Which gear do you tow in?

[BurtonRob]

Perhaps I'm turning into a serious anorak but I was wondering what gear most folk tow in. My galaxy is six speed, I tend to chug along in fifth gear on cruise control. Is there an optimum number of revs I should aim for for best economy. I know max torque is at fairly low revs but what is most efficient revs to run at. Any advice would be appreciated, incidentally I have been towing for years and generally work on the principle that if the car feels to be running smoothly all is well.
Thanks for you help

Rob

 

[ProfJohnL]

Hello Rob.

What is the best gear to use obviously depends on the car, its load and trailer, road and traffic conditions at the time.

I go for the highest gear where the car will continue to too keep up with general flow of traffic (not exceeding speed limits) and change down if necessary. Both my cars are diesels and develop plenty of torque at relatively low revs (approx 2000 rpm), and both can tow on M-ways in 5th gear (5speed gear boxes), except on the steeper sections.

Its what comfortable for you, Just bear in mind that there is no way a towing car will perform as sprightly as when its solo.

 

[JeffD]

Ummm this is one of those 'do I tow in the turbo range or not' questions I think. I tow with an Smax (2.2) and 60mph is 1800rpm in 5th (turbo) or 1600rpm in 6th(non turbo). My car is happy in 6th on the flat and slight incline but does lose speed if the slope increases, necessitating a gear change to maintain the speed but it does more mpg in general.
I guess 5th will provide easier cruising for motorways/ dual carriageways but at a few mpg less.

Jeff

 

[Steve L]

To be quite honest there are so many variables between each vehicle that we can only give general advice.

In the interest of fuel economy I tend not to rev above 2'000 rpm in my Jag diesel and change down the gears at 1500 rpm to maintain pulling power. Like John, I can stay in top gear on the flat maintaining a steady 55 to 60mph.

Choosing the gears to drive in is a very important safety factor.
One example being while climbing hills. If you stay in too higher gear you have the engine labouring and straining the drive train. This can put excess stress on your clutch and dual mass flywheel which are expensive items to replace.

The other is using the gears for controlled deceleration. As a general rule of thumb you should go down a hill in one gear higher than you would expect to climb the gradient in. This provides engine assisted braking which reduces brake fade. By thinking through the process you will have the time and the braking ability should the unexpected happen.

By being a steady and anticipative driver you can get very good mpg towing and have negligable extra wear on the mechanicals of the car. For example, I get 38mpg towing our 900Kg caravan and as yet have not had to change the brake pads on my current car. My last car was a rover 75 and that did a simlar mpg and about 27k miles to a set of front brake pads. The rears hadn't been changed by me.

I don't see the need to rush when towing our van as to me the holiday has started the moment we leave the house and not at the time we arrive at the site.

 

[JonnyG]

steve mate, i think you meant one gear lower going down the hill than when climbing up it, we dont want the outfit running away downhill.

 

[drsorento]

cruising always tow in 5th (5 spd gearbox)

 

[otherclive]

Haven't a clue the Geartronic auto box looks after that and for most occasions runs between 1600-2000rpm which keeps the engine spinning nicely. when I had a manual Saab turbo that towed within a similar rev band too. I don't like to labour an engine with low revs ut alternately will periodically take them to near the red line otherwise modern high torque slow revving motors can develop wear lips in the bore if revs aren't varied over long distances and high mileages. This can lead to mechanical failure if the engine is then revved hard. Bit different from when I used to run in racing two strokes by revving them to near seizure point (in the pits on a stand)

 

[Lutz]

Actually, the question raised can be likened to "how long is a piece of string?"

 

[GeorgeandAde]

What gear do you tow in????????
Usually shorts,T shirt,trainers and sunglasses if its nice

Sorry.......couldnt resist

 

[ProfJohnL]

Duplicate post

 

[Raywood]

In theory the best gear is the one where the engine produces the most torque as that is where it is most efficient. My feeling is that in most cases fifth gear is the one as you have more control but it all depends on the car and caravan spec. If the car has a display showing mpg you might try to see what the reading is in each gear on a flat bit of road but it is not totally accurate as even minor changes in the level can affect the reading.
The best way to save money is reduce the speed by a couple of miles per hour.

 

[ProfJohnL]

Hello Ray,

The engines efficiency does not necessarily follow the torque or power curves, so the optimally efficient engine speed is difficult to specify.

Especially with modern engines being controlled by an ECU with a 'map' you cannot assume that the amount of fuel being fed to the engine is directly proportional to the depression of the accelerator.

If you kept the engine in its torque band, the it will be more responsive, but that might trade off against noise or other comfort factors.

With engine speed being dictated by the choice of gears and the road/traffic conditions, no one can perfectly maintain an engine at its optimal RPM, so efficiency will be far from constant. even the relatively gentle inclines on motorways will upset the optimal RPM range.

 

[BurtonRob]

-align: left;Thanks for the replies, I take LUTZ point , I probably didnt frame the question well. I was trying to ask if the recent that generate maximum torque are actually the best revs to aim for when crui sing along the motorways. My galaxy always feels a bit more comfortable with the revs a little higher. Rob

 

[BurtonRob]

Forgive the typing errors, accidentally left spell check on my phone. I'm in Millau
Rob.

