Best way to slow down.

I think you are confusing differential loading vs engine braking with respect to F-1 cars.

Ideally you have slowed the car down pre apex and are back on the throttle for the exit... The quick Change of gears is much more to be in the best gear and torque range for the exit as that is where the speed and time comes from.

I have driven a number of California's but not on the track... The 599 on the track requires you to tread lightly on acceleration or else the to comes in or you spin with out it

 

Of course, as you keep slamming others for, I didn't say anything about you slamming the brakes on.

I'm not getting dragged into another one of these endless debates with you about your unique interpretation of the dynamics of an automobile. You've still got me looking for F1 drivers pushing that neutral button every time they get loose (I haven't caught one yet).

You may have your opinion on how to prevent the suspension getting "unhinged" in a corner, and anyone reading it is free to form their own opinion of your interpretation of physics. You might be on the verge of a breakthrough in vehicle design leading to rear-only brakes! It's huge in the lower classes of go-karting.

P.S.- I'll leave you with this experiment: fill a glass with red wine or Coke or the beverage of your choice. Run up to the top of first gear and drop the throttle. See which way it goes.

 

OK, I think you've maxed yourself out in this discussion. So let's call it a break. Please consider what I wrote in an objective manner.

 

Progressive braking is preferable for long corners but in some situations like if you are contesting a sharp corner with another car, you would need to slam on your brakes as you try to brake late into a corner. Getting into the right gear for a faster exit would be part of that maneuver.

I don't know what you're complaining about. I have to answer poorly-thought-out challenges from several nonbelievers on this thread. You only have me to contend with and you don't have to add to the list of poorly-thought-out messages if you don't wish to.

As for the neutral button, I play with that and the "+" paddle all the time in my Cali30 to build up some muscle memory.

If you read what I wrote you'll see that someone else on Fchat has already enlightened readers with the same idea back in 2008. I am not inventing anything new.

As for why it's "huge in the lower classes of go-karting" as you say. If you can figure that out you might find it enlightening.

Sorry, that's not a good experiment because a fluid, like wine or Coke, is elastic when placed in an open container. Since it is not restrained or "tethered" to the car in any way it will behave according to Newton's First Law. It will splash.

Everything else that is tied down or "tethered" to the car will simply suddenly decelerate with the throttle lift-off. (HINT: it would be a very crappy car if it dives every time you suddenly lift throttle or perform a harsh downshift. Remember, your head doesn't bob as much as your passenger's because you're driving and automatically poised to anticipate the car's reaction.)

Anyway, I've already suggested a much better analogy with my bike braking experiment.

 

if the COG of a car is higher than the centre of the wheels the car will dive either if you brake with front, rear, left or right brakes. I don't see how this can be difficult to understand.

A more interesting question would be; if the car is on a treadmill that magically matches the speed of its wheels at all times in the opposite direction, will the car dive and pitch during braking and acceleration?

 

So, back to the OPs question...

Firstly, never put the car in neutral when slowing down. By doing this, you have given away the option to accelerate if needed and that's a safety issue. Also, if you do need to accelerate and out it back in gear, you will find it hard to do this smoothly and will jerk away which isn't cool, smooth or good for the clutch/transmission. Secondly, Ferraris are great for heel/toe gear changes so try and learn to do those as they aren't that hard to do once you've spent a bit of time practicing. Unlike on a race track, on the street you will not be operating the engine anywhere near max revs most of the time. Hence, one or two well executed down shifts when braking adds to the enjoyment of the car and is safer overall. Simple.

 

+1

I've never understood the (mostly American) fascination with shifting into neutral when slowing down, or after a hard pull on the motorway, or when generally doing nothing on the motorway and shifting it into N. It's always been affling to me.

 

We shift into neutral when we're slowing to a stop so we can have that task complete and done and not have to think about it any more! Now our right hand is free to hold a french fry or our cellphone.

I've never observed the others.

 

OK, I apologize for the irritation that showed in my previous message, I really try to stay more level in my communications these days (although I really am irritated that I always look at the steering wheel when I see an F1 driver have a moment now).

I believe we are equating nose dive with weight transfer to the front, correct? Of course, we should also recognize that even when we don't see the nose diving, there is still the same phenomenon at work, just to a smaller degree that we don't notice. We should all be able agree that looking out the windshield and trying to decide if the car is diving is not the definitive measure of anything.

