Brake Pad Balance Issue

[Woodsman44]

I have stock Brembos and stock rotors with Raybestos ST47 up front and Hawk DTC-60 out back for my track setup. My plan was to run ST47 front and ST45 or ST43 rear but I could get them in time for my track day. Anyways, ABS was kicking in way too early and caused a few pucker moments at VIR. The brakes were decent in the initial braking but a few times ABS took complete control during the last 50 feet before turn in. My car wasn't tail happy during braking so my guess is the rear pads have too much bite in relation to the fronts, which is causing ABS to kick in too soon. And, no I wasn't braking too late - actually braking too early from the lack of confidence in the brakes. What do you guys think?

Related mods: NT01 315's on 18's square, motul 600, brake ducts, stock suspension, competition mode, steel wool/ brake cleaner on rotors and bedded pads when swapped.

[Synner]

1) Use matched pads
2) ABS kicking in in the last 50 feet means you're braking too hard too late, no matter what you might think you were doing. Too hard and too early are vastly different things. Brake hard early to avoid overheated rotors in the last 50'.

[X25]

Originally Posted by Synner

1) Use matched pads
2) ABS kicking in in the last 50 feet means you're braking too hard too late, no matter what you might think you were doing. Too hard and too early are vastly different things. Brake hard early to avoid overheated rotors in the last 50'.

+1

These cars come with EBD, so the brake balance will be more or less maintained. If your rears were too strong, you'd actually get tail happy, not the other way around.

If you engage ABS too fast, you can engage ice mode, which would limit your decel to 0.6G. The only way out during the braking would then be pumping brakes, which could get nerve-wrecking. You need to find the highest brake pedal pressure that would bring the tires to ABS threshold, but not actually engage it.

[JusticePete]

Any chance you data log your runs?

[Woodsman44]

So are you guys running the same pads front and rear? Since this was my first track day with this car it could be that I'm not used to the feel of the brakes yet. I've tracked a C5 corvette and mustang and neither of them had this issue. It seems like the ABS is kicking in way too early and I've never had the pedal go completely "numb" like that. Does the Camaro like a little less aggressive pad like ST43 F/R?

JusticePete - I was using Harry's lap timer but I didn't have the accelerometer setup correctly so I basically just have lap times.

[Norm Peterson]

I would expect pads with aggressive bite, or too aggressive for the tires and/or ambient temperatures would put you into the ABS early-on in a braking event. Late in the braking event sounds more like differences in pad mu vs temperature if it isn't just that you're standing on the pedal harder toward the end.

It is at least possible for a pad mismatch to be more than the EBD can fully cope with, but this could get really complicated.


Norm

[JusticePete]

ICE Mode occurs when the ABS computer cannot stop / correct all four wheels from reading the same 0 (or designated trigger) RPM with the level of pedal pressure applied. That tells the system it is on ice. Extremely aggressive pads combined with hard braking will frequently generate ICE mode. The 1LE ABS cal is more aggressive than the SS. 1LE owners will see this less frequently.

There is pad tuning required with different compounds. I like XR1 and XR3 pads with the four post OE setup and XR1 / XR2 with the 6/4 setup. DTC70/60 works for a lot of drivers. If we had more data, especially wheel RPMs at the time of your ABS action we would have better information. Based on experience, the rear pads had too much bite.

[Woodsman44]

JPete - Thanks that's helpful. I have HP Tuners so I'll try logging to see exactly what's going on - but that makes sense. If the data shows the rears going to 0 RPM first then I know I have too much bite in the rear and vice versa. I've never had ICE mode engage on past vehicles which makes me think my pad setup isn't idea.

Norm - Are you suggesting there is more bite once the pads are hot at the tail end of the braking zone and me not adjusting pedal pressure accordingly could potentially be causing it?

[Norm Peterson]

For some pads, mu continues to increase with rising temperature up to well over 1000°F. For other pads, mu noses over and starts to drop sooner (the curve takes on a more 'rounded' shape either side of peak). Hawk has provided a rather useful graph as far as this concept goes - if your brakes were 'balanced' with identical pads, swapping to a DTC70/HT10 or even DTC70/DTC50 could put you in the position - almost certainly on the track - where the DTC70-braked axle becomes "overbraked" relative to the other axle.

One of these things leads to the other - the 'underbraked' axle won't be generating enough braking force at the tires, so you'll step into the pedal harder as you realize that you aren't slowing down as rapidly as you should be (or need to be) . . .


Norm

[130R]

I'm curious why you chose to go with the ST47. That seems like a lot of pad, even for a 100 TW tire.

For an insight, pull the ABS fuses and see how easy it is to lock the tire with that pad. I think you might be surprised...

[X25]

Originally Posted by 130R

I'm curious why you chose to go with the ST47. That seems like a lot of pad, even for a 100 TW tire.

For an insight, pull the ABS fuses and see how easy it is to lock the tire with that pad. I think you might be surprised...

I don't know the OP's personal choices / experience, but would like to add my 2 cents: most of my track experience comes from Corvettes, and their brakes are definitely much stronger, with a much stronger initial bite, too. ST43s on the C6 Z06, for instance, is incredibly strong, and feels like it's all the pad you'd ever need, both on stock C6 Z06 calipers, and StopTech ST60 calipers I've later used them with.

