Do folk really perceive RWD to be dangerous?
Discussion
GravelBen said:
Hol said:
I have owned two Forester Turbos and I admit to going out in the snow for fun as their assymetrical AWD was perfect for forward momentum going UP a snowy/icey hill. I also have a pair totally unused Forester sized snowchains in my garage loft, as I never needed them over 7 winters.
But despite its grip in getting me up hills and through deep snow, it had the same problem with physics that every other car on summer spec tyres has - when going DOWN an Icy slope (the hilly type, not a cold TG china-man).
My point is that the tyres would loose physical adhesion, due to the weight of the car overwhelming the ability of the front tyres to grip to the slippery surface.
Bit off topic here but hey...But despite its grip in getting me up hills and through deep snow, it had the same problem with physics that every other car on summer spec tyres has - when going DOWN an Icy slope (the hilly type, not a cold TG china-man).
My point is that the tyres would loose physical adhesion, due to the weight of the car overwhelming the ability of the front tyres to grip to the slippery surface.
While there is of course only so much traction the tyres are able to provide, a decent 4wd system can make better use of that traction in deceleration as well as acceleration. The torque transfer through the drivetrain works both ways to help avoid single-wheel lockups, as well as applying engine braking across 4 contact patches instead of 2. If you just stomp on the brakes and rely on ABS (as many people do!) you probably won't notice any difference though.
It may well be that your icy slope was just too slippery even for engine braking with those tyres, but the 2wd cars traction limit would have been exceeded by more than the 4wd.
It is an interesting experiment to slowly descend a slippery slope in a 4wd using only engine braking to control the speed (especially if in low range), and then see just how little force can be applied on the brakes before the vehicle starts to slide and you lose steering control. Certainly increases your respect for engine braking!
Wheel braking is wheel braking. - Whether it be via the disks, the drivetrain or a combination of both.
The contact point between the car and the 'surface' of the road is thre tread. If the tyre tread of four wheels cannot grip an icy slope, then your are screwed no matter how good your drivetrain.
I have personally been sat stationary on an icy hill in a snow flurry unable to take my foot off the brake, as the fully working handbrake iteself would not hold the car. The back wheels just slipped and I needed to lock all four wheels to hold me.
Try the engine braking next time and see how you go - I've descended snow/ice safely and controllably with low range engine braking when even my gentlest touch on the brake pedal caused an instant lockup and slide.
You're right that no grip is still no grip, but the 4wd can operate closer to that limit than a 2wd with the same tyres.
Anyway, back to people being irrationally scared of Rwd!
You're right that no grip is still no grip, but the 4wd can operate closer to that limit than a 2wd with the same tyres.
Anyway, back to people being irrationally scared of Rwd!
Edited by GravelBen on Friday 24th October 13:34
SonicShadow said:
I think a skid pan day should be a mandatory part of the driving instruction process - for most people, the first time they learn about how a car behaves and responds in low grip conditions is when it goes wrong for them on the public road. Surely it would be better to demonstrate this to every new driver in a controlled environment? Plus it's quite fun when there's no risk of ending up in a ditch or embedded in a hedge 
"A little knowledge is a dangerous thing" applies here I think...GravelBen said:
Try the engine braking next time and see how you go - I've descended snow/ice safely and controllably with low range engine braking when even my gentlest touch on the brake pedal caused an instant lockup and slide.
Ben,In think I see where you were going now.
I get the whole engine-breaking-down-the-hill bit - in fact I could write my own essay on it, if I wanted to.
But, I have not been talking about moving down a hill as the total master of your own timeline and steering control choice.
I am talking about having to stop for a sudden/unavoidable incident directly where the limiting factor is breaking/static grip.
Hol said:
I am talking about having to stop for a sudden/unavoidable incident directly where the limiting factor is breaking/static grip.
Ah, I see where you're coming from. It would still help spread the brake loading more evenly between the wheels to a degree (most cars having a strong front brake bias), but I agree that it won't make much difference in modern cars with ABS, EBD etc. Maybe more impact on the chances of steering around the obstacle than on whether or not you can stop in time.Edited by GravelBen on Friday 24th October 14:23
james_gt3rs said:
"A little knowledge is a dangerous thing" applies here I think...
