The curious case of the Atom 4 brakes

[plip1953]

Are these not the 9444 AP 5000R pro calliper suitable for 13” wheels and therefore 280mm discs as the other calliper 9440 are for 28mm thick discs when the 9444 take a range of thicknesses including standard Ariel size of 24mm I believe.

https://apracing.com/race-car/brake-cal ... s-13-wheel



https://apracing.com/race-car/brake-cal ... iston-area

Corten-Miller are offering the CP9440 front and CP9441rear calipers.

https://apracing.com/race-car/brake-cal ... iston-area

https://apracing.com/race-car/brake-cal ... iston-area

The difference between the two is that the 9441 has smaller pistons which means that master cylinders can be the same size front and rear. It would also be possible to run with 9440s (or potentially 9441s) both front and rear.

[Corten-Miller]

You will need a minimum of a 15” wheel to accept the front brakes, “15” team dynamics don’t fit” they have a terrible step in the barrel of the wheel , Braid’s or similar are the recommend choice. The factory 16”F and 17”R standard wheel option work. We have had a new production run of the RS14 pad commissioned to work with the new calipers at 18mm while retaining the 25mm disc thickness.

[Monza]

[Curves Junkie]

The difference between the two is that the 9441 has smaller pistons which means that master cylinders can be the same size front and rear. It would also be possible to run with 9440s (or potentially 9441s) both front and rear.

What is the correct size for the AP Master Cylinders by using the 9441 front and rear?

You will need a minimum of a 15” wheel to accept the front brakes, “15” team dynamics don’t fit” they have a terrible step in the barrel of the wheel , Braid’s or similar are the recommend choice. The factory 16”F and 17”R standard wheel option work.

When the 9440 not fit at front with TD 15'' - will fit the AP9441 at front/rear with the team dynamics 15/16'' then?

[Corten-Miller]

The difference between the two is that the 9441 has smaller pistons which means that master cylinders can be the same size front and rear. It would also be possible to run with 9440s (or potentially 9441s) both front and rear.

What is the correct size for the AP Master Cylinders by using the 9441 front and rear?

We have done the development work so not sure why you would need to move the calipers around? Any changes you make to caliper positioning will need testing and the process of R&D starts again.

You will need a minimum of a 15” wheel to accept the front brakes, “15” team dynamics don’t fit” they have a terrible step in the barrel of the wheel , Braid’s or similar are the recommend choice. The factory 16”F and 17”R standard wheel option work.

When the 9440 not fit at front with TD 15'' - will fit the AP9441 at front/rear with the team dynamics 15/16'' then?

The new calipers are physically larger you can’t use the TD 15” wheels or at least not with our conversion as you would then need to move the centreline of the brake assembly.

[plip1953]

What is the correct size for the AP Master Cylinders by using the 9441 front and rear?

To an extent that will be down to individual preference, but the key point at this stage is that equal sizing seems to work (both in theory and in practice). As a starting point I'd probably suggest a pair of 0.7" MCs, but 0.75"s should also be good. Including a rear proportioning valve can provide an extra layer of adjustability.

[Curves Junkie]

[mention]Corten-Miller[/mention] and [mention]plip1953[/mention]
Many thx for ansering and the informations.

[reg]

A dry day, without much crap on the roads so time to begin bedding the pads in. The balance is very good, at lower speeds bite is good, at higher speeds, feel like they have a bit to go yet. Modulation is good, no unexpected lockups and consistent each time. They remind me a lot of the Alcons in my 3.5, in how they feel, ultimate power prolly not too much different as mechanical grip is limited in any Atom. the big news is pedal length is consistent and it repeats, that part is night and day different. Really makes a good difference in the confidence in the car. The next test will be on track, but on the road the 5000s are a lot better than stock. There are loads of different compounds available for this caliper, might try rs14, we will see. Really pleased with the setup.

