Heated Discussion bout cars

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Combustion

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It was Saturday midday and we were bored, I'm young, 21, my two friends are about 30 so they get the experience points, we get into a serious debate about 3 car issues, and I'd like your input.

Point 1: A FWD car will accelerate harder than a RWD.

I disagree with this one, I think the RWD car will accelerate just as hard as an FWD (we compared front engine cars for this one), maybe the FWD will have the initial ahead because of the more weight on the drive wheels but surely once the weight has shifted to the back the RWD will accelerate harder than the FWD since the more it accelerates the harder it pushes on its drive wheels creating more traction? We assumed no spinning, and that the driver is capable of getting the perfect revs to keep the tires on the limit of spinning.

They insist that 'pulling' (FWD) is much more powerful than 'pushing' (RWD) and that is also the reason the RWD will slide from side to side. I say that RWD slides because the drive wheels are fixed and so any lateral forces on the drive wheels cannot be compensated for as easily as with the FWD. Although I agree pulling will create a more stable straight line because pushing creates a large moment around the back which magnifies even slight lateral movements many times over.

Point 2: A FWD will handle better and take a corner faster than a RWD.

I'm not 100% sure on this one, but what I do think is that if the FWD loses traction on the turn then there is no bringing it back whereas a RWD you can counter the oversteer. Also they say that turning the wheel left/right very slightly continuously during a turn will make the car go faster round a turn because it makes the tires screech less. I do the same on turns but only to counter small imperfections in the road, if I had a perfect road I would use a continuous smooth motion during the turn. They say this is wrong. This is assuming cornering at traction limit.

For RWD, they say that if you break traction at any point you will not go as fast round a corner as if you are always at traction. I agree up to a point, because I say it all depends on the corner and road surface. I used an ice hairpin to explain, if you are always at traction in the hair pin then you must go very slowly at the apex and exit otherwise you will slide outwards. However if you are turning and sliding just before the apex you can bring the back of the car around much faster and then accelerate harder out of the corner.

Point 3: Thick tires create more traction than thin tires in the dry and vice versa for the wet/snow. The reason being that more rubber hits the road. We assumed rubber compound, tire diameter, tire depth, tire tread all being same, just tire width varying.

I agree that thick tires are better for dry and thin for wet/ice but for different reasons. I think that both thin and thick tires will generate the same traction in dry. This because although more rubber hits the ground, less pressure is acting per square inch so less grip is generated per square inch.

The fact that F1 cars use thick tires is not for more traction but for 'better' traction, ie. more tire stability round corners, and since there is more rubber the tire will last longer. Thin tires would burn up at the forces they would encounter from an F1 engine.

Thin tires are better in snow because they dig deeper into the snow, just like an ice skate, there is a much larger pressure per square inch, which lets the tire 'break' the snow quicker (this could be crap, I'm not sure, it's just what I think)

I lose the experience contest, and since I'm acting upon logic rather than experience I'm probably wrong, but I'd like someone who actually knows for sure who is right in each case.

Cheers
Combustion
 
1:

Presumably if you had exactly the same car, but one with front-drive and one with rear-drive, and you're pushing or pulling around exactly the same mass, under normal street driving conditions it isn't going to make any difference. At the limits of traction a rear-drive car will have the advantage of weight transfer, and will, in fact, have more traction, which will make the jump off the line faster than a front-drive car.


2:

At the absolute limits a rear-drive car can go faster around a corner than an identical front-drive car due to the fact the front wheels are not only turning the car, but are also powering it too. And rear-drive cars often have far more neutral weight distribution (50:50).

Introduce the concept of the traction circle to your friends.


3:

You're right. Absolutely right. Traction (friction), ideally, has nothing to do with tire width.

F1 cars need big, fat tires to compensate for the very large acceleration they possess when going around corners. They'll actually shift weight off of the "inside" part of the tires (the regions on the tires' surfaces closest to the apex of the turn). They have a lot more surface area and can supplant this loss of traction on the "inside" with the "outside" parts of the tires. Very powerful street cars do the same, and have fat tires for the same reason.

