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MineralWhiteF80
The general concerns with retrofit kits are:
1. Use of stock rotors (this specific kit offers same diameter rotors but they’re 4 mm thicker) doesn’t address the issue of lack of thermal mass. The F8x Blue calipers are not limiting factor. So a kit that swaps calipers, 6P or 4P, but uses the same rotors is at best for aesthetics only. Also, just because a caliper has more pistons, doesn’t make it a better caliper. PFC only offers their race calipers with 4P front and rear until they were selected by Porsche as the official brake supplier for the 991 GT3 R. Porsche demanded a 6P front caliper.
2. Caliper, or a true brake system, bias calculations are rarely done and the calipers (actually, it should be with rotor diameter and pad radial depth) have either too much or too little piston area. You end up with a long brake pedal if caliper has too much piston area or a rock solid no travel brake pedal if the piston area is too small.
3. Availability of rotors. Are the rotors stocked so when you need a rotor replacement it can be ordered and received in a few days? If the rotors being used are from an unnamed source then you’re limited to (rely solely on) the vendor of the retrofit kit. They close up shop, you’re stuck with a kit without replacement rotors (Paragon rotors are good and they likely won’t be going out of business). Sparta was a brake caliper and rotor manufacturer that offered kits for the e9x M and f8x. Well, they went out of business so users had no options for caliper rebuilds, replacement rotors, and replacement pads. For new rotors they’d have to have custom rotors made by Coleman but it doesn’t solve the lack of brake pads (could use Carbotech to make custom pads is one option).
4. Availability of pads and brake compounds. A lot of the time the calipers used in retrofit kits use an obscure pad shape (with no FMSI profile #) and a very limited brake compounds. Does the vendor stock pads do when you need them, you can get them. Again, if they go out of business then you’re SOL (ZL1 1LE should have a decent number of pads and compounds available).
5. Proper pad and rotor ring swept area/pad radial depth. Too small of a pad radial depth means a significant portion of the rotor IR is not being fully utilized. The other concern is pad overhang on the rotor OR which results in a lip forming on the rotor OR. This means you’ll have to replace rotors every time you replace pads.
6. Caliper not centered on rotor can make it difficult to install new pads.
7. Caliper selected uses a thicker rotor. This can result in cases where, even with brand new pads, the caliper pistons are significantly extended out of the caliper. This can get pretty bad when the rotor thickness is too thin and the pad thickness also is too thin. This can affect brake pedal feel and/or create a safety issue if there’s significant caliper knock-back.
8. Is the caliper used in the retrofit have pad knock-back issues? If it is, are anti-knock-back springs available for the caliper? One of the worst feelings is when you’re entering a brake zone, you go to hit the brake pedal and you find it sitting on the floor! Double pumping a brake pedal is a straight section gets old fast.
9. Quality of rotors used in kits that come with aftermarket rotors. This is extremely important if you’re planning on tracking the retrofit kit. Failure of an inferior made rotor can result in a major accident or the rotors only last a couple/few days before needing to be replaced. Unless I missed it, they don’t say how many rotor vanes there are and are the rotor vanes straight or curved? Paragon rotors are superior to their custom 2-piece rotors.
These are all legitimate objective concerns/issues with the use of a generic retrofit brake kit. Yes, people will add in their subjective opinions on these retrofit kits. Some are based on an actual experience, some of it is speculation. If you’re fine with the objective concerns associated with retrofit brake kits, then go ahead and buy it. However, be aware that ZL1 1LE owners upgrade their brakes to high-end aftermarket brake kits. This kit offers the same diameter rotors (optional 10 mm larger diameter rear rotors - were brake bias calculations done with the larger rear rotor & piston area?) for the front and only a 4 mm thicker rotor (is it thicker rotor faces or is it taller vanes?) so what is the actual increase in thermal mass? I personally have upgraded to Essex/AP Racing CP9668/CP9449 kit on the f82 and on my e92 Ms PFC zr54/zr45 & ZR31/ZR31 kits. They pay for themselves if you frequently go to the track. Also, there’s a BimmerWorld/Alcon brake kit with similar performance and cost as the Essex/AP kit.
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