Who's running 2 pot calipers front and rear? - Page 6 - LotusTalk - The Lotus Cars Community
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post #101 of 156 (permalink) Old 01-05-2018, 05:31 PM
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THE 41.3 mm piston at the rear is a little bit too big for the stock 2 pods front. A reducing valve is required. Ap racing are doing another version with smaller piston size, donít remainber the size, but they are perfect size, more difficult to find in US.

On my car, I installed a wilwood handbrake caliper, light and easy to fit. You can find a picture by following my thread.

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post #102 of 156 (permalink) Old 01-05-2018, 05:59 PM
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THE 41.3 mm piston at the rear is a little bit too big for the stock 2 pods front. A reducing valve is required. Ap racing are doing another version with smaller piston size, donít remainber the size, but they are perfect size, more difficult to find in US.

On my car, I installed a wilwood handbrake caliper, light and easy to fit. You can find a picture by following my thread.
Did you run the 41.3 mm piston caliper?

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post #103 of 156 (permalink) Old 01-05-2018, 08:26 PM
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YES

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post #104 of 156 (permalink) Old 01-05-2018, 10:00 PM
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Thanks. There's also the CP5316. Same body but 38.1 mm bore instead of 41.3 mm bore. Sounds like that might be the safer, more conservative option. In terms of piston area ratio, the ratios are thus:

Stock AP 2 pot front / Brembo slider rear: ~60/40 but with slider inefficiency probably closer to ~70/30 (see discussion below)
Stock AP 2 pot front / Stock AP 2 pot rear: 50/50
Stock AP 2 pot front / AP CP 5317: ~53/47
Stock AP 2 pot front / AP CP 5316: ~57/43

I'm not sure if the stock master cylinder has front-rear proportioning built in to change the bias though.

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post #105 of 156 (permalink) Old 01-06-2018, 04:58 AM
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For me, the CP5316 should be perfect. The brake ratio required depend also of tire. More sticky tire required more front brake, street tire required more rear bias. I run with the 41.3 with a reducing valve adjusted to around 10% reduction on rear with Hoosier R7. The disc I use are same size on all wheel, 295mm (28 front, 25 rear thickness). The cool thing with the AP twin pot at the rear and front is the wheel can be small in front (I am using 15 inchs wheel Teams Dynamics), and all calipers are using the same pads and compound.

The bad side of the 2 pots caliper compared with a 4 pots: the pads need to be turned after every track day, the pad is short and have tendency to wear with a taper. But it is a easy job, 2 min per wheel.

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post #106 of 156 (permalink) Old 01-06-2018, 08:48 AM
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Thanks. There's also the CP5316. Same body but 38.1 mm bore instead of 41.3 mm bore. Sounds like that might be the safer, more conservative option. In terms of piston area ratio, the ratios are thus:

Stock AP 2 pot front / Brembo slider rear: ~75/25
Stock AP 2 pot front / Stock AP 2 pot rear: 50/50
Stock AP 2 pot front / AP CP 5317: ~53/47
Stock AP 2 pot front / AP CP 5316: ~57/43

I'm not sure if the stock master cylinder has front-rear proportioning built in to change the bias though.
Thank you for that, but I just want to point out one correction. Even though the Brembo slider caliper has only a single piston, assuming the caliper slide mechanism is working (and not sticking), the clamping force with the one piston will be the same as if the caliper had two pistons (one piston acting on each pad). The single piston exerts a force on the brake pad that's proportional to the piston area, but that force is still balanced by an equal and opposite force on the other brake pad, it's just that the opposite brake pad is rigidly supported rather than supported by a piston (and in theory wears equally). By my calculation, the stock AP 2 pot front / Brembo slider rear area ratio is 60:40, which isn't bad. Unfortunately in actual use the sliders tend not to work that well, as evidenced by uneven pad and disc wear and a reduction in rear braking.

-Ed
'08 Arctic Silver Exige S240
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post #107 of 156 (permalink) Old 01-06-2018, 09:17 AM
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Thank you for that, but I just want to point out one correction. Even though the Brembo slider caliper has only a single piston, assuming the caliper slide mechanism is working (and not sticking), the clamping force with the one piston will be the same as if the caliper had two pistons (one piston acting on each pad). The single piston exerts a force on the brake pad that's proportional to the piston area, but that force is still balanced by an equal and opposite force on the other brake pad, it's just that the opposite brake pad is rigidly supported rather than supported by a piston (and in theory wears equally). By my calculation, the stock AP 2 pot front / Brembo slider rear area ratio is 60:40, which isn't bad. Unfortunately in actual use the sliders tend not to work that well, as evidenced by uneven pad and disc wear and a reduction in rear braking.
The problem with single piston calipers is that once the clamping force begins, the sliders become loaded thus some of the clamping force becomes transferred to trying to move the caliper. I believe the conciseness is a reduction of 20-30% loss in clamping force.

Later,
Eldon
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post #108 of 156 (permalink) Old 01-06-2018, 11:56 AM
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The problem with single piston calipers is that once the clamping force begins, the sliders become loaded thus some of the clamping force becomes transferred to trying to move the caliper. I believe the conciseness is a reduction of 20-30% loss in clamping force.

