It might be interesting to look at 1 particularly hard corner in isolation with non-averaged values across 5 or so laps too.

- Andrew

Sheesh I guess I can't count either so I shouldn't be so harsh.
:bonk:
I dig the responses and look forward to hearing more thoughts from others.
:cheers:

As for the braking Gs vs turning Gs, could this be blamed on ABS? The tires require some slip angle to generate that maximum cornering g force. Likewise, I'd imagine they would require some slip before producing maximum braking force, but perhaps ABS kicks in before enough slip is generated to produce the maximum braking force? It'd be like measuring maximum cornering force but leaving stability control on.

Just a thought, since in my head weight transfer can't account for it.

Also, do you mind posting your raw data? I'd like to take a look.

That's a good question, and I wish I had an answer. The OBD doesn't provide an ABS event signal, and I can't reliably detect anything. There aren't any telltale valleys in the brake pressure signal like you'd expect to see, and I'm not even sure where exactly the OBD system measures brake pressure. I'm assuming it's in the ABS pump assembly after the master, but I don't know if it's before or after the ABS pump. If it's before, it's unlikely it would show up as dramatically as it would if it were after.

As far as sharing raw data, I'm sorry, that's against company policy. I don't mind sharing plots of certain things for the sake of discussion, but considering we're collecting all this data for the purpose of developing parts for sale, we need to treat it as intellectual property. I really hate to say no, but it's above my head.

Jake

You'll probably be getting more weight transfer under braking than cornering since the sway bars will adding to roll resistance but not doing anything for brake dive.

It's probably a mix of that, slip "angles", and tire design (different tread patterns are better at different directional loads).

Fair enough. I'll just ask you to do the work for me. :thumbsup:

Could you show that same plot, with those exact same braking events, but with deceleration on the y-axis (as opposed to the "gain")? And don't average it, take the highest value per braking event.

My thought process is this: A small amount of brake fade that simply requires more pedal pressure to achieve the same braking force will not necessarily make you slower. Yes, you will show a lower "gain", but if you are braking at the same rate (deceleration is the same), then your lap time should be the same. If you are actually getting brake fade to the point that the deceleration you are capable of is diminished, you will see that in the plot I proposed above.

I love educational threads like this!

Here's what you proposed:

http://i.imgur.com/nTaouBG.jpg

A linear trendline does show a decrease across the session, but I wouldn't consider it significant enough to be an indicator. Perhaps if you folded back in peak pressure you MIGHT see something, but I'd bet there's too much noise in the pressure signal. I think until I get temperature data in here, it's going to be tough to quantitatively identify fade. That's definitely the goal, though.

Thanks for this :respekt:

Two things from this. First, It's interesting that the max braking force doesn't align at all with the max gain (although in hindsight maybe this should have been obvious). And second, if you were to plot simply the highest braking force per lap, you would see it increase for the first three laps, and then decrease for all of the rest. I think maybe that is evidence of your fade. Cool stuff.

Does your datalogger accept innovate serial data input?
I use the innovate TC-4 (sitting here with one in my hand) and it reads 4X thermocouples.
A roll of TC wire would be relatively cheap to run one to each caliper.

Have you at least tried the temp sensitive caliper & rotor paint that indicates max temps? They have stickers too.
It doesnt give you realtime data, but it will warn you if you have overheated or are getting close.

If you get the caliper temps above some critical temperature (400 F rings a bell but dont quote me) , you ruin the seals and the pads wont retract.
Then they drag and overheat more frequently (thermal runaway).

Are these runs with ABS completely disabled?
My experience of max braking of .8 Gs is in a car without ABS.
It would be interesting to see one of your plots with ABS and one without.

If you look at a brake pressure plot, you'll see a few hundred psi of variation across a braking event due to pedal modulation. That's why I took the average, which is plotted on that first one I posted as that thin gray line. By "braking force" do you mean the line pressure, or the resultant deceleration?

I don't believe it accepts RS232 input as well as OBD. I think it's either/or. I've got some of the Aim TC Hubs I'll be installing on the car in the very near future. I'm planning to use them for tire temps for a few tests, but after I get enough tire data, I'll use them for other temps like diff, brakes, etc. Thermal stickers will be going on the car shortly.

ABS wasn't disabled, no. Just the "pedal dance."

Resultant deceleration