MG-Rover.org Forums banner

1 - 20 of 74 Posts

·
Registered
mg_tf
Joined
·
1,996 Posts
Discussion Starter · #1 ·
I havent asked a dumb question for aday or two now, so here goes...

What would you guys say is the main difference driving a RWD, what do you do differently to a FWD? Specifically in the wet on roundabouts...?

mikef
 

·
In the Garage
MG TF
Joined
·
33,113 Posts
I havent asked a dumb question for aday or two now, so here goes...

What would you guys say is the main difference driving a RWD, what do you do differently to a FWD? Specifically in the wet on roundabouts...?

mikef
Slow in, fast out. Do all the braking before you get to the corner/roundabout and only put the power down after the apex of the bend.
 

·
Registered
Joined
·
17,936 Posts
I havent asked a dumb question for aday or two now, so here goes...

What would you guys say is the main difference driving a RWD, what do you do differently to a FWD? Specifically in the wet on roundabouts...?

mikef
Err. be more carefull and don't push your luck? :_poke:
 

·
Registered
Joined
·
17,936 Posts
Slow in, fast out. Do all the braking before you get to the corner/roundabout and only put the power down after the apex of the bend.
Thats only if you don't want to slide a li'l bit ;)
To tell the truth, the back end on my TF has skipped out twice, both times I caught it, but it was still bloomin' scary! :scary:
 

·
Registered
Joined
·
17 Posts
Slow in, fast out. Do all the braking before you get to the corner/roundabout and only put the power down after the apex of the bend.
Sorry, I disagree somewhat with the fast out part. The common mistake with a RWD car is that people get on the throttle too soon, causing an oversteer, often followed by some fishtailing. What you do with a RWD car is steering into the turn later, an only get on the throttle when the car is driving in a straight line.

The problem with a midengined car is that there is more mass in the back, so once you're oversteering, it's harder to correct. The weight distribution however enables you to enter a corner faster, which I wouldn't do on the public road, though.
 

·
Registered
mg_tf
Joined
·
1,996 Posts
Discussion Starter · #9 ·
I often think of doing a track day....but I worry about the stresses and strains of taking a road car around the track. I don't have race brakes or tyres, let alone the strains put on the car by aggressive cornering.

Maybe I worry too much....

mikef
 

·
Registered
Joined
·
6,086 Posts
I tend to find I drive the F alot smoother (in technique terms) echoing Chris T's comments.

Braking early is a must, also, when cornering maintain a constant - if you are accelerating don't lift off or brake.

I've had the back end step out on a few occasions in mine, it has always (to me atleast) been quite easy to correct with some countersteering. :)
 

·
Registered
Joined
·
1,030 Posts
Sorry, I disagree somewhat with the fast out part. The common mistake with a RWD car is that people get on the throttle too soon, causing an oversteer, often followed by some fishtailing. What you do with a RWD car is steering into the turn later, an only get on the throttle when the car is driving in a straight line.

The problem with a midengined car is that there is more mass in the back, so once you're oversteering, it's harder to correct. The weight distribution however enables you to enter a corner faster, which I wouldn't do on the public road, though.
the theory of slow in fast out is true of any car, any race driver will tell you this!

The principle is to get the car balanced before entering the corner and then drive into the apex. Once passed the apex slowly increase the throttle to ensure most momentum entering the straight. This method differs depending on corner type though.

if you waited until the car was straight then you wouldn't have a chance in hell on a race track. That said your opinion is a safe driving method which is suitable to public roads ;)
 

·
Registered
Joined
·
33,210 Posts
The main difference with a RWD car is that the rear of the car wants to overtake you. If you accelerate hard the rear accelerates slightly faster than the front. I know this sounds daft, but think about it. The only thing driving the front forward is the acceleration of the rear, unlike a FWD that drags the rear along with it. If your car is anything but straight when you lose traction on acceleration the rear will succeed.

Another point to note is aggresive engine braking. This will lock the rear wheels causing the car to spin as the front wheels still have traction and will slow quicker than the rear.

RWD requires more skill and more understanding than FWD. This is one reason that I love it so.

P.S. RWD is nothing new to us bikers. In fact the forces involved are much worse on a bike as you only have 2 contact points with the road and power to weight ratio is far superior to any car.
 

·
Registered
Joined
·
7,233 Posts
I often think of doing a track day....but I worry about the stresses and strains of taking a road car around the track. I don't have race brakes or tyres, let alone the strains put on the car by aggressive cornering.

Maybe I worry too much....

mikef
North Weald is an activity day and really quite kind to your car, nothing really to hit eather ;)
As far as track days are concerened, a few have set-up cars but most are pretty standard, even the tyres but expect a bit of shoulder scrub. Fortunately there are normally at least 2 MG sessions split between experienced and novice.
Certainly teaches you how your car handles and when its starting to break away.
 

