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BRZ First-Gen (2012+) -- General Topics All discussions about the first-gen Subaru BRZ coupe


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Old 05-22-2013, 04:49 PM   #113
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Originally Posted by strat61caster View Post
Not at all. Most of the physics of the vehicle is determined by the weight distribution. How the car FEELS in the end can come down to the suspension. Suspension compensates for the way the mass moves, moving the mass will have a greater effect on the car than changing the suspension. You can make a Mid-engined car feel like a front engine, front wheel drive boat, but you can't make a front engined boat feel like a mid engine sports car. You can probably do a passable impersonation but odds are you end up sacrificing stuff that made you go with the initial layout (comfort, utility, cost, etc.), see your MR2 example.
Isn't how the car feels the most important part? Who cares if the designers are cheating Newtonian physics? A semi-related example would be the Nissan GT-R: It's a heavy car that goes around tracks faster than simulations say it should. I recall some Ferrari engineers saying the car is so fast because of how it feels (inspiring driver confidence, etc.)

The suspension doesn't "compensate" for anything - The goal of the suspension is to a) control the mass of the car (ideally preventing body roll) and to b) keep the tires in as constant of a connection with the pavement as is possible (ideally minimizing camber change in bump and rebound.) Traditionally it has been impossible to maximize the effectiveness of both goals A and B, however with new active suspension technologies (See: McLaren 12C) it's possible to do a lot, and have some added benefits like increased ride comfort.

I'll conclude with the Porsche 911 and the Ford Focus ST. Both cars are excellent performers, despite having disadvantageous engine positions. The recent 911s don't have the nasty handling characteristics associated with a swing-axle suspension geometry, and the Focus doesn't feel like a front wheel drive car, again thanks to a lot of chassis/suspension work.

I don't think anyone will argue that the optimal place to put an engine is between the axles. I COMPLETELY agree that a mid-engine platform is the best starting point. My argument is that this isn't as important as having a good chassis setup.

Hopefully that ramble was at least slightly coherent.
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Old 05-22-2013, 05:13 PM   #114
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Isn't how the car feels the most important part?
Absolutely, for most people this is true. If you're chasing performance then we'd be having a slightly different conversation.

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Who cares if the designers are cheating Newtonian physics? A semi-related example would be the Nissan GT-R: It's a heavy car that goes around tracks faster than simulations say it should. I recall some Ferrari engineers saying the car is so fast because of how it feels (inspiring driver confidence, etc.)
What you're saying here agrees with what I said, the suspension/technology is COMPENSATING for the excessive mass and the unequal weight distribution (53/47)

When a car is designed, they figure out the packaging first based either on performance, utility, or marketing goals. Placement of the engine and figuring out where the mass is located, creating a simplified model and analyzing it is how a suspension gets developed, a different mass profile will result in a radically different analytic model with a completely different feeling when driving and a completely different suspension setup.

I think we are in agreement though, a suspension makes a chassis configuration work (well or poorly) but I argue that placement of mass is more important than this developed suspension when it comes to handling, it's the physics. You can slam your Mustang and make it stiff as a rock and it can outgrip a brand new Ferrari or whatever super car but you are inherently fighting the physics of the vehicle whereas a mid-engined or rear-engined would be more agreeable to the rigors of a track due to their inherent instabilities. As per your original example, Toyota used the suspension to compensate for a twitchy mid-engine platform with the MR2. An unstable system is quicker to respond, that's why the 911 works so well ("nasty" is subjective, as stated earlier I think it's brilliant).

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The suspension doesn't "compensate" for anything - The goal of the suspension is to a) control the mass of the car (ideally preventing body roll) and to b) keep the tires in as constant of a connection with the pavement as is possible (ideally minimizing camber change in bump and rebound.) Traditionally it has been impossible to maximize the effectiveness of both goals A and B, however with new active suspension technologies (See: McLaren 12C) it's possible to do a lot, and have some added benefits like increased ride comfort.

I'll conclude with the Porsche 911 and the Ford Focus ST. Both cars are excellent performers, despite having disadvantageous engine positions. The recent 911s don't have the nasty handling characteristics associated with a swing-axle suspension geometry, and the Focus doesn't feel like a front wheel drive, again thanks to a lot of chassis/suspension work.
I'm a bit confused here, I guess A is for comfort and B is for performance but the first paragraph doesn't say anything about how the suspension interacts with the mass other than that new technologies mean we have better control, which is true. The second paragraph just illustrates how incredibly different those vehicles are due to the placement of their engine and how much work went into compensating for that; torque vectoring, active suspension compenents, special differentials etc.

