Traction Control vs LSD

Gloomendoom

flang wrote: »

My Z3 has both LSD and switchable TC. RWD if useless in the snow anyway but with TC switched on the car wont move despite putting the pedal to the floor. Turn the TC off and off you spin, the LSD helps a lot if one wheel has traction and the other doesn't.
My old e36 without TC or LSD just puts all power to the slipping wheel.

RWD with no weight over the rear axle can be a problem in snow. I managed to drive a powerful RWD car (with TC turned on all the time) to the South of France last winter when all the planes were grounded. Old RWD VW Beetles aren't too bad in the snow either.

Traction control can actually complement a LSD because most require some level of grip to both wheels to function. Zero grip to one wheel means no drive to the opposite wheel, just like an open diff.

almillar

Twinkle - you haven't told us what car you've bought, but if it has a limited slip differential I guess it's a rear wheel drive one, and therefore the wrong car if you're bothered about snow and ice!
Everything else being equal, front wheel drive or four wheel drive beats rear wheel drive in these conditions.
TC has been pretty well explained - it can't magic up grip from nowhere.
ABS pumps the brakes very quickly if it detects they're going to lock.
Limited slip diff (for example at the rear) prevents the 2 rear wheels from turning at a big difference in speed from each other, often around 1.5. IE if you go around a left hand corner, the right wheel has to roll further than the left. This is 'slipping' in the differential (box of gears) which is allowed, up to a 'limit' at which the axel sort of turns solid and connects the two wheels.

gilbert_and_sullivan

[QUOTE=almillar;48153887.
Limited slip diff (for example at the rear) prevents the 2 rear wheels from turning at a big difference in speed from each other, often around 1.5. IE if you go around a left hand corner, the right wheel has to roll further than the left. This is 'slipping' in the differential (box of gears) which is allowed, up to a 'limit' at which the axel sort of turns solid and connects the two wheels.[/QUOTE]

Far better explanation than mine, not easy to put it in simple terms.

The trouble with LSD is that inexperienced RWD drivers think it helps them to stay on the road when they are giving it big footfulls of throttle, whereas the opposite is true, without LSD the chances are that one wheel will spin itself silly whilst the other stays at road speed, this keeps the car in some sort of stable motion whilst making the driver feel they are in control.

With an LSD equipped RWD car, both wheels will spin up instead of one, if left unchecked and someone hasn't perfected their drifting technique with steering and throttle control to balance the wheelspin then a full oversteer spin out is on the cards.

I've known quite a few LSD equipped RWD vehicles catch their drivers out.

almillar

Yep. I've had 2 different RWD cars over the last 2 winters - a 1995 BMW323i with no LSD and a 2004 Mazda RX8 with an LSD.
2 pretty different cars, and the Mazda was FAR worse. I couldn't get it past my own living room! As above, having the wheels lock together (for this is what an LSD does sometimes) is as often a bad idea as it is good. 2 wheels spinning isn't much better than 1! TC on/off, any gear, hopeless. Only way I eventually did get out after the snow had reduced a bit was to put as much heavy stuff in the boot that I could fit in, and even then it was pretty hopeless. Back end stepped out on me going up a straight hill at 30mph, and I got overtaken going down a 30mph hill doing about 15mph by a Focus!

Gloomendoom

I found that loading up the boot made a huge difference. If you have RWD it might be worth buying 10 or 20 bags of sand and putting them in the boot if you want to use your car in the snow.

Weird_Nev

In my experience of Traction control systems, they're as individual as the cars they're fitted to.
The main thing is to learn how YOUR car behaves with and without traction control enabled. In 99% of situations, Traciton control is a beneficial driver aid and is best left alone.
If you're setting lap times, or driving in very extreme conditions, then there are times when it can be useful to switch it off.

Have a read up on the capabilites of the traction control system fitted to your car: Some simply monitor driven wheels versus undriven wheels, or compare it to data in the engine control unit to ascertain if wheels are spinning or slipping. Some monitor yaw rates of the car, or steering and throttle inputs. Some cars just throttle back the engine in response to breaking traction, more advanced systems may brake individual wheels, throttle back the engine, or even use a trick differential(s) to actively send torque to a wheel that has grip available. These tend to be called "stability Control" or something like that. Braking a spinning wheel has almost the same effect as some types of Limited slip differential - Ferraris' "E-diff" works in this way.

But to say "traction control works like a Limited Slip Differential" is a massive over-generalisation and probably not helpful in understanding what traction control actually does to help you out of sticky situations (or stop them developing in the first place).

Without knowing your car and the systems it has, it's not possible to say how it will behave particularly in slippery conditions. One thing work noting is that Ice is simply very slippy. Unless you've got studded tyres, no amount of electronics or mecanical trickery will be able to move a car on real, proper ice. We rarely get sheet Ice in the UK thankfully, but when we do it causes accidents a-plenty!

Honestly, the best advice I can give is to go on a "car limits" day or try and get time on a skid pan. That will really help you get your head around controlling a car in low friction conditions, and if you can take you own car allow you to explore the limits of what driver aids it has, and their effects on the cars handling. Even a trackday is useful in this respect if you're a keen driver.

50Twuncle

almillar wrote: »

Twinkle - you haven't told us what car you've bought, but if it has a limited slip differential I guess it's a rear wheel drive one, and therefore the wrong car if you're bothered about snow and ice!
Everything else being equal, front wheel drive or four wheel drive beats rear wheel drive in these conditions.
TC has been pretty well explained - it can't magic up grip from nowhere.
ABS pumps the brakes very quickly if it detects they're going to lock.
Limited slip diff (for example at the rear) prevents the 2 rear wheels from turning at a big difference in speed from each other, often around 1.5. IE if you go around a left hand corner, the right wheel has to roll further than the left. This is 'slipping' in the differential (box of gears) which is allowed, up to a 'limit' at which the axel sort of turns solid and connects the two wheels.

My car is a Suzuki Swift SZ4 - A mere 1.2 engine - front wheel drive (obviously) - but I was surprised to find that, apart from ABS - It comes with (switchable) Traction Control !!!

spiro

In the past I had a car with traction control but it was fitted with an 'ice mode' to cater for bad weather.

As already said in ice and snow with a RWD car the best thing you can do it put a couple of large heavy paving slabs in the boot over the back axle to aid traction in the first place.

almillar

That traction control won't have to do much in a FWD 1.2 car in the dry, but could be useful in poor conditions. General advice (yes general) would be to leave TC on all the time, but if you get stuck, or know that the TC won't help you, turn it off for just that moment (getting up a hill in the snow for example).