GR Yaris Thoughts on aftermarket discs and calipers choice

991RS

991RS

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On my last trackday I lost the brakes twice whereas it was 2°C !
Girodiscs, Endless MA45B pads and Goodridge braided brake lines
Endless RF 650 brake fluid
KW V4 clubsport
Michelin CUP2 245 on 8,5 TC105X wheels
Pushing hard, especially on brakes

So I begun a quest to upgrade.
First, HRNSHN full cooling ducts is ordered (ducts extensions and hoses) but I am afraid it's not going to be enough so I am looking at discs and brake calipers but damn it's very hard to find the right part.

DISC :
My parts seller (Wouter from Co-ord sport netherlands) found a disc that sound promising : AP racing reference 5772
362x32mm but a lot lighter than OEM and even lighter than girodiscs whereas it's bigger.
OEM disc : 9,85kg (my measurement on a worn disc so a bit lighter than new)
Girodiscs : approximately 8kg, I don't have the precise weight, I could not weight before installing.
AP racing CP5772 : 6,99kg according to AP racing on their website
(there is also CP4542 cheaper but heavier)

Weight is very important to me and here we are talking about rotating mass ! So I would be very happy with one kg less compare to Girodiscs
Defintely the AP racing CP5772 would be an improvement for heat management.
Endless are more expensive but I guess I should dig a little bit more their product maybe.
About TDE (track day engineering) ceramic discs, I am really sorry about this but I dismissed this option for 3 reasons :
- TDE is not a big name, yeah I know I am not helping them by not buying but there is a crucial lack of feedbacks on their products even for other brands (Mazda, Ford)
- Price is almost too cheap for a ceramic disc, I know it's refurbished but Idon't know how they produce such a cheap ceramic disc.
- The finish is just horrible, plenty of holes and cracks in a new disc,this is not confidence inspiring at all.

I've watched Rothelli Racing's video about those discs, it helped but not enoug to trigger a buy. I am a bit saddened because I would have been very happy with the weight saving !

CALIPER :
4 pistons or 6 pistons ? That is the question...
OEM caliper : 2,9kg (source)
AP racing pro 5000R CP9446 4 pistons : 2,23kg
AP racing pro 5000R CP9660 6 pistons : 2,78kg
Endless 6 pistons : too expensive
Both APracing caliper would require custom parts to fit.

6 pistons would improve brake performance and heat management, but Ithink it might be overkill for the car and the limiting factor would be the tyres. And I am afraid of screwing the brake balance. I would not like to need to upgrade rear brakes....(just from a financial POV and because they are good enough)
4 pistons : It would definitely be my choice if I was sure it would improve a little bit brake performance and heat management. But I am afraid it won't be an upgrade over OEM calipers wich are already very good.

So it'swhere I am in my quest .
I know a lot of guys will think OEM calipers are fine and this is true but I want my car to brake flawlessly even on hard long summer session. And anyway I will soon burn my dust boots (maybe they are already) so it's my excuse to upgrade 😂 (yes I know I could buy a cheap refection kit 😂)

Sorry for my english, I am french
 
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My initial thought is, work as much as you can on the cooling. I assume you have titanium shims in place? Are the brake shields still in place? Do you know what temperatures you are getting?

Nothing wrong with the brake hardware itself what I can tell, pads are as they are, steel is steel although there are potential difference in disk venting, this is where your focus should be, not weight. https://apracing.com/race-car/brake-discs/disc-cooling
If disk venting is similar, just changing disk and calipers won't necessarily help if cooling is the culprit, they will still overheat.... Unless the OE calipers are blocking due to heat and the AP doesn't.

The weights of the AP disks is without the bell, the bell is where typically the largest weight difference is but it matters less as rotating mass close to the rotation centre. But AP is good stuff and may last longer and be cheaper long term if you wear brakes a lot. But again, not for the weight difference per se.
 
Ah yes I knew it but I forgot about it 😣
I think the weight should be pretty good even with the bell.

I don't have the titanium shims, I am not quite sure it would be enough to avoid brake failure on a hot day but maybe I am wrong.
 
991RS said:
I don't have the titanium shims, I am not quite sure it would be enough to avoid brake failure on a hot day but maybe I am wrong.
Click to expand...

