CCBs triggering ABS

[Coby147]

A lot of threads talk about CCBs in the wet with regards to lack of bite etc. Does everyone also find the ABS kicks in very early making it hard to modulate?

I've gone from Porsche 992 CCBs where I thought it was the weight distribution as even on steals they required some preloading and finesse so as to not unsettle the car. Now with BMW CCBs I notice the same in the wet that the ABS triggers way too early and I can't quite get that threshold braking accurately when driving spiritedly in the wet.

Are there any tips for getting the maximum braking in the wet and keeping out of the ABS zone? On steals I can get to max braking quickly and if ABS triggers you can ease off a fraction. With CCBs it seems once the ABS triggers you have to lift off a lot so do you have to just squeeze on the brakes more slowly and then play with the ABS limit? Also the back end seems to get lose which in the 911 again I thought was the weight distribution but the same is happening in this BMW M5CS which didn't happen in a standard M5 without CCBs.

I appreciate getting the brakes up to temperature helps significantly. However if you leave home on a cold, wet morning and have to do an emergency stop how would you go about this?

Thanks. Any advice would be really appreciated as braking and corner entry is usually where I make up most time and now feel like I have no confidence to accelerate!

[GreenV8S]

If you're lapping in a high performance car that is in danger of overheating organic/metallic brakes then carbon ceramic brakes may be beneficial once they are up to temperature.

You shouldn't be anywhere near those conditions on public roads. When you leave home on a cold, wet morning you'd be far better off with organic/metallic brakes.

[Coby147]

I completely agree but this neither helps me nor answers my question.

[E-bmw]

Have you looked at the other part of the equation, as in tyres?

[GreenV8S]

Coby147 said:

I completely agree but this neither helps me nor answers my question.

Let me rephrase the answer. Brakes designed to work under high heat conditions can be dead and grabby when cold. That's the price you pay for having racing brakes on a road car. When the brakes are cold, organic/metallic brakes will typically work better. If you don't need the high temperature performance and are unhappy with the performance when cold then you can probably resolve the problem by reverting to organic/metallic brakes.

[Truckosaurus]

E-bmw said:

Have you looked at the other part of the equation, as in tyres?

Indeed. Is a fancy car with carbon brakes going to have similarly fancy tyres such as the P4S that whilst good on track are poor on cold, damp, roads?

[LennyM1984]

Coby147 said:

A lot of threads talk about CCBs in the wet with regards to lack of bite etc. Does everyone also find the ABS kicks in very early making it hard to modulate?

I've gone from Porsche 992 CCBs where I thought it was the weight distribution as even on steals they required some preloading and finesse so as to not unsettle the car. Now with BMW CCBs I notice the same in the wet that the ABS triggers way too early and I can't quite get that threshold braking accurately when driving spiritedly in the wet.

Are there any tips for getting the maximum braking in the wet and keeping out of the ABS zone? On steals I can get to max braking quickly and if ABS triggers you can ease off a fraction. With CCBs it seems once the ABS triggers you have to lift off a lot so do you have to just squeeze on the brakes more slowly and then play with the ABS limit? Also the back end seems to get lose which in the 911 again I thought was the weight distribution but the same is happening in this BMW M5CS which didn't happen in a standard M5 without CCBs.

I appreciate getting the brakes up to temperature helps significantly. However if you leave home on a cold, wet morning and have to do an emergency stop how would you go about this?

Thanks. Any advice would be really appreciated as braking and corner entry is usually where I make up most time and now feel like I have no confidence to accelerate!

Are you talking about driving on a public road or a track? From the last paragraph I am going to assume track (as you really shouldn't be driving anywhere near these limits on a public road).

This sounds like a characteristic of the manufacturer's brake bias. Most road cars are set with a significant bias towards the front axle (locking the fronts first is significantly less dangerous than locking the rears first). In the wet, you won't be able to apply maximum braking force on the front due to the reduced grip. When you are racing, you can move the bias backwards but on a road car you can't typically do this. Hence the front locks up (or ABS triggers) before you get anywhere near the maximum braking force the car is capable of (maximum braking force here being when the front and rear axles are applying as much retardation force as they are capable of giving the level of grip).

In short, there isn't a huge amount you can do about it. Be smoother rolling onto the brakes (so as to avoid too abrubt a transfer of weight) or go full race car and fit a pedal box and a bias adjuster (just don't let your kids anywhere near the adjuster - my daughter helpfully twizzled the knob on my race car without thinking to mention it!)

[Coby147]

Thanks for the replies. I didn't think there was a solution other than slow modulation. It's a shame they are actually worse than steals for road driving in bad weather.

