you seem to think there's a contrast between what I said and the review you posted.
What I wrote was from my own viewpoint. I don't care much about straight line acceleration. There are stock SUVs that do much better than A3 3.2 or WRX in straight line. I wouldn't like one of those either. What I appreciate is nimble, responsive car. That means light weight. That means the car lets you do what you want and not interfere with electronics too easily.
Take note that the review you posted did not talk about the car's behavior in bad conditions, oversteer, understeer, weight shifting in corners, and how the electronics kick in.
Living in a country with lots of snow and ice, I want to know what the car does when grip disappears and the car goes into slide. You might not have to.
The last S3 quattro 1.8T should be a much better driver's car with only 1400kg of weight to lug around and better weight distribution for having a smaller engine.
From what I understand, under "snow and ice" conditions you want a car that is heavy, and NOT one that is light. Truthfully, I haven't yet driven the A3. But It's definitely up there on my shopping list. From the photos I've seen, I also like the TT aluminum like trimming the A3 sports. Been waiting for the new VW Golfs to arrive to see how they compare..
I think, but am not sure, that as far as weight is concerned we're looking at a ratio of contact patch to weight, which produces pressure at each wheel. Hence, you often see pretty skinny (and hard) snow/ice tires on Rally Cars in winter conditions. More weight through a skinnier cross section, equals more pounds per inch through each corner, and more bite into the ice, and more grip -- particularly at the front wheels which seem to act more like little studded rudders at times.
I don't think it's as easy as "more weight equals more traction" when on the ice. On pavement it is absolutely untrue, rubber being a strange material that grips better with less force applied. Take a few pounds out of a car, and all else (structural stiffness) being equal, it should generate more grip. On loose surfaces, weight might help in some places and hurt in others. Good for traction off the line, but still bad when you're trying to change directions for example. And if that weight comes with a higher center of gravity, eek, look out. When snow storms hit, I routinely see SUVs stuck out in a ditch before I see any other type of vehicle.
For the most part that is true except when racing, more contact patch is wanted in dry conditions. Particularly in AutoX. I have 3 under my belt (only last half of the summer) and you learn quickly the tendencies of certain types of tires and how different widths work. A 225 width tire certainly does wonders over a 205. That is why next summer I am upgrading from A/S tires to a tire specific to summer driving and AutoX (Kumho Ecsta MX or similar) and in a 205/55R-16 to a 225/50R-16. Same dia, more width. It will be a little heavier but will grip MUCH more (it's proven) and can handle heavier cornering loads which means it should flex a bit less.
Maybe we need an AutoX/car tech discussion too! Or I can just crawl back to my 3 Subaru forums for that.
When the car has grip (no wheelspin), your acceleration is determined by a = F/m, acceleration equals force per mass. The less mass and more force you have, the better.
In slippery conditions, the limiting factor to how much force the car can apply to the road is friction. This friction is
F = umg,
where u is a constant between 0 and 1 that reflects how slippery the road is, m is the car's mass, and g is the gravitic constant.
Now, let's look at the original equation:
a = F/m = umg/m = ug.
Therefore, if the car is on flat slippery surface, its weight has nothing to do with whether the car will move. It only depends on how slippery the surface is, and how good your tires on that specific surface.
A more realistic model would show that weight is not actually neutral but detrimental to driving in a lot of ways. However, this model is enough to show weight is never beneficial.
When it comes to the tyres, if the road surface is flat (asphalt or ice, doesn't matter), you always get most grip with wide slicks. This is why track racing cars always use them. The reason we don't use slicks in the "real world" is water, gravel and snow.
As Matsu said, rally drivers often have less wide, harder tyres. This is firstly because they drive closer to "real world conditions" than track racers, and secondly, because they want to be able to break the grip smoothly. The rally course's friction is unpredictable, and if the car accidentally lost grip in a corner the car would crash. This is why the drivers break the grip before corner and let the car slide. This makes the car's behaviour more predictable and the driver can go faster.
Oh absolutely. Rubber is a weird substance. Decrease weight/pressure, and grip actually goes up. All else equal, a lighter car, with bigger tires will generate more grip, no question (on a dry track). I should have specified the peculiar condition of snow/ice which has some funny attributes.