Oh, you really should get ti shims, they work as heat isolators and protect the caliper and dust boots etc from overheating by changing the heat path and heat balance. That together with the full cooling ducts probably solves most of your issues!
 
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I believe the TDE discs are made by surface transforms - they’re not refurbished, they are a proper bit of kit. I haven’t swapped discs yet, but did have fade on track first time out, and used pretty much a full set of pads. I swapped fluid & pads and added hrnshn vents and HEL shims, and have had no problem since then. I still have the dust shields in place.

Lower unsprung weight is great, but the disc is also your heat sink… That said, the oem discs feel unnecessarily heavy compared to other options. I’m not sure there is a compelling reason to change callipers, apart from the TDE carbon discs needing them as they are wider.

As above, I would definitely start with the vents and shims, they are super cheap compared to the other options.
 
Get your self titanium or other isolated shims and cooling ducts. If it is not enought I have seen nice Carbon kit from dna racing. The rottor should be from rear lambo.

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doabackflip said:
I believe the TDE discs are made by surface transforms - they’re not refurbished, they are a proper bit of kit
Click to expand...
Sorry but this is not correct.

TDE discs are refurbished from Brembo discs : source (first line of the 2nd paragraph)

I highly doubt ST make those discs because ST discs are way more expensive : approximately €7200 for 2 discs (inluding VAT).
If ST discs make those discs I guess they could be cheaper because they are refurbished but then why it's not sold under ST brand...

Another point : Their is 2 types of ceramic discs and ST discs (very smooth surface) are not the same as TDE discs (very rough surface).
The nomenclature behind this is long fiber vs short fiber OR high content of fiber VS low content of fiber.

You can clearly see the difference on OEM discs : for example Porsche PCCB VS Maclaren discs.

So it would be very surprising that ST which is used to make one kind of discs changed their process.
Finally, I like ST discs a lot and I know them well. I have never heard that they make those discs.
 
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Damn nobody want me to change the calipers ! :ROFLMAO: :ROFLMAO:

Some more inputs :

- Very interesting video from a very interesting guy about big brake don't stop you faster but are better for heat management
first part on you tube
2nd part on you tube

Yes when you have bigger diameter discs you increase the leverage effect but that's marginal
Yes when you have 6 pistons calipers you increase pad surface but that's marginal
It seems that big brake kits are (almost) only better for heat management.

- I had the chance to have some precious informations from a brake engineer and he confirmed that a bigger pad result in greater heat distribution and so less heat fade. Also he said that he wouln't expect front and rear brake balance to be greatly affected by using a 6 pot front as rear brakes on a front engine 4wd car will not be worked hard.

So finally I might go for 6 pistons calipers :oops: and I guess you won't like that ! :ROFLMAO:;)
 
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If I tracked the car a lot would likely swap both discs and calibers. so It sounds like a feasible choice. then you also have better options to use wider disc too that will not likely have heat issues anymore. I think the stock disc sizing is not correct for the car for heavy track use but just guess.
 
Onehp said:
Oh, you really should get ti shims, they work as heat isolators and protect the caliper and dust boots etc from overheating by changing the heat path and heat balance. That together with the full cooling ducts probably solves most of your issues!
Click to expand...
Yeah, @DeanoC tested pre- and post-titanium shims and they make a big difference to the temps in the caliper and therefore the fluid. Something like 45°C.

GR Yaris - Titanium brake caliper shims

Hey everyone. For those of you who migrated over from the other place you may remember we come up with some titanium brake caliper shims after I melted my seals. Well my track day buddies have asked me to make some for the Clios out there and there may be an opportunity to run a few more GR ones...
www.gr-zoo.com www.gr-zoo.com
 
Carbon shims are out there and seem to me to be a better insulator than a metal. However.... if you insulate the caliper from the heat guess where the heat remains. I do not know which would be best and believe it would depend on the individual circumstance.
 
banzai2 said:
Carbon shims are out there and seem to me to be a better insulator than a metal. However.... if you insulate the caliper from the heat guess where the heat remains. I do not know which would be best and believe it would depend on the individual circumstance.
Click to expand...
True, but I'd say they should only really be used with race pads which can handle much higher temps than stock pads.
 