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My argument is that this isn't as important as having a good chassis setup.
Yup, with enough money you can make a school bus handle like a lotus, agreed. But why bother with that kind of effort when you can start with an MR2? Design is a world filled with shades of gray.
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Old 05-22-2013, 06:17 PM   #115
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Porsche maintenance is stupid expensive...
This is a myth. Of the 15 Porsches I've owned, I wouldn't call any of them stupid expensive. More than most cars? Sure. But stupid expensive? No.

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The parts cost more...
Mostly true. But oil and filters aren't unique. Neither are the plugs. ..or brake fluid. Really general maintenance isn't bad at all.

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..you need more special tools..
Very rarely, actually. I've never needed any special tools. (Admittedly, I haven't done all the maintenance on my Porsches.)

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...and they require more frequent maintenance than most other cars.
Modern Porsches (including the 986/987 Boxster / Cayman) have 15k service intervals. Most owners change the oil once a year or 7500 miles. I change the oil in all my cars at 5k intervals. Since I don't put a lot of miles on the Porsches, they fall into the once a year category.

Older Porsches might have more maintenance, but that's typical of any older car. It's simply the difference in buying a new car v and old car. But, as old cars go, the 911s I've owned (save for one I "bought cheap") have been incredibly reliable and have cost very little to maintain.

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Old 05-22-2013, 08:00 PM   #116
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Originally Posted by strat61caster View Post
What you're saying here agrees with what I said, the suspension/technology is COMPENSATING for the excessive mass and the unequal weight distribution (53/47)
I disagree. However, if two cars are the same in design, except that one car is mid-engined, and the other is front or rear-engined, then the suspension setup on the second (non-mid-engine) car will differ from the first car to "compensate" for not having the same weight distribution. There's no use further arguing this point.


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a different mass profile will result in a radically different analytic model with a completely different feeling when driving and a completely different suspension setup.
Not really.


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Originally Posted by strat61caster View Post
I think we are in agreement though, a suspension makes a chassis configuration work (well or poorly)
Agreed!


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but I argue that placement of mass is more important than this developed suspension when it comes to handling, it's the physics. You can slam your Mustang and make it stiff as a rock and it can outgrip a brand new Ferrari or whatever super car but you are inherently fighting the physics of the vehicle whereas a mid-engined or rear-engined would be more agreeable to the rigors of a track due to their inherent instabilities.
Making a car lower and stiffer is usually a very good way to destroy the handling and grip of the car. The wheels need to be able to move relative to the sprung mass of the vehicle in order to handle bumps and other parts of the road that aren't completely smooth, like race track curbs. Also, suspension compliance is essential for maintaining control of the vehicle while cresting a hill.


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As per your original example, Toyota used the suspension to compensate for a twitchy mid-engine platform with the MR2. An unstable system is quicker to respond, that's why the 911 works so well ("nasty" is subjective, as stated earlier I think it's brilliant).
There is nothing inherently unstable about a mid-engine design. In fact, a mid-engine design increases the natural stability of the vehicle.

The 911 was unstable when lifting-off the throttle mid-corner because the swing-axle suspension would unload, causing rebound and massive camber change, resulting in a large loss of grip at the rear of the car. This caused inexperienced drivers to spin, because the front of the car still had grip to turn, while the rear needed more grip than was available to maintain the turn.

The current 911 has a LOT of corner exit stability, apparently because the engine is over the rear wheels. As a consequence, it requires more care (to avoid stable understeer) when initially turning in, because there is less weight over the front wheels. I'm still working through the physics behind why this happens, but I know for a fact that this is the case.


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I'm a bit confused here, I guess A is for comfort and B is for performance but the first paragraph doesn't say anything about how the suspension interacts with the mass other than that new technologies mean we have better control, which is true. The second paragraph just illustrates how incredibly different those vehicles are due to the placement of their engine and how much work went into compensating for that; torque vectoring, active suspension compenents, special differentials etc.
They are both for performance, but reducing body roll can also increase comfort. To clarify, goal B is to minimize camber change in bump and rebound (as the wheel travels up and down from it's steady-state position). To explain part A very generally, if the body rolls, the wheels roll side to side with it, resulting in camber change (relative to the road surface.), which is a Bad Thing. Also, if the wheels go up and down and camber changes, that's a Bad Thing as well.


TL;DR - A car with a "bad" engine placement (non mid-engine) can be a great car if the suspension is good, but with a "bad" suspension, a mid-engine car will be shit.
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Old 05-22-2013, 08:06 PM   #117
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Small addition: The rotational moment of inertia in a mid-engine car is usually smaller than that of a front or rear engine car, which allows the car to turn more quickly. This also means that a mid-engined car may spin more quickly if the driver looses control.
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Old 05-22-2013, 08:27 PM   #118
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Porsche maintenance is stupid expensive. The parts cost more, you need more special tools and they require more frequent maintenance than most other cars.
Is this from personal experience? I think you're exaggerating a bit. You gotta stop drinking that kool-aide.

