RWD Track impressions.
#32
06-17-2008, 07:50 PM
Good write-ups by all. I love my AWD, but then, I'm a green student and AWD inspires confidence in me. But I love to read about the experimentation by those that have the means and desire to pursue advanced at one-ment with machine and the road.
#33
06-17-2008, 09:09 PM
Looking forward for data analysis Tom, thanks for taking the time.
If on your first outing you are as fast as when you were AWD, expect another 1-2 seconds easily with another session or two if you take the time to improve the settings and driving style. I would have expected you to be slower. The LSD will cause understeer, the impact of the removal of the front diff on handling is negligeable in relation to mass transfer, since it is located very low in the chassis, centered, and on/behind the front axle not ahead of it, you need to dial your suspension accordingly to the new handling characteristics due to the loss of pull from the front and the new presence of LSD in the rear, not due to the weight bias.
Experiment more with trail braking, and throttle steering, you can also feel much more the impact of mass transfer on handling while cornering and exiting as you apply the throttle and release vs. when you are in 4WD mode.
After some time, throttle application becomes second nature and you don't even need to be extra careful, you feel the limit, and end up going faster as confidence in the new setup and predictability of how the car will behave grows. A LOT of suspension fine tuning is required with the help of the datalogger and attention to the car behaviour while driving.
If on your first outing you are as fast as when you were AWD, expect another 1-2 seconds easily with another session or two if you take the time to improve the settings and driving style. I would have expected you to be slower. The LSD will cause understeer, the impact of the removal of the front diff on handling is negligeable in relation to mass transfer, since it is located very low in the chassis, centered, and on/behind the front axle not ahead of it, you need to dial your suspension accordingly to the new handling characteristics due to the loss of pull from the front and the new presence of LSD in the rear, not due to the weight bias.
Experiment more with trail braking, and throttle steering, you can also feel much more the impact of mass transfer on handling while cornering and exiting as you apply the throttle and release vs. when you are in 4WD mode.
After some time, throttle application becomes second nature and you don't even need to be extra careful, you feel the limit, and end up going faster as confidence in the new setup and predictability of how the car will behave grows. A LOT of suspension fine tuning is required with the help of the datalogger and attention to the car behaviour while driving.
#34
06-17-2008, 09:28 PM
Thank you both HeavyChevy and Tom for the writeups; they are quite educational. This is not a thread of AWD vs RWD; it is good to see both are working depending on ones need... Great win/win situation.
#35
06-18-2008, 02:50 AM
Join Date: Jul 2006
Location: ga
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Looking forward for data analysis Tom, thanks for taking the time.
If on your first outing you are as fast as when you were AWD, expect another 1-2 seconds easily with another session or two if you take the time to improve the settings and driving style. I would have expected you to be slower. The LSD will cause understeer, the impact of the removal of the front diff on handling is negligeable in relation to mass transfer, since it is located very low in the chassis, centered, and on/behind the front axle not ahead of it, you need to dial your suspension accordingly to the new handling characteristics due to the loss of pull from the front and the new presence of LSD in the rear, not due to the weight bias.
Experiment more with trail braking, and throttle steering, you can also feel much more the impact of mass transfer on handling while cornering and exiting as you apply the throttle and release vs. when you are in 4WD mode.
After some time, throttle application becomes second nature and you don't even need to be extra careful, you feel the limit, and end up going faster as confidence in the new setup and predictability of how the car will behave grows. A LOT of suspension fine tuning is required with the help of the datalogger and attention to the car behaviour while driving.
If on your first outing you are as fast as when you were AWD, expect another 1-2 seconds easily with another session or two if you take the time to improve the settings and driving style. I would have expected you to be slower. The LSD will cause understeer, the impact of the removal of the front diff on handling is negligeable in relation to mass transfer, since it is located very low in the chassis, centered, and on/behind the front axle not ahead of it, you need to dial your suspension accordingly to the new handling characteristics due to the loss of pull from the front and the new presence of LSD in the rear, not due to the weight bias.
Experiment more with trail braking, and throttle steering, you can also feel much more the impact of mass transfer on handling while cornering and exiting as you apply the throttle and release vs. when you are in 4WD mode.
After some time, throttle application becomes second nature and you don't even need to be extra careful, you feel the limit, and end up going faster as confidence in the new setup and predictability of how the car will behave grows. A LOT of suspension fine tuning is required with the help of the datalogger and attention to the car behaviour while driving.
