Fwd...

What makes FWD the ideal drivetrain for autocrossing? I thought RWD had better handling?

how do you figure FWD is better?
imho:
RWD > FWD
AWD > FWD
mid-RWD > FWD

simply on the fact that your tires can only do 100% total work, if the front tires have to pull to that takes from overall capability. some people like FWD better because it works better with their driving style.

:1:

seriously, FWD is usually inferior to RWD or AWD. That's not to say well set-up FWD cars can't compete with RWD.

how do you figure FWD is better?
imho:
RWD > FWD
AWD > FWD
mid-RWD > FWD

simply on the fact that your tires can only do 100% total work, if the front tires have to pull to that takes from overall capability. some people like FWD better because it works better with their driving style.


I heard lots of people say that FWD is the best for soloII

Thats what makes you Auto Newb, you believe what dellusional people say...

Hey hey, I have been meaning to change this stupid name, I only used this name so people had no reason to flame me in the engineering/technical forum. It's like a safety precaution. But lots of people say that the only good thing about FWD, is soloII and rallying (except for AWD).

the only good thing about FWD is economy... and rain drifting. it's efficient, but you can't run a lot of power.

answer to your question: it's not.

Oh, that sucks, but isn't there more drivetrain hp losses in RWD cars?

Not if its Mid Engine

Actually, if you're going to be going around tight corners and such RWD has little to no advantage over FWD, especially on a flat course.
FWD has it's advantage in that it pulls the car rather than pushes it, and this has it's advantage anytime you want the car to go where you point it.
The advantage is lost when you have wider turn and straight aways, where you gain enough speed to make understeer in the FWD car exceed that of it's RWD counterpart.
Other advantages have less to do with handling, such as that usually you can get a FWD car for less than RWD, etc.

Hmm... Cool

Actually, if you're going to be going around tight corners and such RWD has little to no advantage over FWD, especially on a flat course.
FWD has it's advantage in that it pulls the car rather than pushes it, and this has it's advantage anytime you want the car to go where you point it.
The advantage is lost when you have wider turn and straight aways, where you gain enough speed to make understeer in the FWD car exceed that of it's RWD counterpart.
Other advantages have less to do with handling, such as that usually you can get a FWD car for less than RWD, etc.

Cliffs Notes: In low speed cornering, RWD doesnt have as much of an advantage, and FWD cars are cheap to buy.

But what about a slalom or an S curve 2stroke?

When it comes to high speed performance, when on throttle, FWD cars tend to understeer. That gap between FWD and RWD is less significant in lower power applications, but when the power is much higher than stock, the gap is very significant.

Either way, not trying to start a "flame war." But the debate was that he was told that FWD was superior to all other racing layouts in AutoX and we wanted to point out that he was mistaken.

No, FWD is not supperior to all layouts, but under many circumstances, FWD can certainly "pull its own weight" at autocross. It depends alot on the driver and what style of driving they want to do, FWD has it's advantages, though I wouldn't say it's the 100% best choice all around, but if you're tight on money it might be.

FWD holds the most understeer among them all. MR is my personal favorite.

Any car with a front mounted engine will want to understeer. However, that FWD will have more understeer than RR, is somewhat missleading. Once again I'll note that when Toyota's first front driver, the Corolla-Tercel was introduced, test drivers were impressed by the fact that it exhibited less understeer than any of Toyota's other cars (which were all rear wheel drive at this point in time) Generally cars come from the factory "tuned" for understeer, because this supposedly feels "safer" to drivers (remeber the Corvair?).
It's not that FWD has to be so heavy on it's helping of understeer, it's that companies want it to be.

FF cars are usaully inferior, but has two exception though;the 320horse FWD Alfa Romeo 147 GTA and the integra hype R

"Any car with a front mounted engine will want to understeer"

Have you seen a Porsche 944? Front engine, rear transmission, 51/49 weight balance. Center of mass is about at the center of the car.

by changeing the sway bars you can tune your fwd to be really nice without any major understeer. And I read that too 2strokeblock that fwd cars are tuned to have understeer, i think thats dumb, how can you feel safer when your car does not want to go into a corner?

on the drag strip i love my FWD car, 2.0 60FT is why. But on the street i spin the tires like crazy.

"Any car with a front mounted engine will want to understeer"

Have you seen a Porsche 944? Front engine, rear transmission, 51/49 weight balance. Center of mass is about at the center of the car.