Thin(ner) tires in the snow are not advantageous because of the higher "pressure per square inch" (which is a goofy statement: pressure is, inherently, a per area measurement. In Imperial units pressure is often reported in units of PSI: pounds (force) per square inch (area). Pounds per square inch per square inch is just... wrong, don't you think?). Remember, you just said traction isn't a function of tire width, so don't go contradicting yourself. ;)

Think of snow as a fluid, like water. Say a fat guy and a skinny guy are having a swimming race. Assuming they both possess the same strength and, ideally, the same weight, the skinny guy is still going to win. Why? Because the fat guy's girth is physically getting "more in the way" than the skinny guy. There's equal pressure acting against the two, but, as we said earlier, pressure is force per area. The fat guy's got a lot more area, right? So that means there's more force pushing against him.
Or think of a speedboat and a barge. The barge is inherently slower for the same reason: a larger area.

Skinny tires in snow are like the skinny guy in the swimming race. They cut through the snow/water easier than their wider counterparts because they don't have as much snow/water in their way.






And turning the wheel back and forth around a corner is just stupid. The smoother the turn you can make the faster you'll go. Turning the wheels back and forth does nothing but slow you down.
 
Firebird
1:
Thin(ner) tires in the snow are not advantageous because of the higher "pressure per square inch" (which is a goofy statement: pressure is, inherently, a per area measurement. In Imperial units pressure is often reported in units of PSI: pounds (force) per square inch (area). Pounds per square inch per square inch is just... wrong, don't you think?).
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Bah you know what I meant, I normally use metric and was concentrating so hard on what word you use for centimeters that I messed up, yes its pounds per square inch :guilty:.

Remember, you just said traction isn't a function of tire width, so don't go contradicting yourself.
Click to expand...

I was thinking along the lines of that since the weight is acting over a smaller area, the tire would break the snow and touch the road sort of thing, just like a normal shoe will go through the snow but a snowshoe will stay on the surface.

So basically thin tires are better because of less drag? I never thought about it like that...

Techincally doesn't that mean that a car on a dry straight road that was going for a top speed record would want thin tires as well, seeing as air is just a very low viscosity liquid?
 
Well, of course in the dry AWD makes very little difference and - on cars running the same fwhp - may actually be slower due to transmission losses.

But carry on, by all means.
 
Combustion
I was thinking along the lines of that since the weight is acting over a smaller area, the tire would break the snow and touch the road sort of thing, just like a normal shoe will go through the snow but a snowshoe will stay on the surface.
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A snowshoe DOESN'T touch the ground though, and that's the point. The fastest way to get through snow in a car is not to sink into the snow, it's to get through with the most ease. Ideally you'd want to "float on" (i.e. "not sink into") the snow, but with a 2000-4000lbs car you'd need a lot of surface area to make a noticeable difference in how deep you sink. Fat tire, skinny tire... your car is still going to sink into the snow no matter what. It's better to design it to minimize rolling resistance.

So basically thin tires are better because of less drag? I never thought about it like that...

Techincally doesn't that mean that a car on a dry straight road that was going for a top speed record would want thin tires as well, seeing as air is just a very low viscosity liquid?
Click to expand...

Fluid, not liquid. Fluid.

And yes, the engineers designing land-speed record cars consider tire width to be very important. But they also need to deal with issues of heat, so they're often quite wide still (if I remember correctly Thrust SSC had 10" and 6" wide wheels). They're notably thinner than F1 tires though, since they don't need to turn.

The best example of this kind of design is cars in solar races. They usually run on bicycle-sized wheels and tires to reduce rolling resistance.

Passenger cars designed for fuel economy also have relatively thin wheels and tires, such as the Toyota Prius.
 
FWD cars will be more stable thru acceleration and cornering, but I don't think they'll be any faster IMO. On a slippery surface, FWD cars will be safer to drive faster for most people, but I think most of sports cars are RWD or AWD for an reason.
 
