Agreed but if 40 mph gets you 45mpg then going slower at 45mph is worse than going at 50mph
Fuel price discussion thread (was ‘chaos’)
- Thread starter watercooledman
- Start date
Agreed but if 40 mph gets you 45mpg then going slower at 45mph is worse than going at 50mph
Agreed. If you look at studies, depending on the car, there isnt a great difference between 60mph and 70mph for the mpg once you have got up to speed. However once you break the speed limit and go 80mph is massively more fuel than going from 60-70mph.
So perhaps the answer is not to drop speed limits but just get people to stick to them or enforce them.
Do enough people break them by a large enough margin to have any real world gains on fuel economy though? (I don't know the answer to that).
The problem is it is something which needs "overthinking" to turn theory and ideals into actual meaningful results and there are reasons why the current speed limits are what they are (some of those reasons might be outdated).
53% of car drivers on motorways and 56% in 30mph zones
13% of car drivers break the speed limit on motorways by 10mph or more.
So yeah, with more than half of driver breaking the existing limits, how much fuel is going to be saved by cutting the speed limits if these drivers keep breaking them?
And a big reduction in fuel use could be made by just getting the UK public to all stick to the existing speed limits.
....back in the room recovering from 174.9 Momentum moment at tesco cambridge - need a few prozacs
the frictional data I suggested are not instantaneous power, they are energy dissipated (joules) over a given distance, at a higher speed that distance is dispatched in a shorter time, so unless the frictional power ratios up matching the speed, you would expect lower energy at the higher speed.
some ev data - just need to find the ICE equivalent
..
where is the real data ? or a link to an appropriate paper
the frictional data I suggested are not instantaneous power, they are energy dissipated (joules) over a given distance, at a higher speed that distance is dispatched in a shorter time, so unless the frictional power ratios up matching the speed, you would expect lower energy at the higher speed.
some ev data - just need to find the ICE equivalent
I know the difference between a watt and a joule. You seem to confuse power with energy though.....back in the room recovering from 174.9 Momentum moment at tesco cambridge - need a few prozacs
where is the real data ? or a link to an appropriate paper
the frictional data I suggested are not instantaneous power, they are energy dissipated (joules) over a given distance, at a higher speed that distance is dispatched in a shorter time, so unless the frictional power ratios up matching the speed, you would expect lower energy at the higher speed.
some ev data - just need to find the ICE equivalent
..
Yes that’s one of the first google pics if you search. And that ‘motor and stuff’ is related to efficiency of motors not drivetrain friction …
And clearly 70mph needs 50% more energy than 50mph in this single speed EV
Soldato
- Joined
- 19 Oct 2002
- Posts
- 17,691
- Location
- Shakespeare’s County
Jpaul. ICE doesnt work like that EV graph. Google pumping losses and volumetric efficiency. One day something will go in that head of yours rather than just blunderbus linking this forum as a excuse for knowledge.
Oh and work on the quote feature before you master powertrains…
Oh and work on the quote feature before you master powertrains…
The graph even says it's per mile on the title and on the labelled axis. So it doesn't matter how long it takes to cover that mile, the values per mile are still the same.
In fact, the original source cited for that graph even directly addresses the incorrect point you're trying to make:
https://www.tesla.com/blog/roadster-efficiency-and-range said:
Last edited:
the graph relates to ev behaviour, but with a minima at 15-20mph , shows that if you drove at 10mph you would be less efficient, so slowing down doesn't help, or you disagree ?
(reminder - the original example budforce raised was comparing a journey completed @1500 rpm in 1st and 6th gear)
and ... the time aspect is epitomized in an ev graph where the duration of the trip is directly proportional to the energy consumed by auxiliary equipment like an electric/resistive heater for in car climate - which relates to power versus energy.
an ICE will usually dissipate more heat if you drive faster, but obviously a heater is constant - barring wind-chill losses )
That was an engine. Not an electric motor !
That electric motor will be 96% efficient peak. Outside peak like very low speed it will be 60%. This isn’t friction this is how a electric motor works and why you see this on that chart. Anyone can read a chart but understand why is the real
Understanding. And no amount of copy and pasting will help if you don’t have the ability to read what others say AND LEARN.
The point was slowing down from 70 to 50mph. Nothing. Else. Nothing about 10mph on a motorway. Nothing about having to sit at 1500rpm. It’s tedious how you can’t just accept something, rather create random arguments to have. Do you have some sort of issue with agreeing ?
That electric motor will be 96% efficient peak. Outside peak like very low speed it will be 60%. This isn’t friction this is how a electric motor works and why you see this on that chart. Anyone can read a chart but understand why is the real
Understanding. And no amount of copy and pasting will help if you don’t have the ability to read what others say AND LEARN.
The point was slowing down from 70 to 50mph. Nothing. Else. Nothing about 10mph on a motorway. Nothing about having to sit at 1500rpm. It’s tedious how you can’t just accept something, rather create random arguments to have. Do you have some sort of issue with agreeing ?
Yes, I do disagree.
The graph shows that 10mph is slightly less efficient than 15mph but to conclude that "slowing down doesn't help" is clearly wrong when looking at the graph as a whole.
Man of Honour
- Joined
- 21 Nov 2004
- Posts
- 46,384
Super 1.71. Was expecting worse. Noticeable difference on the final price though.
Soldato
- Joined
- 19 Oct 2002
- Posts
- 17,691
- Location
- Shakespeare’s County
Technically that gap isnt big enough to be considered worse.
defacto memorada less pence per litrage of hydrocarbon doesnt expel the correction of fuel and hence running cost for one's chariot..
jpaul x
defacto memorada less pence per litrage of hydrocarbon doesnt expel the correction of fuel and hence running cost for one's chariot..
jpaul x
ironically energy consumption/power analysis is part of my profession, but on the micro chip level, where,
you have the dilemma to do tasks quickly on fast transistors that have a lot of current leakage/get hot (kinda like aero impact), or more slowly on less-leaky transistors, and you have a limited smartphone battery autonomy.