Goldenhue22

I was just coming back with and dumb remark to your dumb response. And I didn't put any "info" in my post because it is common sense. 2+2=4. But to Buger first. I was saying in snowy conditions a 4WD vehicle will stop faster than a RWD vehicle because of the much better traction. Obviously in dry conditions a RWD car will stop sooner.

To you Hercules here are some web pages for you:

1) This is from www.rearwheeldrive.org

Traction in Snow and Ice. When not under hard acceleration front drive cars have more weight over the front wheels. This gives more traction for acceleration in very slippery conditions. This is the biggest perceived advantage to a front drive car. However, today's rear wheel drive cars with traction control and independent suspension do very good in the snow. For areas that have extreme amounts of winter weather this may be enough to justify a front wheel drive car.

2) According to AAA's website: Front-wheel- drive vehicles generally handle better than rear-wheel-drive vehicles on slippery roads because the weight of the engine is on the drive wheels. The back end of rear-wheel-drive cars tends to lose traction and slide side-to-side during turns on icy roads because there is little weight on the drive wheels. Many vehicles today are equipped with four, or all-wheel dive, which helps maintain traction in difficult conditions.

Hmmmm, Hercules biased opinion or AAA...whom does the bell toll?

Goldenhue22

Which brings me to another common sense statement that putting sand in the trunk of a RWD car WILL, I repeat WILL, give more traction. It is impossible for it to make it worse. Again...according to AAA, "Front-wheel- drive vehicles generally handle better than rear-wheel-drive vehicles on slippery roads because the weight of the engine is on the drive wheels." Apply that same concept for putting sand bags in the trunk of a RWD car and you have more weight pressing down on the drive-wheels and thus better traction. This is complete common sense and only someone that is completely and utterly biased wouldn't agree.

dying_here

im sorry i just scanned through this thread really fast, 4 pages .. grr. but so in summery Without any winter tire, and w/ just LSD. The RX-8 should be fine on snow w/ a few sandbags?? Im from Edmonton/alberta where it snows quite alot and the city seems to be too poor to actually shavel everything but the highway.. kind of ..

theonly reason i ask is because i heard the IS300 ( RWD) slips pretty bad in snow ( w/o snow tire that is).

sorry if its a stupid question just quite important since .. well the road is mostly covered w/ snow if not half the year, and i wont ever had a chance to get a beater since i live on Campus and only 1 parking spot

Hercules

On braking, both cars have 4 wheel disc brakes. The AWD has NOTHING to do when braking. Tires of course do make a difference.

Second, I apologise as to my laughing, I kinda caught the thread in mid-discussion and as a result felt you meant that FWD cars are better than RWD cars period. It was a laughable matter that I think you'd agree on

However I am still right on the braking and you are wrong The fact that the SUV has nothing to do with braking. Both cars use four wheels to brake, and presumably both cars use the electronic aids.

In braking the car that brakes better on dry, will brake better always. AWD has nothing to do with that.

Buger

I assumed that you were talking about snowy conditions but I still don't understand why any AWD or 4WD SUV will stop quicker than any RWD vehicle.

In snowy conditions, the AWD or 4WD vehicles distribute the torque better for acceleration but do nothing to help braking yes? Regardless of whether the vehicle is a 4WD Pathfinder, a FWD Mazda6, or a RWD RX-8, there is still 4WB (4 wheel braking) yes?

Hercules

You mirrored me for once!

Buger

Hi Dying_Here,

I don't think the RX-8 with DSC and snow tires will have any problems in the snow (even without sandbags). If the left or right rear wheel of the RX-8 does not have traction, the DSC will be able to apply brake force to the wheel that is slipping. Torque will be applied to overcome the brake force to still turn that wheel and twice as much torque can be applied to the other wheel.

I believe the IS300 may not be quite as good in the snow because most of the weight is in the front (54/46) although the drive wheels are in the back.

