I'm a few days late here, but just caught the posts above about RWD and AWD and platform sharing. While the Accord, Acura TL, Acura MDX, and Honda Pilot are considered to "share" the same platform, there's actually quite a big difference between the cars and the trucks.
One of our members, I think it was Juice, posted a pic of a Pilot frame. Yes, you read that right, FRAME. As in, full frame, like what cars used to sport when tailfins were all the rage and the naughtiest song lyrics were in Elvis songs ("number 47 said to number 3, you're the cutest jailbird I ever did see"...hmmm, I didn't realize there were co-ed prisons back then! ;-). So, the Accord and Pilot really aren't as much alike as you might think.
RWD or AWD would take up a lot of space in something like a Civic. They can do it on a CR-V, because that sits up high, so the mechanicals don't intrude as much into the passenger cabin.
It would also add a lot of weight. A Subaru Impreza might have AWD, but guess what? It's about the size of a Civic but weighs as much as a typical mid-sized car from 1980!
I could see something like an Accord or TL being a candidate for conversion to RWD or AWD, as the cars are physically bigger, so the driveshaft and rear differential wouldn't take up as much room. But I couldn't see that happening to a Civic...at least not easily.
Yes, the Accord platform is not at all similar to the Ody, which is not very similar to the Pilot or MDX. They each have a platform that is heavily modified from one to the next. The Accord for example, uses a completely different subframe up front. The sedan and coupe both use double wishbones, while the Ody uses struts. Meanwhile, the Ody does not have a rail support structure like the Pilot. Now, the Pilot is not a body on frame design, it just uses rails as reinforcement for the unibody chassis. But the Ody has none of that. Here's the pic you are probably thinking of.
As for the Civic using AWD, certain models do have it. The Stream (Civic MPV/Wagon thingy) has an option for AWD. But the system that works with that platform is RT4WD. RT4WD weighs about half as much as VTM-4 or other systems like Quattro and 4-Motion. The problem with RT4WD is that it is designed to be an all-weather system. It is a reactive design and does not provide any significant handling advantage on dry roads.
when, technically, as a platform gets beefed up does it stop being unitized (UniBody is actually a Chrysler-coined term from 1960) and become body-on-frame?
Most, if not all, unitized cars have a front and rear sub-frame...some are just longer than others. And in the 60's, some unitized cars were so fragile that they had to be beefed up with frame rails. I know I've seen some early 60's Chevy II's like that, that had these thin rails that connected the front and rear subframes. However, the whole assembly didn't look like it would stay together if you took the body away.
That Pilot frame, however, looks like one piece to me. Except for being shinier, having the engine facing the wrong way, and the rails not being nearly as beefy, it really doesn't look so different from the frame of my '57 DeSoto!
Honda calls the Odyssey/Pilot/MDX platform as... Global Light Truck Platform, probably because it is quite a bit different from the Global Midsize Platform it is apparently derived from (Accord, TSX, TL).
OTOH, CRV/Element use the same platform that Civic/RSX do (Global Compact Platform).
It's Csaba Csere's column for those familiar with Car and Driver.
It's of particular interest because they use the TSX and 325i as a point of comparison. I'm not going to quote the whole article, but here are some of the main points:
"Given the enormous expense of replacing a front-drive car with a rear-drive one, no car company would do it just to provide the marketers with a new talking point"
"the definition of traction is grip that allows acceleration. Grip for cornering and braking is completely different, and there's no evidence that front drive provides any advantage in these areas during winter driving"
"but if you really want secure winter handling, you need to change to snow tires. Four snow tires will improve traction as well as braking and cornering grip to the point where the winter merits of front and rear drive are rendered irrelevant."
"Once we get away from the slippery stuff, rear drive has traditionally displayed better handling because it splits the duties of steering, cornering, acceleration, and braking more equitably among the four tires."
"Honda Accords and Nissan Altimas come with 240-hp V-6s, and 300-hp luxury sedans are everywhere. At these power levels, front drive has reached the limit of its competence."
