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P3D+ Street/Track/Time Trial Build
- Thread starter MasterC17
- Start date
What's the point in spending the extra money just to fit thicker pads? It's not like we'll be entering any endurance races any time soon in our Model 3s
Got it.What's the point in spending the extra money just to fit thicker pads? It's not like we'll be entering any endurance races any time soon in our Model 3s
On second thought - if I would be targetting track only with my setup - I would go for 9668. It's a cheaper pad per mile and gives more time before the pad will overheat and start boiling brake fluid. The weight difference is not that big.
I doubt you'd get any issues boiling fluid with any of the BBKs (assuming you're using racing fluid).
One thing to remember - there won't be so many 25mm thick pads to choose from.
I've looked at all the brake conversions available for the Model 3 now and I'd say once you've moved to larger rotors (372x34 or 380x36) with better cooling, the choice of caliper is going to be down to personal preference based on looks, how you get the pads in and out and what choice of pads are available for it.
AP/Essex, Brembo and RB all have several options for calipers and I expect they will all work well on track.
If you're building a dedicated track or race car then you might want to make different choices.
IMO it's not worth going with the 9668 Calipers considering the extra money and weight for 7mm of pad thickness. Keep in mind, not only is the caliper heavier but so is the pad. Keeping in mind the MS Calipers I was running had 16mm pads that only wore about 1mm for every two track days, I'm just not sure it's going to be beneficial enough to justify.
If this were an enduro car it might make sense for thermal reasons, but in reality no one is running more than a 30 minute session and of that 30 minutes maybe 10 minutes is at full power?
If this were an enduro car it might make sense for thermal reasons, but in reality no one is running more than a 30 minute session and of that 30 minutes maybe 10 minutes is at full power?
beastmode13
Member
I probably agree that thick pad is not THAT necessary and better have more pad choices, but about ducts not necessary on any BBK on M3P, I have doubts.
In my past experience once you use proper pad compound for the temperature - you will boil brake fluid next. Unless you have enough rotors cooling and that requires full-size ducts with collection at the front bumper (M3 has no pretty place for that so far). And that was on 2500 lbs full weight cars with smaller power levels. Here we deal with 4250 lbs car.
Let's take a calculator:
Weight: 4244 lbs (total weight).
Tires Limit: 1.35 G.
CG: 16.5 inches (1 inch lowered from P version).
Braking: 145 -> 40 mph (3.5 sec).
The front axle takes 70% of all braking power with such tires and CG.
Deduct 90kW for regen - 323kW per rotor in the front.
Say rotor disc is grey cast iron with 15 lbs weight each.
The temperature increase of the rotor is +614F (341C) from single braking.
Let's imagine stupid straight acceleration and brake cycle. M3P needs 21 seconds to go from 40-145 mph - your rotor needs to cool with an average power of 54kw. Considering that cooling power proportional to the rotor temperature vs ambient you would need double of that at peak. In real life, certainly, your equilibrium will be much higher, so ~70kW.
Do you feel that the unducted rotor can do 70kW cooling? Not sure? Let's see from another example.
Say you've got rotor exhaust temperature 270F. Now you need to push through rotor 1638 CFM of air with quite significant pressure drop to actually get that 270F. And if you think that rotor can work as an effective fan - 1600 CFM is an airflow of 8-inch deep 15-inch diameter real fan without any resistance rotating at similar RPM. So you going to be underperforming at cooling without ducts anyway - each lap your rotors going to be significantly hotter and hotter.
Certainly, those calculations are for the toughest possible track. In real life it's somewhat lower. But you would need to run at quite high equilibrium temperatures to compensate for that anyway. And you're going to be creeping temperature into the caliper, so eventually, it will boil - best fluid works at much lower temperatures than you're going to run on rotors.
The main temperature creep is from pad temperature down to piston. A smaller area of piston contact (grooved) and stainless material instead of aluminum will slow down this process, but then, again - even MUCH lighter cars boil fluid without ducts within the first hot 15 minutes. Having a lower pad temperature due to its size allows it to slow down caliper warming. Larger caliper also gets to lower temperature. Unless your track too round or you're not braking late enough or you're just ok with 1-2 hot laps.
Anyway, if you see mistakes in my assumptions here - let me know. My experience that M3P can keep adequate power much longer than brakes and heavier rotors with better airflow and the larger surface area won't cover this difference without ducts (or, some other forced cooling).
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I appreciate the detail and calculations, but I think we'll find out whether thicker pads are necessary once a few have tried their BBKs on track.
There may be a special track somewhere which is ultra hard on brakes and could cause issues, but none spring to mind in my neck of the woods. I'll be using calipers with 16.8 or 18mm pads myself.
There may be a special track somewhere which is ultra hard on brakes and could cause issues, but none spring to mind in my neck of the woods. I'll be using calipers with 16.8 or 18mm pads myself.
I'm impressed you took the time to run through the math for the thermal dissipation. Your assumption that every corner at every track has a 145-40 MPH braking zone however is simply not realistic.
For example, and using my SS 1LE personal best. My favorite local track (Grattan Raceway), the braking zones go something like this:
141-61
90-58
82-47
103-71
75-48
108-42
As you can see, it's quite varied.
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That's for sure. You also going to have more time to cool it down than straight acceleration back. But then, again, in my practice - without ducting you're going to overheat lighter, lower power car on sticky tires with similar-sized rotors if you don't do cool-down laps often.
And the last off-top, sorry
since I had a calculator.Tesla would need to have roughly 25kWh of the latest tech supercapacitors to have maximum braking/acceleration up to 250mph.
That's roughly 5600 hp where 5100 spent on acceleration, 450 on air drag and 50 on rolling resistance. That's 0-250mph in 8.4 seconds in slightly more than 1/4 mile and the same for 0-250 without any mechanical brakes.
But if we put more power into downforce we can put more power with speed. So anyway, in the next 10 years supercapacitors going to kill all those stupid brakes and we will see 10000 hp road cars making 0-250mph in 6 seconds and back.
VIR is shut down for the next 14 days due to the Virus. Guess my next track event is going to be in April...
Hm wonder what the barrel diameter is? How much bigger of rotors are they?
I have only done autox for now, moving into road courses this year more which is why it wasnt necessary before. My 18" signature wheels do have quite a bit of clearance
Rotors are 372mm compared to 355mm. Not sure what the barrel diameter of the ARC-8's is.
Finishing up some more things. MPP Cyber Arms and Dorman studs. The only item I have left to install is the front lower control arm bushings! Now I just need an event to attend that isn't cancelled
Well after having two events cancelled, it looks like an early June event at VIR Full is a go!
Getting prepared with the MPP Front Lower Control Arm Bushings!
Getting prepared with the MPP Front Lower Control Arm Bushings!
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