AWD vs. RWD on a road course? Street?
08-20-2002, 03:19 AM
#1
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AWD vs. RWD on a road course? Street?
OK guys help me solve a little friendly argument I'm having with a co-worker. My feeling is that HP and weight being equal that a RWD car will handle better and be faster on a road course as well as the street when compared to and AWD car. This argument is excluding rain, snow etc. I'm arguing that a good driver will use a little oversteer in the RWD car to his advantage and that RWD tends to give more warning when near the limit. I also feel RWD is makes much better use of the available HP to propel the car out of corners and down the straights. He thinks I'm completely wrong or it only matters if we are talking about really good drivers who can fully take advantage of a car. He thinks the average amateur driver will be faster with AWD. Since I have no racetrack experience other than the dragstrip (where RWD rules the roost BTW) I thought I put this question to those of you who actually race.
08-20-2002, 10:36 AM
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There may just be too many variables to settle this argument fairly. Road cars or race cars? By which I mean, how much do you spend for the electronic/mechanical controls of the AWD splits? Front/rear splits on AWD cars can run from 90%/10%, to the extremes of off road with full locking diffs. Dry or wet conditions? Equal brakes? ref. C4S vs. C2S. on and on....
Anywho's, with that caveat, the only comparison I can make is from what I've seen at numerous DE events, and this is only a comparison of Porsches. With "amateur" drivers, I notice very little difference. Not enough for me to notice anyway. With experienced drivers, the C2's tend to be consistently slightly faster than C4's in the dry.
Anywho's, with that caveat, the only comparison I can make is from what I've seen at numerous DE events, and this is only a comparison of Porsches. With "amateur" drivers, I notice very little difference. Not enough for me to notice anyway. With experienced drivers, the C2's tend to be consistently slightly faster than C4's in the dry.
08-20-2002, 11:28 AM
#4
Race Director
[quote]Originally posted by Tom:
<strong>AWD Audis got themselves banned from Trans Am a few years ago because no one else could keep up with them.</strong><hr></blockquote>
I have to agree with the history lesson learned from the Audi story: AWD can be faster. HOWEVER:The driving style is very different for an AWD car: the line, the turn in, the apex: all these variables are different due to the different handling/traction characteristics of AWD cars.
[quote]Originally posted by Vinny:
<strong>snip...the only comparison I can make is from what I've seen at numerous DE events, and this is only a comparison of Porsches. With "amateur" drivers, I notice very little difference. Not enough for me to notice anyway. With experienced drivers, the C2's tend to be consistently slightly faster than C4's in the dry. </strong><hr></blockquote>
While the AWD on a modern 911 is a race-bred system, it is still engineered for street use. The audi AWD was fully for the track. That makes a difference, plus the fact that an AWD system will add more weight to the car. And the drivers of the C4 are probably driving the 'wrong' line: ie: one that does not allow the driver to take advantage of the AWD system.
Most instructors teach a line that is optimal for RWD cars, since probably 90% of the cars out there are RWD. Thus, many C4 drivers, even the experienced ones, will run this line.
Oh, and for street/real world driving: AWD is tons safer than RWD: that's why I have two Subarus! You just gotta deal with the torque steer that AWD/FWD cars exhibit.
Cool question.
-Zoltan.
<strong>AWD Audis got themselves banned from Trans Am a few years ago because no one else could keep up with them.</strong><hr></blockquote>
I have to agree with the history lesson learned from the Audi story: AWD can be faster. HOWEVER:The driving style is very different for an AWD car: the line, the turn in, the apex: all these variables are different due to the different handling/traction characteristics of AWD cars.
[quote]Originally posted by Vinny:
<strong>snip...the only comparison I can make is from what I've seen at numerous DE events, and this is only a comparison of Porsches. With "amateur" drivers, I notice very little difference. Not enough for me to notice anyway. With experienced drivers, the C2's tend to be consistently slightly faster than C4's in the dry. </strong><hr></blockquote>
While the AWD on a modern 911 is a race-bred system, it is still engineered for street use. The audi AWD was fully for the track. That makes a difference, plus the fact that an AWD system will add more weight to the car. And the drivers of the C4 are probably driving the 'wrong' line: ie: one that does not allow the driver to take advantage of the AWD system.