I'm not done yet, but they have a picture of the new RL too. Looks pretty sharp. They have a test of the new Legacy Outback turbo, and the new Saab 9-2x (Subaru WRX). The title of the Saab article is "Sushi rolled in a Swedish pancake". I love Car and Driver.
the new Malibu Maxx LT trying to compete with the Accord and Camry:
"Options on our tester included a rear DVD/audio child-sedation system ($995), OnStar ($695), and XM satellite radio ($325). That nudged the total close to $27,000, navel-deep in the V-6 Honda Accord and Toyota Camry territory. Which, for a car bearing the Malibu monkier, strikes us as the fiscal equivalent of poking a stick at the tiger that lunched on Roy."
in a Carol Burnett sort of way. But seriously, by the time you loaded up a DVD system, satellite radio, and that other frilly stuff, would that get you a similary-equipped Accord or Camry V-6, or just a fairly basic V-6?
I got my C&D July issue last week and glanced thru it. I did look at the FWD vs RWD article, and thought about something that Csaba apparently didn't.
Weight shift doesn't happen in a constant proportion. We tend to be mesmerized by 50-50 weight distribution but in reality, how much weight on driving wheels exists under various situations (for traction purpose) is all that counts. Honda typically places its engine just in front of the front axle, as opposed to on or after it. So, while there is a weight shift backwards, much of it happens to be on the driving wheels. If they had placed the engine/transmission on or behind the front axle in front drivers, then I can see his point.
I thought, it would be a good idea to actually come up with traction measurements under different situations for various cars rather than using a generalized statement.
But then, I consider mid-engine/RWD as optimum layout for perfect weight balance. Most of the weight is on driving wheels during acceleration, and nearly perfect weight distribution during braking, and of course, not having to worry about drive train up front allows room to work on other aspects of a car. So, where is the next NSX?
I don't know the exact trim specs of the Malibu Maxx, but an Accord LX V6 with DVD would go for around $25,500, while an Accord EX V6 with DVD would go for around $28,500. So I think that C&D's observation was reasonably accurate.
"Honda typically places its engine just in front of the front axle, as opposed to on or after it. So, while there is a weight shift backwards, much of it happens to be on the driving wheels."
I cannot imagine the weight shift to the drive wheels on a FWD Honda is going to be anyhere near the weight shift to the driven wheels of a typical front engine-RWD car. I'm sure Csaba knows what he's talking about, he is an automotive engineer. Besides, that doesn't negate the point that "rear drive has traditionally displayed better handling because it splits the duties of steering, cornering, acceleration, and braking more equitably among the four tires."
"It looks awfully complicated and expensive. I don't know if I would want that on one of my cars."
Well, that's your call. Increasingly expensive and complex systems are becoming a hallmark of this class of cars. SH-AWD doesn't worry me any more than many of the complex systems already available on competitive cars. And it's not like Acura is the only manufacturer that does complex AWD, or that they don't have experience in AWD.
The early praise from C&D is very encouraging. Sounds like it may be a very effective competitor against the RWD alternatives in its class.
"Well, that's your call. Increasingly expensive and complex systems are becoming a hallmark of this class of cars."
No doubt, I agree. I prefer a little more simplicity and a regular RWD or FWD car provides that. I wouldn't even want to know how much some of these complex and expensive gizmos are going to cost to fix when the mileage gets up there.
I'm no engineer, but Honda's SH-AWD seems to be different and more complex than any other AWD system out there, after all, Car and Driver says, "Acura re-invents AWD" or something to that effect.
"I prefer a little more simplicity and a regular RWD or FWD car provides that."
Although C&D's early comments certainly seem to suggest that SH-AWD will be able to provide benefits that neither of those other 2 configurations are capable of. I guess it's up to each of us to decide how much complexity we're willing to embrace to realize the advantages of advanced technology.
"I'm no engineer, but Honda's SH-AWD seems to be different and more complex than any other AWD system out there, after all, Car and Driver says, "Acura re-invents AWD" or something to that effect."
