Upgrading to 2 pot calipers for the Rear. Pad Recommendations? - LotusTalk - The Lotus Cars Community
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post #1 of 60 (permalink) Old 07-30-2018, 08:29 AM Thread Starter
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Upgrading to 2 pot calipers for the Rear. Pad Recommendations?

This is my next little project on the car. I have BOE's radial mounts and a set of front 2-pot calipers. Plan to install soon. I don't have the brake bias cage.

What kind of brake pads are people running with this setup? From what I understand, you want a different compound between front and rear. This is for track purposes.

Also, I don't have instructions on the radial mounts. Looks pretty simple...but I haven't dug in there yet to see. If anyone has any insight on that.

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post #2 of 60 (permalink) Old 07-30-2018, 09:02 AM
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I recently did this on my street driven exige that may see the track one day but otherwise I enjoy spirited driving on back mountain roads.. I went with Ferodo from BOE on both front and rear 2-pots and Bosch pads from RockAuto for my parking brake. after bed-in per Ferodo instructions I'm very happy with them.

and I used this guide to help me install:
https://www.lotustalk.com/forums/f91.../topics/392066

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post #3 of 60 (permalink) Old 07-30-2018, 09:09 AM
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...and if you plan to keep the factory rear caliper for parking then make sure you get as much fluid out before closing up the inlet/outlets - I failed to do this and when the fluid heated up it expanded enough to apply the parking brake!!

I ended up removing the plug (I used an old bleeder...) for a few days and would clean up the expelled fluid every chance I could.
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post #4 of 60 (permalink) Old 07-30-2018, 09:32 AM
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https://www.boefab.com/blogs/tech/st...ime-every-time

Haven't done this yet either, planning to try gloc r10/8 or maybe 12/10 at first. Depending on how things go next stop might be XR3/4

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post #5 of 60 (permalink) Old 07-30-2018, 09:33 AM Thread Starter
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Originally Posted by lt1_fd3s View Post
...and if you plan to keep the factory rear caliper for parking then make sure you get as much fluid out before closing up the inlet/outlets - I failed to do this and when the fluid heated up it expanded enough to apply the parking brake!!

I ended up removing the plug (I used an old bleeder...) for a few days and would clean up the expelled fluid every chance I could.

Thanks for the link, that'll help for sure.

I have the Ferodo DS2500, and plan to swap and use them on the street. But now want a more track-focused pad. I'm just not sure though, I think you want a step up in pad aggressiveness up front. I read through the other long thread about 2-pot calipers in the rear, and someone mentioned CL8 front, CL6 rear.
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post #6 of 60 (permalink) Old 07-30-2018, 09:44 AM Thread Starter
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Originally Posted by jds62f View Post
https://www.boefab.com/blogs/tech/st...ime-every-time

Haven't done this yet either, planning to try gloc r10/8 or maybe 12/10 at first. Depending on how things go next stop might be XR3/4
Thanks a lot, I read through the other braking pad article on their site but not this one. I see they recommend xr3 front, xr4 rear.

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post #7 of 60 (permalink) Old 07-30-2018, 01:39 PM Thread Starter
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FYI, reached out to BOE and got this response:

No formal instructions, The CV shafts need to be loosened at the spindle nut and tapped back inward on both sides in order to get the front two bolts out of the rear hub assembly, and then fit the bracket and new M12 socket head bolts to the car. Lotus torque spec for these bolts is 90 Nm. We also put blue loctite on these bolts at reassembly. You can choose to leave the OEM rear caliper on the car in order to retain the parking brake as well, just plug the OEM brake line entry with a spare bleeder screw.

Pad compound: Start with RC8 Front/ RC6 (CL) rear and see what you think. If running Cobalt, XR3 front XR4 rear.

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post #8 of 60 (permalink) Old 08-15-2018, 06:19 PM
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I was always curious why people choose different compounds over proportioning valves.
Valves cost next to nothing - so cost wouldn't be the reason.
What else then?

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post #9 of 60 (permalink) Old 08-16-2018, 06:12 AM
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I was always curious why people choose different compounds over proportioning valves.
Valves cost next to nothing - so cost wouldn't be the reason.
What else then?
Why cut into brake lines when compound changes are easier to do? Why introduce another joint into a safety related system on street cars? Some folks prefer to leave valves for race cars and keep their street cars stock-ish.
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post #10 of 60 (permalink) Old 08-16-2018, 06:33 AM
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...What kind of brake pads are people running with this setup? From what I understand, you want a different compound between front and rear. This is for track purposes...
The stock brakes are biased ~60% front and 40% rear. Depending on what 4piston caliper/rotor size that you are using up front you will probably be changing to ~53%/47% .

We ran the same compound front and rear in Lotus Cup with our 308BBK at the front and stock 2piston caliper at the rear. Our Elise would stop on a dime. Here's a cool video of the car setting the fastest lap in Lotus Cup:
The bias on this set up is 53%/47%. Remember you are changing the bias with the calipers so it may be best to change only one variable at a time. Bring an alternative pad set to test later in the day once you are dialed in.

