FWD

[Speed898]

Hello everyone this is my first post and I just want to know what is your technical opinion of fwd cars, I have a classic mini and have been thinking about buying an engine swap kit, they make both rwd and fwd swap kit for it, I know almost all professional racing cars are either rwd or awd but just how much of an advantage does rwd have over fwd?

[DiogoBrand]

I don't think there's any big advantage to making a mini RWD. The power and weight figures don't justify it, and since the wheelbase and rear weight are relatively small you may strugle for traction and stability.
If you plan on a high increase in power, and/or any competitive application then RWD may help, but otherwise I wouldn't do it.
To me the Classic Mini formula is pretty much perfect as it is: small and nimble car with a power figure that matches the car, and FWD suits this formula very well.

[Speed898]

It will be my weekend track car and plan on using it in some time attacks, I don't have an exact power figure yet but it will be in the 300 to 400 hp range. I know that the main disadvantages in fwd car are:
-Under acceleration, weight is shifted to the rear.
-torque-steer
I do like the simplicity of it being fwd instead of having to cut the chassis to get it to be rwd, that why I asked this question to see just how much of a disadvantages I am at when racing against rwd cars and if rwd would be worth it.

[strad]

I would not suggest converting a Mini to rear wheel drive but in general I despise FWD. Giant farce perpetrated on the public to make it cheaper and easier for the manufacturers.

[Speed898]

I would not suggest converting a Mini to rear wheel drive but in general I despise FWD. Giant farce perpetrated on the public to make it cheaper and easier for the manufacturers.

I am a big fan of rwd, I grew up around them, but recently I been taking a liking to fwd cars, they give you a new feel and my new daily driver is fwd. But back to the mini, I am trying decide on which drive sytem to go with, the main thing I want is great handling that's my main concern everything else is second, I would like to keep it fwd since it's a very simple setup and very compact since everything is upfront, but if I am at a great disadvantages when racing against rwd car, then going the rwd route would be the better option. So I ask the question to see if any one had any suggestions to help tackle the disadvantage that comes with running forward wheel drive

[DiogoBrand]

If you are planning on getting over 300hp then it actually becomes hard not to recommend going for RWD, FWD probably can't handle so much power that well. But keep in mind that the short wheelbase and low weight will likely make it tricky to tame all those horses going into the rear wheels.

[strad]

the main thing I want is great handling that's my main concern

Well then you do not want FWD with it's inherent understeer.. not to mention it's short wheelbase .. ever seen footage of Mini rollovers? Or any short wheelbase front wheel drive car?
Best bet is to invest in a lowering/handling package .
There was a great quote from a Ford executive when asked about some even hotter SVT Focus or the like was forth coming and he said that "Ford was not in the business of putting their customers in the weeds."
You get into that kind of horsepower thru FWD you better really be on your game.
Good Luck .... seriously

[Speed898]

Yea rollover is taken into consideration. I plan on lowering the car, upgrading the suspension and adding aero parts to it.
I want to do something similar to this
http://jalopnik.com/5397825/huge-front- ... n-tcs-fwd/ with the mini, since I seen this car run before and it amazing that its a fwd car. But if you guys are recommending for me to go with rear wheel drive instead I will look more into it, I just want to see if I could still work with the fwd design of the mini without having to chop up the chassis.

[giantfan10]

Yea rollover iso taken into consideration. I plan on lowering the car, upgrading the suspension and adding aero parts to it.
I want to do something similar to this
http://jalopnik.com/5397825/huge-front- ... n-tcs-fwd/ with the mini, since I seen this car run before and it amazing that its a fwd car. But if you guys are recommending for me to go with rear wheel drive instead I will look more into it, I just want to see if I could still work with the fwd design of the mini without having to chop up the chassis.

pros and cons:
FWD:
+ Handling characteristics are easier for inexperienced drivers to control
- Weight is very poorly distributed (60% front, 40% rear, or worse)
- Heavier front makes the car understeer (front plows) at handling limits
- Front wheels are providing force to go, turn, and stop. Easy to overwhelm them
Uneven traction/power application causes the wheels to turn the steering wheel without driver input. As a result, FWD is very bad at putting down more than about 200 hp without electronic aids. plan on having electronic aids on your mini?
- When the car accelerates, its weight shifts back onto the rear wheels, reducing traction at the front. This causes wheelspin and exacerbates torque steer.
Notice that FWD's advantages are primarily in packaging, cost, and ease of use, and its downsides are primarily in handling. See why one would not use it in a sporty car?
RWD:
xcellent weight distribution (easy to achieve 50/50, which dramatically improves handling)
+ Rear wheels only handle propulsion; front wheels only handle turning and stopping. Separating these jobs allows them to utilize the maximum amount of traction, improving handling at the limit
+ When the rear wheels lose traction, it is possible to "steer" the car using the throttle (more throttle to kick the tail out for a tighter turn, less to bring it back in line)
+ Rearward weight transfer creates better traction when accelerating
+ Symmetrical design
+ Not that much more drivetrain loss than FWD
- Poor traction in slippery conditions relative to FWD unless ballast is added above drive wheels
- Handling characteristics are harder for inexperienced drivers to control
So RWD is harder to use, but all of its positive characteristics aid in power delivery and handling. Perfect for a sports car!

there you have your answer lol =D>

[Tim.Wright]

How does the RWD solution work? Is the engine also mid/rear mounted? I assume the the suspension would have to be completely new too sin the stock spindles wouldn't have the necessary interface for a CV joint.

