Lextreme II
Active Member
Perhaps this item will interest someone Rotora Big 6 Pistons Brake
Rotora Big 6 Pistons Brake
- Thread starter Lextreme II
- Start date
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LOL completely the opposite Jibbby :haha:
The larger (or more) front pistons take more fluid so before they have filled the rears are already at lock up pressure... so you get REDUCED braking at the front and horrible rear bias.
You are correct to say you need to get it all just right and in most cases a brake bias valve can be installed to get you sorted.
In most cases the master cyl won't need to be touched unless the pedal travel becomes too long.
As 80% of braking is done by the front once the setup is balanced you can often get away with just a pad upgrade on the rear but if you are going all out then yes a rear caliper/rotor upgrade would be the go
Easy, the system you replaced had a similar piston volume. You would not have decreased rear braking effort but comparatively it would be les than the front.
All you are doing is moving a volume of fluid with the master cylinder into the brake caliper at a ratio to increase the braking force. The brake cylinders need a set volume of fluid to work as do the rears and the bias between how much each gets is fixed in a factory setup.
Now stay with me here JiBBBy....if the new front calipers require a lot more fluid (as a BIG brake upgrade will) then the fixed bias won't be able to supply enough to the fronts before the rear gets what it needs and they will lock up BEFORE the fronts.
This why you will find that nearly all BIG front brake kits require an adjustable bias valve to reset the rear bias.
If you put your car on a brake dyno you would have found that by reducing the rear bias you would have improved braking further again. There is a fair bit of slack but into the factory setup, as with most factory parts, so a lot of brake upgrades using factory calipers will deliver a worthwhile result. Once you move to the genuinely big aftermarket calipers you will fined exactly as i have described. I have done this many times Jibbby
Like I said before, bigger heavier duty brakes are more for heat managment. Normal street use, they are almost pointless and nothing more then show. On the other hand, at the track is where the differance will be seen. You take your car and another identical car to yours but with bigger brakes on it that are sizes correctly and run them both side by side on Laguna Seca and after a few laps, the other car will out brake you. This is because your brake performance will start to fade away due to the fact that your smaller rotors cant absorb and disapate heat like the bigger supra rotor can.
Another reason for you noticing that the supra setup seemed worse it that the rotors are much larger and heavier and thus have a lot more inertia and thus harder to accelerate and slow down. The same thing happens to cars when you put big huge heavy ass wheels on a it. Reduction of rotational weight always has huge bennifets especially if its out at the wheels cause not only is it less rotational weight, its also less unsprung weight but thats a whole nother story as to why reducing unsprung weight should always be done if it can be. This is all the reason for the use of 2pc. rotor assemblies (i.e. Alloy hats with what ever disk material is being used, be it Iron, Ti, carbon, ect...)
Thanks for the clarification Chris, you have explained the situation more clearly. The bias valve has done the trick for me a number of time now.
As for the long pedal, you need a bigger bore master cyl so you can move more fluid per pedal travel.
The problem with adding more and larger piston calibers to the front end of your car that came stock with 2 piston calipers is the braking power in the back is decreased greatly... Kinda making the up grade counter productive..
It's almost a good idea to upgrade and change out the rear calipers also and master cylinder to get it all just right...
It's almost a good idea to upgrade and change out the rear calipers also and master cylinder to get it all just right...
JustenGT8
New Member
LOL completely the opposite Jibbby :haha:
The larger (or more) front pistons take more fluid so before they have filled the rears are already at lock up pressure... so you get REDUCED braking at the front and horrible rear bias.
You are correct to say you need to get it all just right and in most cases a brake bias valve can be installed to get you sorted.
In most cases the master cyl won't need to be touched unless the pedal travel becomes too long.
As 80% of braking is done by the front once the setup is balanced you can often get away with just a pad upgrade on the rear but if you are going all out then yes a rear caliper/rotor upgrade would be the go
Justen are you laughing at my comments?... Hey it's all good... Curious, if you loose breaking power in the front when upgrading to larger front brake calipers and you loose the rear bias as well then why would anyone then attempt to upgrade the braking system to begin with without changing out all the other stuff?... This happens alot too...
The reason I say you gain more front end braking power is because you have more pistons working against the rotors... Most of the fluid push is directed to the new fronts and less to the rears giving you the decreased braking power in the rears, no?..
I did this upgrade on my SC400 to the Supra 4 pistons front calipers only.. I did not touch the rest of the braking system...What I got is improved front braking and decreased rear braking action.... That is where my comment came from, if I am wrong about that above statemtent of mine it sure didn't show up in my brake swap upgrade....
