Can anyone suggest any negatives of doing this?
The positive is just less weight of course

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  sivia zx ca18et rotors.JPG (15.87 KB)

Wouldn't taking metal out of the hub area just mean more heat is stored in the rotor faces?

unsprung weight mainly

if i had rotors like that i wouldnt need to machine my hubs down to convert my struts to s13 brakes now would i

this is a #OOPS# idea

decreases strength under brakes
decreases strength under acceleration (if on driven axle)
all weight removed from centre so has minimal impact
reduces heatsink effect
will do #OOPS#-all for performance

unsprung weight is relative to sprung weight, so it would slighty assist the springs and shocks to hold the tires on the road moreso on our little sunnys then say a comenwhore, but unless youv added a lot more weight with a big modern turbo engine most ventilated disc mods are mad overkill anyhow. but you be best if it was of great consern to use a two peice rotor with an alloy iner.

Mine are non ventilated sigma ones and would like to lighten them this
way instead of spending a fortune on alloy hat etc.
Its anal and cheap but will it cause strength issues?
need Dattoman1000 the specialist to comment.

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yeah but less unsprung weight helps with steering

Unsprung isn't really the issue here
Its reciprocating mass that is

I think its pointless to try to reduce the weight of a 3.5kg rotor
If you wanted to you could make the hub from alloy

But this sort of weight saving attempt on a street car is not worth it