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Old 06-03-2015, 01:15 PM   #1
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New to data logging. Presently using an Aim Solo. The data is humbling; It's pretty obvious that I need to work on consistency. ... and I guess I'm not really going 175mph before hitting the braking zone at the chicane... it's really only 121.

My question is: If the data says that I can corner at 1.4G, then why is it that I am only able to brake at .88G? Is this difference normal? Or, do I have to work on my braking zone technique?

Last edited by speedj; 06-03-2015 at 01:53 PM.
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Old 06-03-2015, 01:28 PM   #2
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<p>find a way to plot your accel data as a scatter plot like below. Your outer envelope is your &quot;traction circle&quot;. It looks like your data is similar to this set taken from another forum member here.&nbsp;</p><p>&nbsp;</p><p><img src="http://cimg6.ibsrv.net/gimg/www.miataturbo.net-vbulletin/743x774/80-129392d1418768512_lateral_g_data_analyses_question _traction_circle_e204f7cc539e9846b94fd214617949599 58589b4.jpg" title="" /><br /><br />&nbsp;</p>
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Old 06-03-2015, 03:54 PM   #3
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Quote:
Originally Posted by cyotani View Post
<p>find a way to plot your accel data as a scatter plot like below. Your outer envelope is your &quot;traction circle&quot;. It looks like your data is similar to this set taken from another forum member here.&nbsp;</p><p>&nbsp;</p><p><img src="http://cimg6.ibsrv.net/gimg/www.miataturbo.net-vbulletin/743x774/80-129392d1418768512_lateral_g_data_analyses_question _traction_circle_e204f7cc539e9846b94fd214617949599 58589b4.jpg" title="" /><br /><br />&nbsp;</p>
Sweet! Do these numbers generally reflect average grip for a track Miata?
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Old 06-04-2015, 11:24 AM   #4
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probably need to work on braking I would think. I am on NT-01s and If I am consistent with braking its -.1 to -.3 vs. the cornering. If I am average, it will be ~-.4

Depends a lot on tires btw. I have been led to believe that braking Gs will be higher than cornering on a slick (and the opposite for a street tire), but I am not sure.

Lat/long acceleration numbers are heavily dependant on tires, so its hard to gauge what is "average" for a miata...unless you have a tire in mind.
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Old 06-07-2015, 08:01 PM   #5
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Where is the G Sensor located? The sensor should be located as close as possible to the vehicle's centre of motion as possible. If the sensor is too high then it will be influenced by tilt, hence why having it as low as possible. The sensor measures relative to its position.

Tyres stop cars hence braking G is a product of tyre grip, same as for cornering. Tyre slip is impacted by weight transfer, in braking you are transfering weight to the front wheels, how this is transfered is controlled by your suspension. Do you have a brake pressure sensor to tell you how and when you are braking?

For my car (from my data) my front wheels loose grip (Federal FZ201's), braking in a straight line when I have only 360kg of weight over the rear wheels. The brake pressure is about 730 psi on the front. So when I look at my data I look for how close I am to the 730 psi brake pressure and the weight transfer clacs. Sorry I don't have the G force for this on me at the moment for this braking.
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Old 06-07-2015, 08:01 PM   #6
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I have 2 G force sensors in my car, 1 (Innovate) that is under the passenger's seat and 1 in the VBox Lite that sits low behind the drivers seat. I find there are small diferences between the 2, however I use the Innovate in preference to the VBox due to where the Innovate sensor is.

Last edited by Eipgam; 06-07-2015 at 08:19 PM. Reason: Double post
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Old 06-09-2015, 12:25 AM   #7
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My logger is on my steering wheel; in place of the airbag. Unknown if this effects it's operation.

In evaluating my braking performance with that of others, what braking g force should I shoot for? (2400# car, no aero, bilsteins with 850/400 springs, fresh 225 Hoosier R7's, ABS with prop valve, BBK front/sport brakes rear with Performance Friction race pads.)
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Old 06-09-2015, 01:09 AM   #8
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That is a very hard question to answer. It depends on approach speed it you trail/left foot brake as well as chosen line, track surface etc. Do you know what G force your brakes will lock up at?

I have had a quick look at some of my data from 2 different tracks (Queensland Raceway Clubman circuit and SMSP South). The 2 on the right are from QR, a few days apart and no changes between the car. The left one is from SMSP South and it was my first time there, hence the lack of hard braking.

The car is a naturally aspirated 1992 Miata (MX5 NA6), with a 1.9ltr Mazda BP motor/ITB's/PS1000, 205/50/15 FZ201's, NB8B (Sport) brakes with winmax W5's at the front and W3's at the rear.

QR Scatter Plot by Eipeip, on Flickr

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Old 06-10-2015, 05:56 PM   #9
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Thank you.

I have suspected that there is a problem in my ABS braking system, or perhaps a problem in my application of the brakes at threshold. So far, I have spent several races trying to sort this problem. In taking advise from the forum I have tried several options including prop valves, different brake pad types (Hawk, Carbotechs and Performance Friction) and changing the bore size on my rear brakes from sport to standard. Still, it seems to go into "ice mode"... the pedal just gets hard and I don't stop as quickly as I'd like. I've received advise that I should "not apply the brakes as hard"... and that seem unintuitive, especially as you roll past the brake markers 5,4,3 and you are still not slowing down well.

If you can stop at -1g with 205-50 FZ201's, then I should be able to decelerate at more than -.8g that with 225 Hoosiers. Getting frustrated with the abs and I'd like to pitch it.
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Old 06-10-2015, 06:27 PM   #10
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Hard brake pedal as you press harder but nothing sees to happen? This is an indication of fade, pads too hot. There are 3 types of brake fade, fluid too hot, pads too hot and pad knockback.

Have you adjusted your suspension settings? Tyre pressures? Your suspension controls how the weight is transfered, especially when braking hard. You want to weight to slowly be transfered to the front and not a single instantaneous transfer.

As an example this is data from one of my spins (solid) and the same corner without a spin (dotted lines) Green =brake pressure, blue = rear wheel weight, grey = speed

1.15 sec decided to brake, there is still weight being transferred to the rear as car is still accelerating.
1.31 sec braking commenced, weight coming off rear wheels. However the spin (solid lines) track for the brake pressure has a much steeper curve. Therefore more weight is loaded to the front.
1.8 sec max weight transfer to the front has been achieved in the spin track, but in the non spin weight and brake pressure is still building
2.95 sec this is the start of the spin. Surprisingly this is where I started to trail brake and commenced turning in for the 'normal' lap. Further the braking duration was about the same.

It looks like the brakes were applied too hard in the initial instance, this caused too much weight to go to the front. A very slight movement of the car caused the oversteer as the rear had no grip. The slight movement more than likely was a result of the heavy braking.
Spin Breakdown on Flickr

This shows what the rear suspension (red/dark blue) is doing before and during the spin. Everything is fine up to about 1.6 secs and this is where the rear suspension started to indicate weight being shifted to the outside (LH).


Spin on Flickr

Video of the spin. I have chopped over 1 sec from my time since this video.
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