Justen my boy, how do you explain that?
The reason I say you gain more front end braking power is because you have more pistons working against the rotors... Most of the fluid push is directed to the new fronts and less to the rears giving you the decreased braking power in the rears, no?..
I did this upgrade on my SC400 to the Supra 4 pistons front calipers only.. I did not touch the rest of the braking system...What I got is improved front braking and decreased rear braking action.... That is where my comment came from, if I am wrong about that above statemtent of mine it sure didn't show up in my brake swap upgrade....
Justen my boy, how do you explain that?
cjsupra90
New Member
What I think he is saying is that you are loosing braking abillity if you get to big and just lock up the front wheels to soon.
Another thing to remember is that its not the number of pistons, it the sq/in of area that is offered. As the number count goes up, then size decreases. The main reason for more pistons it to equalize the pressure across the length of the pad and thus make the pad more effective.
Take my upgrade that is on my supra. Designed by me too. Is 6pot front calipers on 330mm rotors. Even though I am using 6pots vs. stock single pot calipers, the actually piston sq/in area decreased by a very small amount but the braking ability increased substanually. This is due to better pads and larger diameter rotors (i.e. more mechanical leverage). Having larger rotors allows for better heat absorbsion and dissapation and there for less likely to fade.
The whole true point of a big brake kit is Heat Managment. On a track car, this is critical.
Another thing to remember is that its not the number of pistons, it the sq/in of area that is offered. As the number count goes up, then size decreases. The main reason for more pistons it to equalize the pressure across the length of the pad and thus make the pad more effective.
Take my upgrade that is on my supra. Designed by me too. Is 6pot front calipers on 330mm rotors. Even though I am using 6pots vs. stock single pot calipers, the actually piston sq/in area decreased by a very small amount but the braking ability increased substanually. This is due to better pads and larger diameter rotors (i.e. more mechanical leverage). Having larger rotors allows for better heat absorbsion and dissapation and there for less likely to fade.
The whole true point of a big brake kit is Heat Managment. On a track car, this is critical.
JustenGT8
New Member
Easy, the system you replaced had a similar piston volume. You would not have decreased rear braking effort but comparatively it would be les than the front.
All you are doing is moving a volume of fluid with the master cylinder into the brake caliper at a ratio to increase the braking force. The brake cylinders need a set volume of fluid to work as do the rears and the bias between how much each gets is fixed in a factory setup.
Now stay with me here JiBBBy....if the new front calipers require a lot more fluid (as a BIG brake upgrade will) then the fixed bias won't be able to supply enough to the fronts before the rear gets what it needs and they will lock up BEFORE the fronts.
This why you will find that nearly all BIG front brake kits require an adjustable bias valve to reset the rear bias.
If you put your car on a brake dyno you would have found that by reducing the rear bias you would have improved braking further again. There is a fair bit of slack but into the factory setup, as with most factory parts, so a lot of brake upgrades using factory calipers will deliver a worthwhile result. Once you move to the genuinely big aftermarket calipers you will fined exactly as i have described. I have done this many times Jibbby
You know what's interesting about these big brake swaps is that alot of people don't realise is that you can get much improved braking power just by switching to Drilled and Slotted rotors and high quality brake pads rather then upgrading to a larger front brake assembly...
Again, I did the Supra big brake swap temporarily and noticed a more responsive brake peddle but the actual braking stop distance was not that greatly improved off of the stock setup... I went back to my stock 2 piston front calipers and went with the D/S rotors and OEM pads instead.... What I found is that simple improvement gave me the best braking I've ever had in my SC400... Go figure?
I am a believer in D/S rotors period......
Again, I did the Supra big brake swap temporarily and noticed a more responsive brake peddle but the actual braking stop distance was not that greatly improved off of the stock setup... I went back to my stock 2 piston front calipers and went with the D/S rotors and OEM pads instead.... What I found is that simple improvement gave me the best braking I've ever had in my SC400... Go figure?
