RE: VW's VAQ 'diff' explained
Discussion
But it's natural split in the majority of cases (unless overdriven) is 50:50 split. This is what I'm talking about. No matter what the electronics pre-empt you physically cannot drive the rears with more bias than the fronts unless the fronts are spinning. The way the VW literature reads, it gives the impression that the car can be RWD...which strictly speaking it can be, but not in a way that a RWD car can (as in the rears will never be the lead axle....it relies on some slip, or at least some pre-empted slip on the front).
Having had a lot of experience of true mechanical 50:50 with a centre diff and Torsen at 40:60 rear bias, Haldex in the golf just doesn't feel anything other than FWD with the rears as a traction aid. That's my genuine subjective assessment of it. It in no way feels driven from the rear. It feels more FWD than it does 4WD as a 40:60 split Torsen feels more RWD than 4WD with 50:50 with a centre diff unsurprisingly in the middle!
For me personally, I like the feeling of some instability. Whether this is provided by RWD only or an overspending rear axle with Yaw Control I don't mind, but FWD with hang on rear haldex just isn't as adjustable as the other 3 options. For me, that's what I'm of the opinion that I'd rather just have a good LSD or eDiff on something like the Golf as the 4WD aspect offers very little to the cars dynamic repertoire and seems to be providing something I don't need. I appreciate that on snow and ice, the out and out performance/acceleration of the R will be a huge amount better, but my own car spends so little time driving in these conditions I find it irrelevant.
I can appreciate true mechanical 4x4 as it's more transparent.....you need a different driving style, but as the wheels are always driven and don't require any kind of pre-emptive electronics or wheel slip, there's more that can be done to enjoy it.
I think for the majority of owners/road drivers, the Haldex offers a very good solution to providing excellent traction with very little on cost in the car. Something like the R8 setup just isn't realistic in something like a Golf or an A3, and probably only 1% of owners would appreciate it!
Having had a lot of experience of true mechanical 50:50 with a centre diff and Torsen at 40:60 rear bias, Haldex in the golf just doesn't feel anything other than FWD with the rears as a traction aid. That's my genuine subjective assessment of it. It in no way feels driven from the rear. It feels more FWD than it does 4WD as a 40:60 split Torsen feels more RWD than 4WD with 50:50 with a centre diff unsurprisingly in the middle!
For me personally, I like the feeling of some instability. Whether this is provided by RWD only or an overspending rear axle with Yaw Control I don't mind, but FWD with hang on rear haldex just isn't as adjustable as the other 3 options. For me, that's what I'm of the opinion that I'd rather just have a good LSD or eDiff on something like the Golf as the 4WD aspect offers very little to the cars dynamic repertoire and seems to be providing something I don't need. I appreciate that on snow and ice, the out and out performance/acceleration of the R will be a huge amount better, but my own car spends so little time driving in these conditions I find it irrelevant.
I can appreciate true mechanical 4x4 as it's more transparent.....you need a different driving style, but as the wheels are always driven and don't require any kind of pre-emptive electronics or wheel slip, there's more that can be done to enjoy it.
I think for the majority of owners/road drivers, the Haldex offers a very good solution to providing excellent traction with very little on cost in the car. Something like the R8 setup just isn't realistic in something like a Golf or an A3, and probably only 1% of owners would appreciate it!
Edited by RacerMike on Thursday 31st July 11:29
Max_Torque said:
Regarding front to rear torque splitting systems like Haldex Et-al... (snip)
Yes; it's easy to think about these systems simply in terms of F/R "torque split". You've expertly described the fundamental difference between these and the sort you get on a Mitsubishi Evo etc.The way I think about these systems is that FWD-based Haldex (or similar) AWD is great for when you want to "add traction" - in cars like the Evoque, Freelander etc. it does the job. However in anything with sporting pretensions, "on demand" systems are best when added to to a RWD-based chassis.
RacerMike said:
But the wording implies (or at least gives the impression in the VW marketing literature) that you can have a 0:100 split. Whilst I agree that this is theoretically possible if you lose traction on the front two wheels, it's still only a 'hang on' rear end. A true 4WD coupling with a centre diff can permanently modify the torque split to the rear or front. Ultimately, all 4WD systems have some advantages and disadvantages (Torsen being next to useless when stuck for instance), but my comments were directed at the implication from VW that the Haldex is able to make the car 'rear wheel drive' which whilst technically true, is the same as saying that a Golf GTI can be '1 wheel drive'. True, but only because of the natural loss of traction and inherent behaviour of an open diff, active or not.
When I test drove the new Golf R, I described it as 'my Mk5 GTI with another 30bhp and loads of traction'. It never feels anything other than FWD.....which makes me wonder whether there's really much point when you an have this VAQ diff.....
Exactly. I felt the same with the Insignia and old S3...in fact, I found the latter less adjustable / playful (call it what you will) than a good FWD chassis and not a patch on the Japanese rally reps. - If only you could get something like an Evo IX/X drivetrain with an S3 body/interior and a more characterful motor!When I test drove the new Golf R, I described it as 'my Mk5 GTI with another 30bhp and loads of traction'. It never feels anything other than FWD.....which makes me wonder whether there's really much point when you an have this VAQ diff.....
