Upgrading brakes. All at once?
Discussion
Hi guys
I have just purchased an e61 5 series for the daily grind and the rear discs and pads are about 2-3k away from needing changing, but there is recent history of a front disc/ pad change. iDrive reports 38k until replacement.
So, I'm thinking of going for some more performance oriented braking, perhaps some drilled/ grooved discs and performance pads. My question is, is there any issues with upgrading the rear, running it until the front run out and then upgrading the fronts? Or is it advised to do the whole lot at the same time?
I have just purchased an e61 5 series for the daily grind and the rear discs and pads are about 2-3k away from needing changing, but there is recent history of a front disc/ pad change. iDrive reports 38k until replacement.
So, I'm thinking of going for some more performance oriented braking, perhaps some drilled/ grooved discs and performance pads. My question is, is there any issues with upgrading the rear, running it until the front run out and then upgrading the fronts? Or is it advised to do the whole lot at the same time?
No you can upgrade axle by axle as I assume the car has some auto brake distribution.
Not sure it's worth spending that much on the rears though.
Not actually sure it's worth spending that much at all actually, depending on how you use the car. The limiting factor often is front tyre grip.
Not sure it's worth spending that much on the rears though.
Not actually sure it's worth spending that much at all actually, depending on how you use the car. The limiting factor often is front tyre grip.
On almost all modern cars, the rear brakes are over-designed. This is because the electronic brake distribution sends far more pressure to the rear under low decelerations (where there is little weight transfer off the rear so sufficient grip), in an attempt to reduce front wear.
As a result, you'll gain nothing at all by upgrading your rear brakes - they're far from the limiting factor in a full-anchors stop, where they are probably only using about half of their capability as the higher weight transfer means they are sent less pressure and do less work.
ETA - If you do insist on upgrading the rear brakes - even if you were on track day rubber I don't think you'd need to - then it depends on what EBD system the car has. If it will automatically detect the decelerations generated for a given line pressure and adjust its distributions accordingly, then you'll be fine whatever you do, because it will fix the distribution for you. This seems unlikely, though, and it's quite possible that it won't be able to operate properly if you change the effective diameter of your disc. For that reason wouldn't recommend fitting larger discs at one end of the car only, as you might foul up the brake distribution.
As a result, you'll gain nothing at all by upgrading your rear brakes - they're far from the limiting factor in a full-anchors stop, where they are probably only using about half of their capability as the higher weight transfer means they are sent less pressure and do less work.
ETA - If you do insist on upgrading the rear brakes - even if you were on track day rubber I don't think you'd need to - then it depends on what EBD system the car has. If it will automatically detect the decelerations generated for a given line pressure and adjust its distributions accordingly, then you'll be fine whatever you do, because it will fix the distribution for you. This seems unlikely, though, and it's quite possible that it won't be able to operate properly if you change the effective diameter of your disc. For that reason wouldn't recommend fitting larger discs at one end of the car only, as you might foul up the brake distribution.
Edited by McSam on Tuesday 26th February 12:15
Kozy said:
Uprated discs won't affect anything bias-wise, but pads may do. As McSam points out, if the pressure/torque relationship changes (through increased pad friction) then the EBD/ABS may not work as effectively.
Surely if you change the disc effective radius, that'll change your wheel torque for a given clamp force? This won't be expected by the EBD system. I agree that changing the discs within the same size won't matter, though.I didn't mention pad friction coefficient as it seems to vary wildly anyway
McSam said:
Surely if you change the disc effective radius, that'll change your wheel torque for a given clamp force?
You are correct, however people rarely increase the disc size without doing a 'BBK' of some description, which will usually incorporate a caliper change also. Since he only mentioned discs and pads, I assumed standard sized stuff and stock calipers. Digitalize said:
I'd just do fronts, unless going significantly bigger than standard the rears will be fine. Under hard braking the rears won't be doing much anyway, as all the weight will be on the front.
Usual misconception. The rears typically contribute about 20%, I wouldn't call that insignificant, especially in an emergency. They also do more for stability and handling, than outright stopping force.