Skid cars/pans are very useful, if only to highlight how difficult it can be to correct some skids in a small area (especially front push).Fwiw, most of the people I saw having a go when I did were were quite brutal with on/off throttle, sawing at the wheel and all over the place.
Having an understanding of weight transfer and practising/programming your brain not to slam shut the the throttle when slip occurs can be very beneficial. The session I went to was fun, although the instruction was very basic. Prior knowledge helped.
When I talk about handling, I'm talking about reasonably high speeds, not mucking about at roundabout speeds. Handling has nothing to do with getting around such things, with them it is a matter of throwing the thing at them, then exploiting their vices to get out at as high a speed as possible.
I am also not talking about entering a corner at 5 or 6 tenths, many peoples idea of 10 tenths, then accelerating hard, scrabbling for traction on the way out.
To set the subject, I rarely exceeded 8.5 or 9 tenths in an open wheeler, & still hold lap records I set when ladies still found me sexy, quite a few decades ago.
Secondly, I have lost cars at as low as 7 tenths, & rarely exceed that on the public roads. Few keep up with me. The tenth system to be of any use must be that 10 tenths is the speed where you just may get round the corner, if you have done everything perfectly, & are lucky, as a handful of gravel would have you off.
I used a technique in practice where I would occasionally enter a corner at 10 tenths, start to loose the thing, then retreat to about 7 tenths to get round the corner. This was slow, but did show you where the limit was. It told you where not to go in the race.
Most of todays drivers will have difficulty understanding what I am about to describe, as todays cars power steering is so lacking in feel, that they have probably never experienced it. Todays F1 power steering must have feel, so perhaps some road cars do too, but I have not driven one. My S2000 is dreadful in that respect, almost bad enough to have talked me out of the car. My TR7 with it's Armstrong steering is the most communicative I have found in years.
In the F1 Brabham Repco, [1130 LBS, with about 330 BHP in Oz trim], the second ess at Warwick Farm was a brilliant corner. You arrived just a little, perhaps 5 MPH, too fast to take it. Slowing such a little always has the car unbalanced at turn in. You applied perhaps 65 degrees of wheel at turn in, & applied enough power to hold the tail, still light from braking.
Once balanced you would feed in a little more power, & a slight lightness in the wheel would warn you the front was losing grip. 2 or 3 degrees less lock would have it grip enough to set the tail off. Another 5 or so degrees less lock would get the tail back, & you had to put it all back on, as you would be getting wide of your line.
This would happen 2 or 3 times more on the way to the apex. I did have a photo of this car, just before that apex. It showed the car with enough attitude for the body to be aiming a foot or more inside the safety fence, & the inside front wheel aiming for a point 4 or more feet inside the fence. Unfortunately that photo, along with most of my favourite stuff turned into a block of paper mache, when I took it sailing around the pacific islands.
By the apex the steering would be almost straight, & with 50% or more throttle on, the car would accelerate to the exit on throttle steering only, reaching full throttle as early as possible. All this was assuming you did not stuff it all up, & go fishtailing down the road like a learner.
Thinking about this, I must admit, I would have lost the tail without some power application. I must have been doing something unconsciously with the steering wheel, when I backed off to catch a big tail wag.
Of course this was a Brabham, the most forgiving open wheeler ever to race. It was a totally different business in a Lotus.
I am also not talking about entering a corner at 5 or 6 tenths, many peoples idea of 10 tenths, then accelerating hard, scrabbling for traction on the way out.
To set the subject, I rarely exceeded 8.5 or 9 tenths in an open wheeler, & still hold lap records I set when ladies still found me sexy, quite a few decades ago.
Secondly, I have lost cars at as low as 7 tenths, & rarely exceed that on the public roads. Few keep up with me. The tenth system to be of any use must be that 10 tenths is the speed where you just may get round the corner, if you have done everything perfectly, & are lucky, as a handful of gravel would have you off.
I used a technique in practice where I would occasionally enter a corner at 10 tenths, start to loose the thing, then retreat to about 7 tenths to get round the corner. This was slow, but did show you where the limit was. It told you where not to go in the race.