This is straight from my Porsche maintenance manual:

1) oil and oil filter every 10,000 miles or 1 year
2) spark plug every 40k or 4 years
3) drive belt replacement 60k or 6 years
4) tranny fluid replaced every 120k or 12 years

Yes, if you blow an engine the Porsche engine is more expensive than the subaru. It's a more expensive and powerful car.

I haven't had to purchase any special/expensive tools to change the oil or brakes. Track consumables are linearly comparable in price if you take size of pads/rotors into account. It's not exponential.
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Old 05-22-2013, 08:38 PM   #119
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The current 911 has a LOT of corner exit stability, apparently because the engine is over the rear wheels. As a consequence, it requires more care (to avoid stable understeer) when initially turning in, because there is less weight over the front wheels. I'm still working through the physics behind why this happens, but I know for a fact that this is the case.
When you brake, weight transfers onto the front wheels (it's why you get lots of brake-dive on cars with soft / long-travel suspensions). Because a majority of a 911's weight sits over the rear wheels, a 911 that's "coasted" into a corner will have more grip at the back than at the front, which leads to understeer. Applying throttle before you're fully turned in exacerbates this problem by transferring even more weight to the rear wheels.

That's why you need to trail-brake 911's into corners. Then-- once you're turned in-- you can roll onto the throttle very heavily since the weight transfer results in a ton of rear-end grip, which means you can really put power down effectively. Basically the 911's weight distribution means you can brake very, very hard into a corner (because the weight distribution that is rear-biased in a neutral state becomes fairly evenly distributed under braking), and then accelerate very hard out of a corner once properly turned in (since you end up with an ungodly amount of rear-end grip). They really don't like meandering into corners. Also, you have to be careful with the back end-- it breaks free slowly but there's a lot of mass back there which means lots of inertia once it goes.

The feel of driving a 911 is a bit different than most cars, but its super fun once you get used to it. You can really use braking / throttle lifts to steer the car from the back end-- very involving and very satisfying when you get it right, and there's just so much grip when you do!
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Old 05-22-2013, 08:52 PM   #120
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Excellent explanation, thanks for that!
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Old 05-23-2013, 09:44 AM   #121
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Lots of excellent posts on this page explaining the nuances of a 911's handling (and its advantages). Also good info on Porsche maintenance, which I've been trying to spread as well.

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I knew a guy who ran an independent Porsche shop, you know what the standard rate was for 2 new OEM tires on the rear of a 911?
$900

2 tires, unmount old ones, dispose, mount new ones.


Of course if you buy the tires you want (they usually aren't nice easily available sizes like a Toyota uses which is where the additional cost comes in) the price difference is negligible, find a reasonable tire guy and it won't cost you any more than any other car with the same size wheels. But still
OEM replacement tires are expensive, regardless of the car maker. An OEM replacement set of tires for my S2000 is $870. Of course I'd go with the Dunlop Star Specs for $670 instead. Better tire, 23% lower cost. The same can be done with Porsche. Their tire sizes aren't "that" unique that you're forced into just their OEM replacement offerings.

Likewise track pads for the Porsche cost more than my S2000. But from talking to people at the track their pads were wearing much better than mine (sliding caliper FTL ). So while their pads might cost 150% more, they were also lasting twice as long.
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Old 05-23-2013, 12:09 PM   #122
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TL;DR - A car with a "bad" engine placement (non mid-engine) can be a great car if the suspension is good, but with a "bad" suspension, a mid-engine car will be shit.
This is the crux of it, I'm sure we could argue all day long (I'll be sure to bring my vehicle dynamics textbooks to help me with the math!) but we essentially agree.

A point about when I said "stiffen and lower" what I really meant was lowering the c.g. (generally good for dynamics as I do not have to explain) and stiffening the chassis so you can allow the suspension to be compliant and hug the road. Too many shortcuts in my explanations Of course you're absolutely right, done incorrectly it will likely be detrimental to performance.

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Small addition: The rotational moment of inertia in a mid-engine car is usually smaller than that of a front or rear engine car, which allows the car to turn more quickly. This also means that a mid-engined car may spin more quickly if the driver looses control.
This is why it's unstable, it takes less for it to loose grip compared to a car with a more dispersed mass. This is also why the 911 handles so well, with all the mass at the rear it's easy to lose control because it acts almost like a pendulum (which you mentioned) but with a proper control system (read: good driver) it can respond very quickly, which is why I'm so in love with it

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