Elan BBK comparison, kits lack important specs

[isuzuowner]

The Elan is graced by at least two big brake kit alternatives, but seem to have little to no technical information or published specs to make educated decisions by. Has anyone actually calculated out the theoretical braking force of the stock brakes and the aftermarket alternatives? Has anyone actually figured out all the specs of the kits? Lots of comments based on seat-of-the-pants driving on public roads, but no quantifiable comparisons. And what about the rear brakes that are not even passing MOT? If the big brake kit actually increases front braking force noticeably, the rear brake inadequacy would be even more noticeable. If the big brake kit is compatible with the inadequate rear brakes, then it can’t provide much increase in braking force.

TCE provides an online brake force calculator:
http://www.tceperformanceproducts.com/bias-calculator/

The specs for the stock Elan:
Leg input in pounds: 60
Master cylinder diameter 1: .875 inch
Front caliper piston diameter: 2.047 inches
Piston area: 3.291 sq.in.
Front pad coefficient of friction: .3
Front rotor diameter: 10 inches
Front pad radial height: 1.73 inches
Rear caliper piston diameter: 1.38 inches
Piston area: 1.496 sq.in.
Rear pad coefficient of friction: .3
Rear rotor diameter: 9.3 inches
Rear pad radial height: 1.3 inches

Front rotor torque: 2716 in.lb.
Rear rotor torque: 1193 in.lb.
Bias: .702

Pretty healthy theoretical numbers for 1990. But this assumes the calipers work well, and in real life, GM cars (the source of those donor parts) are known for pretty poor braking performance.
Currently, small economy cars are making up around 3200 in.lb. in front brake force, and benchmarks like the Impreza STi and Mitsubishi Evo are making 6200-6800 in.lb.


The Wilwood build-your-own-brake-kit discussions talk about 12.19 inch rotors that are .81 inches wide (narrower than the stock rotors, not quite as much heat resistance/capacity as the original 1 inch wide rotor).
And Dynalite caliper (sometimes the Dynapro/Midilite caliper), most often cited with a 1.38 inch piston size.

For the Dynalite 1.38 inch four piston calipers, and Q brake pad with a peaky .37-.47 friction coefficient.
Leg input in pounds: 60
Master cylinder diameter: .875 inch
Front caliper piston diameter 1: 1.38 inches
Front caliper piston diameter 2: 1.38 inches
Piston area: 2.991 sq.in.
Front pad coefficient of friction: .37-.47
Front rotor diameter: 12.19 inches
Front pad radial height: 1.7 inches

Front rotor torque: 3862 in.lb. (3131 in.lb. without changing brake pad variable and .770 bias)
Rear rotor torque: 1193 in.lb. (unchanged)
Bias: .805

Without the increase in friction compound, this is a pretty expensive dollar-spent-per-performance-increase, because the 1.38 inch x 4 piston caliper is actually smaller piston area than the original 2.047 inch x 1 piston caliper. 3.291 sq.in vs. 2.991 sq.in. Less piston area means less clamping force.
There is also a large reduction in piston movement with fixed calipers vs. compound calipers. Compound calipers have to use that single piston to push the pad against the inside surface of the rotor, and then pull the caliper frame holding the outer pad against the outer surface of the rotor. That’s a lot of space and takes a lot of fluid. Fixed calipers have pistons on both sides of the rotor and just move the pistons against the pads to squeeze rotor in one motion, with less fluid required to do so. So with the smaller four piston caliper, the brake pedal movement is reduced to the point of being an on-off switch with no space to modulate the pedal.

