4 wheel drive & the real world

[RobM77]

goldblum said:

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.

Ah, ah I wouldn't class that as handling. For example, setting camber angles to produce the desired temperature distribution across the tyre, adjusting tyre pressures to work the tyres optimally, or perhaps adjusting dampers for a given track - that's just optimising a car. Just a difference in terminology though I'm sure? I class 'handling' as how a car reacts to inputs and how a car moves around, so in other words everything that's not to do with outright grip in a corner. You're right though, I suppose there is a significant overlap and potential interplay between handling and performance - for example if you set up my first ever race car, which was FWD, to grip perfectly in a corner, then you'd actually go slower, because the way the car would handle with perfect camber on all four wheels wasn't workable in the context of a quick lap; we actually reduced rear end grip to go faster.

[prg123]

Might be worth looking at this......

http://www.autocar.co.uk/car-video/winter-tyres-vs...

- Pete

[nickfrog]

RobM77 said:

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

Not sure I have, I am out of my depths as it is

Found this though on another thread :

HiRich said:

Fc=m v2 /r
Fc= Centripetal Force = Sum of the four Grip Forces from the four tyres = G1+G2+G3+G4
m = mass of vehicle
v = velocity
r = radius of corner.

[nickfrog]

goldblum said:

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) ?

Well I'm talking everyday folk who are bored of their performance car wheelspinning in the wet when pulling out of a junction or during a nippy overtake. So which do you think I mean? .

I have no idea as my Michelin Supersports give me HUGE lateral grip AND traction in the wet, at least for road use. But then again, I have a NA engine, I short shift if need be and I don't use the throttle as an on/off switch ;-)

But surely we all know that things are essentially about tyres anyway. Witness little Swifts at the Ring on 888 making performance cars look like boats, at least up to the apex and even sometimes in the ensuing traction zones.

Edited by nickfrog on Thursday 30th January 18:11

[Mastodon2]

Scuffers said:

Who said in the dry?

Read what i said.

Then, if your still up for it, come and prove me wrong.

This is some of the most ridiculous posting I've seen on PH for a while. Do you think he is going to rock up in a million pound car to race you along the backroads of southern England? And do you honestly drive flat out on C and D roads, like an undiscovered Seb Loeb?

[RobM77]

nickfrog said:

RobM77 said:

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

Not sure I have, I am out of my depths as it is

Found this though on another thread :

HiRich said:

Fc=m v2 /r
Fc= Centripetal Force = Sum of the four Grip Forces from the four tyres = G1+G2+G3+G4
m = mass of vehicle
v = velocity
r = radius of corner.

Ah, that's for the wooden wheeled car on wooden floorboards, as I quoted in my post. Real life grip will be roughly proportional to that, but it's the departure from linearity which I didn't realise - that's what would cause imbalance between lateral grip available and lateral grip required (mv^2/r), which for a given speed is still linear for a real car. I'll have a dig around when I've next got some time spare

[nickfrog]

Sorry Rob I can help any more! I would assume that there must be huge disparity between say a road tyre and a race tyre where the manufacturer will try and "delay" the start of the "loss of linearity" so I don't know what equation or even what parameters would reflect that.

[Pixelpeep]

prg123 said:

Might be worth looking at this......

http://www.autocar.co.uk/car-video/winter-tyres-vs...

- Pete

Really interesting video

[nickfrog]

This is good too RWD and winter tyres VS 4WD and summer tyres on snow http://www.youtube.com/watch?v=STaximkaQxo

So much for the superiority of 4wd on snow although obviously 4wd+winters would be the perfect belt and braces snow/ice/cold solution. Farcical in most of the UK IMO.

[RobM77]

nickfrog said:

Sorry Rob I can help any more! I would assume that there must be huge disparity between say a road tyre and a race tyre where the manufacturer will try and "delay" the start of the "loss of linearity" so I don't know what equation or even what parameters would reflect that.

It's ok, I'll look into it when I have some free time I love Physics so it's no chore! (unlike what's keeping me in the office tonight...).

[tr7v8]

nickfrog said:

This is good too RWD and winter tyres VS 4WD and summer tyres on snow http://www.youtube.com/watch?v=STaximkaQxo

So much for the superiority of 4wd on snow although obviously 4wd+winters would be the perfect belt and braces snow/ice/cold solution. Farcical in most of the UK IMO.

I assume they are both manuals? I suspect the Subaru may be Auto. Also the M3 will have a LSD which the 4 x 4 won't. LSD makes a huge difference (sorry) my Alfa 75 was very controllable in snow on standard summers because of 50/50 weight distribution & the LSD. Also very torquey so no need for revs.
My Jaguar S-type auto 2.7D on summers was hopeless. Light on the rear, no LSD & peaky torque from the diesel matched with the auto.

