negative camber roll centre adjusters - now talking scrub radius also

[SeptemberSquall]

negative camber rcas as i understand it basically have two sets of bolts, one on the inboard side which secures the adjuster to the steering arm, and one on the outboard side which secures the adjuster to the bottom of the strut.

this presents a potential problem now that suspension bump forces exert a shear load on those bolts, where previously the only load on the bolts was axial load (compression/tension).

problem or no problem? discuss

[oldcorollas]

depending on scrub radius, the load wasn't only axial previously.
NCRCA will in crease scrub radius no?

the load only goes up strut and reaction force is from spring etc..

the LCA just keeps bottom of strut in place from side/front/rear loading of tire as you turn and stop....

scrub radius change is more of an issue?

[WDE_BDY]

Decent quality RCA's will have proper locators to address this sort of issue.



The T3 ones for example are better located than the factory steering arm/strut setup. Standard setup generally just run locator pins in the bolt holes.

Callum

[SeptemberSquall]

depending on scrub radius, the load wasn't only axial previously.
NCRCA will in crease scrub radius no?

the load only goes up strut and reaction force is from spring etc..

the LCA just keeps bottom of strut in place from side/front/rear loading of tire as you turn and stop....

scrub radius change is more of an issue?

head hurts
scrub radius is still not clear to me
back to phun again but don't think he covers it

[SeptemberSquall]

head hurts
scrub radius is still not clear to me
back to phun again but don't think he covers it

ok much better handle on it now

basically a car with negative scrub radius is prone to self-centre under braking and acceleration, reducing torque steer and improving joe-bloggs-friendliness

a car with positive scrub radius will be more prone to tramline and seem more toey to drive, as for with significant toe out

in general is there a downside to increasing the scrub radius a moderate amount?

[Billzilla]

ok much better handle on it now

basically a car with negative scrub radius is prone to self-centre under braking and acceleration, reducing torque steer and improving joe-bloggs-friendliness

a car with positive scrub radius will be more prone to tramline and seem more toey to drive, as for with significant toe out

in general is there a downside to increasing the scrub radius a moderate amount?

You're quite right - a touch of negatice scrub is a good thing and makes the steering dynamically stable. Positive scrub makes the car wander around over single-wheel bumps and so on.
Karts use a heap of positive scrub but they also use very different geometry to road cars.

It's also a reason why I really don't like those camber adjusters, and also wheels with a heap of offset. Both are not very good.

[SeptemberSquall]

You're quite right - a touch of negatice scrub is a good thing and makes the steering dynamically stable. Positive scrub makes the car wander around over single-wheel bumps and so on.
Karts use a heap of positive scrub but they also use very different geometry to road cars.

It's also a reason why I really don't like those camber adjusters, and also wheels with a heap of offset. Both are not very good.

i'd have thought that in a mac strut suspension, setting the base of the strut +15mm approx outboard would change the scrub radius towards the negative, rather than towards the positive (presuming sai is inclined towards the centre of the car from the point of intersection with the ground (is this positive or negative sai?))

see paint masterpiece

[Billzilla]

i'd have thought that in a mac strut suspension, setting the base of the strut +15mm approx outboard would change the scrub radius towards the negative, rather than towards the positive (presuming sai is inclined towards the centre of the car from the point of intersection with the ground (is this positive or negative sai?))

see paint masterpiece

Nah waaay positive.
Nasty.

[SeptemberSquall]

but isn't negative scrub radius achieved when the sai intersects the ground outside the centreline of the tyre's contact patch?

and increasing the steering axis angle of inclination is going to move that point outboard more?

[Billzilla]

In your diagram, point B is a little negative scrub, point A is lots of positive scrub.

The camber RCA thingy move the strut outwards from the ball joint, thus increasing positive scrub.

[SeptemberSquall]

ok thx
i had my negative and positive back to front
makes sense your way now that i think about it some more

[oldcorollas]

postive scrub could also make steering more heavy etc.. more fighting with wheel...

i'm glad my cars steering is not like the kart i was driving yesterday.. arms are still sore

[Turdinator]

Interesting. This is a concern i have had myself with the offset RCAs. Has anyone used the T3 ones?

Could you combat this by using more negative offset on the wheels being used? Eg nissan silvia (-40 i belive) wheels on a TA22 (-25 from memory)?

[RobertoX]

Yes you could but then you run into issues with the wheel hitting the strut which is annoying.

[twentyEight]

Could you combat this by using more negative offset on the wheels being used? Eg nissan silvia (-40 i belive) wheels on a TA22 (-25 from memory)?

Don't you mean an offset of +40 on the Silvia and +25 on the TA22?