Control arms to increase shock travel, autocrossers?

[boomslang]

I plan on a mild drop with Bilstein B14 PSS coilovers.

I thought that using LCA's that increase shock travel might be a good idea (VooDoo13 or Stance).

Are there negative consequences handling-wise to using this method versus using taller than factory top hats for more shock travel?

[wootwoot]

I asked about this a while ago and no one with any real knowledge said anything about it. Maybe they missed my thread....

I think a down side to using that style of control arm is that the lower arm will be at a different angle than the upper arm, causing some geometry issues and likely messing with your camber curve. At least that is was what I gathered when trying to do the same research you are doing now.

[wparsons]

A benefit to the LCA is that you gain bump travel between the shock body, bump stop and top hat, so if you're bottoming out the bump stop but not the shock internally you need this. If you're bottoming out the shock internally only then the top hat will help you.

Originally Posted by wootwoot

I think a down side to using that style of control arm is that the lower arm will be at a different angle than the upper arm, causing some geometry issues and likely messing with your camber curve. At least that is was what I gathered when trying to do the same research you are doing now.

The shape of the arm doesn't change the geometry like that. What matters is where the pivots are, not if it's curved/bent. There is a slight change in the geometry to the shock with it being curved, but that is a tiny difference and doesn't change the roll center or camber curve.

[Captain Snooze]

Originally Posted by wparsons

The shape of the arm doesn't change the geometry like that. What matters is where the pivots are, not if it's curved/bent.

This.

[wootwoot]

Interesting.

So if there is no down side, why doesn't everyone run their suspension this way? Other than cost...

[boomslang]

Originally Posted by wparsons

A benefit to the LCA is that you gain bump travel between the shock body, bump stop and top hat, so if you're bottoming out the bump stop but not the shock internally you need this. If you're bottoming out the shock internally only then the top hat will help you.

So in the BRZ/FRS with a sub 2" drop, which do you generally bottom out on? Or is it shock brand dependent?

[SomeoneWhoIsntMe]

Originally Posted by wootwoot

Interesting.

So if there is no down side, why doesn't everyone run their suspension this way? Other than cost...

mostly because it's non-standard

it turns 1" drop springs into a 2" drop and so forth. introduces potential issues where your max bump travel on the shock may be beyond reasonable in terms of other components. your bump stops may no longer save your axles from exploding or the roll center becoming subterranean.

it's just another adjustable component you can tune. IMO, I'd *only* buy LCA's with a dropped shock mounting point, and even if I was happy with my previous ride height / bump travel you can always just run longer rear shocks and add helper springs to your setup to get some extra droop easily.

[wootwoot]

Originally Posted by SomeoneWhoIsntMe

mostly because it's non-standard

it turns 1" drop springs into a 2" drop and so forth. introduces potential issues where your max bump travel on the shock may be beyond reasonable in terms of other components. your bump stops may no longer save your axles from exploding or the roll center becoming subterranean.

it's just another adjustable component you can tune. IMO, I'd *only* buy LCA's with a dropped shock mounting point, and even if I was happy with my previous ride height / bump travel you can always just run longer rear shocks and add helper springs to your setup to get some extra droop easily.

If you had a coilover that could be set at stock height, couldn't you use the control arms to drop the rear of your car and keep all your rear travel? Or am I missing something?

[Racecomp Engineering]

Droop travel is still important too...bump is nice but droop is still worth having.

- Andy

[SomeoneWhoIsntMe]

Originally Posted by Racecomp Engineering

Droop travel is still important too...bump is nice but droop is still worth having.

- Andy

Andy,

any chance you guys would come out with a speedway / afco eyelet shock mount onto a steel plate that fits the rear shock towers? it'd be nice to just run double eyelet shocks instead of the stock stuff.

[Shankenstein]

*sarcasm* While we're at it... let's throw in some drop spindles to save your CV joints and steering. Scrub Scrub Scrub.


\sarcasm
As the guys have mentioned, offset lower control arms will give you more shock travel for the same body height... similar to raised top hats. The net effect on your geometry is pretty minimal.

You only need this if your desired ride height is pushes the shock into a significantly non-linear region (in the system dynamics sense). If you're at this point, I'd really look at how gnarly the geometry has gotten. Underground roll centers and steep camber/toe curves. Moving (and reinforcing) some of your points might be able to get you back in the sweet spot (area A):

[wheelhaus]

Originally Posted by wootwoot

If you had a coilover that could be set at stock height, couldn't you use the control arms to drop the rear of your car and keep all your rear travel? Or am I missing something?

Yes and no... I wonder how much additional travel is really usable inside the fender above stock max bump travel...

Using a drop arm would require that coilover to be extended like you mentioned, but the coilover would need to be designed around a longer bump stroke and longer spring to make it usable.

Part of the reason for shorter stroke is due to the nature of stiffer (read heavier sprung) coilovers. They're typically use springs that are much stiffer than stock. As a loose example: if an OEM spring is say 200lb/in, it may require 4" of compression to settle under the vehicle's weight (droop). If an aftermarket coilover has a 400lb/in spring, then it would only need 2" of compression/droop to settle, but since you're 1" lower, that leaves only 2" of bump room (3 -1 = 2). Another reason is the risk of spring binding if they are compressed too much. This breaks things. The only way around this and regain more droop/bump is to use highly progressive springs (where the spring rate becomes stiffer as it's compressed) or helper springs. Progressive springs are harder to valve for, and helper springs aren't really usable since they're really soft and designed to be compressed flat.

[SomeoneWhoIsntMe]

Originally Posted by Shankenstein

*sarcasm* While we're at it... let's throw in some drop spindles to save your CV joints and steering. Scrub Scrub Scrub.

\sarcasm
As the guys have mentioned, offset lower control arms will give you more shock travel for the same body height... similar to raised top hats. The net effect on your geometry is pretty minimal.

You only need this if your desired ride height is pushes the shock into a significantly non-linear region (in the system dynamics sense). If you're at this point, I'd really look at how gnarly the geometry has gotten. Underground roll centers and steep camber/toe curves. Moving (and reinforcing) some of your points might be able to get you back in the sweet spot (area A):

more like this



/completelyserious

also... how does the drop upright save your CV's? distance from the differential to the wheel centerline is the same either way, the axles know about as much about suspension geometry as most of ft86club.

[wparsons]

Originally Posted by boomslang

So in the BRZ/FRS with a sub 2" drop, which do you generally bottom out on? Or is it shock brand dependent?

Totally dependent on ride height and shock.

Originally Posted by wootwoot

Interesting.

So if there is no down side, why doesn't everyone run their suspension this way? Other than cost...

Only good if you have coilovers, and most people looking at slamming their car aren't worried about bump travel. From what I've seen, most people serious enough about tracking their cars to consider this also keep the ride height high enough that it isn't a big concern.