Most instructors teach a line that is optimal for RWD cars, since probably 90% of the cars out there are RWD. Thus, many C4 drivers, even the experienced ones, will run this line.
Oh, and for street/real world driving: AWD is tons safer than RWD: that's why I have two Subarus! You just gotta deal with the torque steer that AWD/FWD cars exhibit.
Cool question.
-Zoltan.
08-20-2002, 11:30 AM
#5
Burning Brakes
All things being equal (including weight) I would think AWD would be faster because you are distributing the driving torque amongst more wheels and thus maximizing the total tractive forces rather then just loading up two wheels. But as Vinny said there are alot of variables to consider.
08-20-2002, 12:07 PM
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By the way, Q. Boom, what do you have packin' in that 10 sec. Mustang? My very first car was a '69 with a 302 (that's before they became 5.0's) 
With the tires of the day and my newbie driving skills it would take me 10 seconds to pull out of the driveway.
It was my only ride, and just a "JOY" in the snow. Terrific smiles for dollars quotient...fond memories.
With the tires of the day and my newbie driving skills it would take me 10 seconds to pull out of the driveway.It was my only ride, and just a "JOY" in the snow. Terrific smiles for dollars quotient...fond memories.
08-20-2002, 04:28 PM
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Equal cars I think the AWD would win on a road course. He should be able to get on the throttle earlier and has more traction under acceleration. If it was legal in ALMS I bet the GT3RS would have it.
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08-21-2002, 12:57 AM
#8
Burning Brakes
The only times that AWD is faster is when there's too much power to hook up with just 2 tires driving. With most street cars the threshold is probably around 300 hp. A new 996 with huge rear tires can probably handle a little more. If 2 tires are enough to hook up the power out of the turns, the rwd will be faster not only because of the cornering advantage you mention, but also because it won't have another differential wasting some of the power.
08-21-2002, 02:37 AM
#9
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I posted the question here mainly due to the fact that Porsche has relatively equal cars in the C2S and C4S with the main difference being RWD vs. AWD. My question was aimed at all around usage for the car in the dry i.e. some dry track time and some dry street time. Obviously as road conditions worsen the traction threshold for a RWD car becomes it's weak point. Thanks for the replies, keep them coming.
PS to the question of my 10sec Mustang, I'm on the verge of trading it's engine to my brother in exchange for a 79 widebody targa roller, boxes of parts and some cash. My plan is to convert the car back to a super reliable (and cheap to maintain) bracket car using a junkyard 351w. The motor I'm getting rid of is a '69 block 351w punched out to 410", steel billet crank and rods, custom 13.5:1 Probe pistons, TFS "Street Heat" Stage IV heads, ported and polished Edelbrock Super Victor Intake, Carb Shop 950cfm carb, MSD 7al3 ignition with crank trigger, Essex fuel system with 5/8" feed and 3/8" return lines at 45PSI before the regulator, Moroso 7 quart drag pan, neutral balance on the crank, Ram billet flywheel, Summit balancer, Crane Gold race rockers (1.7 ratio) Manley hardened pushrods, triple valve springs, Crane solid lifters, custom grind Crane cam approx .695" lift and 310 degree duration @ .050. All told roughly 650+ HP comes on like a light switch at 3000 rpms, I shift a custom built pro-shifted Top-loader 4-spd at 7000rpms with a B&M verti-gate inline shifter sending power to a very beefed up 8.8" Ford rear end with Strange Engineering axles, spool and 4.10 gears on 10x28" slicks (15 PSI) Best 60' time was 1.45 seconds and best ET was 10.72 at 133mph if I remember right. I haven't raced it in 3 seasons due to work and a 3 yr old daughter. Someday I might build another super fast drag car but for now I'm vey content to be seriously ill with this P-car bug that has bitten me.
I'm even planning my first DE for early next spring!
