Sorry can’t get that measurement at the moment, away at work for another month, but do have an old set of rotors in the garage if you can wait?
Cheers, I'll keep plugging along until it is time to hit the go button.
One of the good things about doing things like this as a hobby is that simple economics of production aren't quite the same level of concern. So instead of just making a mounting hat that can be turned out on a lathe of completed on a mill, I decided to unnecessarily optimise my the mass using the topology study I did earlier and some realising values.
I calculated the loads properly this time:
An F1 can slow down at 5g, so I used that as my starting point.
So for my car I rounded up to 2T, and then split that between the two front wheels assuming 100% of the braking force per wheel., so 1T=10kN per wheel.
That means that to slow down at 5g, each wheel experiences 50kN.
Using the rolling diameter of 0.6m the torque applied (and assuming zero slip) at each wheel is 30kNm.
At the 108mm PCD the force applied is now 3/0.108 = 280kN. I applied this across the 5 bolts, so 56kN at each bolt. I then fixed the rotor PCD so that the whole thing would be getting twisted as if the rotor is stationary and the force is being applied without any slip.
Using the scenario of a two wheel, 2T formula one car slowing down at 5g these hubs have a minimum factor safety of 1. So with a more realistic expectation of ~1g each hub has a FOS >5.
It also weighs in at 645g.
With the rotor I've selected, if the hub were steel the total mass would be ~10.8kg. With the aluminium hats, the total mass is lower than OEM at ~9kg. Due to the large rotor I've selected, the thermal mass is higher than OEM but the total mass is lower.
Is any of this necessary? No.
Are you likely to feel the difference using an unobtanium alloy saving you an extra 150g from something normal like 6061-T6 (which is used on race cars). Definitely not.
Am I getting them quote in 7075-T651 because I can and I'm doing this for fun and idgaf? Yes, yes I am.
I'm scared to see how much this monstrosity costs...
The rotors I've picked are directional, maintain the full 57mm swept area (they have a 61mm annulus) and were used by Holden Special Vehicles for silly cars like the Maloo, Coupe GTO and other things with 2T and 6.0L V8s. So there will be no silliness about using narrower pads, or needing to offset the caliper, no dogbones etc. There was also a suitable rotor by Wilwood, but I went with DBA just because of local supply and a significant reduction in shipping costs.
The rotors typically cost ~$300 AUD each, and the simple hats (I'm waiting to hear back on my monstrosity hats) cost ~$300 AUD each. So about $600AUD a corner (Currently about 300GBP). At least in AU, that will be comparable to the cost of the OEM rotors by the time you factor in shipping. I've been somewhat mindful of costs, looking at what aftermarket stuff exists and so far its still worth the exercise. Time to get onto the rears!