Fuel economy and how to save fuel. What can we agree on.?

[Neverfuel]

I think that it is a good thing you have FCM... A truck has a shorter braking distance than a car - good luck.

Sorry to make a point of this one Jaapv, but this is my specialist area. A vehicle that has air brakes has something called "brake lag" which is the time it takes for the air brake system to compress the air in the system and do any useful work - usually about 1/5 of a second. A car has hydraulic brakes, so they act instantly. Both have:

A. Reaction Time (about 2/5 of a second), and
B. Braking Time (depends on the road surface, weather, tyres, speed etc.).

So a car in front of a vehicle that has air brakes will stop quicker, if the reaction times and the braking times are the same, hence the car will be hit by the larger vehicle due to the brake lag in the larger vehicle.

The way it works the other way round is that car drivers cannot see round the larger vehicle in front and therefore the driver in the larger vehicle has already reacted to the danger (which the car driver cannot see). As the reaction time is less than the brake lag in the larger vehicle, and usually there is more rubber on the road, it SEEMS to stop quicker.

Hopefully you see what I mean - the car driver will always stop quicker, side by side. But that a tailgating car driver has restricted restricted visibility, he/she removes the brake lag disadvantage - introduced by the air brakes of the larger vehicle. Meaning he/she cannot stop as quickly as the larger vehicle they are following.

So being a car driver, you can chose which end of the vehicle you want to be crushed!

 

[anko]

Guys, stop beating up Vince. I can imagine "van" works like a red flag to some of you, but he did say "using ACC to maintain a safe distance"

 

[jaapv]

Which does not always work well enough. I have had the FCM coming in when driving on ACC a few times. Despite that the minimum distance of ACC is insufficient by far to get into the wind shadow of a van. One must close up quite a bit more.
Btw, the fine for tailgating is 250 Euro I believe.

 

[Neverfuel]

£100 and three points on your licence in the UK.

 

[maby]

£100 and three points on your licence in the UK.

Is tailgating a specific offence here, or is it just an example of driving without due care and attention or some such?

 

[Neverfuel]

£100 and three points on your licence in the UK.

Is tailgating a specific offence here, or is it just an example of driving without due care and attention or some such?

I think it is put in that bracket, from a legal perspective, along with using a mobile phone, lane hogging, cutting in too close in a line of traffic etc. They were brought in in August as spot fines, to reduce the burden on the court system.

 

[Neverfuel]

Guys, stop beating up Vince. I can imagine "van" works like a red flag to some of you, but he did say "using ACC to maintain a safe distance"

Safe distance in good weather is at least 2 seconds to the vehicle in front, more at higher speeds. That's too far to get the benefit of an aerodynamic tow. Think how close F1 cars have to be to get dragged along, before they can use it to their advantage to overtake, and how short the distance is before they are in "dirty air".

Too close for me...

 

[Vince31]

Thanks for all the comments guys about drafting using the Active Cruise Control. I don't have the car yet and certainly don't contemplate drafting any vehicles in my current car, I know the dangers! My question was really to see if the Active Cruise Control function on the 4HS, which automatically brakes even at speed, would even allow you to get close enough safely to benefit from any effect.

 

[Neverfuel]

Thanks for all the comments guys about drafting using the Active Cruise Control. I don't have the car yet and certainly don't contemplate drafting any vehicles in my current car, I know the dangers! My question was really to see if the Active Cruise Control function on the 4HS, which automatically brakes even at speed, would even allow you to get close enough safely to benefit from any effect.

ACC setting 3 (default) is about 4 seconds at motorway speeds, 2 is about 3 seconds and the lowest setting is about 2 - the braking can be quite harsh on the lowest setting. All settings seem to bring you to a stop with the same gap to the vehicle in front though, so I think an algorithm works out the distance according to speed. I'll do some tests and find out more.