4 wheel drive & the real world
Discussion
goldblum said:
RobM77 said:
goldblum said:
IATM said:
Output Flange said:
You don't need 4WD.
If they're your choices get the M135i if that's your preference and a set of winter tyres. Job jobbed.
100% rightIf they're your choices get the M135i if that's your preference and a set of winter tyres. Job jobbed.
I agree RWD cars are great fun in the wet, my AMG is brilliant - now I've taken the winters off. Off the line power and overtaking in the rain in a 4x4 is less nerve-wracking though.For a fun drive I'd take a RWD set up, if I was commuting everyday in poor conditions I'd take a 4x4.
With regard to wheelspin etc, nobody's timing you on the road. To compare like with like, if I was offered a 335i with an LSD or a 335i without an LSD, I'd take it without, even though the car woul probably be quicker with it, because subjectively I prefer open differentials. Many would prefer it with, but that's entirely subjective.
RobM77 said:
What objective measures of handling are there then? I suppose there are some broad parameters that you could use to quantify how 'well' a car handles, but surely it's largely a subjective thing, and judging by driving various cars it's actually quite an art form achieving what most people regard as good handling?
With regard to wheelspin etc, nobody's timing you on the road. To compare like with like, if I was offered a 335i with an LSD or a 335i without an LSD, I'd take it without, even though the car woul probably be quicker with it, because subjectively I prefer open differentials. Many would prefer it with, but that's entirely subjective.
Matters not whether someone's timing you or not. Some simply like to retain more performance and grip in the wet than a powerful RWD car offers. With regard to wheelspin etc, nobody's timing you on the road. To compare like with like, if I was offered a 335i with an LSD or a 335i without an LSD, I'd take it without, even though the car woul probably be quicker with it, because subjectively I prefer open differentials. Many would prefer it with, but that's entirely subjective.
Dave Hedgehog said:
goldblum said:
300bhp is right.
Personally I'll take a RWD V8 for the summer months and a AWD V8 for winter, thanks. Perhaps you have some underwear recommendations for me as well?
RS6 as a daily and then 911 GT3 or C63 Black as a playthingPersonally I'll take a RWD V8 for the summer months and a AWD V8 for winter, thanks. Perhaps you have some underwear recommendations for me as well?
sorted
goldblum said:
RobM77 said:
What objective measures of handling are there then? I suppose there are some broad parameters that you could use to quantify how 'well' a car handles, but surely it's largely a subjective thing, and judging by driving various cars it's actually quite an art form achieving what most people regard as good handling?
With regard to wheelspin etc, nobody's timing you on the road. To compare like with like, if I was offered a 335i with an LSD or a 335i without an LSD, I'd take it without, even though the car woul probably be quicker with it, because subjectively I prefer open differentials. Many would prefer it with, but that's entirely subjective.
Matters not whether someone's timing you or not. Some simply like to retain more performance and grip in the wet than a powerful RWD car offers. With regard to wheelspin etc, nobody's timing you on the road. To compare like with like, if I was offered a 335i with an LSD or a 335i without an LSD, I'd take it without, even though the car woul probably be quicker with it, because subjectively I prefer open differentials. Many would prefer it with, but that's entirely subjective.
with regular road going cars I've always found winter tyres have more of a bearing in the snow than a 4WD system. They only exception would be living in the sticks and offroading.
Surely it's per circumstance though, over the last 12 months I've only had more than a few inches of snow once and even that only got to about a foot. I had a 1 series at the time which handled fine when the traction controlled was disabled (as much as you can disable it anyway).
On track I've always preferred testing RWD cars but anything over 500BHP starts to become a little wasted in wet conditions (or worse).
Surely it's per circumstance though, over the last 12 months I've only had more than a few inches of snow once and even that only got to about a foot. I had a 1 series at the time which handled fine when the traction controlled was disabled (as much as you can disable it anyway).
On track I've always preferred testing RWD cars but anything over 500BHP starts to become a little wasted in wet conditions (or worse).
