PCCB GT3 will I notice the reduction in unsprung weight

PCCB GT3 will I notice the reduction in unsprung weight

Author
Discussion

Adrian-9iafn

Original Poster:

269 posts

71 months

Thursday 24th May 2018
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Interested to see if this is noticeable and worth the extra for this (Plenty of opinions on the other advantages/disadvantages)


Phooey

12,574 posts

168 months

Thursday 24th May 2018
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No.

<end thread>

Dr S

4,995 posts

225 months

Thursday 24th May 2018
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It's nuances rather than night and day. In the 7,2 there was some crisper initial turn-in - largely a sharper reaction to initial steering wheel movement - and I found the ride a bit more compliant

Porsche911R

21,146 posts

264 months

Thursday 24th May 2018
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Yes

turn in is far faster.

go buy a bike wheel for £20 then go buy a £1k Carbon wheel, spin it in your hand and then try and change it's direction.

light wheels and PCCB are an amazing feeling.

Edited by Porsche911R on Thursday 24th May 08:37

Twinfan

10,125 posts

103 months

Thursday 24th May 2018
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Porsche911R said:
go buy a bike wheel for £20 then go buy a £1k Carb on wheel, spin it in your hand and then try and change it's direction.
That demonstrates the principle, but you've got to add the suspension/steering rack/EPS into the equation.

I would say back to back on otherwise identical cars you might notice a slight difference.

Adrian-9iafn

Original Poster:

269 posts

71 months

Thursday 24th May 2018
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Thanks for the info, I do really like the idea, seems the premium on the secondhand market is circa £5k as the PCCB cars seem to be more heavily specced as well (Im looking for a 991.1)

Im far from the best driver in the world but do feel differences with small changes in tyre pressure, increases in damping etc (I spent weeks setting up KW's on my BMW M5 with bump and rebound for example) So looks like I would notice the 'non braking' advantages.

Koln-RS

3,849 posts

211 months

Thursday 24th May 2018
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You may not notice it, per se, but it's definitely there with notable benefits that should add subtle improvements to ride and handling.

What you will notice is the lack of brake dust and corrosion, and the longer life of the discs.

LaurasOtherHalf

21,429 posts

195 months

Thursday 24th May 2018
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Back to back in identical cars (987 Spyder at Porsche Silverstone Experience) the difference was massive. Totally different and a major positive in favour of the ceramics for me.

LaSource

2,622 posts

207 months

Thursday 24th May 2018
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More noticeable in back to back tests. I drove two otherwise identical GT4s at Spa - one steel and on PCCB. the PCCB car had noticeable lighter steering and turn in.

However, if you had only one car or the other and did not do a back to back test then you wouldn't necessarily find one was lighter/heavier - if you see what I mean.

In terms of track performance / braking distances, we found the cars to be broadly similar (or perhaps driver differences will be greater than braking performance differences)


Having said all that, I have a preference for PCCBs smile

Geneve

3,857 posts

218 months

Thursday 24th May 2018
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Also a big fan of the pccbs on the sporting Porsches - had them on my last seven.

Lovely brakes, with lots of nice benefits.

Taffy66

5,964 posts

101 months

Thursday 24th May 2018
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Porsche911R said:
Yes

turn in is far faster.

go buy a bike wheel for £20 then go buy a £1k Carbon wheel, spin it in your hand and then try and change it's direction.

light wheels and PCCB are an amazing feeling.

Edited by Porsche911R on Thursday 24th May 08:37
I agree..All the engine does is rotate the driven wheels..The less unsprung mass there is which correspondingly reduces rotational inertia, is akin to having more power at the wheels when you accelerate..The same benefits are replicated when you slow down as Mr D alluded to in his bicycle wheel analogy..
This is why by reducing unsprung mass is easily equivalent to reducing other mass by a factor of seven times .

Taffy66

5,964 posts

101 months

Thursday 24th May 2018
quotequote all
There are two important distinctions to remember when debating the relative merits of PCCBs..The one benefit is purely having less unsprung mass which benefits spring compression and rebound, giving only tangible benefits when driving over rough roads..
The other benefit is reducing rotational inertia which benefits acceleration,braking and turn in..The benefits of reduction in rotational mass is increased exponentially the further this weight reduction is from the hub centre..An extreme example of this is by comparing a new heavy full tread tyre to a lighter tyre with no tread..The worn tread being the furthermost mass from the centre of the hub will reduce rotational mass exponentially more than if the equivalent reduction of mass was from a brake disc eg
This is why fitting Mg rims with a 12Kg weight saving, will offer more benefits when compared to PCCBs with the same 12Kg weight saving..
When i spec my new RS i will get both the Mg wheels and PCCBs for a total unsprung weight saving of 30Kgs which will be very noticeable compared to the same RS with Al rims and steel brakes..

Yellow491

2,911 posts

118 months

Thursday 24th May 2018
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Taffy66 said:
Porsche911R said:
Yes

turn in is far faster.

go buy a bike wheel for £20 then go buy a £1k Carbon wheel, spin it in your hand and then try and change it's direction.

light wheels and PCCB are an amazing feeling.

Edited by Porsche911R on Thursday 24th May 08:37
I agree..All the engine does is rotate the driven wheels..The less unsprung mass there is which correspondingly reduces rotational inertia, is akin to having more power at the wheels when you accelerate..The same benefits are replicated when you slow down as Mr D alluded to in his bicycle wheel analogy..
This is why by reducing unsprung mass is easily equivalent to reducing other mass by a factor of seven times .
Sounds like you are all taken in by the marketing.
Do proper back to back tests,of acceleration,braking and turn in and out and see what you get.
Do porsche change the springs,damping rates etc between steel and ceramic,no i think is the answer.
Normaly unsprung mass is a multiple of 3.5
Ceramics are also a stupid price and fragile compared to steels.