I wanted to be difficult and say something that was neither FWD, RWD or AWD:(
 
Don't forget that FWD cars understeer like a bastard, and if you make too many sharp turns at highspeed you could break the pinion or snap something. RWD cars generally handle better than FWD cars because of not only better weight distribution, but also because the drive wheels are not steering as well. Think of it as rock climbing. Try pulling yourself the whole wall while also reaching left/right as you go about your route. That's FWD. RWD would be like you using your legs to push you up as your arms guide you along your' way. It's less straining, less diffucult, and generally quicker.

When it comes to slippery surfaces though, FWD is perfectly fine in a low traction environment for the regular driver (ie Highways + black ice etc) because they can correct the oversteer or eventually pull themselves out of the spin. But when it comes to racing, however, and you're trying to turn on a slippery surface, don't count on actually turning. The amount of mass behind the engine and drivewheels still wants to go forward, but that one small percentage of mass at the very front of the car wants to around the corner. With that, you end up in the wall and disqualified.

With a RWD vehicle however, assuming you're also trying to go around the corner as fast as possible, then you're likely to experience oversteer. This is because there's a very high possibility of wheelspin, which results in loss of traction, which results in the rear end of the car wanting to continue going forward. BUT, because the front wheels are steering it, they continue to face the corner as the ass end of your car swings out, assuming you've retained traction on the front wheels. This is known as a drift.

In AWD, all four wheels are driving simultaneously, albeit sometimes with a different percentage of power. Usually, an AWD vehicle will have the power bias towards the rear of the vehicle (a Skyline is like 90% RWD at 100mph, the EB110S is consistently 27% FWD and 73% RWD, the Murcielago is 21% FWD and 79% RWD), for handling purposes. The AWD on a rally car, however, is designed for very low traction environments. This is so they can swing the car around before it enters the corner, and is thus driving while countersteering, so that it doesn't have to correct itself out of the corner while losing time. If you were to do this on pavement/asphalt however, you're just a showoff. The AWD in sports cars for the road, however, is usually used as a safety precaution (they don't anticipate everyone to be racing their cars for one), so that when you spin out, you still have the pulling to hopefully help correct the oversteer, and the pushing to hopefully help correct the understeer. There are tradeoffs in all forms, but I'd go with AWD because some more complex systems can switch between AWD/FWD/RWD.
 
sounds like your friends are honda owning ricers who insist on stuffing 305mm tyres under their guards. just because you're 21 doesn't mean you can't be smarter than a couple of 30 yearolds. remember that

1- for a normal street car with not much power, generally fwd will be quicker because of less power loss through the transmission. as you add power, up to the level of a decent street car, the advantage of rwd traction becomes apparent, the fwd will just bag up the front wheels. adding more power there then reaches a point when you can't put down that much power through two wheels without major modifications (custom rear end geometry, larger tyres, slicks, etc) so awd becomes the leader

2- your friends have never heard of understeer

3- if you have skinny tyres and your friend has big fat wide tyres and you both hit a section of road with water across it, you will drive through it safely and your friend will aquaplane and run off the road. wide tyres create a "wave" if you will in front of them, pushing more water ahead, so much so the tread pattern can't disperse it and water goes under the tread and the wheel loses grip. skinny tyres have less rolling resistance, so they will slice through water kindof like a knife. up to a point, width doesn't really make THAT much of a difference, like i can put 165 or 185 tyres on my corolla and wet driving difference is negligible. go up to 205s and you tend to have a car that's too light to stay on the road in the rain

i have no idea about snow, except hearing from friends who've been on holiday in new zealand, you need chains or you die
 
You can set up a FWD to have no understeer at all, but ultimately RWD is better. 4WD is only better because of the electronics that control it. 4WDs are for those who can't drive though...we should ignore them :p
 
Your friends are stupid. End of discussion.
 
