Standard brakes compared with upgraded.

Hi all, maybe some of you will be interested in the attached figures.
In thinking about upgrading brakes, I wanted to try to quantify the more important parameters and look at the percentage improvements that might result.


Using Mathcad, I based the calcs on my cars cylinder and piston size / pedal ratio / disc size / pad area / wheel size / car CG height etc etc.
The calc method is based on solving brake balance and pedal effort required to get both front and rear tyres at the limit of braking for a given braking system.
In practice the balance would need to be a bit further to the front to avoid skipping of the rear.

The basic parameters are pedal effort, heat dissipation per unit pad area and line pressures, lots of other stuff is calculated along the way too, but I have just tabled the basic ones in the attached file. It's a work in progress, for example I dont have exact piston diameters for the standard calipers (think they are 1.75"), and the most difficult thing to quantify is the cg height (I guessed 15") but I think it gives a reasonable idea of what the effects are.

I have already removed the servos from the car and done a track day without, so I know that among other things I need to reduce the pedal effort, my rear pads also wore out, while the fronts are still useable, a consequence of using a rear brake setup sized for a front heavy car.

The cases I have used are based on keeping my 15" wheels, but I think the 315mm disc would be too big to fit, so I compared with a 295mm disc too. The small size CP5000 caliper has a smaller pad area than the standard front, increasing the heat dissipation per pad area, so the medium size caliper is a must for the front.
So with the options I have used, I am seeing a predicted reduction in pedal effort of around 45%, and a reduction in heat dissipation per pad area of 15%(front) and 33% at the rear. Bigger improvements would of course be available with larger discs / calipers in 17" wheels, maybe I'll look at those later.
Any comments suggestions (clean ones anyway) /ubbthreads/images/graemlins/grin.gif welcome.
regards
Dave

Dave
You may be interested in this.

Dave

Thanks Dave, I'll play with that one too, see how they compare. /ubbthreads/images/graemlins/smile.gif
regards
Dave

[ QUOTE ]
The cases I have used are based on keeping my 15" wheels, but I think the 315mm disc would be too big to fit

[/ QUOTE ]

Hi Dave -

Speak to Roy Smart - 315mm into 15" can fit (4-pot Alcons) and looks great too! /ubbthreads/images/graemlins/smile.gif

Dave Gilling,

Very useful attachment, Thanks

Andy Besic

Thanks Paul,
I see that the Alcon calipers do add a very small radius over and above the disc because they are open and use the two 'bridge bolts' to maintain rigidity. I think that is similar to the Willwood superlights mentioned in other braking posts. I can see why running without the bridge bolts would allow caliper flex and resultant pad wear and braking problems.

In talking to BG developments, I think that I had underestimated the piston size in the Granada fronts, I have a new size of 2 1/8" If anyone can confirm the correct piston diameters for the front and rear calipers I would be grateful.

Using the new size changes the balance and effort figures for the standard setup, and suggest that my brake balance bar needed to be set well to the rear to get the rear brakes doing any work.
That does agree with my experience since I wound the balance a long way back, still did not lock up back wheels, and wore the rear pads out v quickly.

BG developments are sending me a catalogue so I can check dimensions properly and said that they can add a handbrake attachment with separate pads to the rear calipers, although that would add to the cost. It is used on Aston Martins and the like. The description given reminded me of the handbrake on a Jag XK150 - two cable operated levers with pads pivoted at the end of the caliper and squeezing the disc when applied.
Although no one has yet said they used BG developments, they do say they have supplied brakes for both replica and original GT40's.
regards
Dave

BG have been around a long time; I last dealt with them 15 years ago. They know their stuff but can be quite slow when a custom setup is involved. I now do all this design/machining myself which makes them look expensive.

Colin Artus

Alcon caliper as fitted to Roys Mk1 - an older photo as disc size was then smaller. /ubbthreads/images/graemlins/smile.gif

Bob Green supplied my AP brakes & also fabricated my bells & brackets. I found him to be very helpful & full of usefull information. His machining is top quality & most operations are carried out 'in house'.

