RichFL

I'm wondering if someone would give me a primer on interpreting GSum data? On my last outing at Sebring my highest GSum readings for 3 of my 5 fastest laps occurred in turn 11 and were 1.66, 1.58 and 1.54. One run showed the highest value in turn 3 at 1.6 and another in turn 5 at 1.54. I'm driving a 2011 Carrera S with street tires.

What's the data telling me?

Thanks for your help.

Caddell

The max GSum values are something you can (and maybe should) look at at some point but as you are starting to use this channel, I like to see folks study the shape of the curve and not a max value.

Consider the way you drive your car. You are trying to run your car at the outside edge of it's 'Performance Envelope'... Maximum braking/acceleration g's (Long g's), and maximum cornering g's (Lat g's). The GSum channel mathematically combines these 2 channels of information.

Think about if you were going down a long straight section and as you are approaching a corner you apply the brakes in a straight line. Your Long G values will increase to reflect your braking and your Lat G values have not changed in any real way as you are braking in a straight line. Then as you begin to turn into the corner you will need to 'trade' some of the braking Long g you are using to Lat g and your goal of course is to do this in a smooth process.

As you travel further into the corner you will have at some point traded all braking Long g's for full cornering Lat g's and this should be done in a smooth way for maximum grip and always staying at or near the 'Performance Envelope' of you and your car. If you do this correctly, the GSum value climbs under braking and stays at your maximum value as you transition from braking, to cornering, and then to acceleration.

Drop me a note with your email address and I can send you a good example and a poor example if it will help.

Matt Romanowski

Roger gave a great explanation. Another way to think of GSum is if you took a G-G diagram and measured the distance from the origin (center) to each point on the graph and made them into a line graph. The number on the GSum plot directly relates to how far out you are on the G-G plot, so the same idea apply.

The GSum should smoothly rise up to a plateau, without any dips, then go back down. If it rises and dips, it's the same as the G-G plot moving inward then back out (like when you brake in a straight line, come off the brake, then turn). You're goal is to keep the car using the maximum amount of traction available. A great article (if I do say so myself!) on this is at http://www.trailbrake.net/featured-a...he-g-g-diagram

Matt Romanowski

Here are a couple of images so you can see the connection of the G-G diagram and the GSum.

The absolute value of the GSum has some meaning in it's a figure for how much work your tires can do, but it's not an end goal. It's the overal picture of your performance envelope.

RichFL

Thanks for the info. I understand the concept, but achieving good results will be a challenge. My Gsum graph looks more like Himalayan Mountain peaks!

Matt Romanowski

The execution is the hardest part. One of my favorite former Skip Barber instructors always said he could teach a monkey to drive the line and to build exit speed, but entry speed was the scary hard part that most people never get really good at. I know it's the challenge for me. I can either do it too good or not good enough. Nailing it is the challenge (the data above is mine).

ir_fuel

And when you see G's go up and down you need to figure out why they do that

DTMiller

Is GSUM the sum of the absolute values of Lat G and Long G or is it more complicated than that?

ProCoach

GSum is not strictly the addition of total lateral g's plus total longitudinal g's. It's just a simple equation. The square root of total lat g plus the square root of total long g equals the square root of total g's (GSum). So, it's not possible to do .95g lat plus -.67g braking and come up with 1.62g sum. It's actually 1.16 GSum...

I think people get WAY to hung up on the absolute number when they should be focusing on the relative number between corners/braking zone transitions to corners and off corner acceleration numbers. So much of this is influenced by the topography of the track.

I am flying to the Glen to work with someone that I have spent several weekends with focusing primarily on how to remove the "dip" Matt points out between the perfectly good long g reading under braking and the perfectly good lat g reached under sustained cornering.

Almost every advanced driver can do individual skills very well, but few can "meld" them together to make a seemless transition between good individual skill executions.

It takes a long time for people who are not in the seat EVERY weekend for a long time to begin to build the knowledge base and the belief system to begin to bridge those gaps.

I look at talented amateurs (who can drive circles around many, if not most "pros") like redcar1 and Mike Hedlund and see that they can and have done this, so this CAN be done by people who apply themselves and use these tools to guide their progress, formulate and execute plans and to then validate their results.

The reason why the dip occurs is simple. People's sphincter pressure sensors go OFF the scale when trying to compress all that HAS to happen to MAKE THIS HAPPEN. So, how do you fix this? Gradually, incrementally and with SO clear a vision, that it almost becomes automatic.

A keen understanding of vehicle dynamics is a must. You MUST know what the car is going to do BEFORE it does it.

Great stuff. Great measure that helps people a LOT and cuts straight to the chase...

amso3

Hey RichFL

Are you going to be at PBOC next weekend? I'll be there both days, driving in Super Solo, not instructing so I and can help you with data if you like

Matt Romanowski

Technically it's the vector sum of the lat g and long g.

RichFL

Jerry - I'll be at PBOC and will look for you. Thanks for the heads up.

mglobe

Gsum = sqrt(lat_g^2+long_g^2)

amso3

For those that are more of a visual learner. This is the circle of friction, the most that the tires can take on that vehicle