And that's how innovation is achieved. If SH-AWD lives up to its promise and is a major success, I doubt that many people are going to fret about complexity being turned up a notch in a class where very complex systems are already the norm.
I cannot imagine the weight shift to the drive wheels on a FWD Honda is going to be anyhere near the weight shift to the driven wheels of a typical front engine-RWD car. I'm sure Csaba knows what he's talking about, he is an automotive engineer.
I hope. ;-)
No doubt that weight balance is going to be different, and that wasn’t my point. My point was generalization on weight shift, especially using TSX as an illustration, instead of, say, Altima (engine placed aft/on top of front axle). Engineers would actually analyze stuff and explain with greater detail than Csaba did in his evaluation. I’m a big fan of him and this is nothing major, just something that stood out in the article.
"especially using TSX as an illustration, instead of, say, Altima (engine placed aft/on top of front axle)."
I don't think this matters with regards to weight shift under acceleration. When you're accelerating hard, the weight shifts to the rear of the car regardless of where the engine is relative to the front axle.
"Oh, weight does shift, but how and how much, are not carved on stone."
How the weight shifts IS carved in stone though. I've only had basic college physics and even I can figure that one out. It doesn't matter where the engine is, when you accelerate hard, weight is shifted off of the front wheels to the rear wheels. That's "how" weight shifts under accleration, is it not? "How much" may not be carved in stone, but "how" is.
What assumptions? The assumption that you're accelerating forward and not in reverse? Accelerating in reverse is the only situation where the weight won't shift to the rear wheels during acceleration. Other than that, there are no other assumptions that would change the rule.
Weight will transfer rearward. That is no-brainer. But how, and how much depends on the chassis set up.
If you're wondering about "how", let me clarify. If most of the frontal weight sits in front of the axle, when the vehicle accelerates, that extra weight goes on top of the driving wheels. OTOH, if the frontal weight sits after the front axle, it takes away the traction from the front wheel.
Weight shift pattern isn't an issue here, how it affects traction is.
"If most of the frontal weight sits in front of the axle, when the vehicle accelerates, that extra weight goes on top of the driving wheels. OTOH, if the frontal weight sits after the front axle, it takes away the traction from the front wheel."
Like I said before, it does not matter where the engine is relative to the front axle, the weight is ALWAYS going to shift towards the rear tires during acceleration, taking weight off the front tires at the same time.
You are trying to say that since the TSX's engine sits in front of the front axle that the extra weight from the weight shift is going to go to the driving wheels. This is completely false.
Weight transfer is going to depend on where the total vehicle center of gravity is, both fore aft and height of the CG. Additionally it is going to depend on acceleration rate and there would also be some affect from suspension spring and damping rates, and if you want to get precise, even the rotary moment of inertia of the vehicle would play a small part. You are never going to get all this information on competing vehicles, so arguing about it is fruitless.
About all you can argue about is that during acceleration, downward force will tranfer to the rear. Unless you have enough torque to break the wheels loose, acceleration performance will not matter whether it is front or rear wheel drive. Handling may be another matter, but there are also so many factors involved in handling around curves that again I wouldn't want to predict how one particular front wheel drive car will perform compared to another rear wheel drive car.
Unless the wheels start spinning (burning rubber), the weight transfer has not limited your ability to accelerate with a front wheel drive car, as you still have enough weight over the front wheels and thus frictional force between the tire and the pavement to use all the torque applied.
"Unless the wheels start spinning (burning rubber), the weight transfer has not limited your ability to accelerate with a front wheel drive car, as you still have enough weight over the front wheels and thus frictional force between the tire and the pavement to use all the torque applied."
That is true as long as you don't have too much power. I was never debating that point.
I just don't understand how we are still talking about this. It is as simple as it gets. Any kindergartner who has been on a teeter-totter should be able understand this concept. One side goes up, the other MUST go down.
Let me ask you a simple question. Why do you think Honda's engineers chose to place engine just in front of the front axle? Why couldn't they have done it right on the axle (or after the axle like Nissan does, or the C-series V6 were)? The latter would also allow for shorter front overhang and potentially, shorter length of the car.