 

[ProfJohnL]

Hello Rob,
Assuming I have de scrambled your last but one posting,
It all depends on what you mean by best:-
Most responsive
Quietest.
Most economical

For the most responsive, then keep the revs in the peak torque range.
For the quitest, that depends on the individual car and the prevailing road conditions
For the most economical again that depends on the individual car and is not necesarily in the peak torque band.

They all also depend on the individuals driving habits, so no one can give you simple answer to your question.

 

[xtrailman]

Modern diesels are now higher geared to keep emissions down, so generally they like to run just above max torque, or inside the max torque range if it has a flat curve.
My xtrail runs mainly in 5th gear towing 1565kg, speed will quickly drop off on a long incline if i allow the speed to drop below 2000 rpm which is max torque, although 90% is still available at 1750 rpm.
The 2012 versions are geared even higher!

Solo it is completely different.

 

[Martin24]

I tend to avoid shorts so stick to cargo's or 3/4 cropped whilst cruising along the motorway flat and up most hills in 6th with the occasional drop to 5th when over taking and whatever gear feels comfortable when going downhill.

 

[seth1]

I would have to agree with Raywoods reply,the point at which max torque is made and the gear in which the road speed is matched is the best gear to tow in.Either side of that engine speed is going to waste fuel.Contary to what has all ready been written the throttle pedal is still in proportion to the amount the engine responds when the pedal is depressed,for example if the throttle is depressed by 100% the engine ecu will command 100%throttle.The only time this will change is on a zero% throttle opening and coasting down hill were as the fuel will be cut off completely even below the idle amount.The renault engine has a progressive torque curve then Ray?There cant be many small diesel car engines with a true flat torque curve has i cant see how it would work for them with so little gears.

 

[Gybe]

Let the auto box work it out.

 

[ProfJohnL]

Hello Seth,

You state:

Contary to what has all ready been written the throttle pedal is still in proportion to the amount the engine responds when the pedal is depressed,for example if the throttle is depressed by 100% the engine ecu will command 100%throttle.

Modern engine management units use a "map" that looks at the the throttle pedal position, and in conjunction with data from other sensors determines how much fuel to feed to the cylinders, thus the fuel metering does not proportionally match the peddle position.

For example an engine turning at low RPM if given 100%fuel, may actually flood, and if not stall may at least splutter. So ECU's will recognise the low RPM and on demand for full power will meter the fuel in a progressive manner to provide a smooth pick up.

Systems now often include RPM limiters, which means if you demand full throttle, the system will allow the engine to speed up but then it will limit the fuel to prevent over speed.

When people opt for a remap of the system, the fuel metering is one of the criteria that are often adjusted, that would not be possible if the throttle peddle directly controlled the metering.

This flexibility in the metering means that the manufacture/programmer can play with the torque and power curves, by changing the ratio of peddle depression to the proportion of fuel metered.

 

[seth1]

Ok John,forget about remapping as this causes more confusion.O.E equipment sees what ive explained.100% of the throttle potentiometre will command 100% throttle from the EDC control unit,as long as the conditions are correct.(not in derate)
What you refer to is the parametres of the map.But once these are programmed they dont change.They work by hex.Even with a remap your only letting things work outside of set ranges.The 100% throttle is uneffected.
As for full throttle at low engine speed it wont make it stall but the oposite as in speed up,remember the map controls this now.The days of AFC(air/fuel control) have gone.Stoichometric comes to my mind.With that mindset you would have a situation were the engine would never gather any engine speed.It is also agaist eu ruleing to be able to effect the action of a throttle device.By this i mean a long time ago we had situations were sump plugs were dropping out due to defective sumps.In America were the engines originated from they had a system were they went in to derate and shut down.In this country that parametre had to be disabled due to legislation.
Todays diesel are limiting the torque output more so than the engine speed,ive never had mine on its max engine speed. Never needed to.Were at a place now were torque can be ramped up but engine speed left the same due to pwm(pulse width modulation)

 

[JonnyG]

Quote...
"For example an engine turning at low RPM if given 100%fuel, may actually flood, and if not stall may at least splutter. So ECU's will recognise the low RPM and on demand for full power will meter the fuel in a progressive manner to provide a smooth pick up".

hi Prof, and the above might have merit in a car driven by a petrol engine but this cannot be used as an example for a diesel driven engine. Too much fuel will merely come out as black smoke, no spluttering no flooding no stalling as the diesel is a compression engine
and therefore needs no spark, the systems you describe involve a spark plug fouling up......

 

[xtrailman]

I would have to agree with Raywoods reply,the point at which max torque is made and the gear in which the road speed is matched is the best gear to tow in.Either side of that engine speed is going to waste fuel.Contary to what has all ready been written the throttle pedal is still in proportion to the amount the engine responds when the pedal is depressed,for example if the throttle is depressed by 100% the engine ecu will command 100%throttle.The only time this will change is on a zero% throttle opening and coasting down hill were as the fuel will be cut off completely even below the idle amount.The renault engine has a progressive torque curve then Ray?There cant be many small diesel car engines with a true flat torque curve has i cant see how it would work for them with so little gears.

Yes the xtrail is progressive.
But lots of the latest engines give max torque from around 1800rpm to around 2500 rpm. Cx-5, BMW x3, vag 138bhp engine etc.

 

[seth1]

yes it will allways be a comprimise in a small diesel engine.