[plip1953]

A dry day, without much crap on the roads so time to begin bedding the pads in. The balance is very good, at lower speeds bite is good, at higher speeds, feel like they have a bit to go yet. Modulation is good, no unexpected lockups and consistent each time. They remind me a lot of the Alcons in my 3.5, in how they feel, ultimate power prolly not too much different as mechanical grip is limited in any Atom. the big news is pedal length is consistent and it repeats, that part is night and day different. Really makes a good difference in the confidence in the car. The next test will be on track, but on the road the 5000s are a lot better than stock. There are loads of different compounds available for this caliper, might try rs14, we will see. Really pleased with the setup.

Sounding really good. Now you have the AP Pro 5000 R calipers, but with the smaller piston combination version on the rear (ie CP9440 front and CP9441 rear) I believe you are now running equal sized master cylinders? Size? As yet, have you worked out where the sweet spot for the brake balance setting?

[reg]

Currently it appears that it’s pretty much even. The balance bar is level. It’s running equal master cylinders. It’ll need pushing on track but on road it’s pretty good.

[reg]

Last minute decision to go to Bedford today. It was f*cking freezing at 0600 when I departed, didn't warm up much by the time I arrived. But, it was dry, and was going to get warmer, especially with some coffee.

Rewind a few months and the last Bedford day I attended was a nightmare. Trying to get the OE brakes on song we fitted RS14's, changed the master cylinders and added a brace. Long story short, the balance was all wrong, rears locked all the time and it just made the car a pig to drive.

I had driven the car with the new calipers retaining the ZZR's, IME they are hopeless in anything other than very warm track day conditions. As soon as the 52's were back on the car felt far more compliant. Set the tyre pressures once and left them alone. First few laps was on the road settings, went ok, back in a got some fuel. At this point swapped to the track settings. This transforms the turn in and grip.

Pedal remained exactly at the same point all day. I like 1144's, but IMO they aren't up to the job on track, purely on a personal point of view in respect to bite at higher speeds. However, saying that they stayed consistent and although definitely overheating it didn't get in the way. No long, or changing feel and the balance with the bias at 50/50 was really good. As confidence grew braking became later and harder. I think this is the first time I can say that leaning on the brakes in the 4 game me a good feeling. With the OE setup it was possible to go fast (for me) but the feedback was always a bit odd, it's difficult to explain. What isn't difficult to explain is enjoying a car on track requires confidence, the OE setup never gave me this, I feel the upgrade has delivered this. It's close to the old 3.5 now.

Next step is to fit a set of RS14s, TBH, I think it will take this to the next level.

Anyway. Good to catch up with faces old and new at the track. Bedford is a really underrated track IMO...although they are very strict on noise.

[plip1953]

Pedal remained exactly at the same point all day. I like 1144's, but IMO they aren't up to the job on track, purely on a personal point of view in respect to bite at higher speeds. However, saying that they stayed consistent and although definitely overheating it didn't get in the way. No long, or changing feel and the balance with the bias at 50/50 was really good. As confidence grew braking became later and harder. I think this is the first time I can say that leaning on the brakes in the 4 game me a good feeling. With the OE setup it was possible to go fast (for me) but the feedback was always a bit odd, it's difficult to explain. What isn't difficult to explain is enjoying a car on track requires confidence, the OE setup never gave me this, I feel the upgrade has delivered this. It's close to the old 3.5 now.

".....although definitely overheating...." Do you mean the brakes were overheating?

[reg]

Hi Phil, discs had some colour and you could smell the pads. It never changed the performance of them but I think a more aggressive pad would be better.

[plip1953]

Hi Phil, discs had some colour and you could smell the pads. It never changed the performance of them but I think a more aggressive pad would be better.

Both fronts and rears? It's clearly something to keep an eye on.

[reg]

RS14's arrived so today took the 1144's out and replaced. Used the time honoured approach of a piece of string to hang them along with pipe lagging to protect the powder coat on the wishbones.

I have the anti-rattle springs fitted which tbh I think I will remove as they make pad changes a little more of a faff, I think without the springs youcan change from the top without removing the caliper...anyway, it's a 10 min job. The 5000's are super nice to work with, no pins to drift out.





Will bed them in tomorrow. 1144's had some glazing, not sure if this is just the drive back from Bedford or something else? Will update tomorrow.