Most of todays drivers will have difficulty understanding what I am about to describe, as todays cars power steering is so lacking in feel, that they have probably never experienced it. Todays F1 power steering must have feel, so perhaps some road cars do too, but I have not driven one. My S2000 is dreadful in that respect, almost bad enough to have talked me out of the car. My TR7 with it's Armstrong steering is the most communicative I have found in years.
In the F1 Brabham Repco, [1130 LBS, with about 330 BHP in Oz trim], the second ess at Warwick Farm was a brilliant corner. You arrived just a little, perhaps 5 MPH, too fast to take it. Slowing such a little always has the car unbalanced at turn in. You applied perhaps 65 degrees of wheel at turn in, & applied enough power to hold the tail, still light from braking.
Once balanced you would feed in a little more power, & a slight lightness in the wheel would warn you the front was losing grip. 2 or 3 degrees less lock would have it grip enough to set the tail off. Another 5 or so degrees less lock would get the tail back, & you had to put it all back on, as you would be getting wide of your line.
This would happen 2 or 3 times more on the way to the apex. I did have a photo of this car, just before that apex. It showed the car with enough attitude for the body to be aiming a foot or more inside the safety fence, & the inside front wheel aiming for a point 4 or more feet inside the fence. Unfortunately that photo, along with most of my favourite stuff turned into a block of paper mache, when I took it sailing around the pacific islands.
By the apex the steering would be almost straight, & with 50% or more throttle on, the car would accelerate to the exit on throttle steering only, reaching full throttle as early as possible. All this was assuming you did not stuff it all up, & go fishtailing down the road like a learner.
Thinking about this, I must admit, I would have lost the tail without some power application. I must have been doing something unconsciously with the steering wheel, when I backed off to catch a big tail wag.
Of course this was a Brabham, the most forgiving open wheeler ever to race. It was a totally different business in a Lotus.
This thread is worrying me as I have mainly owned and driven RWD cars since I passed my test in 1982. I spent the 2 previous years on L plates driving my FWD Renault 6
I also ride motorbikes and have done so since passing my test in 1980.
I'm not a slow driver and I drive in all weathers but I can only recall getting the back out in my current E36 a few times last year (for fun) because the rear tyres were worn. It once fishtailed in the wet when I was overtaking someone but I wasn't going too fast and the back end of my Boxster once gave me a scare when I gave it some welly mid corner. I had just got into it so I put that down to cold tyres.
So either I'm a driving God or I'm not driving like a loon
I've tried reading all the great posts about what to do in the event of this and that, but if I have to think it through, it will be too late.
I also ride motorbikes and have done so since passing my test in 1980.
I'm not a slow driver and I drive in all weathers but I can only recall getting the back out in my current E36 a few times last year (for fun) because the rear tyres were worn. It once fishtailed in the wet when I was overtaking someone but I wasn't going too fast and the back end of my Boxster once gave me a scare when I gave it some welly mid corner. I had just got into it so I put that down to cold tyres.
So either I'm a driving God or I'm not driving like a loon
I've tried reading all the great posts about what to do in the event of this and that, but if I have to think it through, it will be too late.
james_gt3rs said:
SonicShadow said:
I think a skid pan day should be a mandatory part of the driving instruction process - for most people, the first time they learn about how a car behaves and responds in low grip conditions is when it goes wrong for them on the public road. Surely it would be better to demonstrate this to every new driver in a controlled environment? Plus it's quite fun when there's no risk of ending up in a ditch or embedded in a hedge
"A little knowledge is a dangerous thing" applies here I think...Hol said:
. . . . . . .
Wheel braking is wheel braking. - Whether it be via the disks, the drivetrain or a combination of both. . . . . .
I'm afraid it isn't. Braking using the discs can result in lock up and complete loss of traction on very slippery surfaces if the pedal pressure is not regulated extremely carefully - very difficult to do. Engine braking, on the other hand, due to drive being maintained via the transmission means that the wheels will not lock up on very slippery surfaces.Wheel braking is wheel braking. - Whether it be via the disks, the drivetrain or a combination of both. . . . . .
Garvin said:
Hol said:
. . . . . . .
Wheel braking is wheel braking. - Whether it be via the disks, the drivetrain or a combination of both. . . . . .