Brian

Buger

I started my post before I saw yours but I just type slower.

dying_here

wat about w/o the DSC?? just the GS trim and without snow tires

Goldenhue22

Even if all wheels do some sort of braking they don't do the same amount of braking due to traction. While the front 2 wheels, in a RWD car, will be scrapping for the pavement, errr snow, it won't find it and whoops you keep on going. Actually, you'll most likely skid off the road first into a tree or something else so you may stop faster just due to Newton's second law. A 4WD vehicle provides MUCH more traction and STABILITY in braking especially in slippery conditions, mainly because the wheels aren't just *trying* to brake they do brake. Make your arguement to FWD vehicles, you'll lose everytime to a 4WD car.

eccles

Indeed, with all other things being equal, 2WD, FWD, 4WD, LSD, all make absolutely no difference to braking ability. Anyone who says otherwise has no grasp of the principles.

But fresh snow is one of only two situations where ABS is actually a disadvantage; the other being loose gravel or dirt. Under those conditions, a locked wheel will build up a wedge of loose material in front of it, which will actually help it stop better than a wheel which is not allowed to lock.

(On my friend's Porsche Boxster, disabling the Traction Control also disabled the ABS. I wonder if the RX-8's DSC override will also cut the ABS. I doubt it.)

eccles

Sorry, I appear to have mislaid my Cretin/English dictionary. Can someone please translate that for me?

Midnight Flyer

Goldenhue where in the world do you live and how many years have you been driving in the snow? I have almost thirty years up here in snowy Canada, with much of that in Northern Ontario.

In dealing with FWD, RWD or AWD they only have to do with acceleration. The operative word being Drive, not Stop. There are two important things to consider. First is where the motor is relative to the drive wheels. An old VW Beatle, which was RWD will accel. as well as any FWD car because the motor was over the drive wheels . AWD has 4 wheels working to move the car forward so regardless of where the traction is it will find it.

In a RWD car with the motor in the front adding sand to the trunk will increase the traction to the drive wheels but may have other bad concequences such as changing the weight distribution and messing up the cornering and other properties of the car. I prefer the handling of my Miata (RWD) to that of my Intrepid (FWD) or even my wife's Jeep (AWD) in winter. That is not to say that the FWD and AWD cars don't accellerate faster, just that I prefer the handling of the car.

My Miata has a 50/50 weight dist. That means that the weight over the drive wheels would be the same regardless if it was FWD or RWD. In a Focus or something that has FWD and say a 60/40 weight dist. there would be more weight over the front wheels so it could accelerate a bit better.

When it comes to stopping it all has to do with the weight of the car. When you slam on the brakes the weight of the car shifts to the front wheels which is why they are biased to brake harder then the back wheels. All cars have about the same size contact patch to the ground on the four tires but the weight of the cars is different. Simple physics will tell you that it take longer to stop a heavier object moving at a given speed then a lighter object traveling at the same speed. As I mentioned in my previous post they showed it on tv just a couple of night ago here, the AWD SUV stopped about 4 times further then the FWD civic or whatever it was on the same surface.

As far as putting weight in the trunk of a RWD car, if you brake hard and the car is just slightly out of line, the rear end will swing around faster then you can say "ouch" and now you are going sideways. That is why I would rather keep my 50/50 weight dist of the Miata and loose some acceleration in favour of better handling.

When dealing with cornering, on snow, I like to have the two front wheels work at turning the car and the two back wheels work at moving the car forward. With a FWD car the torque of the motor pulling the car works against the friction of the wheels trying to turn the car which is why FWD cars understeer so badly. With AWD, they usually bias the cars as RWD so that while the front wheels turn under power a bit, it is not as bad as a FWD car.

Take any performance driving school and they will show you that a tire has only so much grip. That grip can be distributed to start, stop or turn the car. Sort of like the equation

START + STOP + Turn = Grip.

The value of Grip is preset by the size and condition of the tires. So if you increase the value of Stop, you have to decrease the value of turn by the same amount in order for the equation to work.

Finally there is the skill of the driver to consider. The reason most mfg. are going to FWD is because people don't know how to drive well enough to get out of trouble with a RWD car. When a person starts to loose control of a car the usual reaction is to take the foot off the gas and press on the brake. In a FWD car this will usually save the person from an accident, but not always. In a RWD car the proper reaction to correct the loss of control may actually be to step on the gas. Can you say oversteer? :D It all depends on the circumstances.

How will the RX8 handle in snow? I don't know but I can't wait to find out.

MikeW

Simple physics say your are wrong.