BlackNSX
You can set up a FWD to have no understeer at all, but ultimately RWD is better. 4WD is only better because of the electronics that control it. 4WDs are for those who can't drive though...we should ignore them :p
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I generally think of 4wd cars as those that only use mechanical means to split the torque and AWD uses electronics and favors either fwd or rwd most of the time. I most certainly wont ignore them. Remember 4wd and Awd only help your grip in acceleration; braking will be the same (maybe worse because of added weight) and cornering will be slightly less responsive than Rwd.

An advantage that rwd cars of any sort of power is that they can be pulled out of understeer with the throttle.

The reason fwd cars have been heralded for adverse weather driving (well not so much any more) is not that they perform any better or have higher limits, but rather that when you go past the limits it calmly understeers, meaning if you end up hitting something it will mre likely be with your front end. Air bags and crumple zones work well in this situation. Rwd has the potential to spin the car making it either uncontrollable or allowing an accident at an odd angle. The question of which car will find its limits first has already been posted.
 
Combustion
Point 1: A FWD car will accelerate harder than a RWD.

I disagree with this one, I think the RWD car will accelerate just as hard as an FWD (we compared front engine cars for this one), maybe the FWD will have the initial ahead because of the more weight on the drive wheels but surely once the weight has shifted to the back the RWD will accelerate harder than the FWD since the more it accelerates the harder it pushes on its drive wheels creating more traction? We assumed no spinning, and that the driver is capable of getting the perfect revs to keep the tires on the limit of spinning.

They insist that 'pulling' (FWD) is much more powerful than 'pushing' (RWD) and that is also the reason the RWD will slide from side to side. I say that RWD slides because the drive wheels are fixed and so any lateral forces on the drive wheels cannot be compensated for as easily as with the FWD. Although I agree pulling will create a more stable straight line because pushing creates a large moment around the back which magnifies even slight lateral movements many times over.
Click to expand...

Remeber, though, that you can only have a certing amount of power going through the front wheels (up to about 250-300hp) before the car torque steers into the nearest wall, whereas rear drive can have a lot more power put through the wheels and still stay fairly straight.

Combustion
Point 2: A FWD will handle better and take a corner faster than a RWD.

I'm not 100% sure on this one, but what I do think is that if the FWD loses traction on the turn then there is no bringing it back whereas a RWD you can counter the oversteer.
Click to expand...

...assuming it's the driving wheels that have lost grip. If the rear wheels on a FWD car lose grip, it's a lot easier it rescue than an understeering RWD car. Give it a load of right foot and watch the front pull the car back in line. Watch a BTCC race for an example of this.
 
BlackNSX
You can set up a FWD to have no understeer at all, but ultimately RWD is better. 4WD is only better because of the electronics that control it. 4WDs are for those who can't drive though...we should ignore them :p
Click to expand...

this actually raises a good point - alot of newer awd cars (and even new cars in general) are coming out with alot of driver assists, how can you tell how much is the driver and how much is the car?

at the local race series i compete in (with my real car) there is an average guy with an evo 6.5 makkinen. he runs similar times to two very experienced and highly skilled drivers who have an ae86 sprinter with suspension mods and honda crx with a mines motor

at last meet, the driver of the evo, was talking to me. he said "it's funny you know, i go into a corner a bit wrong and the car kinda corrects itself" to which i replied "yeah dude, ayc!" and he goes "haha, corrects for bad driving"

now no doubt the evo 6.5 is an awesome car, but i'm an amateur driver too and i can't get within 5 seconds of the sprinter or the crx. how much of that 5 gap seconds do you think is driving aids? a similar amateur driver in a fairly stock vr4 galant is only a second or two behind the evo...
 
Are these friends the kind of people who think they're cornering fast when they understeer through a corner at full throttle with the wheel at full inward lock? They sound like the type to me.

Think of it this way. With an FR car, it's possible to take a corner at a high speed without any unwanted understeer or oversteer becoming an issue. But an FF car can't do that at all. Cornering technique consists of figuring out how fast you can go without understeer, it's an eternal compromise.
 

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