Quote:
Originally Posted by Ilia@IND
What many mean when they say that an LSD equipped RWD car is just as good as AWD is that, in a RWD car one is able to adjust the attitude and direction of the vehicle easily in inclement weather.
A skilled driver is easily able to control the exact direction and yaw of a RWD car in any weather condition, and this makes RWD preferred to many enthusiasts.
AWD is excellent from a traction and straight line acceleration standpoint, but does not ultimately yield more mechanical grip in a cornering condition- although it does allow you to put a bit more power down while cornering, more easily.
I personally will take the RWD car on any day, in any condition. I prefer being in complete control of my car's behavior at all times.
|
Quote:
Originally Posted by JoeFromPA
AWD allows for superior control in a turn than RWD does. With rWd you can correct understeer with throttle or change the point of the nose travel through controlled rear slippage. But you can't control oversteer with RWD nor can you accelerate during a rear end slip.
With AWD you can do those things. You can use the gas to straighten out an oversteering car. You can induce oversteer if desired. Etc.
An LSD is an improvement over an open diff but it doesn't create throttle control at two ends of the car like AWD does.
|
In general I agree with both of what you have said. RWD will be more "fun" in the snow because you have more flexibility to rotate (i.e. induce yaw) the car since you only have one axle (the rear) putting down the power. AWD generally allows you to accelerate more confidently out of corners and would be less "fun" since power is going to both axles and you're less likely to unsettle the car when applying throttle.
I would clarify what Joe said about not being able to control oversteer in RWD; you can - just reduce your throttle
I would interpret the "AWD vs. RWD in the snow" comment differently than Ilia. I think most people are concerned with traction and not getting stuck rather than evaluating handling limits. Although I will concede finding those limits on an empty snow-covered road or parking lot is a lot of fun
AWD vs. RWD vs. LSD (limited slip diff) depends on your situation. Pure RWD or FWD with open differentials will put down the power fine in dry conditions but begin to suffer when it's wet, snowy, or icy. As mentioned in the article, an open differential will allow the wheel with less grip to spin and throw away much of your ability to accelerate. This is where an AWD system or LSD helps.
AWD will distribute power between axles (front and rear) whereas an LSD distributes power across one axle (left and right). If your left rear wheel is on ice, for example, and AWD system will transmit power to the front axle. Most AWD vehicles have an open front differential, so with your left rear wheel spinning, power would be going to the right rear and probably your left front wheel assuming both of those have traction. With AWD and open differentials front and rear, you would essentially have 2WD (two wheels with tractive effort). Without AWD (i.e. RWD with open differential) you would have 1WD (in this case the right rear wheel). And with this 1WD open differential scenario, the power the right rear wheel can put down is only as much as the left rear can put down on its very slippery icy - not much.
An LSD helps in a similar way but across the axle. In the same scenario, an LSD would allow torque transfer to both the left and right rear wheels, allowing you to accelerate if you have grip on the right rear wheel. Again, you have true 2WD with an LSD, or 1WD with standard RWD and one spinning wheel.
As you might expect, AWD + one (usually rear) LSD yields 3WD when one wheel is slipping and true 4WD would be available with AWD and LSDs on both axles.
So, AWD vs. RWD depends on which wheels are slipping and which have grip. It's impossible to predict this for every scenario, of course, but you might expect since the front wheels are farther from the spinning rear wheel than is the right wheel, you would have a better chance of accelerating with AWD than RWD + LSD because those would be farther from the slippery surface plaguing your rear spinning wheel. But in the situation where there is a long icy patch at a stoplight from everyone trying to accelerate, both left wheels might be on ice and so RWD + LSD would benefit you by putting power down to the dry right side rear wheel.
You could also think about weight transfer affecting traction too (more weight over wheels yields more traction). Think about accelerating in reverse up a hill. Your rear wheels are relatively lightly loaded compared to the fronts, so even with a RWD + LSD your traction could be minimal. AWD helps in this scenario since a lot of the weight is over the front wheels giving them more grip, and AWD would transfer some power to these fronts.
Each system has its benefits. On newer vehicles the downsides of open differentials can be partially overcome with traction control (TC) and/or having the brakes "act as an LSD." My suggestion is AWD + rear LSD + TC + snow tires. On bad weather days you will blow by practically everyone. Ask me how I know