Eeek, emergency edit there Gon. I'm not exactly sure it comes down to that on ice. Yes lighter is always better, even on ice, but I'm not sure wider is neccessarily better for ice tires, and not for the exact reason you describe, though that may be a part too. I'd figure that on the mangled icy track where a Rally Car might work, a narrow tire might generate more grip if only because it can dig into (and even form slight) ruts where a wide tire might just slide across. Tread pattern would play a big role too.
True, rally drivers seem to live by controlled slides, but I don't think that is exactly the orthodoxy at work when they choose thin hard front tires.
Eeek, emergency edit there Gon. I'm not exactly sure it comes down to that on ice. Yes lighter is always better, even on ice, but I'm not sure wider is neccessarily better for ice tires, and not for the exact reason you describe, though that may be a part too. I'd figure that on the mangled icy track where a Rally Car might work, a narrow tire might generate more grip if only because it can dig into (and even form slight) ruts where a wide tire might just slide across. Tread pattern would play a big role too.
True, rally drivers seem to live by controlled slides, but I don't think that is exactly the orthodoxy at work when they choose thin hard front tires.
It's precisely that "digging in" what makes the treaded narrow tyre good in snow, gravel etc. When I said slicks are also good on ice I meant smooth, clear ice without snow. Theoretically slicks would be best on that surface, but in practice there's always loose material like snow so treaded tires are better.
It really is a major factor for rally drivers to be able to break traction smoothly. If they didn't need to do that, they'd still use treaded tyres to counter the bad driving conditions, but they'd use wider ones. A wide tyre retains its grip longer, but when it breaks loose, the car jerks heavily and it's difficult for the driver to control it precisely.
Looking at the civilian market, tyre width actually makes modern sport cars (with very wide wheels) less predictable and safe than the old ones, that break grip smoothly so that the driver can anticipate the behavior.
F(longitudinal) = ma, where m is mass and and a is acceleration. That's okay.
F(vertical) = N(ormal force) = µmg, where µ is the static coefficient of friction and g gravity.
The forces are 90 degrees apart.
Now, let's talk weight transfer, which is still F=ma, just more complex. Typically, the "weight" of the vehicle transfers to the rear when accelerating forward. More specifically, a torque is acting on the center of mass of the vehicle with respect to the tires. This increases the force on the rear wheels, increasing contact patch, increasing grip (I made this last part up).
In summary, I'll take a 2-wheel drive 911 Turbo GT2 for acceleration runs, thank you.
So far it has been a very reliable and enjoyable car. Lot of zip for a 4 cylinder wagon. Done quite a bit of cross-country travel and a fair amoun of dirt road rambling in the mountains of Wyoming and Idaho.
Great car. The only thing that bugs me is that the arm rest on the door is really hard so if you put your elbow there while driving for hours on end you can get a stiff arm, etc.
That and the back seat lever thingy can be a pain in the butt to grab hold of sometimes.
F(vertical) = N(ormal force) = µmg, where µ is the static coefficient of friction and g gravity.
The forces are 90 degrees apart.
Nope. I did not discuss the vertical forces at all. In the vertical direction the sum of forces acting on the car (weight G = mg, support N) equal 0, since the car is not accelerating up into the air or downward through road surface.
The 406 coupe was awesome. A guy I knew in Australia had one a few years ago when I spent some time there.
As for subarus, I like them, but they're so damn ugly. I must say, though, that I really get a kick out of it when people drive 3rd gen Rx-7's in rally. (It actually does happen) I was slipping and sliding at 5mph in the snow this week.
A little update on the 7:
Over the next two years I'm making a project out of it. I'm going to try to make it GT-spec with the fire spitting side pipes and 9 inch wide tires. I'm looking to find a daily beater right now. I kind of like the subaru's, but they're ugly and it's hard to get over that. Plus It looks like I'll be moving to Florida in 2005, so that 4 wheel drive will be a waste of time. In Jersey, the "wintery mix" at least makes having the traction control pretty useful.
Oops. My mistake. F = µN is the resistive, horizontal force of friction.
Quote:
Originally posted by The Power of X
Would ya give it a rest guys.
When engineers collide.
Subaru is my 2nd favorite maker of boxer engines.
And if I can convince my wife to ignore the mouth-breathing intake and 747 wing in the back, I'd like to get the WRX-STi next year. Otherwise it's an Audi S4 Avant (station wagon).
....And if I can convince my wife to ignore the mouth-breathing intake and 747 wing in the back, I'd like to get the WRX-STi next year. Otherwise it's an Audi S4 Avant (station wagon).