Dave Hedgehog said:
goldblum said:
I thought about the V10 RS6, must confess... .
the new one is bonkers simo1863 said:
with regular road going cars I've always found winter tyres have more of a bearing in the snow than a 4WD system. They only exception would be living in the sticks and offroading.
Surely it's per circumstance though, over the last 12 months I've only had more than a few inches of snow once and even that only got to about a foot. I had a 1 series at the time which handled fine when the traction controlled was disabled (as much as you can disable it anyway).
On track I've always preferred testing RWD cars but anything over 500BHP starts to become a little wasted in wet conditions (or worse).
Surely it's per circumstance though, over the last 12 months I've only had more than a few inches of snow once and even that only got to about a foot. I had a 1 series at the time which handled fine when the traction controlled was disabled (as much as you can disable it anyway).
On track I've always preferred testing RWD cars but anything over 500BHP starts to become a little wasted in wet conditions (or worse).
Pretty much exactly what I've found. If you only get a few weeks of snow a year, then I'd say buy the car you prefer and stick winter tyres on it for the winter. My parents live in the sticks and when it snows often drive on virgin snow filled roads; they have three RWD cars and nothing else, but just use winter tyres in winter with no issues. I think if they lived somewhere that got months of proper snow though they may convert to 4WD with winter tyres, but I suspect that doesn't apply for the majority of us - although the OP didn't say where he was from I don't think? I don't think a 4WD on summer tyres really makes much sense though just for snow unless you personally prefer the handling for the rest of the year - I'd always buy the car I prefer on a typical UK day (10 degrees and drizzle probably!) and then get winter tyres to make it work in cold or snowy weather.Can we do a summary and sign this one off? 
There are different sorts of cars. Some people like some setups more than other setups.
(I like them all)
Buy the one you like best.
Manage bad winters with winter tyres, or stay indoors.
ps don't forget the REAL issue with a bad winter is ground/snow clearance under the car?
There are different sorts of cars. Some people like some setups more than other setups.
(I like them all)
Buy the one you like best.
Manage bad winters with winter tyres, or stay indoors.
ps don't forget the REAL issue with a bad winter is ground/snow clearance under the car?
goldblum said:
Dave Hedgehog said:
goldblum said:
I thought about the V10 RS6, must confess... .
the new one is bonkers you forget its a 2 tonne family wagon
I think there's pretty much a consensus, yes. Buy the car you like driving the best and then put winter tyres on it in the winter if you want them. The slight complication is that on summer tyres 4WD copes best, then FWD then RWD, but I must confess even the worst combo, RWD and snow, I've experienced many many times and always coped ok, just be very gentle with the throttle and be sensible about what routes you take.
One last thing to remember is that Volvo are Swedish and made RWD cars up until relatively recently, BMW are from Bavaria in southern Germany and Mercedes and Porsche aren't too much further north than that. They're all RWD and in snowier places than the UK; they just change their tyres in winter time.
goldblum said:
Matters not whether someone's timing you or not. Some simply like to retain more performance and grip in the wet than a powerful RWD car offers.
By grip do you mean lateral or longitudinal (traction) ? Weight increases traction
Weight decreases lateral grip
A 4wd will therefore have LESS lat grip than the equivalent car with 2wd, wet or dry.
The hope is that the added traction and the ease with which it's applied will more than compensate for this. And I am sure it often works on the road.
For me though, I'd rather compromise traction than apex speed, including on the road, while preserving the pleasure of doing the throttle modulation myself, including getting it wrong if it comes to that.
Edited by nickfrog on Thursday 30th January 17:28
nickfrog said:
goldblum said:
Matters not whether someone's timing you or not. Some simply like to retain more performance and grip in the wet than a powerful RWD car offers.
By grip do you mean lateral or longitudinal (traction) ? 
. RobM77 said:
Wookie's dead right of course (as he usually is)RobM77 said:
What objective measures of handling are there then?
