Brake discs - AP rotors worthwhile?

Hi Folks

Once again I impose on your collective experience. I am running my S2 (111s not exige - sorry) on the oem crossdrilled discs, pagid RS42’s and braided lines. Great braking ability, but the discs are well and truly dying. With the added cooloing of my radiator, I am finding water temp on the track constant at 88 C and oil peaking at 106 C (never over 110). I am being seriously limited in the time I can spend out on the track, by brake fade - I start to get juddering and sponginess of the pedal after 5 or so hard laps. I would really like to be able to stay out longer and not have to worry about this. Plans have suggested ali belled rears - similar to the eliseparts ones, and Ali-belled AP rotors for the front. They said on a road car, the AP rotors for the rear don’t work so well with the handbrake.

HAs anyone tried this sort of combination and will this really limit the fade? I presume the rate of wear will be far less on the AP’s than OEM. I plan to stay with standard calipers for the time being.


I am sure the Plans solution is tested and performs very well, but in my opinion is not so natural to experience all these brake troubles after just 5 hot laps. Have you changed the brake fluid and did a good bleeding?

Ali bells and AP rotors seem to be very well regarded. Something may be coming up about this soon, so keep your eyes peeled.

you have to be clear that there’re two types of brake fade:

  1. fluid boil - you get a spongy pedal as a result
  2. overheating the pads - you just lose the braking performance, but doesn’t necessarily affect pedal feel.

When was the last time you changed your brake fluid? The fluid will absorb moisture over time and reduces the boiling point as a result.

Just switch to RS14s with new brake fluid should do the trick

Thanks for the responses. My fluid was replaced in late November. I am definitely not boiling the fluid. After 5 or so laps, I am experiencing juddering and a whining noise at the front under braking. The brake feel definitely starts to go downhill, but returns to normal after a few minutes of cooling. The discs realy have started to suffer and were looking seriously blued after the last outing. The pads seem to be wearing ok. I was initially reluctant to go for 14’s as I use the car a lot on the roads and the 42’s seem to work rather better when cold.

I await keen ly any news re AP rotors. Thanks Steve.

Have you followed the Ohlins thread,
I sort of hijacked it and it’s now about my brake problems. Sound very similar to yours.

Thanks Simon - that is all extremely relevant. I just want a setup that I do not have to worry about. The car stays cool now, so I would otherwise like to get longer sessions before the brakes go. A good friend with a 111s like mine has the same problem, no better after new discs.

Sounds like AP’s are increasingly appealing.

That’s your solution: 295mm AP’s and whatever in the back.
Plans are putting you in the right direction.

If you still have problems, you’ll have to think about ducting

So are the back not as critical? By using the standard Ali belled rears, I will save a fair bit.

I have asked plans to get me some 295 front AP discs.


AP’s all the way!!! You wont go far wrong with AP stuff.


The blokes at plans reckoned the rear AP’s were a hassle to fit and not good on a road car where you might want the hand brake.

Hence the suggestion of their standard ali-belled rotors.

Yes, the rears are not critical as they don’t do as much work as the fronts.
Even when I was having all sorts of problems with the stock ones, the rears were ok.

Std alloy belled at rear will be Ok.

Yeah I don’t run the standard rear callipers and I have no hand brake, so the AP’s were not a problem.

I had a chat to a bloke on Seloc who suggested that the AP rotors from eliseparts are a higher spec to those at plans. On the other hand, plans felt there non-AP ali-belled rotors are better than the eliseparts ones.

Does anyone have any info on this. Ie - does it really matter?

I don’t think either Plans or Eliseparts supply the 3000 series AP which are the proper ones that I think Lotus supply and hence Sean has. 5000 series are Clubman spec.

Does it matter? Personal opinion I guess. All I know is that I tried a car with stock calipers and AP 3000 rotors (295 up front) and it felt great.


It sounds to me from your description that you have two things happening. The sponginess of the pedal definitely sounds like your fluid getting too hot. In my opinion you should flush your brake system with a quality Dot 4 fluid before every track day.
The juddering on the other hand sounds like a pad to rotor transfer problem. Let me explain� On a properly operating brake system (one where the pads have been properly bedded) a layer of material from the pads will bond itself to the surface of the rotors. This �transfer layer� is the actual surface that the pads now wear against. At temperature, the material of the pads will re-bond with the transfer layer on the rotor at a molecular level and subsequently be sheered apart again during braking (this is your friction). So actually very little rotor wear is experienced under these conditions. The transfer layer is continually being laid down and wore off. Now this only happens at higher brake temperatures (actually depends on the heat range of the pads). If you use your car on the street with a high temp/semi abrasive pad such as the RS42�s it is possible to wear the transfer layer completely off during day to day driving since you are not getting the brake system up to the proper temperature to replenish the transfer layer. When this happens you are going to the track with a car that�s brake pads and rotors have essentially not been bedded in (bedding is the process of creating a proper transfer layer). Now if you go out on track and proceed to go at it, even know you may have warmed the brakes up before really stomping on them, the transfer layer is not there. Using the brakes in this way before the pads have been properly bedded (transfer layer created) can create hot spots on the rotor which can change the metallurgy of the iron. These hot spots will now not wear at the same rate as the rest of the rotor causing high spots. These hot spots now will not allow a proper even pad transfer layer to be deposited on the rotor. The result is a brake system that feels normal at lower temps but when elevated to the temp where the transfer layer relationship between the pad and rotor comes into play the unevenness of the layer causes an inconsistency in the friction level at different areas of the rotor. This is what is causing the juddering. And let me guess, you can feel it more in the wheel than in the brake pedal?
At this point your rotors are binned. Once you get hot spots on in the rotor there is no saving them. It is very hard to successfully run a track worthy brake system on both street and track without running into these problems.
What I would suggest is that you get a second set of rotors and (better pads i.e. RS14) and put them on only for the track (bedded in properly of course). I�ll bet your current setup still feels fine on the street. I would leave them on the car for street use.
I feel for you Andrew, I went through the same scenario with my S4 Esprit. Sometimes you just can�t have your cake and eat it too.

as a newbie to this level of brake chat, can you let me know the best way to bed in the pads - got some new RS42’s going onto the car on Monday, along with some braided lines.


Here’s a good tech artical that will answer your question.

Pad and Rotor Bed-In Theory


Excellent stuff - thanks.

excellent stuff indeed - many thanks