Geneve

3,857 posts

218 months

Thursday 24th May 2018
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They aren't expensive compared with most other manufacturers, and they can be 'cost neutral' over the extended life of the car. Or, in the case of some models, where they add value at resale.

The 'fragility' issue was really only evident with the very first generations. Since the last 12 years, we've seen significant advances in the manufacturing, materials, cooling, f/r bias, durability and longevity. They're now a mainstream product fitted to hundred of thousands of cars without any issues, and the critics site circumstantial evidence, really based on early variants.

If a car is going to be used extensively on track, then may be there are steel alternatives, although I know many of the pccb equipped PEC cars have had a hard life with no issues.

What people favour is purely a personal choice, but it would be quite wrong to say that ceramics don't provide any advantages.

isaldiri

18,412 posts

167 months

Thursday 24th May 2018
quotequote all
Taffy66 said:
The other benefit is reducing rotational inertia which benefits acceleration,braking and turn in..The benefits of reduction in rotational mass is increased exponentially the further this weight reduction is from the hub centre..An extreme example of this is by comparing a new heavy full tread tyre to a lighter tyre with no tread..The worn tread being the furthermost mass from the centre of the hub will reduce rotational mass exponentially more than if the equivalent reduction of mass was from a brake disc eg
.
Does anyone here who believes ceramics provide a big advantage in feel due to lower rotational inertia actually notice a difference when fitting a brand new set of tyres compared to the previous well worn set?

Taffy66

5,964 posts

101 months

Thursday 24th May 2018
quotequote all
isaldiri said:
Does anyone here who believes ceramics provide a big advantage in feel due to lower rotational inertia actually notice a difference when fitting a brand new set of tyres compared to the previous well worn set?
I'm merely using a worn tyre versus a new tyre as an example how theoretically rotational inertia increases the further away it is from the axis of rotation.
Rotational inertia is a property of an object which can be rotated,or how difficult it is to change the velocity around a centre axis.The rotational inertia of an object depends on its mass and the distribution of that mass in relation to the centre axis.
When the mass moves further away from the axis it becomes more difficult to change the rotational velocity of the entire wheel.This is because the mass is now carrying more momentum with it around the hub axis(higher speed).
Momentum of inertia has a formulae as follows:

MoI = m x r/2
A lot of the benefit of PCCBs reduced MoI is lost due to having bigger diameter discs and heavier calipers as shown by the formula above..

Yellow491

2,911 posts

118 months

Thursday 24th May 2018
quotequote all
Proper maths and testing needs to be done,not ear say,or i think!
I put steels on my cgt,did not notice any change really apart from the noise of clacking discs when cold.
As to noticing the change in mass from tyre wear,i would say you need to be the late and great senna.
To make a differance in such a lardy car that you would really notice,you would need to shed 200kg plus.Bigger discs = more weight,in pads,wheels ,tyres, etc and then re weight the car and adjust springs rates ,dampers etc
The new ceramic discs are still fragile for track use etc,as a pure road car a no brainer on ceramics.

isaldiri

18,412 posts

167 months

Thursday 24th May 2018
quotequote all
Taffy66 said:
I'm merely using a worn tyre versus a new tyre as an example how theoretically rotational inertia increases the further away it is from the axis of rotation.
Rotational inertia is a property of an object which can be rotated,or how difficult it is to change the velocity around a centre axis.The rotational inertia of an object depends on its mass and the distribution of that mass in relation to the centre axis.
When the mass moves further away from the axis it becomes more difficult to change the rotational velocity of the entire wheel.This is because the mass is now carrying more momentum with it around the hub axis(higher speed).
Momentum of inertia has a formulae as follows:

MoI = m x r/2
A lot of the benefit of PCCBs reduced MoI is lost due to having bigger diameter discs and heavier calipers as shown by the formula above..
I'm aware of the maths regarding rotational inertia thanks.

My point was that you said the impact of less unsprung weight from the mag wheels and ceramic rotors would be very noticeable. Others have said rotors alone make a big difference. The tyre is obviously furthest from the rotational centre and the weight difference of a new vs a worn tyres is considerable. No one has ever mentioned putting on a new tyre results in negative feel unlike those saying here the ceramic rotors make a big difference when the rotation momentum isn't going to be hugely different. Curious that....

Koln-RS

3,849 posts

211 months

Thursday 24th May 2018
quotequote all
Is there much/any difference in the weight of a new v worn tyre? I thought most of the weight was in the carcas.
Certainly I think most people can feel the benefits of a new v old tyre in terms of ride, handling and grip, but not weight.
But do agree unsprung weight saving has lots of advantages - so the lightest brakes, wheels, tyres must make sense

Taffy66

5,964 posts

101 months

Thursday 24th May 2018
quotequote all
The benefits of upgrading from steels to PCCBs needs to be considered on a case by case basis.A car which benefits most by upgrading to PCCBs in purely terms of braking performance is also gaining the least amount in terms of reduced MoI and unsprung weight.
As an example at one extreme is the new Porsche 911T which has relatively puny steels and there is a massive gain in braking ability due to the much larger 410/390mm PCCBs..On the other hand in this instance there is only 10Kg weight saving, and since the rotors of the PCCBs are so much larger in diameter no benefits in MoI..
The other extreme is upgrading the 380/380mm steels on 991 Turbo,991 GT3 and GT4 where the steels are already pretty big and heavy and are great at braking..The benefits on MoI and unsprung weight is signiicant however, since there is a total 18Kgs saving and the diameters are very similar in size between the steels and PCCBs.