May be this will help you understand the "how" part.
"Let me ask you a simple question. Why do you think Honda's engineers chose to place engine just in front of the front axle?"
I can tell you with absolute certainty that they didn't do it with the expectation of eliminating rear weight transfer during acceleration. Honda is good, but they cannot overcome the laws of physics.
"May be this will help you understand the "how" part."
I am not the one who needs help understanding this concept.
Probably to make everything fit they way they wanted it. Which car are we talking about, btw?
If the TSX... then remember it was designed as a family car, at a smaller size than the Altima. The priority was interior space, which means pushing the engine as far forward as possible. Maybe they should've tried to put the steering system between the engine and the radiator...
If we're talking about a larger car then I can see less reason for it, but I'd still guess that Honda would rather give you lots of extra interior room while giving up a little bit of performance, than redesigning a BMW. It makes their jobs harder, to have to make a well handling FWD car, and I applaud them for that.
*now for a physics lesson*
To clarify the weight transfer thing... when accelerating, the road is pushing forward on all the contact patches. Let's say the car is facing left and accelerating. Imagine that it's pinned to a wall through its center of gravity. The horizontal forces (all pointing left) on the bottom of its wheels will A) move it forward and rotate it clockwise.
How it rotates depends on three things; A) the force at the wheels (acceleration rate X mass of car), the vertical distance from the forces' axes (the road, basically) from the center of gravity, and C) the rotational inertia of the car.
So the most pronounced weight shifts would be in a mid-engined, short-wheelbase, light car that has been lifted way off the ground. Its suspension determines the car's front and rear displacements, but the wheels are still being loaded/unloaded the same. What's the point, I do not know.
I belive that Honda is going through a transition at this time, it is trying to get away form the light little cars that Japan is famous for, its looking ahead of this time, and most definately it will take them back a little but at the end of the day this will allow them to stay ahead in the future, thats what makes Honda great. The new cars that are coming in are more solidly built, the feel of the car is more europian right down to the way the doors work, and this suggests a trend to increse the level of the car intirely to europian levels (say VW) but keeping the prices low, Soon say in about 5 years or so all their cars will be better than anythihng europe can offer at they same prices they are operating currently. So peeps relax and watch Honda get better as they always have.
"I can tell you with absolute certainty that they didn't do it with the expectation of eliminating rear weight transfer during acceleration."
Definitely not. I wasn't expecting you to guess for Honda's engineers, but your own analysis as to why it would be done. And when did I argue against a rearward weight shift? Obviously, you aren't getting my point.
Weight shifts rearwards, thats a fact. And optimal use of the shift would be towards improved traction, correct? By placing the heaviest component (engine/transmission) slightly in front, the same is being accomplished! While not the best way to do it (also requires a longer overhang and an overall, longer chassis), the effect of this set up is not the same as it would be in a mid-mounted FWD chassis (perhaps a reason why front driver Nissans are more prone to torque steer).
Torque steer in Sentra SE-R had me think about gearing, and I calculated thrust to find out if it was unusually high for a front driver, and it was. Nissan geared it too short for the torque and weight that the car carries. No wonder, it had massive torque steer, and that was a safe assumption (or conclusion).
Until, I calculated g's for current (Japanese) Integra Type-R, which matches that of the SE-R (via shorter gearing, and lighter weight). But, I've not seen a mention of torque steer associated with the ITR. So, what about my earlier conclusion?
"If the TSX... then remember it was designed as a family car, at a smaller size than the Altima. The priority was interior space, which means pushing the engine as far forward as possible."
TSX has a total length of 183 inch, which is about 6 inch shorter than Accord and 10 inch shorter than Altima, and fits in compact sedan category unlike the other two midsizes.
By placing the engine on top or slightly behind the front axle, it would actually be possible to shorten the cars overall length, or relocate some stuff from between engine and firewall to between engine and radiator.
