Upgrading to 2 pot calipers for the Rear. Pad Recommendations? - Page 2 - LotusTalk - The Lotus Cars Community
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post #21 of 60 (permalink) Old 08-21-2018, 11:09 AM
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Originally Posted by andreas2 View Post
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.
Based on just the ratio of piston sizes, the bias currently comes out to 53%/47%. But different tire contact patches and weight distribution will affect how it all plays out. Most of my weight savings on the car are at the rear (lighter muffler, lighter battery, and taking the passenger seat out), so besides my 205F 245R tire widths, my weight distribution may have shifted forward slightly from stock. The CP5316s would have yielded a 57%/43% bias (using the stock front caliper), which would have been a more conservative starting point, but I decided that I'd rather start with a little too much rear brake bias and then soften the rear bite with pads or a reduction valve rather than dummying-down the front braking. Also, the price for the CP5316 was over 60% higher than the CP5317, so that made the initial choice even easier.

At Laguna, I was running on well-worn Bridgestone RE71R's, but I also sometimes run Hankook Z214s (C71 on the front and C51 on the rear). The "looseness" depends on how hard and late your brake, and how much trail braking you use, especially in off-camber or top-of-the-hill turns, so Laguna may not have been the most representative test case for general use. We'll have to wait for fall to try it on some other tracks. I should also add that I run on an OS Giken LSD, which has partial lock-up on decel (to combat "the cha-cha" under severe braking), so YMMV.

Because nothing was in stock, it didn't matter what color I wanted, so I ordered red just to be weird. From the time I ordered them in January, the planned lead time started at 8 weeks, and just kept moving out 8 weeks at a time. By May I was pretty much willing to take any color they had, but they just hadn't made any.

As far as parking brakes, I'm trying to be pragmatic (cheap). Eliseparts was selling a custom mechanical parking brake which was plug-and-play, but it wasn't cheap, and they stopped making them. If I really wanted to be weird about the unsprung weight of the stock rear calipers, I would just take them off and keep a block of wood in the trunk, as race cars don't need parking brakes. But my car's a street car, and I've developed well enough as a driver to know that my driving mistakes cost me a lot more time than an extra couple of pounds on each rear corner. Unless the track is really bumpy, or you regularly ride the curbs, I don't think the expense of custom parking brakes is worth the money. I'm all about "bang for the buck".

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Originally Posted by jds62f View Post
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.
I am a long-time customer of the Lotus shops here in the US, but sometimes it is just cheaper to source some of the standard items from UK shops, especially since the pound has been weak the last few years. There are also a ton more S2 Lotuses in the UK, so their customer base is just bigger. You just have to creep around on the internet with the right part numbers and specs, make contact with some of the Brits, develop some comfort with them, and see if their price plus overseas shipping saves you money or not. And unless the item is not in stock, it seldom takes longer to ship it here than if it was coming from somewhere in the US (but yes, the shipping will cost more). In my case I ended up purchasing the calipers from a "Tuner" shop in the UK because they were an AP dealer, and got the hoses from one of the UK Lotus shops. By purchasing the calipers from a domestic (British) shop, I was able to save a substantial amount of money, and ended-up getting a new set of 5317's for less than a lot of people pay for a used set of Lotus front calipers here in the States.

p.s. I need to test more, but I think that the 53%/47% brake bias may have actually gotten the car to the point where the ABS is now working properly by modulating both the front and rear brakes. So far the only adverse difference I noticed was in trail braking in "unweighted" situations, which very well may be corrected by a lighter touch...

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post #22 of 60 (permalink) Old 08-24-2018, 02:54 PM
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Quote:
Originally Posted by Fireball View Post
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.
Hello all. I've taken a break from the forum, but I'm back-ish.

I also installed CP5317s in the rear, along with the BOE brake bias change. I can confirm that you need a banjo fitting or a workaround for the calipers. I actually used the normal attachment style, as on the front calipers, and simply closed the input port with a bolt. That seems to work fine, but obviously you lose the ability to bleed from both sides.

I can't comment on balance because the bias change allows me to change it to whatever I want. However, losing the power booster significantly changed the effort level of the brake pedal, of course. While they are now much heavier than before (and your first time using the brakes will be shocking, I guarantee it), I quite like their feel. There's definitely a much broader range of force to modulate the brakes, but it does take getting used to.

