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I'd think it's a given that there'd be vectoring on the rear axle with a form of limited slip diff. I also recall a track review that mentioned that torque is not only vectored front to back but side to side which also seemed like a given to me. Have you looked up any Porsche published marketing info? Can't imagine this should be hard to confirm.
Have a bit that came with the car, but I have been unsuccessful in finding quality (detailed) technical information such as what Jean dug up on the active aero - that was very good literature. I suspect that Jean knows some people...
*Hoping Jean steps in with detailed technical info*
All PDK cars with PTV actually have PTV+ which is a variable differential lock that is controlled by the computer. This allows the diff to be completely open when traction is adequate, which helps with turn in and if the rear tires start to lose traction on one side the diff lock can progressively engage to limit the speed difference between the two rear wheels.
This makes sense to me, thank you.
This is not a mechanical torque vectoring device which typically involves planetary gearsets to transfer torque from one wheel to the other, proactively sending power to the outside wheel and accelerating it faster than the inside wheel. In most cases when the diff lock is engaged enough torque is transferred away from the inside wheel to eliminate wheelspin. If the car is cornering especially hard, PTV will brake an inside wheel to cause the outside wheel to receive more torque and spin faster. This is less efficient than a torque vectoring diff but is a rare enough occurrence that Porsche has decided to go with a more mechanically simple route than Audi with their Sport Differential, largely because the cars need it much less.
OK, I think I understand what you are saying - computer is still controlling (front?) but using the brakes to control traction?
Front diff is open and there is no vectoring afaik, but the standard PSM will eliminate wheelspin on the front axle by braking individual wheels, as on virtually any modern AWD car now that stability control is ubiquitous.
Continuing the thought from above, so with the front open diff, the car still puts power to both wheels, but it is controlled (limited) by the brakes? Isn't this hard on the brakes - driving power through them, but effectively 'brake standing' in order to maintain traction and/or stability?
What I thought was interesting in the snow was that I could feel front right/left scrambling for traction but the display showed equal power to both. I think it was more effective than the system in the 996tt, it most certainly felt planted when power was applied, but I was expecting more evolution of the hardware.
I will search to see if there is more technical bulletins available. Thank you for the input.
Continuing the thought from above, so with the front open diff, the car still puts power to both wheels, but it is controlled (limited) by the brakes? Isn't this hard on the brakes - driving power through them, but effectively 'brake standing' in order to maintain traction and/or stability?
What I thought was interesting in the snow was that I could feel front right/left scrambling for traction but the display showed equal power to both. I think it was more effective than the system in the 996tt, it most certainly felt planted when power was applied, but I was expecting more evolution of the hardware.
I will search to see if there is more technical bulletins available. Thank you for the input.
The biggest difference between the 996TT AWD system and the 991 is PTM- porsche traction management. On the 996TT there is a viscous coupling which is strictly a mechanical device that reacts to differences in speed from input to output. So when rear wheels slip the coupling locks up and more power goes to the front. It's a reactive system in that additional power goes to the front only after it slips. 997TT and above have a haldex coupling which is an electronically controlled clutch pack that can be proactive as well. For instance if you jam the throttle the car will proactively send torque to the front before any wheelspin because it was programmed to do so.
As far as the car sending power equally to the front wheels, it's better to think of the car as sending power to the front differential, which then naturally splits torque evenly left to right. Remember that this is torque, not speed. If one side has a lot of available traction and the other side has almost none, the wheel without traction spins very quickly. Since it's not grabbing, it requires very little torque to spin. The other side doesn't spin much if at all because it's receiving the same amount of torque. What the braking of the spinning wheel does is provide enough torque on the spinning wheel so that the equal amount on the other side with traction will actually turn.
PTV can be hard on brakes but the braking system is already overspeced on our cars and the actual braking function would rarely if ever be invoked on the street. As for front axle slipping keep in mind that the brakes have significant thermal capacity and stopping a spinning wheel is well below the limits of the system as engineered. Also, this is something that only occurs momentarily as the car hooks up and all wheels are grabbing. Remember that from a standstill your car only needs a little bit of torque to move, and that's basically what the brake is absorbing. Much less, say, than actually stopping the car from speed.
All this engineering happens because on a road course with ample traction, an open diff works the best. It is most efficient and helps with turn in. You only want a limited slip occasionally, so the tech allows you to either have a virtual one in the front, or a mechanical plate diff in the rear as situations warrant.
I'm a bit confused by your comment on the torque display, as on my car the torque split display only shows front-rear torque split, not left to right.
Had an opportunity to get the car out in the snow and give the Michelin Alpins a bit of a go - phenomenal, best snow tire coupled with a very smart AWD system and the car was rock solid.
I am curious though - when in a slippery condition, does anyone know how drive torque is managed? The torque display shows how much to the front diff, but beyond that, does anyone know if it is being managed at each wheel as well? I found the car loosened up the further clockwise I turned the dial, but the torque display was pretty static.
Cheers,
I was invited few years back somewhere close to the North pole to drive the 991 turbo for 3 days and I totally understand what you are saying. There is little that can be more fun than this and the cars are unbelievable in slippery conditions, especially in long drift turns at high speeds >100mph on snow or ice, the car drives itself..