Kozy said:
Usual misconception. The rears typically contribute about 20%, I wouldn't call that insignificant, especially in an emergency. They also do more for stability and handling, than outright stopping force.
I did understand that, probably what I should have said is that they aren't at their limit so need upgrading. In my car upgrading the rear brakes actually makes it worse until you fit a brake bias.Digitalize said:
I did understand that, probably what I should have said is that they aren't at their limit so need upgrading.
That's a fair one. The trouble is, while they aren't at their limit (either in terms of force/grip or heat capacity), not upgrading them in line with the fronts in terms of force reduces their effectiveness through increased front bias. Overall, the total deployable braking force reduces, if the tyre friction remains the same.Interested to how it makes your car worse. Have you tried, or is it more common knowledge for that model?
Kozy said:
Interested to how it makes your car worse. Have you tried, or is it more common knowledge for that model?
It's common knowledge, its a Fiesta Mk5 Zetec S, has drums on the back, if discs are fitted without a bias the rear braking becomes too strong and has a tendency to try and lock up and kick the back end out, especially if you remove the ABS system at the same time.Digitalize said:
It's common knowledge, its a Fiesta Mk5 Zetec S, has drums on the back, if discs are fitted without a bias the rear braking becomes too strong and has a tendency to try and lock up and kick the back end out, especially if you remove the ABS system at the same time.
Well that's not normal, drums are inherently far more powerful than discs, they usually require far less pressure than discs due to the way they self-servo. Must have been some weedy assed drums they were using on the car as stock?Case in point, there's a vendor on a prominent US Honda forum that sells brake kits, the guys runs a full NSX brake swap on his personal Civic with the OE drum prop valve and he says he's never locked up the rears, and the braking is fantastic. The NSX rear brakes are somewhere in the order of 140% stronger than the most powerful FWD brakes Honda were using at the time, and the front brakes are actually less powerful than some of the offerings on the likes of the ITR, as to be expected between a 60/40 and a 40/60 weight distribution. So essentially he fitted a brake system that should have been dangerously rear biased, and yet it just worked...
Not saying you're wrong at all, just bizarre how the Fiesta brake swaps work the opposite way... What car are the rear disc swaps coming from?
Kozy said:
Well that's not normal, drums are inherently far more powerful than discs, they usually require far less pressure than discs due to the way they self-servo. Must have been some weedy assed drums they were using on the car as stock?
Case in point, there's a vendor on a prominent US Honda forum that sells brake kits, the guys runs a full NSX brake swap on his personal Civic with the OE drum prop valve and he says he's never locked up the rears, and the braking is fantastic. The NSX rear brakes are somewhere in the order of 140% stronger than the most powerful FWD brakes Honda were using at the time, and the front brakes are actually less powerful than some of the offerings on the likes of the ITR, as to be expected between a 60/40 and a 40/60 weight distribution. So essentially he fitted a brake system that should have been dangerously rear biased, and yet it just worked...
Not saying you're wrong at all, just bizarre how the Fiesta brake swaps work the opposite way... What car are the rear disc swaps coming from?
The entire braking system is pretty terrible as standard.Case in point, there's a vendor on a prominent US Honda forum that sells brake kits, the guys runs a full NSX brake swap on his personal Civic with the OE drum prop valve and he says he's never locked up the rears, and the braking is fantastic. The NSX rear brakes are somewhere in the order of 140% stronger than the most powerful FWD brakes Honda were using at the time, and the front brakes are actually less powerful than some of the offerings on the likes of the ITR, as to be expected between a 60/40 and a 40/60 weight distribution. So essentially he fitted a brake system that should have been dangerously rear biased, and yet it just worked...
Not saying you're wrong at all, just bizarre how the Fiesta brake swaps work the opposite way... What car are the rear disc swaps coming from?
Usually a Fiesta ST or Racing Puma (More Expensive though), they just make the back end a lot twitchier, I've seen and felt it in action, where a drum'd car is more stable underbraking than a disc'd one.
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