Pace dropped after upgrade

[JAL racing]

2019 GT base. 25 hours of track time, my pace at the local track is 1:50. Pace improved steadily from hour 0 (2:10). Every week I was getting a little bit faster and smoother.
Then I installed the Brembo 6 piston calipers in the front and put on Hawk DTC-70 in the front and DTC-60 in the back. I did no changes to the ABS and the master cylinder.
I was amazed at how well the car braked. Fantastic! Couldn't wait to test it out on track. My pace went to 1:58 (consistent). I was puzzled. Weather conditions were not different from when I was driving my 1:50 pace with the base brakes that I had to nurse to last a full session. I was expecting to be at least as fast with the Brembos.
I decided it must have been an off day.
I went again tonight. Same weather conditions. Same 1:58 pace.
I don't understand. I don't feel any different, yet I am much slower with significantly better and safer equipment.
Does anyone know what could be the cause?

 

[TMSBOSS]

Have you shortened braking distance? If you are still braking at same point as before, you may slow down.

 

[JAL racing]

Have you shortened braking distance? If you are still braking at same point as before, you may slow down.

That's what I was thinking and yes, initially I did but progressively inched my way to a later braking point... So maybe my turn-in was the same as before, but at a much slower speed... I don't know. Pedal operation also went from needing a ton of pressure (base brakes) to being able to brake with my ankle joint, no upper leg strength required with the Brembos. So maybe I don't brake hard enough and too early (braking distance too long).
I remember reading somewhere in this forum that aggressive pads and 6 piston calipers was not what the base GT ABS system was designed for... And also something about the PP1 master cylinder being different?

 

[PatientZero]

Do you have any data from before and after so you can compare your corner speeds? It would seem like you are over-braking, all else being equal.

How old are your tires?

 

[TMSBOSS]

Do you have any data from before and after so you can compare your corner speeds?

Exactly. depending On your data device, braking points may also be recorded.

 

[Bill Pemberton]

I know this sounds simplistic , but how old are your tires. Figured you reckoned this into the equation, but have you heat cycled them out. It is not uncommon for folks to see drops due to weather , tire age , etc. and as they slow they figure it might be from a recent change, when it can be traced to simpler things at time. Sounds like you are addressing the braking distances and hitting things later , but you may just be going through a quite typical period of adjustment. Changes often throw drivers off because they are so used to the set up they had for a long time that any new set up can throw off the rhythm. Lastly what was the temperature at the track the last few visits compared to earlier when you were running --- some tracks can get a bunch slower when there are major temp changes ( part track surface , part tire compound ).

 

[blacksheep-1]

I know this sounds simplistic , but how old are your tires. Figured you reckoned this into the equation, but have you heat cycled them out. It is not uncommon for folks to see drops due to weather , tire age , etc. and as they slow they figure it might be from a recent change, when it can be traced to simpler things at time. Sounds like you are addressing the braking distances and hitting things later , but you may just be going through a quite typical period of adjustment. Changes often throw drivers off because they are so used to the set up they had for a long time that any new set up can throw off the rhythm. Lastly what was the temperature at the track the last few visits compared to earlier when you were running --- some tracks can get a bunch slower when there are major temp changes ( part track surface , part tire compound

I wish all of you guys could've been at Daytona with Alessandro to witness this in person, 1 or 2 psi dramatically effects where the tire "comes in" at, you can actually move your fast time up and down several laps depending on the pressure of the tire. It was the most dramatic example that I have ever seen.

 

[JAL racing]

Thanks for the valid points gents...my tires are date stamped 18/21. Michelin Pilot Sport 4S (yes, not a proper track tire!). They have been wearing evenly with my alignment settings and frequent rotation (305x19 square setup). They have 36 lapping sessions (cycles). After researching this forum I adjust pressure to 34 PSI hot and this has given me the most regular, consistent pace and grip through my sessions. Environmentals were roughly the same, within a few degrees. I do not think my driving is at the level where this can matter that much. To give you an idea of my inexperience, another driver (ex national karting champ) with S550 PP1 completely stock except for 295x11 300TW tires runs this track around 1:43. My pace was 1:50 before the Brembos, 2:00 after. So there are a lot of seconds for me to improve on my line, braking and acceleration alone before one or two PSI make a big difference I think. I'm no Alessandro.
On data: thanks for the suggestion. I will look at the traces and compare to the previous good sessions and will likely have my answer.
Bill mentioned I may have been too set in my old ways and adjusting to the new setup, and this is what I was suspecting, given all other variables seemed to have remained the same (I think!). I was expecting a much smaller difference, not 10%.
I did read several posts about people upgrading base brakes to Brembos without changing ABS or Master cylinder without any issues. I also read Terry Fair's thread about how much these matter. And I expect they do, at his level of driving. I'm not sure how much base MC and ABS with big brakes and wide tires mess up the ABS and overall braking for someone like me, if at all?