The latter configuration would be similar to that used in Acuras using C-series V6 engines, a reason those cars had long wheelbase and short frontal overhang. The interior space may not be affected (unless everything else needs to be pushed backwards).
Nissan's front drive cars sharing engines with FM RWD platform have engine aft front axle.
"And when did I argue against a rearward weight shift?"
"If most of the frontal weight sits in front of the axle, when the vehicle accelerates, that extra weight goes on top of the driving wheels."
That's where you argued against a rearward weight shift. When a vehicle accelerates, the weight shifts to the rear (it doesn't shift to the TSX's drive wheels and then stop), which means that weight MUST have been shifted off the front, which in the TSX's case, is where the drive wheels are. When was the last time you saw the front of a car dive down when accelerating? Never, and it doesn't matter where the engine is. You need to stop this.
Rearward weight shift doesn't stop on rear axle of RWD vehicles either! The same laws would apply. Traction on drive wheels will be determined by how much of the weight shifts to the drive wheels. By moving weight in front of the drive wheels the emphasis is to put more weight on drive wheels. This is similar in concept to RWD vehicles, including mid-engine and exclusing rear-engine.
And how about those rear engine Porsches compared to their mid-engine competition?
This is what happens in a free market economy. Its not that Honda has slipped or become any less reliable. Its that other car makers have caught up with Honda/Toyota and consumers are finding this out day by day, article by article, review by review they read. Why pay MSRP for a Honda or Toyota when you can go elsewhere and get the same quality for less $$.
"Rearward weight shift doesn't stop on rear axle of RWD vehicles either!"
So what? That doesn't mean that there isn't extra downforce being applied to the rear wheels that wasn't there before acceleration.
"Traction on drive wheels will be determined by how much of the weight shifts to the drive wheels."
Yes, and there is no weight being shifted to the drive wheels on a FWD car during hard acceleration. All you have to do is look at the car when it's accelerating. What does it look like? The front end goes up, and if that's an indication to you of weight being shifted to the drive wheels of a TSX, then I don't know what else to say.
You're stuck in the first gear. Let me try to clarify, one last time.
During acceleration, weight shifts rearwards. This is no issue. But if you place weight in front of the drive wheel, the weight will move towards the drive wheel instead of moving away from it. True? If you agree, we're on the same page. If you don't, I have tried enough.
"But if you place weight in front of the drive wheel, the weight will move towards the drive wheel instead of moving away from it."
That does not matter. The weight of the engine is still sitting on the front wheels no matter where the engine is placed in a front engine FWD car. When you accelerate, this weight is being shifted towards the rear of the car. If the front of the car raises up in the air during acceleration, how could there possibly be extra downforce being applied to the front wheels?
Comments
One of our members, I think it was Juice, posted a pic of a Pilot frame. Yes, you read that right, FRAME. As in, full frame, like what cars used to sport when tailfins were all the rage and the naughtiest song lyrics were in Elvis songs ("number 47 said to number 3, you're the cutest jailbird I ever did see"...hmmm, I didn't realize there were co-ed prisons back then! ;-). So, the Accord and Pilot really aren't as much alike as you might think.
RWD or AWD would take up a lot of space in something like a Civic. They can do it on a CR-V, because that sits up high, so the mechanicals don't intrude as much into the passenger cabin.
It would also add a lot of weight. A Subaru Impreza might have AWD, but guess what? It's about the size of a Civic but weighs as much as a typical mid-sized car from 1980!
I could see something like an Accord or TL being a candidate for conversion to RWD or AWD, as the cars are physically bigger, so the driveshaft and rear differential wouldn't take up as much room. But I couldn't see that happening to a Civic...at least not easily.
http://4hs.org/pv/2003/09/17/HON2003091760521_pv.jpg
As for the Civic using AWD, certain models do have it. The Stream (Civic MPV/Wagon thingy) has an option for AWD. But the system that works with that platform is RT4WD. RT4WD weighs about half as much as VTM-4 or other systems like Quattro and 4-Motion. The problem with RT4WD is that it is designed to be an all-weather system. It is a reactive design and does not provide any significant handling advantage on dry roads.
