Single lower control arm

[gotswrv]

Okay I'm going to assume that persons reading this have looked behind there wheels at some point.

I have been giving some thought to making a set of lower control arms for the front end. I'm thinking the rearward mount will have to be moved outward some and possibly up/down. I haven't done any measuring, just sorta brain storming. The goal would be to lose alot of the akward transition between on and off throttle, and wheel hop. I'm thinking the 2 lower ball joints allow for uncontrolled (non-repetative) motion. Making every turn a new experence. Not what I like.
I have given thought to creating a new ?Compression arm? that clamps on to the ?Lateral arm? and losing the second ball joint. Leaving a vertical pivit point near the clamping point. I think this would create a possibly strange state of dynamics, and a little bushing binding, but might give me an idea of weather or not the first mentioned idea could be succesfull, without having to make up a jig, and create new mounts, etc.

I'm looking for constructive input. I don't mind being told I'm a dumbass, as long as you're smart enough to explain why.

Ohh, I'm working on a 95' TSi AWD and 99' RS... Just for those who need to know.

Thanks,
Sam

 

[jtmcinder]

First, let's be clear about what switching to a true lower A-arm will and won't do. It wil not have any effect on wheel-hop, since wheel-hop is caused by energy being stored in the various bushings and motor-mounts, and then being released suddenly as traction drops. If that's the main problem, add at least some inserts to your motor mounts and replace the bushings on the lower LCA and upper pivots.

However, switching to a true lower A-arm where the inboard pick-ups are far apart and do not rotate around a common axis will causes all sorts of problems. Most of all, in bump, the lateral arm will pull the bottom of the wheel inwards, while the compression arm will pull the bottom of the wheel back. The first of these is countered by the swing of the upper A-arm, but the latter is not. So you will lose caster in bump.

I agree that the twin, offset, lower ball-joints are a bit annoying, in that they cause the shock's shaft to point in all sorts of direction in bump and steering, as well as being a nightmare to model, but we're pretty much stuck with it. The on-throttle/off-throttle weirdness is more a function of the dynamic toe provided by the squishy bushing in the compression arm. If you learn how to predict this, however, you will find that it helps performance: the toe-in during braking can stablize a car made twitchy by static toe-out, and the toe-out during acceleration can allow you to put a bit more power down on corner exit.

Let me put it this way: Motor mounts and bushings: $100. A proper alignment: $75. Seat time: priceless.

- Jtoby

 

[gotswrv]

I think the seat time is really messing with me. The TSi is not a regularly driven vechile. I think I have crazy bushing somewhere too. I haven't found it in the front, and haven't looked in the rear. The front end parts have me too broke to start on the rear right away. Anyway I get big understeer(most of the time) up to around 50mph. Above the car becomes fairly neutral, until 65-70mph. Things at highway speed can be tricky, especially if the brakes are used, big oversteer. Below 50mph there is just no feeling in the car. I'm in the process of replacing front laterals, front hubs, front axels. I have 17's, and a set of Super Street Tiens going on, along with a small 16G FMIC and a blow thru setup. So I guess I'll hold off and see how much improvement those "mods" make. I know I was in need of an alignment too. I just don't think the dual ball joints are going to be my friend....

Thanks for the info
Sam