How Much Better Are UK Rear Brakes?

[a98pmalcolm]

After some advice from scott regarding replacing one of my Jspec rear calipers due to seizing im highly considering getting some UK rear brakes as there bigger and duel piston not single.

 

Just asking people if they think there alot better? Is it worth £300 upgrading to used rear calipers or just replace the one siezing reat j spec caliper i have for £100?

 

Opinons?

 

Thanks

Paul

[Scott]

You can't put UKs on the back with Jspecs on the front bud. That would upset the brake balance farrrr too much. You don't want the rears braking better than the fronts in any situation.

[dr_jekyll]

dont do it mate . i took uks off the rear of mine and i have 4 pot fronts. too much braking at the back and when the rear goes light in a big stop you dont want it to lock . if it locks it will try to overtake the front. bare in mind the rear wheels have alot of breaking assistance from the engine

[Guigsy]

dont do it mate . i took uks off the rear of mine and i have 4 pot fronts. too much braking at the back and when the rear goes light in a big stop you dont want it to lock . if it locks it will try to overtake the front. bare in mind the rear wheels have alot of breaking assistance from the engine

 

you took uk rears off and put jspec rears on when you have uk fronts? are you saying toyota were wrong and 4 pot fronts and 1 pot rears is better? erm.....

[Scott]

you took uk rears off and put jspec rears on when you have uk fronts? are you saying toyota were wrong and 4 pot fronts and 1 pot rears is better? erm.....

 

 

He doesn't have UK fronts, he has 4 pot fronts

 

LS400 ones IIRC. Not quite the stopping power of the UKs, thus throwing out the bias.

[dr_jekyll]

He doesn't have UK fronts, he has 4 pot fronts

 

LS400 ones IIRC. Not quite the stopping power of the UKs, thus throwing out the bias.

 

what he said . knowbody mentioned uks and the striped out rear of my j=spec is alot lighter than the rear of a uk so if i did have uks a probably would have done the same in the name of balance.

[a98pmalcolm]

ahhh i see. ok guys thanks for the advice... Still learning with the supras and high performance cars.

 

So we need to make sure we have better brakes at the front before upgrading the rears..

[dr_jekyll]

ahhh i see. ok guys thanks for the advice... Still learning with the supras and high performance cars.

 

So we need to make sure we have better brakes at the front before upgrading the rears..

 

precisley. its never good to lock brakes but its alot safer to have fronts that lock before the rears. locking rears will turn you around

[Chris Wilson]

I wrote this years ago, may help:

 

Brake upgrades can set out to try to achieve several objectives.

The commonest are to increase resistance to fade and or increase

braking effort for a given pedal effort. IE, the pads are

pushed against the discs harder for a given pedal effort than

before the upgrade, or the brakes will stop the car from 100 MPH,

hard, for more times before fade sets in, than previously. The feel

from the pedal, that almost intangible quality, can also be addressed

and sometimes improved upon by brake size, or pad material changes, or

brake flexi hose upgrades to something less squashy than rubber.

It's easy to get carried away by the thought of brake upgrades.

The limitation in most cars as to how short a distance they can

stop in is tyre friction. Leaving aside pedal feedback, and fade,

it is almost certain that a Supra on stock Jap spec brakes will

stop in just as short a distance as one with an AP six pot kit on

it, a Brembo kit, Pauls KAD kit, or whatever. It may not feel to

the driver that it does, but usually such is the case if you just

nail the pedal as hard as you can. The fancy kits may *FEEL* to

stop the car faster, due to less pedal effort, and a better bite,

but in reality, if you hit the pedal as hard as you can with stock

Jap spec brakes, UK spec brakes, AP kit, KAD, whatever, the car

will stop in the same distance. Repeat this test 10 times and stock

Jap brakes may be on fire and long since faded, or the fluid boiled,

UK ones may be very hot and bothered, but the upgraded ones will

probably still be working within pad, disc and brake fluid temp

limits. Add in the intangible "feel" factor, and a desire to brake

as hard as possible, using as little skill as possible, but WITHOUT

relying on the ABS to take over, and for sure a well set up brake

upgrade may well allow more finesse.

