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The PdV-01 wheel is done! Kind of. I'm being lazy because I know manufacturing these wheels can not happen before both the brakes and coilovers. Lets recap and cross out what is done and highlight my current priorities...
OK, so the critical wheel FEA step is complete. According to industry standard I'm taking my wheel design well above and beyond what any other wheel designer would do except for suppliers of professional racing cars, which I'm on par with and ultimately is the quality/strength level I want to target for the business.
Cheap rebuildable coilovers. Done. BC Racing is perfect so far. I'm currently seeking out local shops with a shock dyno to help with all the tuning I'll be doing so I don't have to buy a dyno.
On to the good stuff. I have been hyper-focused on the F30 front brake kit so in this post I'll cover a couple things.
Unbeknownst to some (dare I say many), a race car does not stop faster with 8ft rotors and 34 piston calipers. For the Volvo S60R and BMW F30, Brembo 4 piston calipers and big rotors are standard with exception for some BMW models. Sticking to the readily available 345 to 380mm rotor options seems reasonable. So what do I really want to achieve?
The intent was always to use Wilwood calipers but not Wilwood rotors. I didn't know about their lug drive system at the time. Sourcing the bobbins or whatever system you want to use, was a surprising task at first. I am confident I just didn't find the right source online to sell me copious amounts of floating rotor hardware. People need replacements right?
Well I'm glad cause when I dug deeper into the Wilwood catalog I discovered the lug drive system which is, to be honest, fucking awesome. Zero bolts required, no safety wire needed, and no expensive bobbins or other hardware. For $20 a rotor you get a big ass retaining ring and some steel inserts.
Young engineers, perk up! How do I design my rotor hat to work with their floating hardware when I know tight tolerances are involved? I bought one of their rotor hats that had 12 "lugs" and took very accurate measurements of all 12 lug features. Pretty simple and I'm highly confident after considering the average, max, min, median, and standard deviation I'll nail the fit on the first try even if it means my tolerances are a little tighter than whatever Wilwood has on their drawings.
Rotors done. For now, my rotors are aligned with the stock rotor centerline but I am considering moving it away from the wheel as much as possible to improve caliper clearance.
This is the important bit and required some research to be safe. My customer's lives are in my hands after all! Safety is of course the under-appreciated aspect of engineering I hear about from other engineers seeking fame/fortune/gratitude. ;)
So I read some books and research papers with sweet titles like "Brake Design and Safety", "Braking for Road Vehicles", and one particularly interesting one called "FEA Analysis and Correlation of Thermo-Mechanical Deformations of a Disc Brake Rotor".
Side note for engineers, read that last paper and make sense of the section with figures 12-15. I verified it with my own FEA but unfortunately can't package the lug drive rotor to mount on the inboard rotor face without moving the caliper closer to the wheel and there is no room for that. The benefit of not extending the rotor hat of course is the reduced cost of hogging out a smaller billet of aluminum.
To summarize, a vehicle's stopping power is obviously based on tire performance and there is a force balance between the tire and the brake pad, the pedal and the calipers, as well as between the front and rear systems that needs to be considered. So now I have that Matlab script. Fun stuff!
At this point I can say I have some system requirements and those need to drive component requirements. An important one would be how much torque is applied to the caliper bracket based on the pad pressure/friction requirement and the moment created by the offset of the rotor centerline to the caliper's radial mounting bolts? Then go a level deeper to find that the stiffness of the caliper and the radial bolt pretension is so important to the bracket itself, you can't easily and accurately analyze just the bracket in a component level FEA in Solidworks. That isn't a terrible thing, I want to verify and instruct on assembly bolt torques that are safe and can be verified in an assembly level FEA.
I hope by now it is abundantly clear that I'm trying to discuss the engineering process as much or more so then what I'm designing, why, and how many cool colors it can come in. If you are enjoying this please comment and let me know.
Below is a list of rotor and caliper combinations to help sort out my options and ensure I can set and meet certain design targets. If you compare the M sport and M performance data you'll notice some variation in the calculated bias and ratios on what is for all intents and purposes an identical car. Take that variation and then assess how Stoptech modified the system for their kits and you start to see what can change and by how much to maintain a properly functioning brake system.
So now I have 3 Wilwood options to move forward with and ultimately every customer will as well. Base and M sport guys can save some money by going with FNSL6R calipers. They just have to decide if they want to maintain the stock pedal characteristics or move toward something that might improve pressure modulation and make heel/toe maneuvers a little easier.
The issue with the two other FNLS6R options with 381mm rotors is, the FNSL6R caliper is not supposed to be used with rotors larger than 355mm. I'm still looking into this but assuming that's true then a different, more expensive caliper is required called the Aero4. The Aero4 is a serious caliper yet can still come with piston dust seals if you wanted. The Aero4 combo would increase torque a lot and reduce piston area, perhaps too much. Some testing is required but its potentially a killer racing package for less then $2500.
In terms of caliper bracket design, I think I'm good to go on the FNSL6R version. Stress levels are low at unrealistically high max torque, like under 120MPa low for 6061-T6 which is perfect.
For the nerds that might be reading this, my sim setup was an assembly (most parts hidden in pics) with a dummy steel (for stiffness) caliper, the bracket with steel spacers, and dummy knuckle mounts that were fixed in space. Preloaded bolts were used with global contact, no penetration, and 0.2 friction coefficient.
Bolts were used but the final design will have studs which makes caliper installation a bit easier and I think makes for a more professional look.
I've rambled on long enough. I do want to end with one bling bling progress pic. Almost all of my current F30 projects are fully detailed and assembled in CAD now.