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Pete. (l33t FS)
Pete. (l33t FS) MegaDork
11/9/21 11:24 p.m.

Accelerating any car through a corner will cause it to naturally understeer.  You're transferring load to the rear.  If it's neutral in steady state cornering, adding power will increase rear grip and reduce front grip.  More vertical load = more traction, less vertical load = less traction.  One of the idiosyncracies of pneumatic tires is that they are nonlinear that way.

Obviously, if you overpower the tires, that will affect things, but this isn't "cornering", its "a burnout" smiley

This isn't always a problem, but a trait that can be exploited.  I like having the ability to power out of problems.  It inspires confidence in a way.

GameboyRMH
GameboyRMH MegaDork
11/25/21 8:51 a.m.
slantsix said:

Is that something that a low pressure - say 2# residual pressure valve inline with each of the brake lines (say one to the front and one to the rear) would solve?  I was just curious and maybe I should post that question elsewhere. 

 

Thanks,

Greg

The cause of it comes down to the rotor deflecting relative to the caliper basically because of wheel bearing play - all bearings have some amount of play and this issue commonly affects high-end race cars with big rotors. If you keep residual pressure in the system, the most that might do is cause the calipers to fight the rotors more when it happens - the car will automatically brake a bit in hard turns as the pads will resist being pried apart more (and I expect you'd get a hint of brake dragging on the straights too). The best solution is to look for heavier-duty wheel bearings if you're not already using the best ones out there, but the issue is kind of unavoidable with larger brakes, you see drivers doing this with brand new factory-backed race cars.

slantsix
slantsix Reader
11/25/21 12:41 p.m.

In reply to GameboyRMH :

Thanks for the explaination!

 

Greg

slantsix
slantsix Reader
11/25/21 12:42 p.m.

In reply to GameboyRMH :

Thanks for the explaination!

 

Greg

Jeff Mosing
Jeff Mosing New Reader
11/26/21 7:49 a.m.

Vic Elford has a great book that covers the 911, boxsters, even Cayennes.  I highly recommend it:

 

https://www.amazon.com/Porsche-High-Performance-Driving-Handbook-Elford/dp/0760327548?asin=0760327548&revisionId=&format=4&depth=1

BA5
BA5 Reader
4/25/22 10:25 a.m.
Pete. (l33t FS) said:

They apply to a lot of cars, really.  Given that so far nobody has offered me a seat in their 911, I can speak only from conjecture here.  But it seems like the 911 doesn't reward proper technique so much as punish improper.

I should modify it to say 'the laws of physics'.

aircooled
aircooled MegaDork
4/25/22 2:11 p.m.
Pete. (l33t FS) said:

In reply to aircooled :

I'm not sure it's steering with the throttle so much as keeping it from looping with the throttle.  Definite coffin-corner action happening there: can't lift, hope you have enough acceleration to keep it from looping, and that you won't accelerate yourself too fast for the corner.  (Note that car is a short wheelbase model, which are supposed to be extra-"fun"),,,,

Super late reply I know, but in my case, lower speed AutoX, it really is a lot of throttle steer:  Come into turn, let off a bit, car rotates into corner, point at apex, hammer throttle, car sticks.  Mid corner, need more turn, let off throttle, car rotates, then hammer it when you have the turn (my car generally will not overpower the rear tires with AutoX tires on at speed).  Of course in AutoX, you generally use very little brake.

Now, high speed, as shown in the video above, yeah, that's a bit of a different, and deadly, high speed dance (not that I do high speed track racing).  Even still, if you are mid-corner, and you have the power on, you can always let off a bit to get more turn (and slow you a bit).  That is why it's generally best (safest) to be in a corner at part throttle, you have room to add or subtract traction from the rear.

Of note, the early 911's are 86.5" wheelbase, latter extended to 89.5".  The Corvair is 108", so a lot more rotational inertia!

I have to say, even as a rear engine guy, that video is a bit of a pucker fest.  That car is trying to kill him!  (and I like it)

Imagine, take a bunch of pro drivers, but them in short wheel base 911's on fast twisting courses.  Tell me that wouldn't be super entertaining to watch!   (hello first season of IROC!!)  Probably way more interesting then most current road racing (for the spectator at least).

VolvoHeretic
VolvoHeretic Reader
4/25/22 4:23 p.m.

Hmmm... So, is this an example of good corner control or bad?

 

Dale_Gribble
Dale_Gribble New Reader
4/28/22 11:12 p.m.
Pete. (l33t FS) said:

One more video.... Swing like a hammer.  Video should start close to the end, but the full six minutes is a fun watch for all the air cooled six noises.

 

"I decided to devote my life to it, and not get sidetracked by all the other bullE36M3 that life has to offer." - Cliff Burton

Balls of steel, and probably large ones too.

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