73 lbs isnt negligible no matter how low it is concerning balance unless it's unsprung weight. In fact that same 73 (well 53 or so) lbs is more negligible to acceleration than it is to handling by a large margin because of the reasons you mentioned. I'll give you that it wouldnt be as bad as if it were ahead of the axle. But the car will handle better with the driveshaft in the car, even in RWD. I'm not interested in putting an LSD in the car, getting more rear end grip and consequently more push.
I've done more than enough tracking to know how to apply throttle, granted it's still tricky with turbo's and lots of torque. I have data too and can show exactly where the RWD would hurt you at Barber. And when I go back I'll have data showing how much faster I will go.
The best thing is that we can all weigh the options and decide what's best for us individually. But at least we have two sides of the coin to see from a track perspective.
#36
06-18-2008, 07:25 AM
Registered User
Very surprised in both Tom's and Dez' reviews... I expected what Tom reported... I agree 110% with Jean. PMI is going to be impacted much less, given where the weight is in the chassis. Removing it isn't the same effect as the whole "full tank of gas vs. 1/4 tank of gas" comparison...
Mike
Mike
#37
06-18-2008, 08:37 AM
Looking forward for data analysis Tom, thanks for taking the time.
If on your first outing you are as fast as when you were AWD, expect another 1-2 seconds easily with another session or two if you take the time to improve the settings and driving style. I would have expected you to be slower. The LSD will cause understeer, the impact of the removal of the front diff on handling is negligeable in relation to mass transfer, since it is located very low in the chassis, centered, and on/behind the front axle not ahead of it, you need to dial your suspension accordingly to the new handling characteristics due to the loss of pull from the front and the new presence of LSD in the rear, not due to the weight bias.
Experiment more with trail braking, and throttle steering, you can also feel much more the impact of mass transfer on handling while cornering and exiting as you apply the throttle and release vs. when you are in 4WD mode.
After some time, throttle application becomes second nature and you don't even need to be extra careful, you feel the limit, and end up going faster as confidence in the new setup and predictability of how the car will behave grows. A LOT of suspension fine tuning is required with the help of the datalogger and attention to the car behaviour while driving.
If on your first outing you are as fast as when you were AWD, expect another 1-2 seconds easily with another session or two if you take the time to improve the settings and driving style. I would have expected you to be slower. The LSD will cause understeer, the impact of the removal of the front diff on handling is negligeable in relation to mass transfer, since it is located very low in the chassis, centered, and on/behind the front axle not ahead of it, you need to dial your suspension accordingly to the new handling characteristics due to the loss of pull from the front and the new presence of LSD in the rear, not due to the weight bias.
Experiment more with trail braking, and throttle steering, you can also feel much more the impact of mass transfer on handling while cornering and exiting as you apply the throttle and release vs. when you are in 4WD mode.
After some time, throttle application becomes second nature and you don't even need to be extra careful, you feel the limit, and end up going faster as confidence in the new setup and predictability of how the car will behave grows. A LOT of suspension fine tuning is required with the help of the datalogger and attention to the car behaviour while driving.
I think that full suspension setup, wider front tires, and possibly the most important aspect the 50/80% LSD lock up together is what does the trick.
Therefore Dez and my comparo's are not apples to apples and he also is a better driver than I so again pilots not equal.
Anyone who tracks there car regularly (read I would trust them) is welcome to come and drive my car and see what they think.
you would not be able to tell much difference if just driven on the street.
again, I DO NOT recommend doing to your cars what I have done, this was a personal decision for me and my tracks and style and level of hp and the desire to persue really *** kicking track times.............others results my vary.
tom
#38
06-18-2008, 10:00 AM
RWD Track impressions
Ton,
Have you or are you considering strengthening the bottom end on your car given your past experience? Tracking a TT/GT2 w/ 600hp (whp?), it would weigh heavily on my mind. Thanks for your input. Great thread.
Have you or are you considering strengthening the bottom end on your car given your past experience? Tracking a TT/GT2 w/ 600hp (whp?), it would weigh heavily on my mind. Thanks for your input. Great thread.
