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Discussion Starter · #1 ·
I can't find info on the proportioning ratio of the stock master and whether the ABS unit has a proportioning valve inside of it. I'm trying to calculate brake distribution of the stock system so that I can figure out a proper rear upgrade path that gets a better distribution changing out as few parts as possible. Any info along these lines would be most appreciated. :)
 

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Honestly........... and I am no expert on this but have taken advice from a chosen few.

The stock brakes are more than adequate for a street car or heavily tracked car. I have experimented with several pads, Ferrodo's, Padgids, and Carbone Lorains.

The CL pads with stock brakes do everything I need them to so far.
 

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Honestly........... and I am no expert on this but have taken advice from a chosen few.

The stock brakes are more than adequate for a street car or heavily tracked car. I have experimented with several pads, Ferrodo's, Padgids, and Carbone Lorains.

The CL pads with stock brakes do everything I need them to so far.
I have to disagree. I found my stock brakes (2007 Exige S) fading with just street use. I would have liked to try the 2008 AP Racing 4-pots in the front but I went with the 4-wheel AP Racing BBK. Scary strong and take some getting used to. Probably the only BBK I haven't installed brake ducts for.

San
 

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I can't find info on the proportioning ratio of the stock master and whether the ABS unit has a proportioning valve inside of it. I'm trying to calculate brake distribution of the stock system so that I can figure out a proper rear upgrade path that gets a better distribution changing out as few parts as possible. Any info along these lines would be most appreciated. :)
One could have pressure transducers and log the line pressure. And one could also use the wheel speed and the chassis speed (GPS) to determine slip.
At that point one knows slip versus line pressure.

As you avatar suggests that you are doing AutoX, then using bity-ier pads in the read is another way increase rear bias.
After that the work becomes more involved.
 

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What you are looking for is called brake torque bias... I'm at work right now, so I don't have all the information right at hand. All can be found on the APRacing website.
 

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There are a couple threads concerning front calipers to rear that may help you. Do a quick search for that subject.
 

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re: Brake bias

Some notes:

1. Street cars have a lot of front brake bias. Lotus brakes maybe good for the street, but the bias is way off optimal. This is done for safety. an average person can deal with the car sliding straight (too much front brake) versus controlling overseer (spin).

The braking force is sufficient, if you can lock your current wheel/tire combo. Therefore, stock brakes are sufficient for stock wheels/tires.

(If you change to slicks + aero, we can start changing the brake hardware. If the brakes overheat after track use, we can start changing hardware.)

Like all stock cars, Lotus comes with a combination (front and back) master cylinder. The proportioning valve is inside> (Used to be outside in early '70's cars, but it is cheaper to make it all integrated for the OEM.)

If You do not like the brake bias:

1. Take the M/C apart. Remove the prop valve. Insert adjustable aftermarket one in the rear brake line. AP is great. Willwood or Tilton is cheaper for same part. ABS and brakes will continue working (better).

2. Change pad compound front to rear.

3. Put front brakes on rear wheels.

4. Go to racing pedal set-up with 2 M/C's and balance bar.

I would do all of the above, before I went to the $$ track set-up. If You track the car, then a $$ track set-up is the right choice.

There is also a highly subjective area of brake feel....

Anton
 

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Discussion Starter · #10 ·
I'll only answer these quickly:
1. I know the possible solutions, including the front caliper on the rear. I'm trying to figure out the math so I can actually calculate what the right answer is instead of blindly trying things.
2. If you're overwhelming the stock brakes on the street, either you're driving well over 100mph and stopping to 50mph many times a minute, your brakes are completely broken, or you're not running the right pads.
3. The car will eventually be a national-title-contending autocross car. "Good enough" isn't what I'm looking for, "the right answer" is.
4. Prop valves induce a knee in the curve. I would much rather fix the actual base bias, not introduce second order variables into the mix.
 

