The benefit is lost weight, and ease of custom brake setups. It is easier to make a custom bell to suit a standard bolt disk than make a 1 part disk. Also a 300m bolt disk is £50 cheaper than typical 1 part disk, but for motor sport you are recommend to replace the alloy bell every season.
There are to types of alloy disk bell combo's float and non floating. This is to do with the way they are bolted together and is to mange the different rate of expansion between alloy and steel.
BMW e21 race car supercharged s14 cage and fabrication by www.chizfab.com
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