For a start, the front disc brakes are slightly smaller, measuring 11.8" compared to 12.6" for the Platinum. It sports 17" alloy wheels wrapped in 215/55/R17 tyres, instead of 18" alloys (but still comes with a full size spare).
Most notably, it misses out on the LED daytime running lights (DRL) which have given the Optima its signature look over the last year. Cornering lamps and LED rear fog lamps are also omitted but all other safety features including a full compliment of airbags and electronic stability control are standard.
On the comfort side, the Si comes with a standard key (as oppose to the smart key with push button start on Platinum), cloth trim instead of leather, standard seat adjustments (no power) and does away with the wood-look interior trim. One of the more pleasant features of the Platinum, the ventilated driver's seat, is also missing, as is the front seat warmers.
For those with a keen eye, a different radiator grille is used and there are no sports bumpers, rear lip spoiler or rear LED combination lamps. The Si still keeps features like cruise control and leather steering wheel, but no longer has the TFT instrument cluster screen, scuff planels or sports pedals.
Audiophiles are likely to stick with the Platinum's premium Infinity sound system with 6 CD changer as the Si lacks both features. However the entry model does have full Bluetooth (phone/audio) and iPod/iPhone support as well as six speakers.
When you add all those features together, the Platinum's $6,500 additional asking price ($36,990) seems pretty darn reasonable. Nonetheless, the new entry model into the Kia Optima range is sure to bring in more customers as Kia expands its lineup to capture additional marketshare in 2012.
Read: Kia Optima Review