Appropriate use of 4-Hi and 4-Low is of utmost importance for the longevity and protection of your transmission, drive-train and transfer box components. Each gear selection has a very specific function and as a 4 wheel drive owner you need to understand what the differences are and exactly when the situation calls for the correct gear selection.
What is the difference between 4-Hi and 4-Low and when should you use it? 4-Hi propels all 4 wheels and should be engaged when the driving surface becomes slippery and the risk of losing traction on your wheels increases. 4-Low utilizes lower gear ratios from the transfer box for optimum traction and maximum power. 4Low should only be used at low speed when off-roading over difficult terrain such as rock crawling, sand and steep slippery inclines.
The next part will discuss what 4 High and 4 Low means and the maximum speed you should drive in 4 Lo. To find out more about the correct usage of 4-Hi and 4-Lo and the different functionality of each, continue reading…
What Does 4 High And 4 Low Mean?
The 4 symbolized in “4-Lo” indicates that your vehicle is in 4 wheel drive mode. This means all 4 wheels are being propelled forward at the axles by the engine via the transmission and transfer case. The “lo” represented in “4-Lo” indicates that low range mode has been engaged in the transfer box. Most off-road 4×4 vehicles have a 2H, 4H and 4-Lo setting. Vehicles with 4-Lo are equipped with a transfer case which uses much lower gear ratios to utilize the available power and torque of the vehicle easier.
4-Lo mode allows the vehicle to drive through difficult terrain with more ease without placing undue strain on the gearbox, clutch, transfer case and engine. Difficult terrain could be any of the following:
- Loose beach sand
- Thick mud
- Rock crawling
- High Sand Dunes
- Steep loose Inclines
- Long tricky declines
- Deep River crossings.
4-Lo uses shorter gear ratios, hereby keeping the revs high and always in the vehicles power range. This makes stalling more difficult in 4 Lo. Many people are under the impression that 4-Lo increases the vehicles torque, however it does not increase but only utilizes the existing torque easier and quicker by keeping the vehicle in a higher rev-range and in the highest torque band of the vehicle. This ensures the vehicle’s power is readily available.
When To Use 4 Hi And 4 Low?
Low-range or 4-Lo is a very powerful function of a 4WD and allows you to accomplish feats no 2WD ever could. You engage low-range to get you through soft sand, over tall sand dunes, up steep hills and down difficult mountain tracks. It will even get you through deep mud or snow, and it’ll help you drive over boulders and deep ruts with ease. Use it wisely and your 4WD will, not only take you to many amazing places, but also bring you back home safely. The lower gearing also improves your 4×4’s capabilities because it uses the vehicles engine braking, which helps to control your progress and speed going downhill. This allows for more controlled handling without placing all the stress on the brakes alone.
As mentioned earlier, 4-Lo is used only when you require optimum traction and absolute maximum power. This is only to be engaged when the terrain is really difficult and driving conditions forces you to lower your speed and gear selection down to 1st or 2nd gear. Extreme rock crawling when you need to negotiate each obstacle slowly and precisely will call for 4-Lo. Driving through thick loose beach sand with a load will require 4-Lo to prevent damage to your vehicles clutch or to decrease the risk of overheating the gearbox if you are driving an automatic 4 wheel drive vehicle. When doing any deep river crossings you are better off engaging 4-lo to ensure you are getting optimum traction and using the power available to you sufficiently.
Each and every off-road situation or obstacle needs to be carefully calculated and assessed by you before you decide to take it on. However a good rule of thumb is always to judge the speed vs the difficulty you are required to succeed. Always remember “As slow as possible and as fast and necessary”, no more, no less. Generally, if you cannot engage 4-Hi 2nd or 3rd gear to cross an obstacle or if you feel the obstacle will place too much mechanical stress on your vehicle then you are better off engaging 4-lo and rather take it slow and steady.