#39
06-18-2008, 10:15 AM
ok here is a vid my friend in his GT3 posted running behind me last weekend in the open passing session at Chin Sebring, Fathers day.
you can see how the car handles from the view behind, comments welcome, Mike, Dez, Jean.............
http://www.youtube.com/watch?v=ZkRA-S50bgo
you can see how the car handles from the view behind, comments welcome, Mike, Dez, Jean.............
http://www.youtube.com/watch?v=ZkRA-S50bgo
#41
06-18-2008, 12:00 PM
I apologize for the long post that follows, but I am not sure if I understand things correctly but if you are trying to make a decision on whether RWD is faster than AWD or viceversa, then we can look at this in two ways.
1) you go 2WD by removing all the components of 4WD, hence benefiting from weight loss, and you also do the suspension and gearbox modifications that are needed to make it handle consequent with the 2WD needs
or
2) you go 2WD by not investing any money in doing the changes (components and setup) and you keep the weight unchanged.
I can tell you straight forward that option number 2 does not make any sense, and it is better to stay 4WD, there is no debate!
I will comment on a few things I have seen written, and realize that most people know all of this, so I am not preaching anyone:
1) LSD. Yes it will increase push, however you need (and CAN) dial the suspension accordingly to neutralize as much as you would prefer, and even get oversteer instead of understeer at corner exit. Sway bar settings, wider front track, different toe-out, different compression in the front and rebound in the rear, different springs, different camber, tire pressures, and of course driving style (deeper braking into the turn)…among others. It is not all about camber!
The advantages of LSD in corner exit on a high powered 911 are not debatable! And this is where you win races.
2) Weight. The advantages of total weight savings are certain. A lighter car will reduce the polar moment while cornering, and the mass transfer under braking. All else being equal, it will go faster than a heavier car, I think it is no debate?
3) Front/rear weight bias in standstill. Myth. If you want to go faster make sure “load change” is top of mind, not the fr/rr weight balance at standstill!.
Weight transfer under braking is directly proportional to CG height, , long Gs, and overall weight and inversely proportional to wheelbase(in forward motion) or track (in lateral motion) To maximize cornering grip you must minimize load transfer. To maximize braking grip, you must minimize load transfer.
This is what happens under braking:
a- 996TT, 4WD, weight: 3,400 lbs
Under 1 G braking force: Load transfer from rear to front = 560lbs.
Total weight under braking:
Front: 1915lbs Rear: 1473 lbs. Fr/Rr weight bias under braking: 57%-43% vs. 40%-60% at standstill.
b- 996GT2, 2WD, weight: 3,168lbs,
Under 1 G braking force: Load transfer from rear to front = 515lbs.
Total weight under braking:
Front: 1703lbs Rear: 1465 lbs. Fr/Rr weight bias under braking: 54%-46% vs. 37.5%-62.5% at standstill.
So from the above it is clear that the Gt2 with its lighter weight, and lower CG (lower height) is better off, as the load transfer is 45lbs less than the TT , but more importantly, the weight distribution under braking is 54% front vs. 57% front for the TT. Therefore the grip on the rear tires is higher under braking and your long G in deceleration improves. I have not even talked about better suspension, stiffer springs, and geometry by changing to GT2 hubs or dampers. in reality the GT2 has an even better weight bias under decelration and cornering due to its suspension setup.
In acceleration it is the opposite, the lighter front and load transfer to the rear will increase grip on the rear tires vs a 4wd setup that has tracton in the front and minimizes load transfer to the rear..Win-win.
c- The GT2 has a wider track in the front and narrower track in the rear than the 996TT, this improves handling in corners and reduces understeer as well. You need to fit wider tires in the front in relation to the rear if you are going to 2WD.
d- The front differential is located in the middle of the car, so the polar momentum of inertia from the differential or (lack of) in turns, is almost inexistent ( in relative terms vis a vis the overall mass of the car on both sides of it.) The torque tube of the 4Wd is in the center, so the same applies, no effect on cornering. So both 2Wd and 4Wd are at par here.
If you re-read, I was not saying 73lbs is negligeable, I was saying the impact of those 73lbs in cornering or load transfer is negligeable, due to its location (below center of gravity and in the middle!)!
In summary, there is a reason that the GT2 handles better than the 996TT on the track, the 996GT2 Mk1 was ranked 8th. overall in cornering grip (lateral Gs) up there with the CGT, whereas the 996TT was ranked 30th. both on street tires, in Hockenheim by the same magazine and driver. This is independent from HP.