For a fact, the physics of the matter dictate that decelerating a car through action of the wheels, will induce "weight transfer" to the front. This is most obvious on a sprung vehicle such as a car or a bicycle with a front suspension but will happen to any arbitrary wooden block being slowed by a force acting below the center of gravity. Here's a neat dynamics lesson online: https://courses.engr.illinois.edu/tam212/ava.xhtml

But let's try flipping the scenario! There appears to be a theory presented here that depending on which end of the car the braking force comes from, weight transfer can be avoided. Let's try accelerating instead of braking. We all know that induces rearward weight transfer, just like braking induces forward weight transfer. Rear wheel drive drag cars pop wheelies or run wheelie bars to counteract the effects... And front wheel drive sucks because weight transfer takes all the weight off of your drive wheels!!! These are all commonly accepted facts, right? These are well-known examples of the fact that it doesn't matter which end of a car is imparting the acceleration to the car body, the body will react the same.

 

+1

Me neither. It's better to be in proper gear at whatever speed the car is in. Most accidents occur when inattentive drivers rear-end other people at the stops. As pointed out by subirg, you want to be ready to move if you suddenly find you have to.

It's also wonderful to feel the tug of a smooth torquey engine revving at the correct gear all set to go. That's one of the thrills I live for when I drive a good car.

 

COG has nothing to do with the bike example I used to demonstrate what happens when you have 100% rear brake bias. The bike weighs 16 lbs and has a very high COG because I weigh 170 lbs. ...but even with such a high COG it just skids. It doesn't pitch forward... why? Because the pivot (decelerating rear wheel) for the COG is BEHIND the rider (driver).

I was also trying to give a hint to don_xvi about his mention of "rear-only brakes! It's huge in the lower classes of go-karting"... why that is so. I suspect they are also lower-powered karts that can stop well enough using rear-brake only and would be much safer for rookies who may not brake as carefully as more seasoned drivers in "higher classes of go-karts". Much less likely to pitch the whole kart, driver and all, right over the front wheels!

I don't get why it's so hard for some people to understand it helps to offset front braking bias by applying a bit of engine-braking. It's been clearly discussed and used in F1 and managing brake bias but some folks here just don't want to acknowledge it.

 

Excuse me, but after a certain point I couldn't read anymore. In all of what I did read. I heard no mention of heel&toe ... wouldn't that be both braking and using the engine to modulate corner entry ... for just stopping ... slam on the brakes

G

 

Don, I appreciate your trying to keep the discussion objective and less personal. I also like to discuss ideas, hopefully by using clear explanations and quoting references to more knowledgeable sources. I apologize if I also come across being a bit too aggressive at times, but I only do that to stay level with the challenge. It's not personal.

Yes, there is still going to be suspension compression and the front end will still do most of the braking and I feel it's actually preferable to have a slight "nose dive" than to try and keep the car perfectly level ...and overdo it.

Thanks for the link. The models presented are perhaps a bit circumspect and I'm still digesting what the material. But here's my direct answer about engine-braking.

Engine-braking simply modulates the brake bias. The car pitches over the nose because in most setups, the front brake bias is rather huge - in effect, the front of the car is slowing faster than the rear. So the front wheel is acting as a pivot for the weight of the car that's behind the front wheels.

Think of a typical comical scenario involving the Three Stooges chasing a guy. The guy runs through a doorway and slams the door on Moe. Moe comes to a dead stop, falls down and then Larry and Curly skid as they try to stop, then trip over Moe on the floor, wind up going through the door panel.

Now imagine Larry and Curly doing some fancy back-paddling on top of skidding, just in the nick of time, piling into Moe instead of flying over him. That's kind of what I mean by engine-braking.

Engine-braking reduces front brake bias, and by doing so also affects the suspension load (weight distribution) over the 4 wheels and therefore the attitude of the suspension. The car becomes more stable, better set up to change direction and better able to apply traction upon corner exit.

You always want more weight on the rear wheels when you corner. That's why race cars have rear wings!

Weight transfer caused by braking can only be modulated, can't be eliminated unless the car uses a computer and sensors to detect weight transfer and then modifies brake bias automatically. If you are doing it manually by engine-braking, it depends on how good you are at juggling the brakes with timing the downshift to achieve a desired amount of engine drag (you do not slip the clutch - you just try to downshift smoothly and avoid unsettling the suspension in the middle of a corner).

I think the rear squatting seen when accelerating from stop may be due to Newton's 3rd Law. Imagine the whole car dangling in the air being supported only by a big hand with thumb and fingers holding the drive axle. The force vector from the rear axle is rotational so if you then start the engine, the car will simply rotate an spin around the drive axle.

