Don, I appreciate the informal atmosphere but as a sign of respect I would prefer to be called Michael or 4th_gear instead of "dude". Thanks. The bike analogy was purely introduced to discuss "NOSE DIVES" with Entropy in this early post and it was commented upon by Igor Ound and a few others afterwards. Igor Ound made some interesting comments and I responded to those but I have no intentions of continuing a discussion on bikes stopping straight unless it illuminates something new about the OP's question of slowing down as regards track and driver education. I want to stay on topic. Please also remember - I already said I only brake when stopping in a straight line. So there is no point in discussing that. OTOH, engine braking is a cornering technique used to control speed and the chassis. I would be interested if you have something to add and describe regarding controlling speed in corners.
The engine is rigidly attached to the car and all forces, save aerodynamic, are reacted at the four contact points. Doesn't matter if the engine is oriented longitudinally or laterally, running or not. Agree with Don_xvi, understand the simple bike FBD first (2D), after which the 3D problem (turning) will become obvious.
https://www.youtube.com/watch?v=NbLhHtaVIO4 Good sir, please construct a 4 corner free body diagram similar to the one you made before for the bicycle and apply braking forces through the various wheels and analyze the moments created. Note that applying the braking force to either end produces a moment that makes the car want to pivot forward about the CG. The result of the rigid car body having this moment on it means it tries to push the front wheels into the ground harder and the rears less so, a phenomenon commonly referred to as "weight transfer". With that, I just have to put you on block to prevent the temptation to continue reading all your stuff. Your unique version of physics is too much like a car crash, I can't help looking at it, but then it sticks in my mind and makes me crazy. This stuff is well understood, but then every time someone tries to explain any of it to you, you start spewing more and more nonsense. We're not reading every message because you're drowning us in bull****, dude. P.S.- funny enough, in the vehicle design world, we often model a car like a bike using a "bicycle model".
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I agree with you about the 4 contact points but I disagree with you about the movement from the engine not mattering. The angular momentum of all moving parts of the vehicle will combine to create the total effect on the contact patches. There's a familiar contraption called the gyroscope. Its effect is most acutely felt on a motorbike. I can look up a reference for that if you like. As regards the FBDs for simple bikes, I've already drawn them but they are not motor-driven and do not have a transmission. If you know something interesting about bike FBDs that will make your point you can draw them and post them too. You are welcome to modify the ones I posted.
I'm sorry to inform you that contrary to what you may be used to believing, juvenile YouTube music videos do not actually make your arguments appear more correct. But hey, if you prefer style to substance... You also seem to be stuck on discussing braking in a straight line while I am discussing slowing for corners. But hey, if you think they are the same thing then I would like to see your proof. Maybe you can make some FBDs too. Okay, hurl verbal abuses and then run away. Is that what you do whenever someone disagrees with you? It's curious you claim to know something important but won't or can't actually describe it clearly, illustrate it or direct readers to a useful Web link that helps to settle the debate (or if you prefer, the argument). No problem, let me do it for you. Here's a direct quote from the webpage of an F1 fan in his 50s from Croatia who created an F1 dictionary on the Web. ...his entry on Engine Braking:"...When the engine is spinning with trottle closed, it has the tendency to slow down, mostly because of the compression effects in the cylinders. A coefficient is used in combination with an offset which generates a negative torque. This effect helps a lot in braking for F1 cars, and most other cars. You can feel the effect by driving and letting go of the throttle and feeling how fast the engine tries to brake the car (the rolling resistance of the tires will generally be a secondary effect)..." There are many such references on the Internet that point to the fact that engine braking has been and is, used to advantage in F1 cars. Good night.
