Have we mentioned we really, really like this car?
You have a couple of times! But that is ok. Us mere spectators like it also!
With our BMW 318is project now done—and a stint at VIRginia International Raceway in our bag—it was time to start having fun driving the car. Our first real shake-down trip came when, after displaying the car in our booth at the Carlisle Import show, we drove it through the mountains of Virginia on our way back to VIR. This time, we were running the car at HyperFest, the largest NASA event on the East Coast.
Unsurprisingly, our car passed NASA tech with no issues and we were off to run VIR again.
This time around, we adjusted the rear anti-roll bar to the stiffest position. During our comparison test at VIR a month earlier, James Clay had told us the rear end was twitchy and that the car would be faster and more fun with a tweak or two. He was right, as our 318is now handled flawlessly on the big track.
From there we drove home to Florida with no issues and got 30 mpg, cruising at 80 mph, with the A/C keeping us perfectly comfortable, achieving our goal of building a competent track car that can also easily rack up miles and miles of highways and back roads. Have we mentioned we really, really like this car?
Have we mentioned we really, really like this car?
You have a couple of times! But that is ok. Us mere spectators like it also!
It seems counter-intuitive that stiffening the rear sway bar would take the twitchiness out of the rear end. Is this a BMW thing? On most cars, stiffening the rear end would cause more oversteer (or less understeer), right?
losendos said:It seems counter-intuitive that stiffening the rear sway bar would take the twitchiness out of the rear end. Is this a BMW thing? On most cars, stiffening the rear end would cause more oversteer (or less understeer), right?
Right; increasing roll stiffness increases load on already loaded tire, which coefficient of friction has typically already peaked. However, BMW trailing arm geometry was never ideal, and 318is is not real heavy, so reducing suspension excursion for improved geometry may have helped more than increasing tire load hurt (with better camber).
Exactly - Carroll Smith and Fred Puhn's books are great if the car has a well-designed suspension in the first place. But as I learned when autocrossing an MGB some 20+ years ago, adding a stiffer front anti-roll bar REALLY reduced understeer. Why? The B's front end has a pretty hefty positive camber gain under roll, for gobs of safe, confidence-inspiring understeer. Reducing body roll reduced camber gain, which in this case was a good thing, as it meant the tire rolled onto its sidewall less than with the stock bar.
The "hot trick" back then -- legal in E Production road racing, at least -- was to move the inboard suspension mounting point UP and OUT, tilting the lower control arm so that body roll gave more NEGATIVE camber. The Butch Gilbert chassis I put a "good school and regional motor" in back in the day stuck very well in the front, compared to my old autocross MGB.
Displaying 1-4 of 4 commentsView all comments on the GRM forums
You'll need to log in to post.
