Better brake fluid?

[ChrisD]

I know most road cars suffer from brake pedal going soft and spongy after a few laps on track due to the brake fluid boiling.

I'm doing my first track day in the supra next weekend and thinking it might be worth preempting that problem and putting some better fluid in it, but just wondering if other people have tracked theirs yet and found the stock fluid to be fine?

If the stock fluid is not up to the job and you replaced yours, is there anything special to know about the requirements for this car or will any DOT4 or DOT5.1 fluid be fine (I know the service manual says DOT4, but 5.1 is compatible with 4)

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[racer01]

I know most road cars suffer from brake pedal going soft and spongy after a few laps on track due to the brake fluid boiling.

I'm doing my first track day in the supra next weekend and thinking it might be worth preempting that problem and putting some better fluid in it, but just wondering if other people have tracked theirs yet and found the stock fluid to be fine?

If the stock fluid is not up to the job and you replaced yours, is there anything special to know about the requirements for this car or will any DOT4 or DOT5.1 fluid be fine (I know the service manual says DOT4, but 5.1 is compatible with 4)

I did a few days at the track a few weeks ago. The Supra stock pads are decent for what the are, but just can't take much track heat before the pedal gets soft. Its not fluid boiling, but just overheated pads which start to create a long pedal and the feeling of less coefficient of friction. I did high temp fluid just to be on the safe side, but even Motul RB600 only has a wet boiling point about 50F higher than the stock stuff if I remember my research properly. I'd say you would be fine with stock fluid, but then again it was pretty cheap and easy to buy a self bleeder and some fluid and spend 30 min flushing the stock fluid out.
I was (still am) really kicking myself for not getting the Counterspace Garage: https://www.counterspacegarage.com/blog/brakes/brake-pads-for-2020-toyota-supra-gr/
pads before hitting the track, as I spent all weekend taking it easy on the brakes just to make them last and wish I could have spent more time just enjoying driving.

 

[ChrisD]

I did a few days at the track a few weeks ago. The Supra stock pads are decent for what the are, but just can't take much track heat before the pedal gets soft. Its not fluid boiling, but just overheated pads which start to create a long pedal and the feeling of less coefficient of friction. I did high temp fluid just to be on the safe side, but even Motul RB600 only has a wet boiling point about 50F higher than the stock stuff if I remember my research properly. I'd say you would be fine with stock fluid, but then again it was pretty cheap and easy to buy a self bleeder and some fluid and spend 30 min flushing the stock fluid out.
I was (still am) really kicking myself for not getting the Counterspace Garage: https://www.counterspacegarage.com/blog/brakes/brake-pads-for-2020-toyota-supra-gr/
pads before hitting the track, as I spent all weekend taking it easy on the brakes just to make them last and wish I could have spent more time just enjoying driving.

Thanks for the info, much appreciated.

Any reason you didn't go for the RBF660 stuff? That's what I was going to use. Has a higher boiling point than the RBF600 stuff (when new anyway).

I hadn't considered the pads just not being up to the job to be honest but that is a good point. Doesn't seem like StopTech or EBC are making pads for this car yet. The only ones I could find are the Counterspace ones you linked and unfortunately they're not in the same country as me and wouldn't be here in time for my track days I've got booked.

Guess I'll just replace the brake fluid with the RBF660 anyway if you didn't have any problems with the RBF600.

Oh how did you find out what boiling point the stock fluid had by the way? I looked through the service manual and couldn't find any exact spec on the fluid. All I could find was that it has to be DOT4.

 

[racer01]

Thanks for the info, much appreciated.

Any reason you didn't go for the RBF660 stuff? That's what I was going to use. Has a higher boiling point than the RBF600 stuff (when new anyway).

I hadn't considered the pads just not being up to the job to be honest but that is a good point. Doesn't seem like StopTech or EBC are making pads for this car yet. The only ones I could find are the Counterspace ones you linked and unfortunately they're not in the same country as me and wouldn't be here in time for my track days I've got booked.

Guess I'll just replace the brake fluid with the RBF660 anyway if you didn't have any problems with the RBF600.

Oh how did you find out what boiling point the stock fluid had by the way? I looked through the service manual and couldn't find any exact spec on the fluid. All I could find was that it has to be DOT4.

Brake fluids are like oil....whole can of worms there picking one but I use charts such as this: https://www.pegasusautoracing.com/group.asp?GroupID=BRAKEFLUID
and
https://parsbrorc.com/?page_id=33

The RB600 is a great value for the performance and I have used it in the past and was readily available. The RB660 is quite a bit more expensive, and actually has the same (lab tests) or slightly lower wet boiling point. Once you crack the bottle it starts absorbing moisture so I always just compare wet boiling points. I go with the cheap stuff and if I ever go fancy with brake fluid it is straight to the Castrol SRF for me!

