Roll Center design theory

[Salt Racer]

...What would be the difference between a well thought out suspension consisitng of decent wheels and tires, mostly bolt on parts, like tubular control arms, del a lum everything, matching spring rates, matching valved shocks, matching sway bars, decent weight balance, etc.... compared to something where all the calculations have been made, like unsprung weight, scrub radius, backspacing, custom spindles, spline swaybars, everything measured out, and all that other crap...

It depends on many things, like baseline, type of tracks, etc.

It's possible to go fast in a well-sorted bolt-on car with somewhat crappy geometry. Shock tuning, roll rate distribution, and driver ability go a long way. But how long can you keep going? And what would happen if you go over the limit a little while going through a 100+mph sweeper? Would the car remain predictable or go completely haywire? How about transitions?

That's where good geometry makes difference. It makes a car easier to drive fast and consistently, which takes a tremendous amount of load off the driver. This is somewhat irrelevant for casual track users like us, but it makes a big difference in real wheel-to-wheel racing - the difference between 1st place and also-runs as Wally pointed out.

Some of what we talk about, namely scrub radius, side scrub and bumpsteer, also make the car easier to drive even on street. Some even have significant affect on ride quality. Equally-sprung, identical cars would have totally different ride quality depending on geometry.

As for Dennis' spindles, I'd say the return of his investment will be significant, judging from where he started from. In terms of lap time, the new spindles may not pick up 3 seconds, but he will be able to tell the difference (ease of driving) and his lap times will be more consistent. As a secondary effect, this will probably results in slightly better lap time in many cases (more concentration, confidence, maybe faster exit speed, etc). It's guaranteed to make ride quality better. Tire will wear better also.