The AP Racing big brake kit?

[steve b]

That's interesting to know.

I have bought a CAD program and plan on teaching myself and making some brackets (have a slight issue of a Haematology MSc to pass before I start that distraction  :-) :-) :-)  ) 1st little project I think will be extender brackets for the standard calliper so I could stick some alloy belled Elise 288mm discs on the rear.

The thing to find would be a twin pot that has a cable handbrake then just make an adapter bracket to fit to whatever sized discs you want  :-) :-) :-)


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[dj2k21]

Twin pot with cable handbrake would be a bmw e30 then  s:) s:)

[steve b]

Just been looking and they appear to be single piston sliding caliper like our stock ones?


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[dj2k21]

Hmmm maybe it's e36 . I shal have a look

[steve b]

http://www.bigbrakes4u.co.uk/hi-spec-brakes/hi-spec-rear-sva-brake-calipers/hi-spec-sva-ultralite-2-sierra-lug-handbrake-caliper/prod_1306.html

Looks like HiSpec do a load of MOT passing rear calipers (to be properly MOT or SVA legal you need a cable operated handbrake).


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[jonty]

Steve I think I saw from your build thread that you had bought these brakes, but only just seen this thread.

The important thing is the ratio of master cylinder piston area and caliper piston area, as this determines the force on the pad. Pad area is largely to do with heat dissipation and has little bearing on force applied to the disc, since the larger the pad the lower the pressure over its surface, so overall braking effort is the same regardless of pad size.

The size of the 4/6 pot total piston area of an aftermarket caliper relative to the original single pot (x2 because it slides and acts as a twin) won't always be changed, but where it is changed this is most likely where any stopping distance improvement comes from (or conversely the problems other people mention if the calcs are incorrect/not done). This is because if the front to rear bias can be optimised to get all 4 tyres loaded to their maximum at the same time then this  - as I'm sure you and most reading this know - results in best performance. If one end of the car locks first then the other tyres aren't working to the maximum and so the stop is slower. The reason it may not be optimised as standard by the OEM is because under normal braking conditions people use maybe 20-30% of the braking capacity, so there is only 20-30% of the load transfer to the front- so I would expect most systems as standard to be overly rear-biased when viewed from a peak performance point of view.

have a look at these http://www.phatboybrakes.com/PB-product-reviews.php Performance Ford magazine pages from "Phatboy Brakes". They are a manufacturer much like K-Sport. My theory is that the reason they see the improvement through each of the stages is that the front bias is being improved each time, so all 4 tyres work equally well.

You'll probably find the piston sizing and disc diameter of your K-Sports give slightly higher area and torque, so it should be quite easy to calculate how much change has been introduced from the disc diameter, and how much from the piston area. Do you fancy getting the vernier calipers out to get some rough sizes for us?

[steve b]

I shall get measuring  :-) :-) :-)

[steve b]

The K Sport 6 pots have 2 x 34mm & a 24mm on each side of each calliper.


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[jonty]

The K Sport 6 pots have 2 x 34mm & a 24mm on each side of each calliper.

cool, that's equivalent to 53.75mm single slider/twin pot diameter.

Disk is 285mm, yeah? Any idea on pad depth? So I can calculate torque compared to stock

anyone got stock size piston/pad measurements for comparison?

[steve b]

Hi, pad is 132mm x 50mm, disc is 286mm.

Steve


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[steve b]

Stock front 116.6mm x 47mm, 255mm disc  :-) :-) :-)


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[jonty]

13% more torque from disc diameter, let's see what the stock piston dia is to get a full comparison  s:) s:)

[steve b]

 m http://www.frenkit.es/docs/caliper.pdf m

Doesn't say year but MR2 fronts are 36mm or 51mm.

Rear 44mm.


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[jonty]

only one I can see is 51mm, sounds about right  s:) s:)

that gives 11% more force at the piston, plus 13% more torque equals 24% more front braking effort. That's quite a change!

*EDIT*
assuming equal bias as stock, and then front +24%:
1:1 = 1/(1+1) = 1/2 = 0.5 = 50% front
1.24:1 = 1.24/(1.24+1) = 1.24/2.24 = 0.55 = 55% front

so actually only 5% bias shift....

I'm looking forward to seeing your results on track Steve!

[jonty]

ok from rear piston and disc sizes I get:

Stock bias 55.4% front
k-sport bias 61.3% front

[steve b]

Thanks for the info Jonty  :-) :-) :-)  sounds like it will be fine.

[jonty]

yeah it sounds a sensible sort of figure. Static balance is 44.4% front from some measurements I saw in a quick search (480kg:600kg with driver, 20kg of tools and 1/2 full tank), so a 15% dynamic transfer doesn't sound that wild.

Jonty

[steve b]

[jonty]

Are these on yet steve? Some initial thoughs? And if you have a weight for the caliper i'd be interested to hear!

[steve b]

Not on yet as the cars over at Nickson Motorsport, the calipers weigh :-



plus the adapter bracket.  Don't know what a standard caliper weighs, if steel which I think they are I'd have thought more.

[jonty]

Cool, that's pretty light! It'll be good to see them fitted to the car and also what Nickson has done  s:) s:)

[steve b]

Nicks works going to be quite limited, posted about it here :-

 l viewtopic.php?f=7&t=39442&start=30 l


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[jonty]

ah yeah, I've just had a look- I'm happy to ditch the softop and also can trailer the car about if need be, so can drop the tank before getting this sort of work done- I have a cage in my 200sx and it makes such a huge difference to how it drives I don't think I'll ever have a track car that doesn't run a full cage on it's required modifications!

keep the posts coming in your build thread mate, it's cool to see progress!

[steve b]

Going to wait until after next track day before I give judgement on if front upgrade only works or not.  Braking feels MASSIVELY more powerful at the front, only need very gentle pressure on the pedal (with old calipers and Carbotechs if I stamped on the pedal and tried to push it through the floor in the dry it wouldn't lock up).  Now bit to hard on the pedal and its ABS galore, but on road I don't really have a reference point on if less pressure pulls the car up as fast.  On my local track I will be able to tell easily as I know exactly where my old braking points were.


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[steve b]