There are plenty of objective tests you can use for handling to obtain things like yaw rate and damping, roll rate or frequency response (and many others) which are used as benchmarks to assess basic vehicle behaviour. However they are relatively difficult to record reliably, accurately and repeatably, they require a lot of work to turn into useful data (i.e. it takes ages to carry out and the instrumentation and post-processing is a pain in the cock). Plus they actually relate to very basic vehicle behaviour that is far more easily assessed by a skilled driver. However they are helpful for validating changes or progress, formally identifying handling issues or assessing behaviour against benchmark vehicles which would otherwise rely on subjective scores and opinions from small groups of self interested individuals (of which I am one)!
There are also tests such as lane changes at particular speeds (which can be VERY 'entertaining' in some cars, and not necessarily ones you would expect) but they're more about validating basic vehicle handling safety.
nickfrog said:
Weight decreases lateral grip
Are you sure about that? Doesn't the vehicle's mass cancel out in the equations? Just asking the question - I'm no authority on this or anything and I have seen what you're saying quoted before, but here's my reasoning:I thought that the grip available was roughly proportional to mu*R (mu = coeff of friction, R = reactionary force between tarmac and tyre; only proportional to, not equal to, because a tyre to tarmac interaction is not straight plane surface friction, which is why contact patch size makes a difference), so the greater the mass the greater the grip; but the lateral force required to hold a given line is surely F=mv^2/r (m = mass, v = angular velocity, r = radius of corner). Equate those two and the m cancels out and you're just left with corner radius and speed squared. In other words, the heavier the car, the more grip it generates, but equally the more grip that car will need to stay on the corner, and the two increase together perfectly. In practise, on a constant radius circle a 500kg Caterham won't generally generate more lateral g than a 2000kg BMW M5 for example (both will probably be about 1g); the Caterham will get its advantages over a lap in agility (intertia), braking (F=ma) and acceleration (F=ma) won't it?
I always assumed this was why downforce made cars quicker - the extra reactionary force going down through the tyres increases the vehicle's effective weight in a Mu*R sense, so giving more grip, but crucially it doesn't increase the vehicle's inertial mass for the mv^2/r component, so the car corners quicker. So for example a 600kg F1 car could have the grip of a 1300kg saloon on slicks, but only feels the inertial lateral acceleration of a 600kg car.
Forgive me if there's a mistake in that - I'm very busy at work! I was just curious, that's all.
The Wookie said:
RobM77 said:
Wookie's dead right of course (as he usually is)RobM77 said:
What objective measures of handling are there then?
There are plenty of objective tests you can use for handling to obtain things like yaw rate and damping, roll rate or frequency response (and many others) which are used as benchmarks to assess basic vehicle behaviour. However they are relatively difficult to record reliably, accurately and repeatably, they require a lot of work to turn into useful data (i.e. it takes ages to carry out and the instrumentation and post-processing is a pain in the cock). Plus they actually relate to very basic vehicle behaviour that is far more easily assessed by a skilled driver. However they are helpful for validating changes or progress, formally identifying handling issues or assessing behaviour against benchmark vehicles which would otherwise rely on subjective scores and opinions from small groups of self interested individuals (of which I am one)!
There are also tests such as lane changes at particular speeds (which can be VERY 'entertaining' in some cars, and not necessarily ones you would expect) but they're more about validating basic vehicle handling safety.
As I said (straight after the bit you quoted), these are things that you can measure, but ultimately it'll be subjective won't it? For instance, a low polar moment of inertia will enable a car to rotate quickly to turn into a corner, so may initially be thought of as being good for handling, but that may not actually be desirable when it comes to trimming the car's line in a corner. The Porsche 968 for example was hailed as a great handling car, and this was largely down to its transaxle layout at the rear giving a mass to balance against the front and a higher polar moment of inertia than, for example, a Lotus Elise, which is equally regarded as a good handling car, but for totally different reasons. Equally, weight distribution: 50:50 is often seen as perfection, but as I'm sure you'll be aware, a lot of people rather like the 911's rather more rear-biased weight distribution.
