First RWD Impala spy pics?

[MonaroSS]

Originally Posted by 1931Chevy

If this car is on epsilon 2 then this is AWD what you are seeing here , I dont believe that GM will use epsilon for RWD since thats Zetas work and remember that Epsilon engine force is the ecotec family and the v6 family and thats where they need to concentrate their efforts because the MPG needs to go up

Originally Posted by 63GrandSport001

I think that offering the Impala in FWD, AWD, and RWD is going to cost more then what its worth to do.

This could also be GM testing AWD on the Buick as well though, its really hard to say what it is.

AWD behaves more like FWD in terms of understeer. In fact AWD's often have even less dynamic responses than FWD, and AWD's don't lift the front inside wheel off the ground either.

There is no reason to believe that the cost would be more than it's worth. Indeed, innovative design that uses as much commonality as possible could make a RWD variant LESS expensive than the AWD version. And AWD is worth it as there are those who want it, just like RWD would be worth it as there are those who want it.

[zete]

Originally Posted by MonaroSS

AWD behaves more like FWD in terms of understeer. In fact AWD's often have even less dynamic responses than FWD, and AWD's don't lift the front inside wheel off the ground either.

There is no reason to believe that the cost would be more than it's worth. Indeed, innovative design that uses as much commonality as possible could make a RWD variant LESS expensive than the AWD version. And AWD is worth it as there are those who want it, just like RWD would be worth it as there are those who want it.

One thing I've always wondered about is this. If a FWD/AWD platform exists, why can't it also house RWD? What within the platform has to change to effectively eliminate the FWD portion of the AWD platform to provide a RWD chassis?

I'm not an automotive engineer -- computers are my thing -- but if the room is there for the drivetrain to go to drive the back wheels for AWD then why can't you simply eliminate the FWD portion to create a RWD car? Since Epsilon II was designed to be FWD or AWD it only seems to make sense to me that you can also make a RWD car with that platform. And as a selling point, it would be an awesome one for GM. Get the car in the flavour you like/prefer, and everyone's happy.

There's probably some perfectly logical reason this can't be done, but I'd love to know what it is.

[ohmywrd8]

Uhhh that's the Lacrosse or whatever they soon want to call it.

[MonaroSS]

Originally Posted by zete

One thing I've always wondered about is this. If a FWD/AWD platform exists, why can't it also house RWD? What within the platform has to change to effectively eliminate the FWD portion of the AWD platform to provide a RWD chassis?

I'm not an automotive engineer -- computers are my thing -- but if the room is there for the drivetrain to go to drive the back wheels for AWD then why can't you simply eliminate the FWD portion to create a RWD car? Since Epsilon II was designed to be FWD or AWD it only seems to make sense to me that you can also make a RWD car with that platform. And as a selling point, it would be an awesome one for GM. Get the car in the flavour you like/prefer, and everyone's happy.

There's probably some perfectly logical reason this can't be done, but I'd love to know what it is.

You are correct in that it is perfectly possible to have a transverse mounted engine at the front of a car drive the rear wheels. The reason it does not normally happen is like that is two fold. Firstly, most AWD's made from FWD only send half the power to the rear wheels and so the driveline and rear diff are usually too small and not strong enough to take all the power. But this could be corrected simply by upgrading the component set. It is the second reason that makes this route unappealing from an engineering point of view. And that reason is that RWD does not go well with heavy front weight bias if improved handling is what you want.

As can be seen by the pics below, by retaining the FWD set-up and simply taking the drive to the rear only you only move the centre of mass for the diff rearwards. The mass of the engine and gearbox would still be centred well ahead of the front axle. Certainly this could still work, but the reason to offer a RWD only from a FWD is to provide better handling dynamics, but those dynamics may not be improved enough simply by taking the drive to the rear in a nose heavy car.

However by turning the engine 90 degree and mounting the gearbox behind it then the weight does move substantially rearwards and this does make for much better handling dynamics.

[zete]

Originally Posted by MonaroSS

You are correct in that it is perfectly possible to have a transverse mounted engine at the front of a car drive the rear wheels. The reason it does not normally happen is like that is two fold. Firstly, most AWD's made from FWD only send half the power to the rear wheels and so the driveline and rear diff are usually too small and not strong enough to take all the power. But this could be corrected simply by upgrading the component set. It is the second reason that makes this route unappealing from an engineering point of view. And that reason is that RWD does not go well with heavy front weight bias if improved handling is what you want.

As can be seen by the pics below, by retaining the FWD set-up and simply taking the drive to the rear only you only move the centre of mass for the diff rearwards. The mass of the engine and gearbox would still be centred well ahead of the front axle. Certainly this could still work, but the reason to offer a RWD only from a FWD is to provide better handling dynamics, but those dynamics may not be improved enough simply by taking the drive to the rear in a nose heavy car.

However by turning the engine 90 degree and mounting the gearbox behind it then the weight does move substantially rearwards and this does make for much better handling dynamics.

Ah. So the bay area for the engine and transmission in a FWD car is simply not oriented correctly to handle the engine and transmission in the proper configuration to move the weight backwards. Unless they can somehow put the transmission in the rear of the car, I suppose.

[63GrandSport001]

I seriously think that it makes no sense to make the next generation impala on the FWD plaform...

when they brought the Impala back they did not have a RWD platform to put it on as the Chassis the 1994-1996 Impala SS was riding on was very old and ended. At the same time Chevy really didn't have a good sedan to compete with the Honda Accord and Toyota Camry. The Impala filled that gap in although it didn't compete with them on equal footing as the Camry and Accord were I-4 and V-6 cars while the impala was V-6 only and was a bit bigger (seats 6).