To determine if I really even needed to upgrade I made a few assumptions. Knowing the Supra is built in Austria and using the Z4 chassis it starts life a typical BMW. I did a little googling and found almost all BMW's use the same Pentosin DOT 4, and then looked up the part number and found things like this.....https://www.bimmerworld.com/Brakes/...scosity-Brake-Fluid-81220142156-Pentosin.html

I am not 100% sure this is the exact fluid in the Supra, but pretty confident and it is actually pretty decent fluid with a dry BP of 509F and 338F wet. I went with known good track fluid just for peace of mind, and glad I did as I know I got the brakes smoking hot and it was just one less thing to worry about. Was definitely more kicking myself for not going ahead and getting the CSG pads that were available at the time (CP). Now that the C2 are out, I'll likely get those for the front and hopefully they will make the CP for the rear here soon.

If/when you bleed the brakes one thing to note is that the pedal travel is really, really long. I say this as when you get that soft pedal on the track after the brakes get hot, it is good to know that even though it feels like the pedal is about to hit the floor, it may not be completely out of travel even though it feels like it. As soon as I got that really long pedal I really started cool down laps, etc. and it was a good thing. My stock brake pads started smearing pad material pretty pad when they got overheated and actually grooved the rotors a good bit. Pedal feel and rotors cleaned up pretty quickly once I did some street driving after the track day, but the grooves are still easy to see and feel when I run my finger across the face of the rotor. Not ruined but not great. Just FYI

 

[ChrisD]

Yeah it is definitely a can of worms like you say, but all of the articles I've read suggest that it takes several months/years for the brake fluid to absorb moisture and get to its "wet" state. Supposedly around 2 years before your average brake fluid will be at its wet boiling point figures according to this article: https://www.epicbleedsolutions.com/resources/faq/dry-and-wet-boiling-points-dot-brake-fluid/

I also spoke to an automotive engineering friend who works at a race team and he said the only time the brake pedal will go real soft and have long travel is when there's air in the brake fluid either due to needing bleeding or due to it boiling and forming bubbles. He said "brake pads are sintered and discs are iron, they don't go 'soft' ".

I also found an article from a brake pad manufacturer that said:

• When brake pads over heat: The brake pedal remains firm and solid but the car will not stop no matter how hard you push on the pedal
• When the brake fluid is boiling: The brake pedal becomes soft and pedal travel increases because gas is compressible

From your description it sounded more like your pedal went soft and had long travel? So it seems like it was your fluid boiling rather than the pads over heating (of course pads might have been over heating as well).

 

[racer01]

Yeah it is definitely a can of worms like you say, but all of the articles I've read suggest that it takes several months/years for the brake fluid to absorb moisture and get to its "wet" state. Supposedly around 2 years before your average brake fluid will be at its wet boiling point figures according to this article: https://www.epicbleedsolutions.com/resources/faq/dry-and-wet-boiling-points-dot-brake-fluid/

I also spoke to an automotive engineering friend who works at a race team and he said the only time the brake pedal will go real soft and have long travel is when there's air in the brake fluid either due to needing bleeding or due to it boiling and forming bubbles. He said "brake pads are sintered and discs are iron, they don't go 'soft' ".

I also found an article from a brake pad manufacturer that said:

• When brake pads over heat: The brake pedal remains firm and solid but the car will not stop no matter how hard you push on the pedal
• When the brake fluid is boiling: The brake pedal becomes soft and pedal travel increases because gas is compressible

From your description it sounded more like your pedal went soft and had long travel? So it seems like it was your fluid boiling rather than the pads over heating (of course pads might have been over heating as well).

Interesting topic....so many variables. I have been through many, many types of brake "failures" and exceeding manufacturer design parameters. Boiled fluid, overheated pads, cracked rotors (seriously cracked, not crazed) broken disc mounting to hat hardware, tapered pads, pad knockback, etc, etc. Your race engineer buddy is kinda right for a race car....in general soft pedal means boiled fluid. Street pads on the track however can definitely exceed their useful temperature range, and in many cases they loose coefficient of friction as they overheat (pads don't grab the rotors as well for a given pressure) and therefore it takes much more brake pressure to get the same stopping force which equals a "long pedal". There is some give in the system, brake line swelling, caliper flex, etc so more pressure equals more pedal travel . Lots of reports of this issue in the Supra tracking with stock pads....just think of it as a nice warning that things are getting too hot.
I am sure I didn't boil my brake fluid....normal pedal feel came back immediately with a few miles of street driving which definitely won't happen with boiled fluid. I could also tell it wasn't boiled fluid while on the track as the pedal would come back with a few minutes of taking it easy on the brakes.

Lots of ways to get a soft pedal without boiling the brakes.....tapered pad wear is a big one. Also pad knockback is another fun one that will scare the crap out of you....luckily the Supra doesn't seem to suffer either issue (yet).