991RS said:
Damn nobody want me to change the calipers ! :ROFLMAO: :ROFLMAO:

Some more inputs :

- Very interesting video from a very interesting guy about big brake don't stop you faster but are better for heat management
first part on you tube
2nd part on you tube

Yes when you have bigger diameter discs you increase the leverage effect but that's marginal
Yes when you have 6 pistons calipers you increase pad surface but that's marginal
It seems that big brake kits are (almost) only better for heat management.

- I had the chance to have some precious informations from a brake engineer and he confirmed that a bigger pad result in greater heat distribution and so less heat fade. Also he said that he wouln't expect front and rear brake balance to be greatly affected by using a 6 pot front as rear brakes on a front engine 4wd car will not be worked hard.

So finally I might go for 6 pistons calipers :oops: and I guess you won't like that ! :ROFLMAO:;)
Click to expand...
Again the question is what temps do you have.
Your brake fluid will boil at approx 300°C, while the pads can take 800°C. So if the pads are at their limit, then you need bigger ones/6 pot. But if it's just the brake fluid, then shims are your friend.

BTW those aren't just any metal shims, rather a specific grade titanium that has very low heat conductivity, 20x less then aluminium and close to carbon, depending on the matrix used there.

6 piston calipers allow for bigger pads which reduces heat stress, but at the same time it reduces the exposed area of the brake disk and thus reduces cooling of the disk a little. Disks that are cooled, also relatively cool the pads...

Or you just want 6 pot calipers, well can't argue with that ;)
 
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Onehp said:
Again the question is what temps do you have.
Your brake fluid will boil at approx 300°C, while the pads can take 800°C. So if the pads are at their limit, then you need bigger ones/6 pot. But if it's just the brake fluid, then shims are your friend.

BTW those aren't just any metal shims, rather a specific grade titanium that has very low heat conductivity, 20x less then aluminium and close to carbon, depending on the matrix used there.

6 piston calipers allow for bigger pads which reduces heat stress, but at the same time it reduces the exposed area of the brake disk and thus reduces cooling of the disk a little. Disks that are cooled, also relatively cool the pads...

Or you just want 6 pot calipers, well can't argue with that ;)
Click to expand...
If their heat conductivity is so low then they are not titanium but something combined with titanium. A grade of titanium would be either its purity or maybe an alloying element. If I am wrong please post the specific composition of this amazing material as I have a hypersonic missile I am trying to develop and it would massively help with heat rejection.
 
banzai2 said:
If their heat conductivity is so low then they are not titanium but something combined with titanium. A grade of titanium would be either its purity or maybe an alloying element. If I am wrong please post the specific composition of this amazing material as I have a hypersonic missile I am trying to develop and it would massively help with heat rejection.
Click to expand...
Engineering metals are as good as always alloys. Anyway, look up Ti-6Al-4V – Grade 5
 
I understand alloys can be good eg Steel Hastelloy C virtually the same as the example you mentioned. Re my point, if you completely blocked heat transfer from the pads to the calipers would that benefit your brake performance? I think there are many variables at play here. The calipers and brake fluid would be cool but the disks and pads would be hotter. There will be an optimum point for each brake system which absent experimentation is likely unknown as well as being subjective.
 
banzai2 said:
if you completely blocked heat transfer from the pads to the calipers would that benefit your brake performance? I think there are many variables at play here. The calipers and brake fluid would be cool but the disks and pads would be hotter.
Click to expand...

I think broadly speaking, yes, that would benefit your brake performance. The pad and disc can take much higher temperatures than the brake fluid (800 vs 300C), and the disc has loads of airflow so can get rid of the heat, nothing good comes from heating up the caliper (you can damage the seals) and the brake fluid.
Increasing the calipers/pad size will increase the amount of heat they can absorb, and reduce heat transfer to the fluid but they can’t dump the heat as well as the disc (hence why you get water cooled calipers in some race cars). It’s worth noting that worn brake pads have less mass, so less capacity to absorb heat.
As someone mentioned above, once you get past a fairly basic level of braking system, pretty much all the benefits are in heat management.
There are two types of brake fade, boiled fluid (soft pedal) and excess pad/disc temperature - what you change depends on what problem you are trying to solve, but increasing airflow/cooling is cheap with no downside (and I think shims are in this category too), while bigger hardware typically increases unsprung weight and can do real damage to your wallet.
Don’t get me wrong though, I also love shiny things! 😀
 
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