The new PTM system actually reads driver intentions through steering and throttle inputs and anticipates corrections on snow. It manages the throttling and wheel slip electronically. The system reads the different friction coefficients for every wheel, and transfers torque based on delta between them to always optimize grip. The way they do it is sensors read slippage on the front and rear axles, longitudinal and lateral acceleration as well as over- and understeering and the algorithms and programming change torque distribution in microseconds. Traction is managed by the PTM clutch and torque, >10% can be transfered to the front axle, which then acts like a virtual longer wheelbase and manages mass transfer much more efficiently.
Check the link below at a local autocross yesterday and how wheel speeds (can see it on the left side of the dash) constantly change front /rear and left/right with the PTM and TC engaging to maximize grip. I slowed down the speed to see changes better. You can also see the mass transfer % reading.
I was invited few years back somewhere close to the North pole to drive the 991 turbo for 3 days and I totally understand what you are saying. There is little that can be more fun than this and the cars are unbelievable in slippery conditions, especially in long drift turns at high speeds >100mph on snow or ice, the car drives itself..
The new PTM system actually reads driver intentions through steering and throttle inputs and anticipates corrections on snow. It manages the throttling and wheel slip electronically. The system reads the different friction coefficients for every wheel, and transfers torque based on delta between them to always optimize grip. The way they do it is sensors read slippage on the front and rear axles, longitudinal and lateral acceleration as well as over- and understeering and the algorithms and programming change torque distribution in microseconds. Traction is managed by the PTM clutch and torque, >10% can be transfered to the front axle, which then acts like a virtual longer wheelbase and manages mass transfer much more efficiently.
Check the link below at a local autocross yesterday and how wheel speeds (can see it on the left side of the dash) constantly change front /rear and left/right with the PTM and TC engaging to maximize grip. I slowed down the speed to see changes better. You can also see the mass transfer % reading.
How would this relate to traction while Launching a TTS ? The manual states the rear differential control goes from a fixed percentage in Normal or Sport to an Active Control in Sport Plus. I wonder if Sport Plus would provide more tractive effort with a 5600rpm 10psi launch ?
In Sport Plus the PTM tuning is more aggressive and activates the launch control acceleration booster which primes the PTM clutch and supports optimal acceleration from a standstill. The PTM is activated and regulated fully electro-hydraulically only, it's a completely new single design vs. the 997 and transfers optimally power to the front wheels >10%. The rear differential is a fully variable electronic lock managed by PTM and Porsche Torque Vectoring +. The launch control booster in Sport Plus is what you are probably referring to.
The 991 has a longer wheelbase by 100mm vs the 997, coupled with a faster and more precise new PTM, chassis/suspension dynamics and dynamic engine mount system, give the great launch performance.
I was invited few years back somewhere close to the North pole to drive the 991 turbo for 3 days and I totally understand what you are saying. There is little that can be more fun than this and the cars are unbelievable in slippery conditions, especially in long drift turns at high speeds >100mph on snow or ice, the car drives itself..
The new PTM system actually reads driver intentions through steering and throttle inputs and anticipates corrections on snow. It manages the throttling and wheel slip electronically. The system reads the different friction coefficients for every wheel, and transfers torque based on delta between them to always optimize grip. The way they do it is sensors read slippage on the front and rear axles, longitudinal and lateral acceleration as well as over- and understeering and the algorithms and programming change torque distribution in microseconds. Traction is managed by the PTM clutch and torque, >10% can be transfered to the front axle, which then acts like a virtual longer wheelbase and manages mass transfer much more efficiently.
Check the link below at a local autocross yesterday and how wheel speeds (can see it on the left side of the dash) constantly change front /rear and left/right with the PTM and TC engaging to maximize grip. I slowed down the speed to see changes better. You can also see the mass transfer % reading.
How would this relate to traction while Launching a TTS ? The manual states the rear differential control goes from a fixed percentage in Normal or Sport to an Active Control in Sport Plus. I wonder if Sport Plus would provide more tractive effort with a 5600rpm 10psi launch ?
I have never even tried the launch control - does it really load 10 pounds of boost before you release the brakes? Instinctively, I would think things will grenade after a few times of doing that.
I have never even tried the launch control - does it really load 10 pounds of boost before you release the brakes? Instinctively, I would think things will grenade after a few times of doing that.
?? Never even tried launch control??
That was one of the first things I tried, after I got the car and had it all warmed up. Check out this video, I think you'll be ok!
I have never even tried the launch control - does it really load 10 pounds of boost before you release the brakes? Instinctively, I would think things will grenade after a few times of doing that.
8-10 depending on the atmospheric conditions. You can do it all day long with zero issues. There are vids out on 50 launches in a row without cool down.
At Porsche Barber, they let rookies launch for 8 hours straight in the same TTS. Zero issues.
Yeah, no - I've never done that. Impressive though.
The best I have done is there is a little straight on my way to work in the morning and if the sun, moon and stars happen to align (no one in the space), I will mat it from a standing start and get into third, but not the top, and that is pretty impressive to me.
On the highway, I've maybe put my foot (really) into it a few times, but very rarely do I go anymore than 40km/h over the posted limit as it now results in immediate impound, license suspension and fines...
8-10 depending on the atmospheric conditions. You can do it all day long with zero issues. There are vids out on 50 launches in a row without cool down.
At Porsche Barber, they let rookies launch for 8 hours straight in the same TTS. Zero issues.
Bulletproof engineering.
That is pretty cool - very bullet proof, somewhat helps me feel better about the reliability of the TTs PDK too.
01-26-2020, 01:21 AM
Check out this video, I think you'll be ok!