 

[ArizonaBOSS]

It's hard to say without data traces, but I'd bet you're overslowing significantly now.

 

[Coz]

Are you downshifting more in order to power out of the corners? If so, then this is an indication of overbraking.

 

[JAL racing]

Are you downshifting more in order to power out of the corners? If so, then this is an indication of overbraking.

No... I pretty much run the whole track in 3rd gear. Top speed at the end of the esses and the long straight is 100-110mph. Slowest speeds after hairpins are about 45mph. I have 3:55 gears and an MT-82 D4.
I'm aware this is poor driving, I use the 3rd gear from slow speeds to help me modulate the acceleration when the steering wheel is not straight to lower the risk of snap oversteer coming out of a turn into a straight portion.
I figured removing a downshift into the turn and an upshift after the turn would help me focus on feeling what the car is doing. I am not an expert driver and this is my first car with more than 150hp.
My son who was watching told me I was way slower than usual in the turns, so maybe you're right and I overbrake. Which would have a compounding effect coming out of the turn since I stayed in 3rd gear. Accelerating from 45 happens faster than from 40...X11 corners, that's easily half a second from braking too much, and another half from not accelerating fast enough... Ten seconds per lap..

 

[bob]

Well...I find the S550 difficult to drive. I have a 2019 GT A10 PP1 converted to racecar. A small single roll bar change cost me 4 seconds. Putting the other one back on degrading tires got my time back. If there is a sweet spot to this chassis I have not found it yet. I'm getting faster at it but it is taking effort.
I'll say things people do not believe. The S550 chassis in near street trim or as a converted amateur racecar using stock ABS is tire limited in stopping even with DOT-R race trires. The 4S tires even more so. I'll say blasphemous things...the 6 pot brembos of the pp1's is not helping you and your laptimes prove it. They are also heavy as f**k!. All you do with big brakes is carry more weight in the worst possible place and that slows you down, That and other driver things can cost you 8 seconds. Let's say the base brakes are OK and you nurse them by last session. You can maximize the lighter base brake set-up with different pads and cooling set-ups and perhaps make them very competitive. Brakes are all about heat. You need weight and speed to make heat. Your weight and speed at this time is at the base brake level. You need to learn to carry more speed or add more power to make more speed to use the heat capacity of the big brakes. That's it.

Big brakes on stock ABS tire limited does not make you stop shorter. It adds capacity and endurance to the brake system so you can beat them for a long time. A classic case in point is about 20 of us were racing in vettes in T1 pre-2012. We would crack a new stock rotor in 3 trackdays racing and warp and spread the caliper in 6 months. Finally we were allowed bigger brakes and 4 pot calipers for safety. In about 5 years on that set-up I had to rebuild the calipers once and rotors lasted an entire season. But the stopping distance did not change. Pedal feel and modulation were better as you notice with the big brembos because the capacity of the system is higher.

So what you need to do is work you way back to lap time by relearning the car to carry more speed and or allow the car to carry more speed through suspension changes and or power changes. I'm not a big believer in aero with these cars. Yeah it works but these cars are flying bricks and aero driving is a whole other level of driving complexity. Work the mechanical side of things 1st.

 

[AJ Hartman]

A $400 AiM Solo would tell you exactly where your time was lost. When I got one in 2012 and learned how to look into data, I really started dropping time and could also go back and look at previous time at the same track to know if I was moving the right direction or not. Just a raw lap time doesn't tell you much.

 

[Bill Pemberton]

Simple yet strong way to go faster ----- actually study and analyze your sport/hobby like anyone who wants to understand where to find improvement. Great comment AJ !!