You might want to check out the next generation Legacy GT set to debut in January. Also, a WRX STi Wagon is said to be in the works. There are a number of us pushing SOA pretty hard for it, especialy because of the utility aspect and a little bit of sleeper-ness compared to Sedan. Also we are trying to get SOA to bring the std STi RA wing/look over. Much more subtle-like the regular WRX sedan wing.
Comments
you seem to think there's a contrast between what I said and the review you posted.
What I wrote was from my own viewpoint. I don't care much about straight line acceleration. There are stock SUVs that do much better than A3 3.2 or WRX in straight line. I wouldn't like one of those either. What I appreciate is nimble, responsive car. That means light weight. That means the car lets you do what you want and not interfere with electronics too easily.
Take note that the review you posted did not talk about the car's behavior in bad conditions, oversteer, understeer, weight shifting in corners, and how the electronics kick in.
Living in a country with lots of snow and ice, I want to know what the car does when grip disappears and the car goes into slide. You might not have to.
The last S3 quattro 1.8T should be a much better driver's car with only 1400kg of weight to lug around and better weight distribution for having a smaller engine.
From what I understand, under "snow and ice" conditions you want a car that is heavy, and NOT one that is light. Truthfully, I haven't yet driven the A3. But It's definitely up there on my shopping list. From the photos I've seen, I also like the TT aluminum like trimming the A3 sports. Been waiting for the new VW Golfs to arrive to see how they compare..
I don't think it's as easy as "more weight equals more traction" when on the ice. On pavement it is absolutely untrue, rubber being a strange material that grips better with less force applied. Take a few pounds out of a car, and all else (structural stiffness) being equal, it should generate more grip. On loose surfaces, weight might help in some places and hurt in others. Good for traction off the line, but still bad when you're trying to change directions for example. And if that weight comes with a higher center of gravity, eek, look out. When snow storms hit, I routinely see SUVs stuck out in a ditch before I see any other type of vehicle.
Maybe we need an AutoX/car tech discussion too! Or I can just crawl back to my 3 Subaru forums for that.
In slippery conditions, the limiting factor to how much force the car can apply to the road is friction. This friction is
F = umg,
where u is a constant between 0 and 1 that reflects how slippery the road is, m is the car's mass, and g is the gravitic constant.
Now, let's look at the original equation:
a = F/m = umg/m = ug.
Therefore, if the car is on flat slippery surface, its weight has nothing to do with whether the car will move. It only depends on how slippery the surface is, and how good your tires on that specific surface.
A more realistic model would show that weight is not actually neutral but detrimental to driving in a lot of ways. However, this model is enough to show weight is never beneficial.
When it comes to the tyres, if the road surface is flat (asphalt or ice, doesn't matter), you always get most grip with wide slicks. This is why track racing cars always use them. The reason we don't use slicks in the "real world" is water, gravel and snow.
As Matsu said, rally drivers often have less wide, harder tyres. This is firstly because they drive closer to "real world conditions" than track racers, and secondly, because they want to be able to break the grip smoothly. The rally course's friction is unpredictable, and if the car accidentally lost grip in a corner the car would crash. This is why the drivers break the grip before corner and let the car slide. This makes the car's behaviour more predictable and the driver can go faster.
Eeek, emergency edit there Gon. I'm not exactly sure it comes down to that on ice. Yes lighter is always better, even on ice, but I'm not sure wider is neccessarily better for ice tires, and not for the exact reason you describe, though that may be a part too. I'd figure that on the mangled icy track where a Rally Car might work, a narrow tire might generate more grip if only because it can dig into (and even form slight) ruts where a wide tire might just slide across. Tread pattern would play a big role too.
True, rally drivers seem to live by controlled slides, but I don't think that is exactly the orthodoxy at work when they choose thin hard front tires.
Originally posted by Matsu
Eeek, emergency edit there Gon. I'm not exactly sure it comes down to that on ice. Yes lighter is always better, even on ice, but I'm not sure wider is neccessarily better for ice tires, and not for the exact reason you describe, though that may be a part too. I'd figure that on the mangled icy track where a Rally Car might work, a narrow tire might generate more grip if only because it can dig into (and even form slight) ruts where a wide tire might just slide across. Tread pattern would play a big role too.
True, rally drivers seem to live by controlled slides, but I don't think that is exactly the orthodoxy at work when they choose thin hard front tires.