There is later discussion about using the Wilwood 1.62 inch four piston caliper
Leg input in pounds: 60
Master cylinder diameter: .875 inch
Front caliper piston diameter 1: 1.62 inches
Front caliper piston diameter 2: 1.62 inches
Piston area: 4.112
Front pad coefficient of friction: .37-.47
Front rotor diameter: 12.19 inches
Front pad radial height: 1.7 inches

Front rotor torque: 5322 in.lb. (4315 in.lb. without changing brake pad variable and .822 bias)
Rear rotor torque: 1193 in.lb. (unchanged)
Bias: .851

This is a really good match for the 7/8 inch master cylinder that has very close to the same pedal movement of the factory brakes, but a huge amount of increase in stopping force, and an excellent range of pedal movement (matching the original brakes) for really good pedal modulation.

There is mention of using a Wilwood 1.75 inch four piston caliper (6210 in.lb. with .37 cf pad), which seems to have been dropped from discussion, probably a good idea, because it is probably a little too large for the 7/8 inch master cylinder.

But it looks like all of the Wilwood setup requires a 16+ (maybe a 17) inch wheel to fit over the rotor and caliper. And none of this does anything to improve the rear braking problem. So this increases the tendency of front brake lockup and sliding in a straight line, without being able to turn or change direction during heavy braking.
There is also a side branch suggesting the Powerlite caliper for a 15 inch wheel kit. But this caliper is too small both in piston area and pad size, and has really limited pad availability outside Wilwood’s own pads. Definitely not a good choice for a front caliper.


The Hi-Spec brake kit brings about all kinds of questions and concerns. They state rotor diameters of 11.2 inches, 12.2 inches, and 13.19 inches. But nowhere do they state what the caliper piston diameter included with the kit is.

For the two smaller kits:
The Billett 4 (regular) caliper says it is available with 1.36, 1.52, and 1.62 inch diameters on the page to purchase the caliper individually. The pad pattern looks like their own design not shared with anything, so selection is confined to what they offer, most of which are in the .40-.45 friction coefficient range. And the rotor is from another road car (?) (not a high quality racing alloy like the two piece rotors), redrilled to fit the Elan bolt pattern (?).
The Billett 4 310 for the larger rotor kit shows only 1.52 inch diameter currently available (other sizes out of stock?) on the page to purchase the caliper individually. The pad pattern is shared with 1964-1968 AC Cobra, which sounds impressive, but has a tall 1.98 inch pad height, is not exactly modern, and may not be offered in a lot of compound options in the current market.

The two larger kits use the Monster 4 330 caliper, but the intimidating name does not hold up to the revelation that this caliper is available only with a staggered piston size of two 1.52 inch diameter and two 1.62 inch diameter, providing less clamping force than the largest Billett 4 (regular) caliper, or the better Wilwood choice. If this is the upgrade caliper over the Billett 4, then it implies that their kits with the Billett 4 are using smaller piston sizes than what the Monster 4 used in their larger kits for the Elan. The Monster 4 caliper uses what looks like an AP pad pattern, relatively common, but it is also a taller pad at 1.95 inches.

That taller pad is an important detail. The braking force is calculated based on the distance of the center of that pad from the axis of rotation of the brake rotor. A taller pad moves that point closer to the middle and reduces the braking force. That reduces the advantage of the larger diameter rotor by the same amount as ½ the increase in pad height.

Again, Hi-Spec does not state what size pistons are in the calipers of the kit they sell for the Elan. It is sort of implied that the customer contact them and they choose what size based on what the customer tells them they are using the car for. If this is accurate, what they deliver to one customer may be very different from what they deliver to another customer. And it is implied that there is no need for a rear brake upgrade with their product. So they may very well be tailoring their brake kits to provide maximum bling with minimum increase in braking force, to match those inadequate rear brakes that the front brake kit is “designed to be compatible with”.

Add to this the detail that people here state that Hi-Spec has very poor customer service and ability to deliver orders with the color of caliper the customer specified. Who knows what piston size they substitute and if the customer even notices? And the overwhelming suggestion to buy the Hi-Spec product through a dealer, who may or may not be relating the customer’s needs accurately and may or may not know how to put together a brake kit for a FWD performance car.

