I did some more researching and found that the ITR wheels have 5mm more offset than the GSR wheels. 2 wheels x 5mm would give it the 10mm wider track then.
Here's what I found in an ITR review at www.canadiandriver.com :

While the Type R's four-wheel independent double-wishbone suspension is similar to other Integras, it's been beefed up to improve high speed handling. The front suspension consists of an L-shaped lower control arm, an upper control arm, a coil-over shock absorber, a stabilizer bar and a performance rod. The front spring rate has been increased by 22 percent with a 115 percent increase in compression damping and a 70 percent increase in rebound damping.

The rear double-wishbone suspension components consist of upper and lower control arms, a trailing arm, a coil-over shock absorber and a stabilizer bar. Damping rates for the rear suspension have also been increased with compression damping settings in the progressive-valve unit increasing by 66 percent, and rebound damping going up 31 percent.

Three other factors have also helped the Type R's handling: a lower overall vehicle height (by 15 mm) and aerodynamic refinements that result in 30% less lift and 1% less drag; a reinforced unit body structure; and high-performance tires. The Type R is equipped with Bridgestone Potenza RE010 performance tires, similar to those found on the NSX. The Type R's 6 x 15 inch aluminum wheels have a 5 mm greater offset than the GS-R.