Roll Center Height/Roll Resistance

[clarkspeed]

I'm using the SusProg3d. I played with the demo version for awhile before I bought. Works ok once you get used to it. You can learn a lot just playing with it. I was amazed how sensitive roll center was to ride height and camber on strut suspensions. I now try to set my ride heights to the millimeter. And you can figure out what is BS and what is not on this forum. I wish I had bought years ago instead of copying others.

[heavy85]

Care to share any insight you've gained studying the geometry and effects of changes?

[letitsnow]

Dont know anymore but many moons ago the hot stock fwd autox setup ran huge front bars even though they were front heavy. Rules limited spring & rear bar changes so front was all they had to work with. Theory was the improved camber control due to limiting roll was the dominant factor and produced the best lap times.

 

I'm starting to think my car (240Z) is limited by camber control more than anything. It's running 425F / 375R springs, stock front bar, no rear bar, front inner pivot up 5/8", front 3/4" 'bumpsteer' spacers. Went to stock front bar this year as the big front bar had braking issues where it would want to lock the inner front unless braking perfectly straight and it tended to push center off. 3.5 deg camber up front and 2 deg rear on RS-3 street tires and I'm still wearing off the out edges and while some better it is still pushing corner off more than I would like. This is on road courses too not tight autox where one tends to abuse the edges more. It's still quite fast but lays over more than I think it should to produce highest possible grip. This is actually my biggest goal for the winter off-season to figure out and build whatever I need to make some gains here. I'm thinking more track width and more caster (from just over stock now) is the starting point but am still very much in the early planning stages and open for discussions.

 

Cameron

 

PS - finally getting around to re-read Carroll Smith's 'Tune to Win' again (last time was ~15 years ago) and highly recommend it as a very readable, insightful book that's still relevant 30 years after it was written.

 

Stock now allows changing front or rear bars. For the last 5 or 6 local autox events I drove a friends H stock EF civic dx sedan(79whp of fury ) with koni yellows and a 24mm rear sway bar, stock front, on star specs or occasionally a set of super dead v710's. Front shocks full soft, rears full hard, rear bar full hard. We managed a bunch of top 10 PAX finishes, he took top PAX once, and I took 5th a couple times.

 

 

As for your outer tire wear, I wonder if the softer sidewall(relatively speaking) of the RS3 makes it want more camber, some google searching results in lots of people saying they are wearing the outer edge on all types of cars. Might be interesting to see how a stiffer sidewall reacts, there's a bunch of new street tires coming out next year, so it might be a decent excuse to try one.

[letitsnow]

Just remembered I built a solidworks sketch model back in my mini-baja days that let me model and measure a SLA suspension, might have to look into building one for a strut. Care to share some pickup point locations?

[clarkspeed]

Pickup points can vary greatly from car to car. Especially the strut tops. Not too hard to measure. I leveled the chassis on jack stands and plumbbob points to tape on the floor. Took about 3 h ours ea. Front and rear.

[heavy85]

Ahh hell. 25" tire + zg flairs + functional headlights = max ~6 deg caster which is where I already was. Im finding to be able to add any more caster or even go much wider requires major surgery with these 25" tires . The tire gets into the fender even with it trimmed all the way to the flair and it even hits the headlight housing when steered. Taller bumpstops could help but Ive only got a little over 2" of bump travel the way it is.

 

Now need a plan B ?

 

 

[JMortensen]

Move headlights to the grill?