In the case of a RWD car, since the non-drive front wheels are actually pressed against the ground, the front suspension will then compress. Newton's 3rd Law will predict an equal force pushing back against the front suspension and the front end will tip back, compressing the rear suspension. The whole suspension will settle down once the car starts moving forward because more and more of the force from the rotating axle will translate into forward motion rather than downforce on the ground beneath the front wheels.

In the case of a FWD car, I think you can see the car will have a tendency to lift the back end, until the car starts moving forward and the power is translated into forward motion.

 

So, you're braking heavily into a corner. Weight is transfering forward. Front end compresses. Let's assume your brake bias is such that the rears are not quite at threshold. Let's also say the fronts are at threshold.

You downshift (because you have to), and some amount of engine drag is applied to the rears, adding to your overall braking (additional brake capacity exists because the rears are not at threshold yet). Are you saying that this additional braking just compresses the rears and does not transfer more weight forward, and will not further compress the front?

 

on the bike you don't go over the bars when braking with the rear because it hasn't got enough grip and simply skids. If you attach a rope from a wall to the rear wheel and ride fast until it tenses, you will definitely go over the bars. Or if the rear wheel gets trapped in a manhole. It will always dive at the front if the COG is higher than the wheel's axle, even if less when braking with the rear.

 

Or if the handlebar hits a guide wire on a telephone pole. Ask me how I know.

 

Engine-braking simply adds braking force onto the rear axle as the rear brakes are also mounted on the same axle. The front end dive is due to the front brakes having a bias so when you add more braking force on the rear axle, the bias is reduced and the nose dives noticeably less. It's that simple.

Nobody likes the handling of their car when the car's nose is diving because the suspension is obviously unevenly loaded, unhinged. So engine-braking also helps handling. When you match the downshift properly the speed of the engine will also be in the power band of the engine's torque curve so your car will accelerate optimally when you exit... on a suspension that is glued to the road, because of engine braking.

Whenever I do this, my car feels really pumped, smooth and fast. It feels perfectly connected to the road.

 

Yes, there are some merits to your points and I started to put together a reply but realized it's going to be quite lot more complex than I had expected. I'll post a reply after I get a good night's rest.

 

I apologize.
My communication skills have deteriorated after years in industry writing nothing much more than emails, and I've never had the patience to teach, which is what is needed here. This endless typing isn't some Socratic debate process whereby we will find the truth together, the facts here have long been known and are well understood. As the dynamics of a motor vehicle is a big part of my job, we discuss this kind of stuff every single day in the office and we are all on the same page understanding that acceleration induces the phenomenon known as weight transfer.

An understanding of free body diagrams would be a good entry to understanding what's happening. Torque=Force x Moment Arm. Key to a lot of this discussion. I don't remember if those are introduced in high school physics or if it was freshman college physics. We engineers use them all the time to understand what forces are acting where and what impact they will have.

A few quick points:
- Take note of which brake makes the bicycle slow down faster, the front or the rear. The front works better because of weight transfer.
- Rear brake go-karts spin out or oversteer on the brakes a lot. They're harder to drive.
- You have no control over how much engine braking you apply (you've even stated that you don't modulate the clutch), so it's a poor way to try and extract maximum grip since it can't be fine-tuned to maintain the max
- Try some drop-throttle during limit or near-limit cornering in a pre-ESC zoom-zoom FWD Mazda. Countersteer. Clean shorts. Understand weight transfer.

P.S.: Look up anti-squat and consider if that helps provide that connected-to-the-road feeling you get. And then just go enjoy the drive.

 

Haven't noticed that, nor can I imagine what would cause it. In my experience, braking of whatever sort, at whichever end, causes weight transfer forward, and hence some amount of dive. If you're correct, pure rear braking would lift the front end. I'm pretty sure that never happens.

 

it happens (with either front or rear braking) when the COG is lower than the wheels' axles. Anyway dive and pitch is different from weight transfer, which during braking always happens towards the front. It can be of different proportions, though, if the braking axle is only the front one or the rear one. Imagining as an extreme a virtual instant braking force like a rope attached respectively only on the front or the rear axle, the weight transfer will be much more pronounced when attached to the front axle, to the point it would be able to tipple over the car. Obviously this doesn't take in consideration the fact that the rear axle will never have as much braking power as the front one, exactly because of the weight transfer itself.

 

Good morning.

