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You can carry a lot of speed and thus show high g's through the downhill turn onto the front straight. That's most likely where that 1.7 came from. Not unusual for LRP as far as I am aware. Lots of compression grip.
Speaking of COTA and G-Sensor readings, here's another way to look at it. This is part of the data readout from the Sport Chrono after one on my recent autocross runs... although it was just in a COTA parking lot. It shows a peak left-turn G of 1.31 on the first run and a right-turn peak G of -1.23 G on the second. Too bad I never had what I considered an ideal run that day so that both were on the same run.
The longitudinal G's weren't too impressive since the course started with a zig-zag (to prevent launches?) and was pretty much a never-ending series of turns so I was never on full brakes (although I think in retrospect I should have braked harder in a few places).
The thing of interest in both of these is that the highest G moments were under moderate braking so the front end was loaded and the car is at a relatively low speed. The tires were normal street summer tires.
Actually your higher g's may have been an abrupt uphill turn, we just covered this in a track walk this week (Bertil Roos Racing). We have two similar hard left hand turns, both are perfect for trail braking. One is at the end of a downhill (Turn 7) and the other is at the end of an uphill (Turn 10), both have positive camber on the inside. I've always been able to take Turn 10 MUCH faster than Turn 7, the track walk proved why it worked this way due to the slope in elevation.
Point is, your car loads much better when gravity is helping, thus magnitudes of better grip going uphill versus downhill. I'll see if I can pull g's on the two turns to show the difference.
Also, as Subshooter points out, lateral g's peak at the tire's grip point when the car starts to slide - no more increasing g's beyond that point. Trail brake and slide into a section of outside curbing, witness how quickly the curbing stops the lateral movement, and then go check your g meter
"Sorry but you guys are mistaken on this point. The coefficient for static friction is > than the coefficient for kinetic friction.
In other words, once your tires start to slide, the g forces will decrease. I'd be happy to go through all the math and newtons equations at the risk of being a nerd and boring everyone."
You are indeed correct!
Caused by retired Nuclear Engineer 'brain fart'!-Richard
So let's continue to nerd out! Here is a nicely written article that addresses lateral adhesion: http://racingcardynamics.com/racing-...lateral-force/. In earlier years when I was a video game programmer I did the physics model for a car racing game (Supercar Street Challenge on the PS2) and tried really hard to use realistic physics calculations when possible. I spent a lot of time studying longitudinal and lateral slip ratios for the tire traction models. There wasn't a lot online at the time but I did manage to snag a book on the subject written by tire engineers in Detroit.
Interestingly, you DO actually get more tractive force applied when you spin your tires a bit on launch, but only within limits. Look up longitudinal slip ratio if interested. But as I understand it, when you are in a turn the tire face is experiencing some twist/crawl/roll due to the steering angle and lateral forces so the rules there are different.
"Sorry but you guys are mistaken on this point. The coefficient for static friction is > than the coefficient for kinetic friction.
In other words, once your tires start to slide, the g forces will decrease. I'd be happy to go through all the math and newtons equations at the risk of being a nerd and boring everyone."
You are indeed correct!
Caused by retired Nuclear Engineer 'brain fart'!-Richard
It's all good. I am still working as a nuclear engineer. How else can I afford these cars?
"Sorry but you guys are mistaken on this point. The coefficient for static friction is > than the coefficient for kinetic friction.
In other words, once your tires start to slide, the g forces will decrease. I'd be happy to go through all the math and newtons equations at the risk of being a nerd and boring everyone."
You are indeed correct!
Caused by retired Nuclear Engineer 'brain fart'!-Richard
There are some posts made by the software engineer who does the tire models for the Assetto Corsa game, and you can check the tire definitions for different tires in the car data. Regardless of what you think of the game in general, this particular engineer (who was into non-game simulation before) places a strong emphasis on tire behavior before slip as opposed to when slip started to happen. He would never use the same friction for both.
Actually your higher g's may have been an abrupt uphill turn, we just covered this in a track walk this week (Bertil Roos Racing). We have two similar hard left hand turns, both are perfect for trail braking. One is at the end of a downhill (Turn 7) and the other is at the end of an uphill (Turn 10), both have positive camber on the inside. I've always been able to take Turn 10 MUCH faster than Turn 7, the track walk proved why it worked this way due to the slope in elevation.
Point is, your car loads much better when gravity is helping, thus magnitudes of better grip going uphill versus downhill. I'll see if I can pull g's on the two turns to show the difference.
:
Wouldn't gravity be working against you at the end of an uphill? The suspension would be unloading wouldn't it? Therefore reducing available grip?
Wouldn't gravity be working against you at the end of an uphill? The suspension would be unloading wouldn't it? Therefore reducing available grip?
And there isn't an abrupt uphill turn at LRP.
The extra suspension load here does not come from gravity.
In comes from (the direction of) the impulse vector being forced to change upwards. That causes centrifugal forces vectored toward the bottom of the car. It doesn't matter whether you go from horizontal to uphill or from downhill to horizontal, the suspension load extra is almost the same.
Wouldn't gravity be working against you at the end of an uphill? The suspension would be unloading wouldn't it? Therefore reducing available grip?
And there isn't an abrupt uphill turn at LRP.
The crest of the hill is just past the apex, so the entire braking zone (and turn in) is uphill. After the apex, yes the car unloads - which is the other half of the corner and partly why it is everyone's favorite - huge rewards for a good driver
Does PDCC reduce lateral g-force? Or does g-force register regardless of the roll counterbalance performed by PDCC?
Well, if the sensor is mounted in the body then reducing body roll will increase the values read by the meter (for the same actual car path wrt the tires).
11-02-2016, 06:11 PM