Worst case scenario for the Hi-Spec Billett 4 kits:
Leg input in pounds: 60
Master cylinder diameter: .875 inch
Front caliper piston diameter 1: 1.36 inches
Front caliper piston diameter 2: 1.36 inches
Piston area: 2.905
Front pad coefficient of friction: .40
Front rotor diameter: 11.2 or 12.2 inches
Front pad radial height: 1.98 inches

Front rotor torque: 3564 (11.2 inch rotor) or 3950 (12.2 inch rotor)
Rear rotor torque: 1193 in.lb. (unchanged)
Bias: .770 or .805

Only option on Hi-Spec Monster 4 kits:
Leg input in pounds: 60
Master cylinder diameter: .875 inch
Front caliper piston diameter 1: 1.52 inches
Front caliper piston diameter 2: 1.62 inches
Piston area: 2.905
Front pad coefficient of friction: .40
Front rotor diameter: 11.2 or 12.2 inches
Front pad radial height: 1.95 inches

Front rotor torque: 5285 (12.2 inch rotor) or 5796 (13.19 inch rotor)
Rear rotor torque: 1193 in.lb. (unchanged)
Bias: .847 or .869


PNM offers a big brake kit with even fewer published specifications.
They list rotors at 10.8 and 11.14 inch diameters, which both appear to be a one piece rotor borrowed from another vehicle (not a racing alloy), with five lug bolt pattern that they have redrilled in the most ugly manner possible.
They do not mention caliper piston size, availability of more than one size, or any option or choice of size. The calipers look like the Hi-Spec Billett 4 with a different paint job and name printed on the front.
Interestingly enough, there is a group buy with these are the same sketchy details without any of the important specifications.

Worst case scenario for PNM’s brake kits:
Leg input in pounds: 60
Master cylinder diameter: .875 inch
Front caliper piston diameter 1: 1.36 inches
Front caliper piston diameter 2: 1.36 inches
Piston area: 2.905
Front pad coefficient of friction: .40
Front rotor diameter: 10.8 or 11.14 inches
Front pad radial height: 1.98 inches
Front rotor torque: 3405 (10.8 inch rotor) or 3537 (11.14 inch rotor)
Rear rotor torque: 1193 in.lb. (unchanged)
Bias: .757 or .770

PNM also shows a rear brake kit, similarly with no specs. Their rear brake kits do not include a rotor, skipping one important way to increase braking force on an end of the car recognized to need more braking force.
Somebody states that the caliper is from a “VW Golf Mark IV”. This would have a 1.5 inch diameter piston with a pad that has a 2.0 inch pad height. The piston is larger, but the additional pad height moves the center of the braking force closer to the center of the rotor, effectively reducing the rotor diameter.
So the rear braking force without changing the rear pad coefficient increases from 1193 in.lb. to only 1287 in.lb. Some gain from piston size, some loss from pad height.
The calipers may work better, but that is not a big difference in braking force. It is going to take a big bump in friction coefficient to get this combination to work well with any of the big brake kits. That pattern is available in racing compounds. Something in a non-streetable .55 cf is going to yield 2360 in.lb. of braking force. But they will be noisy and excessively dusty. Backing that down to a streetable .44 cf and all you can get is 1888 in.lb. That will probably limit the front braking force to 5000 in.lb. without biasing problems. Not enough to work with the Wilwood 1.62 inch four piston calipers on the 12.19 inch rotor or the two larger Hi-Spec kits.


As far as knowing what you get, the Wilwood build-your-own-brake-kit at least allows the buyer to know what they are getting before they buy it and/or before interrogating the customer-service-challenged brake kit maker.

A good recipe for an Elan brake kit would be the Wilwood calipers in a 1.62 inch piston size for the front. Then the two piece Elise rear rotors (11.5” x 1” vented)(Sector111) for the front, and a solid 10 1/2 or 11 inch two piece rotor on the back. Dynalite Two or Powerlite 4 piston Wilwood calipers (in the smallest available piston sizes) on the back because they work so much more smoothly than the compound calipers with integrated parking brake. And a separate mechanical caliper for the parking brake. This combination would make it pretty easy to get 6000 in.lb. of braking force out of the front with a relatively mild and streetable pad, and match the rear braking force at around 2100 in.lb. to eliminate bias problems, making the car very safe and balanced for hard deceleration turning and left foot braking.


