Slightly OT: one for the anti 4x4s?

It depends on the conditions - knobbly tyres can be fantastic in the dry, but leathal in the wet, and to an extent the reverse can be true. My first bike was a Suzuki TS100 which came with knobbly tyres which where factastic in he dry but hopeless in the wet - the same goes for the XCL's I had on Knobby. Yet the OR's I had on the 90 were great in the wet but somewhat iffy in the dry. It's impossible to generalise.

Richard

ABS just looks for a wheel rotating at a different speed to the avarage of the rest, and applies/releases the brake to get it back in sync. Most systems will realise that since the car is moving all the wheels should be rotating, and does the same to avoid skidding. It will cetrainly provide the best possible braking in almost all conditions (though some systems cannot cope with loose gravel under all 4 wheels - LR's can - another LR world first at the time) - however, it can't perform mircles (despite Audi/BMW owners seeming to think so). There are, as Austin says, some circumstances where a skid may be desirable, just what those are is a subject of some debate.

Richard

Not really, if you've got the brakes on then the only way a 4x4 drivetrain can affect things is if it locks all the diffs giving you a form of traction control, but only one vehicle that I know of does that, the Volvo C303.

We are talking about stopping distances remember, so throwing in stuff about getting more grip going round corners is a whole different argument.

Why mention wet conditions? Tyres aren't equal in the dry.

Er, so what about the engine? It has no effect of braking control? A center diff (unlocked) has no impact on braking? Brakes don't operate in isolation from the rest of the vehicle. Try taking a shock absorber off and see what happens to your brakes!

Who said anything about corners? Not me....

No I really do give up!

Richard

Not as much as the brakes!! And if you're stopping hard then engine braking isn't of much interest unless of course your brakes are so screwed that they can't slow you down enough.

That's very different to the engine, the shock absorbers help keep the wheels on the ground, but when the brakes are on hard, a 4x4 drivetrain isn't going to be affecting things much, if at all.

Some cars have absolutely appalling rear visibility. In the US most drivers don't seem to reverse unless there is no option, and given the view out of the rear of the last car I hired over there (a chevolet of some flavour) I can see why. Being a saloon it had a relatively high rear window, at a very flat angle which would have been hard enough to see out of to start with (couldn't have seen a bollard when reversing, for example), then they put a spoiler across it! Talk about a tool not fit for the job. I have much better visibility out of the back of the 101.

Lizzy

The only effect I can see for a four wheel drive drive train (and then only for constant four wheel drive and in gear)is to even out braking effort to some extent - if one wheel locks it increases the braking on the other three through the drive train, but I would not expect the effect to be noticeable. JD

Especially not with the clutch in, which most would have in an emergency stop situation.

The Volvo C303 has a nice system, when you whack the brakes on it engages drive to the front axle, which is the Defender equivalent of locking the centre diff. This helps to prevent the rear wheels locking which is a problem in an empty load-carrying vehicle, especially a forward control like the C303. There are more modern systems which are better of course, but for a 1960's truck it was a good idea. That's a situation where a 4x4 drivetrain has been designed explicitly to help under braking, but it's the only one that I'm aware of.

Ten Jolly Junior points and a Gold Star to that man! Only the effect is quite (relatively speaking) marked - the inertia in a (particularly steel) wheel and tyre can be quite significant, as the diffs etc all count and provide something of a damping effect when a wheel is thinking about locking up.

Richard

With the effect, if any, being even more marginal at low speeds of course due to the reduced inertia.. Plus of course if a car has ABS it's not relevant at all, and if it doesn't have ABS it's only relevant if the driver has managed to get the braking into a zone in which such a marginal effect comes into play - close enough to the tyres unsticking that it makes a difference. Not even F1 drivers can always prevent a wheel locking during a race when they're expecting to brake hard and they've practiced like mad on that same bit of track so your average driver wrangling kids won't manage it. They're going to either brake less than they could, or to just mash the pedal and lock up, not get it to a point at which inertia of drive shafts becomes relevant!

All in all, no a 4x4 drivetrain has no noticeable effect on braking, certainly not enough to compensate for things like the additional weight transfer to the front due to higher centre of gravity, and all the other stuff that the average 4x4 has to put up with that the average saloon car doesn't.

I'm perfectly happy to know that my vehicle is more hazardous to a pedestrian than the average saloon car, given the chances of me hitting someone it's not something I can be bothered to worry about. There are far more lorries on my tiny local roads than 4x4s and they come round the corners on the wrong side of the road, which is rather scary....

I'll let Marky-Mark know they've got it all wrong. He's going to be very disappointed!

Richard

On or around Fri, 20 Oct 2006 11:21:56 +0100, Ian Rawlings enlightened us thusly:

the viscous diff on the classic RR T-boxes probably transfers some torque under braking, in a situation where one or more wheel would otherwise lock...

OK, my consultancy rates are reasonable ;-)

Bear in mind though that at the level of a racing outfit, small differences count but they don't at the level we were talking about, and I've been saying that any differences are going to mean bugger all on the school run!

Make the little buggers walk - or if they're too far then give Austin the work.

School run indeed - whatever next?

Being hit by a schoolbus or a refuse truck isn't going to be any better either, so should they be banned from going anywhere near schools, don't see anyone complaining about them ?

I have proof that my limo was able to stop quicker than the sandhurst trained a-hole in a hot hatch who slammed into the back of me some years ago. He mouthed off in superior manner at me, as these upper class idiots are apt to do, but I won the insurance excess off him in court.

Larry

Indeed, however as far as I'm concerned the majority of the damage is done by the majority of the people, 10 cars are more likely to kill kids at schools than 1 4x4 or 0.5 school busses but you're not going to get politicians, local councillors or pressure groups campaigning about the majority of the people!