Always ensure you keep the risk of vehicle damage to an absolute minimum. This will mean you will at times have to exit your vehicle and walk the terrain or the obstacle first to determine the best driving line and if there is any risk of stalling or if a roll-back or even a rollover is a possibility. This is something you want to avoid at all cost. It is best to be safe than sorry and i always say, if you have the functionality on your vehicle, use it. Do not try to be macho!!!!
Can You Drive In 4 Hi On The Highway?
The simple answer here is a definite NO! Please do not do this. Low range is generally for slow-going so do not use it for high-speed driving on any surface. In fact, do not use low range at speeds faster than 40 mph as a general rule. With that being said, you will not even be able to travel fast enough to keep up with the slowest highway traffic. Also, every highway has a minimum legal speed too. I don’t think a 4×4 in 4-Lo could even reach the minimum speed of a highway.
Driving in 4th or 5th gear in 4-Lo is like going 3 gears back on your gearbox. For example, in Lo-range, when you are in 3rd gear it is almost the same as being in 1st gear in 4-Hi. And 4th gear in 4-Lo will be like driving in 2nd gear in 4-Hi. So ask yourself if you would drive in 2nd gear on any highway? I think you know the answer to that question.
|Low Range (4-Lo)||Hi-Range (4H)|
|3rd Gear||1st Gear|
|4th Gear||2nd Gear|
|5th Gear||3rd Gear|
Apart from the above mentioned, your risk of causing major damage to the transfer case, gearbox, drive-train or engine is substantially increased. That is because most vehicles are designed to drive 4-Lo for short periods through difficult terrain or obstacles. Not for overly-extended periods at high revs. Once you are off the 4×4 trail sand, snow or rocks, switch your vehicle back to 2H before you reach the highway.
How Fast Can You Drive In 4 Low?
When you are driving below 15 mph and you are negotiating a difficult or tricky obstacle then 4-Lo is perfect. Remember, If the driving conditions are extremely slippery like on snow or ice or you are doing a steep uneven mountain track, or driving through thick mud, beach sand or river water, then these are perfect conditions to engage 4-Low. If the driving conditions allow you to drive faster without risking damage to your 4×4 and you can safely go over 15 mpg, you can then confidently switch back to 4-High without any risk. Always ensure you stop first before engaging 4-Lo and slow down before reverting back to 4-Hi.
4 Low or 4 Hi in Sand?
The first thing you should do before venturing on sand is to decrease your tire pressure. 16 psi is usually the magic number without too much risk of de-beading the tire from the rim. However, that being said, sand can be a slightly trickier situation to negotiate because the driving conditions can vary vastly.
For example, if the sand is compact and wet then a 4×4 could easily drive over it without causing undue strain to the transfer case and gearbox. The vehicle would basically glide over the surface without any difficulty. However, if the sand is thick and loose and the surface is uneven with dunes to climb, without a shadow of a doubt, select 4-Lo and approach with caution.
On sand you always want to travel as fast as necessary but as slow as possible. Keep the momentum going and do not allow your revs to drop too low. 4-Low in 2nd and 3rd gear is perfect for sand driving. If you are climbing loose sand dunes, you will need to stay in 3rd gear low-range and climb it out by keeping the vehicle in the power band range.
You will need to know your vehicles rev range and where it starts to dip off and change up to a lower gear before it is too late. Sand driving requires constant negotiating and concentration on both the terrain ahead as well as your rev counter. Higher revving gas (petrol) vehicles generally do well in sand as they have a wider rev range to play with. Diesel vehicles have a smaller shorter rev range and requires more gear shifting if you are driving a stick-shift (manual).
Look after your 4×4 and it will look after you. Get to know your vehicle and its capabilities as well as its shortfalls. Remember, if you are driving below 15 mph and negotiating a tricky obstacle then 4-Lo is perfect. If you can exceed 40 mph without risking vehicle damage then 4-Hi is safe to engage. Once you leave the trails and head back onto bitumen disengage 4H and select 2H where only the rear wheels will propel the vehicle forward.
Happy 4 Wheeling and remember, Safety First!!!