FWD castor/camber angles

[peugeot106]

right!! firstly a quick hello to the forum.. after viewing for a while i decided it was time to join as quite frankly you all seem a lot smarter than the average small hatchback forum!!

i will try to keep this introduction brief... i`m in the process of taking my peugeot 106 from everyday car to track toy.. a photo history can be found here:

http://smg.photobucket.com/albums/v1...106/?start=all

in an effort to expand my knowledge from "low and stiff = good" to things a little more technical ive been reading a few books 1 of which is *competition car suspension by allen staniforth* and 1 topic that particularly got me thinking was castor/camber angles!!

for those not familiar with the 106 turrets there are 2 std positions for the topmounts- NON PAS vs PAS ..

NON PAS positioning = top mounts further forward= lighter steering + less castor...

PAS positioning = top mount further back + heavier steering (counteracted by power steering) but greater castor angle which results in dynamic camber???

it would seem that increasing the castor is indeed a very worthwhile act as during turning the dynamic camber is increased.. buying swanky billet top mounts and yanking the sturt tops inwards (static camber???) just results in inside edge tire wear...

the thing is the limiting factor is the fact peugeot placement of the holes in the turret top...

seeings as my shell is currently recieving much welding/cage/rust repairs/strut top reinforement the more i think about the latter the more it seems an ideal opportunity to possibly relocate the std positions back another 10mm (which my very poor maths works out at an extra 2degrees (possibly just over) extra from the PAS position)

at first i didnt think there`d be enough room but now i`ve removed the scuttle panel (for extra throttle body trumpet/filter room) its free`d up a fair bit of space around the area:



now am i on the right track with this train of thought? or are there far more important things i should address first??

many thanks in advance for any help and for taking the time to read all of the above

stuart

[peugeot106]

i addition to my ramblings above i have quired the genuine peugeot sport preperation documents..




- A cette assiette, les reglages preconises sont:

carrosage - 2deg 30` de negatif
chasse - 3deg 40` avec DA
chasse - 2deg 40` sans DA
parallelisme - 2mm e pincement

which i THINK!!!! translates to:

2degrees and 30 minutes negative camber
3 degrees and 40 minutes castor WITH power steering
2 degrees and 40 minutes cator WITHOUT power steering

[forestdweller]

Hello. I'm also new and still learning, but here's what I can offer for what it's worth. It sounds like you're preparing your car for real track work. If so, the turns you encounter will be fairly open compared to what would be encountered in an autocross or gymkana event. You can do a basic Ackerman steering calculation based off turn radius and your wheelbase to find the theoretical required steering angle for some of the turns you expect to encounter. I think you'll find that at the typical steering angles of a road course, the "dynamic camber" changes from the caster angle aren't that great. Optimizing your static camber angles to work with your chosen tire (er, Tyre) should be more of a priority. The Peugeot sport numbers may be fairly close to what you want for caster.

Now we'll see what the actual experts have to say...

[Notso Swift]

I presume you are running "R type" tyres and not slicks
WIthout being 106 specific, but based on 3 FWD race cars over 20 years (and now a 4WD, which isn't much differrent)

Start with 2-3 deg camber.
As MUCH castor as you can handle, 7 degrees is not unheard of in FWD, , but it is often hard to get that much, I would see 3-5 as a minimum. mover the bottom baljoint forwad for an extra couple of degrees.

If you have to drive it to and from the track, then I would probably only have 1 deg Camber and 3 castor


THe Diff will make a big difference as well, because if it is open you need to maximise traction at all times
2 mm toe out is about right, (per side) but again if you use it on road I would reduce this to 1mm per side.

[spannerman5298]

Ok,so im new to the forum but been prepping cars for 15 years or so.Notso swift has it spot on!!
A couple of cars i have run before (both race winners) were the same type of car but for different championships and the difference in set ups centered around the diff. The first car ran a fierce plate diff and ran 3.5 deg camber but standard caster settings due to the regs requring std top mounts.
The 2nd car ran an open diff (hot hatch regs) and we struggled with traction using the set up from the other car so redused the static camber to 1.5 but ran about 5 or 6 deg castor!
Also noticed ur considering relocating the turret on the body shell. Doesent say if ur doing track days or competing but i would advise against as most championships dont allow this.

