(Home) Driving in snow

last night was the first time i have driven my model f in snow after the heavy fall we had in highworth last night and she is better than a snow plough and it dosnt have 4wd and i got home before my hub and he has 4wd .

- (#8180) ruthlaurahowse, 29 Jan 04 01:58

We had snowfall on the isle of wight yesterday evening!! The children were delighted! If you gathered up all the snow on the ground in our garden into one place one could probably make a half-sized snowman! We didn't do that, instead, yesterday evening the family went out and had a jolly good snowball fight.
Now, I have a Masterace Surf with 4WD. I had read that one must NOT use 4WD on tarmac - presumably this could cause some damage? The question I have is, under icy conditions where the roads may be a mixture of good grip tarmac & iced tarmac - the journey being about 15 miles - is it ok/advisable to use 4WD - what is the actual problem in using 4WD on tarmac?

- (#8180) Peter Dawson, 29 Jan 04 06:45

Hi Peter, that was the most bizarre hour of weather wasn’t it. Clear sky turned to thunder storm, then hail, then driving rain turned to snow that was enough to cover everything with a good coat. All in the space of about half an hour. Then the next hour saw the snow partially melt and then freeze into thick ice.

Anyway 4x4
When cornering, the inside wheels always turn slower than the outside wheels.
On slippy surfaces one wheel can turn quickly and rob its opposite of drive.
In order to get drive to the front wheels, they have to be locked at the hub. This locking mechanism ensures that the turning speed of each front wheel is the same. If one wheel hits a slippy bit, then it can’t turn quicker than the other front wheel, and so drive to the front is maintained. That's good for slippery surfaces but not grippy tarmac. If the wheels are locked, not only are the tyres quickly worn away on every corner, but the added strain on the axle, transfer box, and transmission is greater, and will cause excessive wear which ultimately leads to failure in one or more.

- (#8180) dave Bright, 29 Jan 04 07:46

To follow on from Dave's post, the problem is far more fundamental than he suggests, as he rightly says, the inside wheel on any car will travel less distance than the outside whell during cornering, thus we have differentials fitted between each driven wheel, as the name suggests, this accounts for the difference in wheel distance travelled. When you go into four wheel drive, the transfer box will try to run the front & rear axles at exactly the same speed, but because the front wheels may not rotate exactly the same amount of times as the rear ones, you have to rely on one of the wheels to be able to 'slip' a little whenever you are not travelling in an exact straight line. Permanent four wheel drive vehicles have a third differential fitted between the front & rear axles to take up this difference. To provide them with a locking facility, to avoid the problem of one wheel spinning & no drive to all other wheels, they have 'diff locks' fitted, which will prevent the centre diff taking up the difference.

The Townace system has no centre differential, therefore one wheel must slip to take up this difference, if you were to run on even just wet tarmac, you would not derive enough slip to take up this difference. On dry tarmac you could wind up the diffs in as little as 10 metres or so, this is in effect where so much strain gets put on all the gears in the diferentials, that the slack has gone out of them & the gears are all bound together, in this case you might get away with just towing the vehicle back in the direction it came from, but you might damage many drive train gear companents.

The best practice in this kind of weather is to do the following:-

run all the time with the front hubs in the locked position, this will allow you to hit the 4WD button at up to 50 Kmh whilst on the fly. Only apply 4WD when on ice, mud or other slippery surface. Once back on a good surface, TURN IT OFF IMMEDIATELY. If the green light doesn't go off, it hasn't disengaged, in this case, try braking, slowing down, or even stop & select N neutral R reverse then back to D drive to disengage. Once light is out you are in 2WD and OK on tarmac.

Never select 4WD when on the fly above this speed, or if the front hubs aren't locked, as you will damage the transfer box. If you select the 4WD without locked front hubs, you still only have rear wheel drive, but have got the option to use Low Ratio.

Note, some early Townies have a lever to select 4WD, in this case some of them must stop in order to select 4WD, other can select on the fly if hubs locked.

You must always come to a complete stop before selecting low ratio in the transfer box.

Hope this helps those of you who are novices to the 4WD scene.

Regards Rob.

- (#8180) Rob Drinkwater, 29 Jan 04 13:53

Thanks guys, that's very informative. I'm trying to get my head round all the information. This is how I reconcile what you're both saying (and I'm making some wild guesses) - please check this out and let me know if I'm going in the right direction.

Front wheel hubs locked, 4WD not selected:
Benefits: can select low ratio, front wheels can still run at different speeds (i.e. round corners) due to front differential, front & back wheels can still run at different speeds due to 4WD not selected, is traction better?
Drawbacks: slight increase in friction/petrol consumption due to locked hubs, anything other drawbacks?
Question: can the diffs get 'wound up' if you keep making turns in the same direction?!

Front wheel hubs locked, 4WD selected:
Benefits: applies drive to front wheels as well as back therefore power spread over four wheels and more traction results, front wheels can still run at different speeds (i.e. round corners) due to front differential.
Drawbacks: significant increase in friction/petrol consumption, lack of centre diff makes this usable ONLY on truely slippery surfaces.

Appreciate your comments.
- (#8180) Peter Dawson, 30 Jan 04 08:31

Vaguely right, in the hubs locked no 4WD selected, then you have no drive to front wheels but can run on dry surfaces fine. In this mode you cannot select low ratio!

Hubs locked & 4WD selected, you must be on the slippery stuff, this will give you better grip than 2WD, but relys on one wheel at least slipping, if only a small amount. From here you can select low ratio.

You are right, running with the fron thubs locked might cost you a few tenths of a MPG, not worth worrying about, you will get a bit more noise from it, and it is good to run like this occasionally anyway, as it churns up the diff oil & keeps all the parts running as well. Same as it is good to stop & select 4WD with the hubs unlocked & use low ratio periodically as well, as this lubricates & protects all components.

HTH Rob.
- (#8180) Rob Drinkwater, 30 Jan 04 14:52