Author Topic: Track day brakes  (Read 8929 times)

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Doug Gould

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Re: Track day brakes
« Reply #15 on: September 30, 2017, 09:07:07 PM »
The standard 156 brakes should be adequate for club track days. If the brakes can lock the wheels (activate ABS) then they are effective enough. The rest is about fade. Use good fluid. Standard should be adequate, but I'd use Motul 600. Most people don't spend enough on pads. I've found Ferodo 2500 pretty good. If you need a higher friction co-efficient, try Ferodo 3000. But 2500 has nice feel. Endless Type R are good. I use them on the front of my GTV6. Or Pagid. I think the Pagid Orange are similar to Ferodo 2500. Get them all from Barrie Smith Motorsport.
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warsch

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Re: Track day brakes
« Reply #16 on: October 03, 2017, 10:48:21 AM »
I have a "set" of 330brembos, rotors, uprights, GTA steering idler arms with new hub bearings and 2L hubs pressed in - built and available, complete plug and play. They came off a GT and were destined for sooty but the hubs (splines) supplied were not correct, and I can't be arsed pressing them out and getting new hub bearings again. Make me an offer, they're in Brisbane, sitting in the shed, gathering dust, looking forlorn and shiney

Thank's for the offer. I'm really tempted but I am confident that I don't need GTA brakes to improve my track results. That is a nice upgrade but as of now the standard brakes (with new fluid, braided hoses, and better pads) are sufficient for my skills and standard 2.0 engine. I'll keep your offer in mind in case I would have some spare cash to go for the bling factor.

johnl

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Re: Track day brakes
« Reply #17 on: October 03, 2017, 01:03:55 PM »
Also you will pretty quickly learn that in an underpowered car like a 2 litre Alfa the worst thing you can do at the track  is PUT YOUR FOOT ON THE BRAKE PEDAL. A good lap time is usually always predicated  on slow in fast out ( not the other way around)  and maintaining as high a corner speed as possible.

I think the first sentence of this is an odd way to look at it. I agree with the rest (though 'slow in' means the fastest entry speed compatible with maintaining the fastest corner speed without loss of speed in the corner due to having 'overcooked' it...).

Some thoughts on brakes:

Limiting brake use will badly affect lap times. ‘Slow in’ can only occur if you can slow the car down from speed, so regardless of how powerful the car may be, hitting the brakes hard has to happen. You need to be on the brake for the shortest distance possible, which means as hard as possible, for the shortest time possible.

Keep in mind that in racing you not only need good brakes for lap time, you need to be able out-brake other cars going into corners (or at least not get out-braked by other cars). This puts a lot of heat into the brakes, a lot more than braking earlier and for longer.

Braking more gently for longer means you’ve started braking earlier and from a lower speed (and likely been out-braked by someone with better brakes...), so there is less kinetic energy to convert into heat, so it’s easier on the brakes but does nothing for the lap time (or in the braking duel...). Braking harder for a shorter distance and time puts more heat into the brakes more quickly, and the brake has to be able to cope with that.

The brake has to be able to cope with whatever heat it is going to experience for the entirety of the event in which it is competing, and this means that the pads must be fit for purpose. Fit for purpose means that the pad shouldn’t give off excessive gas at the temperature it will experience in use. Excessive ‘out-gassing’ means that so much gas is coming out of the over-heated pad that it creates a high pressure gas layer between the pad and the rotor, which effectively acts as a very efficient lubricant. This is the dreaded ‘pad fade’ and can occur abruptly, and can cause dramatic braking loss, but the pedal will still be firm (this is quite different to fade caused by boiling fluid, when the pedal will go soft, maybe even all the way to the floor).

A given brake can be improved with pads more suitable for higher temperature, but the temperature can also be reduced. One way to assist this is to duct air to the brake. If this doesn't work, or higher temp pads don't work or can't be found, another way is to increase the size of the brake. Note that the pads get hot from friction, but that very little of this heat can escape from the pad directly into the environment, the vast majority must conduct into the rotor, and from the rotor is dissipated into the environment.

A larger rotor will not only have a larger thermal mass (all else being equal), so can absorb more heat before it gets too hot (for the pads to quickly enough dissipate enough heat into), but more importantly it will have a larger surface area, and therefore will be able to dissipate that heat more rapidly (radiate it into space, and conduct it into the air passing over the rotor), so the rotor will heat up more slowly during brake application and cool down faster after brake application (and so keep pad temperature down).

Larger pads will remain somewhat cooler because there is X friction acting over a larger pad area (i.e. more pad absorbing X heat), and pad heat will transfer more readily via the larger pad area into the rotor (from where it will be dissipated into the environment). The pads still rely on the rotor to dissipate the heat, so a smaller rotor will be a ‘heat bottleneck’, and even larger pads will still get too hot (maybe just not quite so quickly).