 

Herein though lies the rub.

 

Upgrade only the fronts and the brake balance of the stock car may

well be compromised. Let's take stock brakes. You press smoothly on

the brake pedal with (say) 50 pounds force. The car stops fine. 70

pounds, the fronts are just beginning to lock (car makers ALWAYS aim

for the fronts to lock first, as rear wheel lock makes the car very

unstable and liable to swap ends). The rears are doing as much work

as the brake engineers deemed safe to prevent premature rear lock up.

The ABS cuts in, and maximum retardation has been reached. Now, take

a car with big front discs and calipers. Only 40 pounds pressure now

gives a smooth, lock free and powerful retardation. 50 pounds and the

new, more powerful, (for the same pedal pressure), fronts are locking.

The ABS cuts in. BUT, and this is the crux, those original rear

calipers and discs are still well below the caliper pressure where

they are able to achieve maximum retardation without fear of the

rears locking.

 

In other words the FRONT brakes are doing TOO MUCH work, albeit without

breaking into a sweat, and the rears are, to exaggerate a bit,

just along for the ride. The BEST scenario is to upgrade front AND

rear brakes, carefully ensuring the original balance of effort at any

given brake pedal pressure remains as designed, but that the more efficient

front AND rear brakes stay cooler for more hard stops, and that old

intangible "feel" from the brake pedal is improved, at lower rates of

driver effort on the pedal. The latter may or may not be good or

desirable, and can be engineered out by changing BOTH front and rear

caliper piston sizes, or pad areas. In a race car the balance would

be adjustable via 2 brake master cylinders, with a driver selectable

change in mechanical leverage effort between front and rear brake circuits,

one cylinder operating the front brake calipers, the other the rear. This

can also be achieved on road cars, but to do so is usually complex and

expensive, especially if ABS and brake circuit failure safeguards are to be

maintained. It is far easier to calculate the caliper and disc sizes, along with

pad area and compound to achieve this, as near as available off the

shelf equipment will allow.

 

Caveat. I said before makers engineer more effort on the front brakes to

encourage straight line stopping if the tyres are locked up . They err on

the excessive side, as, in the wet, the rear tyres can take a lot more

braking effort than in the dry, due to less weight transfer onto the front

tyres, as they will lock before as much weight is transferred when the grip

of the road surface is reduced. So adding yet more front brake effort worsens

this existing imbalance, especially in the wet. If it were not for the

ABS the front wheels would be locking up very early. On the Supra a

relatively sophisticated ABS allows some effort to be taken off JUST

the fronts, and an artificial and very inefficient balance is returned.

On cars with lesser (1 or 2 channel) ABS, or no ABS at all, a brake

upgrade on just one end of the car can be lethal.

[dr_jekyll]

i dont have bs chris, i found with the 2 pot rears any big stop coupled with a downshift or 2 would lock the rears as the front were still rotating due to the weight shift going forward. (track car only) . i found that running the 1 pot rear with the 4 pot fronts the car stays straiger in the big stops but even still the rears can lock before the fronts.

 

im in no way saying the front brakers arnt good enough as the car losses speed verry well . i just think that on the nose heavy supe the 1 pot rear coupled with the engine braking with the down shifts offer pleanty of stoping power on the rears. with the abs i can see where further complicatins can come in , but i dont use abs ......... because im a real man:cool:

[Chris Wilson]

Engine braking during downshifts on track?? Oh dear, I think I could find you a bit of lap time improvement there

[a98pmalcolm]

Nice post Chris, was a good read, some helpful info

[Chris Wilson]

Thanks, I wrote it years ago and keep meaning to tidy it up so it reads a little better, but never seem to get round to it

[dr_jekyll]

Engine braking during downshifts on track?? Oh dear, I think I could find you a bit of lap time improvement there

 

allways listening, please educate....

