Swapping front hubs for more caster?

[afterburner]

Maybe they mount it in front, so they can use longer struts - that way the strut can extend beyond the center of the hub without interfering with the axle shafts...

[macspring]

I know quite a few cars that run those GC top mounts on road going cars. Definitely requires some modification/welding to implement. And of course there are compromises in harshness, but trade offs are there.

For the C4, there are PNP options available for an adjustable top mount...

http://www.2bennett.com/body_camber.plates.html

That was the link that I was really thinking of, rather that the 034 one.

Has anyone tried these on the urS4 or urS6 ? They look like good stuff and have the advantage of bolting on.

Or has anyone tried to make them work on a B4 ?

Thanks.

[G60Rallye]

Do you have any pics of the WRC stuff Hamish?

Looks to be running a lot of caster. However it depends where the ball joint is connected to the hub.

It is obviously done to be able to get very long travel suspension in. It does however offer the strut at an angle towards whatever the wheel hits.

[andy10v]

It is obviously done to be able to get very long travel suspension in. It does however offer the strut at an angle towards whatever the wheel hits.

Long travel and deals better with impacts when travelling forward at speed, like a modern downhill bike setup.

[Error404]

yup, **** loads of travel and high rake angle. The downside is more dive under braking, but I guess they have some funky anti-dive geometry built into their setups to combat that
Can't really see what kind of caster angle they are running in the pictures as you can't see the bottom joint

[G60Rallye]

Would I be right in saying that pushing the hubs forwards from swapping them side to side will help with giving more steering self centring?

[Error404]

Unfortunately not, you'd lose it even more steering self-correction as the trail is reduced.



Line A - B is the strut axis

To increase trail you need to move the hub rearwards in relation to the imaginary point at which the strut axis intersects the ground

[G60Rallye]

Yes but as well as moving the wheel centre forwards it has increased the strut angle. So point B has also moved forwards.

Also from using that diagram it does increase the caster as well? Or is it assumed that line A to B passes through the bottom ball joint?

[Donnie]

Fit bigger wheels to increase trail for a given castor angle

[Error404]

Yes but as well as moving the wheel centre forwards it has increased the strut angle. So point B has also moved forwards.

Also from using that diagram it does increase the caster as well? Or is it assumed that line A to B passes through the bottom ball joint?

The strut angle can be different to the strut axis (caster angle), the strut angle is based on the hub design rather than the relationship between the strut mounting points.

Line A-B (strut axis) is a theoretical line drawn through the strut mounting points (which are the top mount bearing and the bottom ball joint). So this line (the strut axis) is fixed in this scenario as you are not moving or changing the strut pivot points.

The centre of the contact patch is directly below the hub centre. As the hub centre is moved forwards the contact patch does so also, and the contact patch moves closer to the point where the strut axis (A-B) intersects the ground, so the trail is reduced.

[Rusty]

Thinking out loud - reversing the hub wouldn't change the castor but would just push the wheel forwards (S2 s are a trailing calliper). To change the strut angle, you'd need to change the ball joint or top mount position.

Some nicely designed suspension arms would do the trick.

[Donnie]

If you are wanting to increase the self centering effect you could increase the offset. Alternatively increasing the kingpin inclination (with positive offset) will help too. I think I'm right in saying that vw/audi saddle there steering systems with negative offset geometry to improve stability on differential grip situations. As the cars are quattros i.e. the front wheels are both driven and braked, then interfering with castor to improve self centering can actually reduce stability under drive.
If your looking to re engineer your geometry I'd consider converting to positive offset. this would remove some of the inherent numbness.

[Error404]

The offset is negative on all ABS cars AFAIK. I have tried an increase in scrub radius and all you get is tramlining and squirm under braking, there is no noticeable increase in steering self-center or steering feel or feedback. I've not calc'd it so maybe it is not possible to add enough to overcome the zero offset condition, although with his wide arches, maybe Hamish will be able to on his shorty.

Audi seem to have used a high SAI angle on our Mcstrut set-up to make up for the lack of caster, but IMHO adding extra caster is the way to go (within reason) as you also get the benefit of dynamic camber recovery as well as a stronger self-centering effect and better straight line stability. You don't get any appreciative self-centering effect off the SAI for the first 1/4 turn of steering input in my experience.

[quattro84]

Nice, always thought it to be possible but never tried it.

High scrub does not work for this purpose, too much heat & tire degradation being generated there.

But watch out, applying more caster will jack the car up from the inner ackermann radius wheel, which for shorter wheelbased can lead to rear wheel lift & too much weight transfer in shorter radii corners. exceeding maximum grip level -> understeer again.
Next to that this can't be overcome with anti roll bar whilst cornering since the wishbone angles are not that different.

Current WRC's need those big tubes to (try to) overcome buckling due to that insane angle of tilting. And yes they have massive anti diving/lift geometry & more...
Latvala testing Fiesta WRC:






Prospeed took a more aggressive approach to improve caster levels by moving the top mount backwards:


Rear wheel lift on "tight" radius cornering.




I was on the hunt for some typ85 rally homologation papers but up to now haven't recieved anything. From what i heard from a former team chef they ran 8 - 11 degrees of camber on the coupe quattro's to improve handling.

Next to that it will not be easy to run higher camber levels for Hamish since he is in need of maximum contact patch to be able to transfer that amount of power... so improving cornering by applying more castor makes perfect sense.

[my2000apb]

great thread!