Putting this in as neutral terms as possible, the level of discussion about big brake kits for the Elan has lacked some pretty important details: caliper piston size, brake pad friction coefficient, brake pad radial height, any mention of measured braking force, and any mention of front-rear brake bias and balance. Without these details, it is impossible to compare options, or even predict the level of improvement (or lack of improvement) that a brake upgrade may provide compared to the stock brake system. The intentional omission of these details by the retailers seems to indicate that they are hiding this from their customers on purpose. An uninformed customer without any way to compare, just keeps coming back and spending money, never knowing if that money was well spent or not.

I’ve presented this information in the hope that the owners of these vehicles will raise the level of discussion on this topic.

[Brit-Car-Nut]

Me thinks you need to find a new hobby. Attacking everything in a forum about a car you don't even have is fruitless and truly annoying.

[Simon_P]

The Elan is graced by at least two big brake kit alternatives, but seem to have little to no technical information or published specs to make educated decisions by. Has anyone actually calculated out the theoretical braking force of the stock brakes and the aftermarket alternatives? Has anyone actually figured out all the specs of the kits?

Keep reading and you'll find it - Many of the kits were produced as the result of discussion here, or developed by people on here.

[dapinky]

The Elan is graced by at least two big brake kit alternatives, but seem to have little to no technical information or published specs to make educated decisions by. Has anyone actually calculated out the theoretical braking force of the stock brakes and the aftermarket alternatives? Has anyone actually figured out all the specs of the kits? Lots of comments based on seat-of-the-pants driving on public roads, but no quantifiable comparisons. And what about the rear brakes that are not even passing MOT? If the big brake kit actually increases front braking force noticeably, the rear brake inadequacy would be even more noticeable. If the big brake kit is compatible with the inadequate rear brakes, then it can’t provide much increase in braking force.............


............I’ve presented this information in the hope that the owners of these vehicles will raise the level of discussion on this topic.

(1) plenty of braking force data on the forum - for ALL known systems

(2) plenty of information on how to improve the rear braking (or more importantly, balance it, to the OE system or the Upgrades).

(3) there is more than plenty of discussion about it all.

(and yes, unlike my electronic knowledge, my knowledge on THIS subject is good enough to considered an 'Expert' by the UK Legal system)

[Simon_P]

one important way to increase braking force on an end of the car recognized to need more braking force.

Factually incorrect and potentially dangerous statement to make. It is limited to 20% by a bias valve, and yes we've been through the maths!

I’ve presented this information in the hope that the owners of these vehicles will raise the level of discussion on this topic.

I’ve presented this information in the hope that new members will do a bit more reading before posting lengthy ill informed monologues.

[Simon_P]

(and yes, unlike my electronic knowledge, my knowledge on THIS subject is good enough to considered an 'Expert' by the UK Legal system)

Thats never stopped me engaging in discussion with you Dave

[AnonImouse]

Has anyone actually calculated out the theoretical braking force of the stock brakes and the aftermarket alternatives?

A PhD in tribology calculated mine.

[dapinky]

Thats never stopped me engaging in discussion with you Dave

Engaging in discussion to clarify 'facts' against 'opinions' is somewhat different to posting half a page of drivel from the internet which may or may not be at all relevant (or even correct), and then scaring people into believing that their car is dangerous and inviting 'discussion' on a matter which many do not follow (or even pretend to understand).

Whilst i am happy to engage in discussion with anyone who actually understands the basic concepts (or even the more advanced ones!), I see no need to give a full and frank explanation to someone who only wants to stir up grief, or who wouldn't understand/accept the answers.