Most, if not all, unitized cars have a front and rear sub-frame...some are just longer than others. And in the 60's, some unitized cars were so fragile that they had to be beefed up with frame rails. I know I've seen some early 60's Chevy II's like that, that had these thin rails that connected the front and rear subframes. However, the whole assembly didn't look like it would stay together if you took the body away.
That Pilot frame, however, looks like one piece to me. Except for being shinier, having the engine facing the wrong way, and the rails not being nearly as beefy, it really doesn't look so different from the frame of my '57 DeSoto!
OTOH, CRV/Element use the same platform that Civic/RSX do (Global Compact Platform).
Why, was there a prize!?!?
It's Csaba Csere's column for those familiar with Car and Driver.
It's of particular interest because they use the TSX and 325i as a point of comparison. I'm not going to quote the whole article, but here are some of the main points:
"Given the enormous expense of replacing a front-drive car with a rear-drive one, no car company would do it just to provide the marketers with a new talking point"
"the definition of traction is grip that allows acceleration. Grip for cornering and braking is completely different, and there's no evidence that front drive provides any advantage in these areas during winter driving"
"but if you really want secure winter handling, you need to change to snow tires. Four snow tires will improve traction as well as braking and cornering grip to the point where the winter merits of front and rear drive are rendered irrelevant."
"Once we get away from the slippery stuff, rear drive has traditionally displayed better handling because it splits the duties of steering, cornering, acceleration, and braking more equitably among the four tires."
"Honda Accords and Nissan Altimas come with 240-hp V-6s, and 300-hp luxury sedans are everywhere. At these power levels, front drive has reached the limit of its competence."
Has Car and Driver been reading this thread?
Anything else of note in the July issue?
this has been a very interesting and worthwhile thread. good job, nvbanker.
~alpha
I'm not done yet, but they have a picture of the new RL too. Looks pretty sharp. They have a test of the new Legacy Outback turbo, and the new Saab 9-2x (Subaru WRX). The title of the Saab article is "Sushi rolled in a Swedish pancake". I love Car and Driver.
"Options on our tester included a rear DVD/audio child-sedation system ($995), OnStar ($695), and XM satellite radio ($325). That nudged the total close to $27,000, navel-deep in the V-6 Honda Accord and Toyota Camry territory. Which, for a car bearing the Malibu monkier, strikes us as the fiscal equivalent of poking a stick at the tiger that lunched on Roy."
They're funny.
Weight shift doesn't happen in a constant proportion. We tend to be mesmerized by 50-50 weight distribution but in reality, how much weight on driving wheels exists under various situations (for traction purpose) is all that counts. Honda typically places its engine just in front of the front axle, as opposed to on or after it. So, while there is a weight shift backwards, much of it happens to be on the driving wheels. If they had placed the engine/transmission on or behind the front axle in front drivers, then I can see his point.
I thought, it would be a good idea to actually come up with traction measurements under different situations for various cars rather than using a generalized statement.
But then, I consider mid-engine/RWD as optimum layout for perfect weight balance. Most of the weight is on driving wheels during acceleration, and nearly perfect weight distribution during braking, and of course, not having to worry about drive train up front allows room to work on other aspects of a car. So, where is the next NSX?
I cannot imagine the weight shift to the drive wheels on a FWD Honda is going to be anyhere near the weight shift to the driven wheels of a typical front engine-RWD car. I'm sure Csaba knows what he's talking about, he is an automotive engineer. Besides, that doesn't negate the point that "rear drive has traditionally displayed better handling because it splits the duties of steering, cornering, acceleration, and braking more equitably among the four tires."
It looks awfully complicated and expensive. I don't know if I would want that on one of my cars.
Well, that's your call. Increasingly expensive and complex systems are becoming a hallmark of this class of cars. SH-AWD doesn't worry me any more than many of the complex systems already available on competitive cars. And it's not like Acura is the only manufacturer that does complex AWD, or that they don't have experience in AWD.
