RE: Haldex - the truth!
Discussion
kambites said:
I think if you took a standard Haldex equipped Golf (for example) and sent all of the power to the rear wheels, it would still feel FWD. What we feel a FWD is more to do with relative spring and damper rates and suspension geometry at the front and back of the car than the actual place the drive is going to.
Whilst I think its true that a front driver tends to be more nose heavy, having all the hardware at the front, I don't buy this statement. Are you saying that all FWD manufacturers deliberately engineer/set-up their cars to feel different to RWD? balls-out said:
Whilst I think its true that a front driver tends to be more nose heavy, having all the hardware at the front, I don't buy this statement. Are you saying that all FWD manufacturers deliberately engineer/set-up their cars to feel different to RWD?
Yes, you set up suspension fundementally differently for FWD and RWD cars in order to get handling balance correct and to aid traction. A FWD car will typically be softer in roll at the front than the rear and a RWD car the opposite, that's why FWD cars tend to cock a rear wheel under steady-state cornering and RWD cars cock a front wheel. It's also the single biggest contributor to how a car can "feel" RWD or FWD at well below the limits of traction. Edited by kambites on Tuesday 24th March 16:50
kambites said:
balls-out said:
Whilst I think its true that a front driver tends to be more nose heavy, having all the hardware at the front, I don't buy this statement. Are you saying that all FWD manufacturers deliberately engineer/set-up their cars to feel different to RWD?
Yes, you set up suspension fundementally differently for FWD and RWD cars in order to get handling balance correct and to aid traction. A FWD car will typically be softer in roll at the front than the rear and a RWD car the opposite, that's why FWD cars tend to cock a rear wheel under steady-state cornering and RWD cars cock a front wheel. It's also the single biggest contributor to how a car can "feel" RWD or FWD at well below the limits of traction. Edited by kambites on Tuesday 24th March 16:50
kambites said:
Even a humble diesel Golf will be neutral-ish for a moment, if you lift off completely at the limit.
Edited by iloveboost on Tuesday 24th March 18:12
tomjol said:
In other words, it's always been "pre-emptive" in most situations, just got (a lot) better over time.
Thanks for the explanation. I didn't know that the system locks up pre-emptively to prevent wheelspin. The problem is that people like me read a press release where it may say something like: 'Haldex pump speed reaction time decreased and full locking speed is now achieved in just an 1/8 of a revolution'.We're not engineers so were assume (wrongly) that locking speed is the most important factor, and that Haldex doesn't lock until it detects a change in wheel speed. I know it frustrates people like you that know everything.
It's just one of those car myths. Some people here say that there's no proper substitute for a centre Torsen diff. There must be some truth to that, but these are probably the same sort of people that say there's no substitute for vinyl. I know Haldex is fundamentally a maximum of 50/50 without brake assist (or with torque vectoring near 75/25 on the outside wheel) but it's not a 'bad' system. Most of the myths about it being rubbish, is probably because it seems to be sold on mainly Volvo and VAG cars. Both manufacturers engineer in moderate understeer, and 'bad' handling on track isn't the fault of the Haldex system. However it does add weight, reduce fuel economy and add cost.
As usual, the point is well and truly missed once more!
The real reason a front transverse engined car will never "handle" like a front longitudinal engined rwd car is because of the static weight distribution, and very little to do with how much % of torque you send to the back (which incidentally, is also fairly irrelevant). Lets face it, every single 4wd Audi which has been released since 1990 has had "a more rear biased torque distribution" according to the marketers, in which case, by nowthey should be approximately 237% rear biased, and yet, yup, they still understeer (due to the engine and Xmission hanging out the front of the car by about 3 feet....)
The real reason a front transverse engined car will never "handle" like a front longitudinal engined rwd car is because of the static weight distribution, and very little to do with how much % of torque you send to the back (which incidentally, is also fairly irrelevant). Lets face it, every single 4wd Audi which has been released since 1990 has had "a more rear biased torque distribution" according to the marketers, in which case, by nowthey should be approximately 237% rear biased, and yet, yup, they still understeer (due to the engine and Xmission hanging out the front of the car by about 3 feet....)
Most 4wd Audis aren't transverse engined. Although obviously most of the Haldex ones are. 
Unfortunately even the longitudinal engined ones have the engine rather a long way forward. I'm not convinced that's the primary cause of their rather front-lead chassis balance though. I suspect they do that because Audi want them to do that. It's easy enough to get a front weight biased car to oversteer by playing with the suspension setup if you want it to.
Unfortunately even the longitudinal engined ones have the engine rather a long way forward. I'm not convinced that's the primary cause of their rather front-lead chassis balance though. I suspect they do that because Audi want them to do that. It's easy enough to get a front weight biased car to oversteer by playing with the suspension setup if you want it to.
Edited by kambites on Tuesday 24th March 19:08
Pants on fire PH! Combined with electro steering its one more nail in coffin of the driver's car. Manufacturers are figuring clever ways of selling cheaper made cars for more money.
I love RWD, have a good one. Also love my big barge permanent 4wd practicality when the family goes skiing.
I love RWD, have a good one. Also love my big barge permanent 4wd practicality when the family goes skiing.
kambites said:
Most 4wd Audis aren't transverse engined. Although obviously most of the Haldex ones are.
