Category Archives: Offroad Driving

DRIVING IN SNOW AND ICE

This is what the Institute of Advanced Motorists recommends for driving in snow and ice.

When driving in snow, get your speed right – not too fast so that you risk losing control, but not so slow that you risk losing momentum when you need it – and brake, steer and accelerate as smoothly as possible.

Start gently from stationary, avoiding high revs. If you get yourself into a skid the main thing to remember is to take your foot off the pedals and steer.

Only use the brake if you cannot steer out of trouble.

Double or even triple your normal stopping distance from the vehicle in front. Drive so that you do not rely on your brakes to be able to stop – on an icy surface they simply may not do that for you!

If your vehicle has ABS in very slippery conditions it will not give you the same control it would in others. Do not rely on it.

Plan your journey around busier roads as they are more likely to have been gritted. Avoid using shortcuts on minor roads – they are less likely to be cleared or treated with salt, especially country lanes.

On motorways stay in the clearest lane where possible, away from slush and ice. Keep within the clear tyre tracks if you can.

Stay in a higher gear for better control, and if it is slippery, in a manual car move off in a higher gear, rather than just using first.

On a downhill slope get your speed low before you start the descent, and do not let it build up – it is much easier to keep it low than to try to slow down once things get slippery

In falling snow use dipped headlights or foglights to make yourself visible to others (especially pedestrians) – but as conditions improve make sure your foglights are only on if necessary as they can dazzle other drivers

If you are following another vehicle at night, using their lights to see ahead can cause you to drive dangerously close – keep well back from other traffic.

Also see our post on preparation for winter driving

Axle tramp… what is it?

Axle tramp is bump steer with torque.

A ‘tramping’ axle is more common with a leaf-sprung suspension than with independent or coil suspension, because the latter types have widely-based control arms or wishbones to control axle rotation. When you feed engine braking torque into an axle, the axle tries to rotate with the force that’s turning or stopping the wheels.

A leaf spring has to perform the double duty of suspending the axle and resisting torque, so can suffer ‘wind up’ when there is a great deal of torque applied, letting the axle rotate forward or backward a little then whipping it back into line. A severely tramping axle losses contact with the road and can result in loss of vehicle control.

Axel Hop… Whats is it?

Axle hop is bump steer gone mad.

Axle hop is an uncontrolled movement of the axle, usually brought about by inadequate or ‘tired’ shock absorbers trying to cope with a series of bumps or corrugations. In cases of sever axle hop, the 4WD will ‘dance’ all over the road and become uncontrollable.

Bump steer, axle hop and axle tramp can be experienced virtually any 4WD if you push hard enough on rough roads, so it’s important to know your vehicle’s degree of axle control. Driving technique – minimizing savage acceleration and braking – can reduce axle misbehavior.

Another value technique is to find the ‘sweet spot’ when running on corrugated roads – that speed which provides the best ride and good directional control.

Bump Steer… What is it?

‘Bump steer’ is a term used by road testers, but often misunderstood by some of the people who use it – let alone readers to interpret it. Bump steer describes a steering effect caused by suspension movement as the vehicle passes over undulations.
Bump steer is often confused with axle hop or axle tramp.

The classic bump steer effect is noticed in leaf-sprung 4WDs, because a leaf spring is longer when flat than it is when positively or negatively curved. The lengthening and shortening takes place all the time there is suspension movement and that fore and aft movement causes the axles to change their ideal right angle position across the chassis.

If you look at a leaf-sprung 4WD from the side as it moves over a hump, you can see the slight rearward movement of the axles. The more the suspension deflects, the greater the angling effect of the axles and the more self-steering effect on the vehicle.

When bump steer is more noticeable in leaf-sprung vehicle, you can have bump steering effect with coil-sprung axles, because their pivot on control arms which move through arcs, which can impart some steering effect.

Bump steer is often noticed at the front of 4WDs that have a ‘live’ front axle, rather than independent, wishbone suspension. Because the two front wheel are linked by a tubular axle beam and a steering tie rod, when one wheel encounters a bump, the reaction is fed to the other wheel.

Bump steer, axle hop and axle tramp can be experienced virtually any 4WD if you push hard enough on rough roads, so it’s important to know your vehicle’s degree of axle control. Driving technique – minimizing savage acceleration and braking – can reduce axle misbehavior.

Another value technique is to find the ‘sweet spot’ when running on corrugated roads – that speed which provides the best ride and good directional control.