Rear Disc Brakes

[SwiftDB4]

It is possible to fit 3 MC in with original floor mounted pedals. This is on an S1 with S2 Spyder frame. Tight but works.

[BDA]

First, I should mention that I have Banks vented front discs , Banks rear discs, std. dia. M/C, and dual Lockheed boosters. I also have a much bigger chin spoiler than stock.

I have really only noticed the fronts locking up severely (with a lot of accompanying tire smoke!) in panic stops at relatively low speeds. I don’t think I’ve had what you would call panic braking at high speed but I’m sure I have had a reason for heavy braking at relatively high speed and I don’t recall a lot of drama.

I have theorized that aerodynamics plays a part since at low speeds, the front would be “lighter” than at higher speeds. For TC road tests, aero could also play a role since I understand even the stock chin spoiler is effective and I would guess their braking test are probably from higher speeds (60mph+?).

Another factor could be that at lower speeds, you don’t get as much weight transfer to the front wheels.

Just a few thoughts on the issue of front wheel lockups under braking...

[Clifton]

It is possible to fit 3 MC in with original floor mounted pedals. This is on an S1 with S2 Spyder frame. Tight but works.

Is this your car? I would love to see more of how the balance bar was done.

[literarymadness]

A couple of interesting observations from road tests back in the day.

Road &Track November Issue, 1973:

The brakes when used as Lotus engineers intended them (slowing for corner), are excellent: good control and easy to modulate. But in panic braking the rear end of our test car locked near the end of the stop, causing the back end to swerve. So stopping distances are only average. We had expected better, especially since the 70-series radials are one size larger at the rear.

Motor Sport February, 1972:

Quite Frankly we were disappointed in the wet weather handling of the car: the rear broke away much more quickly than one would have expected and sometimes the front caught us out and went first...we did not expect this from a Lotus

I can tell you first hand that a panic stop in the rain is not pretty which is why I went to rear discs to begin with.

[jbcollier]

That would be with the 1.5" wide drums.

With my S1, I have driven in all weathers and made some strong stops -- I tend to drive so as to avoid full-on panic stops.  I have not noticed any issues other than the need to "squeeze" the brakes just like I do on my motorcycles and bicycles.

[literarymadness]

@JB: The Fed-spec TCS (1650 lbs.) is 20 to 25% heavier than your S1. Your car's lighter weight definitely has the stopping advantage over a TCS.

[GavinT]

My S1 has Wilwood 4 pots all round (1.75" F and 1.375" rear). I have 13" wheels and I believe the rotors are 10" front vented, rear solid.

That's a notable advantage of multi-pot callipers.
Because they're compact you can utilise larger discs for a given wheel size. Obviously they also increase the torque leverage, too.

It is possible to fit 3 MC in with original floor mounted pedals. This is on an S1 with S2 Spyder frame. Tight but works.

Thanks for the pic, Swift.
Three MC's doesn't look as crowded as I'd imagined.

I kept floor mounted and used a dual master as I didn't want to cut out my frunk. If you want tandem masters you can make it work.

Thanks for the pic, Clifton.
Can't quite figure it out but is the balance bar articulating on a pivot within that structure?

No Gavin, 13" would be very optimistic 

I'm using 15" wheels. I haven't checked but would imagine that 245mm (GT6) and 240mm would be about the best you could get with 13" wheels.

Ha . . . I'm nothing if not optimistic.
Probably 15" wheels are the go, anyway.


Interesting link, JB.
I hadn't previously devilled into the finer points of twin MC's all that much. It takes very little travel on the balance bar to distribute pressures changes, so that's good.

Here's the notes on the Tilton adjustable prop. valve with some explanation of their workings.
Any glaring issues here?

https://tiltonracing.com/wp-content/uploads/2013/07/98-1261-Brake-Proportioning-Valve.pdf

[literarymadness]

Got this article about brake biasing and performance from a site called Brakepedia sponsored by Brakes-shop.com

https://www.brakes-shop.com/brakepedia/general/brake-bias-and-performance

[jbcollier]

The problem is that the brake bias we want on clean, dry pavement is entirely different from what we want on a slippery wet road.  Other than converting to ABS brakes, there isn't a safe way to get both.  The best method would be to fit an adjustable proportioning valve that works via rear suspension height, reducing the rear braking as the rear suspension rises.  This would be very difficult to implement.

I think the best compromise is to set up the brakes for clean, dry pavement and use tires that perform very well in the wet.

[Clifton]

Thanks for the pic, Clifton.
Can't quite figure it out but is the balance bar articulating on a pivot within that structure?


https://tiltonracing.com/wp-content/uploads/2013/07/98-1261-Brake-Proportioning-Valve.pdf

Yes, the pivot is at the bottom.

[4129R]

First, I should mention that I have Banks vented front discs , Banks rear discs,

For the record, I have just ordered spare disc pads for Banks for their ventilated front and solid rear discs.

The front pads are TRW GDB 327, from a Citroen Saxo or Peugeot 106

and the rear pads are TRW GDB 472, from a range of Ford cars.
Equivalent Part Numbers:-
Febi Bilstein: 16169, BELACO: BC398, BORG & BECK: BBP1302, BREMBO: P 24 018, DELPHI: LP507, EEC: BRP0537, FERODO: FDB398, LPR: 05P677, MINTEX: MDB1287, MOTAQUIP: LVXL520, PAGID: T5006, QUINTON HAZELL: BP364, TRW: GDB472, FORD: 1543375 .

[cazman]

Clifton - is your balance bar adapter custom made?

[Clifton]

Clifton - is your balance bar adapter custom made?

Yes, custom. I used the factory pivot bushings and rod and kept the same ratio on the pivot that Lotus used. The balance bar part is off the shelf. Just the box that holds it all is custom. It bolts to the factory holes on the frame. I ended up adding a remote adjuster to make adjustments easier. If you can weld, it's an easy part to make.

The bias and feel is perfect. Slightly firmer than a vacuum boosted car. I may have had 3 or 4 front inside tire lock ups out of maybe 150 ish autocross runs trail braking into a low speed turn, common. Never both locking when pointed straight.

[cazman]

I have been thinking about doing the same. I did not think there was room though. What is the pivot bushing? I have a push rod and the MC - what else is there?

What size MC bores did you use?

[BDA]

First, I should mention that I have Banks vented front discs , Banks rear discs,

For the record, I have just ordered spare disc pads for Banks for their ventilated front and solid rear discs.

The front pads are TRW GDB 327, from a Citroen Saxo or Peugeot 106

and the rear pads are TRW GDB 472, from a range of Ford cars.
Equivalent Part Numbers:-
Febi Bilstein: 16169, BELACO: BC398, BORG & BECK: BBP1302, BREMBO: P 24 018, DELPHI: LP507, EEC: BRP0537, FERODO: FDB398, LPR: 05P677, MINTEX: MDB1287, MOTAQUIP: LVXL520, PAGID: T5006, QUINTON HAZELL: BP364, TRW: GDB472, FORD: 1543375 .

Great information! Thanks!