2stroke is corect, a front mounted engine car will have a higher polar momentum and will help understeer

2stroke is corect, a front mounted engine car will have a higher polar momentum and will help understeer

The higher polar moment of inertia will not effect the under-steer characteristics of the vehicle, but it will effect the steering responsiveness. It is still possible even with a front engine vehicle to achieve a near 50/50 weight distribution, so it possible to achieve near neutral-steer handling. With FWD under-steer is generated from the increase in front wheel slip angles as the vehicle accelerates.

The higher polar moment of inertia will not effect the under-steer characteristics of the vehicle, but it will effect the steering responsiveness. It is still possible even with a front engine vehicle to achieve a near 50/50 weight distribution, so it possible to achieve near neutral-steer handling. With FWD under-steer is generated from the increase in front wheel slip angles as the vehicle accelerates.


Yeah it will its basic physics. The further forward the weight is the more polar momentum the car will have, meaning all that weight will resist turning. And what does it it mean when the car is resisting turning? Understeer.

This is why you want the most weight like the driver or the engine as close as posible to the rotational center of the car. This is wjy midengine designs are the best.

And the reason Most FWD cars tend to understeer, is for three reasons:
1. Most are econocars with understeer dialed in from the factory since its safer.
2. They have a lot of weight up front(engine, transmission, diff etc) causing a great polar momentum.
3. If you aplly power during a turn you can overwork the tires and lose grip, especially with an open diff.

However they can stil make good racers with good design and excelent suspension geometry setup.

Yeah it will its basic physics. The further forward the weight is the more polar momentum the car will have, meaning all that weight will resist turning. And what does it it mean when the car is resisting turning? Understeer.

This is why you want the most weight like the driver or the engine as close as posible to the rotational center of the car. This is wjy midengine designs are the best..

I agree that a vehicle with a high inertia will resist acceleration, and with high polar inertia will resist rotation. So to achieve a given acceleration it will take more force for a vehicle with the high inertia compared to a vehicle with low inertia.

I don’t agree that this resists to rotation is the same characteristic as under-steer. For example take a vehicle with neutral steering traveling around a skidpad at a constant speed. If the vehicles speed is increased an increase in lateral force must be generated by both the front and rear tires to maintain the same radius of curvature. Since this vehicle has neutral-steering no change in steering input is required. Now if the polar moment of inertia is increased along with the speed, even more lateral force will be required than was needed previously. But the font and rear lateral forces increase proportionally and so the steering characteristics remain the same. Still the vehicle will not require any change in steering input.

In other words the PMoI effects the vehicles resists to rotations or responsiveness of the vehicle. The steering characteristics (under/over/neutral) are effected by load distribution, tire characteristics/setup, drive type (F/R/A WD).

See also:

http://autozine.kyul.net/technical_school/handling/tech_handling_4.htm
http://www.siu.edu/~ritzel/courses/302s/vehicle/vehicledynamics.htm
http://www.rqriley.com/suspensn.html

I agree that a vehicle with a high inertia will resist acceleration, and with high polar inertia will resist rotation. So to achieve a given acceleration it will take more force for a vehicle with the high inertia compared to a vehicle with low inertia.

I don’t agree that this resists to rotation is the same characteristic as under-steer. For example take a vehicle with neutral steering traveling around a skidpad at a constant speed. If the vehicles speed is increased an increase in lateral force must be generated by both the front and rear tires to maintain the same radius of curvature. Since this vehicle has neutral-steering no change in steering input is required. Now if the polar moment of inertia is increased along with the speed, even more lateral force will be required than was needed previously. But the font and rear lateral forces increase proportionally and so the steering characteristics remain the same. Still the vehicle will not require any change in steering input.

In other words the PMoI effects the vehicles resists to rotations or responsiveness of the vehicle. The steering characteristics (under/over/neutral) are effected by load distribution, tire characteristics/setup, drive type (F/R/A WD).

See also:

http://autozine.kyul.net/technical_school/handling/tech_handling_4.htm
http://www.siu.edu/~ritzel/courses/302s/vehicle/vehicledynamics.htm
http://www.rqriley.com/suspensn.html

Well of course steps can be taken to compensate for a high polar momentum up front. And its not the only element to affect handling.

However it will still affect the car in a negative way, and the car will have higher natural tendency to understeer than a midengine car. So again its something that can be compensated for but it will always be better to start off with a superior mid engine platform that a front engine one.


Also its not that hard to make a car steer neutral around a skidpad since its a steady state corner. However in the real world corners varie infinitelly and its much harder to tune a car to steer neutrally in most of them. This is why according to Maserati engineers a rear bias is actually preferable to even the classic 50/50 distribution, and i would think a porche engineer would agree with him.