[Scott]

allways listening, please educate....

 

 

Never drove on a track in anything other than a go-kart but I'm going to guess it has to do with getting the balance spot on for the entrance and exit of the corner. Gearing down will throw the weight forwards and backwards with each change. Best to just dip the clutch, brake like a bandito while selecting your exit gear and blip the throttle when the time is right to lift

 

I take it you heel toe?

[dr_jekyll]

sometimes. i just grab the gear im going to need on the exit as im braking in a straght line on entry . i find it allows be to brake later and then im all set to focus on an apex and get on the pedal early .

[Scott]

sometimes. i just grab the gear im going to need on the exit as im braking in a straght line on entry . i find it allows be to brake later and then im all set to focus on an apex and get on the pedal early .

 

Is it fun track days you are on or serious ones?

 

You should be at the upper end of the power band of your exit gear, getting ready for a quick change and a full shunt of the beginning of the next gears power band. This would mean that engine braking should be impossible without over-revving the engine, using that particular method of course.

 

Could make up a bit of time as Chris said in this instance

 

That is for serious driving though, not for open trackdays.

[dangerous brain]

Replacement J-spec callipers £64 on brakeparts international mate.

[Guest wantthatone]

Is it fun track days you are on or serious ones?

 

You should be at the upper end of the power band of your exit gear, getting ready for a quick change and a full shunt of the beginning of the next gears power band. This would mean that engine braking should be impossible without over-revving the engine, using that particular method of course.

 

Could make up a bit of time as Chris said in this instance

 

That is for serious driving though, not for open trackdays.

hes very serious scott about it, this is'nt farting about on track days mate

[Westy]

You learn something new everyday! Good read!

[Ian C]

Never drove on a track in anything other than a go-kart but I'm going to guess it has to do with getting the balance spot on for the entrance and exit of the corner. Gearing down will throw the weight forwards and backwards with each change. Best to just dip the clutch, brake like a bandito while selecting your exit gear and blip the throttle when the time is right to lift

 

I take it you heel toe?

 

From what I understand of it, you want the driveline to be engaged as much as possible, so approaching a corner with the clutch in isn't the way to go. Probably a balance thing, or smoothness/rhythm - CW probably knows why.

 

The reason Craig is locking his rears up is because he's on the brakes hard for a corner and then applies a load of engine braking as well by downshifting. This asks too much of the rear tyres and they lock up. You heel-toe as you downshift in order to match the rpms to the road speed for the gear you are changing down into, and this avoids any engine braking. That means no shifting of the weight around upsetting the car, and no running out of grip on the rear tyres and locking them up. You should be in your exit gear before you turn the steering wheel into the corner - shifting gear mid corner will cause you to unbalance the car and slide/skid. If you can shift mid-corner and not slide, you aren't going fast enough

 

So the upshot is, you're sacrificing braking ability because you aren't changing gear in the best racing style. Loads of time to be gained, and also consistency.

 

Obviously there are some exceptions to this, like fast sweeping bends and gentle entry/exit sections. Also, caveat - while I know the theory I'm crap at putting it into practice

Edited April 22, 2011 by Ian C
forgot a bit (see edit history)

[marc_p]

Heel and toe is what Chris is on about, it's kinda tricky to get used to at first to get it right but once you have it spot on you will notice a difference, to program it into you though, just try and get into the habit of doing it all the time that's what I did and eventually I just found myself doing it without thinking about it, but I do it everywhere now it's just how I drive and is as natural as changing gear.

[Jellybean]

Can somebody give a break down of best practice technique for what to do before a cornor ,entry, in transition, exit. I tried heel toe once or twice but found my feet difficult to stretch across the break and accellerator , I am size 11 . Maybe I am doing it wrong? How do people cope with twin and triple clutches while racing, must be tough with a heavy pedal

Edited April 23, 2011 by Jellybean (see edit history)

[Jellybean]