(besides which, if it all goes wrong, and I have to give my full explanation in Crown Court, I'll be paid a hell of a lot more than if I write it here )

[isuzuowner]

Me thinks you need to find a new hobby. Attacking everything in a forum about a car you don't even have is fruitless and truly annoying.

Recognizing the weaknesses is a valuable way to determine what improvements need to be made.

The Isuzu cars are always compared to and categorized as being slightly less potent than the Elan.
The Elan is/was stated to be the "best handling front wheel drive production car (in stock form)". Once a Civic or Integra owner bolts on a set of medium quality coilovers, the comparison is gone. The amount of money and hours of development in performance tuning the Honda cars dwarfs most everything, and especially the Elan. In the organized racing scene, the Elan is recognized as a nice little care that "can not possibly compete on the same level as the cars it is matched against". These are not my words, but I can not disagree.
Meanwhile, people with Isuzu cars have been slowly chipping away and eliminating the many deficiencies they recognize the cars have, and improving the performance level to the point that modified Isuzu cars are turning faster lap times than Elises. I'm not seeing anything like that level of potency in the Elans.
Improving the performance level of the Elan will help improve the reputation of the Isuzu cars.

The Elan makes for a very good exercise for brake upgrades. Because it allows more freedom in rotor dimension than the Isuzu cars.
Comparing real numbers with the discussions on this forum, there is a distinct lack of mention of piston size for the Hi-Spec and PNM kits.

I've searched this forum, Hi-Spec's website, and PNM's website. I find no mention of piston size, brake pad coefficient, brake pad radial height, or calculated braking force. I found this to be extremely disturbing in the "group buy" thread, where Elan owners were discussing buying a product with absolutely none of these details at all.

If these specs are well hidden, point to it.

If these specs are different from what I have been able to track down and decipher, point it out.

Otherwise, you are flatly dismissing data that you don't like for no other reason than the fact that you don't like it.

[Fredjohn]

I am not a qualified engineer, be it mechanical, electrical or any other. But I do as much of my own maintenance as my self taught skills allow. I am therefore a potentially dangerous DIYer whose jobs and judgement should not be trusted, and I should not be let loose on any car. And my opinions should not be uttered......

SO here they are. I have put "upgraded" brakes front and rear on my M100. Why? Because the standard brakes require too much regular maintenance, whereas the Wilwood fronts require very little and the rears usually fail MOTs not because of the footbrake but because of the handbrake (parking brake). PNM/Hi-spec now at the rear, which I think is a MK4 Golf caliper.

From reading lots of posts on this forum, which is one of the best, sensible, knowledgeable friendly and helpful forums around, I believe the majority of users fit "upgraded" brakes for similar reasons. Not per se for improved performance, which may or may not be a side benefit. The maintenance issue is important because for most of us the Elan is a second (or third or fourth!) car and doesn't get used regularly to keep them in good nick.

For me the proof of the pudding is in the use: I have driven some 5000 miles with modified brakes and find them excellent. Some of this driving was more than spirited over several steep twisty Alpine passes, including Stelvio, as well as fast motorway cruising. Brake performance was in no way compromised, with no fading or drop in efficiency. And no problems at all with the MOT, foot or hand brakes. All well balanced numbers on the brake machine read-out confirm my practical testing: on a flat straight road slamming the brakes on from 60-70mph with no hands on the wheel and the car pulls up dead straight with no fuss or bother.

Disc diameter and thickness, piston diameter and area etc etc etc hold no interest for me: so long as they fit inside the wheel (be it 15" or 16" as appropriate), do not foul anything and last (and by no means least) they work. I'm happy and pleased I took a decision totally without any informed data from Wilwood, PNM or Hi-spec.

Just my opinion though based on driving my car, which is what they are for..........

PS just to confirm my unskilled amateur DIY status my 1969 Elan, which I have owned since 1984, has been maintained by me for all of that time, has covered some 30,000 miles in France from the UK and passed it's MOT 1999-2012 with no issues, and then after 4 years being "SORNED", I rebuilt the braking system with refurbished calipers and servo and it passed it's MOT first time.

