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S2 Braking System

From Nick Adams (Lotus Life BBS): The S2 discs are a more conventional design than those used on the S1 (which were iron copies of the MMC discs used on the S1. The S2 discs are fed with cooling air from the back face, i.e. the side furthest from the wheel. This results in a better air supply than on the S1 which had front fed discs, primarily for reasons of strength of the MMC used early on. The S2 discs also feature longer, curved internal flow passages which increase the disc stability and reduce hot spot formation. The revised hole pattern has been specified to complement the new vane arrangement. The discs are not handed, so the same disc is used on the right and left hand sides of the car. The cooling air flow through the left and right discs is identical and the flow rate is purely a result of pressure differential between the centre of the disc and its rim; the shape of the vanes and the direction of rotation does not affect the flow rate significantly.

Some noise from the brakes themselves is to be expected but there is a fix to stop brake pads banging in the callipers. Another problem is that of vibrations making their way back to pedal unit, causing it to vibrate at lower speeds. This is still under investigation by Lotus.

Although not significant for road use, improved cooling will come from the discs rotation being correct and most brake manufacturers do state a preferred rotational direction for their discs.

Brake Feel

The Elise brakes need to be bed in properly to reach optimum performance and my dealer improved the feel on my car by doing a succession of hard stops from about 70mph. This is described in the following post by Nick Adams on the Lotus Life BBS.

With new pads and discs, or just new pads fitted run the car around for 10-20 miles using the brakes gently as normal to bed the two surfaces together. Once this has been done, check the surfaces of the discs and make sure here are no signs of any scoring or damage. Assuming all looks well take the car to an appropriate piece of quiet and straight, well sighted road and perform half a dozen medium pressure stops from 50 mph down to 20 mph to warm the brakes up. Avoid more than a minute between each stop so that the temperatures do not get a chance to deteriorate too much. Once the brakes are warm and the coast is clear, perform 2 or 3 hard stops from 70mph (where local laws allow!) to 20 mph, braking as hard as you can without locking up. Do not come to a halt between each stop, do them as fast as you can to get the brakes really hot. On the third stop come to a halt and keeping your foot on the brake press the brake pedal down as hard as you can and hold it there for at least a couple of minutes, don't apply the handbrake. This hurts if you are doing it right! This will bed the pistons, shims and pads together and will compress the pad material, giving a hard and repeatable pedal. Once the 2 minutes have passed, release the pedal and go for a short drive, using the brakes as normal to let everything return to normal temperatures. The brakes are now fully bedded in and ready for use in anger. Recompressing the pads once every few thousand miles to the above procedure will help keep the pedal firm, especially if you don't normally use the brakes hard.

Sticking Pads

The unservoed brakes on the S1 were criticised for not having enough initial bite when first applied, so Lotus used higher "grab" pads on the S2 to improve this. A byproduct of these pads is they tend to stick to the disc over a period of time, in damp or humid conditions this can happen within a couple of hours. This is something that affects the S1 as well but not to the same extent. Normally the stiction is limited to a clunk on pulling away, but with wet weather or if the car has recently been washed, the stciking can be quite severe. It's a case of they all do that. Never put a car back in the garage having just washed it. Go for a quick drive to dry the brakes off first. If poosible, park it with the handbrake off.

Upgrades

First of all, the Elise brakes are extremely good to start with. Since they are non-servoed, some people (especially those used to servo assisted brakes) find the intial bite lacking and the feel slightly 'wooden'. Once familiar, it is hard to go back to a normal car. The disks on the S2 are different to those used on the S1. They are the same diameter, but have a different offset and venting.

Pipework

As standard the Elise does not come with braided steel brake hoses. These prevent the pipe walls from flexing when higher temperatures are reached and thus allow a more consistent pedal pressure and feel to the braking system. This is probably the first thing to change to improve the brakes.

Brake Fluid

A better quality brake fluid will improve brake feel and a higher temperature grade will also help under hgih stress conditions.