The early praise from C&D is very encouraging. Sounds like it may be a very effective competitor against the RWD alternatives in its class.
No doubt, I agree. I prefer a little more simplicity and a regular RWD or FWD car provides that. I wouldn't even want to know how much some of these complex and expensive gizmos are going to cost to fix when the mileage gets up there.
I'm no engineer, but Honda's SH-AWD seems to be different and more complex than any other AWD system out there, after all, Car and Driver says, "Acura re-invents AWD" or something to that effect.
Although C&D's early comments certainly seem to suggest that SH-AWD will be able to provide benefits that neither of those other 2 configurations are capable of. I guess it's up to each of us to decide how much complexity we're willing to embrace to realize the advantages of advanced technology.
"I'm no engineer, but Honda's SH-AWD seems to be different and more complex than any other AWD system out there, after all, Car and Driver says, "Acura re-invents AWD" or something to that effect."
And that's how innovation is achieved. If SH-AWD lives up to its promise and is a major success, I doubt that many people are going to fret about complexity being turned up a notch in a class where very complex systems are already the norm.
I hope. ;-)
No doubt that weight balance is going to be different, and that wasn’t my point. My point was generalization on weight shift, especially using TSX as an illustration, instead of, say, Altima (engine placed aft/on top of front axle). Engineers would actually analyze stuff and explain with greater detail than Csaba did in his evaluation. I’m a big fan of him and this is nothing major, just something that stood out in the article.
I don't think this matters with regards to weight shift under acceleration. When you're accelerating hard, the weight shifts to the rear of the car regardless of where the engine is relative to the front axle.
We must ask Honda why they choose to place engine in front of the front axle.
How the weight shifts IS carved in stone though. I've only had basic college physics and even I can figure that one out. It doesn't matter where the engine is, when you accelerate hard, weight is shifted off of the front wheels to the rear wheels. That's "how" weight shifts under accleration, is it not? "How much" may not be carved in stone, but "how" is.
True, but not without assumptions. With specific examples, it should work better, and it didn't. It ends up being an incomplete statement to me.
What assumptions? The assumption that you're accelerating forward and not in reverse? Accelerating in reverse is the only situation where the weight won't shift to the rear wheels during acceleration. Other than that, there are no other assumptions that would change the rule.
If you're wondering about "how", let me clarify. If most of the frontal weight sits in front of the axle, when the vehicle accelerates, that extra weight goes on top of the driving wheels. OTOH, if the frontal weight sits after the front axle, it takes away the traction from the front wheel.
Weight shift pattern isn't an issue here, how it affects traction is.
Like I said before, it does not matter where the engine is relative to the front axle, the weight is ALWAYS going to shift towards the rear tires during acceleration, taking weight off the front tires at the same time.
You are trying to say that since the TSX's engine sits in front of the front axle that the extra weight from the weight shift is going to go to the driving wheels. This is completely false.
About all you can argue about is that during acceleration, downward force will tranfer to the rear. Unless you have enough torque to break the wheels loose, acceleration performance will not matter whether it is front or rear wheel drive. Handling may be another matter, but there are also so many factors involved in handling around curves that again I wouldn't want to predict how one particular front wheel drive car will perform compared to another rear wheel drive car.
YES!!!
And if downforce is transfered to the rear, you must lose downforce on the front. It's really simple as far as physics are concerned.
That is true as long as you don't have too much power. I was never debating that point.
I just don't understand how we are still talking about this. It is as simple as it gets. Any kindergartner who has been on a teeter-totter should be able understand this concept. One side goes up, the other MUST go down.
May be this will help you understand the "how" part.
I can tell you with absolute certainty that they didn't do it with the expectation of eliminating rear weight transfer during acceleration. Honda is good, but they cannot overcome the laws of physics.
"May be this will help you understand the "how" part."
I am not the one who needs help understanding this concept.
If the TSX... then remember it was designed as a family car, at a smaller size than the Altima. The priority was interior space, which means pushing the engine as far forward as possible. Maybe they should've tried to put the steering system between the engine and the radiator...