Of course bigger brakes weigh more. This is static mass added to the cars overall weight, but more importantly it is both rotational mass and unsprung mass. Increased unsprung mass means that the suspension mass is a bit harder for the dampers (shock absorbers) to control, and may affect handling significantly (probably not enough to really be noticeable on a road car, but a difference that may show up on the stop watch with a track car).

Rotational mass has more affect on acceleration than does static mass (think of the rotors as if they were flywheels), so there will be a slight impact on acceleration (again probably a non issue for a road car, but maybe significant on the track). Conversely, once at X rpm, rotational mass is harder to slow down when braking, so will add heat stress to the brake, but the greater heat dissipation of the larger brake should / ought to more than make up for it.

So, it can depend on how the track car is being used. For a lap dash or hill-climb then bigger brakes may do more harm than good, because a smaller / lighter brake with well chosen pads may never overheat. For circuit racing, where the brakes get hammered over and over for many laps, bigger brakes, within reason, are nearly always better. Everything is a compromise.

Of course minimising heat will also minimise heat in the fluid. As has already been said, contaminated fluid will have a lower boiling point due to absorbed water, so no matter what the fluid must be at least reasonably fresh.

For a road car, an important consideration is that large wheels and tiny little brakes just look ridiculous. Who has not noticed all those hoony cars with 20” wheels and tiny little stock brakes, lost in the void...

Regards,
John.
« Last Edit: October 03, 2017, 01:21:17 PM by johnl »

johnl

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Re: Track day brakes
« Reply #18 on: October 03, 2017, 03:56:20 PM »
More thoughts on brakes:

Apart from stopping hard and resisting fade, another important aspect of how brakes function is how they feel. A firm pedal with a predictably consistent travel improves brake feel, inspires driver confidence and makes it easier to heel / toe accurately and consistently.

Rigidity in the entire system is important. It’s essential that all the pedals, brackets etc. be as stiff as reasonably possible (an example; CB7 Accords are known to flex the bulkhead slightly - where the master cylinder attaches - when the pedal is pushed hard. I added a brace abutting the end of my Accords' MC which made a noticeable improvement to pedal feel, albeit relatively slight).

It’s also important that the hydraulic tubes and hoses don’t expand excessively with high fluid pressure . The metal tubes are OK, but stock rubber hoses generally do expand appreciably and contribute to unwanted pedal travel and a feeling of sponginess. Nylon (?) hoses reinforced externally with a braided metal sheath are typically significantly less prone to swelling under pressure than stock rubber hoses, and the main reason they are so commonly used on racing cars. However, it’s my understanding that to fit them to a road registered car will require official approval and an engineers’ report (?).

Callipers can (do) suffer from flexure as well, and are a source of pedal sponginess. The piston or pistons exert a lot of force, which tends to elastically ‘spread’ the calliper away from the rotor. The stiffer the calliper the better, but as a general rule a stiffer calliper will be heavier. Callipers with pistons on only one side of the rotor (i.e. sliding pin callipers) tend to be less rigid than callipers with opposed pistons (and no sliding pins), but it’s my understanding that this is not a given.

If there is an opposed piston calliper that can be fitted in place of the sliding pin calliper, then this is likely to be a significant improvement. Is the GTA front calliper an opposed piston design? I don’t know, but if it is then it would be worth considering I would think. At the same time you can take advantage of fitting the larger diameter GTA rotors (would probably have to). Such a modification may or may not require an engineers’ certificate, since the parts are available on another version of the same car (...?). If I were a bit less cash strapped at the moment I would seriously consider researching this a bit more deeply with a view to upgrading my own front brakes (mostly in an attempt to gain a more consistent pedal, I think the car actually stops OK as it is).

I suspect it’s less likely that there might be an easily fitted / adapted opposed piston calliper for the rear brakes, probably because the calliper also needs to incorporate a handbrake mechanism. I think it’s less of an issue with the rear callipers because it’s likely that the rear brake line pressures will be quite a lot less than the front line pressures (?), so spreading of the rear callipers is likely to be a less significant issue.

Even slightly worn wheel bearings will cause a lot of pad ‘knock-off’, which is a bad thing for a consistent pedal.

Regards,
John.
« Last Edit: October 03, 2017, 04:11:14 PM by johnl »

bazzbazz

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Re: Track day brakes
« Reply #19 on: October 03, 2017, 10:42:31 PM »

If there is an opposed piston calliper that can be fitted in place of the sliding pin calliper, then this is likely to be a significant improvement. Is the GTA front calliper an opposed piston design?

