Originally Posted by Nautik
I'm not 100% certain but the current ISF has had some significant changes in the suspension (maybe some other areas too). The changes were enough that in the Feb 2011 issue of C&D the ISF ran an almost identical time around VIR as the M3... I was surprised to say the least.
Here is what the article said about the performance of the IS-F:
"Three years back, an IS F turned a less-than-impressive 3:14.0. We said then, “A little attention to springs and damping might make this eager contender a real champ,” as the stiffly sprung F zapped confidence in high-speed corners.
Boy, were we right. Lexus has since tweaked all suspension elements. Spring rates are down in the front and up in the rear, and there are larger anti-roll bars, stiffer subframe bushings, and longer bump stops, which effectively increase spring rates when the car is nearing its maximum roll angle. Lexus also lightened the front hubs and control arms and slapped a Torsen limited-slip differential in the rear axle. The result is BMW M3–matching performance around VIR (3:05.4). That’s heady company for Lexus to be keeping. Especially considering that the IS F weighs 3801 pounds (195 more than the M3) and makes only two additional horsepower, at 416.
Lexus also redesigned the gauges, enlarging the tachometer and relocating it to the center of the instrument binnacle. But it could have removed the thing altogether because we did not so much as peep at it: The IS F’s audible shift warning is plenty loud, even when you are wearing a helmet. While the alert is slightly obnoxious on public roads, it lets you keep your eyes up when driving on a track.
The old F rolled around on the track like a keel-less boat in gusting winds. The aforementioned updates quell this tendency and increase confidence. Our backside impressions are supported by numbers: The F exits sector two 13.1 mph quicker than before, at 109.1. Steering is communicative, and the chassis is set up for safe, moderate understeer, but vector adjustment is just a throttle tweak away—the torquey engine (371 pound-feet) can break the rear tires loose easily. The brakes are fantastic, too. The pedal might be a tad wooden (more pliant pine than hard oak), but the system remains fade-free after multiple laps of abuse, something none of the other large sedans could claim this year. The 180-degree character change performed by this Lexus gives us hope that Toyota can still make fun-to-drive cars. Now where’s our Supra? "