It's precisely that "digging in" what makes the treaded narrow tyre good in snow, gravel etc. When I said slicks are also good on ice I meant smooth, clear ice without snow. Theoretically slicks would be best on that surface, but in practice there's always loose material like snow so treaded tires are better.
It really is a major factor for rally drivers to be able to break traction smoothly. If they didn't need to do that, they'd still use treaded tyres to counter the bad driving conditions, but they'd use wider ones. A wide tyre retains its grip longer, but when it breaks loose, the car jerks heavily and it's difficult for the driver to control it precisely.
Looking at the civilian market, tyre width actually makes modern sport cars (with very wide wheels) less predictable and safe than the old ones, that break grip smoothly so that the driver can anticipate the behavior.
By the way, a few terms in the world or rallying and racing in general:
asphalt=Tarmac
controlled (well, I don't know if it is ever totally under control) sliding=Drifting
Gotta love WRC.
Originally posted by Gon
F =ma, as edited by GoED
um... no.
You're actually describing two different forces.
F(longitudinal) = ma, where m is mass and and a is acceleration. That's okay.
F(vertical) = N(ormal force) = µmg, where µ is the static coefficient of friction and g gravity.
The forces are 90 degrees apart.
Now, let's talk weight transfer, which is still F=ma, just more complex. Typically, the "weight" of the vehicle transfers to the rear when accelerating forward. More specifically, a torque is acting on the center of mass of the vehicle with respect to the tires. This increases the force on the rear wheels, increasing contact patch, increasing grip (I made this last part up).
In summary, I'll take a 2-wheel drive 911 Turbo GT2 for acceleration runs, thank you.
So far it has been a very reliable and enjoyable car. Lot of zip for a 4 cylinder wagon. Done quite a bit of cross-country travel and a fair amoun of dirt road rambling in the mountains of Wyoming and Idaho.
Great car. The only thing that bugs me is that the arm rest on the door is really hard so if you put your elbow there while driving for hours on end you can get a stiff arm, etc.
That and the back seat lever thingy can be a pain in the butt to grab hold of sometimes.
Hey, you guys like those new Legacy pics? Want to see some more?
Originally posted by GardenOfEarthlyDelights
F(vertical) = N(ormal force) = µmg, where µ is the static coefficient of friction and g gravity.
The forces are 90 degrees apart.
Nope. I did not discuss the vertical forces at all. In the vertical direction the sum of forces acting on the car (weight G = mg, support N) equal 0, since the car is not accelerating up into the air or downward through road surface.
The friction force F = µmg is horizontal.
Originally posted by FellowshipChurch iBook
Not a fan of Subaru,
I rather like this French concept car....
407 Elixir
Fellows
The 406 coupe was awesome. A guy I knew in Australia had one a few years ago when I spent some time there.
As for subarus, I like them, but they're so damn ugly. I must say, though, that I really get a kick out of it when people drive 3rd gen Rx-7's in rally. (It actually does happen) I was slipping and sliding at 5mph in the snow this week.
A little update on the 7:
Over the next two years I'm making a project out of it. I'm going to try to make it GT-spec with the fire spitting side pipes and 9 inch wide tires. I'm looking to find a daily beater right now. I kind of like the subaru's, but they're ugly and it's hard to get over that. Plus It looks like I'll be moving to Florida in 2005, so that 4 wheel drive will be a waste of time. In Jersey, the "wintery mix" at least makes having the traction control pretty useful.
Anyway. . . FLORIDA!!!
Originally posted by Gon
The friction force F = µmg is horizontal.
Oops. My mistake. F = µN is the resistive, horizontal force of friction.
Originally posted by The Power of X
Would ya give it a rest guys.
When engineers collide.
Subaru is my 2nd favorite maker of boxer engines.
And if I can convince my wife to ignore the mouth-breathing intake and 747 wing in the back, I'd like to get the WRX-STi next year. Otherwise it's an Audi S4 Avant (station wagon).
Originally posted by GardenOfEarthlyDelights
Subaru is my 2nd favorite maker of boxer engines.
After Porsche that is.
Originally posted by GardenOfEarthlyDelights
....And if I can convince my wife to ignore the mouth-breathing intake and 747 wing in the back, I'd like to get the WRX-STi next year. Otherwise it's an Audi S4 Avant (station wagon).
You might want to check out the next generation Legacy GT set to debut in January. Also, a WRX STi Wagon is said to be in the works.