Speed limit to be raised on motorways?

[Cyclone 10]

I haven't looked for data, but my gut feeling was that the lowest speed you can maintain in your highest gear would be the most efficient. So it would be about 30 for me, any slower and I have to run the engine through more cycles for the same total distance.

[John X 10]

I haven't looked for data, but my gut feeling was that the lowest speed you can maintain in your highest gear would be the most efficient. So it would be about 30 for me, any slower and I have to run the engine through more cycles for the same total distance.

 

That would be true if it weren't for the effects of momentum!

 

John X

[Eater Sundae 12]

I haven't looked for data, but my gut feeling was that the lowest speed you can maintain in your highest gear would be the most efficient. So it would be about 30 for me, any slower and I have to run the engine through more cycles for the same total distance.

 

My car has a small diesel engine, and 30 is just about comfortable in top on a flat road (eg Penistone Road), but any sort of incline or extra load to accelerate makes it better to drop a gear. I've tried to check whether the on board instantaneous mpg read out shows 4th or 5th gear as being better, but nothing conclusive (and I don't know if the instantaneous read out is accurate, although the average read out is accurate).

[ElasticMan 10]

It's a saving of 7.5 minutes for every hour of driving (at the speed limit on the motorway). If you commute for an hour each day, each way, then that's 1hr and 15 mins saved every week!

 

Except that you are assuming that the entire journey is spent driving at the maximum legal speed. This is never going to happen. You would be lucky to be able to manage 10 mins of clear road never mind an hours worth.

[ElasticMan 10]

I haven't looked for data, but my gut feeling was that the lowest speed you can maintain in your highest gear would be the most efficient. So it would be about 30 for me, any slower and I have to run the engine through more cycles for the same total distance.

 

My understanding is that there is an efficiency 'sweetspot' - which for a modern diesel is about 1800-2000 RPM - any lower and other factors such as airflow mean that its actually less efficient.

 

For me this is about 65 in 6th Gear.

[Cyclone 10]

That would be true if it weren't for the effects of momentum!

 

John X

 

How does momentum alter this?

[Cyclone 10]

Except that you are assuming that the entire journey is spent driving at the maximum legal speed. This is never going to happen. You would be lucky to be able to manage 10 mins of clear road never mind an hours worth.

 

You made the same assumptions in your example.

[LDeville 10]

Hi

 

As no one esle has had the foresight to ask, we will. The lorry speeds, are they to remain the same??????????????????????????????????????

[cheeksfull 10]

Hi

 

As no one esle has had the foresight to ask, we will. The lorry speeds, are they to remain the same??????????????????????????????????????

 

They will have to stay the same. Lorrys are restricted to around 55-56 mph, so it would be difficult to update all trucks, plus it would be dangerous to go much faster

[LDeville 10]

They will have to stay the same. Lorrys are restricted to around 55-56 mph, so it would be difficult to update all trucks, plus it would be dangerous to go much faster

 

Hi

 

Lorries are restricted, but can easily be adjusted, fact.

 

Lorries are governed by the 56 mph but the facts remain factual, ie we often see them do 70 mph downhill and even on the level they manage a good 60mph plus.

 

 

.

[cheeksfull 10]

Hi

 

Lorries are restricted, but can easily be adjusted, fact.

 

Lorries are governed by the 56 mph but the facts remain factual, ie we often see them do 70 mph downhill and even on the level they manage a good 60mph plus.

 

 

.

any HGV that does 60 mph on the flat has been doctored. 55-56mph max, unless its a Morrisons or Sainsbury wagon. They set their vehicles at 52mph. Any fool who does 70 mph down a hill with a 44 tonner, wants his licence revoking, put many peoples lives at risk. Now thats a fact.

[LDeville 10]

any HGV that does 60 mph on the flat has been doctored. 55-56mph max, unless its a Morrisons or Sainsbury wagon. They set their vehicles at 52mph. Any fool who does 70 mph down a hill with a 44 tonner, wants his licence revoking, put many peoples lives at risk. Now thats a fact.

 

Hi

 

We agree, but fact remains factual that most are over the 56mph, fact.

 

these lorries especially the ones that carry waste, cab is very high up and they often shoot past at 40/50 in 30 zones - speeding in lorries must carry a mandatory ban, fact