With the 2008 Malibu being as good as it is Chevy really does not need two vehicles to compete in this segment anymore IMHO. The Impala would also be giving up sales to the Malibu as well so it can be made less fuel efficient without having as big of an impact on GMs CAFE. Also RWD doesn't have to mean that the car cant or wont meet the harder standards (that it doesn't have to meet anyways).

[1931Chevy]

Originally Posted by MonaroSS

The answer is simple and makes complete sense. The Impala and this LaCrosse both are LWB EPII so under the skin they are sister cars. If you are testing a new platform and there is a complete version of that available to test that gives the most accurate information, why would you use an old vehicle that is only an approximation? The situation with the Volt is that they don't have the new platform yet and they are testing not the platform but the drive train set. Here they are testing not just drive train but the EPII platform in RWD format too. Also, it would be likely that the RWD option developed for an EPII Impala may also be made available eventually for the Buick.



That is not a RWD Buick made in AU, it is the exact same Buick LaCrosse prototype as I propose is being used as an Impala mule, and in Buick form it is a US/China project that does not involve Holden.

I still say this car is FWD and AWD, considering that GM Europe is the one in charge of Epsi 2 it should be normal to have prototypes of next generation cars that are coming around, and think about if Epsi is capable of RWD then why build Zeta and spend billions on dollars for a RWD platform then, sometime ago there was some talk that Ford D3 platform could be configured for RWD use but until this day there is no word on that. And I think is cheaper to design one platform specifically for RWD and one for FWD AWD because as you explained the only way it will work is by moving the engine and tranny position for each configuration and at the end you will need one line for each application so the only way I see the Impala as RWD is if they move it to Zeta and maybe it could happen since Oshawa will be the Zeta base for the Camaro and thats the Impala plant too but I bet my ass on Epsi 2 and FWD AWD configuration

[mikmak]

Originally Posted by zete

Ah. So the bay area for the engine and transmission in a FWD car is simply not oriented correctly to handle the engine and transmission in the proper configuration to move the weight backwards. Unless they can somehow put the transmission in the rear of the car, I suppose.

Please don't get him started on the whole transaxle thing





It all seems possible to me but not likely. This is the type of innovation that 1.)the public wouldn't understand, and 2.) is out of character for modern GM. I really hope they are trying it.

[gmhashope]

Well considering the Insignia is going to offer AWD from the start on EPII it would not be surprising for the LaCrosse/Invicta to be offered with AWD from the start too since they are both on EPII. I don't think this is a RWD Impala.

[member12]

Sorry, but that is a front drive car.

No modern RWD car has that kind of front overhang with so little space between the front doors and the axle.

It's probably the Buick LaCrosse.

[MonaroSS]

Originally Posted by mikmak

Please don't get him started on the whole transaxle thing

As I was about to say to zete........

You are correct and yes you could use a transaxle gearbox like the Alfetta Alfa Romeo's of the mid 70's, or like the Corvette.

Actually, if I were in charge (and not people like mikmak) I would seriously consider using a transaxle for a vehicle like this. It makes perfect sense, especially as it's main detraction is overcome in an application like this, which is that it can't have an AWD version. But if the platform were to already have an FWD/AWD alternative anyway, it wouldn't matter.

My main premise for speculating this topic is the pics of the car at speed. They do not show a FWD vehicle in action. Yes some have said that this may be an AWD version, but even then the vehicle's attitudes are wrong for an AWD. I was raised on this stuff, suspensions and handling, as my dad was a specialist in it. And my keen eye tells me things and my keen knowledge of Holden tells me they never built an FWD/AWD car.

Also, we do know this is a turbo I4 and this means something to this debate. These cars are mid to large and were not meant to have this engine. But Lutz has proposed using this engine in larger cars to get both performance and good fuel economy from the package. If that is true then they would not be testing an AWD version, as everyone knows that AWD's get poor specific fuel economy compared to FWD and RWD due to extra weight and mechanical losses. It makes more sense that this I4 turbo, as a CAFÉ performance champ, is in either a FWD or RWD and it doesn't look like a FWD in action.

On a straw poll it seems that most people don't buy my rationale, but that just makes it better if some serious auto journalists see my suggestion, does a little digging and exposes the story as correct. I'll say I was wrong if the car fails to surface, so I am at risk even if it is just a test vehicle for RWD that they then decide against. But if it does come to light I will say, "I told you so, I told you so, oh and I told you so".

[JBMX928]

thanks for the pics.

[MonaroSS]

Originally Posted by member12

Sorry, but that is a front drive car.

No modern RWD car has that kind of front overhang with so little space between the front doors and the axle.

It's probably the Buick LaCrosse.

It would if it were both FWD/AWD and RWD. You can't argue that it is NOT RWD based on that observation - it is a mere generalisation of no necessary engineering consequence. The overhang and axle to door gap has no bearing on the capacity of a platform to be RWD.

Perhaps NOW a modern RWD car does have so little space........

[BBDOS CV8]

It's possible it has a RWD-oriented engine. But why not just use a short Commodore a la Camaro? I'd say this is engineering development work on adaptive AWD. The fact they are still hiding the body indicates close-to-production Lacrosse.

Good catch on the pics of the front wheel lift. Perhaps they have the AWD manually locked onto 'dry, sport' mode with power through the rears for handling eval? They might be doing mapping the computer to assist in it choosing a bias? Could be tuning AWD stability control?

With modern computer-controlled AWD it could be set by switch or automatically assigned with up to 100% rear bias. Holden does all sorts of development for GM, not just RWD and has AWD experience with Adventra, Coupe4 and Captiva. So they might be assigned to co-work with Saab, who obviously have a big stake in this.

[GM-10]

Originally Posted by 5 watt

the gap between the front door and wheel say no.

AWD which is Epsilon II capable would explain away a good bit of this argument.

I wish you were right...but in the end-I think its wishful thinking.