Jack Webb big brakes

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ScottR400D
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Which could be made worse by improving the front braking, for similar reasons as I suggested? 

Richard Price
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"Front pads are the ferodo "race"that came with the brake set up.....Any thoughts"

It would be helpful to understand exactly what front pads you are running. Both DS2500 and particularly DS3000s require some heat in them to work effectively (with DS3000's working best when the discs are glowing red hot!)

If you have a standard pad in the rear, but a competition based pad in the front, you may well have brakes that work from cold in the back, but not the front. If its a track only car, and you know that, then that's not a problem, where as you build heat, the balance will improve, but, for a road car, that is not very safe....

You comment that the rear brakes get hot. That is not unusual, and, in itself, not as much a problem as a characteristic. Quite a lot of the available stopping power of our cars actually comes from the rear brakes, but, on standard cars, the discs are solid and cooling is poor. By increasing the disc and pad size, and adding vented discs that dissipate the head better, you exaggerate the temperature imbalance between front and rear.

In an ideal world, the brake sizes would be specified so that heat built up and was dissipated at the same rate on both axles. However, there is not "one size fits all" solution to suit all 7's. Overall weight, weight distribution, along with tyre sizes and and compounds all affect that "ideal". ECR's car have a heavy Vauxhall XE in the front, where the 'Busa car that I've driven this year has a vastly different dynamic......

I'd really want to fully understand exactly what you have before making any other change.

For optimum braking performance, front to rear balance is paramount. To that end, I've been running a modified pedal box with dual master cylinders and a bias bar to enable adjustable front/rear balance for the last ten years.

 

 

 

 

 

 

Richard Price
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Oops.

It's just been pointed out to me that my opening statement in the above post did not make sense,....

I've just edited it to correct it.

If you look at the chart below, you see that DS3000s have close double the stopping power at 500°C that they do when stone cold (note that the chart starts at 150°C, but road cars will often be braking from stone cold).

Additionally, DS3000s are at their optimum between 500 and 700°C (that is in the range where the discs are glowing red hot)

In contrast, a typical standard pad will work at its best from cold, typically getting worse the hotter they get.

So, if you have different pads front and rear, whatever front/rear balance you cold is unlikely to be what you have warm, and different again when hot. 

https://www.ferodoracing.com/products/car-racing/racing-brake-pads/ds3000/

7 wonders of th...
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I can confirm that despite what the graph says...... DS3000 do work very well from cold, far far better than the previous 1144's and maintain a consistent feel as they warm up to.

Expensive but a very good material.

Simon.Rogers
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Everything Richard has said is correct but I am with 7 Wonders on the DS3000.  Still stops more agressively than the 1144 from cold has great feel and progrssion.  

I have used 1144 on all axles, DS2500 all axles and as currently DS3000 on all corners.  I have also run various mixes of pad on the front and rear.  Its been dependant on the tyre used and the the front weight/engine combination about which has been best.  On the new AVON Slick compound and construction I am now back to DS3000 as I said but with the full bias bar pedal box.  I could not run the DS3000 on the front with the Busa without that upgrade.

www.meteormotorsport.com
timb2117
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Ok hear the ideas and experience oozing, I have double checked the fronts are ds2500 and as the rears are unknown then that is a good place to move to I will find out what they are and try to balance up, also some more track/road testing with heat in.

I guess I am trying for (as stated by you guys) something that may not exist, good power, modulation and stopping evenly on track then without changing anything good cold performance on the road. I'll at least  have  a lot more idea of the variables after this thread though thanks.

My aim being to follow Chapman's ethos of drive to track and drive home, however a lot has changed in 60 years..... 

7 wonders of th...
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I guess I am trying for (as stated by you guys) something that may not exist, good power, modulation and stopping evenly on track then without changing anything good cold performance on the road.

It does exist...... DS3000  Thumb Up 

Richard Price
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I don't doubt DS3000s "work" from cold.

However, they look like they "work" much better when hot.

With large ventilated discs on the front, and smaller solid discs on the back, where the ventilated fronts are also exposed with good air flow around them and the rears are enclosed with poor airflow, The rate of change of the brakes performance due to temperature is likely to be distinctly different. Whatever front to rear balance you have cold is likely to be very different to what you have when the brakes are at their normal working temperature. (whatever "normal" is. On a road car, I doubt DS3000s will ever reach their maximum performance. On a sprint / hillclimb car, braking is likely to be different each time the brakes are used during a run... The longer the run, the more bias will move to the rear....)

For ultimate stopping power both axles have to be working effectively. When I first went to dual master cylinders, I was surprised how much the bias could be wound to the rear, and how much better the car stopped!

 

elie boone
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Once i tried to cool the rears by a 60mm tube starting next to the roll cage and blowing direct to the caliper but it didn't had much effect.

7 wonders of th...
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They do indeed work from cold and the difference between hot and cold is less on DS3000 than others I have used, ie the CoF is more constant and less susceptible to change in temperature.

By upgrading from standard to big brakes you are in effect causing the imbalance in terms of thermal management and braking torque, adding the AP master cylinder worsens this still as the increase in bore decrease power to the rears.

Upgrade the disc diameter (but keeping it solid) alters the feel of the system and offers an increase in torque, however i have yet to see a 7 that requires these kind of braking the big brakes can generate, or heat they can dissipate..... remember they were fitted for endurance racing untill CC's marketing dept decided they would make a good money spinner on the upgrades list.... Big brakes are also very heavy and you can make a very noticeable reduction in rotational and unsprung mass (circa 3.5kg per corner) by looking at alternatives (class regs permitting if your competing) 

I run drilled solid discs all round and altered the % difference between piston CSA's when I specced my new calipers all round, thus permitting more rear braking.

Cooling could be effectively ducted to the rears but you ideally need to tab or paint the discs pre and post to see what operating windows your working in.

A bias set up is the ideal and is on my list for some time very soon, many ways of achieving both feel and balance, the variations you will see on similar race cars is vast, each driver having their own preference...