As you say though, having things one can measure can really help put a context on subjective analysis and help to judge changes to a car's setup.
RobM77 said:
nickfrog said:
Weight decreases lateral grip
Are you sure about that? Doesn't the vehicle's mass cancel out in the equations? Just asking the question - I'm no authority on this or anything and I have seen what you're saying quoted before, but here's my reasoning:I thought that the grip available was roughly proportional to mu*R (mu = coeff of friction, R = reactionary force between tarmac and tyre; only proportional to, not equal to, because a tyre to tarmac interaction is not straight plane surface friction, which is why contact patch size makes a difference), so the greater the mass the greater the grip; but the lateral force required to hold a given line is surely F=mv^2/r (m = mass, v = angular velocity, r = radius of corner). Equate those two and the m cancels out and you're just left with corner radius and speed squared. In other words, the heavier the car, the more grip it generates, but equally the more grip that car will need to stay on the corner, and the two increase together perfectly. In practise, on a constant radius circle a 500kg Caterham won't generally generate more lateral g than a 2000kg BMW M5 for example (both will probably be about 1g); the Caterham will get its advantages over a lap in agility (intertia), braking (F=ma) and acceleration (F=ma) won't it?
I always assumed this was why downforce made cars quicker - the extra reactionary force going down through the tyres increases the vehicle's effective weight in a Mu*R sense, so giving more grip, but crucially it doesn't increase the vehicle's inertial mass for the mv^2/r component, so the car corners quicker. So for example a 600kg F1 car could have the grip of a 1300kg saloon on slicks, but only feels the inertial lateral acceleration of a 600kg car.
Forgive me if there's a mistake in that - I'm very busy at work! I was just curious, that's all.
Edited by nickfrog on Thursday 30th January 17:53
The initial setup of a racecar/bikes handling is completely objective. Subjective elements - how a car 'feels' to the driver - are generally dialled in later. Do an internet search for 'handling set up for XXXX Nurburgring' : http://www.f1technical.net/features/816 and you will be given a set of technical measurements to inform you how to adjust a number of the car's functions so it handles better on the track and results in quicker lap times. Hopefully. These are all objective measurements. Whether you like the effect or not is subjective.
nickfrog said:
RobM77 said:
nickfrog said:
Weight decreases lateral grip
Are you sure about that? Doesn't the vehicle's mass cancel out in the equations? Just asking the question - I'm no authority on this or anything and I have seen what you're saying quoted before, but here's my reasoning:I thought that the grip available was roughly proportional to mu*R (mu = coeff of friction, R = reactionary force between tarmac and tyre; only proportional to, not equal to, because a tyre to tarmac interaction is not straight plane surface friction, which is why contact patch size makes a difference), so the greater the mass the greater the grip; but the lateral force required to hold a given line is surely F=mv^2/r (m = mass, v = angular velocity, r = radius of corner). Equate those two and the m cancels out and you're just left with corner radius and speed squared. In other words, the heavier the car, the more grip it generates, but equally the more grip that car will need to stay on the corner, and the two increase together perfectly. In practise, on a constant radius circle a 500kg Caterham won't generally generate more lateral g than a 2000kg BMW M5 for example (both will probably be about 1g); the Caterham will get its advantages over a lap in agility (intertia), braking (F=ma) and acceleration (F=ma) won't it?
I always assumed this was why downforce made cars quicker - the extra reactionary force going down through the tyres increases the vehicle's effective weight in a Mu*R sense, so giving more grip, but crucially it doesn't increase the vehicle's inertial mass for the mv^2/r component, so the car corners quicker. So for example a 600kg F1 car could have the grip of a 1300kg saloon on slicks, but only feels the inertial lateral acceleration of a 600kg car.
Forgive me if there's a mistake in that - I'm very busy at work! I was just curious, that's all.
Do you have an equation or graph that summarises the mass vs lateral grip relationship? I'd be interested to know what it looks like
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