FWD vs. RWD. vs. AWD

[KnifeEdge_2K1]

I think you are still right.

Everything is relative, it may not be a high aerodynamic downforce setup for a champ car, but I am sure it is still monstrous compared to any other car tested. In addition to the wings the underbody (and I suspect some body panels) also contribute to the downforce. The article mentions that even with the low aerodynamic downforce setup the car can still drive upside down at 150 mph (the car weights 1560 lbs).

Add to the above that the car has open wheels and I would guess that by design the car has a very high coefficient of drag. As you said drag is going to increase non-linearly with speed, usually it is assumed to be proportional to the square of the speed. However, I believe most of the time the coefficient of drag is not constant and changes with speed. So you can end with the drag-velocity proportionality increasing by a power 2+, in which case even 800 bhp quickly becomes insufficient to accelerate further.

i thought coefficient of drag was constant as long as temperature was constant ... since that's the only variable that affects the viscosity of the air true that the air builds up at higher speeds and creates shockwaves but that only happens when ur going like mach speed

[Alastor]

i thought coefficient of drag was constant as long as temperature was constant ... since that's the only variable that affects the viscosity of the air true that the air builds up at higher speeds and creates shockwaves but that only happens when ur going like mach speed

You could be right, I may misunderstand the concept.

This graph is from my fluids book:



The above graph shows the drag coefficient as a function of Reynolds number for various objects. The Reynolds number is a function of velocity (U), size (D), and kinematic viscosity (v). Therefore, I interpreted the graph to indicate the drag coefficient was a function of velocity as well as viscosity.

What are you thoughts?

[meenkeene518]

well the only problem is with the power. if you give something enough power it will go fast. you can make a brick go 200 if its got enough power. it would make sense that the Cd number would remain constant with tenprature because of air demsity and that sort. if the Cd number changes that means that something would be making the air work harder to achieve its goal, be it temprature design turbalnce whatever it may be.

[Alastor]

it would make sense that the Cd number would remain constant with tenprature because of air demsity and that sort.

It makes sense for simplification of a lot problems, but the flow around a body changes with velocity. Where the flow is laminar or turbulent is changing with velocity and that is going to have a direct effect on the drag. Or things like vortex generation (useful or otherwise) is going to be changing with velocity also effecting drag.

Is this change in fluid flow at different velocities accounted for by a single drag coefficient? Or is the coefficient of drag only applicable to a given shape at a given speed?

if the Cd number changes that means that something would be making the air work harder to achieve its goal

That is what I was trying to get at, if the vehicle has a high coefficient of drag then even 800 bhp quickly becomes insufficient.

[kennyknoxville]

where i live its AWD>FWD>RWD.
lots of snow

[beejium]

beej, it woudl help if you posted location as we'd understand what type of FWD cars you've been exposed to.
Mini's won Monte Carlo rally, not bad for "regular driving"

any fwd i have seen has been pretty terrible. the best i have driven was an isuzu impulse. i live in central ny were there are a lot of people who put bodykits on neons, honda civics, and such. oh yea can't forget the fart pipe's on all of them. i can't say that i have driven a mini. if you have a suggestion for a fwd i will gladly try it.

[2ndclasscitizen]

Honda Integra type R or S, Renault Sport Clio, VW Golf GTi, Astra SRi Turbo (dunno if you get those in the US), Alfa Romeo 146 GTA (don't think the states get these either), Mitsubishi FTO, New Mini Cooper S (Works or normal) A Euro Ford Focus, Peugeot 206 GTi 180, ah thats all i can think of for now, they're all pretty good for arse draggers

[Matra et Alpine]

any fwd i have seen has been pretty terrible. the best i have driven was an isuzu impulse. i live in central ny were there are a lot of people who put bodykits on neons, honda civics, and such. oh yea can't forget the fart pipe's on all of them. i can't say that i have driven a mini. if you have a suggestion for a fwd i will gladly try it.

Yah, common problem, the 'ricer' image ruins it as all they seem to want is to look different or to get more power that they can't use.
Try to get a ride in any of the cars 2ndclasscitizen has listed and try to not be too influenced by those who think adding a 4inch can makes a car faster or cooler

[teatako]

i cant believe anyone actually takes fwd seriously for performance. god.

[auditeetee]

Just another point. AWD cars have an advantage being easier to handle for the average guy or even more so his wife or blonde on the street. AWD will give you better control.

We have dragged 500HP cars and RWD you have to control the car from losing control same for FWD cars. AWD much easier to control. Nuff said.

RWD more fun than AWD for sure. I doubt anybody will disagree with this?

AWD is only good for off the line acceleration it has been proven. After the 100kph is reached, the RWD will have the upper hand. But even so, comparing the skyline GTR and Porsche to others, they still do well with the way the power shifts more and more to the rear wheels. And around corners, take an expert driver, they will drive the RWD better but take 2 average drivers doing the nurburgring and the one driving the AWD will win. It has been tested before.

Argue?

[Matra et Alpine]

Good effort at re-awakeing an 8 year old thread

Agree AWD is inherently "safer" for Joe Bloggs driver.

But getting "fun" with AWD depends on the surfaces and the tech, eg old school Audi works Quattro transmission on gravel is THE best fun to be had as you have to pendulum to get tight corners. Even more "Scandinavian flick" than you do in a RWD.
Take any of the ultimate AWD rally cars and they pack more fun than can cope with !
Higher speeds in AWD and the fun is there if the driver has the balls

Off the line acceleration for AWD ONLY if grip limited. RWD with good weight balance/transfer and decent tyres will generally win as it doesn't lose so much power in the transmission and has higher weight transfer to driven wheels.
Check out the fastest hillclimb and sprint cars, RWD

FWD no fun ? Try a modern well setup performance hatchback with FWD and it'll surprise. eg record holder for hillclimbs in Scotland -- a Rover 25 ( ok has a Judd ex-BTCC engine ). The MAIN THING is FWD has a totally different driving style with a decent setup and LSD from the "hot hatch" brigade. Personally I like all formats for differing reasons and in ideal world would pick dependant on the road , conditions and how brave I feel

Argue? NO ...... discuss

[clutch-monkey]

i somewhat disagree with AWD being inherently safer for the average/clueless.
in my experience it means they are simply going faster when it does let go (and often snaps faster than RWD when it does).
i guess it lets them go faster than they are truly prepared for.

[RacingManiac]

AWD is too broad of a term though....I mean a GTR AWD system vs a Subaru vs an Audi(and Haldex and normal Audi is different again)....not all of those behave the same...

[Ferrer]

i somewhat disagree with AWD being inherently safer for the average/clueless.
in my experience it means they are simply going faster when it does let go (and often snaps faster than RWD when it does).
i guess it lets them go faster than they are truly prepared for.

I agree completely with that. Also, even in two wheel drive cars, the higher the grip levels are the worse the potential consequences are if you start exploring the limits of the car.

[Matra et Alpine]

GT-R is the most boring car to drive VERY fast and safe.
Beyond the obvious mistake of a long straight then a tight corner, it does well at applying braking to keep the car in place. Not seen one get it wrong on the 'ring yet.
Have had an owner tell me tho' that he's never been so bored going so fast He switched off the TC and said slower, but enjoyed the car more.