amount of droop of LCA (Z offset) at normal position, and desired bump/droop range would also be helpful, but not necessary..

something like the following pic

**RobertoX** · 15-06-2008, 05:47 PM

Hey OC, I use a little program called "Susprog" for this type of stuff. I've never done a mac strut model on it before but can give it a go to verify your summs if you like. What values are you using?

**big_zop** · 15-06-2008, 05:54 PM

Originally Posted by RobertoX

Hey OC, I use a little program called "Susprog" for this type of stuff. I've never done a mac strut model on it before but can give it a go to verify your summs if you like. What values are you using?

Is this commercially available and if so, where can i get a copy?

**RobertoX** · 15-06-2008, 06:13 PM

Yup, here: http://www.susprog.com/

I got it from this bloke: http://www.bevenyoung.com.au/ I think it cost me about $60 or something like that (I got a discount because I was doing FSAE).

**big_zop** · 15-06-2008, 06:41 PM

Thats great, but if only i knew about it last year when i was doing FSAE! lol

**oldcorollas** · 15-06-2008, 06:44 PM

hey RobertoX,
yah i know about susprog, but thats no fun

and you should pay for it if you want a legal version...
does it do drag link steering as well?
edit: the only thing i haven7t bothered to take into acount yet, is the effect of castor on camber from KPI, but it is a very small change for low castor.. will implement later.

as an example, try..
STx=193
STy=20
STz=500
KPI=10deg
LCA length = 300
radius rod offset;
Bx=100
By=400
Bz=-100

and + or 1 100mm bump/rebound from the LCA being flat.

or really.. whatever bump range in whatevrer increments....

thanks!

be interesting to compare