Darius Juca

It allways depends on the driver mainly but usually RWD is faster due to weight and ballance . I do love the AWD for their traction and they are forgiving...........

DDP

here ya go

FSAEracer03

I have to disagree. In the real world, there never really is an "all things equal" situation. AWD robs power and adds weight. They're great in non-dry situations, but otherwise don't pose gains over rear-drive.

Even in a perfect world where weight, center of gravity, wheel hp, gearing, etc. are all equal the AWD car still can't get past one fact: they overwork the front tires. FWD and AWD cars can be setup up to have stiff rears and induce oversteer on will, but they don't act neutrally in a steady-state corner. They do require very different driving styles, but AWD just scrubs off too much speed with understeer just like FWD does. You can't ask the front tires to take large sideloads while still having to apply a driving force.

rhesus

Isn't that where this supposedly 'smart' LSD comes into play?

Tomas L

Yes, in the real world things will not be "all things equal". In the real world it will even be hard to compare two RWD cars with each other due to the fact that most design decitions imposes compromises which will make them good at different things.

In a very low power car running on a dry high speed track rwd will be faster due to the weight added. But you don't have to add much power before the scale tips over. Even in this rwd forum we see people claiming that over 350 rwhp is meaningless because of traction problems. At that power level AWD will absolutely give a gain even with the added weight.
I don't think this is correct. In medium to high speed corners, the steering angle will be small and therefore the extra load added to the front wheels by this will be small. Much smaller than the extra load you put on the rear wheels on exiting that corner in an rwd car. Here you can apply more accelerating force if you split it on four wheels (not an 50-50 split though).
In a low speed corner the steering angle will be larger and the front tires will be much more loaded than the rears. Still, out of the corner when you start to straighten the front wheels you will get better acceleration with awd because of the lack of grip on an rwd car. You may have to select another line through the low speed corner with awd.

Tomas

Tomas L

Yes, a lot can be done with smart control over the front/rear drive split.

Also remember that the optimum value for things like weight distribution will be different on an awd car compared to an rwd car.

RKD in OKC

Didn't AWD Audis compete in the Speedvision GT series for years.

All of the car models in that series are handicapped in some way to even out the competition. To find the the answer as to which configuration was better one might find what the specs were for the different RWD cars were compared to the Audis.

hmd

Well it's all theoretical you have to nominate the 'real' 4wd and rwd cars you want to compare, as I have.

I know which one I would pick between a 951 rwd or 996 TT 4wd

rhesus

951 and STi was what I was thinking.
With the 951 having about 300 RWHP and some minor suspension upgrades.

sweanders

BMW and Porsche have well working AWD systems and yet they build their cars intended for track use with RWD. Doesn't that fact tell you something?

hmd

well mine 951 had only factory 250bhp with 968CS M030 suspension and Street Legal Race tyres Dunlop DO1J.

a 300rwhp would be something else

FSAEracer03

Well... not to sound offensive, but you can think what you like, but physics is physics. There is such thing as a traction circle and it's a nice graphical representation of what I'm talking about. Combining cornering loads with accelerational loads gives you a higher combined force on a tire. It's the same principle that lead to "brake in a straight line." I won't go into trail braking for now, but that's a rule of thumb.

Over 350whp useless? Ha, that kinda made me chuckle You might want to ask anyone in mid-level racing categories what they have to say about that. Hell, ask some of the lower level classes and club racers what they have to say about that.

Sorry Tom, but spend more time at the track, drive more on the track and take higher level classes on this stuff... I think you'll see why all of the top forms of road racing seem to be strictly RWD.

...Anders, that's a very good point. Relates to this very well.

sweanders

The point about certain power levels becoming useless does apply in some types of racing where tire sizes are limited. And I've heard 928 racers say that once they get a bump from 500 to 550 rwhp the power became very hard to apply without spinning the wheels. There are both advantages and disadvantages with AWD systems, I've had the pleasure of driving a 650 hp 993tt track toy were the owner/driver has disconnected the front wheels because of "plowing" tendencies creating understeer (all four wheels spinning with R-compounds) when exiting corners.

For me I'd always prefer a rwd track car, on the street I'd probably go a different route because of the limited grip because of surface and tires. I just love the way a AWD car pulls you out of a drift when the front wheels hook up.

Rob in Oz

Interestingly, our club had a sprint day at a "power" track and there was a WRX STi along, as wellas a Ferrari Modena 360. As has been said before, a lot is driver dependent, but here's some times to look at. BTW, my club is extremely competitive, with most cars running semi-slicks and suspension/engine mods, so don't be misled by the 2.7 911 being right up there - it weighs 900kg and does 13.7 in the quarter.....

Mine is the 944T (the only one!) - on street tyres.

Regards

Rob

Pos Vehicle Cap Fastest Lap
1 993T 3.3 1:17.86
2 993TT 3.6 1:18.86
3 993GT2 3.6 1:20.25
4 930 3.4 1:21.88
5 GT3 3.6 1:22.28
6 GT3 3.6 1:22.43
7 GT3 3.6 1:22.49
8 996TT 3.6 1:22.82
9 GT3 3.6 1:23.49
10 993TT 3.6 1:24.57
11 930 3.3 1:24.64
12 911 3.6 1:24.75
13 GT3 3.6 1:25.10
14 996TT 3.6 1:25.89
15 996TT 3.6 1:26.10
16 911 2.7 1:27.10
17 911 3.6 1:27.12
18 911 3.6 1:27.26
19 911 3.0 1:27.46
20 911 3.0 1:27.69
21 964RS 3.6 1:27.86
22 911RS 2.7 1:28.32
23 GT3 3.6 1:28.43
24 911 3.6 1:30.17
25 964C4 3.6 1:30.23
26 Boxster S 3.2 1:30.28
27 Ferrari 360 Modena 3.6 1:30.33
28 968CS 3.0 1:30.75
29 Boxster S 3.2 1:30.88
30 911 2.8 1:31.75
31 911 3.0 1:32.74
32 911 3.2 1:32.79
33 944T 2.5 1:32.86
34 Giocattolo 5.7 1:33.21
35 Subaru WRX STI 2.0 1:33.27
36 911 2.7 1:34.16
37 911 3.6 1:34.84
38 Renault Clio Sport 2.0 1:35.14
39 911 2.7 1:44.11
40 928 4.5 1:51.54

Tomas L

One reason might be this, from the FIA GT2 technical regulations:
First, I think you failed in your effort not to sound offensive. Feel free to comment my post with technical arguments, otherwise I have better things to do with my spare time.
I agree that there is a point mid corner where awd will lessen the front wheel grip. At this point however you're more or less at constant speed and even if you loose some speed here, and it woun't be much, it's very difficult for someone to overtake. Very soon after you begin to accelerate (with an rwd) out of the corner you have to increase your turning radius (straighten the front wheels) otherwise you will end up outside the traction circle for the rear wheels which are transmitting all accelerating force. At this point you will have excess grip at the front wheel which can be used for transmitting more driving force to the track. With a properly designed awd control system you can use this grip, to say that you will be slower if you use all availible grip is really beyond my knowledge of physics.
AWD, if properly designed, only adds weigth, complexity and some drivetrain loss. Depending on the application these factors may overshaddow the gains made by awd, but to say that awd as a principle has disadvantages is something I don't understand.

Did it really become faster as an rwd? It certainly feels more comfortable with rwd because of this but it should really be slower, unless Porsche dialed in way to much front drive split for this application.

Tomas