Both ships only got max turn rates at max speed. You can got test it yourself instead of sitting here arguing with me.
I understand that. However, what you are failing to understand is that turn rate is dictated by several factors (engines, ship's inherit turn rate, inertia, impulse speed, consoles, etc). Cruisers have a lower inertia (lower impulse speed) and a lower turn rate. Since the modifiers provided by equipment (and probably inertia and impulse speed) are from percentages, a lower numerical value with have a lower gain from the modifiers with percentages.
It is not a straight 2x turn rate. Your Chimera has a higher turn rate value and higher inertia (probably), the latter case means that your Chimera's impulse speed is higher.
It's very easy to test this.
Go to the Sol System (not sector space). Set your power settings to something like Offensive or Defensive mode. Go at your fastest speed without going into max impulse and check your character sheet (movement tab). It should tell what your max impulse speed and turn rate is (without diverting all power to your engines).
Switch to Speed mode, which will set your engine power to 100. You'll now see your turn rate and impulse speed increase.
For instance, my Tactical Escort Retrofit, at 52/30 engine power, has an impulse speed of 28.10 and a turn rate of 42.6. If I switch to an engine power of 100, my impulse speed goes 32 and turn rate of greater than 45 (can't remember off the top of my head).
Inertia affect your turn rate and your speed, and they are additional modifiers. Period. Lower inertia has a lower speed and turn rate. Higher inertia has a higher speed and turn rate. Unfortunately, I have yet to find any information on what the percentage is exactly.
But my example of 50% is assuming you have consoles to help you increase your turn rate. In that case, the math is correct. 6 + 50% = 9. 14 + 50% = 21. But, because of your ships inertia and impulse speed, the actual turn rate will be different.