More examples, both on street tires, Sport Auto, Hockenheim, cornering speeds:
Turn 1
GT2: 128mph – TT: 122mph
Turn 2
GT2: 78mph – TT: 76mph
Turn 3
GT2: 108mph – TT: 101mph
Turn 4
GT2: 53mph – TT: 53mph
Turn 4
GT2: 78mph – TT: 74mph
1) you go 2WD by removing all the components of 4WD, hence benefiting from weight loss, and you also do the suspension and gearbox modifications that are needed to make it handle consequent with the 2WD needs
or
2) you go 2WD by not investing any money in doing the changes (components and setup) and you keep the weight unchanged.
I can tell you straight forward that option number 2 does not make any sense, and it is better to stay 4WD, there is no debate!
I will comment on a few things I have seen written, and realize that most people know all of this, so I am not preaching anyone:
1) LSD. Yes it will increase push, however you need (and CAN) dial the suspension accordingly to neutralize as much as you would prefer, and even get oversteer instead of understeer at corner exit. Sway bar settings, wider front track, different toe-out, different compression in the front and rebound in the rear, different springs, different camber, tire pressures, and of course driving style (deeper braking into the turn)…among others. It is not all about camber!
The advantages of LSD in corner exit on a high powered 911 are not debatable! And this is where you win races.
2) Weight. The advantages of total weight savings are certain. A lighter car will reduce the polar moment while cornering, and the mass transfer under braking. All else being equal, it will go faster than a heavier car, I think it is no debate?
3) Front/rear weight bias in standstill. Myth. If you want to go faster make sure “load change” is top of mind, not the fr/rr weight balance at standstill!.
Weight transfer under braking is directly proportional to CG height, , long Gs, and overall weight and inversely proportional to wheelbase(in forward motion) or track (in lateral motion) To maximize cornering grip you must minimize load transfer. To maximize braking grip, you must minimize load transfer.
This is what happens under braking:
a- 996TT, 4WD, weight: 3,400 lbs
Under 1 G braking force: Load transfer from rear to front = 560lbs.
Total weight under braking:
Front: 1915lbs Rear: 1473 lbs. Fr/Rr weight bias under braking: 57%-43% vs. 40%-60% at standstill.
b- 996GT2, 2WD, weight: 3,168lbs,
Under 1 G braking force: Load transfer from rear to front = 515lbs.
Total weight under braking:
Front: 1703lbs Rear: 1465 lbs. Fr/Rr weight bias under braking: 54%-46% vs. 37.5%-62.5% at standstill.
So from the above it is clear that the Gt2 with its lighter weight, and lower CG (lower height) is better off, as the load transfer is 45lbs less than the TT , but more importantly, the weight distribution under braking is 54% front vs. 57% front for the TT. Therefore the grip on the rear tires is higher under braking and your long G in deceleration improves. I have not even talked about better suspension, stiffer springs, and geometry by changing to GT2 hubs or dampers. in reality the GT2 has an even better weight bias under decelration and cornering due to its suspension setup.
In acceleration it is the opposite, the lighter front and load transfer to the rear will increase grip on the rear tires vs a 4wd setup that has tracton in the front and minimizes load transfer to the rear..Win-win.
c- The GT2 has a wider track in the front and narrower track in the rear than the 996TT, this improves handling in corners and reduces understeer as well. You need to fit wider tires in the front in relation to the rear if you are going to 2WD.
d- The front differential is located in the middle of the car, so the polar momentum of inertia from the differential or (lack of) in turns, is almost inexistent ( in relative terms vis a vis the overall mass of the car on both sides of it.) The torque tube of the 4Wd is in the center, so the same applies, no effect on cornering. So both 2Wd and 4Wd are at par here.
If you re-read, I was not saying 73lbs is negligeable, I was saying the impact of those 73lbs in cornering or load transfer is negligeable, due to its location (below center of gravity and in the middle!)!
In summary, there is a reason that the GT2 handles better than the 996TT on the track, the 996GT2 Mk1 was ranked 8th. overall in cornering grip (lateral Gs) up there with the CGT, whereas the 996TT was ranked 30th. both on street tires, in Hockenheim by the same magazine and driver. This is independent from HP.
More examples, both on street tires, Sport Auto, Hockenheim, cornering speeds:
Turn 1
GT2: 128mph – TT: 122mph
Turn 2
GT2: 78mph – TT: 76mph
Turn 3
GT2: 108mph – TT: 101mph
Turn 4
GT2: 53mph – TT: 53mph
Turn 4
GT2: 78mph – TT: 74mph
Last edited by Jean; 06-18-2008 at 12:42 PM.