First of all, I must remind everyone that if several people take an interest to prove their points against mine that I am only one person, with family and friends, personal affairs to attend to. So I would appreciate a bit of patience if you can wait for my reply. If you consider endless typing challenging, you can imagine having to reply to several people's ideas instead of just one. I am likely doing a lot more thinking and writing than you are.

Next, to refocus the discussion to the OP's question and to stay on topic. Let me reiterate what I said in my first post: When combined with judicious control of the brakes, careful rev matching can add engine braking to reduce front end dive (weight transfer) and set up the chassis for faster corner entry and faster exits.

And here's how I prefer to slow down:

SLOWING REAL FAST (in other words, STOPPING):
- apply brakes

SLOWING IN A STRAIGHT LINE:
- apply brakes
- downshift to match slower vehicle speed

SLOWING FOR A CORNER:
- apply brakes before entering corner
- downshift to match slower speed just before entering corner
- continue to apply throttle to keep engine speed in power band of engine
- reduce throttle if cornering speed cannot be maintained, downshift to maintain engine revs, repeat if necessary
- stay off brakes​

 

Now, to answer some questions...

Good to bring up the importance of torque, the moment of force. I was just about to do the same.

I did not question that. I always said you need to combine braking and engine braking. So please avoid giving the false impression that I do not brake or think braking is bad. Otherwise new readers to the thread will think I never brake.

You made the "lower class go-kart" reference and I obliged by explaining why they only used rear brakes. I didn't say lower class go-karts are good or better than "higher class go-karts". That's all.

100% brake bias, front or rear, is bad. Again, I promote balancing front and rear braking.

NOT TRUE. Engine braking can be easily controlled, with practice. Slipping the clutch to engine-brake is the wrong technique, slow and also bad for the clutch. Instead you should de-clutch and blip the engine while very briefly in neutral.
Engine-braking is highly sensitive to engine speed and transmission gearing. So the amount of engine-braking you produce depends on a combination of:
1) how hard you braked before downshifting
2) what gear you are downshifting to
3) how hard you blip the engine before downshifting
4) how quickly you downshift after you blip
5) whether you apply some throttle after you downshift

Keep in mind there's almost no engine-braking at lower engine revs in high gear.

ESC? LOL. My Canadian E30 did not even have ABS. Drove that car for 16 years.

Sorry, I won't be explaining anti-squat for you. I'm just explaining rev-matching. If you bring up the topic and want to discuss A/S you'll need to do some more typing yourself.

 

Yes, I believe your discussion of the effects of the COG merits more careful exploring. I'm not an engineer and only completed 1st year physics in university so I'll have to comment on this one very carefully.

However, as I mentioned in my last post, I'm glad Don mentioned torque or the moment of force... as it applies to rotational force acting an axis. I believe this applies to my bike example and proves some of what you wrote last night. If that's true it would also disprove what I said about rear braking not creating any weight transfer. Instead, as you are asserting, rear braking would create LESS weight transfer than front braking. I think you're right about that. However, your assertion about the cyclist flipping over when the bike is suddenly stopped from the back is not accurate, the cyclist is flung FORWARD because he is not perfectly fixed to the rest of the bike. His arms fail him. Most of the effect is due to forward momentum, a small part of it is likely due to the lesser rotational moment (torque) from a COG effect... again I would say most of it is due to forward momentum, not rotational moment.

Another interesting observation about the cyclist being flung is that once he leaves the stopped bike, if his hands/arms are rigidly gripped on the bars (even for a fraction of a second) they will act as a fulcrum or pivot... so of course, his body will then rotate around his grip on the handlebars.

I'll try to understand this better and hopefully provide some drawings.

Finally, I also realized another aspect about engine-braking, which ironically may indicate that it actually isn't completely a rear-braking action at all because engine-braking actually occurs inside the engine. The rear axle (namely the rear tire patches) are involved only as far as how efficiently they are transferring the change in torque from the engine/driveline to the ground. I'll try to understand this better so more later...

 

I don't know why you choose to make such comments above ? It's rude and really points to your inability to absorb the learnings of others.

As to me maxing out my contribution - you sir don't get to determine that.

When you slow down any moving vehicle with wheels the weight transfers to the front....

f1 solved the Un -hinged suspension problem with active suspension that is the only way I know of keeping a constant tire patch at all times - those actuators compensated for weight transfer forward and laterally

Engine braking had very little to do with it. Perhaps some classroom time at Skip,Barber or Bertil Roos would help you understand vehicle dynamics better