I'd be happy to reccomend his services. /ubbthreads/images/graemlins/grin.gif

Bill - I have taken some pics of Roys new setup with 315mm discs and he is putting some words together re the process and what needs to be considered. Once complete I'll email you the pics + text - regards Paul

ps - here is a current pic of front nearside setup.

Paul, if it is not too much trouble, I would be interested in the pictures and text as well. Thanks

Dave, are you saying that the GTD/Granada standard master has a 5/8" bore diameter?

Would anybody know what the stroke might be for a "granada" master. If it isn't from a granada then what is it?

Also does anybody know what the total Vac. boosted peddle ratio on a standard GTD setup might be? I'm guessing about 5 or 6 to 1, Without booster looks like about 3 to 1.

Thanks, H Jones

Hi Greg - no problem. Once I have the text I'll forward it + pics. /ubbthreads/images/graemlins/smile.gif

Just catching up here guys, I'm in Hongkong this week and only just managed to log in.
Thanks for that Paul can't access my email at the mo for some reason, but look forward to seeing that info. Last week I sent in data to BG Developments, Alcon and Hi Spec, so hope to catch up with that when I get back.

Howard, I dont know what the standard Granada bore is. My pedal box is a Tilton and has 5/8" front and rear mcyl bores.

regards
Dave

ps Hope you aren't too snowed in in the uk but it's not much better here, haven't seen the sun in the 4 days I've been here!

Sun? Que?

I have been experimenting with the ‘MikesBrakes’ Spreadsheet (thanks Dave it’s a great help and thought provoker).

I have the advantage of some actual braking figures taken as part of the SVA test - I knew there had to be a silver lining /ubbthreads/images/graemlins/smile.gif

E.g.
Weight 1306Kg with driver (80Kg) 600 front, 706 rear
Weight distribution @ 10% deceleration, 43% front
Weight distribution @ 37% deceleration, 51% front
Front maximum brake force with servos 573 Kg, rear 456Kg
Front maximum brake force without servos 573 Kg, rear 229Kg
(theoretically servos are rated at 1.9 times which seems about right)
Notice front is unchanged – the tester did comment on this, now either he made an error by not reseting something (unlikely) OR the fronts can lock the wheel without the servo (probable?)
GTD pedal ratio is very close to 4:1, so total ration with servos a healthy 7.6:1 for 7 stone weaklings!

I have also done a COG calculation by weighing some items I can (wheels etc) an estimating others. On my GTD it comes to around 17” however the actual COG of the engine and chassis make a large effect and these are estimated. The engine centre I guessed as the camshaft (seemed reasonable after staring at it for some time!). The chassis I thought at sill height (15”) but this might be on the high side. I think I would err on the high side as I am a bit paranoid of having too much rear braking in the wet!!

At the moment I amended MikesBrakes sheet which I will share but ideally need to tidy it up, unfortunately I do not have the password for the file, anyone? Or must I remake it all?

QUESTION: how much should one allow for the rears being wider in the COF figure?? I have 335 rears and 235 fronts so simplistically you could use this ratio (about 1.4) BUT the weight at the rear on a wider tyre produces a lower pressure compared to the front so in reality (and in the wet) you can’t really use this factor directly. OK if fatter tyres didn’t give more friction then we would have skinnies or at least the same width on the rear – so does anyone have a physical formula to calculate it?

Second question: the COG moment is calculated using the wheelbase but the COG horizontally is well forward of the rear wheels so surely the distance from the front to the COG should be used?

You can infer the CG height by weighing the car on 4 scales with two (front or rear) lifted a couple of feet. This will cause the weight at the other end to increase due to the shift of the cg toward the rear. You can back out the cg height from the change in weight, the wheelbase, and the height you lift the scales.