#42
06-18-2008, 12:02 PM
really it is not all about the speed or who is the fastest. I was on track with about 15 guys I knew with every car imaginable. It is about us all driving our own personal dream cars and having fun.
I have driven plently of GT3's and my heart rate doesnt increase a beat.
As I am walking up to my car I get excited!! The speed, power, torque, braking, and handling and looks of the wide body excite me.
that's what this is all about, I love the Twin Turbo, period.
I will be racing this weekend at Sebring, in our 944's and again in two weeks, so I get plently of other stuff to drive, no GT3 in my future........Now a Cup car is a different story!!!
I instruct for PCA and mostly Chin, I race with NASA and PBOC, cant beat the TT as a DE instructor car!
wow Jean just saw your post, beat mine, good stuff, thanks for taking the time to try and educate us, love your posts!!
I have driven plently of GT3's and my heart rate doesnt increase a beat.
As I am walking up to my car I get excited!! The speed, power, torque, braking, and handling and looks of the wide body excite me.
that's what this is all about, I love the Twin Turbo, period.
I will be racing this weekend at Sebring, in our 944's and again in two weeks, so I get plently of other stuff to drive, no GT3 in my future........Now a Cup car is a different story!!!
I instruct for PCA and mostly Chin, I race with NASA and PBOC, cant beat the TT as a DE instructor car!
wow Jean just saw your post, beat mine, good stuff, thanks for taking the time to try and educate us, love your posts!!
#43
06-18-2008, 12:19 PM
Tom,
I have no question on your ability on tracks. Since I have not track yet (will be), I don't really know what excites me on the track. I thought it was mostly to get the best time. For myself, I love twin turbo too, it was my dream car and that doesn't change. GT3 doesn't do much for me. So, we are on the same page... except for the tracking skills and knowledge.
I have no question on your ability on tracks. Since I have not track yet (will be), I don't really know what excites me on the track. I thought it was mostly to get the best time. For myself, I love twin turbo too, it was my dream car and that doesn't change. GT3 doesn't do much for me. So, we are on the same page... except for the tracking skills and knowledge.
#44
06-18-2008, 12:21 PM
ok here is a vid my friend in his GT3 posted running behind me last weekend in the open passing session at Chin Sebring, Fathers day.
you can see how the car handles from the view behind, comments welcome, Mike, Dez, Jean.............
http://www.youtube.com/watch?v=ZkRA-S50bgo
you can see how the car handles from the view behind, comments welcome, Mike, Dez, Jean.............
http://www.youtube.com/watch?v=ZkRA-S50bgo
, the video is not clear at all, I cannot see properly the brake lights.If I were to say three things, it would be late apex, entering too fast and can brake deeper (causing slow exit), not using full track especially under acceleration on exit. This is where your high hp turbo is supposed to make the gains.
Looks like you can mash the throttle much harder and earlier on exit but you need to be straight.
I might be wrong, but that's all I can say from this video, I don't know the track, bumps and grip levels.
I am sure many others can give much better feedback.
Thanks for sharing.
#45
06-18-2008, 01:46 PM
Tom it is very easy to preach when others are driving , the video is not clear at all, I cannot see properly the brake lights.
If I were to say three things, it would be late apex, entering too fast and can brake deeper (causing slow exit), not using full track especially under acceleration on exit. This is where your high hp turbo is supposed to make the gains.
Looks like you can mash the throttle much harder and earlier on exit but you need to be straight.
I might be wrong, but that's all I can say from this video, I don't know the track, bumps and grip levels.
I am sure many others can give much better feedback.
Thanks for sharing.
, the video is not clear at all, I cannot see properly the brake lights.If I were to say three things, it would be late apex, entering too fast and can brake deeper (causing slow exit), not using full track especially under acceleration on exit. This is where your high hp turbo is supposed to make the gains.
Looks like you can mash the throttle much harder and earlier on exit but you need to be straight.
I might be wrong, but that's all I can say from this video, I don't know the track, bumps and grip levels.
I am sure many others can give much better feedback.
Thanks for sharing.
when I post from inside my car looks like I am getting my guts shaken out!
thanks for your help, I will learn from it.
as for not being able to see the brake lights, well I will leave that one up to you