Good luck, be safe and have fun!

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post #11 of 60 (permalink) Old 08-16-2018, 06:50 AM Thread Starter
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The stock brakes are biased ~60% front and 40% rear. Depending on what 4piston caliper/rotor size that you are using up front you will probably be changing to ~53%/47% .

We ran the same compound front and rear in Lotus Cup with our 308BBK at the front and stock 2piston caliper at the rear. Our Elise would stop on a dime. Here's a cool video of the car setting the fastest lap in Lotus Cup: HERE The bias on this set up is 53%/47%. Remember you are changing the bias with the calipers so it may be best to change only one variable at a time. Bring an alternative pad set to test later in the day once you are dialed in.

Good luck, be safe and have fun!
Hi Shinoo,

Thanks for the info. My first step was (per BOE's Braking Tech Article) to upgrade the rear with another set of stock 2 pot calipers. So I'm basically running 2 pot all around. Which is why they suggested a different compound between front and rear. I guess the next stages would be 4 pot fronts, and then maybe the brake bias cage or proportioning valves (which I didn't even realize existed).

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post #12 of 60 (permalink) Old 08-16-2018, 07:14 AM
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I'm running CL8 front and CL6 rear and it works ok on my auto-x car. This car has 275/35/15 Hoosiers on the front and 275/35/17 Hoosiers on the rear. If I was street driving with something like a 205/235 combo, I'd be inclined to run Hawk HP+ on the front and stock in the rear. The CL pads are murder on discs and are wayyy too touchy for anything less than threshold braking. I'd prefer a little more pedal effort which is making me lean towards the booster delete/bias cage.

The S240 I picked up has Ferodo DS2500s on it and I can't wait to put the stock pads back on. I can almost literally breath on the brake pedal and get the car to stop. Forget heel/toe on the street. Wayyy too touchy. I mean, I can let my foot just touch the pedal and the car stops. Forget using any kind of pressure. Ugh. Terrible. I prefer my leg to get into the braking. I prefer some resolution. Digital brakes suck.
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post #13 of 60 (permalink) Old 08-16-2018, 10:36 AM
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Quote:
Originally Posted by glagola1 View Post

The S240 I picked up has Ferodo DS2500s on it and I can't wait to put the stock pads back on. I can almost literally breath on the brake pedal and get the car to stop. Forget heel/toe on the street. Wayyy too touchy. I mean, I can let my foot just touch the pedal and the car stops. Forget using any kind of pressure. Ugh. Terrible. I prefer my leg to get into the braking. I prefer some resolution. Digital brakes suck.
The 240s and 260s have just terrible brakes. The marketing dpt got ahold of those and went with 4 pots married to the stock rear sliders. You end up with a terrible braking car. I wrote a bit about that in the two articles on the BOE website....

the 240s would be a better car with standard brakes on them... or put 4s in the rear.

The whole BBK thing is just not great on these cars and is perfectly awful when only the front is converted (like the 240 and 260 cars). Some of that can be undone with our Biasing cage, but the slider int he rear is terribly inconsistent, so the results won't be nearly as good as they can be with a radial setup.

By far, the best braking I've ever felt on a Lotus is what I had on my racecar. It uses the stock size (and lightest weight) rotors, which are also the cheapest. It also allows for 15" wheels. We've installed the same setup, as have others on several cars now and it's perfectly epic.

The recipe:

Brake Bias Cage (true biasing bar and deletes the booster)
AP "Radi-Cal" Pro 5000R calipers up front (need brackets)
stock or similar calipers in the rear (need brackets)

That combo will whoa the most powerful 111s down time and time again, are cheap to maintain, and by far weigh the least (so they're the fastest, all else equal).
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post #14 of 60 (permalink) Old 08-16-2018, 12:57 PM Thread Starter
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The 240s and 260s have just terrible brakes. The marketing dpt got ahold of those and went with 4 pots married to the stock rear sliders. You end up with a terrible braking car. I wrote a bit about that in the two articles on the BOE website....

the 240s would be a better car with standard brakes on them... or put 4s in the rear.

The whole BBK thing is just not great on these cars and is perfectly awful when only the front is converted (like the 240 and 260 cars). Some of that can be undone with our Biasing cage, but the slider int he rear is terribly inconsistent, so the results won't be nearly as good as they can be with a radial setup.

By far, the best braking I've ever felt on a Lotus is what I had on my racecar. It uses the stock size (and lightest weight) rotors, which are also the cheapest. It also allows for 15" wheels. We've installed the same setup, as have others on several cars now and it's perfectly epic.

The recipe:

Brake Bias Cage (true biasing bar and deletes the booster)
AP "Radi-Cal" Pro 5000R calipers up front (need brackets)
stock or similar calipers in the rear (need brackets)

That combo will whoa the most powerful 111s down time and time again, are cheap to maintain, and by far weigh the least (so they're the fastest, all else equal).
I don't imagine going that route for awhile, but I could see my next step being the brake bias cage with 2 pots all around and equal brake pads all around. Then adjusting a bias to the front. I imagine you've done similar setups out of the shop, and would that be the next logical step up?