[blade7]

RobM77 said:

Porsche aren't too much further north than that. They're all RWD

Are you sure ?

[RobM77]

blade7 said:

RobM77 said:

Porsche aren't too much further north than that. They're all RWD

Are you sure ?

Yes, slight slip from me there (no pun intended). They were RWD only for many many years, but then brought in 4WD due to customer demand after stock brokers crashed their 911s in the 80s

My main point though is that even Volvo and BMW were fine with RWD only for many many years, just relying on winter tyres. The snow we get in the UK isn't a patch on what they get in Volvo or BMW land.

[Scuffers]

Mastodon2 said:

Scuffers said:

Who said in the dry?

Read what i said.

Then, if your still up for it, come and prove me wrong.

This is some of the most ridiculous posting I've seen on PH for a while. Do you think he is going to rock up in a million pound car to race you along the backroads of southern England? And do you honestly drive flat out on C and D roads, like an undiscovered Seb Loeb?

At which point, may i suggest you learn to read?

[blade7]

RobM77 said:

Yes, slight slip from me there (no pun intended). They were RWD only for many many years, but then brought in 4WD due to customer demand after stock brokers crashed their 911s in the 80s

I'm glad you put those smileys in your post, I was laughing too.

[sleep envy]

goldblum said:

sleep envy said:

300bhp/ton said:

aeropilot said:

otolith said:

All that matters in a road car is the entirely subjective preference for how the car feels. It makes chuff all difference how fast it is.

The most sensible post in the whole thread.

I'm not sure it is. Being able to deploy and use the power directly affects how fast something is, and unless you can drive like Tony Pond, powerful RWD cars just aren't as deployable in many conditions.

And I'm not just talking about something like an Elise, which in any guise is relatively low hp and low grunt but with a lot of mechanical traction. I'm talking about cars with proper grunt.

Spinning the wheels is ever so easy with a powerful grunty engine. And in the wet you just can't use the power the same. With AWD it is a far more stable platform and will put the power down. And thus be faster.

Don't forget to wear your nomex underpants when you pop down to Tesco.

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?

XXL to deal with your insecurity.

Why would you want to be going faster than you think is suitable on public road in poor conditions?

Neither can I say I've ever had the need to buy a car to use on public roads with a different transmission dependent on the season.

[uk_vette]

Pixelpeep said:

How much difference does 4wd make in the real world for general day to day getting about and making progress?

I have heard many a horror story about RWD and snow and have personal experience of the issues of trying to put decent power down in a FWD car so in choosing a 'keeper' should 4wd be a must have, a nice to have or a no point to have.

Reason i ask is because i am looking at next car purchase and if i can bin the need for 4wd my options get a lot cheaper!

Basically the A45 and the RS3 tick all of my boxes except price, the m135i ticks all of them except 4wd so can someone give me real world experiences to give me an idea.

I have never driven a powerful RWD car which also concerns me slightly but i can't ignore the price difference.

Help!

.
.
When any one mentions "four wheel drive" this should only be considered with the phrase, Land Cruiser, Land Rover, Patrol, and the like.

four wheel drive cars are pathetic, sorry to say,
get rid of it, and buy a proper four wheel drive.

vette

[deltashad]

uk_vette said:

.
.
When any one mentions "four wheel drive" this should only be considered with the phrase, Land Cruiser, Land Rover, Patrol, and the like.

four wheel drive cars are pathetic, sorry to say,
get rid of it, and buy a proper four wheel drive.

vette

Hmmm... four wheel drive cars are definately not pathetic.

[Heaveho]

uk_vette said:

.
.
When any one mentions "four wheel drive" this should only be considered with the phrase, Land Cruiser, Land Rover, Patrol, and the like.

four wheel drive cars are pathetic, sorry to say,
get rid of it, and buy a proper four wheel drive.

vette

Wrong......never said this on a forum before, but you don't know what you're talking about. Try driving a performance orientated 4wd before you post up rubbish like this. I live by them, but have driven the stuff you refer to through necessity because of work, so I know the difference. Leave this subject to people who have a clue!

[Boobonman]

sleep envy said:

XXL to deal with your insecurity.

Why would you want to be going faster than you think is suitable on public road in poor conditions?

Neither can I say I've ever had the need to buy a car to use on public roads with a different transmission dependent on the season.

Would a RWD car accelerate faster and be able to deploy its power better than a FWD one in poor conditions?

Could the driver of the Focus ST accuse the driver of the 330i of trying to go faster than is suitable?

Could the driver of the 330i ask the driver of the S4 the same?

Of course a 4x4 car will lay its power down better, I think you are being deliberately obtuse.