I wouldn't say the force required is too much for daily driving; I can see myself using this all the time if needed. However, the change in pedal effort required two adjustments for me. First is that my braking technique is different now. Previously, I had my heel on the ground as a pivot, but I now lift my entire leg up from the force and press down. Partly, that's to give myself more leverage, which helps with the pedal effort. However, it also allows me to change my heel and toe technique from side-side to heel-toe. This is useful because the brake pedal has very little travel distance now; I spaced the throttle pedal up a bit, but it still wasn't fully enough to have consistent heel and toe. With my changed braking technique, I'm now much more consistent on heel and toes for the Lotus. The added bonus is my braking technique is different for the Lotus as compared to other cars, and so it seems my brain is storing the muscle memory in different parts as well, which helps because the force required is so different.

Also, I added a handbrake caliper to the rear since I wasn't willing to give up the handbrake. I can give you the contact information of the guy that sells the handbrake caliper if you need it, just PM me. He's great in helping you set it up.

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post #23 of 60 (permalink) Old 08-24-2018, 11:02 PM
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Great to see more discussion on brakes

I am busy installing a set of refurbed 2 pot APRs in the rear or my 2007 Exige, so I'll have the same calipers all round. I am a PFC addict so I'll be using 13 compound in front and 11 in rear. I am pretty scared that I might confuse the ABS (which I am not ready to ditch) so I am preparing to revert. So far, everything I discover about the Brembo rears scares me to death as a track solution (not just the uneven/angled pad wear). It is clearly good/great for the street.

My car is track-only and has been mercilessly tweaked, mostly by me but also by almost anyone of skill in CA and TX (any TX barbs here will elicit some disappointing responses). I think I have about 100 track days ~ 10,000 track miles on the car. It is on its second transmission but is still on the OEM motor (producing, as a guess, about 250hp). The whole story is far too boring for this post.

I'm busily rebuilding my stock Brembo rears (in case I hate the new setup), plus a set I bought from a wrecker (I hate to learn something and not put it to work). I am using the excellent Seloc post as a reference (many thanks y'all at Seloc!).

If anyone is interested, I'll post some supplements to the Seloc post (as they say, you don't have to press that hard to reassemble). I constructed a few trixies.

My observation (not so far, because I have successfully completed one set and they work) is that these calipers are a thing of beauty, are extremely complicated, and I am amazed that they work at all! I really want to meet the guy or gal who designed them.

My sincere apologies, there are two o-rings and a washer missing from the included photo
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post #24 of 60 (permalink) Old 09-04-2018, 06:28 PM
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I tested my AP 2-pots all-round this weekend (16x7, 17x8; A005 hard compound take-offs; PFC 13 in front, 11 in rear).

The stock ABS worked just fine; I had no ice-mode.

The pedal was much less spongy.

The pressure required to go into ABS was 5x less.

The stopping distances were 2x less.

I am still contemplating no-ABS or boost and a bias cage from BOE.

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post #25 of 60 (permalink) Old 09-04-2018, 07:50 PM
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what is it about the 4/2 setup that causes the longer pedal travel vs stock 2/1?

** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

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post #26 of 60 (permalink) Old 09-04-2018, 08:00 PM
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I don't have experience with the 4/2. My guess on the shorter travel 2/1 versus 2/2 is that the flex in the rear single accounts for the extra travel and shallower travel versus braking curve.
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post #27 of 60 (permalink) Old 09-04-2018, 08:21 PM
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Quote:
Originally Posted by shay2nak View Post
what is it about the 4/2 setup that causes the longer pedal travel vs stock 2/1?
I don't know what the piston sizes are on the 4-pots, but whenever you increase the piston area for a given corner, all other things being equal, slightly longer master cylinder travel will be required to move the caliper pistons a given distance.

Having said that, I can tell you that the 2-pots seem to be a bit more sensitive to lateral runout of the brake rotors, resulting in more brake pad "knock-back" as compared to the single-piston calipers which can ride back and forth a bit as the rotor wobbles. I experienced this slightly longer travel when I put the two-pots in the back, until I discovered one of my rear rotors was slightly warped. After I put flatter rotors in, the pedal travel shortened back to where I expected it to be...
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post #28 of 60 (permalink) Old 09-05-2018, 01:08 PM
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There was talk of the brake booster in the Exige/Elise. Anyone tried to use the booster from the Evora when going 4/2 or 4/4? I'm just talking out loud here.

** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

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post #29 of 60 (permalink) Old 09-06-2018, 06:34 AM
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Just another datapoint:

I installed the Lotus 2-pot APR calipers on the rear of my S240 and kept the stock front 4-pot APR calipers. There is a little more pedal travel (as expected), call me crazy but I find it to be an improvement. The reason is because it helps with my heel-and-toe braking. I can't do a true h&t because of the length of legs and my lack of flexibility, so instead I use the left-right sides of the ball of my foot (I also have aftermarket pedal faces that are a bit wider to make this easier). With the stock brake setup (and less brake pedal travel), I had difficulty getting an adequate blip of the throttle, but with the 4/2 caliper setup I find it easier to get a good throttle blip, and the pedal travel now feels normal to me (took little to get used to).

