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WNX700H wrote:Also , the amount of energy you are having to manage is a function of the the vehicle mass and its speed . The mass will remain pretty constant but the effect of extra speed is not linear ie the energy dissipated at 100mph is not double that which would occur at 50 mph. The effect of velocity is a squared function so exponentially increases as speed increases .

This is fascinating reading !!! Good food for thought.

The advice we have been given on our historic setup is that you need to get as much braking effort on the front as possible by retarding the effort from the rear using the brake balance valve. This is to help with the car balance under braking and aid the turn into the corner, too much braking at the rear as we have experienced and are still sruggling with can create an unstable, unpredictable car under braking. Therefore I guess any effort to keep the temperature down needs to be aligned with this in mind ? I don't claim to be an expert by any means - so please shoot me down in flames !!!

Yes understood but you need to optimise the utilisation on the rears as much as possible but stay within the point where the rears lock before the fronts as this will make things very lively , without any vehicle calcs the best way to set this up is on dry tarmac where the weight transference is greatest, if its stable in these conditions then it should be fine in the wet.

When you are braking hard , try pulling up the handbrake progressively and see if you can get some extra decel out of the rears without locking up , this should indicate you could still get more out of the rears by going up a wheel cylinder size or adjusting the shut off valve setting.

Every little helps when you have a marginal situation as folks are describing in this post.

WNX700H wrote:Yes understood but you need to optimise the utilisation on the rears as much as possible but stay within the point where the rears lock before the fronts .

Hmmmmm! have I understood you correctly? if the rears lock first you must run the risk of rear end breaking away. We have this problem on our Appendix K race car, locking up at the rear leading on some occasions, (if not braking in a straight line?) to a spin.

What has been suggested to us as a cure is this simple method to set up the amount of rear braking effort to overcome this problem. Jack the rear of the car up and get someone to sit in and apply the brakes for you, then adjust the rear brakes via the bias valve or other means so that you can just turn the rear wheels by hand with the pedal hard down, no servo of course on a race car.

Any one got views on the likely effectiveness of this rough and ready solution?

regards

steady eddie

You need to get the rears doing as much as possible without making the car unstable . Maximum weight transferance will occur on the dry tarmac where you can pull highest decel.

No idea if the method you use is getting you to that point ie safe utilisation of rears but I doubt it but car will be stable .....

David

I must admit, I've got 1/2" rear cylinders and the bias valve almost closed. There are brakes, but very little.

I did change some brake fluid between my last races, but possibly too little. We just bled to get rid of any air, but it might seem as we should've changed they entire fluid.

We'll start with new pads and new fluid.

David

Thanks for your input, but as ever , there is'nt a clear way forward as I have some nice comp rear shoes that a nice man in South Wales provided and they are doing quite a lot as we get a helluva lot of dust each time we take the shoes off

The pads are Carbon Metallic from Performance Friction which seem to be an industry standard in race and rally Minis on 10" wheels. They don't wear hugely but the disc does suffer with huge heat and our rallying man says that they can see 2 or 3mm taken off an S disc in one rally and the heat just has to go somewhere

We have never tested the car apart from in a practice session so I guess it might benefit from some track time. Trouble is if you do a general test , your'e on track with 400 bhp cars and watching the mirrors all the time and it costs just as much if not more than a race

steady eddie wrote:

WNX700H wrote:Yes understood but you need to optimise the utilisation on the rears as much as possible but stay within the point where the rears lock before the fronts .

Hmmmmm! have I understood you correctly? if the rears lock first you must run the risk of rear end breaking away.

i open my rear bias one turn to the rear in the wet to help combat understeer works for me, and most touring car teams .

but yeah , with brake fluid, we bleed our racers through with new fluid once a season normaly at work. also as with what has been said as soon as the pad is at half it goes down hill, with fast stuff we have huge issues with the pads weadging and brakeing up on the eadges , some pads with the slot in down the middle are not ment to be worn down below the slot like you would with a road car! so often what you would call half worn is it for a race pad.

( i allwase use the metal backing to condition the disc for the next set in my ECO polo chip fat special )

OK so let me explain how the valve functions as folks are commenting that they have the valve nearly closed .... similar to a tap . This is a mis-conception , with a pressure regulating valve when you adjust it you are altering the pressure at which it closes to then shut off any further pressure rise to the rears ( like the valve on the rear subframe ) or then reduces the pressure rise rate at a given pressure ( some adjustable valves are like this.

For a short wheelbase car like the Mini then production vehicles have a shut off valve so above a certian line presssure you get no more pressure rise in the rears. For longer wheel base vehicles they have a reducing valve so up to a given pressure you get the same line pressure as the fronts and then when the valve cuts in the oressure rise rate is a function of the differential areas of the piston in the valve 2:1 ... 3:1 etc

If you are losing mass from the disc then this will not help as the thermal mass of the disc is critical to energy management.