If we're talking about a larger car then I can see less reason for it, but I'd still guess that Honda would rather give you lots of extra interior room while giving up a little bit of performance, than redesigning a BMW. It makes their jobs harder, to have to make a well handling FWD car, and I applaud them for that.
*now for a physics lesson*
To clarify the weight transfer thing... when accelerating, the road is pushing forward on all the contact patches. Let's say the car is facing left and accelerating. Imagine that it's pinned to a wall through its center of gravity. The horizontal forces (all pointing left) on the bottom of its wheels will A) move it forward and
How it rotates depends on three things; A) the force at the wheels (acceleration rate X mass of car),
So the most pronounced weight shifts would be in a mid-engined, short-wheelbase, light car that has been lifted way off the ground. Its suspension determines the car's front and rear displacements, but the wheels are still being loaded/unloaded the same. What's the point, I do not know.
Definitely not. I wasn't expecting you to guess for Honda's engineers, but your own analysis as to why it would be done. And when did I argue against a rearward weight shift? Obviously, you aren't getting my point.
Weight shifts rearwards, thats a fact. And optimal use of the shift would be towards improved traction, correct? By placing the heaviest component (engine/transmission) slightly in front, the same is being accomplished! While not the best way to do it (also requires a longer overhang and an overall, longer chassis), the effect of this set up is not the same as it would be in a mid-mounted FWD chassis (perhaps a reason why front driver Nissans are more prone to torque steer).
Torque steer in Sentra SE-R had me think about gearing, and I calculated thrust to find out if it was unusually high for a front driver, and it was. Nissan geared it too short for the torque and weight that the car carries. No wonder, it had massive torque steer, and that was a safe assumption (or conclusion).
Until, I calculated g's for current (Japanese) Integra Type-R, which matches that of the SE-R (via shorter gearing, and lighter weight). But, I've not seen a mention of torque steer associated with the ITR. So, what about my earlier conclusion?
TSX has a total length of 183 inch, which is about 6 inch shorter than Accord and 10 inch shorter than Altima, and fits in compact sedan category unlike the other two midsizes.
By placing the engine on top or slightly behind the front axle, it would actually be possible to shorten the cars overall length, or relocate some stuff from between engine and firewall to between engine and radiator.
The latter configuration would be similar to that used in Acuras using C-series V6 engines, a reason those cars had long wheelbase and short frontal overhang. The interior space may not be affected (unless everything else needs to be pushed backwards).
Nissan's front drive cars sharing engines with FM RWD platform have engine aft front axle.
"If most of the frontal weight sits in front of the axle, when the vehicle accelerates, that extra weight goes on top of the driving wheels."
That's where you argued against a rearward weight shift. When a vehicle accelerates, the weight shifts to the rear (it doesn't shift to the TSX's drive wheels and then stop), which means that weight MUST have been shifted off the front, which in the TSX's case, is where the drive wheels are. When was the last time you saw the front of a car dive down when accelerating? Never, and it doesn't matter where the engine is. You need to stop this.
And how about those rear engine Porsches compared to their mid-engine competition?
So what? That doesn't mean that there isn't extra downforce being applied to the rear wheels that wasn't there before acceleration.
"Traction on drive wheels will be determined by how much of the weight shifts to the drive wheels."
Yes, and there is no weight being shifted to the drive wheels on a FWD car during hard acceleration. All you have to do is look at the car when it's accelerating. What does it look like? The front end goes up, and if that's an indication to you of weight being shifted to the drive wheels of a TSX, then I don't know what else to say.
During acceleration, weight shifts rearwards. This is no issue. But if you place weight in front of the drive wheel, the weight will move towards the drive wheel instead of moving away from it. True? If you agree, we're on the same page. If you don't, I have tried enough.
That does not matter. The weight of the engine is still sitting on the front wheels no matter where the engine is placed in a front engine FWD car. When you accelerate, this weight is being shifted towards the rear of the car. If the front of the car raises up in the air during acceleration, how could there possibly be extra downforce being applied to the front wheels?