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post #15 of 60 (permalink) Old 08-16-2018, 02:10 PM
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On one end we have the "best of the best" but rather expensive option of AP Radi-Cal in the front + stock AP in the back + bias cage.
On the other end, as the least expensive, we have stock AP front and back + different componds.

Are there any other lower cost alterntives to get more brake while getting close to 55/45 bias?
I understand AP used to offer (not sure if they still do) another caliper similar to our stock. Any other options? Does anyone else make an inexpensive caliper that pairs well with our stock APs either in the front or the back?
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post #16 of 60 (permalink) Old 08-16-2018, 08:02 PM
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You can match a lot of different calipers to these cars from other manufactures (e.g., Wilwood). All you need is a custom adapter / mount to bolt them down.

Eliseparts sells the AP Pro 5000 and EP Tuning calipers (both 4 piston) which bolt right up or may require readily available mounts. Not cheap though.

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post #17 of 60 (permalink) Old 08-17-2018, 08:59 AM
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...So I'm basically running 2 pot all around. Which is why they suggested a different compound between front and rear...
Sorry, I misread. I thought you already had the 4pots up front. Yes, pad compound changes are your lowest cost solution. I would start with a bigger split front to rear to keep it safe. I would stick with one brand and not split brands front to rear. G-loc R12 at the front and R8 at the rear would be a safe start. You could have a set of R10 rears to install if the R8s are working.

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post #18 of 60 (permalink) Old 08-17-2018, 11:34 AM
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For those who didn't find the thread, there is another discussion about rear caliper options here:

https://www.lotustalk.com/forums/f91...70/index4.html

Starting with post #80, it includes an interesting discussion about alternative two-pot brake calipers from AP (p.s. ignore the discussion about alternative mechanical parking brakes -- it didn't go anywhere). Specifically, AP (who manufactures the "Lotus two-pots") makes two other calipers, the CP5317 and CP5316, that have identical mounting and brake pad dimensions to the Lotus two-pots, but come with smaller pistons than the 44mm Lotus calipers (41.3mm for the CP5317 and 38.1mm for the CP5316). This gives you a range of possible "native" brake biases when combined with the stock Lotus two-pots (or each other).

Based on studying this information and the spec sheets from the AP Racing website, I purchased a set of CP5317's from a shop in the UK. I went with the 41.3mm because I use wider rear tires, I figured I could always soften the rear brakes with softer pads, and frankly, they were cheaper than the CP5316's (I can only guess why).

The good news: Using aftermarket two-pot mounts (which are available from several suppliers here and across the pond), they bolt right in, and use the exact same pads as the two-pot fronts, so it makes it easier to carry extra/different pads to the track, as they are all the same. And there is a definite improvement in braking, as the rears are doing a lot more work now.

TBD news: If you really had to be ham-fisted on the brakes to trail brake before, you don't anymore. I ran them at Laguna Seca in July using Carbotech XP10's front and rear, and was almost caught out a couple of times by how much rotation I got in trail braking (once at the top of the Corkscrew). I need some more time running the car on flatter tracks to see if I should tweak the brake bias forward a bit (with less grabby rear pads). It forces you to be more subtle/precise on the brake pedal while rotating the car, but it the long run, it very well may be faster.

The bad news: Although I purchased them at a discount as part of a winter promotion, it took over 5 months to get these. Apparently AP was completely out of stock, and felt that there was insufficient demand to put the next run anywhere near the front of the queue. A lot of grumpy/sad/apologetic emails between me and the retailer (although it basically was out of their hands).



BTW/FYI: What the posts don't mention is that the CP5317 and CP5316 have bleeder screws at the top of each piston (which is good), but that puts the input port on the face of the inside cylinder. When mounted using an adapter bracket on the leading side of the rear hub, the input port is facing directly at the rear shock, so the regular-style Elise/Exige brake hoses will not work. This setup requires a banjo-bolt type attachment to the caliper; the good news is this is essentially the same kind of hose shops sell to put 4-pots on the front, so they are available from a couple of sources off the shelf.

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Last edited by Fireball; 08-17-2018 at 11:49 AM.
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post #19 of 60 (permalink) Old 08-21-2018, 06:21 AM
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Really appreciate the detailed writeup, Fireball. You look to be the first to actually have done this. I suggest updating the original thread as well.

Please keep us in the loop as you gain more experience with the new brake bias. That will help others decide between the two available sizes. You mentioned tire width as a variable, but might also indicate your tire compound, as that will affect weight transfer to the front under braking.

Did you specify the red option and perhaps that caused a delay?

Are you going to tackle replacing the heavy sliders with a dedicated parking brake next? That has been done before, but isn't fully documented. Let me know if you'd like the incomplete info I have.
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post #20 of 60 (permalink) Old 08-21-2018, 09:55 AM
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The lead times are just really long, in my experience. I've been going back and forth on using the lotus vs the 5317 vs 5316. BOE has the 5316 and lines available, but it appears to be the most expensive route.

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