Taking a curve in neutral ?

[Deschodt]

Looong ago when I was learning to drive (and there were not automatics) someone older than me told me you should never take a turn in neutral, the car would not handle well... It's something I'd never do... but I recall it happening once by accident when I was having fun on a mountain road, old car, gear didn't go in at all and I tool a relatively fast corner in neutral...nothing special happened...

Now that decades have passed, and I understand circle of friction better and spent years on track, I'm still struggling with the concept that it may or may not be true... It's obviously not something you'd do on track since you always try to maximize time, nor on the road because you want either some engine braking or the option to accelerate... But say you are cornering at a speed near the tire limit (but not above), other than missing the weight transfer aspect F/R due to deceleration or acceleration (and the % of driving tire lateral grip lost to accelerating or braking) - does it make a different at all to the car handling if you are in gear or not when taking the turn ? The car sure feels less stable... can anyone explain why ?

[GH85Carrera]

I know when driving my 911 I feel better when I am in gear. If I can apply power to come out of a corner it is more fun, and I can control how much power. And never shift gears in a hard corner.

There is an off ramp the I take to get my area of town that has a large fun sweeper and comes to a traffic light where I turn right. I have to come to a stop 80% of the time. I enter the off ramp at 70, and usually just kick it into neutral and coast to a stop. I am still rolling at a decent speed as I hit the curve, but I know the corner very well after taking it for 15 years. Since I will be stopping, or at least slowing to 15 MPH I just let the speed bleed off.

On the street I never corner very hard, lots of unknowns are out there. I learned that lesson long ago (1970s) when turning through a corner and all of a sudden I smelled diesel fuel, and I was sliding sideways towards a tall curb. I made the corner with inches to spare. Evidently some semi dumped fuel from his fuel tank with a bad fuel cap right in the corner.

[SCadaddle]

I can honestly say that I never saw a curve in a soap box derby race. Never.

[Tervuren]

The real reason I would not want to take a curve in neutral is not having the right foot connected to the driving wheels on demand coupled with the potential for a mash up when re-engaging that unbalances the car if poorly done.

[Tervuren]

Clicky arrow.

Originally Posted by Tervuren

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Originally Posted by SCadaddle

I can honestly say that I never saw a curve in a soap box derby race. Never.

[Cajundaddy]

Taking a corner in neutral removes your ability to control weight transfer with your right foot. All you have left is braking, and going for the brakes mid corner transfers weight to the front tires to cause understeer. You can do it but I prefer to have full control of the car with my right foot so I'll keep a gear selected.

[911boost]

I taught my kids never to go through a curve in nuetral but not for some racing type lesson, but because it would take them longer to react to any type of situation if the clutch was in/not in gear. Same as going through an intersection.

[id10t]

Depends on what you are driving, what kinda curve, how you are taking it (at speed?), etc.

I recall when learning to drive in the 356 I tended to want to do that to avoid going too fast or to avoid shifting while turning etc, and I fondly recall dad yelling "keep yer foot on the gas in the corners damnit!"

[Bill Douglas]

It's just the car decelerating. Going at a slow or moderate speed it wouldn't make any difference.

But hard cornering it would be scary. The SC, for instance, would want to swap ends.

[Deschodt]

I agree instinctively it seems like a bad idea, that's not my point, and I understand the argument of having options to balance the car with the gas...

I'm just asking from a physics standpoint, what difference does it make (if any?) to the car's handling if you are taking a curve in neutral vs with engine in gear, coasting (if you like assume it's a slight downhill curve to keep speed constant, also assume not at the limit but quick enough that you'd wanna be in gear, and finally let's say a cayman to avoid rear engine arguments) ..

It sure feels "odd" and less stable if if happens and you ever missed a gear entering a corner... Is it, though ? from a tire/grip standpoint I can't explain why it would be worse or why the car would care at all assuming you are within the grip limits - if anything there would be lower demands from the driving tires, so more "circle of friction" % rubber available for lateral grip. Not at the limit (yet not slow), shouldn't it feel 100% similar and corner the same? Sure doesn't feel like that to me, feel terrible... Just wondering if we had physics gurus here ;-)

[masraum]

Any downhill unpowered racing would perform this all of the time.

I've coasted around corners, not as a regular practice, but it will work fine as long as you don't end up braking mid-corner. I wouldn't want to be going through at the edge of adhesion. but going around well below threshold speed is fine from a dynamics point of view.

[masraum]

Originally Posted by Deschodt

I'm just asking from a physics standpoint, what difference does it make (if any?) to the car's handling if you are taking a curve in neutral vs with engine in gear, coasting (if you like assume it's a slight downhill curve to keep speed constant, also assume not at the limit but quick enough that you'd wanna be in gear, and finally let's say a cayman to avoid rear engine arguments).

neutral vs coasting in gear - coasting in gear will involve engine braking (and aero drag and friction drag) vs coasting in neutral which only has aero drag and friction drag which are likely far less than engine braking. From that point of view, I believe that coasting out of gear would produce better, more neutral (no pun intended) handling than coasting in gear.

