Hi all, does anyone have any idea how much camber and castor results from a certain amount of adjustment of bottom arm/castor rod length? ie how much to lengthen a bottom arm to achieve -2.5deg camber for example?

I am wanting to get the front geometry right on my sunny for rallying, and am going to make non-adjustable modifications to start with (shortening castor rods and lengthening bottom arms) and want to get it roughly right so I don't have to do it again!

I was thinking it would be possible to work it out, IF I can measure the installed length of the struts, from balljoint to strut top. Will give it a go. But qualified opinions are eagerly sought!

I fitted stanza control arms that are 20mm longer. that gave about neg 2 to 2.25 degrees camber.

Thanks for the reply benny, assuming they were for your coupe they would be a fair bit shorter than 310 struts, so for 20mm widening I wouldn't expect quite as much camber increase as you gained. Also your coupe would be lowered too I'm guessing, which would probably have increased negative camber from stock too. I am going the other way unfortunately, will probably end up about 1" higher than stock, which will decrease my negative camber a bit... gonna be one of those suck it and see things I think....
Cheers,
Morgan

Morgan...I have minus 3 degrees camber on the front, but a stiff anti roll bar. You would need 4 degrees if you have a stock roll bar as it would tend to roll more and you would need to adjust this in the camber to keep the face of the tyre on the deck.
BTW I used A032R race tyres..they like between 3 and 4 degrees.
You can usually tell if you have the right camber by getting a cheap infra red temp device $40 at Dick Smith and measure the inside middle and outside of the tyre tread surface. After a hard outing, the temp is around 65 degrees + or - 1 or 2 degrees across the face. This means the tyre is working well everywhere and the car is setup right. If there was a huge disparity on the ouside edge like 6 degrees more, you have too little camber!!! On the inside temp too high then you have too much camber!!....
OK so the castor is a bit different and someone like Harry could help here, but mine is set to about 6 degrees (I think) will help with directional stability:-

Positive caster provides the directional stability in your racecar. Too much positive caster will make the steering effort difficult. Power steering will allow you to run more positive caster. Negative caster requires less steering effort but can cause the car to wander down the straightaway.

one way to get some negative without cutting control arms is to fit 200b steering arms.these are offset outwards,& give an increase of about 1 to 1.5 degrees towards negative.you have to put a spacer under the nut holding the steering arm to the balljoint,but i've talked to two people i trust about this & they can't see any problems with using a big flat washer of the proper grade.you also need to use a 180b (710) outer tie rod to match the steering arm to the tie rod.

you could also bend the struts to achieve some more neg.

i had thought that cut & shut lower control arms were illegal,because some people just butt welded them back together & the welds failed.personally,i seen a lengthen lower control arm that was involved in an encounter with a wall,& the only part of the arm not twisted,bent & buggered was the bit around the weld.that was because the weld was properly strengthened.
as for modifing the castor arm,i've been considering lately if shortening the metal tube
the bushes sit on might work.this is what the nut tightens up against,& if this was shortened,the wheel would be brought forward.it would just compress the castor bushes a bit more than usual.all you would need was a small lathe to do the shortening.
in my opinion,this would be much safer than machining the castor arm itself.

you could also just redrill the crossmember to push the whole lower control arm assembly outwards.if you get it in the proper arc,bump
steer is reduced as well.

my sunny racecar has a redrilled crossmember ,the 200b steering arms & an adjustable castor arm bought from stewart wilkins rallying.it has about 2 degrees negative camber & 5 degrees castor,& it handles & turns in beautifully.

Has anyone mentioned strut tops yet? Are you allowed to run modified tops - this will give you a couple of degrees at least.

I have also moved the pivot point for the lower control arms. We moved ours out and up, also we offset the holes (front to back) which gives the arms static castor. This means you don't put as much load on the bush in the LCA when you crank on the castor.

we are still chasing more camber, legally within our rules, but currently run 4.5 degrees ned and about 6.5 degrees of castor. We can wind on 9 degrees of castor, but the castor shudder at anything under 110% effort is so bad you can't hang on the steering wheel.

Mark.

Cheers fellas,
Craig- yeah I run a similar setup to you in my 1200, also on 032R's.I am running a 20mm bar, have a 24mm to try out but I am going to harder springs first- 250lb. Would love a pyrometer but they are a lot dearer than that here!

as for the sunny....
b310gx, thanks for that info, very interesting stuff. are the 200B arms any shorter than the 310 arms? would be a bonus if I could quicken up the steering a bit. and where are your new new inner pivot holes? I was avoiding altering pickup points for fear of introducing bump steer- perhaps it is necessary if the 200B arms are different???? did the place you bought the setup recommend drilling the holes in a specific place or did you work it out yourself?
Cutting and shutting might not be legal- I don'y know- but by the time I've done it properly you wouldn't notice unless you were really looking for them, and I am confident in being able to do it sufficiently strong and safe. Like you have seen if it is done right it's not a problem.
As for the radius rods I think I will have to turn the shoulder back to get an appreciable gain in castor, there is heaps of thread on the rod so it won't be a problem. The washer is a bit of a pain in the arse though- you can't take it off while you machine the rod! but that's not a biggies either.
I'd like to have a look at these 200B steering arms now, are they the same as an 810 180B? We don't have many 810s or even 610s getting around now...

Mark, yes we can run strut tops, in fact we can do pretty much whatever we like, much freer than it seems it is for you guys in aussie.
I just wanted to avoid making the tops just yet. I'm building this car to a strict budget and timeframe for an event coming up- so yes it is something I will do a bit later but probably not before the first rally. Just starting out simple, see how we like it and we can always get serious after that...

Have returned PM.

Forgot to mention I have also totally removed sway bar.

Your calcs. should give you what you want, regarding lower control arms.

Thanks Gary, got your pm. Will give 25mm a go and see what I get. Still keen to see some 200B steering arms too.
Interesting that don't run a front swaybar! Would you be putting it back on if you softened up the front springs?