Yes tyres are probably an issue, on normal PS4S tyres it would probably be better but these are BMW PS4Ss which are more aggressive for dry weather grip. They wheelspin more, kick the back end out more and understeer more in the wet. Not being able to trail brake because of the ABS issue means I'm not even cornering how I would normally.

Unfortunately I didn't have a choice what the car came with. Due to current life circumstances I've had to consolidate to one car for the next year and went for the M5CS which comes with CCBs. I had an M5/GT3 combo and sadly I feel like I'm driving this slower than the standard M5 I had.

As to driving on road or track - really both but I haven't been on track yet. My first parameter for getting used to a car is getting used to max braking so this is what has been bothering me. Plus I had to make an emergency stop in the first week on cold wet roads (tbh I've driven it in the dry once since I got it) and I didn't think I was going to make the stop. Thanks for the brake bias explanation, that makes a lot of sense and is a factor I didn't consider.

I might try changing the tyres which might help a bit. I noticed on the GT3 cup 2s in the wet had the ABS triggering if you just tapped the brakes.

[LennyM1984]

From what you describe, something doesn't sound quite right. The brakes shouldn't be that grabby as to lock the wheels immediately unless you are really stamping on them quite abruptly.

Are the tyres old? I have the normal PS4Ss on another car (a Porsche) and they are pretty tame. They'll trigger ABS from cold and wet but once warmed up are fine/predictable.

Perhaps the brakes are just more grabby than you are used to and you are being a little heavy handed (footed)? You certainly wouldn't expect to be in the ABS zone when trail braking

[E-bmw]

Coby147 said:

Yes tyres are probably an issue, on normal PS4S tyres it would probably be better but these are BMW PS4Ss which are more aggressive for dry weather grip. They wheelspin more, kick the back end out more and understeer more in the wet. Not being able to trail brake because of the ABS issue means I'm not even cornering how I would normally.

Unfortunately I didn't have a choice what the car came with. Due to current life circumstances I've had to consolidate to one car for the next year and went for the M5CS which comes with CCBs. I had an M5/GT3 combo and sadly I feel like I'm driving this slower than the standard M5 I had.

These 2 statements tell me that unfortunately, you may have chosen the wrong car/spec for your needs.

If you wanted a car that would work well on the track in summer you have the right car/spec, but to drive it on the wet winter roads in the UK, the car/spec is badly compromised.

Perhaps a partial work round could be a second set of wheels with tyres more suitable for the roads, but then this would not help with braking.

Having been in a similar situation a few years ago (with much less budget) I went the other way.

I bought a 328 Sport for the road & fitted TD tyres/pads when I went on track, and this gave me the advantage of having the "road wheels" to use on track as "wets" if the weather suited.

[GreenV8S]

LennyM1984 said:

You certainly wouldn't expect to be in the ABS zone when trail braking

Cold CCBs are likely to need a much higher pedal pressure for a given braking effort. If the car has a pressure based bias valve (which almost all production cars do) then it will be getting less weight transfer than the bias valve is designed for and will over-brake the fronts as a result.

[LennyM1984]

GreenV8S said:

Cold CCBs are likely to need a much higher pedal pressure for a given braking effort. If the car has a pressure based bias valve (which almost all production cars do) then it will be getting less weight transfer than the bias valve is designed for and will over-brake the fronts as a result.

Still though, if you are triggering ABS whilst trail braking, you are probably doing it wrong. If the car didn't have ABS and you tried turning it whilst at the threshold of braking, you'd almost certainly spin or understeer off.

I don't know how to embed a picture but the brake trace ought to look something like this...

https://blayze.io/assets/images/blogs/car-racing/w...

Edited by LennyM1984 on Friday 13th December 10:57

[GreenV8S]

LennyM1984 said:

Still though, if you are triggering ABS whilst trail braking, you are probably doing it wrong. If the car didn't have ABS and you tried turning it whilst at the threshold of braking, you'd almost certainly spin or understeer off.

I don't know how to embed a picture but the brake trace ought to look something like this...

https://blayze.io/assets/images/blogs/car-racing/w...

Edited by LennyM1984 on Friday 13th December 10:57

If you think about the elipse of friction, even while trail braking you want the tyre to be close to the limit of grip. So, even if the amount of braking is not high in absolute terms, if the balance is wrong because the line pressure is higher than expected (for a given amount of braking) then it will over-brake the fronts, so they will suffer more slip and trigger the ABS.

[stevieturbo]

Coby147 said:

Thanks for the replies. I didn't think there was a solution other than slow modulation. It's a shame they are actually worse than steals for road driving in bad weather.

Yes tyres are probably an issue, on normal PS4S tyres it would probably be better but these are BMW PS4Ss which are more aggressive for dry weather grip. They wheelspin more, kick the back end out more and understeer more in the wet. Not being able to trail brake because of the ABS issue means I'm not even cornering how I would normally.