Regarding the original topic, I'm happy with my f/r balance and overall brake performance with Carbotech XP12's front and rear (on the track), but I have 304mm discs on the rear (and stock size 308mm discs and 4-pot calipers on the front), which is a bit unusual. I can trail brake much more effectively with much better, but easily controllable, rotation with turn-in compared to the stock setup. ABS has also been fine (4 track days so far, including several damp sessions). In theory (accounting for piston sizes and counts, and disc sizes) my f:r ratio is now 58:42, versus the stock S240 68:32. Adjustable brake bias would be nice, but right now I don't feel like I need it.

my .02, -Ed
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-Ed
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post #30 of 60 (permalink) Old 09-16-2018, 05:17 PM
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EBC pads

As an economical pad EBC stands out.

I currently have Carbotech XP12 front and XP10 rear.
They are nearing end of life and I wanted something less
aggressive because I mostly drive on the street. They are
good on the street and fade free on the track but they
seem ill suited for cold weather driving. The Carbotech pads
are also hard on rotors and squeal like slit pig at upon low speed stops.

I need an opinion on whether to avoid EBC all together or
which EBC pads are preferable for mostly street. I drive B-roads
mostly where braking can be quite heavy sometimes. (2-3 trackdays
per year at 20 minute sessions.)

From a bit of research I have arrived at this combo:
Yellow/front and Red/rear. The red is a less agressive
pad with less fade resistance compared to the yellow.
The yellow seems to be a light duty trackday pad that
will not fade during a 20 minute session.

Any thoughts?

-Robert

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2008 Exige S240 ST
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post #31 of 60 (permalink) Old 09-17-2018, 12:25 AM Thread Starter
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Quote:
Originally Posted by sleepe View Post
As an economical pad EBC stands out.

I currently have Carbotech XP12 front and XP10 rear.
They are nearing end of life and I wanted something less
aggressive because I mostly drive on the street. They are
good on the street and fade free on the track but they
seem ill suited for cold weather driving. The Carbotech pads
are also hard on rotors and squeal like slit pig at upon low speed stops.

I need an opinion on whether to avoid EBC all together or
which EBC pads are preferable for mostly street. I drive B-roads
mostly where braking can be quite heavy sometimes. (2-3 trackdays
per year at 20 minute sessions.)

From a bit of research I have arrived at this combo:
Yellow/front and Red/rear. The red is a less agressive
pad with less fade resistance compared to the yellow.
The yellow seems to be a light duty trackday pad that
will not fade during a 20 minute session.

Any thoughts?

-Robert

I think the pads are easy enough to swap out that you should really consider a street pad and a track pad separately. If you're only doing 2-3 per year. I would just swap them in the day before as you check over your car in prep.
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post #32 of 60 (permalink) Old 10-28-2018, 04:40 PM
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Fireball,

Any update on running the stock/5317 setup? How is it working out for you?
You mentioned earlier that may be considering reducing the rears. Have you done anything?
If you haven't - do you think doing so would be a good idea?

I am considering the same caliper setup and need to decide on the pads.

Thanks
-Art

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post #33 of 60 (permalink) Old 10-28-2018, 05:27 PM
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I think my 2-pot all round setup is too rear-biased even with a less-aggressive compound on the rear.

I believe the early-engagement of ABS I am feeling is the rears locking.

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post #34 of 60 (permalink) Old 10-28-2018, 07:10 PM
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A few weeks ago I saw someone at the track running stock 2-pots all around with different compounds, and experiencing locking. He couldn't finish the day.
That's why I am wondering if and how to reduce 5317s in the rear.

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post #35 of 60 (permalink) Old 10-28-2018, 07:43 PM Thread Starter
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So after switching the 2 pots all around. Running CL RC8 front, RC6 rear (per BOE recommendation). I'm also experiencing what I think is too much of a rear bias. I feel the rears locking up easily. The rear will lock up and try to slide out on me even in hard straight-line braking.

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post #36 of 60 (permalink) Old 10-28-2018, 09:51 PM
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Who else is running 2-pots all round? I guessed the bias would be okay given the extra rear weight and tire width but it seems the weight transfer swamps the static differences.

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post #37 of 60 (permalink) Old 10-29-2018, 08:49 AM
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Quote:
Originally Posted by gstomp06 View Post
So after switching the 2 pots all around. Running CL RC8 front, RC6 rear (per BOE recommendation). I'm also experiencing what I think is too much of a rear bias. I feel the rears locking up easily. The rear will lock up and try to slide out on me even in hard straight-line braking.
Did you install rears with the same diameter as the front (41.3mm) or the version with smaller pistons (38.1mm)?