It sure feels "odd" and less stable if if happens and you ever missed a gear entering a corner... Is it, though ? from a tire/grip standpoint I can't explain why it would be worse or why the car would care at all assuming you are within the grip limits - if anything there would be lower demands from the driving tires, so more "circle of friction" % rubber available for lateral grip. Not at the limit (yet not slow), shouldn't it feel 100% similar and corner the same? Sure doesn't feel like that to me, feel terrible... Just wondering if we had physics gurus here ;-)

I coasting out of gear, you'd not have any tires doing anything but steering/tracking. I'm not sure what the effect would be at the limit since I've never tried it remotely near the limit. I'm sure that turning the front wheels will scrub speed and initiate deceleration. I would assume that at least initially, most of that deceleration is going to be on the front tires. It seems like that would be especially bad at the limit with a rear or even mid-rear engined car. If you aren't used to that happening without the ability to dial things in with the gas pedal, it might be weird. I assume you could train yourself to take corners like that, there may be some alignment or suspension settings that you could adjust to work better in that situation. Or maybe the upset would be so short settling into deceleration due to tire scrub at both ends of the car that it wouldn't matter as long as your steering input was smooth enough.

[Superman]

All the comments here are good. Having the car in gear give you more control options. With almost any car, having the drive wheels provide at least a little bit of power seems to make the car more stable, particularly with a rear wheel drive car. And perhaps that has to do with how the geometry of alignments is set up.

I'll add one thing, which is sort of just a bit more detail on the above: Cars seem to dive just a tiny bit onto the outside front wheel, in a turn where no power is applied. Perhaps the car is slowing down when no power is applied (on a flat plane). It feels like a tiny bit of power is needed to avoid loading that outside front wheel.

And then there are 911s. As we know, power is absolutely needed for stable turning. If we find ourselves in a situation where we are worried about losing traction and going off the road, the LAST thing you want to do is lift. Lifting transfers weight off the rear axle. This lightens the rear axle; reducing traction, while centrifugal forces are trying to push that engine to the outside of the curve. In a "pucker" situation, we have no choice but to keep our foot on the gas.

[Seahawk]

I have nothing to add other than, on the advice on many other Land Cruiser owners, I put my LC into neutral going down hill all the time...I don't live in the Rockies but I coast into roundabouts (Yes!) all the time but always put it in D 100 yards or so out. It just feels better and more controlled.

I hope Captain Ahab has some insight.

[masraum]

Originally Posted by Superman

All the comments here are good. Having the car in gear give you more control options. With almost any car, having the drive wheels provide at least a little bit of power seems to make the car more stable, particularly with a rear wheel drive car. And perhaps that has to do with how the geometry of alignments is set up.

I'll add one thing, which is sort of just a bit more detail on the above: Cars seem to dive just a tiny bit onto the outside front wheel, in a turn where no power is applied. Perhaps the car is slowing down when no power is applied (on a flat plane). It feels like a tiny bit of power is needed to avoid loading that outside front wheel.

And then there are 911s. As we know, power is absolutely needed for stable turning. If we find ourselves in a situation where we are worried about losing traction and going off the road, the LAST thing you want to do is lift. Lifting transfers weight off the rear axle. This lightens the rear axle; reducing traction, while centrifugal forces are trying to push that engine to the outside of the curve. In a "pucker" situation, we have no choice but to keep our foot on the gas.

Yep, there's always drag on a car from aero and/or due to tire deformation and whatever other factors are causing a car to slow down. When you turn the steering wheel, both front tires will deform and increase drag and deceleration, especially on those two tires, which will cause the car to rotate. Presumably, when the car rotates, the rear tires will also deform and some of the deceleration will be generated by the rear tires as well (although I would think still biased towards the front). I would think the fact that the rear tires are decoupled from the engine and having to provide accelerative forces from the engine would mean that the tires would be able to skew farther into the cornering portion of the friction circle.

[CurtEgerer]

It's trick we occasionally used on snow/ice in a front-wheel-drive car to momentarily interrupt the understeer. But only as a last ditch effort to keep from going off road/track.

[cockerpunk]

why would you?

there are a half dozen, easy, small reasons to not, why would you?

[masraum]

We're all wrong!

[gacook]

Originally Posted by cockerpunk

why would you?

there are a half dozen, easy, small reasons to not, why would you?

That all too human trait that has both led to great innovation and utter disaster--curiosity.

[masraum]

Originally Posted by cockerpunk

why would you?

there are a half dozen, easy, small reasons to not, why would you?

I don't think Deschodt wants to coast around corners. I think a lot of folks that drive, especially manual transmission cars probably do because they have never been told not to and thought it was simpler at some point. And for most of the world that probably drives at 1-3 tenths all of the time, it probably doesn't impact them much at all.