I dont think making things more complex is helping you to understand the answer you are looking for. I tend to make thinks less complex instead of more complex. Lets stick to what we know: - The figure in post #52 shows it all. No need to add more forces/complexity - The forces attack the COG and the patches (as shown in post #52). Nothing else - The formula in post #53 explains it all. No need for any other stuff. - The book states that the braking power of the front brakes is about 65-75% whereas the rear brakes only have (the remaining) 25-35% which has been agreed by 4th_gear. So we just need to ensure that 65-75% of the breaking power is applied to the front axle and the rest to the rear axle. This is usually done in one (or more) of the following ways - Larger brake disk on the front axle than on the rear axle - Different sizes of the brake cylinders - Balance bar to manually adjust the braking balance (only used in race cars) - - ABS There is NO difference if the braking force on the rear axle results from the brakes or from the engine or from any other fact. Its just a force that has impact on the COG and on the patches. To slow down a car in the most efficient way we just need to make sure the brakes on the front axle and on the rear axle are operating at their maximum force so that neither axle is slipping (the braking system of a car is set up so, that the front axle always slips before the rear axle does). This is done by the methods mentioned above. There is NO need to try to improve the braking system by engine braking. As mentioned earlier it is very difficult to modulate the braking power with the engine instead of the braking pedal. BTW: I drive my 575M and my Maser 3200 also in winter on snow (these are my daily drivers and I have winter tires on both cars). One of the first thing you learn with a RWD car on snow is NEVER use your motor for any braking tasks. This could spin the car faster as you may think (because it adds braking power to the rear axle resulting in blocking the rear tires and thus spinning the car). Markus
Markus, I appreciate your genuine interest in the topic and your objectivity. However, the biggest problem I have with the simple approach to braking analysis is that it is being analyzed with the assumption that the car is always going straight. That's completely untrue when you are going into and around a corner. If the textbook does not make a distinction between stopping straight and slowing for a corner then you shouldn't be surprised if I am unconvinced. Simplicity is useful in a classroom where you can isolate factors and explore hypothetical scenarios to understand physics but it would not be helpful if you apply simple textbook or classroom examples while ignoring very important details in a real life scenario. Your car-slowing technique must be different when you go around corners. The car is constantly changing directions while cornering, the contact patches have to deal with constantly changing lateral forces as well as reductions in forward momentum. Hmm. You are perhaps taking an overly simplistic view of a very complex system. For instance, like the simplistic model used by the textbook, you are completely ignoring the tires. They are not there just along for the ride. Do you understand slip angles? Simplicity is desirable when WE exercise sole control over matters. When we deal with Nature, we have to accept complexity. That's what we all learn in life, that for all our simplest desires, it's not so simple in real life. It's good to look at simplicity within the proper context. BTW, you cannot use ABS in a corner and it's just plain BAD for racing. Well, that's not true for me. I have driven BMWs for over 30 years and always used engine braking when road conditions allowed it. I even purposely owned a tricky to drive (high torque RWD, heavy front end, steel suspension) 540is because I liked how I could easily coax it to oversteer. We have real Winters here so I also use high performance Winter tires. I think you car spun because you didn't reduce corner entry speed sufficiently before you downshifted to use engine braking. If you brake sufficiently it reduces the speed of the engine when you engage the lower gear. The amount of engine braking you create depends on how high the engine is revving and the gear that you're in. I've never spun my car from engine braking but I have spun my car from only using the brakes, because the front brake bias unweighed the rear of the car. You have to learn where the thresholds are for your car and then you learn to stay below those thresholds. How far you stay below thresholds depends on how much fun you want to have. I think you are too abrupt with the downshifts. Engine braking is very controllable when you develop a feel for the engine and a feel for the amount of traction the tires communicate to you. That's another reason why I like to own cars for a very long time - I don't track so I have to learn slowly and cautiously on my regular drives but I eventually get very familiar with how they feel and know how to play with them.
Moderators, time to can this thread. some drivers straight line brake and then turn in. Some trail brake. Which ever you are better at or more comfortable with and how a particular vehicle reacts. If you have driven an oval like in a stock car or other even on a short track , its pedal feathered down out of one end,turn2&4, straight ,then turn in pedal down then begin left foot braking. So lets just go out for a drive and have some fun practicing. GTS Bruce
I still say you are wrong. i beleive someone just proved it with the physics ... but you still persist that weight / force etc... does not transfer? I was not able to respond because i was out of town ( country ) ...In lieu of trying to help, I;ll just move on. Have a great time engine braking in your Cali.
You're entitled to your opinion. I apologize if I misunderstood your intentions but it's unfair to put someone down in an open forum, "walk off" and not bother to explain the details behind your assertions. It makes it extremely awkward for the other person to defend himself. Anyway IMO, the physics lesson is incomplete because it only covers stopping the car, not slowing to make the fastest corner. The stats on front-vs-rear braking force illustrates the front brake bias, the "weight transfer" everyone refers to... and it is not a good thing for optimal suspension loading and control, when cornering. Engine braking retards the rear tires. If you engine brake while also applying the brakes, it increases the total rear braking force applied, which amounts to a better front-rear braking balance, thus reducing brake bias, improving suspension balance. Traction improves, car is easier to control. Finally, if you're only engine braking, there is no front braking so no front brake bias, less "weight transfer", chassis is better balanced and you can play with the slip angles if your car is set up right. No hard feelings... enjoy your drives.
You are still not understanding the physics, even the simple 2D bike example. Tell me though, assuming engine inertia has more than a secondary effect on chassis balance in a 'braking' turn, in which direction of turn (left or right) is it beneficial?