Clivey said:
Exactly. I felt the same with the Insignia and old S3...in fact, I found the latter less adjustable / playful (call it what you will) than a good FWD chassis and not a patch on the Japanese rally reps. - If only you could get something like an Evo IX/X drivetrain with an S3 body/interior and a more characterful motor!
Which is what the R was purported to be...but sadly isn't! I agree....something in the same mould as the old Sunny GTI-R would be pretty awesome. Just silly, rear biased with lots of power and in a hatchback shape.The other subtlety often missed is that the static torque distribution needs to match (reasonably closely) the static mass distribution of the vehicle. For a front engined vehicle, this means you generally will always have a static front torque bias.
(the reason for this should be fairly obvious> Namely, you fit 4wd specifically to improve traction (note, NOT grip!!), you need "traction" when using low gears at low speeds. For max traction you need each tyre to provide it's maximum tractive effort. That requires you to apply torque to that tyre in proportion to the normal (vertical) load on that tyre. Hence, a static torque split that matches the vehicles front rear mass split)
(the reason for this should be fairly obvious> Namely, you fit 4wd specifically to improve traction (note, NOT grip!!), you need "traction" when using low gears at low speeds. For max traction you need each tyre to provide it's maximum tractive effort. That requires you to apply torque to that tyre in proportion to the normal (vertical) load on that tyre. Hence, a static torque split that matches the vehicles front rear mass split)
Max_Torque said:
The other subtlety often missed is that the static torque distribution needs to match (reasonably closely) the static mass distribution of the vehicle. For a front engined vehicle, this means you generally will always have a static front torque bias.
(the reason for this should be fairly obvious> Namely, you fit 4wd specifically to improve traction (note, NOT grip!!), you need "traction" when using low gears at low speeds. For max traction you need each tyre to provide it's maximum tractive effort. That requires you to apply torque to that tyre in proportion to the normal (vertical) load on that tyre. Hence, a static torque split that matches the vehicles front rear mass split)
More nose weight = more forward bias = more "nose heavy" dynamics.(the reason for this should be fairly obvious> Namely, you fit 4wd specifically to improve traction (note, NOT grip!!), you need "traction" when using low gears at low speeds. For max traction you need each tyre to provide it's maximum tractive effort. That requires you to apply torque to that tyre in proportion to the normal (vertical) load on that tyre. Hence, a static torque split that matches the vehicles front rear mass split)
Clivey said:
More nose weight = more forward bias = more "nose heavy" dynamics.
If you hit the limits of grip on the front tyres when cornering and applying power, Haldex should shift some power/torque rearwards leaving more of the front grip to be used for the steering.The end result should be less understeer compared to FWD although still more than you'd find on a RWD car, all other things being equal. But of course with RWD you'd have a greater chance of oversteer under power.
It'd be interesting to see a GTi without PP, a GTi with the PP and a Golf-R all compared when cornering at a variety of speeds and conditions.
Lucas Ayde said:
If you hit the limits of grip on the front tyres when cornering and applying power, Haldex should shift some power/torque rearwards leaving more of the front grip to be used for the steering.
The end result should be less understeer compared to FWD although still more than you'd find on a RWD car, all other things being equal. But of course with RWD you'd have a greater chance of oversteer under power.
It'd be interesting to see a GTi with PP compared to a Golf-R cornering at a variety of speeds and conditions.
Agree with your post but realise I could've been more clear. - I'm pointing-out that the more weight over the front wheels, the more compromised the "balance" (of the Haldex system) will be for the reasons explained above. The end result should be less understeer compared to FWD although still more than you'd find on a RWD car, all other things being equal. But of course with RWD you'd have a greater chance of oversteer under power.
It'd be interesting to see a GTi with PP compared to a Golf-R cornering at a variety of speeds and conditions.
Lucas Ayde said:
If you hit the limits of grip on the front tyres when cornering and applying power, Haldex should shift some power/torque rearwards leaving more of the front grip to be used for the steering.
The end result should be less understeer compared to FWD although still more than you'd find on a RWD car, all other things being equal. But of course with RWD you'd have a greater chance of oversteer under power.
It'd be interesting to see a GTi without PP, a GTi with the PP and a Golf-R all compared when cornering at a variety of speeds and conditions.
Yes, this is exactly what happens. But, on the other hand this is also why proper AWD systems (which distribute power fairly evenly) need a slow-in, fast out style, as if you go in too hot, you can actually get more understeer than on a FWD car, as the rears will push the chassis over the fronts. The end result should be less understeer compared to FWD although still more than you'd find on a RWD car, all other things being equal. But of course with RWD you'd have a greater chance of oversteer under power.
It'd be interesting to see a GTi without PP, a GTi with the PP and a Golf-R all compared when cornering at a variety of speeds and conditions.
scherzkeks said:
No Haldex system has ever felt anything other than AWD to me, which by nature/design has both FWD and RWD characteristics when cornering.