Later,
Eldon
That makes sense (and consistent with my statement that "in actual use the sliders tend not to work that well"). They probably do better than that when new and lubed, or newly refreshed, but a 20-30% loss sounds reasonable for more typical conditions.

-Ed
'08 Arctic Silver Exige S240
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post #109 of 156 (permalink) Old 01-06-2018, 01:10 PM
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That makes sense (and consistent with my statement that "in actual use the sliders tend not to work that well"). They probably do better than that when new and lubed, or newly refreshed, but a 20-30% loss sounds reasonable for more typical conditions.
Good points all. I've updated my post above.

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post #110 of 156 (permalink) Old 01-07-2018, 05:44 AM
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EP uprights

I'm in the process of replacing my front and rear hub carriers ("uprights") with the EP uprights (20mm height drop front and rear), keeping the AP Racing 4 pot calipers in front (stock on my S240), but installing the "Lotus" AP Racing 2 pot calipers (44mm pistons) and EP parking brake calipers in the rear. The first pic shows the rear upright (and EP toe link), ready for the calipers. In the second pic you can see the new calipers. I haven't moved the brake hose over yet (that's next), I'm going to replace the stock hose with the Inokinetic QwkBleed hose routed above the upper A-arm, looks like the length will be OK.

As far as front:rear ratio is concerned, besides the rear caliper change (from the Brembo slider to the "Lotus" APR 2 pot caliper), I'm also increasing the rear disc diameter from the stock 288mm to 304mm. The fronts will remain at the stock 308mmm, with new discs front and rear (APR floating hat). Accounting for the disc diameters (multiplying the piston area by the disc radius), the stock F:R ratio was 68:32 (and that's best case, because it assumes the Brembo slider is 100% efficient, which isn't the case as Eldon pointed out). With these changes, my F:R ratio should be 58:42, which I'm hoping turns out to be a good target. I most definitely want to run the same pad materials front and rear. I'm hoping I can get away with not needing adjustable brake bias, but I'll do that later if necessary.
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-Ed
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post #111 of 156 (permalink) Old 01-07-2018, 05:51 AM
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And before anyone gets concerned about my use of the scissors jack, the car is on jack stands, I just use the scissors jack to position the hub assembly, the jack isn't supporting more than about 10 lbs (you can see the spring isn't even contacting the upper collar on the shock).

-Ed
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post #112 of 156 (permalink) Old 01-07-2018, 05:57 AM Thread Starter
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looks nice (and $$$). I wonder if you'll have issues with pedal travel, since it sounds like you're not changing out the brake MC. I know of at least one person who added 4 pot up front and then tried 2 pot in rear, and complained of the length of the pedal after those changes.

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I'm in the process of replacing my front and rear hub carriers ("uprights") with the EP uprights (20mm height drop front and rear), keeping the AP Racing 4 pot calipers in front (stock on my S240), but installing the "Lotus" AP Racing 2 pot calipers (44mm pistons) and EP parking brake calipers in the rear. The first pic shows the rear upright (and EP toe link), ready for the calipers. In the second pic you can see the new calipers. I haven't moved the brake hose over yet (that's next), I'm going to replace the stock hose with the Inokinetic QwkBleed hose routed above the upper A-arm, looks like the length will be OK.

As far as front:rear ratio is concerned, besides the rear caliper change (from the Brembo slider to the "Lotus" APR 2 pot caliper), I'm also increasing the rear disc diameter from the stock 288mm to 304mm. The fronts will remain at the stock 308mmm, with new discs front and rear (APR floating hat). Accounting for the disc diameters (multiplying the piston area by the disc radius), the stock F:R ratio was 68:32 (and that's best case, because it assumes the Brembo slider is 100% efficient, which isn't the case as Eldon pointed out). With these changes, my F:R ratio should be 58:42, which I'm hoping turns out to be a good target. I most definitely want to run the same pad materials front and rear. I'm hoping I can get away with not needing adjustable brake bias, but I'll do that later if necessary.

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post #113 of 156 (permalink) Old 01-07-2018, 06:01 AM
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Your front/rear bias is still a little high for track but is at good spot for the street. Since our cars are mid-engine, you can run a lot more rear bias than you realize. For your case, you are just few percentage points high. Are you keeping the ABS system on the car or disabling it? I learned to hate it so bad that I removed it. You will be very happy that you will be able to start trail braking the car without inducing a push in the car.

Lotus really screwed these cars up when they put 305mm front disk with 4 pot calipers and left 288mm rear with a single pot caliper. The earlier cars that has 288mm front and rear, just need to get rid of the single pot calipers. The one thing that everybody forgets about these cars is that they still are a momentum car when driven correctly.

Later,
Eldon
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post #114 of 156 (permalink) Old 01-07-2018, 06:25 AM
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IF you buy the 5316 caliper, let us know where you purchase it, and price.