[isuzuowner]

I am not a qualified engineer, be it mechanical, electrical or any other. But I do as much of my own maintenance as my self taught skills allow. I am therefore a potentially dangerous DIYer...

...Disc diameter and thickness, piston diameter and area etc etc etc hold no interest for me: so long as they fit inside the wheel (be it 15" or 16" as appropriate), do not foul anything and last (and by no means least) they work.

That pretty much sums up the level of knowledge that appears to be the norm in the forum posts I read, and in the overall field of automotive hobby in general. The difference is that with common cars, there are a lot of people to find out what works and what doesn't, and with the Elan, there are not. It's also why the gentleman in Sweden related the story about not being allowed to renew his vehicle registration until he removed the PNM/Hi-Spec brakes and reinstalled the original brakes, because they could not provide the needed paperwork, and the Swedish government wants to protect their people.

Those details that determine the braking force are the difference between something that works right, and something that seems to work right, and turns around to bite you in the behind in an emergency.
Brakes and suspension can be real close and confidence inspiring when driven on public streets. Only to let you down or cause serious problems when making a panic maneuver or panic stop.
And the only way to really figure out if that is going to happen is put the car on a race track and push it up against its limit. I am not seeing anything like that from the retailers of Elan parts. It's just assumed that they have some level of secret and undisclosed knowledge and should be trusted without question. With engine and power improvements, we have dyno numbers to prove claims. With suspension and brakes, we have slalom and stopping distances, and without that are left only to look at specs and calculations. In this case, none of the above.

[Giniw]

As for your first post and its bias calculations, what type of proportioning and limiting valves did you take into account?

[Elanlover]

Wall of words hurts brain. Must make posts shorter.

[alan e]

that pretty much sums up the level of knowledge that appears to be the norm in the forum posts I read, and in the overall field of automotive hobby in general. The difference is that with common cars, there are a lot of people to find out what works and what doesn't, and with the Elan, there are not. It's also why the gentleman in Sweden related the story about not being allowed to renew his vehicle registration until he removed the PNM/Hi-Spec brakes and reinstalled the original brakes, because they could not provide the needed paperwork, and the Swedish government wants to protect their people.

Those details that determine the braking force are the difference between something that works right, and something that seems to work right, and turns around to bite you in the behind in an emergency.
Brakes and suspension can be real close and confidence inspiring when driven on public streets. Only to let you down or cause serious problems when making a panic maneuver or panic stop.
And the only way to really figure out if that is going to happen is put the car on a race track and push it up against its limit. I am not seeing anything like that from the retailers of Elan parts. It's just assumed that they have some level of secret and undisclosed knowledge and should be trusted without question. With engine and power improvements, we have dyno numbers to prove claims. With suspension and brakes, we have slalom and stopping distances, and without that are left only to look at specs and calculations. In this case, none of the above.[/quote]


Thats why in the UK we have a thing called a MOT now please stop

[Simon_P]

As for your first post and its bias calculations, what type of proportioning and limiting valves did you take into account?

Yes ,which ones early or late?
I knew there was a reason that I did it long hand rather than relying on an online calculator.

[Fredjohn]

I am not a qualified engineer, be it mechanical, electrical or any other. But I do as much of my own maintenance as my self taught skills allow. I am therefore a potentially dangerous DIYer...

...Disc diameter and thickness, piston diameter and area etc etc etc hold no interest for me: so long as they fit inside the wheel (be it 15" or 16" as appropriate), do not foul anything and last (and by no means least) they work.

That pretty much sums up the level of knowledge that appears to be the norm in the forum posts I read.

No it doesn't, it sums up me. This site is full of highly qualified and experienced people, I've met a them, spoken with them, shared pub meals and chats, exchanged ideas and problems and followed the posts.