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post #38 of 60 (permalink) Old 10-29-2018, 08:59 AM
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Originally Posted by artmt View Post
Fireball,

Any update on running the stock/5317 setup? How is it working out for you?
You mentioned earlier that may be considering reducing the rears. Have you done anything?
If you haven't - do you think doing so would be a good idea?

I am considering the same caliper setup and need to decide on the pads.

Thanks
-Art
I ran the stock/5317 setup with Carbotech XP10's all around at Chuckwalla two weeks ago and it was great. Ran on used and then new Hankook Z214 C51s (205/50-16 fronts, 245/40-17 rears). FYI, also running 500/625 lb springs and aggressive damping (which will effect your weight transfer rate), and an OS Giken plate LSD with 50% lockup (I think) on decel. No issues with too much looseness in the braking zones (but it is possible that I happen to do less trail braking at this track). As mentioned in my earlier post, I had a used set of XP8's with me just in case I needed to soften the rear, but never felt the need to put them in. However, as in my prior test, if you have a track with downhill-off-camber or top-of-the-hill braking zones (like Laguna Seca, with low grip to boot), you may experience some looseness at the rear if you trail brake too aggressively. YMMV.

I received a couple of offline questions, so here are a few notes on the install:

- I've seen some write ups where the poster installed the mounts while the upright was still attached to at least some of the suspension, but you will always have to remove at least two of the bearing retainer bolts (three if you are going to re-clock the ABS sensor or use the Elise-Shop caliper mount), requiring you to unbolt the axles and at least slide them inward far enough to remove said bolts. And it's a lot easier to loosen those bolts if the upright isn't flopping around on your lower ball joints. So early on I decided to disconnect the axles, lower ball joints, and upper ball joint block so I could remove the upright, secure it in a bench vise, and work on the upright on the bench. Much easier (and safer), so you can go to town with your 1/2" drive socket and long breaker bar. Using this approach, re-clocking the ABS sensor so that it was pointing towards the parking brake caliper wasn't a big deal. It actually gives you a chance to get in there with a wire brush and scrub out some of the rust, and then hit the bare parts of the hub with some silver anti-seize grease (to provide a heat-resistance anti-rust coating).

- The other thing to keep an eye on is to not put too thick washers on the bolts holding the caliper mounts and bearing blocks to the uprights. The heads of these bolts get REAL CLOSE to the green axle spindle bodies when they are bolted back into the hub. REAL CLOSE.



If you are running the stock Lotus 2-pot calipers on both front and rear, yes, you will have too much rear brake bias, as you have the same rotor diameter, the same size brake pads, and the same diameter caliper pistons (44 mm) front and rear, resulting in a 50/50 brake bias. That's why I took the trouble to go out and get the CP5317s, as they have smaller 41.3 mm caliper pistons. The CP5316s are even smaller at 38.1mm (but they are more expensive).

If you want to play Dr. Frankenstein (and some of us do), besides messing with pad compounds, to shift the bias forward you could also try putting larger diameter front rotors with caliper spacers, or (ugh) reducing the rear pad surface area by grinding some of the lining off to make the pad surface smaller (I can't believe I just suggested that...)

2007 Canyon Red Exige S w/"extras"

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Last edited by Fireball; 10-29-2018 at 01:12 PM.
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post #39 of 60 (permalink) Old 10-29-2018, 09:18 AM Thread Starter
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Quote:
Originally Posted by jdawson View Post
Did you install rears with the same diameter as the front (41.3mm) or the version with smaller pistons (38.1mm)?
almost positive it's the same diameter as the front. I bought them used from a forum member who had the BOE stainless steel pistons installed on them.

And I think it's 44mm front? So I'm running 44mm front and 44mm rear...different compounds but still experiencing too much rear bias...most noticeable in downhill braking (which is expected I suppose). Something I'm gonna have to figure out this off season.

2007 Chrome Orange Lotus Elise

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post #40 of 60 (permalink) Old 10-29-2018, 11:31 AM
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Thank you Fireball.

Quote:
Originally Posted by Fireball View Post
However, as in my prior test, if you have a track with downhill-off-camber or top-of-the-hill braking zones (like Laguna Seca, with low grip to boot)...
My favorite track - Palmer has about 200 ft elevation change, and they run it in both directions - so all of the above applies.
I was thinking that if I have to put in a reducing valve, I might as well spend extra on 5316s instead.
But your report is reassuring enough that I think I will be OK with just softer compound in the rear.

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