I haven't bothered to investigate this yet but I expected someone would to eventually inquire. It is a good question ... and I do have a preference regarding the direction of turn but whether that is due to benefits from physics remains to be determined. Let me think about this for a bit before I answer and perhaps we can explore it together, along with others if they also wish to partake. Unfortunately I have a few other projects I need to catch up on and I am not an engineer or a physicist. As for your throwing in (yet another) unqualified put down, I already mentioned my disdain (anyone's disdain in fact) for when someone directs a criticism in public and does not bother to explain why. It's lazy at best and dishonest at worst. I was trained as a scientist and no scientist would dare to utter a public critique without explanation for fear of appearing hysterical and unprofessional. So I hope we *are* trying to be scientific and professional in our discussions because otherwise we would simply be arguing, and I haven't time to waste on arguing with anyone. I am only interested in constructive debate and learning.
First off, my question regarding turn direction and engine inertia was tongue-in-cheek. Highly doubt even the most skilled drivers would spend the time to compensate for different engine inertia effects when turning left or right. Secondly, the explanation why your statement was wrong has been explained in multiple posts. I was merely pointing out that you were just repeating a mistaken viewpoint. Your dismissal of this, while continuing to insist on discussing higher order problems, makes the whole exercise pointless.
Actually upon checking recollection of my favourite corners, I think I prefer right turns but I can't say if it has to do with physics although the car does feel more natural and more responsive with right turns. As for your being flippant, your profile says you're an aerospace engineer so you should know something about gyroscopes and how they affect moving objects like planes and cars. You haven't commented on how gyroscopic couples act on moving objects. Perhaps you can explain the following excerpt: Image Unavailable, Please Login It says "...Let the engine rotate in the clockwise direction when viewed from the front. Then the reaction couple tends to lift the rear wheels and depress the front ones as shown in Fig. 31.13. Thus the effect is to increase the front wheel loads or decrease the rear wheel loads by..." It also goes on to say "...If during a left-hand turn, the engine rotates in the anti-clockwise direction when viewed from the front, the effect of the reaction couple due to the engine gyroscopic couple is just the reverse of the above situation, i.e., the reaction couple tends to lift the front wheels and depress the rear ones..." So it says the gyroscopic couple from engine rotation can shift the suspension load FRONT-REAR, depending on the direction of engine rotation and whether the car is turning left or right. As an aerospace engineer, how did you miss that? Just how is that possible? I had already pointed out the multiple posts you refer to were discussing a textbook description of stopping in a straight line. When I pointed this out no one, including you, qualified the textbook descriptions with regard to cornering. No one took centrifugal forces into account. In any case, I have just supplied a vehicle dynamics treatise on how engine gyroscopic couple can affect the suspension load of a car when making a corner. Engine braking by changing the torque output of the engine would definitely alter or modulate the engine gyroscopic couple. How sad it must be for you, as an aerospace engineer, that you could not or would not explain or at least recognize the importance of engine braking in vehicle dynamics. If you wish to read the rest of the treatise, here it is ... BTW, it's titled "Stability of a Vehicle Taking a Turn" and it also discusses centrifugal forces on the cornering wheels as well as "Reaction at the Wheels due to Gyroscopic Effect".
My response to all this arcane, theoretical BS: https://www.youtube.com/watch?v=fMxIDCEbA5k The only thing remotely resembling engine braking is a slight lift before the flat-out "Kink" to settle the car.