Everyone has seen F=ma, so F=m(-a) (deceleration), the force is the coefficient of friction (static/dynamic) by the normal force (mass*gravity +- downforce/lift)=mass*acceleration

F/m= acceleration; (coefficient*mass*gravity)/(mass) The masses cancel out, so the determinant of stopping power is gravity(not really changable) and the coefficient of tire/ground friction.

So an 18 wheeler (truck/lorry) can stop just as well as a Miata, if starting from the same speed, with the same tires and adequate brakes on the truck. Actually since there is so much more aerodynamic drag on the truck, the truck would stop before the Miata (assuming the truck did not jackknife)

eccles

F=ma is true whether you're talking about acceleration or deceleration (which is merely acceleration in the opposite direction. At NO time does F ever equal m-a!

You are correct that F/m=acceleration. And granted, the tractive force is to some extent proportional to the mass of the vehicle, but to say that the two masses cancel each other out is patently ludicrous.

An 18 wheeler can stop as well as a Miata? ROFL! Only if it's fitted with retro-rockets. Even with 18 of the world's stickiest racing slicks, there's no way that a semi is ever going to outbrake a regular passenger car, let alone a Miata.

RXhusker

I have got to believe that Mike meant to say that F=ma, so F=m*(-a) (deceleration) not that F=m (MINUS) a

Granted it has been 15 years since my studies in aerospace engineering (Univ. of Colorado) but I seem to recall that even physics this "simple" still hold to the basic laws of the universe including Newton's Second Law of Motion.

On the other hand -- maybe that is one very heavy Miata :p

Actually it may have been better to compare the semi with that rather portly "sporty" car the 350Z :p :D

wakeech

momentum and inertia and kinetic energy = all the same thing. just thought i'd let ya know we were both saying the same thing...

as for MikeW's post, the F on the tyres to road surface is changeable in the real world, with heat tread pattern and whatever... but SUPPOSE it was exactly the same anyways for the Miata and Lorry, the grip is still changeable: normal force is constant with vehicle mass, but you have to remember that there can be a higher specific force (pressure) one the tyres of the Miata (or the Lorry) if there is less rubber to mass (with correctly set tyre pressures)... this would also impact braking on something like a snowy or icy road... especially if there was some amount of snow or slush to cut through.

zoom44

actually wakeech i have inertia whether i am moving or not- momentum is only when you are moving.

Buger

I tried to communicate with the guy but I failed...

MikeW tries to do his profundus maximus thing again ...

We all have to just laugh already... :D

Midnight Flyer

Mike, I'll try to remember that when the 18 wheeler is filling up my rear view mirror. I am sure it will make me feel much better before I try to do a James Bond and go under the trailer. I have sat in a tow truck with a van on the hook and while it may not be as big as an 18 wheeler, when we got cut off it took a lot more time/distance to slow that sucker then my Miata.

The thing to remember in this discussion is that while the tires/brakes on most vehicles are designed to stop the car from 60-0 in about 120 feet, we are not talking about on dry pavement here but rather on snow/ice.

If anyone thinks that an SUV on snow/ice can stop as quickly as my Miata, we can run a simple test.

As I mentioned, on a auto enthusiast program that was shown on TV here last week they showed the test that they did. Three cars, small, midsize and SUV stopping from 60 KPH and 100 KPH and the SUV always went about 4 time further then the small car.

If we use the formula F=M*A, with A being either a + number for acceleration and a - number for deceleration the Mass of the object plays a significant roll in the equation. Sorry if my physics are off but I have been 30 years out of high school. The Force required to move a 1000kg object (my Miata) with an A of say 10 M/S/S is 10,000 Newton Meters ??. The amount of Force required to move the 10,000 kg object (18 wheeler) with the same A would be 100,000 Newton Meters. To slow the same two objects down in the same distance, the force would have to be 10 times more for the larger object. And frankly I don't think that his 18 tires has that much stopping power. He only has 4.5 times the number of wheels I have.

AWD just means you can drive deaper into the ditch.

wakeech

*smacks head really hard* duh... sorry, it's only my empty head which doesn't have interia... :D

zoom44

hey it's not like it's everday i get to tell you that you were wrong about something....


....every other maybe:p