It’s been a long time since we have seen the Mustang with an IRS under it. Gone are the days when they used a Thunderbird V6 IRS suspension and put them under 400HP Cobras. The 2015 Mustang seems to have a decent differential under it. Rumor has it the diff is a "Super 8.8" (not sure what that means but we like the sound of it) and one of the best improvements I have seen is the introduction to a rolled formed wheel bearing. As most know the 03-04 Cobra had the same wheel bearing and spline size as the 6 cylinder Thunderbird, and after putting any HP into them the spline and bearing would break. We used custom hubs to stop the spline breakage but still the wheel bearing was an issue. Well say goodbye to both issues, as the new Mustang has a full 32 spline going into the hub and a beefy 34 spline into the diff, up from the 31 spline of yesteryear.