Roll Centre & Camber

[Rusty]

Saloon is much stiffer; coupe is wobblt and before the facelift coupe, the bodies are a bit wobblier still...

Max stock camber is about 2 deg and castor is 2.75 deg up front. Rear, go 1.0 - 1.5 deg camber and a touch of toe out.

[GazzaG60]

thanks and, wobbly is a good decription. i thought there was somthing wrong with my s2 coupe when i got it. the saloon feels great it must be said.

for the stupid (me) how is this camber achieved without bolts that change it at the shock i can understand the toe is done on the tie rods to the subframe at the rear?

[Error404]

Lower ball is the main adjustment Gaz, you can get a bit more by loosening the strut to hub bolts and having a jiggle.
Biggest limiting factor on the front is tyre width

[BorisShakhov]

I'm now not sure about tilting the struts inwards, as that'll tweak the roll centre down more.].

Forget it mate! As I said before: Strut inclination makes negligible change in a static RC position.

[GazzaG60]

ok, that limits me on the narrow arch then. the ball joint has to be pushed in to clear the arch. inner clearance is no issue. even on the 47et wheels.
fronts so are we saying arch catch and inner tie catch limits. fronts are my biggest issue either way. im yet to see if the clear the arch.

gotta say this area, one i have done little with and know little about is starting to interest me quite a lot. id like to take the car to the track when its done. at least once anyway. next issue will be my driving

how do your top mounts help/change the car feel andy?

[Ahonen]

The biggest difference that inclining the struts would make is to reduce the wheel rate - that is to say you've effectively softened the rear spring - because the spring moves less per unit of vertical wheel movement. There may also be an increase in camber gain (which would give you more camber in the turn), but it's so long since I've worked on a McPherson strut racecar that I can't remember.

Reducing the wheel rate would likely have reduced the ride height if the platform heights were left the same and that would have had the largest impact on the lowering of the roll centre height.

As an aside, I would never, ever intentionally run rear toe out on a racing car, unless I knew exactly what bump steer curves I had and how much rear droop I saw on the brakes. From a 'bloody hell, that swapped ends unexpectedly' point of view, rear toe out can be a bit tricky to manage.

[BorisShakhov]

The biggest difference that inclining the struts would make is to reduce the wheel rate

0,1% from 4kg springs?

rough estimation:
new_strut_length=sqrrt((old_strutlenght*1,02)^2+to pmount_offset^2)

[Ahonen]

0,1% from 4kg springs?

rough estimation:
new_strut_length=sqrrt((old_strutlenght*1,02)^2+to pmount_offset^2)

Yeah, it was just a thought. You're right, it is only a minor change.

I think the only cars I've ever engineered with McPherson struts were Porsches and a couple of Lotus Cortinas and on both of those the main concern was controlling the wayward rear.

[BorisShakhov]

Yeah, it was just a thought. You're right, it is only a minor change.

I think the only cars I've ever engineered with McPherson struts were Porsches and a couple of Lotus Cortinas and on both of those the main concern was controlling the wayward rear.

I haven't got such a great experience, just a math.

[Rusty]

I think the first thing to do is to get the front camber sorted, then it's time to recue the ream camber and make it a smidge toe out. That will adjust it nicely on this setup.

Without coilovers, it's all just tweaking, as the global change that springs offer is more wholesale.

[Rusty]

ok, that limits me on the narrow arch then. the ball joint has to be pushed in to clear the arch. inner clearance is no issue. even on the 47et wheels.
fronts so are we saying arch catch and inner tie catch limits. fronts are my biggest issue either way. im yet to see if the clear the arch.

gotta say this area, one i have done little with and know little about is starting to interest me quite a lot. id like to take the car to the track when its done. at least once anyway. next issue will be my driving

how do your top mounts help/change the car feel andy?

B4 front arches time then

The top mounts have surprised me TBH. I expected night and day difference but while they undoubtedly are doing a good job, the difference over some stock greens has been incremental, rather than order of magnitude and pleasantly, the increase in NVH has been almost imperceptible, which I was surprised by.

The increased castor has made the biggest difference, with an much more obvious self-centreing effect on the steering,even from slow speed, which makes things more positive when turning the wheel, as you know that the front is doing something and although the feel isn't much better, there is more weight and the benefits of dynamic camber are well documented. The ultra stiff bearings are a little stiff, so the looser bearings I've got in the V.2s should offer better, less sticky feel.