Don't slow down, bias the rear brake and drift around the corner. Oh I built most of the body on the Camaro. 4th-gear You must be a blast at a SAE party. no offense. https://www.youtube.com/watch?v=h4awzBQezlE&list=FLaabxB2347u_kOhlw-z2csQ&index=28 https://www.youtube.com/watch?v=J1Nry0e4MQQ
this thread is out of control. Michael, you should continue to enjoy driving your car, and using the techniques that you believe are the best. However, thru this thread (and previous threads regarding vehicle dynamics and driving techniques, it seems 1) you disagree with the absolute laws of physics 2) you disagree, or struggle to understand, the application of those laws of physics in a vehicle environment (combination of systems, incl braking, sway bars, springs, dampers, ABS) and 3) the essential techniques of driving a car - at/near the limit, or racing. Seems like a lot of folks have tried. Untrue. In hard threshold braking, getting the car to pitch ("transfer weight") is critical to maximizing brake/tire performance and slowing the vehicle. Additionally, a careful brake release is required to minimize any additional pitching. Trail braking done well is the perfect example of the need for brake pedal modulation. Plus, in cars with aero (eg. XX, 458C Evo), the aero performance is very sensitive to pitch. Engine braking happens; unless you completely screw up a downshift and lock up the rear tires and destabilize the platform, the goal of heel-and-toe (and the beauty of DCT) is that it matches revs and allows downshifting with the minimal impact on the chassis. Engine braking can be more (higher revs), but measurably the stopping force is substantially less than even light brake. In practice, and in comparison to brake usage, engine braking does little to help stop compared to the brakes. Can you downshift and slow your way down to a traffic light? absolutely. can you feel it? yes. However, the focus of this conversation is on performance oriented chassis performance. +1000. Watch rookie drivers in something like a manual, RWD car in heavy braking/slow corners, or medium speed corners with downshifts required. Errors in their footwork tend to be the cause of a lot of snap oversteer spins, simply due to the disruption of the chassis with the grip indexed forward. You can only "modulate" engine braking by getting on the throttle - which puts weight backwards and encourages understeer. Too much "modulation" results in the car pitching forward/back...which is not what you want to maximize exit speed and allow best mid-corner speed and keep a stable platform. OK, I can help here. Have you driven an XX or race car? I say that because in an XX, Challenge or most any GT car, the process is to downshift in a straight-line under heaviest braking, release the brake pedal (including trailing brake), rolling speed through the corner and having the car positioned to get back to max throttle ASAP. The rule is do not get on the throttle at all until you can get it back to full throttle - we do NOT "downshift continuously" through fast corners - that's a recipe for carnage. You shift down (or up) based on what rolling speed is required and gear works best. Michael, I've suggested this before - Mosport has a great skidpad facility, get a good driving coach (there are many great ones based in/around Toronto) and go practice in your Cali. In fact, bring your hypotheses along and test them. <<end of rant>>
LOL, reminds me one time I took a date out for "a drive" after dinner and movie. She probably swore off dating guys with "sports cars" for good. Unfortunately for me, she wasn't my only date who swore off guys with "sports cars". I'm much better these days. But seriously though, drifting is an extreme stunt that doesn't translate into speed. OTOH, rallying comes across quite different to me because you have sophisticated 4WD, really tight, potentially very slow corners with awful surfaces... so it's pointless to try and finesse your way around them; much better to deploy the tail just before the apex, power your way around, keeping the turbos on the boil so you can fly down the next set of straights. But then I'm just talking. I don't have the background, resources or inclinations to immerse myself in rallying. Stuff like that you need to get in with both feet or you're just dreaming and end up screw1ng yourself.
And the same to you. If we survived this long, we have to be doing something right and maybe part of the problem is that we're not talking about the same things... talking cross-wise. Writing is also not the most accurate way to compare techniques because our choice of words may mislead one another. I used to be on high level negotiation teams and the first order of negotiations was always to agree upon the meaning of the terms we would use in our discussions. We can't do that here, no one's paying for my time. I really think we may be talking about different things. Both fast corners and mid-speed corners allow for engine braking in conjunction with threshold and trail braking. And then there are slow corners where you can only threshold brake and downshift for the apex before reapplying power. You can also make a case for corners that fall between these ad hoc categories. F1 transmission cars allow drivers to use engine braking more easily than cars with manual transmission. That's why XX and F1 cars will downshift so many times before the apex. Watch this video of 599XX runs at Monza I randomly picked off the Internet, they all brake and dowhshift (often 3-4 times) leading up to the apex, then they power out of the corners: [ame=http://www.youtube.com/watch?v=sraMId1-U2w]2012 Ferrari 599XX Evoluzione PURE SOUND & Glowing Brakes[/ame] I appreciate your sentiment but tracking at Mosport would be too much of an expense for me, both financially as well as a drain on my energy and time. I don't get into hobbies unless I can fit them into my life and can do them properly. The Cali is also a wet sump car, not designed for very long track sessions. My reflexes are very sharp. I know race and track speeds require very fast reflexes but I am already very good at skid control under normal road conditions and that is where I do my driving. My reflexes have not diminished since my days on high school and university sports teams. BTW, I will be doing laps on a track, just not the automotive kind. I will be doing it on a track bike on an indoor oval, which I feel is much better physical exercise and less of a drain on my wallet and time. My priorities are different from yours. No ranting needed.
Post of the thread, right there! Not to mention any gyroscopic effects when stirring the whole mess. I've run out of popcorn too. This may just qualify as the craziest thread I've ever read here, and I've read some doozies! 5 pages arguing the fundamental laws of physics! Goodness gracious. Cheers, Ian