This is the important stuff to know as I can't imagine anything worse handling than a RWD drivetrain in a front weight biased vehicle designed for FWD.

[Speed898]

How does the RWD solution work? Is the engine also mid/rear mounted? I assume the the suspension would have to be completely new too sin the stock spindles wouldn't have the necessary interface for a CV joint.

This is the important stuff to know as I can't imagine anything worse handling than a RWD drivetrain in a front weight biased vehicle designed for FWD.

The rwd kit basically looks like this http://www.minimania.com/COMING_SOON__V ... heel_Drive_
It turn the mini into a mid engine car. The entire rear suspension has to be redone

[Vyssion]

... just how much of an advantage does rwd have over fwd?

Actually quantitatively calculating the advantage is tricky due to there being so many factors that make up basis for how a vehicle handles. The major reason that RWD is superior to FWD (oversimplified), is the transfer of effective sprung weight of the vehicle (as people here have mentioned). Basically, as a car accelerates, the centre of mass is shifted backwards which means that there is more weight over the rear wheels; This serves to increase the normal force between the rear tires and road surface. As frictional force is directly proportional to this (normal) force, the rear tires have increased grip under acceleration. The same principles apply with deceleration (braking) which is why our main braking system (brake pedal as opposed to handbrake) is on the front wheels. In vehicle dynamics terms, the transfer of effective mass is explained by Einstein's theory of equivalence, that the effects of gravity and acceleration are equable. This means that as you accelerate, it's as if gravity is acting on the rear of the car more than the front.

I have written a post in another forum which delves into this in more depth here. It is referring to downforce rather than weight transfer, but the physics behind it is the same. If you swap out the "Fd" (Downforce) value for a percentage of additional vehicle weight force being shifted to the rear wheels, you should be able to see how the two are alike.

Essentially, the generation of downforce is the way that allows for the car to (in lamans terms) "be heavier than it actually is, without the bad stuff that comes with an increased weight".

The downforce and the normal (weight) force of the vehicle is the simplified mechanism by which the tyres gain their grip. And again, over-simplifying things for a purely aero discussion, the more grip you have, the faster you can theoretically corner at.
(Can't display an actual 'mu' symbol so will refer to it as C_f from here)

The "N" denotes normal force which is made up of the vehicles weight force and any downforce currently being produced.


If you combine this equation with the formula for centripetal acceleration (which could be adapted to fit a corner if a constant radius)

and rearranged to give:


Then you get the following formula:


This then shows that for a constant coefficient of friction, that velocity is proportional to (meaning that an increase in the right hand side of the equation will increase the left hand side). If this is differentiated to get this in terms of time, it shows that time is proportional to (or simply that it is inversly proportional).

The important term here is this which is often referred to as the "specific downforce" of the vehicle. So if we are to increase this term, by means of increasing downforce or reducing the cars mass, the theoretical maximum velocity we can corner at will increase and hence the time taken to travel the corner will decrease. Add in that since you can carry more speed through the corner, braking time is reduced in the lead up to it and the acceleration beyond it begins from a higher speed, and you can begin to see the benefits.

By increasing mass initially, this would have the effect of decreasing this term, which would be counter productive.

This argument here is purely from an aerodynamic standpoint (and extremely simplified!!!) though and doesn't even mention things like the weight transfer or suspension changes and other vehicle dynamic effects that would be required to handle the higher initial weight during a race. But hopefully it helps explain why it is the way it is!!

[strad]

Whoa ,Whoa, Whoa
IF you want a RWD car..Buy one..I can not see chopping up a Mini to turn it into a RWD car with no doubt many problems to be sorted....go the easy way and get something you like that's rear wheel drive to begin with.

[Speed898]

Whoa ,Whoa, Whoa
IF you want a RWD car..Buy one..I can not see chopping up a Mini to turn it into a RWD car with no doubt many problems to be sorted....go the easy way and get something you like that's rear wheel drive to begin with.

I am not looking specifically for a rwd car, I just want a track day car, something I can take on the weekend to the track, I already have the mini and it just sitting in my garage, since I bought a new daily driver. The conversion for turning it rwd is not as uncommon as you may think. Most kit are pretty good and it just a matter of cutting the chassis a bit to get everything to fit and welding/ bolting it in place. Apart from having the mini already, I also have a savage hayabusa engine that I bought at a junkyard not so long ago for a really, really good price and that will be it's new engine for it. Again I would like to keep it fwd but from what everyone is saying it looks like rwd would be my best option, apart from going with electronic aids which I am pretty sure I can't afford it and I never seen any for sale to the general car market.

[BanMeToo]

Just my opinion... keep it FWD, put down 200 or 250hp, and have fun. If that's not the car you want to track, do what strad said.