32 replies to this topic

[minisilverbullet]

I wonder if there are any sources outlining the brake efficiency of various set ups? 

 

For example 8.42 discs with standard calipers vs 7.5" with 2 pot calipers? 

 

Thanks

 

Craig 

[Will16]

My old Mini, a 1991 had the 8.4" brakes standard, with later servo, and I never touched them, just new pads and discs, with standard rear drums too. I found them really rather good, it used to stop on a 20p, locked up on demand!

My new one, the 1976 has Cooper S 7.5" discs and 2 pot calipers, with early type servo, standard rear drums. I haven't touched them and they passed the mot brake test fine, but they are definatly nowhere near my old 8.4's! Now I'm not sure if new parts would improve this, but the pads have plenty of meat left on them, or maybe them being rebled.

Edited by Will16, 10 December 2015 - 09:47 PM.

[Fast Ivan]

http://www.calverst.com/cc110f.htm

 

as always Keith Calver would have covered this to some degree

[nicklouse]

Not really as the pads are different sizes and the pistons are different in the calipers and MCs.

But the math can be applied to the change in disc size presuming that everything else stays the same.

(Braking Power) = (Caliper power) X (Distance from center of wheel.)

[Cooperman]

Braking efficiency, assuming the brakes are in top condition, is not an issue until or unless the vehicle is driven right on the limit. Then the efficiency is dependant on brake size, tyre type & condition, pad composition/specification and brake fluid.

 

For example, driven very hard (and I do mean hard) a 7.5" brake with carbon-metallic pads will perform better than an 8.4" brake with standard pads or even Mintex 1144 pads.

 

From cold drum brakes will be as efficient as discs, but once the brakes heat up from hard use the drums will fade more easily.

 

This question is really for Minis in competition where the brakes will be operating at maximum temperature for a long period. On the road it is not really an issue.

[minisilverbullet]

The reason I am asking, is I am planning to modify /change my engine, to get the car legally registered with this modification, the info i have received is that i need to change the "whole" braking system to suit. concretely they have mentioned larger discs and new master cylinder. 

 

I find myself in an unfortunate situation of having changed my standard 8.4 brakes to minisport 2 pot calipers and 7.5" discs. I was hoping to find data to suggest this was an improvement 

[nicklouse]

Stop here and go back a step,

You are wanting to fit smaller wheels as well?

[minisilverbullet]

Stop here and go back a step,

You are wanting to fit smaller wheels as well?

Already have. 

[nicklouse]

Then I would be considering the 7.9 kit with 4 pots. If there is one.

No need to change the MC

[Steve220]

Then I would be considering the 7.9 kit with 4 pots. If there is one.
No need to change the MC

This. With brakes, leverage is the key, biggest you can fit under your wheels. Good quality caliper and pads to match!

[Spider]

 

From cold drum brakes will be as efficient as discs, but once the brakes heat up from hard use the drums will fade more easily.

 

 

 OT I know, but I was chatting with a mate recently just on this and he more or less confirmed what I had been privately thinking for years.

 

On our Mokes (with 13" Wheels and a ~24" rolling dia wheel), Brakes have always been an issue as the bigger overall dia wheels have far more leverage over the brakes than what they were originally designed for.

 

Two things that came from our chat;-

 

Neither of us have ever been able to get the stock 8.4" Disc Set up to be able to lock on the front wheels. We have been able to get them to stop fairly good, but not to the point of locking. We have both tried all available pads on the market too. We both also agreed that they were better when warm but not hot or cold.

 

The same Mokes on Drum brakes can lock their front Brakes, but only when cold.

Edited by Moke Spider, 10 December 2015 - 10:40 PM.

[nicklouse]

Craig I would also ask them about the eating of the brakes.

If it just has to show a number on the rollers then go see if you can actually get those figures now. You may find the wheels lock up first.

Then it might be a case of having to add mass to the car to stop the wheels locking.

What I am getting around to saying is that find out the test. Find out how much you need to find to pass. But you might find that you can not pass with that wheel size due to lack of contact surface.

But again if you can pass with current brakes and 50 bags of Spuds in the car is that OK? Or does it have to pass in normal driving trim.


So again find out the tests. Then find out how you sit now. Because if there is no way you can pass the brake test then you are not doing the engine.

[nicklouse]

 
The same Mokes on Drum brakes can lock their front Brakes, but only when cold.

Yep as the torque force of the drum brake is greater.

All the contact force is at the drum circumference. A disc only has a small contact at the circumference.

[spiguy]

Don't know about calculations but from experience of sudden braking, I have found my 7.5" setup from minispares to be excellent. I recently had to brake emergency style when a sheep ran out on the road in front of me. I was doing over 50 mph and stood on the brakes, on a wet road with Yoko A008's, and to be honest I really didn't think I would stop in time, as it was the car drew up perfectly, and very quickly too. Much better than I expected. I certainly think that the smaller disc brakes are more than up to the job on a mini.

[minisilverbullet]

I have just looked out my old MOT certificates. they show the brake efficiency in KN

 

Results on 8.4" discs standard caliper:           year 1 -  left 1.4 / right 1.4

                                                                        year 2 -  left 1.2 / right 1.3

 

Results on the 7.5" discs, 4 pot calipers:        year 1 -  left 1.6 / right 1.6

 

Not sure how rigorous this is in terms of proof of improved efficiency