I'm afraid it isn't. Braking using the discs can result in lock up and complete loss of traction on very slippery surfaces if the pedal pressure is not regulated extremely carefully - very difficult to do. Engine braking, on the other hand, due to drive being maintained via the transmission means that the wheels will not lock up on very slippery surfaces.Wheel braking is wheel braking. - Whether it be via the disks, the drivetrain or a combination of both. . . . . .
Garvin said:
I'm afraid it isn't. Braking using the discs can result in lock up and complete loss of traction on very slippery surfaces if the pedal pressure is not regulated extremely carefully - very difficult to do. Engine braking, on the other hand, due to drive being maintained via the transmission means that the wheels will not lock up on very slippery surfaces.
This is simplifiying things somewhat - engine wise it'll depend on compression ratio amongst other things, and braking wise, the tyre size, brake balance, braking power etc. will affect it. My sportier cars will momentarily lock up under engine braking if I don't blip on downshifts.
mwstewart said:
Garvin said:
I'm afraid it isn't. Braking using the discs can result in lock up and complete loss of traction on very slippery surfaces if the pedal pressure is not regulated extremely carefully - very difficult to do. Engine braking, on the other hand, due to drive being maintained via the transmission means that the wheels will not lock up on very slippery surfaces.
This is simplifiying things somewhat - engine wise it'll depend on compression ratio amongst other things, and braking wise, the tyre size, brake balance, braking power etc. will affect it. My sportier cars will momentarily lock up under engine braking if I don't blip on downshifts.
I will also take issue with sportier cars momentarily locking up under engine braking on VERY SLIPPERY surfaces. For the engine to lock up it has to be pathetic in the extreme and the wheels cannot lock up if the engine is rotating unless the clutch is absolutely so knackered it will slip and the tyres so magnificent they can maintain huge traction on VERY SLIPPERY surfaces.
However, I suspect that your sportier car wheels are not locking up momentarily. You may hear them 'chirp' as their speed of rotation is not matched to the forward velocity of the car but they are not locking up per se.
Garvin said:
However, I suspect that your sportier car wheels are not locking up momentarily. You may hear them 'chirp' as their speed of rotation is not matched to the forward velocity of the car but they are not locking up per se.
'Locking up' is a fairly generic term, for some it will mean the same as slipping.The slip caused when a driver changes down and fails to rev match correctly can be a real problem if the car is on the limit or near it at the time.
If a car is threshold braking for example, and a change is badly matched, the driven wheels will lock.
RobM77 said:
Garvin said:
Hol said:
. . . . . . .
Wheel braking is wheel braking. - Whether it be via the disks, the drivetrain or a combination of both. . . . . .
I'm afraid it isn't. Braking using the discs can result in lock up and complete loss of traction on very slippery surfaces if the pedal pressure is not regulated extremely carefully - very difficult to do. Engine braking, on the other hand, due to drive being maintained via the transmission means that the wheels will not lock up on very slippery surfaces.Wheel braking is wheel braking. - Whether it be via the disks, the drivetrain or a combination of both. . . . . .
If you need a simple version./ to put it another way:
'You are heading down an icy hill and have to brake suddenly to avoid something with no other options. In such a scenario, and AWD car is subject to the same laws of physics as any other vehicle.
161BMW said:
unpc said:
Dunno where this myth came from. I had an E30 325i back in the day and it handled quite badly on the limit and was quite unpredictable. A mate's E30 M3 that I drove many thousands of miles in, was sublime. There was nothing wrong with the geometry of my car but fundamentally cooking E30s were pretty rubbish. I guess the more limited wheel travel of the M3 helped reduce the camber change.
You say the E30 325i handled unpredictably while the E30 M3 was the oppositeDid the E30 325i have LSD or not :-) ?
s m said:
161BMW said:
unpc said:
Dunno where this myth came from. I had an E30 325i back in the day and it handled quite badly on the limit and was quite unpredictable. A mate's E30 M3 that I drove many thousands of miles in, was sublime. There was nothing wrong with the geometry of my car but fundamentally cooking E30s were pretty rubbish. I guess the more limited wheel travel of the M3 helped reduce the camber change.
You say the E30 325i handled unpredictably while the E30 M3 was the oppositeDid the E30 325i have LSD or not :-) ?
I have a Tech1.
Do you have any more mag reviews of E30 325i Sport.
Thank you very much for the post most appreciated!!! :-)
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