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post #115 of 156 (permalink) Old 01-07-2018, 06:33 AM
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Your front/rear bias is still a little high for track but is at good spot for the street. Since our cars are mid-engine, you can run a lot more rear bias than you realize. For your case, you are just few percentage points high. Are you keeping the ABS system on the car or disabling it? I learned to hate it so bad that I removed it. You will be very happy that you will be able to start trail braking the car without inducing a push in the car.

Lotus really screwed these cars up when they put 305mm front disk with 4 pot calipers and left 288mm rear with a single pot caliper. The earlier cars that has 288mm front and rear, just need to get rid of the single pot calipers. The one thing that everybody forgets about these cars is that they still are a momentum car when driven correctly.

Later,
Eldon
Thank you for your comments. FYI I plan to keep the car street legal but only marginally "streetable", the setup will be track focused (ride heights around ~110/113mmm, -3* or more camber). I find your comment about trail braking interesting because on the track, at least into the slower corners (with lower corner entry speeds), I've been able to trail brake with decent rotation with the stock S240 setup. I completely expect my braking to be better with the new setup, and should be able to trail brake more aggressively, but perhaps it says something about the value of keeping the stock rear brakes in good working condition (newish discs and pads with no taper, clean and lubed caliper bolts).

edit: Yes, I do plan to keep the stock ABS, I've learned to live with it. I expect if anything it will be less of an issue with better f:r balance. I can always trial it with one of the sensors unplugged.

-Ed
'08 Arctic Silver Exige S240

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post #116 of 156 (permalink) Old 01-07-2018, 06:41 AM
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looks nice (and $$$). I wonder if you'll have issues with pedal travel, since it sounds like you're not changing out the brake MC. I know of at least one person who added 4 pot up front and then tried 2 pot in rear, and complained of the length of the pedal after those changes.
Thanks! Yes, definitely pricey. I couldn't justify it based on the brake caliper change alone, the uprights are also good for lowering and increased neg camber.

I'll just have to see about the pedal travel. I've seen comments both ways (longer travel and no or minimal change), which suggests bleeding might be the issue. The APR 2 pot calipers are difficult to properly bleed, but I expect the QwkBleed lines will help with bleeding. I hope I don't need to change the MC, but I'll do it if necessary.

-Ed
'08 Arctic Silver Exige S240

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post #117 of 156 (permalink) Old 01-07-2018, 06:44 AM
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Thank you for your comments. FYI I plan to keep the car street legal but only marginally "streetable", the setup will be track focused (ride heights around ~110/113mmm, -3* or more camber). I find your comment about trail braking interesting because on the track, at least into the slower corners (with lower corner entry speeds), I've been able to trail brake with decent rotation with the stock S240 setup. I completely expect my braking to be better with the new setup, and should be able to trail brake more aggressively, but perhaps it says something about the value of keeping the stock rear brakes in good working condition (newish discs and pads with no taper, clean and lubed caliper bolts).
My S260 was horrible trying to trail brake it. If you had any brake at all on corner entry, it would start to push. This probably wasn't helped by the fact that I has not increased the camber, yet. I run close to what you have for ride heights, 110mm / 115mm. I currently only have about 2.2 deg in the front and 3 degs in the rear. I am serious considering shaving the up-rights so that I can get more. You might also want to check the bump steer now that you have gone this low. I used BWR's drop ball joints instead of changing the uprights, little easier and less expensive.

End the end, if you make the car more of a track car, you are going to want to dump the ABS and go to split masters. You can dial in the brake bias for different track conditions. Also, the pedal feel becomes more manageable without the brake booster.

Later,
Eldon
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post #118 of 156 (permalink) Old 01-14-2018, 12:01 PM
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Front Calipers on Rear

Photos of Elise-Parts uprights with 2-pots on the rear of my Exige (16mm drop GT model). Interesting that the calipers mount at the rear of my uprights yet they are on the front of AustenPís. My car is track focussed so I didnít bother with a parking brake.

May have found a reasonably priced, bolt-in larger master cylinder. Will take a couple of weeks to confirm. Will post info when have a definitive answer.

Bob L
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post #119 of 156 (permalink) Old 01-15-2018, 05:06 AM
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Photos of Elise-Parts uprights with 2-pots on the rear of my Exige (16mm drop GT model). Interesting that the calipers mount at the rear of my uprights yet they are on the front of AustenPís. My car is track focussed so I didnít bother with a parking brake.

May have found a reasonably priced, bolt-in larger master cylinder. Will take a couple of weeks to confirm. Will post info when have a definitive answer.

Bob L
The difference is that I have the "Ultimate GT" model in the rear, which are designed to take 2 calipers. My guess is that they move the radial caliper mount to the forward position and keep the slider mount in the stock location because it's easier to reroute the hydraulic line than it is reroute the handbrake cable.

Yes, please do post about the larger MC when you have more info. TIA, -Ed

-Ed
'08 Arctic Silver Exige S240
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post #120 of 156 (permalink) Old 01-15-2018, 06:10 AM Thread Starter
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Looks like calipers are going to cost a pretty penny, at least from Stillen

CP5317 - $332
CP5316 - $420

+ Freight

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