Yes, the 147 GTA has 4 pot Brembos  (2 pistons acting on each side of the disc/rotor)

And I can attest to their stopping power. 
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aggie57

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Re: Track day brakes
« Reply #20 on: October 03, 2017, 11:45:06 PM »
John, with all due respect Paul's point about limiting brake use in a standard car is perfectly valid.  Braking is only part of the equation in fast lap times, in lower powered cars especially.  Momentum is the key to fast times.  You have to maintain momentum.   Let the car slow down to much and its oh so hard to get back up to speed. 

For sure there are places on most tracks where hard braking is required, Dandenong Rd at Sandown for example, a very hard brake in any car.

Personally I reckon if your right foot isn't sore after a few laps in a standard Alfa you're not trying hard enough.  Not from braking, but from mashing that gas pedal into the floor as often and as hard as you can!
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warsch

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Re: Track day brakes
« Reply #21 on: October 05, 2017, 01:02:09 PM »
Thanks for all the input. Braided hoses are legal in QLD, especially if they're ADR approved, as far as I know. I still believe that GTA 4-pot upgrade is not worth it for me now. But either way, I still would have to choose brake pads.

Domenic

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Re: Track day brakes
« Reply #22 on: October 05, 2017, 05:19:20 PM »
Why not give Cameron @ Automotion a call, he's racing an Alfa 147 at the moment, he'd be able to recommend you some pads.

Campbeli

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Re: Track day brakes
« Reply #23 on: April 12, 2021, 07:18:08 PM »
old post i know - but i'm looking at changing pads on a 147 for track work. Ferodo DS2500. Is there a local supplier? All I see  is EB Spares.
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Colin Edwards

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Re: Track day brakes
« Reply #24 on: April 13, 2021, 09:25:27 AM »
Call Maranello Pursang - 03 93869650.  They supply the FERODO race pads for our FF. 
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warsch

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Re: Track day brakes
« Reply #25 on: June 15, 2021, 07:39:24 PM »
Revining an old post of mine.

So first year I was running EBC Yellowstuff in standard calipers, the next year Ferodo DS2500. Both are fairly good, they work on the street when cold and then are good enough to last the usual 15 minute sessions. Have adequate power to stop 2.0 car.

This season I put in Mito Brembo calipers (which are 100% bolt-on, even the brake hose fits) with 305mm rotors (as on GTAs) with circo m119 full racing pads. Well, this setup is obviously great.

Alfatango

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Re: Track day brakes
« Reply #26 on: August 15, 2021, 10:18:33 PM »
I have run ebc blue stuff and yellow stuff and would  recommend both even for street cars. Even in the middle of winter the blue stuff are fine. I am trying the ferodo ds2500 soon so will have something to compare to. The ebcs seem cheaper as you can buy them from ebc directly.

I cant tell much difference between an OEM brake disc and a slotted after market one.

I will be trying some braided brake lines soon so see if that makes a difference.
 
« Last Edit: August 15, 2021, 11:24:26 PM by Alfatango »
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johnl

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Re: Track day brakes
« Reply #27 on: August 16, 2021, 08:37:37 PM »
I cant tell much difference between an OEM brake disc and a slotted after market one.

All else being equal there will be no difference between slotted and unslotted discs, at least not in normal use. A difference will exist only when the pads get very hot, and produce lots of 'outgas' (essentially pad smoke, though not all the gas will be visible). If the pad outgas can't escape from between the pads and disc faces rapidly eniough, then it can prevent the pads maintaining proper contact with the discs, and the friction surfaces effectively become lubricated by the pad gas. This is called 'pad fade'.

Disc slots permit 'outgas' to more easily escape (compared to unslotted discs), so the brakes work better at high temperature even when the pads are substantially outgassing. Disc holes do more or less the same thing, as long as the holes are open to the internal vent voids (allowing the gas to escape to the interior spaces of the disc).

Regards,
John.

warsch

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Re: Track day brakes
« Reply #28 on: August 17, 2021, 09:36:54 AM »
Well, the whole topic is about track day use, so I wouldn't call it normal use. Though I think the difference between rotors would be negligible even then.

Same with braided hoses - I can't tell the difference between regular hoses and steel braided.

Pads make all the difference, backed up by proper brake fluid.

Alfatango

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Re: Track day brakes
« Reply #29 on: August 17, 2021, 12:26:18 PM »
Yeah I find a great set of pads usually around $150 to $200 a corner, proper brake fluid that is bled and good condition tyres makes the most difference to braking. Worn tyres affect the brake pedal feel. Slotted discs arent that much more than OEM so I use them as well.

What brake fluid is everyone running? I just purchased the Penrite Racing Brake Fluid 600 Dot 4.
« Last Edit: August 17, 2021, 01:20:18 PM by Alfatango »
156 2.0 TS Track Car

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2x GT 2.0 JTS Selespeed