Brake Pads

Possible the simplest thing to change and likely to yield the greatest improvement. The brake pads on the S2 are designed to provide an improved initial bite over those used on the S1. Both are designed for normal road use in mind and this means that they need to be quiet and work when cold or wet. No one pad make/type is best for all situations. For fast road use the Mintex 1144 and Pagid RS14 get good recommendations from owners.

A quick summary of the various Pagid pads is:

  • Pagid RS4-2 (blue) are road oriented, meaning they are quiet and good for road and occasional track day use.
  • Pagid RS-15 (black) are track/race oriented, they squeel a bit on the road, have a ceramic additive (therefore discs will wear quicker). Much better frictional (braking) ability. Sometimes need a little warming up. These replace the RS-14 pad which has been discontinued.
  • Pagid RS19 (black) are endurance race oriented. Several teams have got through 24 hour races on one set. Would last most race drivers a full season. Frictional ability is roughtly half way in-between RS4-2 and RS14. Will definately need warming up for road use on the Elise. Only available for the front for the Elise.

Discs

The majority decision seems to be that the MMC disks give better feedback than the iron ones. With the S2 they are not an option as the wheel and drake sizes are different. Like all iron discs, they will go rusty in wet weather. There is nothing you can do about it and it certainly isn't a problem. It also affects all makes of cars.

With iron discs, cross-drilling allows the gases produced when disk pads heat up to escape, improving fade resistance. Grooved disks work on the same principle but are more effective. The down side of both is that they slightly reduce the consistent feedback through the pedal.

The normal brake disks are a combined mounting drum/bell and disk. The physical dynamics of this shape can cause undue stress in extreme temperatures and a better solution is to use a seperate bell and disk. This has the added advantage of saving significant unsprung weight. They is simply no reason to upgrade to bigger disks. Even with 200+bhp and the softest tyres available, you will not need them.

Callipers

There doesn't seem to be any real benefit in changing these. With the S2, there is room for larger callipers (larger wheels used) but this would shift the front/rear braking bias. Again, there is no need to upgrad them callipers. The standard fitment are perfectly up to more power and stickier tyres.

Mounting Points/Linkage

There are no vunerable parts of the assembly that need reinforcing to improve feel and response as far as I am aware.

Anti-lock Braking System (ABS)

The Elise doesn't yet come with ABS for several reasons. Firstly, it takes time to develop and it simply hasn't been a priority for Lotus. Secondly, it costs money to develop and will significantly add to the price of an Elise. And finally, the Elise handling will be slightly compromised by the additional weight of ABS, especially as it is unsprung weight. They is no doubt that it would make the Elise a safer car but, for now it is not an option.

There are various misconceptions about ABS. The first is that a good driver can stop a car quicker without ABS. In both a 'stamp on the brakes' situation or in a drivers 'best effort' situation, this is simply not true. Modern ABS systems are specified to improve braking distances under all conditions and for all drivers.

The second misconception is that ABS quickly locks and unlocks the wheels. This is not true and modern ABS prevents the wheels from locking in all but extreme ice conditions. In order for tyres to maintain maximum grip, they must rotate and ABS is designed to maintain just the right rotation to maximise grip. All tyres have a Mu-slip curve which plots the percentage of slip required for a given level of grip. For a modern tyre the optimum slip is typically about 5%. ABS is also more effective than a human driver because it can adjust braking forces at each wheel in isolation to maintain optimum grip. ABS can take account of vehicle loading, weight transfer and road surface conditions at each wheel. In a non-ABS vehicle there is simply no way to do this and the driver is forced to optimise braking effect at one wheel and thus compromising braking effect at the others. It is this effect that allows an ABS equiped vehicle to steer whilst under hard braking.

It is also worth noting that there are various types and quality of ABS systems available and the most effective ones monitor wheel speeds and vehicle acceleration in various dimensions. Cheaper solutions as used on by some mainstream manufacturers are not as effective as the advanced systems available.

Suppliers

Supplier sites worth looking at are:

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