Braking Gs lower than Cornering Gs
 

I was just watching some footage from last weekend at the track and noticed that my braking Gs were substantially less than my cornering Gs. I don't rely on the numbers my app tells me as far as being accurate, but there is typically a .3-.5g difference between the two and the delta is what I find interesting. The car is running Carbotech XP10s and 245 RE71rs (koni yellow shock, swift spec r springs, camber at -3.2 fron and -2.3 rear in case you needed more). Pro drivers that have been in the car have complimented the suspension balance so I don't think it is an underdamping issue in the front.


What I am trying to understand is if it is time to step up the pads or is the delta pretty standard? The maximum braking reached was pretty consistent through each braking zone (including hard braking zones), so I don't think it is a braking application issue. Also, using the pedal dance.

have you changed the brake fluid? braking is all about pads/rotors/fluid/tires.

Early on, Vorshlag reported seeing 1.4-1.5g under braking on their BRZ using data from their AIM solo. This was on 255 width RS3 tires, Carbotech XP 12/8 combo, and Motul RBF600 fluid. You can probably use that as a point of reference number.

http://www.vorshlag.com/forums/showthread.php?t=8145

I experienced Ice Mode when I tried out the brake pedal dance, is there a chance that's happening to you?

I honestly don't think I would have noticed it if I had not been trying it at an autocross back to back, thought I blew a corner due to driver error, but I did the same thing the next run put 2 and 2 together and went back to the five second press. If I had started the day and consistently activated it I probably would have adjusted my driving around it and not have even noticed it was happening.

Doubtful but worth a shot.

Also, for you is maximum braking using ABS? If you're trying to threshold maybe you're not as close to the limit as you think.

Your phone GPS is only 1Hz. It might not be accurate enough for braking situation.

Cornering is more like a steady state and 1Hz might be less wrong.

If the app get acceleration from accelerometer, it's maybe the same, as you got more time to monitor the acceleration in a corner than in the braking zone.

Phone are great at giving lap time, but they suck at giving top speed, cornering speed and driving line. You need a 10Hz GPS for that.

For accuracy as far as automotive performance is concerned, I never rely on any phone-based app.

-alex

Running Torque 700 fluid. Had about 8 track days on it and a recent bleeding, so not sure that is the problem.




I am running an external 10hz GPS, so I would expect it to be sufficient for braking zones as well. It has no problem showing fast lateral G transitions during turn in, so I don't think that is the issue. I should have posted that in the first post, certainly the 1hz sucks on the phone.


As a previous poster stated, it could be simply be pedal application and not quite reaching threshold, but not sure.



Thanks for the comments so far.

Good point :)

The max lateral G is not making on camber turn ?

It's maybe normal thing. If you are around 1G under braking, that's looks fine to me.

This is the video I was watching when I noticed it, perhaps it will be helpful.


[ame="https://www.youtube.com/watch?v=Ba00Ue-4BKU"]Drivers Edge MSR-C 3.1 PB (FR-S) - YouTube[/ame]

I believe Harry's uses the onboard accelerometer to measure g's, which honestly shouldn't be a problem as they're typically pretty high quality, however the calibration may be skewing your results if Harry's doesn't calibrate exactly correct you may be getting skewed longitudinal readings, I know I didn't feel comfortable with how accurate it was when I last tried it, I consistently had it skewed so my left hand turns were reading higher than the right or vice versa, stationary was like 0.2 g in the upper right quadrant or something. Yours looks a lot better than mine did though so maybe that's not a significant part of the problem.

One thing to note though is there are a few corners where you are braking and turning in at the same time, overlapping inputs like that will take away from your maximum braking capability bringing ABS into the equation sooner but it looks like you are well aware and that's just the nature of the track. At about 43s in you get a good solid braking action as you turn in that surpasses 1g, looks like it's just a matter of finding the limit on the brakes for you.

I just started logging autocross, but I get higher lateral G's than braking. Here's the gg plot. Typical STX trim (coilovers, camber plates, 245 RE71R 17x9, etc).

it sounds like your tires and pads are mismatched so you don't use the full potential of those sticky RE71s, in my experience even the Carbotech XP12s were not adequate for grippy tires.. you definitely need something that has more initial bite and more consistent to use with the RE71s to utilize its full potential..

I still have my brand new Raybestos ST47- F/ ST45 - R set for sale (sale for the use set is pending) contact me if you're looking for some serious track pads ;)