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View Full Version : Fixing LCA suspension geometry after lowering



StimulisRK
02-15-2012, 01:57 PM
I've been reading up alot more on suspension design, and how lowering affects your car overall.

A big thing is the LCA angles - at stock height the LCA angles are angled downward from the center of the car to the ground. Lowering with new springs/coilovers, changes these angles the lower you go; most springs/coilovers change these angles so the LCA's are now angled upward.

1. Why specifically is it bad/not desired to have the LCA's angled up?
2. - Are aftermarket control arms somehow designed to account for this angle change in their geometry? (idk if that's
possible)
- If not possible, is the only way to correct this is to NOT lower your car?
3. What are the long term affects on the LCA's from this?

Thanks for any info, i'm really new to this and wanna learn more

Hasbro
02-15-2012, 02:49 PM
The more the lca is angled up after the "even" point, the more negative camber diminishes , which means less cornering grip. On unequal double a arms the negative camber continues to increase.

For performance you can increase the spring/damper to the point that they travel less which can reduce the lca angle. I'm talking very stiff, though..

Longer aftermarket ball joints act as if the lca isn't lowered quite as much. Also increasing caster can help. Caster gives you more camber in corners and can allow for less static camber which can improve straight line accelleration and braking.

I'm not too worried about the loss of camber from lca angle anymore as there are lots of benefits to be gained from intelligently lowering the EP/DC5. It is a problem, however, if you want to fit in a designated racing class.

Some decent reads:

http://forums.clubrsx.com/showthread.php?t=717355

http://www.motoiq.com/tech/the_ultimate_guide_to_suspension_handling.aspx

http://forums.clubep3.com/showthread.php?t=569763

StimulisRK
02-15-2012, 03:34 PM
The more the lca is angled up after the "even" point, the more negative camber diminishes , which means less cornering grip. On unequal double a arms the negative camber continues to increase.

http://www.motoiq.com/tech/the_ultimate_guide_to_suspension_handling.aspx



Thanks! That motoiq site is really helpful! It really explains the camber change you mentioned.

SHHEP3@UB
02-15-2012, 08:38 PM
Great links! i also am impressed with motoiq. I've been pushing this all to the back of my mind, but this freakish warm weather has been making me think about next season's auto-x.

Hasbro
02-15-2012, 09:47 PM
Motoiq courtesy of SHG_EasyE. Another one worth reading:

http://www.eviltwinmotorsports.com/wp/wp-content/uploads/2011/06/Chassis-Newsletter-2011.6.pdf

SHG_EasyE
02-18-2012, 10:05 AM
I've been reading up alot more on suspension design, and how lowering affects your car overall.

A big thing is the LCA angles - at stock height the LCA angles are angled downward from the center of the car to the ground. Lowering with new springs/coilovers, changes these angles the lower you go; most springs/coilovers change these angles so the LCA's are now angled upward.

1. Why specifically is it bad/not desired to have the LCA's angled up?
2. - Are aftermarket control arms somehow designed to account for this angle change in their geometry? (idk if that's
possible)
- If not possible, is the only way to correct this is to NOT lower your car?
3. What are the long term affects on the LCA's from this?

Thanks for any info, i'm really new to this and wanna learn more

The start, I actually had the chance to look at a stock height RSX the other day. After all i saw online was that "stock height the arms point downward" I had taken it as fact. But in reality, they are pretty much perfectly horizontal at stock height. Pair that with large roll angles due to soft suspension and youre at the same point, or more of an angle than you might be with a stiffer lowered suspension.

Anyway, to answer your questions...

1- Like Hasbro said, when the arms start to angle up, your now losing camber as the sweep of the arm is pulling the lower pivot (lower ball joint) in, and the upper pivot (strut top hat) is staying the same. This is the opposite of what you want when cornering.
2- To my knowledge there are no aftermarket arms for our cars, and even if there were the arm itself plays no part in Z axis correction. This needs to be done via the pick up points themselves (lower ball joint, offset control arm bushings)
3- There are many ways to correct this. There are multiple companies that offer roll center adjusters or "anti bump steer kits" which are lower ball joints that are extended. This lowers the outer pickup point of the control arm to correct both angle and roll center. Angle is corrected by the overall length of the ball joint, and roll center is corrected by the change in actual ball joint cup position.

There are no long term side effects to the arms from being lowered other than slightly faster wear on the front compliance bushing, but even that is not definite.