Unfortunately even the longitudinal engined ones have the engine rather a long way forward. I'm not convinced that's the primary cause of their rather front-lead chassis balance though. I suspect they do that because Audi want them to do that. It's easy enough to get a front weight biased car to oversteer by playing with the suspension setup if you want it to.
Indeed, you can tune the chassis dynamics to make the car have any dynamic trait you want, but it's the STATIC mass distribution that sets the base handling. If you use heafty springs or ARB's to dynamically transfer that weight around, all you do is end up with a great non linearity in the vehicles response. Having a base 50:50 dsitribution means the difference between the static and dynamic performance is small and hence the car generally will drive with a good basic stability, and yet when provoked, with build towards the tyres slip limits in a progressive fashion.Unfortunately even the longitudinal engined ones have the engine rather a long way forward. I'm not convinced that's the primary cause of their rather front-lead chassis balance though. I suspect they do that because Audi want them to do that. It's easy enough to get a front weight biased car to oversteer by playing with the suspension setup if you want it to.
If you have a say 70:30 distribuition, you can get to 50:50 dynamically, but any change in those dynamic conditions changes the balance. Take something like a Scooby, which has a fundamentally poor mass distribution, they don't handle well in extremis precisely because the mass is being used so dynamically.
Why do so few manufacturers run different tyre compounds front and rear to correct the fundamentally poor balance of shopping cars when creating (expensive) hot versions? Surely for the margins on something like the RS3, Audi could have commissioned some softer rear tyres to help neutralise the handling balance?
If Lotus could afford to do it for the Elise, I'm sure VAG can!
If Lotus could afford to do it for the Elise, I'm sure VAG can!
Mr Whippy said:
PH, adverts in articles, in disguise!
I agree!pppppppppppppppp said:
Perhaps PH should stop giving cars positive reviews. They're clearly advertisements for cars.
May I suggest that if you are incapable of seeing which parts of an article are from a manufacturer (the clue's in the fact that they're direct quotes) then you should... urm..... just feck off.
Is this what you really think? I mean that as a serious question.May I suggest that if you are incapable of seeing which parts of an article are from a manufacturer (the clue's in the fact that they're direct quotes) then you should... urm..... just feck off.
...
All this FWD->4WD stuff. I don't like it. Yes, it makes the car a bit quicker pulling away. And it works in the snow. But how about some feedback? Throttle adjustability? Some enjoyment? I haven't found it yet.
Even the very newest and most developed system - in the new Focus RS - is described by the head of global product development as such: "Fundamentally it's front-wheel drive". I admire the effort going in and I'm sure it will become good. But, not yet.
There's only one memorable rear-biased 4wd I've driven, that being a Subaru Impreza 22B with the DCCD fully one way (I forget which way - dial turned towards the front?). This was a decently adjustable car in the right conditions.
iloveboost said:
tomjol said:
In other words, it's always been "pre-emptive" in most situations, just got (a lot) better over time.
Thanks for the explanation. I didn't know that the system locks up pre-emptively to prevent wheelspin. The problem is that people like me read a press release where it may say something like: 'Haldex pump speed reaction time decreased and full locking speed is now achieved in just an 1/8 of a revolution'.We're not engineers so were assume (wrongly) that locking speed is the most important factor, and that Haldex doesn't lock until it detects a change in wheel speed. I know it frustrates people like you that know everything.
It's just one of those car myths. Some people here say that there's no proper substitute for a centre Torsen diff. There must be some truth to that, but these are probably the same sort of people that say there's no substitute for vinyl. I know Haldex is fundamentally a maximum of 50/50 without brake assist (or with torque vectoring near 75/25 on the outside wheel) but it's not a 'bad' system. Most of the myths about it being rubbish, is probably because it seems to be sold on mainly Volvo and VAG cars. Both manufacturers engineer in moderate understeer, and 'bad' handling on track isn't the fault of the Haldex system. However it does add weight, reduce fuel economy and add cost.
To be fair the system is so widely misunderstood that there's little reason to even question it. It was only after buying an older Haldex car that I doubted it, and the information out there on the Internet is so poor that it took quite a bit of digging to uncover anything useful. Had to get hold of various service manuals and associated training material to understand what was actually happening.
NickGibbs said:
Hadn't noticed earlier that you'd written this Nick, didn't mean to be pissy I've just read so many times that "it's FWD until the front slips" and it's just so wrong!Mark Wibble said:
Proof-read police!
"Or least that's what the makers pushing sportier cars would have us believe"
"you already know the bulk of those 300,000 last year were all-wheel drive versions of things the Nissan Qashqai."
"But there are also and more sporting models with AWD"
"Now we're talking to all manufacturers about the possible of having their cars AWD"
"The current fifth-gen Haldex can sends about 10-15 per cent of power to the rear "
"not typical a UK surface""
Normally I'd want to scream at grammar police and tell you to get a life. However I noticed several mistakes when I read the article and agree that its very sloppy!! "Or least that's what the makers pushing sportier cars would have us believe"
"you already know the bulk of those 300,000 last year were all-wheel drive versions of things the Nissan Qashqai."
"But there are also and more sporting models with AWD"
"Now we're talking to all manufacturers about the possible of having their cars AWD"
"The current fifth-gen Haldex can sends about 10-15 per cent of power to the rear "
"not typical a UK surface""
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