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Here is an explanation of the Elise's rear proportioning system.

http://www.lotustalk.com/forums/1246664-post81.html

The Elise uses Electronic Brake Distribution (EBD).
This system is also referred to as Dynamic Rear Proportioning (DRP) and is, as the name implies an electronic system which, through the ABS control valve block restricts the line pressure to the rear brakes automatically to a pre-programmed algorithm. You can consider it as an electronically controlled proportioning valve which measures parameters like the rate of deceleration and rate of pedal application and uses this data to anticipate a rear wheel lock-up and then reduces the braking effort at the rear wheels as necessary. If the ABS system is left to do this, it can only react to a wheel as it starts to lock and therefore the car can already start to spin before the ABS can start to work. In extreme circumstances, if the driver brakes very suddenly the EBD system can lock off the pressure to the rear wheels completely
 

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Unfortunately, I cannot help you with the math but, the only way to address the base brake bias issue is to either; a)increase the the caliper size at the rear or b)remove the entire ABS system and plumb the rears with your own proportioning valve(in which case you may still need to increase the the rear caliper size). The current ABS system contains no magic, in fact, it is a very simple ABS system and is not suited for competition use. I use a front on rear setup but, I need to obtain the AP calipers that have the slightly smaller pistons (43.5 mm). I feel the stock fronts on the rear is just a wee bit too much rear. I'm not a fan of staggerring brake pads for comp applications as they just tend to warm up at different rates which is an issue in and of itself. There has to be someone on LT that can do the fluid math for the factory piston sizes front and rear (I always had to defer to a race engineer pal in the past for my racecar).
 

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Discussion Starter · #13 ·
Unfortunately, I cannot help you with the math but, the only way to address the base brake bias issue is to either; a)increase the the caliper size at the rear or b)remove the entire ABS system and plumb the rears with your own proportioning valve(in which case you may still need to increase the the rear caliper size). The current ABS system contains no magic, in fact, it is a very simple ABS system and is not suited for competition use. I use a front on rear setup but, I need to obtain the AP calipers that have the slightly smaller pistons (43.5 mm). I feel the stock fronts on the rear is just a wee bit too much rear. I'm not a fan of staggerring brake pads for comp applications as they just tend to warm up at different rates which is an issue in and of itself. There has to be someone on LT that can do the fluid math for the factory piston sizes front and rear (I always had to defer to a race engineer pal in the past for my racecar).
Exactly. I'm just trying to do the math so I can see what the right size rear piston is. Good to know that you found the smaller piston as the right answer, since I was figuring that just using the normal front caliper in the rear seemed like a bit too much of a change.

Where did you get the smaller-diameter piston version of the AP caliper? AP proper, or is it an application on another car that's easier to find?
 

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The AP model number is CP5317 which has a 41.3mm bore. The additional upside is that you use the same pads on all four corners. There are very few AP dealers in the states but, Elise Parts in the UK carries them at about $850 for the pair. That price is about right as AP are plenty pricey. I just think it is the simplest solution with the easiest maintenance over the long run as well. I still have the current front AP's on the rear(for the past 18,000miles) but, this is my next upgrade. That piston differential should be about right. I understand everyone's braking technique is a bit different-as for me, I found that increasing those rears allows the car to go way deep without triggering the ABS(on clean, dry pavement and proper tires). Mind you, that shock setup will also have some influence on your results as well.
 

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Exactly. I'm just trying to do the math so I can see what the right size rear piston is.
...
I can help with the math.

Start with the CoG...
Then compute the weight on the front and rear tires are a function of deceleration.
The achieved deceleration will be a function of tire to track coefficient of friction.
What you will find is that the weight bias will move forewords as the friction increases, so the bias may be OK for slicks. I know that it is certainly not optimal in the wet.

Once you understand what you want it to be then, use the master cylinders piston area and the piston area of the callipers.
The swept radius, pad's coefficient of friction, and brake line pressure then determine the stopping deceleration force.

Again the level of braking determines the optimum bias, which is generally never the same, but is generally about ~1-1.1 G on a dry track with semi slick sport tires. The bias may be closer to optimal at a level of 1.5 G and for car with high ride height.
 

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Do you know what the CG height of the Type 111 chassis is? Say from the bottom of the chassis pan, up... Is that also the height of the crackshaft CenterLine?
 
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