Although this thread was born out of my desire for a less stable rear, a run today has shown that at road speeds, the handling is very good and inspires confidence. The sensible manners mean that in the dry, a slight push at the front is easily managed at the limit and the cornering force to get to that point is high with sensible roll on what are off the shelf springs. On the track, the ultimate balance is too sensible and not adjustable enough, in all other states than heavy braking, where the rear brake upgrade has its say... I think that my setup would help with power-on oversteer for corner exit on a big power coupe, where the chassis and structural rigidity are shown up by the pure torque of a big power build and the slower corner entry would be easily overcome by the exit stability.

I only ever start to trouble the front axle on mine in first in the wet and second on horrible, greasy roads, so I can go more aggressive at 360bhp or so.

In conclusion, my next setup will be:

Front camber 2.5-3 deg
Front castor 4.5 deg
Front toe 0

Rear camber 1.3-1.7 deg
Rear Toe marginally out (numbers TBC)

I can't reduce the rear strut angle with my current top mount design, as the rear strut brace locks them in place and I can't modify it.

Front castor increase is due to another 1.5mm top mount offset and 2mm subframe offset. (15+% increase on current)

Front camber will be from replacing the upper M14 bolts with M12 bolts, allowing approx 1mm movement to 60mm spacing, yeilding 1 degree approx. I want to use OE bolts, as they can be tightened to the correct stretch bolt torque & angle, where camber bolts are an unknown. Secondly, The maths indicates that I'l want the max allowable adjustment anyway, so £5 vs £20 is an easy decision.

[andy10v]

It will be interesting to see if the camber is the major factor.

Interesting reading.

So it would be worth drilling out M12 struts to M14 for more camber adjustment Could actually drill it out a lot bigger, and weld on washers so it is fixed at the new position?

[andy10v]

Some struts actually come with slots (google picture)



Would it be better to slot the top or bottom hole?

Both are going to reduce tyre clearance to the steering arm.

Slots with machined washers would be pretty cool

[BorisShakhov]

Although this thread was born out of my desire for a less stable rear, a run today has shown that at road speeds, the handling is very good and inspires confidence.
* Road speed = low Lat G <0,5 roughly. There is no gain from all of you tuning like bars, springs, dynamic camber. So confidence = understeer (its built-in on this lat G)

The sensible manners mean that in the dry, a slight push at the front is easily managed at the limit and the cornering force to get to that point is high with sensible roll on what are off the shelf springs.
* Push = Lat G = Roll = springs, arbs, dampers, dynamic camber start making their job = less udersteer

On the track, the ultimate balance is too sensible and not adjustable enough, in all other states than heavy braking, where the rear brake upgrade has its say...
*You have nearly 2500 kg/m2 of pitch and yaw inertia (typical hot hatch is twice lower) that makes our cars very stable in all stages.


I think that my setup would help with power-on oversteer for corner exit on a big power coupe, where the chassis and structural rigidity are shown up by the pure torque of a big power build and the slower corner entry would be easily overcome by the exit stability.
* It would be as you said if you`ll balance it to neutral handling.

I only ever start to trouble the front axle on mine in first in the wet and second on horrible, greasy roads, so I can go more aggressive at 360bhp or so.
* Built-in understeer, but there you sense it early at lower Gs because tire grip is less then in the dry

In conclusion, my next setup will be:

Front camber 2.5-3 deg
Front castor 4.5 deg
Front toe 0

Rear camber 1.3-1.7 deg
Rear Toe marginally out (numbers TBC)

*Try it on a circle skid test, where you can judge your balance, Lat-G where nose or tail starts pushing, total grip, and tire wear (temp) so you can understand is your camber good or not.
Lat accel=1.22*(rad of the circle in feet/ lap time in sec ^2)
If you will have constant steering wheel angle in all speeds it`s neutral.
If you will need to add SWA to keep radius it`s understeer.

My guess (from what i`ve read above) there will be: linear understeer rise from 0 to 0,7 G ,then it drops sensible but not into oversteer.

I hope you understand my english

[terrybullwon]

Andy have you taken a spring off and measured your toe change under compression.