Weight: standard vs PCCB brakes

andix

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The PCCB doesn't make a huge difference on the Porsche sports cars, unless you fit performance/ track tyres.
With the – super heave & recuperating Taycan – even less so.
The important difference is that they don't rust. Just like the PSCB…
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Bry5on

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Once I have a little time, I’ll do some ballpark math comparisons based on similar sized rotors/calipers on other cars. That might get me to the point where I can quantify the difference. Along with estimated suspension, upright, wheel and tire mass it’ll be possible to quantify the difference in suspension response and ride quality, if any. I expect the inertial effect may be pretty minimal, but the numbers will tell there as well. Remember inertia goes with radius squared, so a mass reduction on a bigger rotor may well have more inertia to spin up and rotate.
Porsche Taycan Weight: standard vs PCCB brakes D4714EA7-6985-4A4E-B1B7-307739FC6E68


I appreciate all the subjective opinions offered, and I almost certainly will be going with the basic setup, but I’d like to see it quantified even just for interest’s sake.
 

Gubbjaevel

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Let's overnerd this, completely!

I'll even pretend I understand 1/3 of what you're about to write!

(I do, genuinely, look forward to quantification.)
 

Mr.Smith

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I would like to see how much more brake dust there is on the cast iron vs the PCCB brakes?
Is it $5600 more dust considering the regen on the Taycan?
 

Gwaihir

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I would like to see how much more brake dust there is on the cast iron vs the PCCB brakes?
Is it $5600 more dust considering the regen on the Taycan?
I’ve had the standard brakes on my 4S since June and my drive has never been cleaner. No rust on the brakes (and the car is always outside). When i compare it to all the other Porsches I have had (normal brakes). There is absolutely no comparison. The 4S wins hands down. Save your money for a different option and have the red brakes. Wheels are still clean and looking great. . . . Regeneration is the big, big difference.
 


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Bry5on

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So I used some analogous cars (991 GT3 and turbo, for example) to find rough numbers for rotor masses in the same size class, and I used photos of taycan brakes to estimate ID of the rotor based on its proportion to OD. With these numbers I am armed with enough information to estimate the brake rotor's contribution to inertia. The numbers for rotation about the axis of the wheel (really relevant only during acceleration, but steering is proportional to it as it turns out) map out below:
Porsche Taycan Weight: standard vs PCCB brakes Screen Shot 2021-03-21 at 12.02.28 PM


So I'm estimating that PCCB does indeed have the lowest rotational moment of inertia and will be the fastest to accelerate and most responsive to steering inputs. It's followed pretty closely behind by the base/4/4S brakes, and the PSCBs are quite a bit worse. What does this mean? Technically, if we lined up 3 identical Taycan 4Ses in a drag race, other than the brakes, the one with PCCBs would win the race, and the one with PSCBs would lose. By very small amounts.

Again, these are estimates, but I believe the above paragraph to be correct. It's also worth noting that the wheel diameter has a much bigger effect on inertia than the brakes, so picking 20" wheels vs 21" wheels is likely to help more in acceleration/steering than PCCB vs standard brakes.

I'm going with base brakes and 20" wheels. :)
 

Jhenson29

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Technically, if we lined up 3 identical Taycan 4Ses in a drag race, other than the brakes, the one with PCCBs would win the race, and the one with PSCBs would lose. By very small amounts.
Even assuming all other things equal, I think that really depends on the motor control and how close it is to its limits.
 
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Pozuelo

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So I used some analogous cars (991 GT3 and turbo, for example) to find rough numbers for rotor masses in the same size class, and I used photos of taycan brakes to estimate ID of the rotor based on its proportion to OD. With these numbers I am armed with enough information to estimate the brake rotor's contribution to inertia. The numbers for rotation about the axis of the wheel (really relevant only during acceleration, but steering is proportional to it as it turns out) map out below:
Screen Shot 2021-03-21 at 12.02.28 PM.png


So I'm estimating that PCCB does indeed have the lowest rotational moment of inertia and will be the fastest to accelerate and most responsive to steering inputs. It's followed pretty closely behind by the base/4/4S brakes, and the PSCBs are quite a bit worse. What does this mean? Technically, if we lined up 3 identical Taycan 4Ses in a drag race, other than the brakes, the one with PCCBs would win the race, and the one with PSCBs would lose. By very small amounts.

Again, these are estimates, but I believe the above paragraph to be correct. It's also worth noting that the wheel diameter has a much bigger effect on inertia than the brakes, so picking 20" wheels vs 21" wheels is likely to help more in acceleration/steering than PCCB vs standard brakes.

I'm going with base brakes and 20" wheels. :)
You are making the wrong assumption that outside diameter of the 21” vs. the 20” is larger. You must look up the actual outside diameter of each, and not only do they vary by rim size (keeping in mind that the aspect ratio of sidewall vs. width is lower in the larger diameter, but even within the same size from each manufacturer, but also different models of tires. Summer, all-seasons, winter tires from the same manufacturer tend to vary. Also as you consume your tire and the tread is diminished, the outside diameter is reduced as well. Probably only Porsche has all the numbers and every time a different tire is introduced, new calculations are to be made.

