Lateral-g Forums - Soft springs/big bars set up question...

Quote:

Originally Posted by DavidBoren (Post 572976)

When dealing with factory A-arms, is the geometry correct for using the more modern approach of high travel/low roll?

Or do you need longer A-arms for that concept to work?

Although a question of general theory, I am asking in regards to my S10. If I use stock A-arms, which originally had stiff springs and a little sway bar, and I install soft springs and a big anti-roll bar, would the additional travel allowed by the softer springs mess with the geometry of this suspension?

Hi David,

This is the second post of your I'm tagging into today. When someone decides to go with a modern high travel /low roll angle front suspension strategy ... with a factory stock suspension ... there are a few things to work out.

The first is pretty basic. You need to find out how far your suspension will compress (from ride height) until it stops. Something will stop it. Either a shock will bottom out, a control arm will hit the frame, a ball joint will angle until it binds, etc. When you find out how far it will travel in dive ... say 2.5" from ride height .. and then something stops it ... you need to make a decision is that enough travel ... or do I want more ... and am I willing to correct the issue to achieve it.

In many production cars ... especially when we lower them ... the two common culprits that limit travel are:
1. The LCA hitting the snubber or frame.
2. The shock bottoming out.

#1 solution options:
a. Remove or trim the snubber if that is what hits first.
b. Trim the metal off that hangs down from the frame that the LCAs are hitting. The metal I'm referring to has no structural value & is simply left over in the punching & forming process during frame manufacturing.
c. Switch to tubular LCAs.

#2 solution options:
a. Buy or make ... and install a taller upper shock mount that allows you to run a longer shock with more travel.
b. Modify your LCA (with plenty of strength in the design & materials) to extend the bottom mounting point of your shock ... that allows you to run a longer shock with more travel.
c. Switch to a LCA with lower bottom shock mounts designed in ... that allow you to run a longer shock with more travel.

So ... after you have enough travel ... whatever that is ... then we can cover the "geometry part" of your question.

The length of the UCAs & LCAs are not a limiting factor to high travel or optimum performance with high travel. Can we achieve better dynamic geometry with longer control arms? Absolutely. Are they required? Absolutely not.

The key parts of your front suspension geometry that will matter when you go to a modern high travel/low roll angle front suspension strategy ... are, in order:
1. Dynamic roll center location (dynamic meaning when the car/truck is in full dive & roll).
2. Camber gain ... don't want too much.
3. Jacking force of the UCAs ... which comes from excessive UCA angle.
4. Bump steer ... don't want too much.
5. Caster gain ... just need to take the amount into account.
* Frankly ... these 5 things matter to optimum handling performance of everyone's front suspension ... regardless of their strategy.

So, to summarize ... the length of the controls is less of an issue. Achieving the desired travel without suspension bind ... and hitting the target with the 5 suspension geometry items listed ... are the key things to focus on initially. Of course, you'll need to work out what spring rates & bar rates front & rear .. along with optimum shock valving. But my tip is to start with what we've covered here.

If you ask me any questions in your thread ... would you please PM me so I know to visit your thread? Thanks !