Editing Brake discs (section)

==Lotus OEM Fitment==
===S1 Elise===
====MMC====
When originally conceived and released, the Elise was supplied with Metal Matrix Composite (MMC) brake discs in combination with specific MMC brake pads.  In general it is agreed that an MMC brake setup provides excellent brake performance and feel.  The only real complaint seems to be that in wet weather the initial bite and performance is poor until the discs are dried by application.  (From VIN 2260 a splash guard was introduced to reduce this problem - Source [http://www.elises.co.uk elises.co.uk])

MMC's differ from normal 'iron' discs in that the friction generated is mostly Adherent Friction rather than abrasive friction (a very good article on the nature of braking can be found [http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml here]).  Essentially when the disc and pad come in contact some of the pad material transfers onto the disc surface, meaning the contact patches between the two are effectively the same material.  As the disc rotates the bonds between the surfaces break and reform creating friction.

One of the benefits of Adherent Friction is that under normal use the discs last a very very long time.  When braking the pads transfer their material to the surface of the disc, and it is this layer that is broken down, not the disc suface.  Therefore the discs suffer very little wear.  Under very heavy use however, the bonds between the pad and disc cannot reform as fast as they are broken down, meaning areas of the disc can lose the material layer entirely.  When this happens the abrasive friction of the pad can score away the disc surface making it too rough to rebuild the original material layer.  If this happens braking performance from the disc is permanently damaged and the disc must be replaced.  For this reason car used on track or running semi-slick tyres may wish to use traditional setups.

MMC discs were also extremely light, reducing the unsprung weight of each wheel.

MMC brake systems were supplied up until VIN 3714, when increased part costs forced Lotus to introduce standard iron brake discs.  Recently Lotus have had trouble sourcing replacement pads, and have offered discounted conversions to iron discs for affected customers.  Third party replacement pads are available from [http://www.eliseparts.com Elise Parts] and [http://www.elise-shop.com Elise Shop].  These alternative pads are also said to improve wet weather performance.  MMC discs are no longer available.

====Standard cast iron====
[[Image:A111J0128F.JPG|thumb|right|Vented S1 OEM Disc]]
These discs followed the MMC disc as the standard brake disc for the S1 Elise from VIN 3715.

Although introduced for cost reasons, Iron disks are better able to withstand the high temperatures associated with track driving and provide better wet weather performance than the previous MMC disks.

The surface of the disks are solid, however they are internally vented to aid cooling.  As the disk rotates at speed, centrifugal forces act on the air inside the vanes, forcing it outwards from the center.  This action then draws fresh, cooler, air from the center of the disc through the internal vanes and out through the holes in the edges. (Lotus Part Number: A111J0128F)


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====Cross drilled====
[[Image:A111J0141F.JPG|thumb|right|Cross drilled and Vented S1 Disc]]
The Sport 135, Sport 160, Sport 190 and 111S models were supplied with iron disks which were vented and cross drilled.  Cross drilling is the name given to drilling holes through the disc.  This has a number of advantages:
* The holes allow for better cooling by drawing more air into the internal vanes.
* The edges of the holes clean pad surface which can provide increased brake 'bite'.
* The holes prevent gasses from collecting between the pad and disc surface
* The holes reduce the weight of the disk, and therefore its inertia and the unsprung weight.

(Lotus Part Number: A111J0141F)


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===S1 Exige, 340R===
The Lotus Series 1 Exige and 340R, were fitted with the same cross drilled disks as seen on the Series 1 111s and Sport 160 editions described above. 
(Lotus Part Number:A111J0141F)


===S2 Elise and Exige===
Series 2 Elises are fitted with 288mm vented iron discs.  308mm 4 piston AP Racing brakes were on option on the Exige S240 and S260.

The discs on the S2 are different from those one the S1.  This is due to the S1 iron discs being a copy of the original MMC discs and therefore an uncoventional size. S2's were shipped as standard with plain discs, with cross drilled versions being available as an option. Later S2's were shipped with the cross drilled discs as standard.

The S2 discs 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 calipers.

===Vauxhall VX220/Opel Speedster===

VX/Speedster discs are also 288mm as on the S2, but there are some differences:

* hubs are 5 stud
* use a bigger center bore
* use a slightly different offset (about 1 to 2mm) because the VX220 uses a different bearing pack. (uprights are identical to the S2 though)
* are almost the same thickness as S2 discs (25mm vs. 26mm), but have a much thicker surface and as a result a much smaller air-gap between the disc surfaces.

The last point makes the VX220 discs significantly heavier than S2 discs (around 750G to 1 Kg each).

The thicker surface should give them a little more heat capacity, but also makes it more difficult for them to shed the heat again.

VX220 discs are actually taken from existing GM cars (Vauxhall/SAAB), eg. Vauxhall Vectra V6 2.5 front discs, and as such they can be obtain from many regular car-parts stores are very low prices.