No Haldex system ever felt other than front wheel drive to me (Audi style front drive at that).It's a bit disappointing that for all your internet research you still can't fathom the fact that FWD/RWD/AWD doesn't dictate how a car corners, it only dictate what the driver can or can't do, and only up to a point. Set up is a far more influencial area than what wheels are driven. Go and drive a DC2 and then a push understeer 3-series and report back.
It's a bit disappointing that based on your posting here you clearly still do not understand the difference between longitudinal adhesion and lateral grip, in other words the concept of traction circle.
Get out more !
Ring on 2/3/4 October ?
nickfrog said:
No Haldex system ever felt other than front wheel drive to me (Audi style front drive at that).
It's a bit disappointing that for all your internet research you still can't fathom the fact that FWD/RWD/AWD doesn't dictate how a car corners, it only dictate what the driver can or can't do, and only up to a point. Set up is a far more influencial area than what wheels are driven. Go and drive a DC2 and then a push understeer 3-series and report back.
Whilst I agree, the setup can only give you certain options that are dictated by the configuration/layout. The layout of the vehicle will play a large part in dictating the handling, which is why manufacturers spend a lot of effort on things like CoG. I know you don't need to be told this but just pointing it out for certain individuals. It's a bit disappointing that for all your internet research you still can't fathom the fact that FWD/RWD/AWD doesn't dictate how a car corners, it only dictate what the driver can or can't do, and only up to a point. Set up is a far more influencial area than what wheels are driven. Go and drive a DC2 and then a push understeer 3-series and report back.
You're quite right Clivey. And that's the heart of the matter : it's the other important parameter but unlike the set up, it can't really be fiddled with as you know. Hence we end up with decent VAG cars that will always be compromised by having so much engine weight ahead of the front axle and therefore compromised polar moment of inertia (no wonder the R8 is the exception !!)
If you start with a balanced package through a good weight distribution you have an optimised package where all of the lateral grip can be distributed equally between front and rear and therefore can be totally used (and at which point, all of the adhesion potential can be used, leaving nothing for traction anyway before starting unwinding lock past the apex, which renders 4wd totally useless whereas the more dynamically compromised package will NEED 4wd to compensate for the inherent imbalance, but at least it helps the novice driver to manage traction).
If you start with a balanced package through a good weight distribution you have an optimised package where all of the lateral grip can be distributed equally between front and rear and therefore can be totally used (and at which point, all of the adhesion potential can be used, leaving nothing for traction anyway before starting unwinding lock past the apex, which renders 4wd totally useless whereas the more dynamically compromised package will NEED 4wd to compensate for the inherent imbalance, but at least it helps the novice driver to manage traction).
Edited by nickfrog on Saturday 16th August 13:25
I think you may be misunderstanding the point of an LSD.
nickfrog said:
You're quite right Clivey. And that's the heart of the matter : it's the other important parameter but unlike the set up, it can't really be fiddled with as you know. Hence we end up with decent VAG cars that will always be compromised by having so much engine weight ahead of the front axle and therefore compromised polar moment of inertia (no wonder the R8 is the exception !!)
If you start with a balanced package through a good weight distribution you have an optimised package where all of the lateral grip can be distributed equally between front and rear and therefore can be totally used (and at which point, all of the adhesion potential can be used, leaving nothing for traction anyway before starting unwinding lock past the apex, which renders 4wd totally useless whereas the more dynamically compromised package will NEED 4wd to compensate for the inherent imbalance, but at least it helps the novice driver to manage traction).
Most road cars have compromised weight distribution and front-mount engines, so it is puzzling that you compare the finer points of the Golf's handling to that of a purpose-built, mid-engined sports car. We do agree that setup is of primary importance, but this is not something you seemed to find important in past discussions (if one could call them that).If you start with a balanced package through a good weight distribution you have an optimised package where all of the lateral grip can be distributed equally between front and rear and therefore can be totally used (and at which point, all of the adhesion potential can be used, leaving nothing for traction anyway before starting unwinding lock past the apex, which renders 4wd totally useless whereas the more dynamically compromised package will NEED 4wd to compensate for the inherent imbalance, but at least it helps the novice driver to manage traction).
Edited by nickfrog on Saturday 16th August 13:25
In terms of the benefits of four driven wheels as related to cornering, aside from being able to put down more power on corner exit than a 2WD car (an obvious advantage in a performance context), and properly driven, an AWD car will lose lateral traction under power at a later point than a comparable 2WD vehicle, as it does not push all power to a single axle, but distributes it over 4 contact patches. Pretty basic, but perhaps was not covered in your copy of the Driving God FAQ -- which also apparently does not approve of HPDE instruction, or worthwhile publications from Milliken, etc. You know, stuff people who've been driving for some 30 years would have sought out out at some point.
scherzkeks said:
and properly driven, an AWD car will lose lateral traction under power at a later point than a comparable 2WD vehicle, as it does not push all power to a single axle, but distributes it over 4 contact patches.
Most cars are set up to understeer at the limit. Asking a vehicle which is already limited by front axle grip to also use that axle to take a share of the drive torque means that under power an awd has got less absolute lateral grip capability, not more.Gassing Station | General Gassing | Top of Page | What's New | My Stuff