PS to the question of my 10sec Mustang, I'm on the verge of trading it's engine to my brother in exchange for a 79 widebody targa roller, boxes of parts and some cash. My plan is to convert the car back to a super reliable (and cheap to maintain) bracket car using a junkyard 351w. The motor I'm getting rid of is a '69 block 351w punched out to 410", steel billet crank and rods, custom 13.5:1 Probe pistons, TFS "Street Heat" Stage IV heads, ported and polished Edelbrock Super Victor Intake, Carb Shop 950cfm carb, MSD 7al3 ignition with crank trigger, Essex fuel system with 5/8" feed and 3/8" return lines at 45PSI before the regulator, Moroso 7 quart drag pan, neutral balance on the crank, Ram billet flywheel, Summit balancer, Crane Gold race rockers (1.7 ratio) Manley hardened pushrods, triple valve springs, Crane solid lifters, custom grind Crane cam approx .695" lift and 310 degree duration @ .050. All told roughly 650+ HP comes on like a light switch at 3000 rpms, I shift a custom built pro-shifted Top-loader 4-spd at 7000rpms with a B&M verti-gate inline shifter sending power to a very beefed up 8.8" Ford rear end with Strange Engineering axles, spool and 4.10 gears on 10x28" slicks (15 PSI) Best 60' time was 1.45 seconds and best ET was 10.72 at 133mph if I remember right. I haven't raced it in 3 seasons due to work and a 3 yr old daughter. Someday I might build another super fast drag car but for now I'm vey content to be seriously ill with this P-car bug that has bitten me.
I'm even planning my first DE for early next spring!
08-21-2002, 04:31 AM
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IMHO, with the proper weight distribution (60%+ rear weight bias in mid-engined car) a rwd car will be superior unless you have stratospheric horsepower levels. With their front engines, the Trans Am cars of the mid 80's had huge amounts of power, especially when compared with their rear grip. In this situation, Audi's awd superiority is not too surprising. Further, Audi's success in the BTCC in the late 90's mostly came against fwd racecars which share many of the negatives of the awd design. Further, the BMW's with their rwd but still poor (in race car terms at least) f/r weight bias were typically the Audi's closest challenger.
Put the engine behind the driver and the rwd car should be superior to the awd in the dry. Even at the same weight and horsepower, the rwd will still be superior because it lacks the added drivetrain drag, weight distribution penalty, and front tire overloading of a awd setup.
The mid engine rwd design reigns supreme for a race car because it allows no driveshaft, a low polar moment of inertia, near equal weight distribution under braking and a largely rearward weight distrbution under acceleration. The 911's rear engine design maximizes the weight distribution advantages for braking and acceleration, at the expense of a higher polar moment of inertia and too little weight over the front wheels on corner exit.
It is highly doubtful that we will ever see any road racing with purpose built racecars allowing 4wd. There were some very early Grand Prix cars that had some successes, as well as less successful Indianapolis cars. The highest level road racing 4wd racecar I can think of right now is the Audi S4 in the Speedvision Cup series, which is far from what I consider to be a purpose built racecar.
On another note, several years ago I remember hearing the WRC guys complaining about the F2 (highly tuned lightweight fwd 2 liter normally aspirated) rally cars actually beating the awd WRC times on tarmac rally stages.
Put the engine behind the driver and the rwd car should be superior to the awd in the dry. Even at the same weight and horsepower, the rwd will still be superior because it lacks the added drivetrain drag, weight distribution penalty, and front tire overloading of a awd setup.
The mid engine rwd design reigns supreme for a race car because it allows no driveshaft, a low polar moment of inertia, near equal weight distribution under braking and a largely rearward weight distrbution under acceleration. The 911's rear engine design maximizes the weight distribution advantages for braking and acceleration, at the expense of a higher polar moment of inertia and too little weight over the front wheels on corner exit.
It is highly doubtful that we will ever see any road racing with purpose built racecars allowing 4wd. There were some very early Grand Prix cars that had some successes, as well as less successful Indianapolis cars. The highest level road racing 4wd racecar I can think of right now is the Audi S4 in the Speedvision Cup series, which is far from what I consider to be a purpose built racecar.
On another note, several years ago I remember hearing the WRC guys complaining about the F2 (highly tuned lightweight fwd 2 liter normally aspirated) rally cars actually beating the awd WRC times on tarmac rally stages.