·
Registered
Joined
·
27,269 Posts
North Weald is an activity day and really quite kind to your car, nothing really to hit eather ;)
Just don't let Stu Dickens talk you into trying out the drag strip to see if you can stop in time. I was a little over enthusiastic and put a flat spot on my tyre :doh:
 

·
Registered
Joined
·
2,749 Posts
Once passed the apex slowly increase the throttle to ensure most momentum entering the straight.
After my 'incident' which saw me spinning and rolling backwards onto the forecourt of a petrol station, I began paying much more attention to the way in which the car 'feels' in corners.... using the forces you experience, you can estimate the cars weight distribution if you get used to it.

What I tend to do coming out of the bends is use the steering wheel as a guide as to how much I can add throttle.... the straighter the steering wheel becomes as I come out of a corner, the further my foot is allowed to go down on the throttle... anyone else do this?
 

·
Registered
Joined
·
821 Posts
Whether a car exhibits understeer, oversteer, or neutral steer is a function, ultimately, of the balance between the vehicle's front and rear grip.

Tyre grip itself is a function of Co-Efficient of friction, Vertical Load applied (as a result of weight transfer) and Slip Angle. Tyre grip itself is merely a measure of the amount of accelerative force that tyre can generate, whether in forwards acceleration, rearwards (ie braking) or transverse (ie cornering).

The levels of acceleration that any given tyre can produce in any given direction can be plotted onto a graph producing what is known as a 'Traction Circle'. If the tyre is operating inside its traction circle then it is gripping, cross the boundary of the circle and the tyre is no longer gripping, but has started to slide. Thus, for eg, at maximum forward acceleration there is no grip available to develop any sideways acceleration and vice versa. Therefore it is possible to accelerate using throttle and corner or brake and corner (known as 'Trail Braking'), however it is a matter of balancing the fore/aft and sideways accelerative forces. This is what racing drivers do because it minimises the amount of time they are off the throttle - the problem is that most road drivers do not have the requisite level of driving skill to achieve this balance.


When a tyre is developing a cornering force, for reasons that are beyond the scope of this post, it actually has to develop a 'Slip Angle', ie the angle between the way the wheel is pointing and its actual direction of travel. As this slip angle increases so does the tyre's level of grip at a proportionate rate up to a maximum value where 'Breakaway' occurs.

So, in the case of understeer, the front wheels are producing less slip angle than the rears, therefore less grip, and, hence, the nose of the car runs wide. In the case of terminal understeer (such as locking up the fronts) then the front tyres have reached the break away point (remember the Traction Circle) and the car ploughs on in a straight line until such time as it has slowed sufficiently to regain grip, or you have run out of road and hit something.

In the case of oversteer the opposite applies, the rears produce less slip angle than the fronts, hence the tail starts to come round. Do nothing here and ultimately the car will spin.

Understeer is, therefore, a stable condition, whereas oversteer is an unstable condition. It is for this reason that road cars are generally set up to understeer (FWD cars are more notorious for understeer because the front tyres which develop all of the steering effort and most of the cornering effort are also those producing all the forward accelerative effort). Understeer is seen as safe for the average punter because if the driver mishandles the controls the understeer will merely continue, if they (as most likely) back off the throttle sharply, or (to an extent) brake then the car will come back into control.

Oversteer, on the otherhand, is seen as unsafe because, if you do nothing, or (worse) mishandle the controls then it will get worse, ultimately resulting in a spin. RWD vehicles are more prone to oversteer in poor conditions for 2 reasons:

1. Power oversteer. This is the most common form. To much power is applied to early. Since the power is applied at the rear wheels they reach the breakaway point earlier than the fronts.

2. Lift-Off oversteer. One of the factors affecting the grip level that a tyre can achieve is the Vertical Load applied to it. When ever a car acelerates, brakes, or corners then weight transfer occurs. In this case, coming off the throttle suddenly causes a forwards weight transfer, so there is less vertical load applied to the rear tyres so there grip is reduced and oversteer occurs.



Remmie said:
The problem with a midengined car is that there is more mass in the back, so once you're oversteering, it's harder to correct. The weight distribution however enables you to enter a corner faster, which I wouldn't do on the public road, though.
I'm sorry but that is totally inaccurate. The front/rear weight distribution is not the sole factor here, but the 'Mass Centroid Axis' and the moments about it. A mid engined car like the F/TF has its mass centroid towards the middle of the car giving it a low 'Polar Moment of Inertia' (PMI). This results in a car that is more nimble because, owing to the low PMI it will not resist direction changes, and will turn in to corners faster. This is why all real purpose designed race cars have been mid-engined since the early 1960s. Even Formula cars have a slight rearwards weight balance because it aids traction.

Take a car with a similar weight distribution overall but with a mass centroid(s) towards the ends of the car and it will have a high PMI. This will make it more stable but ultimately less nimble.