I am a believer in D/S rotors period......
spf_lexus
Active Member
Well I have similar to you guys, supra fronts and larger 95' LS in the rear to compensate.... so i thought. So have I almost made it worse or better? Im thinking now that you take away fluid from the opposing side by requiring more for the larger brakes, hence the bias valve. But what happens if i upgrade the fronts and upgrade the rears to a much larger single piston and larger rotor setup w/ good pads? I have SS lines in front and stock in rear and I have late brakes... I have good brakes when I lay on them but no sensitivity for light stops under 60+.... is it just me? or is it just the heaviness of the LS?
cjsupra90
New Member
Like I said before, bigger heavier duty brakes are more for heat managment. Normal street use, they are almost pointless and nothing more then show. On the other hand, at the track is where the differance will be seen. You take your car and another identical car to yours but with bigger brakes on it that are sizes correctly and run them both side by side on Laguna Seca and after a few laps, the other car will out brake you. This is because your brake performance will start to fade away due to the fact that your smaller rotors cant absorb and disapate heat like the bigger supra rotor can.
Another reason for you noticing that the supra setup seemed worse it that the rotors are much larger and heavier and thus have a lot more inertia and thus harder to accelerate and slow down. The same thing happens to cars when you put big huge heavy ass wheels on a it. Reduction of rotational weight always has huge bennifets especially if its out at the wheels cause not only is it less rotational weight, its also less unsprung weight but thats a whole nother story as to why reducing unsprung weight should always be done if it can be. This is all the reason for the use of 2pc. rotor assemblies (i.e. Alloy hats with what ever disk material is being used, be it Iron, Ti, carbon, ect...)
cjsupra90
New Member
Im not trying to start an agument here, but to bias valves or back proportioning valves have nothing to do with or care what the volume is as they are pressure differential deviced. To much or to little volume does not necessarily mean that you have degraded your brakes.
To make this a little clearer, Yes significantly larger front caliper pistion area will requier more volume and thus at the same original volume, the line pressure will be lower which infact will cause the rear pressure to ramp up fast depending on whats called the knee point of the proportioning valve. So yes, the rears could be comming on faster and stronger but at that same time those larger front calipers have more piston area and thus generate more clamping pressure at a lower line pressure.
There is a lot more to a brake system working correctly then just fluid volume and line pressure. Rotor diameter, and pad material play a significant roll in brake torque.
In the end brake torque that is being generated at the tire contact patch is what you want and need to know, and every part of the brake system and also tire diameter all play rolls in what that torque will be.
Also to note, a cars setup will dictate what kind of bias needs to be run. An example is if a car has been lowered and is running stagered tires sizes usually need more rear bias to be balanced correctly and so on.... A proper brake setup is actually more complicated then most think and really should be left to people that know what they are doing.
One last thing to note here is that brakes dont stop your car, your tires do and thus you can have the baddest brake setup in the world and if your tires are SH!TTY, the car is not going to stop..... I have seen people spend thousands of dollars and brakes and yet buy the cheapest set of tires that they could find in the sizes that they wanted. Those are the people I try to stay in behind of insted of in front of.
To make this a little clearer, Yes significantly larger front caliper pistion area will requier more volume and thus at the same original volume, the line pressure will be lower which infact will cause the rear pressure to ramp up fast depending on whats called the knee point of the proportioning valve. So yes, the rears could be comming on faster and stronger but at that same time those larger front calipers have more piston area and thus generate more clamping pressure at a lower line pressure.
There is a lot more to a brake system working correctly then just fluid volume and line pressure. Rotor diameter, and pad material play a significant roll in brake torque.
In the end brake torque that is being generated at the tire contact patch is what you want and need to know, and every part of the brake system and also tire diameter all play rolls in what that torque will be.
Also to note, a cars setup will dictate what kind of bias needs to be run. An example is if a car has been lowered and is running stagered tires sizes usually need more rear bias to be balanced correctly and so on.... A proper brake setup is actually more complicated then most think and really should be left to people that know what they are doing.
One last thing to note here is that brakes dont stop your car, your tires do and thus you can have the baddest brake setup in the world and if your tires are SH!TTY, the car is not going to stop..... I have seen people spend thousands of dollars and brakes and yet buy the cheapest set of tires that they could find in the sizes that they wanted. Those are the people I try to stay in behind of insted of in front of.
spf_lexus
Active Member
was reading about the rear brake bias with bigger brakes giving a "longer pedal" feel and wondered if thats why mine is? I have supra TT's but I also have 95 caliper/rotor in the rear. I figure it shouldnt change much given what you all have said since the OEM 1995-2000 has the same size fronts anyway. I have a long pedal...I have SS lines too in the front but could this just be a master cylinder issue? its oem w/ 200K on it, possibly needs a refresh?
JustenGT8
New Member
Thanks for the clarification Chris, you have explained the situation more clearly. The bias valve has done the trick for me a number of time now.
As for the long pedal, you need a bigger bore master cyl so you can move more fluid per pedal travel.
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