I drive my car (yes I actually have an Elan or two that allows me to), maintain them as best I can (successfully so far), gleaning useful information from all the helpful knowledgeable people here.

[HJ2]

put the car on a race track and push it up against its limit..

I did, and I am still impressed by the improvement of the 'he who shall not be named' kit over the OEM one.

For now I'll just get a big bag of popcorn and will await any of your contributions with great anticipation

[dapinky]

That pretty much sums up the level of knowledge that appears to be the norm in the forum posts I read, and in the overall field of automotive hobby in general. The difference is that with common cars, there are a lot of people to find out what works and what doesn't, and with the Elan, there are not. It's also why the gentleman in Sweden related the story about not being allowed to renew his vehicle registration until he removed the PNM/Hi-Spec brakes and reinstalled the original brakes, because they could not provide the needed paperwork, and the Swedish government wants to protect their people.

Those details that determine the braking force are the difference between something that works right, and something that seems to work right, and turns around to bite you in the behind in an emergency.
Brakes and suspension can be real close and confidence inspiring when driven on public streets. Only to let you down or cause serious problems when making a panic maneuver or panic stop.
And the only way to really figure out if that is going to happen is put the car on a race track and push it up against its limit. I am not seeing anything like that from the retailers of Elan parts. It's just assumed that they have some level of secret and undisclosed knowledge and should be trusted without question. With engine and power improvements, we have dyno numbers to prove claims. With suspension and brakes, we have slalom and stopping distances, and without that are left only to look at specs and calculations. In this case, none of the above.

I think you'll find that Switzerland and Sweden are not the same place

If you want to spend some time reading instead of writing, may i suggest you look at some of the discussions in these threads (and there are quite a few others if you can be bothered to use the search function):-
viewtopic.php?f=41&t=17770&p=232885&hilit=brake+efficiency#p232770
viewtopic.php?f=23&t=24765&hilit=brake+efficiency
viewtopic.php?f=41&t=23606&p=297334&hilit=brake+efficiency#p297334
viewtopic.php?f=41&t=22545&p=284159&hilit=brake+efficiency#p284154
viewtopic.php?f=41&t=20813&p=264458&hilit=brake+efficiency#p264268

[isuzuowner]

As for your first post and its bias calculations, what type of proportioning and limiting valves did you take into account?

Gross braking force calculated with no reduction included.
A bias valve on a production car is typically a sign of someone in the engineering department not picking the right parts, discovering the error too late, and scrambling to fix that problem too close to the production date.
Remember that it is possible to reduce rear braking force by limiting it with a biasing valve on the back, but it is not possible to increase braking force on the back with a biasing valve.
Start making large increases in front braking force and if no other change is made to the back, the bias valve is going to need to end up turned off and the rear brakes still lacking to keep up with the fronts.

If you have data to include and a the correct coefficient to multiply the rear force number by to add that, please post it.

[dapinky]

If you have data to include and a the correct coefficient to multiply the rear force number by to add that, please post it.

There is no simple coefficient of multiplication - far to many variables, including (but not exhaustively) temperature of brake components, material specifications, weight distribution (which is non-constant, depending upon rate of decelleration), specification of brake fluid (degeneration), etc etc...

...so I'm not sure what advantage publishing lots of meaningless data may prove.

Anyway, my brakes work well enough for me - I can lock wheels if I want to (which i don't!), and it passes the annual MOT test. I have used the car on road and track, and never had any great concerns about the efficiency of my (mainly) OE system.
At the same time, I fully accept that the system can be improved, and an 'off=the-shelf' kit from the few specialist suppliers will appeal to many owners who want them to feel a bit better, and be less of a regular maintenance regime.

Basically, if I can lock the wheels on an OE system, then the car won't stop in a shorter distance with ANY other callipers fitted, as the limiting factor becomes the friction between tyre and tarmac.... the difference is in the force required to engage the wheel lock, and the time at which that rotation is stopped after hitting the 'oh s**t' pedal hard.