The very fact that a low PMI car will change direction fast means that if you get it oversteering and apply the correct amount of opposite lock in time and take the lock off as the oversteer ends then it will come out of the oversteer/spin extremely quickly. What catches most people out is they don't take the lock off fast enough and end up spinning in the opposite direction.

With a high PMI car, while it is more resistant to spinning, once the spin has started, it is far harder and takes far longer, to get the spin to stop.
 

·
Registered
Joined
·
5,647 Posts
Whether a car exhibits understeer, oversteer, or neutral steer is a function, ultimately, of the balance between the vehicle's front and rear grip.

Tyre grip itself is a function of Co-Efficient of friction, Vertical Load applied (as a result of weight transfer) and Slip Angle. Tyre grip itself is merely a measure of the amount of accelerative force that tyre can generate, whether in forwards acceleration, rearwards (ie braking) or transverse (ie cornering).

The levels of acceleration that any given tyre can produce in any given direction can be plotted onto a graph producing what is known as a 'Traction Circle'. If the tyre is operating inside its traction circle then it is gripping, cross the boundary of the circle and the tyre is no longer gripping, but has started to slide. Thus, for eg, at maximum forward acceleration there is no grip available to develop any sideways acceleration and vice versa. Therefore it is possible to accelerate using throttle and corner or brake and corner (known as 'Trail Braking'), however it is a matter of balancing the fore/aft and sideways accelerative forces. This is what racing drivers do because it minimises the amount of time they are off the throttle - the problem is that most road drivers do not have the requisite level of driving skill to achieve this balance.


When a tyre is developing a cornering force, for reasons that are beyond the scope of this post, it actually has to develop a 'Slip Angle', ie the angle between the way the wheel is pointing and its actual direction of travel. As this slip angle increases so does the tyre's level of grip at a proportionate rate up to a maximum value where 'Breakaway' occurs.

So, in the case of understeer, the front wheels are producing less slip angle than the rears, therefore less grip, and, hence, the nose of the car runs wide. In the case of terminal understeer (such as locking up the fronts) then the front tyres have reached the break away point (remember the Traction Circle) and the car ploughs on in a straight line until such time as it has slowed sufficiently to regain grip, or you have run out of road and hit something.

In the case of oversteer the opposite applies, the rears produce less slip angle than the fronts, hence the tail starts to come round. Do nothing here and ultimately the car will spin.

Understeer is, therefore, a stable condition, whereas oversteer is an unstable condition. It is for this reason that road cars are generally set up to understeer (FWD cars are more notorious for understeer because the front tyres which develop all of the steering effort and most of the cornering effort are also those producing all the forward accelerative effort). Understeer is seen as safe for the average punter because if the driver mishandles the controls the understeer will merely continue, if they (as most likely) back off the throttle sharply, or (to an extent) brake then the car will come back into control.

Oversteer, on the otherhand, is seen as unsafe because, if you do nothing, or (worse) mishandle the controls then it will get worse, ultimately resulting in a spin. RWD vehicles are more prone to oversteer in poor conditions for 2 reasons:

1. Power oversteer. This is the most common form. To much power is applied to early. Since the power is applied at the rear wheels they reach the breakaway point earlier than the fronts.

2. Lift-Off oversteer. One of the factors affecting the grip level that a tyre can achieve is the Vertical Load applied to it. When ever a car acelerates, brakes, or corners then weight transfer occurs. In this case, coming off the throttle suddenly causes a forwards weight transfer, so there is less vertical load applied to the rear tyres so there grip is reduced and oversteer occurs.





I'm sorry but that is totally inaccurate. The front/rear weight distribution is not the sole factor here, but the 'Mass Centroid Axis' and the moments about it. A mid engined car like the F/TF has its mass centroid towards the middle of the car giving it a low 'Polar Moment of Inertia' (PMI). This results in a car that is more nimble because, owing to the low PMI it will not resist direction changes, and will turn in to corners faster. This is why all real purpose designed race cars have been mid-engined since the early 1960s. Even Formula cars have a slight rearwards weight balance because it aids traction.

Take a car with a similar weight distribution overall but with a mass centroid(s) towards the ends of the car and it will have a high PMI. This will make it more stable but ultimately less nimble.

The very fact that a low PMI car will change direction fast means that if you get it oversteering and apply the correct amount of opposite lock in time and take the lock off as the oversteer ends then it will come out of the oversteer/spin extremely quickly. What catches most people out is they don't take the lock off fast enough and end up spinning in the opposite direction.

With a high PMI car, while it is more resistant to spinning, once the spin has started, it is far harder and takes far longer, to get the spin to stop.

Or, in not so many words...... Drive to the road conditions........ easy realy!!.;)
 
1 - 20 of 74 Posts
Top