Unfortunately I didn't have a choice what the car came with. Due to current life circumstances I've had to consolidate to one car for the next year and went for the M5CS which comes with CCBs. I had an M5/GT3 combo and sadly I feel like I'm driving this slower than the standard M5 I had.

As to driving on road or track - really both but I haven't been on track yet. My first parameter for getting used to a car is getting used to max braking so this is what has been bothering me. Plus I had to make an emergency stop in the first week on cold wet roads (tbh I've driven it in the dry once since I got it) and I didn't think I was going to make the stop. Thanks for the brake bias explanation, that makes a lot of sense and is a factor I didn't consider.

I might try changing the tyres which might help a bit. I noticed on the GT3 cup 2s in the wet had the ABS triggering if you just tapped the brakes.

Sounds like you have the wrong tyres, not brakes.

And how can the problem be "both", if you haven't been on track yet ?

[Coby147]

E-bmw said:

These 2 statements tell me that unfortunately, you may have chosen the wrong car/spec for your needs.

If you wanted a car that would work well on the track in summer you have the right car/spec, but to drive it on the wet winter roads in the UK, the car/spec is badly compromised.

Perhaps a partial work round could be a second set of wheels with tyres more suitable for the roads, but then this would not help with braking.

Having been in a similar situation a few years ago (with much less budget) I went the other way.

I bought a 328 Sport for the road & fitted TD tyres/pads when I went on track, and this gave me the advantage of having the "road wheels" to use on track as "wets" if the weather suited.

Well I tried to combine the M5 and the GT3. Unfortunately I do a weekly long journey with wife and baby through some roads that can have the worst standing water I've ever seen so the M5 makes perfect sense. I just wanted something with the all weather performance that wasn't as numb as the standard M5. However if the wet grip and braking is compromised I would have just preferred a RWD car!

[Coby147]

LennyM1984 said:

From what you describe, something doesn't sound quite right. The brakes shouldn't be that grabby as to lock the wheels immediately unless you are really stamping on them quite abruptly.

Are the tyres old? I have the normal PS4Ss on another car (a Porsche) and they are pretty tame. They'll trigger ABS from cold and wet but once warmed up are fine/predictable.

Perhaps the brakes are just more grabby than you are used to and you are being a little heavy handed (footed)? You certainly wouldn't expect to be in the ABS zone when trail braking

I don't trigger the ABS when trail braking - I meant because the ABS triggers I don't feel confident trail braking as I'm too busy stting myself wondering if the car will stop for the corner! lol

I think it probably is the tyres.

[Coby147]

Thanks again everyone.

Just 2 points:

1) The BMW * marked PS4S tyres are for better dry grip and almost a shift towards cup 2s. I think this explains a lot compare to the M5 I had on standard PS4S tyres and might be part of the issue. Being a bit more gentle with the brakes and letting them warm up helps but still not as consistent as steals in the wet.

2) I had my first dry drive today in the 2 weeks of owning the car and it was obviously night and day. No issue with the brakes, they were lovely and easy to modulate. Easy to find the threshold just like steals. Tyres are definitely a lot grippier than standard PS4Ss in the dry and more feel.

Seems a shame to buy a set of stand PS4S tyres but might be the way forward. Plus get the geo dialled in.

Also the back end doesn't move around in the same way under hard braking as it does in the wet. It's like it causes a cascade of chaos, try to brake hard - ABS kicks in - back end moves around - miss the entry point - sharper angle - understeer. Just annoying because the standard M5 was a weapon in the wet and I assumed this would be even better.

[stevieturbo]

So you were on track today ? or are you trying to use the roads as a race track ?

Have you considered driving lessons ?

[braddo]

LennyM1984 said:

From what you describe, something doesn't sound quite right. The brakes shouldn't be that grabby as to lock the wheels immediately unless you are really stamping on them quite abruptly.

I would say this is the cause of the OP's issues. It's not the car, the brake bias or the tyres. You simply have to be more progressive and smooth in lower grip conditions (cold and/or wet).

Even more so for 911s and Elises etc where you need weight transfer to enable more braking effort, i.e. don't stamp on the pedal, but brake harder and harder progressively.

[Coby147]

Minor update, so I did some heavy braking from high speed on the motorway, car pulled aggressively to the right needing decent amount of opposite lock. Did a few more high speed braking and actually since then the brakes have a been a lot easier to modulate despite it being -1.

Firstly it obviously shouldn't pull to one side so wonder if there was something up with the brakes or geo (or tyres as the front left seems to get hotter than the front right).

Secondly maybe there was some surface coating from the brakes not being used hard and it's now got a little better.

Either way taking it in to BMW to see why it pulls to the right under heavy braking.