Why Don't Pro Race Cars Use Brake Boosters?

[@hpa101]

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[@gothicpagan.666]

At the higher level of build we use ABS modules. That takes care of brake balance under all conditions and variables. The driver then has a rotational switch with 7 (The most that seems necessary) settings usually programed with 2-3% between settings, which can be selected to suit different parts of a track, or help make the brakes at one end last to a pit window if they are running too hot or when swaping drivers, as each have their own slight preferences. We allways design the pedal fulcrum ratio at atleast 7:1, 9 or even 10:1 if mechanically possible and no servo is used. It all saves weight, but sometimes the drivers insist, if the pedal force required is too high. You can't say to them; "Don't forget leg day" They might take offence.

[@mm6705]

to be fair, pressing that hard with only one leg is terrible for the nervous system and pelvic alignment. There is no shame in designing a system that doesn't require one leg pushing 100+ pounds many times every lap. Anything that can reasonably reduce driver fatigue will produce more consistent laps, lower failure rates... usually faster laps too. I also highly doubt you use asymmetrical density lumbar and rear pelvic padding in the racing seat to account for the forces developed by the left leg. but surprise me. I do appreciate you sharing your racing knowledge.

[@gothicpagan.666]

@@mm6705 Force at the pedal rarely exceeds 30 Lbs, unless the driver has made a mistake. Pressure above 60Lbs is irrelevant as that would generate enough line pressure to lock the wheels, as such braking control is via the ABS valve/modulation frequency

[@bibnakladnistvo]

some single seaters (like some F1 cars) use wide brake pedals where you can hit them with both feet. I have seen 90kg pressure at the pedal in a simple junior formula car...@@mm6705

[@mm6705]

@@gothicpagan.666 Oh, so when the pedal is that heavy, it was an incorrect choice of parts? Between the mechanical advantage of pedal ratio and master cyl piston size you shouldn't need more than30 ish pounds? Thats good to know. I must have had incorrect conclusions from a past data point that was an outlier, thanks for educating me!

[@p0intdk]

This is a great video, but I end up with more question like what if I have ABS? Would dual master still be the way to go? and many other things

[@BySixa]

Folks, quick question for any commenters who know their stuff. 1. 6:1 Master cylinder with brake booster delete on the street. Bad idea or not? (Search chasebays). 2. Pedal box on the street. Bad idea or not? Car will likely be a 600hp rwd setup using 4 or 6 pot calipers, enlarged discs and relatively agressive pads. Intent of the above options 1 and 2 is for the following reasons: - improved brake consistency. - improved brake feel. The build is centered around fun and capable street performance while being good enough to do the odd trackday. It's difficult to ask these questions in mechanic groups or reddit without being laughed out of the place. I feel here, specifically this video, is most appropriate. Thanks!

[@ggud]

The chase bays master setup you mentioned looks interesting, but is very limited in scope of where it would be useful, in my opinion. In this video they mentioned a max pedal ratio of 6:1, but most cars and builders I personally know of have shot for anywhere from 7:1 all the way to 12:1 (off-road truck, more weight, etc). Also, a lot of those setups use smaller master cylinder bores to get a higher brake line pressure from the get go (7/8” to 1”). Rather than swapping a pedal or calipers it might be easier or cheaper (if you don’t already have the biggest possible options in the other areas) to just swap a master cylinder to get a different bore size to achieve your desired feel. That all in one setup might be perfect if the rest of your brake system matched those specs, and there is a bit of adjustment in the prop valve it has, but you’re limited to 6:1 pedal and 1” bore. If you know some specs on your car, there is a very handy calculator (just like the one mentioned in this video) that is extremely helpful and well put together at brakepower.com No ads, free, every variable is explained at the little “?” next to it, and more in depth than most street cars would ever need

[@BySixa]

​@ggud Hey, I've only just seen your comment. No idea how it escaped my notifications. Thanks so much for your reply! It is very helpful

[@RadDadisRad]

Interesting. I have a 1/2 ton truck that makes over double its factory HP. I have upgraded to Alcon calipers and rotors in the front but it doesn’t seem to be enough. I was looking at getting Jeep Trackhawk brakes adapted to my vehicle so that I can have a 15” disc with 6 pot calipers as I currently have a 13.6” disc. That means I’ll have to find a brake master cylinder that will work with those calipers.

[@supersayianjim2]

So maybe a track hawk booster/master combo then?

[@RadDadisRad]

@@supersayianjim2 kinda my thoughts, already balanced for the same size ish vehicle and caliper size.

[@stooartbabay]

Out of interest, can these be used on cars with rear drum brakes? Also, noobie question… is it street legal?

[@neversettle7666]

Can you define 'Doesn't seem to be enough'? Is it pedal feel and stopping ability, if so were the Alcons sized correctly for the master cylinder? Is it fade, if so do they have adequate cooling, pads, fluid?

[@RadDadisRad]

@@neversettle7666 the Alcons come with the Shelby F150. I upgraded to the Shelby braking system and it’s still not enough. Brakes get hot and start to fade slowing down from 130mph. I even have the most aggressive pads that I can find.

[@adematthewsracing]

Lewis Hamilton's brother Nic used a remote brake servo/booster setup in his BTCC Cupra as cerebral palsy means he can't apply high levels of pressure to the pedal for the whole race.

[@TotoGeenen]

What's the benefit of a dual master cylinder setup compared to simple installing a bias valve on the brake lines running to the rear brakes?

[@robair67]

For me, probably the most important thing is pedal feel at the limit of tyre adhesion. With a bias (proportioning) valve in line to the rear, the pressure your foot commands is the full unadulterated value to the front brakes and a proportionally lower value to the rear. That's all fine until you back off the pedal, to modulate traction (say into a tight corner in the wet, for example). As your foot marginally backs off and reduces line pressure, only the front brakes will experience that reduction, UNTIL the reducing line pressure equals and then drops below the bias valve setting. During that small period of time, rear brakes will give the impression they are dragging/binding. Technically, they are, and the lack of direct control over the rear braking effort can be really distracting! With a twin master cylinder setup, they won't be able to do that. That's one of several reasons to use twin cylinder pedal boxes.

[@TotoGeenen]

@@robair67 I see. That makes a lot of sense. Thanks you!

[@mm6705]

is there not a way to have a brake booster that has consistent performance in race applications? Like maybe not a traditional vacuum or pressure setup

[@bibnakladnistvo]

dont forget that the forces in the race car (throwing the driver around) are so great that is it hard to modulate a over servoed pedal.. you need less assistance to be able to modulate the pedal properly. Some cars, like rally cars, are driven with throttle and brakes at the same time, so vacuum servos just do not work..

[@Takeitlightly6]

The interviewers body language has drastically improved

[@tincandavexr4ti783]

They do use master cylinders… all race cars, even modern brake-by-wire systems, use master cylinders. The brake booster on the other hand, is usually ditched for race cars.

[@rebwar08]

You're saying the same thing the video was saying

[@kylelammie4621]

I really like Suspensions Explained's video on brake system calculations. First time I've seen it explained start to finish. kzbin.info/www/bejne/r3LcoKmsqMqEasU