On the Camaro (1LE), the same ST43s feel much softer/weaker, which didn't change much even after I switched to StopTech BBK from the Brembo 4-piston OEM calipers. ZL1 calipers' piston surface look to be significantly bigger than both 4-piston Brembo and StopTech BBK's, so it might help, but I'm guessing the car is just too heavy for the tiny pads, and the limited brake piston surface area on StopTech and Brembo 4 pistons exaggerate the feeling. I switched to ST47, and it helped. In other words, ST47 doesn't feel like having too much initial bite on this car, and I can easily modulate.

[130R]

Originally Posted by X25

ZL1 calipers' piston surface look to be significantly bigger than both 4-piston Brembo and StopTech BBK's, so it might help

Actually, the piston area is slightly larger for the 4-pots compared to the 6-pots, and the clamping force is essentially the same.

A lot of things can affect the way the brakes feel: the amount of assist, pedal ratio, pad/rotor µ, rotor diameter, wheel/tire size & weight, line pressure, etc. That said, I don't doubt what you're saying, I just know how incredibly easy it is to lock my PSS 285's without ABS with a significantly lower µ pad than the ST47.

I'm not necessarily saying the ST47 is a 'bad' choice, it's just that I would assume it might require more finesse than a lower µ pad. Considering most people probably stab the brakes too hard to begin with, a very aggressive pad would only seem to make things worse.

Most street performance pads, which obviously assumes street tires, are around 0.5µ. The ST47, at the temperatures you'd probably see on the track, is 0.85µ. An increase of 0.3µ, can mean an increase of 25% to 30% in rotor torque; that's a lot...

[Synner]

Originally Posted by Woodsman44

So are you guys running the same pads front and rear? Since this was my first track day with this car it could be that I'm not used to the feel of the brakes yet. I've tracked a C5 corvette and mustang and neither of them had this issue. It seems like the ABS is kicking in way too early and I've never had the pedal go completely "numb" like that. Does the Camaro like a little less aggressive pad like ST43 F/R?

JusticePete - I was using Harry's lap timer but I didn't have the accelerometer setup correctly so I basically just have lap times.

My point is a mix and match of brands is a bad idea. They warm up at different rates, bite at different rates, and respond to heat at different rates and in different ways. It's quite possible you're engaging ABS in the rear but you're only at 60% clamping force in the front. When you're overworking a pad you'll boil the fluid very quickly and that will cause the numb or dead pedal.

Bleed everything, use a common brand pad, and see how it goes.

[White_SS/RS]

Originally Posted by 130R

I'm curious why you chose to go with the ST47. That seems like a lot of pad, even for a 100 TW tire.

For an insight, pull the ABS fuses and see how easy it is to lock the tire with that pad. I think you might be surprised...

Originally Posted by X25

I don't know the OP's personal choices / experience, but would like to add my 2 cents: most of my track experience comes from Corvettes, and their brakes are definitely much stronger, with a much stronger initial bite, too. ST43s on the C6 Z06, for instance, is incredibly strong, and feels like it's all the pad you'd ever need, both on stock C6 Z06 calipers, and StopTech ST60 calipers I've later used them with.

On the Camaro (1LE), the same ST43s feel much softer/weaker, which didn't change much even after I switched to StopTech BBK from the Brembo 4-piston OEM calipers. ZL1 calipers' piston surface look to be significantly bigger than both 4-piston Brembo and StopTech BBK's, so it might help, but I'm guessing the car is just too heavy for the tiny pads, and the limited brake piston surface area on StopTech and Brembo 4 pistons exaggerate the feeling. I switched to ST47, and it helped. In other words, ST47 doesn't feel like having too much initial bite on this car, and I can easily modulate.

Originally Posted by 130R

Actually, the piston area is slightly larger for the 4-pots compared to the 6-pots, and the clamping force is essentially the same.

A lot of things can affect the way the brakes feel: the amount of assist, pedal ratio, pad/rotor µ, rotor diameter, wheel/tire size & weight, line pressure, etc. That said, I don't doubt what you're saying, I just know how incredibly easy it is to lock my PSS 285's without ABS with a significantly lower µ pad than the ST47.

I'm not necessarily saying the ST47 is a 'bad' choice, it's just that I would assume it might require more finesse than a lower µ pad. Considering most people probably stab the brakes too hard to begin with, a very aggressive pad would only seem to make things worse.

Most street performance pads, which obviously assumes street tires, are around 0.5µ. The ST47, at the temperatures you'd probably see on the track, is 0.85µ. An increase of 0.3µ, can mean an increase of 25% to 30% in rotor torque; that's a lot...

I run ST43 on all 4 corners, 6 piston ZL1's up front and G2 tires. My experience with them is they are about right for the car/tire. I get just a little bit of tire squeal at the end of my braking zones. Pulls over -1g. I don’t think stepping up to a more aggressive pad will shorten braking zones. The tire is really the limiting factor here since it will only allow so much braking torque before traction is exceeded.