 

[ChrisD]

Well I did my track day today after changing the fluid for RBF660 yesterday, and I gotta say I had absolutely zero problems with the stock pads.

Now I'm not a pro racing driver by any stretch of the imagination but I've done loads of track days and felt like I was being pretty hard on the brakes all day. This was on a tight track that is known for being brutal on brakes as well (completely destroyed some brand new stock pads on my Audi R8 at this track in one day).

I was doing 7 or 8 laps and then 2 cool down laps (around 10 minutes of thrashing it on track before starting cool down laps) followed by about 30 mins of letting the car sit and cool in the pits. But yeah at the end of each of those sessions, after stamping on the brake pedal pretty damn hard at every corner, the pedal feel wasn't really any different to at the start of the day.

So yeah its weird we both had such different experiences on the stock pads. Obviously I was using RBF660 whereas you were using RBF600, but it seems like plenty of people use RBF600 in other track cars without issues. Maybe your track or your driving style is just harsher on the brakes than mine, or maybe you were just doing much longer sessions than me?

 

[racer01]

Well I did my track day today after changing the fluid for RBF660 yesterday, and I gotta say I had absolutely zero problems with the stock pads.

Now I'm not a pro racing driver by any stretch of the imagination but I've done loads of track days and felt like I was being pretty hard on the brakes all day. This was on a tight track that is known for being brutal on brakes as well (completely destroyed some brand new stock pads on my Audi R8 at this track in one day).

I was doing 7 or 8 laps and then 2 cool down laps (around 10 minutes of thrashing it on track before starting cool down laps) followed by about 30 mins of letting the car sit and cool in the pits. But yeah at the end of each of those sessions, after stamping on the brake pedal pretty damn hard at every corner, the pedal feel wasn't really any different to at the start of the day.

So yeah its weird we both had such different experiences on the stock pads. Obviously I was using RBF660 whereas you were using RBF600, but it seems like plenty of people use RBF600 in other track cars without issues. Maybe your track or your driving style is just harsher on the brakes than mine, or maybe you were just doing much longer sessions than me?

Good to hear. I am used to doing 20-25 min sessions with no cool down. Track can make a huge difference....VIR has two braking zones from 140 down to 45-50 mph.
Driving style can definitely make a difference in temps as well.....left foot braking being one big factor these days.

Really don't think fluid has anything to do with it...brake fluid all does the same (till it boils).

Great feedback....Keep tracking that thing and giving us all the feedback and info to work from!!

 

[CSG]

Well I did my track day today after changing the fluid for RBF660 yesterday, and I gotta say I had absolutely zero problems with the stock pads.

Now I'm not a pro racing driver by any stretch of the imagination but I've done loads of track days and felt like I was being pretty hard on the brakes all day. This was on a tight track that is known for being brutal on brakes as well (completely destroyed some brand new stock pads on my Audi R8 at this track in one day).

I was doing 7 or 8 laps and then 2 cool down laps (around 10 minutes of thrashing it on track before starting cool down laps) followed by about 30 mins of letting the car sit and cool in the pits. But yeah at the end of each of those sessions, after stamping on the brake pedal pretty damn hard at every corner, the pedal feel wasn't really any different to at the start of the day.

So yeah its weird we both had such different experiences on the stock pads. Obviously I was using RBF660 whereas you were using RBF600, but it seems like plenty of people use RBF600 in other track cars without issues. Maybe your track or your driving style is just harsher on the brakes than mine, or maybe you were just doing much longer sessions than me?

We worked with a few clients on different brake fluids using the same brake pad and tire compounds, but with different drivers on the same track. What you're experiencing is brake pad fade, not necessarily the brake fluid fading. The pedal pressure and response is different with each type of fade or over-temperature of each component of the brake system. Identifying which over-temp'd is something to consider, but is harder to identify by feel (it's mostly experience based).

Another question to inquire about is what tire are you using and what track are you driving on? This might give a better insight as to what would be more appropriate for track application.

 

[ChrisD]

We worked with a few clients on different brake fluids using the same brake pad and tire compounds, but with different drivers on the same track. What you're experiencing is brake pad fade, not necessarily the brake fluid fading.
...

Did you quote the wrong post by mistake? I didn't experience any problems with the brakes at all, so not sure what you're saying was brake fade.

 

[CSG]

My apologies. I read your statement incorrectly regarding the section of when you described how the brakes felt after 30min long sessions.

All of our Supra clients ran out on track and was losing brakes within the first couple laps on stock brake pads and upgraded fluid. We supplied them with a performance street pad and race pad for testing and haven't heard any issues since. All of the clients using RBF600 experienced some issues with pedal softness, but had less issues with the RBF660. No issues after I had them go with Castrol SRF or Endless RF650.

Curious about what pads you are using for your car?

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