Stopping a Lotus On a Dime Every Time
Posted on 09 May 2017
It’s a common question; “Should I buy a BBK (Big Brake Kit)?”
My answer is almost always no. Now, there’s nothing wrong with bigger brakes when there’s some thought put into them. However, most BBKs have little, to no thought, other than “bigger must be better” and “they look cool”, so people will buy them. Gawd forbid that someone actually buy proper race parts like AP, Brembo, PFC, Alcon, etc, but to make matters worse an unsuspecting soul may fall for heavy and squishy calipers from Willwood or similar because they’re cheaper! The labor is all the same, so why skimp on parts… Or better yet, why buy parts that may not make sense?
Don't over-brake the front!
OEMs err on the side of applying too much front brake bias to a car to help keep them safe. More front bias helps prevent the ends of the car from swapping in a panic situation, but rather causes the car to under-steer or plow forward as the fronts over power the braking.
With a Lotus...
On the track and even the street, to keep the platform steady, you need a healthy dose of rear brake bias. The center of gravity (COG) and suspension setup of the Lotus is such that it does well with a brake bias something close to 55% front and 45% rear (just a baseline, but a good starting point). The factory 2 pots with sliding rear caliper is over 60% front and that’s only if the rear calipers clamp when they’re supposed to--- which they often do not given the slop of the sliders. The worst braking Lotus chassis is the 240/260/Cup Exiges with the 4 piston fronts and sliding rears along with 308mm front discs (standard disc is 288mm). Those cars are nearly undriveable on the track, in my view. The front bias is simply out of hand with that combination: bigger front rotors and calipers.
So how to fix it.
Well, the best solution is run an adjustable biasing system and move to a radial mounted rear caliper. You can fix braking problems in stages as budget and courage allows. I preface the following with this: you will never have a great braking Lotus with the stock sliding rear caliper. Never.
It's not the size that matters as much as it is what you do with it
Our view is that you want to stick with the standard 288mm rotor in most cases. Reasons for this are several. First, it is 15” wheel friendly. Rotational mass is a major enemy. Rubber weighs less than aluminum. So the smaller the wheel, the less rotating mass. 15” wheels are CHEAP and plentiful. We recommend running them on all 4 corners. 288mm rotors are the smallest Lotus rotor, therefore lightest. 288mm rotors are the least expensive and most widely available. They can be purchased for as little as a couple hundred a pair to over $1,000 a pair in a multitude of configurations. Running costs are a real issue, and something to consider. 288mm will whoa even the most powerful Lotus cars down on a repeatable basis just fine if the whole system is engineered well. My personal Lotus has over 500bhp and stops on 288mm rotors…
Radial Mounted Rear Calipers
Make this mod #1. Find a set of front calipers (44mm pistons) and mount them to the rear upright. We make a great bracket for this and there are other competitor versions too. With no other change, running the same caliper front and rear will vastly improve the braking performance. VASTLY. You will likely find that running 1 compound less aggressive in the rear with otherwise equal brake parts front and rear is a great combination. A Cobalt XR3 in front and Cobalt XR4 in the rear with 44mm front and rear 2 pot calipers is pretty great!
Do not run a larger front caliper than the rear unless you have some way to return the bias to close to neutral. A proportioning valve is NOT a great tool for this. Google can explain this in detail. The best tool is a true biasing bar from the likes of Tilton, etc. See our brake biasing cage for a great way to implement a biasing bar. With a biasing bar, you can remove the problematic brake booster and even the ice-mode invoking Lotus ABS.
Why remove the booster? The booster eliminates feedback to the driver. The Lotus brake booster reduces pedal pressure by some 60-70%. To gauge brake pressure, the driver has to feel the difference of just a few pounds of pressure in the heat of track battle with his strongest and largest body lever, his leg. Conversely, with an un-boosted brake system, tire lock-up may be at 100lbs of leg pressure, so he can much more reasonably judge a light brake from a heavy brake when the feedback from 0-100lbs of leg pressure verses 0-30lbs of feedback from a boosted system. Manual brakes are true braking bliss on the track or autocross.
But I want more!
For the crown jewel, once you have adjustable bias, go ahead and replace the front calipers with something special. We use the Radi-Cal from AP. It’s the latest and greatest from AP. Super light, extremely rigid, and a proper race caliper… and yes, we have a bracket for that too!
Hope is not lost if you have a 240/260/Cup
For those with the big 4 pot AP front calipers and big rotors, the fix is a biasing cage and radial mounted rear calipers. This system will work great, it just takes fixing. Again, you need to get the braking biasing closer to 55/45 vs the 80/20 the 240/260/Cup cars have from factory.
Bottom line for Braking Bliss in Steps:
- Close to equal size front and rear caliper and rotors with radial mounted rear caliper. A great setup is the standard Lotus 44mm 2-pot caliper front and rear with 1 compound less in the rear.
- Install a biasing bar setup while deleting the booster and stock ABS
- Add “uber” front calipers like the AP Radi-Cal.
- Install a Bosch Motorsport ABS system (cubic dollars required)