So too many variables with unknown values. Also, outside diameters of all approved tires for a given model are usually within around 3-4% of each other with up to an additional 2% variance due to tire wear. So in most cases, it is negligible. Keep in mind even tire pressures can affect ever so slightly the diameter, and these can be affected by temperature ... it is a very long chain ...
 


Mike in CA

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......Again, these are estimates, but I believe the above paragraph to be correct. It's also worth noting that the wheel diameter has a much bigger effect on inertia than the brakes, so picking 20" wheels vs 21" wheels is likely to help more in acceleration/steering than PCCB vs standard brakes.

I'm going with base brakes and 20" wheels. :)
Thanks for taking the time to do this. Quite interesting.

One additional thing to note with respect to your comment about wheel diameter. Porsche's 19" and 20" wheel offerings on the Taycan are cast while the 21" versions are forged. Forging results in a denser stronger metal than casting and as a result less material can be used to achieve the same or better strength. For this reason, forged wheels are typically considerably lighter than cast ones of the same size.

It would be interesting to know the actual weight of the various Taycan wheels but my suspicion is that the 21" forged options may actually be lighter than the cast 20's; certainly little heavier.
 
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Bry5on

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To have equal inertial effects, the 21” wheels need to be at least 10% lighter than the 20” wheels as most of the weight is in the barrel (21^2/20^2=1.10). This is definitely possible with a 25% stronger material forged wheel, but as you say, gotta know the weights of the wheels to really answer that.
Pozuelo, there are actually not too many variables to be able to quantify this. What you’re referring to is a difference due to tire diameter, I’m speaking strictly to wheel diameter which is pretty easy to quantify. Bigger tires do have a large effect, as you say, but tire pressure generally will not. The diameter of the tire for inertial effects is dominated by the non-deformed portion of its circumference.

As another example: if the 21” wheels with tires installed weigh the same as 20” wheels with tires installed, and tire diameter and width are the same, it’s a pretty safe assumption that moment of inertia of the 21s will be greater.
 
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Pozuelo

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To have equal inertial effects, the 21” wheels need to be at least 10% lighter than the 20” wheels as most of the weight is in the barrel (21^2/20^2=1.10). This is definitely possible with a 25% stronger material forged wheel, but as you say, gotta know the weights of the wheels to really answer that.
Pozuelo, there are actually not too many variables to be able to quantify this. What you’re referring to is a difference due to tire diameter, I’m speaking strictly to wheel diameter which is pretty easy to quantify. Bigger tires do have a large effect, as you say, but tire pressure generally will not. The diameter of the tire for inertial effects is dominated by the non-deformed portion of its circumference.

As another example: if the 21” wheels with tires installed weigh the same as 20” wheels with tires installed, and tire diameter and width are the same, it’s a pretty safe assumption that moment of inertia of the 21s will be greater.
To keep the tire external diameter equal, the width is wider for both tires and wheels, on larger diameter wheels.
See https://www.wheel-size.com/size/porsche/taycan/2020/
 
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Bry5on

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That’s a cool website. You’re right, the tire diameter of the 21” wheels is nominally 10mm shorter, which will help offset some as well. Thanks

Maybe next round I will ballpark the 20 and 21” wheels + tires. We could pretty easily pick the midpoint of the tire sidewall to concentrate the mass of the wheel + tire as an approximation for relative purposes, just like the brakes. We know the 20s + tires are some 60lbs per corner after someone pulled them off to weigh them recently..

edit: quick math shows a 2% larger moment of inertia for the 21s if that approximation holds and the weights are the same. Basically identical, but I’ll take the extra cush, even if the 21s lookway better
 
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the ONLY reasons to consider PCCB's for the Taycan are:

1. you're tracking it (not a good idea) it's fun but it is too big and too heavy and tracks lack fast charging to keep you running all day
2. dust management

dust management is what tips it over the top for me

although with regen carrying 90% of the load that's 90% less dust also…PCCB's are probably a big huge waste on an EV given very very low friction brake usage…

years ago I came to admire "monster cables" ability to "sell" stuff to people - I believe they hit their peak in terms of extracting money out of people with their "gold plated optical" audio cables (think about it)…pure money extraction with no shame.

that's how I feel about PCCB"s on an EV that has 90% of it's braking handled by regen…go Porsche!!!
This isn't a cable that gets hidden. They look awesome & the PSCB rears look puny inside the Mission E wheels. For basically the same price as the Sport Design kit, I went for it. They look incredible. All your comments are correct but weren't relevant to my decision.

*standard brakes weren't an option for me on the Turbo. On a 4S I would get the base brakes with the 20s. PSCB replacement could turn out to be a real gotcha for those who keep the car five years.
 

Mike in CA

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The "90% of the braking is done through regeneration" assertion is interesting because I'm certain that I engage the friction brakes in our e-Tron much more often than that, especially when driving briskly. I'm anxious to experience the Taycan's braking to judge it's characteristics for myself.

Even if the 90% number is accurate, however, there are still times when one needs maximum braking performance and a few feet one way or the other can make an expensive difference. Personally, I want the absolute best brakes I can get on a 2 1/2 ton performance car.

But I'm leaning on a hypothetical. What I wish is that Porsche (or someone) would release comparative information on the stopping distances for the various Taycan brake configurations so we could make an objective judgement.
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