[forestdweller]

I stand corrected.
Live and learn.

[peugeot106]

i doubt very much i`ll use it for racing.. most probably track days and sunny evenings on the backoads... its more an exercise in trying to put theory into practice... the trouble is the theory at present confuses me and the internet has created more "experts" than pirelli`s made tires!!!

the diff at present is just a std affair.. but after having been out in a friends 205 fitted with a quaiffe item i have to say the before and after drives were dramaticaly different considering that was the only difference between the 2 drives... i think its safe to say that will no doubt get added to "the list"...


many thanks for your feedback.. i was beginning to think i`d bored people with my long winded question...

another chapter which got me head scrathing was bumpsteer..

beings as my car is fitted with pug sport coilovers and only now escaping my "yoof" the car does sit quite low.. the wishbones are pretty much level with the road but the steering arms are quite a bit lower at the rack than they are at the steering arm on the strut..

i`m running 300lb front springs so doubt there is much in the way of travel but i have a sneaky feeling that under compression they are causing a fair bit of toe out.. (i`ll have to check this once the cage is in and i begin its mock build up..

some have said the only method is to cut the arm off the strut and lower it.. but surely if i was to remake the steering arms slightly longer and fit rose joints instead of the std tapered ball joint i could play about with the heights and possibly have a similar effect????

[spannerman5298]

The correct way is to lower the arm on the strut and i have tried the repositioning of the track rod ends which made the bump steer worse!! To be honest when we did dial it out the car didnt seem any different than before so probly not worth bothering with!
One thing that may be an issue if the car runs a very low ride height is the cv joints and driveshafts! Had a road car customer with a rather low golf that used to eat joints!!
An easy fix for that would be to tip the engine and gearbox forward on its mounts till the shafts are at a more desired angle and you will also gain some extra room for your throttle bodies !!

[Notso Swift]

Originally Posted by forestdweller

Hello. I'm also new and still learning, but here's what I can offer for what it's worth. It sounds like you're preparing your car for real track work. If so, the turns you encounter will be fairly open compared to what would be encountered in an autocross or gymkana event. You can do a basic Ackerman steering calculation based off turn radius and your wheelbase to find the theoretical required steering angle for some of the turns you expect to encounter. I think you'll find that at the typical steering angles of a road course, the "dynamic camber" changes from the caster angle aren't that great. Optimizing your static camber angles to work with your chosen tire (er, Tyre) should be more of a priority. The Peugeot sport numbers may be fairly close to what you want for caster.

Now we'll see what the actual experts have to say...

The problem with too much static camber is it often hurts tractionand in a FWD it is all about carriying speed then getting the power on (positive and negative )
There are few downsides with lots of castor, if your arms are stong enough. It is not uncommon for production based cars to leave power steering in to enable more. The low steering angle is why you need as much as you can handle, bare in mind you generally messure at 20 deg, which is about as much angle you get on a road course (so agreeing with you, but taking different conclusion for the reasons above)

[forestdweller]

I certainly won't argue with what actually works in the real world. And I agree with the bit about too much static camber limiting longitudinal grip in either direction. I'm just surprised that much dynamic camber is gained even with 7 degrees of caster. Of course there's more going on with suspension movement, camber recovery and such to consider. I just dialed some caster out of my own car (RWD) to lighten and improve the steering feel, but now I'm reconsidering if that was such a good idea...

<apologies if my post is a bit OT>

[GORDON STREETER]

Caster angle will always be a moot point as its always going to be a compromise between straight line stability and cornering ability. But the only way to really find out is by testing and to keep putting more on until lap times start going up. Also you will find as you get better at driving faster you can take some off.

[JamesH]

Originally Posted by GORDON STREETER

Caster angle will always be a moot point as its always going to be a compromise between straight line stability and cornering ability. But the only way to really find out is by testing and to keep putting more on until lap times start going up. Also you will find as you get better at driving faster you can take some off.

Unfortunately, track days don't allow timing so its going to be a difficult job to test for the best setup!

(How may people actually do time on track days?)

James

[peugeot106]

ahhh fortunatly i have invested in a race technologies dash2 display so timing won`t be an issue....

[GORDON STREETER]

Originally Posted by JamesH

(How may people actually do time on track days?)

James

Most I would think (one way or another)