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Discussion Starter #1 (Edited)
At the dealership the other day, there was a 2017 Civic Si whose front brakes caught my attention. The rotors appear to be the same as what I've previously spotted on a '14 RDX, as well as '16 Accord Sport.

These rotors are 312mmx25mm. What intrigues me with these rotors isn't so much their extra diameter, but that the cooling vanes take air from the outboard side rather than the backside where the dust shield generally obstructs the airflow. Also, the top-hat section has holes around its side presumably to also let more air feed the cooling vanes. My gut feeling is that these differences together with the larger diameter improve airflow enough to not need the wider vanes of a 28mm rotor.



When I first spotted this on the RDX, I looked into the possibility of using an RDX caliper on our Civics. However, I found the RDX piston is 60.3mm, which would throw off the brake balance more than I feel comfortable with.

However, seeing the same rotor on a Civic, I took another look. The caliper used on the '17 Civic Si is shared with the '17 Accord Sport and Touring. While I couldn't directly find more details, the caliper rebuild kit is shared with other 9th gen Accords whose calipers are now available aftermarket, and it looks like these use a 57mm piston. This is the same as the popular TSX brake upgrade, and wouldn't throw the brake balance out of whack nearly as bad as the RDX calipers.

While I haven't confirmed it, I would imagine the '17 Si caliper would bolt right up to our knuckles. The rotors definitely fit, though I think the rotor attachment screws holes won't line up. So, if the calipers do fit, this looks like an interesting alternative to the common upgrade of swapping in TSX front brakes.

However, for the time being, I think the TSX option is still more viable as aftermarket parts options haven't yet caught up. While rotors appear to be out there, I don't think the rebuilders have gotten enough cores yet for rebuilt calipers to be available. But maybe in another year or two...
 

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This is actually a really interesting topic, and I would love to know if the '17 Civic Si calipers and rotors would fit our cars. I went through all the trouble of doing the Acura TL Type-S caliper upgrade on my car and it was quit a challenge (and also rather expensive). The rotors of the TL Type-S and the '17 Civic Si are actually very similarly sized, although the Type-S does have 2-pot calipers. It could be a much more approachable upgrade if it was a simple bolt on mod in comparison to all the drilling and spacers needed for the TL Type-S calipers to fit.

Also, I wouldn't worry about the rotor attachment screw not lining up. They do next to nothing on the road and mostly exist just to hold the rotor in place during assembly of the car.
 

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very interesting...so if i'm understanding right, the '17 rotors essentially have a slightly larger diamter, but slightly thinner width than the tsx rotors? seems to me the thermal mass is about the same, yes? with better cooling i can't imagine you'd see less reliable performance.

my old A4 had discs with similar holes around the hub for ventilation, and those brakes were pretty hard to fade under stress, even for a heavy AWD car.
 
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ScottyB
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