01-24-2003, 01:32 PM
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guys, according to Excellence Porsche mag, Porsche test drivers drove the same course at top speeds and the AWD C4S bettered the RWD C2 by several seconds. And we all know, seconds at high speed is a long ways. It was noted that the C2 is faster on acceleration, but still lost the test, by I wish I could recall how much, but significantly.
01-24-2003, 01:46 PM
#12
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Here's another interesting find regarding the AWD vs.RWD debate:
Last fall, in Grassroots Motorsports, they did a AWD vs. RWD vs. FWD comparison test to see which platform was 'King of Grip.' (Cars were: AWD: Subaru WRX, RWD: BMW 3-series, FWD: Acura RSX).
While the cars weren't equal in hp, weight dist...etc, they were pretty close. They ran an autocross type course on a dry and then wet course. IIRC, the course was on Tire Rack's proving grounds. Same type street tires were used for the test.
The results?
In the dry:
1st place: WRX
2nd place: BMW
3rd place: RSX
In the wet:
1st place: WRX
2nd place: RSX
3rd place: BMW.
Seems AWD is the winner. But I'll take a RWD Porsche to play with anyday!
Regards,
-Z.
Last fall, in Grassroots Motorsports, they did a AWD vs. RWD vs. FWD comparison test to see which platform was 'King of Grip.' (Cars were: AWD: Subaru WRX, RWD: BMW 3-series, FWD: Acura RSX).
While the cars weren't equal in hp, weight dist...etc, they were pretty close. They ran an autocross type course on a dry and then wet course. IIRC, the course was on Tire Rack's proving grounds. Same type street tires were used for the test.
The results?
In the dry:
1st place: WRX
2nd place: BMW
3rd place: RSX
In the wet:
1st place: WRX
2nd place: RSX
3rd place: BMW.
Seems AWD is the winner. But I'll take a RWD Porsche to play with anyday!
Regards,
-Z.
01-24-2003, 02:47 PM
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AWD is faster, all else being equal, with the car properly set up for AWD and tracking as such, and driven using the proper line as noted. It's no contest.
Z - you ever track that SVX? That'd be pretty sweet...
Anyway, rather comparing apples to oranges here, but the AWD Escort Cosworth RS that regularly races here (Waterford Hills) regularly embarasses the RWD V8 GT1 Trans-Am type cars. There really is no contest, when you can put the power down so much more efficiently. It take experience to learn to drive, and to know how to set the chassis up properly, but it will be faster. I'd definitely take an AWD over RWD, they're so much faster and just as fun!
Z - you ever track that SVX? That'd be pretty sweet...
Anyway, rather comparing apples to oranges here, but the AWD Escort Cosworth RS that regularly races here (Waterford Hills) regularly embarasses the RWD V8 GT1 Trans-Am type cars. There really is no contest, when you can put the power down so much more efficiently. It take experience to learn to drive, and to know how to set the chassis up properly, but it will be faster. I'd definitely take an AWD over RWD, they're so much faster and just as fun!
01-24-2003, 03:31 PM
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Vaughan: Though the SVX has never seen track time, I did autocross it once: talk about a bull in a china shop! That thing is very nose heavy, and it's AWD system isn't as 'seamless' as when driving on the street in the rain.
Regarding driving the SVX on the track: I suppose it would behave similarly to a 928: it's about the same thing (a grand touring car), but the SVX has AWD to boot!
-Z.
Regarding driving the SVX on the track: I suppose it would behave similarly to a 928: it's about the same thing (a grand touring car), but the SVX has AWD to boot!
-Z.
01-24-2003, 04:35 PM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Kent M. Wood:
[QB]guys, according to Excellence Porsche mag, Porsche test drivers drove the same course at top speeds and the AWD C4S bettered the RWD C2 by several seconds. And we all know, seconds at high speed is a long ways. [QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Different brakes, wider rubber in addition to the AWD difference.
Too many variables.
[QB]guys, according to Excellence Porsche mag, Porsche test drivers drove the same course at top speeds and the AWD C4S bettered the RWD C2 by several seconds. And we all know, seconds at high speed is a long ways. [QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Different brakes, wider rubber in addition to the AWD difference.
Too many variables.